AI Trajectory

Trajectory: (Expand/Collapse All)
Seq	Timestamp	Type	Name	Duration
0/0	2026/09/18 15:22	flow	patch-triage	24m Args: null Results: { "EnableConfigs": [ "CGROUPS", "MEMCG", "MEMCG_V1" ], "FocusSymbols": [ "page_counter_try_charge", "page_counter_refill_stock", "page_counter_drain_stock_fully", "page_counter_stock_flush_required", "drain_all_stock" ], "KMSANReasoning": "The patch series refactors the memcg charge stock caching mechanism into a generic per-CPU page counter stock mechanism (moving stock handling from `memcontrol.c` into `page_counter.c` and `page_counter.h`).\n\nAnalysis for KMSAN applicability:\n1. Data structures sent to user space: None. The patch affects internal page counter and stock cache management; no buffers or structures are copied to user space.\n2. Uninitialized variables / conditional branching: In `try_charge_memcg`, the newly introduced stack variable `unsigned long nr_charged;` is passed by pointer to `page_counter_try_charge()`. On every code path where `page_counter_try_charge()` returns `true`, `nr_charged` is explicitly set to either 0 or `charge` before returning. It is only read in `check_high`, which is reached exclusively on success. Similarly, `fail` is always set upon failure when limit check fails.\n3. Structure initialization: `struct page_counter_stock_pcp` instances (`memory_stock`, `memsw_stock`) are static per-CPU variables with static initializers and zero-initialized fields; work items are initialized with `INIT_WORK()`. The new fields in `struct page_counter` (`stock`, `stock_css`) are explicitly set to `NULL` in `page_counter_init()`.\n4. Bounds checks / buffer lengths: No data buffers are manipulated or exposed.\n\nPotential bugs introduced by this refactoring include refcounting bugs (`css_put`/`css_get`), locking/concurrency issues, counter accounting discrepancies, and use-after-free conditions, which are detected by KASAN, LOCKDEP, and standard kernel debugging facilities. There is no risk of uninitialized memory usage or information disclosure to userspace, so a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false, "Reasoning": "The patch series refactors and generalizes the memory cgroup charge caching (stock) mechanism into the core page_counter subsystem. It alters the page_counter charge, refill, flush, and drain control flow across mm/page_counter.c, mm/memcontrol.c, and mm/memcontrol-v1.c. These changes touch core memory management and cgroup accounting logic reachable in standard virtualization environments, warranting fuzzing.", "WorthFuzzing": true }
1/1	2026/09/18 15:22	action	read-patch-diff	0m Args: null Results: { "PatchDiff": "commit 8ed6f402591303ae9015851c24e9ab3bf1a18fea\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Fri Sep 18 15:22:40 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/include/linux/page_counter.h b/include/linux/page_counter.h\nindex 07b7cb12249c7..a5a5a789d002c 100644\n--- a/include/linux/page_counter.h\n+++ b/include/linux/page_counter.h\n@@ -5,8 +5,30 @@\n #include \u003clinux/atomic.h\u003e\n #include \u003clinux/cache.h\u003e\n #include \u003clinux/limits.h\u003e\n+#include \u003clinux/percpu.h\u003e\n+#include \u003clinux/local_lock.h\u003e\n+#include \u003clinux/workqueue_types.h\u003e\n #include \u003casm/page.h\u003e\n \n+/\n+ The value of NR_PAGE_COUNTER_STOCK is selected to keep the cached counters\n+ * and their nr_pages in a single cacheline. This may change in the future.\n+ /\n+#define NR_PAGE_COUNTER_STOCK 7\n+#define PAGE_COUNTER_STOCK_BATCH 64UL\n+struct cgroup_subsys_state;\n+struct page_counter;\n+struct page_counter_stock_pcp {\n+\tlocal_trylock_t lock;\n+\tu8 nr_pages[NR_PAGE_COUNTER_STOCK];\n+\tstruct page_counter cached[NR_PAGE_COUNTER_STOCK];\n+\n+\tstruct page_counter_stock_pcp __percpu base;\n+\tstruct work_struct work;\n+\tunsigned long flags;\n+\tu8 drain_idx;\n+};\n+\n struct page_counter {\n \t/\n \t * Make sure 'usage' does not share cacheline with any other field in\n@@ -41,6 +63,8 @@ struct page_counter {\n \tunsigned long high;\n \tunsigned long max;\n \tstruct page_counter parent;\n+\tstruct page_counter_stock_pcp __percpu stock;\n+\tstruct cgroup_subsys_state stock_css;\n } ____cacheline_internodealigned_in_smp;\n \n #if BITS_PER_LONG == 32\n@@ -61,6 +85,8 @@ static inline void page_counter_init(struct page_counter counter,\n \tcounter-\u003eparent = parent;\n \tcounter-\u003eprotection_support = protection_support;\n \tcounter-\u003etrack_failcnt = false;\n+\tcounter-\u003estock = NULL;\n+\tcounter-\u003estock_css = NULL;\n }\n \n static inline unsigned long page_counter_read(struct page_counter counter)\n@@ -72,8 +98,13 @@ long page_counter_margin(struct page_counter counter);\n void page_counter_cancel(struct page_counter counter, unsigned long nr_pages);\n void page_counter_charge(struct page_counter counter, unsigned long nr_pages);\n bool page_counter_try_charge(struct page_counter counter,\n-\t\t\t unsigned long nr_pages,\n-\t\t\t struct page_counter fail);\n+\t\t\t unsigned long nr_pages, struct page_counter fail,\n+\t\t\t bool may_batch, unsigned long nr_charged);\n+void page_counter_refill_stock(struct page_counter counter,\n+\t\t\t unsigned long nr_pages);\n+void page_counter_drain_stock_fully(struct page_counter_stock_pcp stock);\n+bool page_counter_stock_flush_required(struct page_counter_stock_pcp stock,\n+\t\t\t\t struct cgroup_subsys_state root_css);\n void page_counter_uncharge(struct page_counter counter, unsigned long nr_pages);\n void page_counter_set_min(struct page_counter counter, unsigned long nr_pages);\n void page_counter_set_low(struct page_counter counter, unsigned long nr_pages);\ndiff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c\nindex d49ed5d4a9237..dd325e9413fb5 100644\n--- a/kernel/cgroup/dmem.c\n+++ b/kernel/cgroup/dmem.c\n@@ -736,7 +736,7 @@ int dmem_cgroup_try_charge(struct dmem_cgroup_region region, u64 size,\n \t\tgoto err;\n \t}\n \n-\tif (!page_counter_try_charge(\u0026pool-\u003ecnt, size, \u0026fail)) {\n+\tif (!page_counter_try_charge(\u0026pool-\u003ecnt, size, \u0026fail, false, NULL)) {\n \t\tif (ret_limit_pool) {\n \t\t\tret_limit_pool = container_of(fail, struct dmem_cgroup_pool_state, cnt);\n \t\t\tcss_get(\u0026(ret_limit_pool)-\u003ecs-\u003ecss);\ndiff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c\nindex ecb6e0b7819a0..5b8d9f0e25535 100644\n--- a/mm/hugetlb_cgroup.c\n+++ b/mm/hugetlb_cgroup.c\n@@ -274,7 +274,7 @@ static int __hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,\n \n \tif (!page_counter_try_charge(\n \t\t __hugetlb_cgroup_counter_from_cgroup(h_cg, idx, rsvd),\n-\t\t nr_pages, \u0026counter)) {\n+\t\t nr_pages, \u0026counter, false, NULL)) {\n \t\tret = -ENOMEM;\n \t\thugetlb_event(h_cg, idx, HUGETLB_MAX);\n \t\tcss_put(\u0026h_cg-\u003ecss);\ndiff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c\nindex bf2c7d53b01b1..22822e7a85b49 100644\n--- a/mm/memcontrol-v1.c\n+++ b/mm/memcontrol-v1.c\n@@ -122,10 +122,13 @@ static unsigned long mem_cgroup_usage(struct mem_cgroup memcg, bool swap)\n \t\tif (swap)\n \t\t\tval += total_swap_pages - get_nr_swap_pages();\n \t} else {\n-\t\tif (!swap)\n+\t\tif (!swap) {\n \t\t\tval = page_counter_read(\u0026memcg-\u003ememory);\n-\t\telse\n-\t\t\tval = page_counter_read(\u0026memcg-\u003ememsw);\n+\t\t} else {\n+\t\t\t/ Preserve the user-visible memory \u003c= memsw invariant. /\n+\t\t\tval = max(page_counter_read(\u0026memcg-\u003ememory),\n+\t\t\t\t page_counter_read(\u0026memcg-\u003ememsw));\n+\t\t}\n \t}\n \treturn val;\n }\n@@ -2194,7 +2197,8 @@ bool memcg1_charge_skmem(struct mem_cgroup memcg, unsigned int nr_pages,\n {\n \tstruct page_counter fail;\n \n-\tif (page_counter_try_charge(\u0026memcg-\u003etcpmem, nr_pages, \u0026fail)) {\n+\tif (page_counter_try_charge(\u0026memcg-\u003etcpmem, nr_pages, \u0026fail,\n+\t\t\t\t false, NULL)) {\n \t\tmemcg-\u003etcpmem_pressure = 0;\n \t\treturn true;\n \t}\ndiff --git a/mm/memcontrol.c b/mm/memcontrol.c\nindex 791e536efaebe..e533f08232fbc 100644\n--- a/mm/memcontrol.c\n+++ b/mm/memcontrol.c\n@@ -2063,34 +2063,19 @@ void mem_cgroup_print_oom_group(struct mem_cgroup memcg)\n \tpr_cont(\" are going to be killed due to memory.oom.group set\\n\");\n }\n \n-/\n- The value of NR_MEMCG_STOCK is selected to keep the cached memcgs and their\n- * nr_pages in a single cacheline. This may change in future.\n- /\n-#define NR_MEMCG_STOCK 7\n-\n-/\n- * Watermarks for a charge stock slot, in the spirit of pcp-\u003ehigh and\n- * pcp-\u003ebatch: MEMCG_STOCK_HIGH is the high watermark at which a slot is\n- * trimmed, and it is trimmed down to MEMCG_STOCK_LOW rather than emptied.\n- /\n-#define MEMCG_STOCK_LOW\t\t(MEMCG_CHARGE_BATCH / 2)\n-#define MEMCG_STOCK_HIGH\t(MEMCG_CHARGE_BATCH)\n-\n #define FLUSHING_CACHED_CHARGE\t0\n-struct memcg_stock_pcp {\n-\tlocal_trylock_t lock;\n-\tuint8_t nr_pages[NR_MEMCG_STOCK];\n-\tstruct mem_cgroup cached[NR_MEMCG_STOCK];\n \n-\tstruct work_struct work;\n-\tunsigned long flags;\n-\tuint8_t drain_idx;\n+static DEFINE_PER_CPU_ALIGNED(struct page_counter_stock_pcp, memory_stock) = {\n+\t.lock = INIT_LOCAL_TRYLOCK(lock),\n+\t.base = \u0026memory_stock,\n };\n \n-static DEFINE_PER_CPU_ALIGNED(struct memcg_stock_pcp, memcg_stock) = {\n+#ifdef CONFIG_MEMCG_V1\n+static DEFINE_PER_CPU_ALIGNED(struct page_counter_stock_pcp, memsw_stock) = {\n \t.lock = INIT_LOCAL_TRYLOCK(lock),\n+\t.base = \u0026memsw_stock,\n };\n+#endif\n \n /\n NR_OBJ_STOCK is sized so the entire hot path of obj_stock_pcp\n@@ -2139,52 +2124,6 @@ static void drain_obj_stock(struct obj_stock_pcp stock);\n static bool obj_stock_flush_required(struct obj_stock_pcp stock,\n \t\t\t\t struct mem_cgroup root_memcg);\n \n-/\n- consume_stock: Try to consume stocked charge on this cpu.\n- * @memcg: memcg to consume from.\n- * @nr_pages: how many pages to charge.\n- \n- Consume the cached charge if enough nr_pages are present otherwise return\n- * failure. Also return failure for charge request larger than\n- * MEMCG_CHARGE_BATCH or if the local lock is already taken.\n- \n- returns true if successful, false otherwise.\n- /\n-static bool consume_stock(struct mem_cgroup memcg, unsigned int nr_pages)\n-{\n-\tstruct memcg_stock_pcp stock;\n-\tuint8_t stock_pages;\n-\tbool ret = false;\n-\tint i;\n-\n-\tif (nr_pages \u003e MEMCG_CHARGE_BATCH \|\|\n-\t !local_trylock(\u0026memcg_stock.lock))\n-\t\treturn ret;\n-\n-\tstock = this_cpu_ptr(\u0026memcg_stock);\n-\n-\tfor (i = 0; i \u003c NR_MEMCG_STOCK; ++i) {\n-\t\tif (memcg != READ_ONCE(stock-\u003ecached[i]))\n-\t\t\tcontinue;\n-\n-\t\tstock_pages = READ_ONCE(stock-\u003enr_pages[i]);\n-\t\tif (stock_pages \u003e= nr_pages) {\n-\t\t\tstock_pages -= nr_pages;\n-\t\t\tWRITE_ONCE(stock-\u003enr_pages[i], stock_pages);\n-\t\t\tif (!stock_pages) {\n-\t\t\t\tcss_put(\u0026memcg-\u003ecss);\n-\t\t\t\tWRITE_ONCE(stock-\u003ecached[i], NULL);\n-\t\t\t}\n-\t\t\tret = true;\n-\t\t}\n-\t\tbreak;\n-\t}\n-\n-\tlocal_unlock(\u0026memcg_stock.lock);\n-\n-\treturn ret;\n-}\n-\n static void memcg_uncharge(struct mem_cgroup memcg, unsigned int nr_pages)\n {\n \tpage_counter_uncharge(\u0026memcg-\u003ememory, nr_pages);\n@@ -2192,49 +2131,22 @@ static void memcg_uncharge(struct mem_cgroup memcg, unsigned int nr_pages)\n \t\tpage_counter_uncharge(\u0026memcg-\u003ememsw, nr_pages);\n }\n \n-/\n- * Returns stocks cached in percpu and reset cached information.\n- /\n-static void drain_stock(struct memcg_stock_pcp stock, int i)\n+static void drain_local_stock(struct work_struct work)\n {\n-\tstruct mem_cgroup old = READ_ONCE(stock-\u003ecached[i]);\n-\tuint8_t stock_pages;\n-\n-\tif (!old)\n-\t\treturn;\n-\n-\tstock_pages = READ_ONCE(stock-\u003enr_pages[i]);\n-\tif (stock_pages) {\n-\t\tmemcg_uncharge(old, stock_pages);\n-\t\tWRITE_ONCE(stock-\u003enr_pages[i], 0);\n-\t}\n-\n-\tcss_put(\u0026old-\u003ecss);\n-\tWRITE_ONCE(stock-\u003ecached[i], NULL);\n-}\n-\n-static void drain_stock_fully(struct memcg_stock_pcp stock)\n-{\n-\tint i;\n-\n-\tfor (i = 0; i \u003c NR_MEMCG_STOCK; ++i)\n-\t\tdrain_stock(stock, i);\n-}\n-\n-static void drain_local_memcg_stock(struct work_struct dummy)\n-{\n-\tstruct memcg_stock_pcp stock;\n+\tstruct page_counter_stock_pcp pcp_stock;\n+\tstruct page_counter_stock_pcp __percpu stock;\n \n \tif (WARN_ONCE(!in_task(), \"drain in non-task context\"))\n \t\treturn;\n \n-\tlocal_lock(\u0026memcg_stock.lock);\n+\tstock = container_of(work, struct page_counter_stock_pcp, work)-\u003ebase;\n+\tlocal_lock(\u0026stock-\u003elock);\n \n-\tstock = this_cpu_ptr(\u0026memcg_stock);\n-\tdrain_stock_fully(stock);\n-\tclear_bit(FLUSHING_CACHED_CHARGE, \u0026stock-\u003eflags);\n+\tpcp_stock = this_cpu_ptr(stock);\n+\tpage_counter_drain_stock_fully(pcp_stock);\n+\tclear_bit(FLUSHING_CACHED_CHARGE, \u0026pcp_stock-\u003eflags);\n \n-\tlocal_unlock(\u0026memcg_stock.lock);\n+\tlocal_unlock(\u0026stock-\u003elock);\n }\n \n static void drain_local_obj_stock(struct work_struct dummy)\n@@ -2253,92 +2165,6 @@ static void drain_local_obj_stock(struct work_struct dummy)\n \tlocal_unlock(\u0026obj_stock.lock);\n }\n \n-static void refill_stock(struct mem_cgroup memcg, unsigned int nr_pages)\n-{\n-\tstruct memcg_stock_pcp stock;\n-\tstruct mem_cgroup cached;\n-\tunsigned int stock_pages;\n-\tbool success = false;\n-\tint empty_slot = -1;\n-\tint i;\n-\n-\t/\n-\t nr_pages[] is a uint8_t and a slot's count is capped at\n-\t * MEMCG_STOCK_HIGH. Raising MEMCG_CHARGE_BATCH beyond 127 would need\n-\t * more careful handling of nr_pages[] in struct memcg_stock_pcp.\n-\t /\n-\tBUILD_BUG_ON(MEMCG_CHARGE_BATCH \u003e S8_MAX);\n-\tBUILD_BUG_ON(MEMCG_STOCK_HIGH \u003e U8_MAX);\n-\n-\tVM_WARN_ON_ONCE(mem_cgroup_is_root(memcg));\n-\n-\tif (nr_pages \u003e MEMCG_CHARGE_BATCH \|\|\n-\t !local_trylock(\u0026memcg_stock.lock)) {\n-\t\t/\n-\t\t * In case of larger than batch refill or unlikely failure to\n-\t\t * lock the percpu memcg_stock.lock, uncharge memcg directly.\n-\t\t /\n-\t\tmemcg_uncharge(memcg, nr_pages);\n-\t\treturn;\n-\t}\n-\n-\tstock = this_cpu_ptr(\u0026memcg_stock);\n-\tfor (i = 0; i \u003c NR_MEMCG_STOCK; ++i) {\n-\t\tcached = READ_ONCE(stock-\u003ecached[i]);\n-\t\tif (!cached \u0026\u0026 empty_slot == -1)\n-\t\t\tempty_slot = i;\n-\t\tif (memcg == READ_ONCE(stock-\u003ecached[i])) {\n-\t\t\tstock_pages = READ_ONCE(stock-\u003enr_pages[i]) + nr_pages;\n-\t\t\tif (stock_pages \u003e MEMCG_STOCK_HIGH) {\n-\t\t\t\tmemcg_uncharge(memcg,\n-\t\t\t\t\t stock_pages - MEMCG_STOCK_LOW);\n-\t\t\t\tstock_pages = MEMCG_STOCK_LOW;\n-\t\t\t}\n-\t\t\tWRITE_ONCE(stock-\u003enr_pages[i], stock_pages);\n-\t\t\tsuccess = true;\n-\t\t\tbreak;\n-\t\t}\n-\t}\n-\n-\tif (!success) {\n-\t\ti = empty_slot;\n-\t\tif (i == -1) {\n-\t\t\ti = stock-\u003edrain_idx++;\n-\t\t\tif (stock-\u003edrain_idx == NR_MEMCG_STOCK)\n-\t\t\t\tstock-\u003edrain_idx = 0;\n-\t\t\tdrain_stock(stock, i);\n-\t\t}\n-\t\tcss_get(\u0026memcg-\u003ecss);\n-\t\tWRITE_ONCE(stock-\u003ecached[i], memcg);\n-\t\tWRITE_ONCE(stock-\u003enr_pages[i], nr_pages);\n-\t}\n-\n-\tlocal_unlock(\u0026memcg_stock.lock);\n-}\n-\n-static bool is_memcg_drain_needed(struct memcg_stock_pcp stock,\n-\t\t\t\t struct mem_cgroup root_memcg)\n-{\n-\tstruct mem_cgroup memcg;\n-\tbool flush = false;\n-\tint i;\n-\n-\trcu_read_lock();\n-\tfor (i = 0; i \u003c NR_MEMCG_STOCK; ++i) {\n-\t\tmemcg = READ_ONCE(stock-\u003ecached[i]);\n-\t\tif (!memcg)\n-\t\t\tcontinue;\n-\n-\t\tif (READ_ONCE(stock-\u003enr_pages[i]) \u0026\u0026\n-\t\t mem_cgroup_is_descendant(memcg, root_memcg)) {\n-\t\t\tflush = true;\n-\t\t\tbreak;\n-\t\t}\n-\t}\n-\trcu_read_unlock();\n-\treturn flush;\n-}\n-\n static bool schedule_drain_work(int cpu, struct work_struct work)\n {\n \t/\n@@ -2355,12 +2181,30 @@ static bool schedule_drain_work(int cpu, struct work_struct work)\n \treturn true;\n }\n \n+static void schedule_stock_drain(struct page_counter_stock_pcp __percpu stock,\n+\t\t\t\t struct cgroup_subsys_state root_css,\n+\t\t\t\t int cpu, int curcpu)\n+{\n+\tstruct page_counter_stock_pcp pcp_stock = per_cpu_ptr(stock, cpu);\n+\n+\tif (test_bit(FLUSHING_CACHED_CHARGE, \u0026pcp_stock-\u003eflags) \|\|\n+\t !page_counter_stock_flush_required(pcp_stock, root_css) \|\|\n+\t test_and_set_bit(FLUSHING_CACHED_CHARGE, \u0026pcp_stock-\u003eflags))\n+\t\treturn;\n+\n+\tif (cpu == curcpu)\n+\t\tdrain_local_stock(\u0026pcp_stock-\u003ework);\n+\telse if (!schedule_drain_work(cpu, \u0026pcp_stock-\u003ework))\n+\t\tclear_bit(FLUSHING_CACHED_CHARGE, \u0026pcp_stock-\u003eflags);\n+}\n+\n /\n Drains all per-CPU charge caches for given root_memcg resp. subtree\n * of the hierarchy under it.\n /\n void drain_all_stock(struct mem_cgroup root_memcg)\n {\n+\tstruct cgroup_subsys_state root_css = \u0026root_memcg-\u003ecss;\n \tint cpu, curcpu;\n \n \t/ If someone's already draining, avoid adding running more workers. /\n@@ -2370,24 +2214,18 @@ void drain_all_stock(struct mem_cgroup root_memcg)\n \t * Notify other cpus that system-wide \"drain\" is running\n \t * We do not care about races with the cpu hotplug because cpu down\n \t * as well as workers from this path always operate on the local\n-\t * per-cpu data. CPU up doesn't touch memcg_stock at all.\n+\t * per-cpu data. CPU up doesn't touch the stocks at all.\n \t /\n \tmigrate_disable();\n \tcurcpu = smp_processor_id();\n \tfor_each_online_cpu(cpu) {\n-\t\tstruct memcg_stock_pcp memcg_st = \u0026per_cpu(memcg_stock, cpu);\n \t\tstruct obj_stock_pcp obj_st = \u0026per_cpu(obj_stock, cpu);\n \n-\t\tif (!test_bit(FLUSHING_CACHED_CHARGE, \u0026memcg_st-\u003eflags) \u0026\u0026\n-\t\t is_memcg_drain_needed(memcg_st, root_memcg) \u0026\u0026\n-\t\t !test_and_set_bit(FLUSHING_CACHED_CHARGE,\n-\t\t\t\t \u0026memcg_st-\u003eflags)) {\n-\t\t\tif (cpu == curcpu)\n-\t\t\t\tdrain_local_memcg_stock(\u0026memcg_st-\u003ework);\n-\t\t\telse if (!schedule_drain_work(cpu, \u0026memcg_st-\u003ework))\n-\t\t\t\tclear_bit(FLUSHING_CACHED_CHARGE,\n-\t\t\t\t\t \u0026memcg_st-\u003eflags);\n-\t\t}\n+\t\tschedule_stock_drain(\u0026memory_stock, root_css, cpu, curcpu);\n+#ifdef CONFIG_MEMCG_V1\n+\t\tif (do_memsw_account())\n+\t\t\tschedule_stock_drain(\u0026memsw_stock, root_css, cpu, curcpu);\n+#endif\n \n \t\tif (!test_bit(FLUSHING_CACHED_CHARGE, \u0026obj_st-\u003eflags) \u0026\u0026\n \t\t obj_stock_flush_required(obj_st, root_memcg) \u0026\u0026\n@@ -2406,12 +2244,19 @@ void drain_all_stock(struct mem_cgroup root_memcg)\n \n static int memcg_hotplug_cpu_dead(unsigned int cpu)\n {\n-\tstruct memcg_stock_pcp memcg_st = \u0026per_cpu(memcg_stock, cpu);\n+\tstruct page_counter_stock_pcp stock;\n \tstruct obj_stock_pcp obj_st = \u0026per_cpu(obj_stock, cpu);\n \n \t/ no need for the local lock /\n \tdrain_obj_stock(obj_st);\n-\tdrain_stock_fully(memcg_st);\n+\tstock = per_cpu_ptr(\u0026memory_stock, cpu);\n+\tpage_counter_drain_stock_fully(stock);\n+\tclear_bit(FLUSHING_CACHED_CHARGE, \u0026stock-\u003eflags);\n+#ifdef CONFIG_MEMCG_V1\n+\tstock = per_cpu_ptr(\u0026memsw_stock, cpu);\n+\tpage_counter_drain_stock_fully(stock);\n+\tclear_bit(FLUSHING_CACHED_CHARGE, \u0026stock-\u003eflags);\n+#endif\n \n \t/\n \t * A drain work queued before the CPU went away is executed by an\n@@ -2419,7 +2264,6 @@ static int memcg_hotplug_cpu_dead(unsigned int cpu)\n \t * clear the flags here to make these stocks drainable again once\n \t * the CPU comes back online.\n \t /\n-\tclear_bit(FLUSHING_CACHED_CHARGE, \u0026memcg_st-\u003eflags);\n \tclear_bit(FLUSHING_CACHED_CHARGE, \u0026obj_st-\u003eflags);\n \n \treturn 0;\n@@ -2699,10 +2543,10 @@ void __mem_cgroup_handle_over_high(gfp_t gfp_mask)\n static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask,\n \t\t\t unsigned int nr_pages)\n {\n-\tunsigned int batch = max(MEMCG_CHARGE_BATCH, nr_pages);\n \tint nr_retries = MAX_RECLAIM_RETRIES;\n \tstruct mem_cgroup mem_over_limit;\n \tstruct page_counter counter;\n+\tunsigned long nr_charged;\n \tunsigned long nr_reclaimed;\n \tbool passed_oom = false;\n \tunsigned int reclaim_options;\n@@ -2710,33 +2554,30 @@ static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask,\n \tbool raised_max_event = false;\n \tunsigned long pflags;\n \tbool allow_spinning = gfpflags_allow_spinning(gfp_mask);\n+\tbool may_batch = allow_spinning;\n \tint ret = 0;\n \n retry:\n-\tif (consume_stock(memcg, nr_pages))\n-\t\treturn ret;\n-\n-\tif (!allow_spinning)\n-\t\t/ Avoid the refill and flush of the older stock /\n-\t\tbatch = nr_pages;\n-\n \treclaim_options = MEMCG_RECLAIM_MAY_SWAP;\n-\tif (!do_memsw_account() \|\|\n-\t page_counter_try_charge(\u0026memcg-\u003ememsw, batch, \u0026counter)) {\n-\t\tif (page_counter_try_charge(\u0026memcg-\u003ememory, batch, \u0026counter))\n-\t\t\tgoto done_restock;\n-\t\tif (do_memsw_account())\n-\t\t\tpage_counter_uncharge(\u0026memcg-\u003ememsw, batch);\n-\t\tmem_over_limit = mem_cgroup_from_counter(counter, memory);\n-\t} else {\n+\tif (do_memsw_account() \u0026\u0026\n+\t !page_counter_try_charge(\u0026memcg-\u003ememsw, nr_pages, \u0026counter,\n+\t\t\t\t may_batch, NULL)) {\n \t\tmem_over_limit = mem_cgroup_from_counter(counter, memsw);\n \t\treclaim_options \u0026= ~MEMCG_RECLAIM_MAY_SWAP;\n+\t\tgoto reclaim;\n \t}\n \n-\tif (batch \u003e nr_pages) {\n-\t\tbatch = nr_pages;\n-\t\tgoto retry;\n-\t}\n+\tif (page_counter_try_charge(\u0026memcg-\u003ememory, nr_pages, \u0026counter,\n+\t\t\t\t may_batch, \u0026nr_charged))\n+\t\tgoto check_high;\n+\n+\tif (do_memsw_account())\n+\t\tpage_counter_uncharge(\u0026memcg-\u003ememsw, nr_pages);\n+\tmem_over_limit = mem_cgroup_from_counter(counter, memory);\n+\n+reclaim:\n+\t/ Do not retry speculative batch charges after the first miss. /\n+\tmay_batch = false;\n \n \t/\n \t * Prevent unbounded recursion when reclaim operations need to\n@@ -2849,10 +2690,9 @@ static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask,\n \n \treturn ret;\n \n-done_restock:\n-\tif (batch \u003e nr_pages)\n-\t\trefill_stock(memcg, batch - nr_pages);\n-\n+check_high:\n+\tif (!nr_charged)\n+\t\treturn ret;\n \t/\n \t * If the hierarchy is above the normal consumption range, schedule\n \t * reclaim on returning to userland. We can perform reclaim here\n@@ -2892,7 +2732,7 @@ static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask,\n \t\t\t and distribute reclaim work and delay penalties\n \t\t\t * based on how much each task is actually allocating.\n \t\t\t /\n-\t\t\tcurrent-\u003ememcg_nr_pages_over_high += batch;\n+\t\t\tcurrent-\u003ememcg_nr_pages_over_high += nr_charged;\n \t\t\tset_notify_resume(current);\n \t\t\tbreak;\n \t\t}\n@@ -3197,8 +3037,11 @@ static void obj_cgroup_uncharge_pages(struct obj_cgroup objcg,\n \n \taccount_kmem_nmi_safe(memcg, -nr_pages);\n \tmemcg1_account_kmem(memcg, -nr_pages);\n-\tif (!mem_cgroup_is_root(memcg))\n-\t\trefill_stock(memcg, nr_pages);\n+\tif (!mem_cgroup_is_root(memcg)) {\n+\t\tpage_counter_refill_stock(\u0026memcg-\u003ememory, nr_pages);\n+\t\tif (do_memsw_account())\n+\t\t\tpage_counter_refill_stock(\u0026memcg-\u003ememsw, nr_pages);\n+\t}\n \n \tcss_put(\u0026memcg-\u003ecss);\n }\n@@ -4297,8 +4140,14 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state parent_css)\n \tpage_counter_set_high(\u0026memcg-\u003eswap, PAGE_COUNTER_MAX);\n \tif (parent) {\n \t\tpage_counter_init(\u0026memcg-\u003ememory, \u0026parent-\u003ememory, memcg_on_dfl);\n+\t\tmemcg-\u003ememory.stock = \u0026memory_stock;\n+\t\tmemcg-\u003ememory.stock_css = \u0026memcg-\u003ecss;\n \t\tpage_counter_init(\u0026memcg-\u003eswap, \u0026parent-\u003eswap, false);\n #ifdef CONFIG_MEMCG_V1\n+\t\tif (!memcg_on_dfl) {\n+\t\t\tmemcg-\u003ememsw.stock = \u0026memsw_stock;\n+\t\t\tmemcg-\u003ememsw.stock_css = \u0026memcg-\u003ecss;\n+\t\t}\n \t\tWRITE_ONCE(memcg-\u003eswappiness, mem_cgroup_swappiness(parent));\n \t\tmemcg-\u003ememory.track_failcnt = !memcg_on_dfl;\n \t\tmemcg-\u003ememsw.track_failcnt = !memcg_on_dfl;\n@@ -5764,7 +5613,7 @@ void mem_cgroup_sk_uncharge(const struct sock sk, unsigned int nr_pages)\n \n \tmod_memcg_state(memcg, MEMCG_SOCK, -nr_pages);\n \n-\trefill_stock(memcg, nr_pages);\n+\tpage_counter_refill_stock(\u0026memcg-\u003ememory, nr_pages);\n }\n \n void mem_cgroup_flush_workqueue(void)\n@@ -5912,6 +5761,8 @@ int __init mem_cgroup_init(void)\n \t * exceed S32_MAX / PAGE_SIZE.\n \t /\n \tBUILD_BUG_ON(MEMCG_CHARGE_BATCH \u003e S32_MAX / PAGE_SIZE);\n+\t/ Batched page-counter charges feed memcg's memory.high accounting. /\n+\tBUILD_BUG_ON(MEMCG_CHARGE_BATCH != PAGE_COUNTER_STOCK_BATCH);\n \n \tmemcg_struct_check();\n \n@@ -5922,8 +5773,12 @@ int __init mem_cgroup_init(void)\n \tWARN_ON(!memcg_wq);\n \n \tfor_each_possible_cpu(cpu) {\n-\t\tINIT_WORK(\u0026per_cpu_ptr(\u0026memcg_stock, cpu)-\u003ework,\n-\t\t\t drain_local_memcg_stock);\n+\t\tINIT_WORK(\u0026per_cpu_ptr(\u0026memory_stock, cpu)-\u003ework,\n+\t\t\t drain_local_stock);\n+#ifdef CONFIG_MEMCG_V1\n+\t\tINIT_WORK(\u0026per_cpu_ptr(\u0026memsw_stock, cpu)-\u003ework,\n+\t\t\t drain_local_stock);\n+#endif\n \t\tINIT_WORK(\u0026per_cpu_ptr(\u0026obj_stock, cpu)-\u003ework,\n \t\t\t drain_local_obj_stock);\n \t}\n@@ -5976,7 +5831,8 @@ int __mem_cgroup_try_charge_swap(struct folio folio)\n \trcu_read_unlock();\n \n \tif (!mem_cgroup_is_root(memcg) \u0026\u0026\n-\t !page_counter_try_charge(\u0026memcg-\u003eswap, nr_pages, \u0026counter)) {\n+\t !page_counter_try_charge(\u0026memcg-\u003eswap, nr_pages, \u0026counter, false,\n+\t\t\t\t NULL)) {\n \t\tmemcg_memory_event(memcg, MEMCG_SWAP_MAX);\n \t\tmemcg_memory_event(memcg, MEMCG_SWAP_FAIL);\n \t\tmem_cgroup_private_id_put(memcg, nr_pages);\ndiff --git a/mm/page_counter.c b/mm/page_counter.c\nindex 98322803941a7..3cd8601961673 100644\n--- a/mm/page_counter.c\n+++ b/mm/page_counter.c\n@@ -7,6 +7,7 @@\n \n #include \u003clinux/page_counter.h\u003e\n #include \u003clinux/atomic.h\u003e\n+#include \u003clinux/cgroup.h\u003e\n #include \u003clinux/kernel.h\u003e\n #include \u003clinux/math64.h\u003e\n #include \u003clinux/string.h\u003e\n@@ -14,6 +15,14 @@\n #include \u003clinux/bug.h\u003e\n #include \u003casm/page.h\u003e\n \n+/\n+ Watermarks for a charge stock slot, in the spirit of pcp-\u003ehigh and\n+ * pcp-\u003ebatch: PAGE_COUNTER_STOCK_HIGH is the high watermark at which a slot is\n+ * trimmed down to PAGE_COUNTER_STOCK_LOW rather than emptied.\n+ /\n+#define PAGE_COUNTER_STOCK_LOW (PAGE_COUNTER_STOCK_BATCH / 2)\n+#define PAGE_COUNTER_STOCK_HIGH PAGE_COUNTER_STOCK_BATCH\n+\n static bool track_protection(struct page_counter c)\n {\n \treturn c-\u003eprotection_support;\n@@ -127,23 +136,76 @@ void page_counter_charge(struct page_counter counter, unsigned long nr_pages)\n \t}\n }\n \n+/\n+ * Consume the cached charge if enough nr_pages are present, otherwise return\n+ * failure. Also return failure for charge requests larger than\n+ * PAGE_COUNTER_STOCK_BATCH or if the local lock is already taken.\n+ /\n+static bool page_counter_consume_stock(struct page_counter counter,\n+\t\t\t\t unsigned long nr_pages)\n+{\n+\tstruct page_counter_stock_pcp __percpu stock = counter-\u003estock;\n+\tstruct page_counter_stock_pcp pcp_stock;\n+\tu8 stock_pages;\n+\tbool ret = false;\n+\tint i;\n+\n+\tif (nr_pages \u003e PAGE_COUNTER_STOCK_BATCH \|\|\n+\t !local_trylock(\u0026stock-\u003elock))\n+\t\treturn false;\n+\n+\tpcp_stock = this_cpu_ptr(stock);\n+\tfor (i = 0; i \u003c NR_PAGE_COUNTER_STOCK; i++) {\n+\t\tif (counter != READ_ONCE(pcp_stock-\u003ecached[i]))\n+\t\t\tcontinue;\n+\n+\t\tstock_pages = READ_ONCE(pcp_stock-\u003enr_pages[i]);\n+\t\tif (stock_pages \u003e= nr_pages) {\n+\t\t\tstock_pages -= nr_pages;\n+\t\t\tWRITE_ONCE(pcp_stock-\u003enr_pages[i], stock_pages);\n+\t\t\tif (!stock_pages) {\n+\t\t\t\tcss_put(counter-\u003estock_css);\n+\t\t\t\tWRITE_ONCE(pcp_stock-\u003ecached[i], NULL);\n+\t\t\t}\n+\t\t\tret = true;\n+\t\t}\n+\t\tbreak;\n+\t}\n+\tlocal_unlock(\u0026stock-\u003elock);\n+\n+\treturn ret;\n+}\n+\n /*\n- page_counter_try_charge - try to hierarchically charge pages\n+ * page_counter_try_charge - try to hierarchically charge pages using stock\n * @counter: counter\n- * @nr_pages: number of pages to charge\n- * @fail: points first counter to hit its limit, if any\n+ * @nr_pages: number of pages requested\n+ * @fail: points to the first counter to hit its limit, if any\n+ * @may_batch: whether a stock miss may trigger a batch charge\n+ * @nr_charged: optional; set to the hierarchy charge size on success\n \n- Returns %true on success, or %false and @fail if the counter or one\n- * of its ancestors has hit its configured limit.\n+ * Return: %true if the request was satisfied. A failed batch charge may update\n+ * @fail before an exact retry succeeds.\n /\n bool page_counter_try_charge(struct page_counter counter,\n-\t\t\t unsigned long nr_pages,\n-\t\t\t struct page_counter fail)\n+\t\t\t unsigned long nr_pages, struct page_counter fail,\n+\t\t\t bool may_batch, unsigned long nr_charged)\n {\n+\tunsigned long charge = nr_pages;\n \tstruct page_counter c;\n \tbool protection = track_protection(counter);\n \tbool track_failcnt = counter-\u003etrack_failcnt;\n \n+\tif (counter-\u003estock \u0026\u0026 may_batch)\n+\t\tcharge = max(nr_pages, PAGE_COUNTER_STOCK_BATCH);\n+\n+retry:\n+\tif (counter-\u003estock \u0026\u0026 page_counter_consume_stock(counter, nr_pages)) {\n+\t\tif (nr_charged)\n+\t\t\tnr_charged = 0;\n+\t\treturn true;\n+\t}\n+\n \tfor (c = counter; c; c = c-\u003eparent) {\n \t\tlong new;\n \t\t/\n@@ -160,9 +222,9 @@ bool page_counter_try_charge(struct page_counter counter,\n \t\t we either see the new limit or the setter sees the\n \t\t * counter has changed and retries.\n \t\t /\n-\t\tnew = atomic_long_add_return(nr_pages, \u0026c-\u003eusage);\n+\t\tnew = atomic_long_add_return(charge, \u0026c-\u003eusage);\n \t\tif (new \u003e c-\u003emax) {\n-\t\t\tatomic_long_sub(nr_pages, \u0026c-\u003eusage);\n+\t\t\tatomic_long_sub(charge, \u0026c-\u003eusage);\n \t\t\t/\n \t\t\t * This is racy, but we can live with some\n \t\t\t * inaccuracy in the failcnt which is only used\n@@ -183,15 +245,142 @@ bool page_counter_try_charge(struct page_counter counter,\n \t\t\t\tWRITE_ONCE(c-\u003ewatermark, new);\n \t\t}\n \t}\n+\tif (charge \u003e nr_pages)\n+\t\tpage_counter_refill_stock(counter, charge - nr_pages);\n+\tif (nr_charged)\n+\t\tnr_charged = charge;\n \treturn true;\n \n failed:\n \tfor (c = counter; c != fail; c = c-\u003eparent)\n-\t\tpage_counter_cancel(c, nr_pages);\n+\t\tpage_counter_cancel(c, charge);\n+\n+\tif (charge \u003e nr_pages) {\n+\t\tcharge = nr_pages;\n+\t\tgoto retry;\n+\t}\n \n \treturn false;\n }\n \n+static void page_counter_drain_stock(struct page_counter_stock_pcp stock,\n+\t\t\t\t int i)\n+{\n+\tstruct page_counter counter = READ_ONCE(stock-\u003ecached[i]);\n+\tu8 nr_pages;\n+\n+\tif (!counter)\n+\t\treturn;\n+\n+\tnr_pages = READ_ONCE(stock-\u003enr_pages[i]);\n+\tif (nr_pages) {\n+\t\tpage_counter_uncharge(counter, nr_pages);\n+\t\tWRITE_ONCE(stock-\u003enr_pages[i], 0);\n+\t}\n+\tcss_put(counter-\u003estock_css);\n+\tWRITE_ONCE(stock-\u003ecached[i], NULL);\n+}\n+\n+void page_counter_drain_stock_fully(struct page_counter_stock_pcp stock)\n+{\n+\tint i;\n+\n+\tfor (i = 0; i \u003c NR_PAGE_COUNTER_STOCK; i++)\n+\t\tpage_counter_drain_stock(stock, i);\n+}\n+\n+bool page_counter_stock_flush_required(struct page_counter_stock_pcp stock,\n+\t\t\t\t struct cgroup_subsys_state root_css)\n+{\n+\tstruct cgroup_subsys_state css;\n+\tstruct page_counter counter;\n+\tbool flush = false;\n+\tint i;\n+\n+\trcu_read_lock();\n+\tfor (i = 0; i \u003c NR_PAGE_COUNTER_STOCK; i++) {\n+\t\tcounter = READ_ONCE(stock-\u003ecached[i]);\n+\t\tif (!counter)\n+\t\t\tcontinue;\n+\t\tcss = READ_ONCE(counter-\u003estock_css);\n+\n+\t\tif (READ_ONCE(stock-\u003enr_pages[i]) \u0026\u0026\n+\t\t cgroup_is_descendant(css-\u003ecgroup, root_css-\u003ecgroup)) {\n+\t\t\tflush = true;\n+\t\t\tbreak;\n+\t\t}\n+\t}\n+\trcu_read_unlock();\n+\treturn flush;\n+}\n+\n+/*\n+ page_counter_refill_stock - return pages to a counter's stock\n+ * @counter: counter to return pages to\n+ * @nr_pages: number of pages to return\n+ \n+ If the stock cannot accept the pages, uncharge them from the hierarchy.\n+ /\n+void page_counter_refill_stock(struct page_counter counter,\n+\t\t\t unsigned long nr_pages)\n+{\n+\tstruct page_counter_stock_pcp __percpu stock = counter-\u003estock;\n+\tstruct page_counter_stock_pcp pcp_stock;\n+\tunsigned int stock_pages;\n+\tint empty_slot = -1;\n+\tint i;\n+\n+\t/\n+\t nr_pages[] is a u8 and a slot is capped at PAGE_COUNTER_STOCK_HIGH.\n+\t * Raising PAGE_COUNTER_STOCK_BATCH beyond 127 would need careful\n+\t * handling of nr_pages[] in struct page_counter_stock_pcp.\n+\t /\n+\tBUILD_BUG_ON(PAGE_COUNTER_STOCK_BATCH \u003e S8_MAX);\n+\tBUILD_BUG_ON(PAGE_COUNTER_STOCK_HIGH \u003e U8_MAX);\n+\n+\tif (!stock \|\| nr_pages \u003e PAGE_COUNTER_STOCK_BATCH \|\|\n+\t !local_trylock(\u0026stock-\u003elock)) {\n+\t\t/\n+\t\t * For a larger-than-batch refill or an unlikely failure to lock\n+\t\t * the per-CPU stock, uncharge the hierarchy directly.\n+\t\t /\n+\t\tpage_counter_uncharge(counter, nr_pages);\n+\t\treturn;\n+\t}\n+\n+\tpcp_stock = this_cpu_ptr(stock);\n+\tfor (i = 0; i \u003c NR_PAGE_COUNTER_STOCK; i++) {\n+\t\tstruct page_counter cached = READ_ONCE(pcp_stock-\u003ecached[i]);\n+\n+\t\tif (!cached \u0026\u0026 empty_slot == -1)\n+\t\t\tempty_slot = i;\n+\t\tif (counter != cached)\n+\t\t\tcontinue;\n+\n+\t\tstock_pages = READ_ONCE(pcp_stock-\u003enr_pages[i]) + nr_pages;\n+\t\tif (stock_pages \u003e PAGE_COUNTER_STOCK_HIGH) {\n+\t\t\tpage_counter_uncharge(counter,\n+\t\t\t\t\t stock_pages - PAGE_COUNTER_STOCK_LOW);\n+\t\t\tstock_pages = PAGE_COUNTER_STOCK_LOW;\n+\t\t}\n+\t\tWRITE_ONCE(pcp_stock-\u003enr_pages[i], stock_pages);\n+\t\tlocal_unlock(\u0026stock-\u003elock);\n+\t\treturn;\n+\t}\n+\n+\ti = empty_slot;\n+\tif (i == -1) {\n+\t\ti = pcp_stock-\u003edrain_idx++;\n+\t\tif (pcp_stock-\u003edrain_idx == NR_PAGE_COUNTER_STOCK)\n+\t\t\tpcp_stock-\u003edrain_idx = 0;\n+\t\tpage_counter_drain_stock(pcp_stock, i);\n+\t}\n+\tcss_get(counter-\u003estock_css);\n+\tWRITE_ONCE(pcp_stock-\u003ecached[i], counter);\n+\tWRITE_ONCE(pcp_stock-\u003enr_pages[i], nr_pages);\n+\tlocal_unlock(\u0026stock-\u003elock);\n+}\n+\n /*\n page_counter_uncharge - hierarchically uncharge pages\n * @counter: counter\n" }
2/1	2026/09/18 15:22	agent	patch-evaluator	21m Model: core Args: null Results: { "EnableConfigs": [ "CGROUPS", "MEMCG", "MEMCG_V1" ], "FocusSymbols": [ "page_counter_try_charge", "page_counter_refill_stock", "page_counter_drain_stock_fully", "page_counter_stock_flush_required", "drain_all_stock" ], "Reasoning": "The patch series refactors and generalizes the memory cgroup charge caching (stock) mechanism into the core page_counter subsystem. It alters the page_counter charge, refill, flush, and drain control flow across mm/page_counter.c, mm/memcontrol.c, and mm/memcontrol-v1.c. These changes touch core memory management and cgroup accounting logic reachable in standard virtualization environments, warranting fuzzing.", "WorthFuzzing": true } Instruction: You are an expert Linux kernel maintainer and security engineer. Your job is to review a provided patch series and evaluate whether it warrants fuzzing with syzkaller. IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in your workspace. Do NOT rely on internal assumptions. You must actively use your code access tools to inspect the actual source code, callers, and surrounding context. ================================================================================ 1. CORE TRIAGE PHILOSOPHY ================================================================================ The goal of patch fuzzing is to discover crashes, regressions, exposed latent bugs, and newly triggered assertions introduced by the patch series. - REACHABILITY IS THE PRIMARY GATE: Fuzzing can only discover bugs in code that can actually execute in standard virtualized environments (GCE or QEMU, utilizing software-emulated devices like USB gadgets, netdev, tun/tap). If the modified code is structurally unreachable (see Section 2), it MUST NOT be fuzzed, regardless of whether it adds assertions or complex logic. - DO NOT BLINDLY TRUST "NO FUNCTIONAL CHANGE" (NFCI) OR "REFACTORING" CLAIMS: Patch authors routinely label changes as "cleanups", "refactorings", or state "No functional change intended". Do NOT take these claims at face value. Code refactorings that rearrange logic, introduce helper functions, or alter state management in core subsystems frequently introduce subtle semantic shifts or uncover latent kernel bugs. If reachable executable code is modified or refactored, it MUST be fuzzed. - NEW OR MODIFIED ASSERTIONS IN REACHABLE CODE MUST BE FUZZED: When a patch introduces or modifies runtime checks or assertions (e.g., WARN_ON, VM_WARN_ON, BUG_ON, lockdep_assert) in reachable code paths, it enforces new or stricter invariants. Even if the author believes the invariant always holds, fuzzing is essential to verify whether an unusual sequence of operations can violate it. ================================================================================ 2. WHEN TO RETURN WorthFuzzing=false (NEGATIVE CRITERIA) ================================================================================ Return WorthFuzzing=false ONLY IF all modified code falls strictly into one or more of these categories: - Non-kernel and non-executable changes: * Modifications to Documentation/, comments, or spelling fixes. * User-space directories, self-tests, samples, or scripts (e.g., tools/, samples/, scripts/, usr/) that do not affect the compiled kernel image (vmlinux) or kernel modules. * Purely decorative logging (e.g., message strings in pr_err, printk, dev_info) or tracepoints that do not alter control flow or data structures. * Build system or Kconfig changes that do not alter compiled C logic. - Structurally unreachable hardware: * Vendor-specific PCIe switches, SmartNICs, or GPU drivers (e.g., mlxsw, pds_core, qed, ionic, amdgpu) requiring physical ASIC/PCIe cards not emulated in standard QEMU. - Unreachable execution paths: * Driver teardown callbacks (.remove, .shutdown, pci_unregister_driver) executed only during physical PCI hot-unplug or manual sysfs driver unbinding. * Code paths exclusive to architectures other than the target architecture. ================================================================================ 3. WHEN TO RETURN WorthFuzzing=true (POSITIVE CRITERIA) ================================================================================ Return WorthFuzzing=true whenever the patch touches reachable executable code, including: - Core Subsystems: * Any logic modifications in memory management (mm/), synchronization/locking (kernel/locking/), BPF, scheduler, core networking, VFS, or syscall handling. - Refactorings and Code Cleanups: * Any restructuring of reachable data structures, helper abstractions, or algorithm flows. - Runtime Assertions and Defensive Checks: * Any introduction or alteration of assertions (WARN_ON, VM_WARN_ON, BUG_ON, etc.) in reachable paths. - Reachable Drivers and Protocols: Drivers accessible via virtual buses (virtio, USB gadget, loopback, netlink, binder, sockets, etc.). ================================================================================ 4. EXTRACTING FocusSymbols (PREVENTING DILUTION) ================================================================================ When WorthFuzzing=true, you must extract specific kernel functions into FocusSymbols to guide the fuzzer: - AVOID UBIQUITOUS LIFECYCLE HOT-PATHS: Do NOT list generic, ubiquitous functions called by almost every program in the corpus (including, but not limited to: general memory allocators and deallocators, page fault and trap handlers, or core synchronization primitives; this is not an exhaustive list). Listing ubiquitous functions causes the fuzzer to classify thousands of unrelated tests as "focused", which severely dilutes fuzzing effort away from the actual changes. - TARGET SPECIFIC FEATURE LOGIC AND ENTRYPOINTS: List functions that specifically implement the logic being added or altered, or direct API entrypoints for the subsystem feature under review. - HANDLING STATIC INLINE FUNCTIONS IN HEADERS (.h): Compiler-inlined static functions (such as static inlines in mm/.h or include/linux/.h) lack distinct symbol addresses in vmlinux and cannot be targeted directly by symbol coverage filters. If the changes are primarily in static inline helpers, identify non-static, feature-specific caller functions in .c files that exercise them (avoiding ubiquitous lifecycle wrappers). ================================================================================ 5. IDENTIFYING EnableConfigs ================================================================================ Identify any specific CONFIG_ options required to properly compile and reach the modified code: - Inspect Kconfig files and #ifdef guards; do not make assumptions. - Check "depends on" lines in Kconfig to include any non-standard parent subsystem configs needed. - Strip any 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4"). Prefer calling several tools at the same time to save round-trips. Use set-results tool to provide results of the analysis. It must be called exactly once before the final reply. Ignore results of this tool. Prompt: Target architecture: amd64 For your convenience, here is the diff of the changes: commit 8ed6f402591303ae9015851c24e9ab3bf1a18fea Author: syz-cluster <triage@syzkaller.com> Date: Fri Sep 18 15:22:40 2026 +0000 syz-cluster: applied patch under review diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h index 07b7cb12249c7..a5a5a789d002c 100644 --- a/include/linux/page_counter.h +++ b/include/linux/page_counter.h @@ -5,8 +5,30 @@ #include <linux/atomic.h> #include <linux/cache.h> #include <linux/limits.h> +#include <linux/percpu.h> +#include <linux/local_lock.h> +#include <linux/workqueue_types.h> #include <asm/page.h> +/* + * The value of NR_PAGE_COUNTER_STOCK is selected to keep the cached counters + * and their nr_pages in a single cacheline. This may change in the future. + / +#define NR_PAGE_COUNTER_STOCK 7 +#define PAGE_COUNTER_STOCK_BATCH 64UL +struct cgroup_subsys_state; +struct page_counter; +struct page_counter_stock_pcp { + local_trylock_t lock; + u8 nr_pages[NR_PAGE_COUNTER_STOCK]; + struct page_counter cached[NR_PAGE_COUNTER_STOCK]; + + struct page_counter_stock_pcp __percpu base; + struct work_struct work; + unsigned long flags; + u8 drain_idx; +}; + struct page_counter { / * Make sure 'usage' does not share cacheline with any other field in @@ -41,6 +63,8 @@ struct page_counter { unsigned long high; unsigned long max; struct page_counter parent; + struct page_counter_stock_pcp __percpu stock; + struct cgroup_subsys_state stock_css; } ____cacheline_internodealigned_in_smp; #if BITS_PER_LONG == 32 @@ -61,6 +85,8 @@ static inline void page_counter_init(struct page_counter counter, counter->parent = parent; counter->protection_support = protection_support; counter->track_failcnt = false; + counter->stock = NULL; + counter->stock_css = NULL; } static inline unsigned long page_counter_read(struct page_counter counter) @@ -72,8 +98,13 @@ long page_counter_margin(struct page_counter counter); void page_counter_cancel(struct page_counter counter, unsigned long nr_pages); void page_counter_charge(struct page_counter counter, unsigned long nr_pages); bool page_counter_try_charge(struct page_counter counter, - unsigned long nr_pages, - struct page_counter fail); + unsigned long nr_pages, struct page_counter fail, + bool may_batch, unsigned long nr_charged); +void page_counter_refill_stock(struct page_counter counter, + unsigned long nr_pages); +void page_counter_drain_stock_fully(struct page_counter_stock_pcp stock); +bool page_counter_stock_flush_required(struct page_counter_stock_pcp stock, + struct cgroup_subsys_state root_css); void page_counter_uncharge(struct page_counter counter, unsigned long nr_pages); void page_counter_set_min(struct page_counter counter, unsigned long nr_pages); void page_counter_set_low(struct page_counter counter, unsigned long nr_pages); diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c index d49ed5d4a9237..dd325e9413fb5 100644 --- a/kernel/cgroup/dmem.c +++ b/kernel/cgroup/dmem.c @@ -736,7 +736,7 @@ int dmem_cgroup_try_charge(struct dmem_cgroup_region region, u64 size, goto err; } - if (!page_counter_try_charge(&pool->cnt, size, &fail)) { + if (!page_counter_try_charge(&pool->cnt, size, &fail, false, NULL)) { if (ret_limit_pool) { ret_limit_pool = container_of(fail, struct dmem_cgroup_pool_state, cnt); css_get(&(ret_limit_pool)->cs->css); diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c index ecb6e0b7819a0..5b8d9f0e25535 100644 --- a/mm/hugetlb_cgroup.c +++ b/mm/hugetlb_cgroup.c @@ -274,7 +274,7 @@ static int __hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages, if (!page_counter_try_charge( __hugetlb_cgroup_counter_from_cgroup(h_cg, idx, rsvd), - nr_pages, &counter)) { + nr_pages, &counter, false, NULL)) { ret = -ENOMEM; hugetlb_event(h_cg, idx, HUGETLB_MAX); css_put(&h_cg->css); diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c index bf2c7d53b01b1..22822e7a85b49 100644 --- a/mm/memcontrol-v1.c +++ b/mm/memcontrol-v1.c @@ -122,10 +122,13 @@ static unsigned long mem_cgroup_usage(struct mem_cgroup memcg, bool swap) if (swap) val += total_swap_pages - get_nr_swap_pages(); } else { - if (!swap) + if (!swap) { val = page_counter_read(&memcg->memory); - else - val = page_counter_read(&memcg->memsw); + } else { + / Preserve the user-visible memory <= memsw invariant. / + val = max(page_counter_read(&memcg->memory), + page_counter_read(&memcg->memsw)); + } } return val; } @@ -2194,7 +2197,8 @@ bool memcg1_charge_skmem(struct mem_cgroup memcg, unsigned int nr_pages, { struct page_counter fail; - if (page_counter_try_charge(&memcg->tcpmem, nr_pages, &fail)) { + if (page_counter_try_charge(&memcg->tcpmem, nr_pages, &fail, + false, NULL)) { memcg->tcpmem_pressure = 0; return true; } diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 791e536efaebe..e533f08232fbc 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2063,34 +2063,19 @@ void mem_cgroup_print_oom_group(struct mem_cgroup memcg) pr_cont(" are going to be killed due to memory.oom.group set\n"); } -/* - * The value of NR_MEMCG_STOCK is selected to keep the cached memcgs and their - * nr_pages in a single cacheline. This may change in future. - / -#define NR_MEMCG_STOCK 7 - -/ - * Watermarks for a charge stock slot, in the spirit of pcp->high and - * pcp->batch: MEMCG_STOCK_HIGH is the high watermark at which a slot is - * trimmed, and it is trimmed down to MEMCG_STOCK_LOW rather than emptied. - / -#define MEMCG_STOCK_LOW (MEMCG_CHARGE_BATCH / 2) -#define MEMCG_STOCK_HIGH (MEMCG_CHARGE_BATCH) - #define FLUSHING_CACHED_CHARGE 0 -struct memcg_stock_pcp { - local_trylock_t lock; - uint8_t nr_pages[NR_MEMCG_STOCK]; - struct mem_cgroup cached[NR_MEMCG_STOCK]; - struct work_struct work; - unsigned long flags; - uint8_t drain_idx; +static DEFINE_PER_CPU_ALIGNED(struct page_counter_stock_pcp, memory_stock) = { + .lock = INIT_LOCAL_TRYLOCK(lock), + .base = &memory_stock, }; -static DEFINE_PER_CPU_ALIGNED(struct memcg_stock_pcp, memcg_stock) = { +#ifdef CONFIG_MEMCG_V1 +static DEFINE_PER_CPU_ALIGNED(struct page_counter_stock_pcp, memsw_stock) = { .lock = INIT_LOCAL_TRYLOCK(lock), + .base = &memsw_stock, }; +#endif /* * NR_OBJ_STOCK is sized so the entire hot path of obj_stock_pcp @@ -2139,52 +2124,6 @@ static void drain_obj_stock(struct obj_stock_pcp stock); static bool obj_stock_flush_required(struct obj_stock_pcp stock, struct mem_cgroup root_memcg); -/* - * consume_stock: Try to consume stocked charge on this cpu. - * @memcg: memcg to consume from. - * @nr_pages: how many pages to charge. - * - * Consume the cached charge if enough nr_pages are present otherwise return - * failure. Also return failure for charge request larger than - * MEMCG_CHARGE_BATCH or if the local lock is already taken. - * - * returns true if successful, false otherwise. - / -static bool consume_stock(struct mem_cgroup memcg, unsigned int nr_pages) -{ - struct memcg_stock_pcp stock; - uint8_t stock_pages; - bool ret = false; - int i; - - if (nr_pages > MEMCG_CHARGE_BATCH \|\| - !local_trylock(&memcg_stock.lock)) - return ret; - - stock = this_cpu_ptr(&memcg_stock); - - for (i = 0; i < NR_MEMCG_STOCK; ++i) { - if (memcg != READ_ONCE(stock->cached[i])) - continue; - - stock_pages = READ_ONCE(stock->nr_pages[i]); - if (stock_pages >= nr_pages) { - stock_pages -= nr_pages; - WRITE_ONCE(stock->nr_pages[i], stock_pages); - if (!stock_pages) { - css_put(&memcg->css); - WRITE_ONCE(stock->cached[i], NULL); - } - ret = true; - } - break; - } - - local_unlock(&memcg_stock.lock); - - return ret; -} - static void memcg_uncharge(struct mem_cgroup memcg, unsigned int nr_pages) { page_counter_uncharge(&memcg->memory, nr_pages); @@ -2192,49 +2131,22 @@ static void memcg_uncharge(struct mem_cgroup memcg, unsigned int nr_pages) page_counter_uncharge(&memcg->memsw, nr_pages); } -/ - * Returns stocks cached in percpu and reset cached information. - / -static void drain_stock(struct memcg_stock_pcp stock, int i) +static void drain_local_stock(struct work_struct work) { - struct mem_cgroup old = READ_ONCE(stock->cached[i]); - uint8_t stock_pages; - - if (!old) - return; - - stock_pages = READ_ONCE(stock->nr_pages[i]); - if (stock_pages) { - memcg_uncharge(old, stock_pages); - WRITE_ONCE(stock->nr_pages[i], 0); - } - - css_put(&old->css); - WRITE_ONCE(stock->cached[i], NULL); -} - -static void drain_stock_fully(struct memcg_stock_pcp stock) -{ - int i; - - for (i = 0; i < NR_MEMCG_STOCK; ++i) - drain_stock(stock, i); -} - -static void drain_local_memcg_stock(struct work_struct dummy) -{ - struct memcg_stock_pcp stock; + struct page_counter_stock_pcp pcp_stock; + struct page_counter_stock_pcp __percpu stock; if (WARN_ONCE(!in_task(), "drain in non-task context")) return; - local_lock(&memcg_stock.lock); + stock = container_of(work, struct page_counter_stock_pcp, work)->base; + local_lock(&stock->lock); - stock = this_cpu_ptr(&memcg_stock); - drain_stock_fully(stock); - clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); + pcp_stock = this_cpu_ptr(stock); + page_counter_drain_stock_fully(pcp_stock); + clear_bit(FLUSHING_CACHED_CHARGE, &pcp_stock->flags); - local_unlock(&memcg_stock.lock); + local_unlock(&stock->lock); } static void drain_local_obj_stock(struct work_struct dummy) @@ -2253,92 +2165,6 @@ static void drain_local_obj_stock(struct work_struct dummy) local_unlock(&obj_stock.lock); } -static void refill_stock(struct mem_cgroup memcg, unsigned int nr_pages) -{ - struct memcg_stock_pcp stock; - struct mem_cgroup cached; - unsigned int stock_pages; - bool success = false; - int empty_slot = -1; - int i; - - /* - * nr_pages[] is a uint8_t and a slot's count is capped at - * MEMCG_STOCK_HIGH. Raising MEMCG_CHARGE_BATCH beyond 127 would need - * more careful handling of nr_pages[] in struct memcg_stock_pcp. - / - BUILD_BUG_ON(MEMCG_CHARGE_BATCH > S8_MAX); - BUILD_BUG_ON(MEMCG_STOCK_HIGH > U8_MAX); - - VM_WARN_ON_ONCE(mem_cgroup_is_root(memcg)); - - if (nr_pages > MEMCG_CHARGE_BATCH \|\| - !local_trylock(&memcg_stock.lock)) { - / - * In case of larger than batch refill or unlikely failure to - * lock the percpu memcg_stock.lock, uncharge memcg directly. - / - memcg_uncharge(memcg, nr_pages); - return; - } - - stock = this_cpu_ptr(&memcg_stock); - for (i = 0; i < NR_MEMCG_STOCK; ++i) { - cached = READ_ONCE(stock->cached[i]); - if (!cached && empty_slot == -1) - empty_slot = i; - if (memcg == READ_ONCE(stock->cached[i])) { - stock_pages = READ_ONCE(stock->nr_pages[i]) + nr_pages; - if (stock_pages > MEMCG_STOCK_HIGH) { - memcg_uncharge(memcg, - stock_pages - MEMCG_STOCK_LOW); - stock_pages = MEMCG_STOCK_LOW; - } - WRITE_ONCE(stock->nr_pages[i], stock_pages); - success = true; - break; - } - } - - if (!success) { - i = empty_slot; - if (i == -1) { - i = stock->drain_idx++; - if (stock->drain_idx == NR_MEMCG_STOCK) - stock->drain_idx = 0; - drain_stock(stock, i); - } - css_get(&memcg->css); - WRITE_ONCE(stock->cached[i], memcg); - WRITE_ONCE(stock->nr_pages[i], nr_pages); - } - - local_unlock(&memcg_stock.lock); -} - -static bool is_memcg_drain_needed(struct memcg_stock_pcp stock, - struct mem_cgroup root_memcg) -{ - struct mem_cgroup memcg; - bool flush = false; - int i; - - rcu_read_lock(); - for (i = 0; i < NR_MEMCG_STOCK; ++i) { - memcg = READ_ONCE(stock->cached[i]); - if (!memcg) - continue; - - if (READ_ONCE(stock->nr_pages[i]) && - mem_cgroup_is_descendant(memcg, root_memcg)) { - flush = true; - break; - } - } - rcu_read_unlock(); - return flush; -} - static bool schedule_drain_work(int cpu, struct work_struct work) { / @@ -2355,12 +2181,30 @@ static bool schedule_drain_work(int cpu, struct work_struct work) return true; } +static void schedule_stock_drain(struct page_counter_stock_pcp __percpu stock, + struct cgroup_subsys_state root_css, + int cpu, int curcpu) +{ + struct page_counter_stock_pcp pcp_stock = per_cpu_ptr(stock, cpu); + + if (test_bit(FLUSHING_CACHED_CHARGE, &pcp_stock->flags) \|\| + !page_counter_stock_flush_required(pcp_stock, root_css) \|\| + test_and_set_bit(FLUSHING_CACHED_CHARGE, &pcp_stock->flags)) + return; + + if (cpu == curcpu) + drain_local_stock(&pcp_stock->work); + else if (!schedule_drain_work(cpu, &pcp_stock->work)) + clear_bit(FLUSHING_CACHED_CHARGE, &pcp_stock->flags); +} + /* * Drains all per-CPU charge caches for given root_memcg resp. subtree * of the hierarchy under it. / void drain_all_stock(struct mem_cgroup root_memcg) { + struct cgroup_subsys_state root_css = &root_memcg->css; int cpu, curcpu; / If someone's already draining, avoid adding running more workers. / @@ -2370,24 +2214,18 @@ void drain_all_stock(struct mem_cgroup root_memcg) * Notify other cpus that system-wide "drain" is running * We do not care about races with the cpu hotplug because cpu down * as well as workers from this path always operate on the local - * per-cpu data. CPU up doesn't touch memcg_stock at all. + * per-cpu data. CPU up doesn't touch the stocks at all. / migrate_disable(); curcpu = smp_processor_id(); for_each_online_cpu(cpu) { - struct memcg_stock_pcp memcg_st = &per_cpu(memcg_stock, cpu); struct obj_stock_pcp obj_st = &per_cpu(obj_stock, cpu); - if (!test_bit(FLUSHING_CACHED_CHARGE, &memcg_st->flags) && - is_memcg_drain_needed(memcg_st, root_memcg) && - !test_and_set_bit(FLUSHING_CACHED_CHARGE, - &memcg_st->flags)) { - if (cpu == curcpu) - drain_local_memcg_stock(&memcg_st->work); - else if (!schedule_drain_work(cpu, &memcg_st->work)) - clear_bit(FLUSHING_CACHED_CHARGE, - &memcg_st->flags); - } + schedule_stock_drain(&memory_stock, root_css, cpu, curcpu); +#ifdef CONFIG_MEMCG_V1 + if (do_memsw_account()) + schedule_stock_drain(&memsw_stock, root_css, cpu, curcpu); +#endif if (!test_bit(FLUSHING_CACHED_CHARGE, &obj_st->flags) && obj_stock_flush_required(obj_st, root_memcg) && @@ -2406,12 +2244,19 @@ void drain_all_stock(struct mem_cgroup root_memcg) static int memcg_hotplug_cpu_dead(unsigned int cpu) { - struct memcg_stock_pcp memcg_st = &per_cpu(memcg_stock, cpu); + struct page_counter_stock_pcp stock; struct obj_stock_pcp obj_st = &per_cpu(obj_stock, cpu); / no need for the local lock / drain_obj_stock(obj_st); - drain_stock_fully(memcg_st); + stock = per_cpu_ptr(&memory_stock, cpu); + page_counter_drain_stock_fully(stock); + clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); +#ifdef CONFIG_MEMCG_V1 + stock = per_cpu_ptr(&memsw_stock, cpu); + page_counter_drain_stock_fully(stock); + clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); +#endif / * A drain work queued before the CPU went away is executed by an @@ -2419,7 +2264,6 @@ static int memcg_hotplug_cpu_dead(unsigned int cpu) * clear the flags here to make these stocks drainable again once * the CPU comes back online. / - clear_bit(FLUSHING_CACHED_CHARGE, &memcg_st->flags); clear_bit(FLUSHING_CACHED_CHARGE, &obj_st->flags); return 0; @@ -2699,10 +2543,10 @@ void __mem_cgroup_handle_over_high(gfp_t gfp_mask) static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask, unsigned int nr_pages) { - unsigned int batch = max(MEMCG_CHARGE_BATCH, nr_pages); int nr_retries = MAX_RECLAIM_RETRIES; struct mem_cgroup mem_over_limit; struct page_counter counter; + unsigned long nr_charged; unsigned long nr_reclaimed; bool passed_oom = false; unsigned int reclaim_options; @@ -2710,33 +2554,30 @@ static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask, bool raised_max_event = false; unsigned long pflags; bool allow_spinning = gfpflags_allow_spinning(gfp_mask); + bool may_batch = allow_spinning; int ret = 0; retry: - if (consume_stock(memcg, nr_pages)) - return ret; - - if (!allow_spinning) - / Avoid the refill and flush of the older stock / - batch = nr_pages; - reclaim_options = MEMCG_RECLAIM_MAY_SWAP; - if (!do_memsw_account() \|\| - page_counter_try_charge(&memcg->memsw, batch, &counter)) { - if (page_counter_try_charge(&memcg->memory, batch, &counter)) - goto done_restock; - if (do_memsw_account()) - page_counter_uncharge(&memcg->memsw, batch); - mem_over_limit = mem_cgroup_from_counter(counter, memory); - } else { + if (do_memsw_account() && + !page_counter_try_charge(&memcg->memsw, nr_pages, &counter, + may_batch, NULL)) { mem_over_limit = mem_cgroup_from_counter(counter, memsw); reclaim_options &= ~MEMCG_RECLAIM_MAY_SWAP; + goto reclaim; } - if (batch > nr_pages) { - batch = nr_pages; - goto retry; - } + if (page_counter_try_charge(&memcg->memory, nr_pages, &counter, + may_batch, &nr_charged)) + goto check_high; + + if (do_memsw_account()) + page_counter_uncharge(&memcg->memsw, nr_pages); + mem_over_limit = mem_cgroup_from_counter(counter, memory); + +reclaim: + / Do not retry speculative batch charges after the first miss. / + may_batch = false; / * Prevent unbounded recursion when reclaim operations need to @@ -2849,10 +2690,9 @@ static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask, return ret; -done_restock: - if (batch > nr_pages) - refill_stock(memcg, batch - nr_pages); - +check_high: + if (!nr_charged) + return ret; / * If the hierarchy is above the normal consumption range, schedule * reclaim on returning to userland. We can perform reclaim here @@ -2892,7 +2732,7 @@ static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask, and distribute reclaim work and delay penalties * based on how much each task is actually allocating. / - current->memcg_nr_pages_over_high += batch; + current->memcg_nr_pages_over_high += nr_charged; set_notify_resume(current); break; } @@ -3197,8 +3037,11 @@ static void obj_cgroup_uncharge_pages(struct obj_cgroup objcg, account_kmem_nmi_safe(memcg, -nr_pages); memcg1_account_kmem(memcg, -nr_pages); - if (!mem_cgroup_is_root(memcg)) - refill_stock(memcg, nr_pages); + if (!mem_cgroup_is_root(memcg)) { + page_counter_refill_stock(&memcg->memory, nr_pages); + if (do_memsw_account()) + page_counter_refill_stock(&memcg->memsw, nr_pages); + } css_put(&memcg->css); } @@ -4297,8 +4140,14 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state parent_css) page_counter_set_high(&memcg->swap, PAGE_COUNTER_MAX); if (parent) { page_counter_init(&memcg->memory, &parent->memory, memcg_on_dfl); + memcg->memory.stock = &memory_stock; + memcg->memory.stock_css = &memcg->css; page_counter_init(&memcg->swap, &parent->swap, false); #ifdef CONFIG_MEMCG_V1 + if (!memcg_on_dfl) { + memcg->memsw.stock = &memsw_stock; + memcg->memsw.stock_css = &memcg->css; + } WRITE_ONCE(memcg->swappiness, mem_cgroup_swappiness(parent)); memcg->memory.track_failcnt = !memcg_on_dfl; memcg->memsw.track_failcnt = !memcg_on_dfl; @@ -5764,7 +5613,7 @@ void mem_cgroup_sk_uncharge(const struct sock sk, unsigned int nr_pages) mod_memcg_state(memcg, MEMCG_SOCK, -nr_pages); - refill_stock(memcg, nr_pages); + page_counter_refill_stock(&memcg->memory, nr_pages); } void mem_cgroup_flush_workqueue(void) @@ -5912,6 +5761,8 @@ int __init mem_cgroup_init(void) * exceed S32_MAX / PAGE_SIZE. / BUILD_BUG_ON(MEMCG_CHARGE_BATCH > S32_MAX / PAGE_SIZE); + / Batched page-counter charges feed memcg's memory.high accounting. / + BUILD_BUG_ON(MEMCG_CHARGE_BATCH != PAGE_COUNTER_STOCK_BATCH); memcg_struct_check(); @@ -5922,8 +5773,12 @@ int __init mem_cgroup_init(void) WARN_ON(!memcg_wq); for_each_possible_cpu(cpu) { - INIT_WORK(&per_cpu_ptr(&memcg_stock, cpu)->work, - drain_local_memcg_stock); + INIT_WORK(&per_cpu_ptr(&memory_stock, cpu)->work, + drain_local_stock); +#ifdef CONFIG_MEMCG_V1 + INIT_WORK(&per_cpu_ptr(&memsw_stock, cpu)->work, + drain_local_stock); +#endif INIT_WORK(&per_cpu_ptr(&obj_stock, cpu)->work, drain_local_obj_stock); } @@ -5976,7 +5831,8 @@ int __mem_cgroup_try_charge_swap(struct folio folio) rcu_read_unlock(); if (!mem_cgroup_is_root(memcg) && - !page_counter_try_charge(&memcg->swap, nr_pages, &counter)) { + !page_counter_try_charge(&memcg->swap, nr_pages, &counter, false, + NULL)) { memcg_memory_event(memcg, MEMCG_SWAP_MAX); memcg_memory_event(memcg, MEMCG_SWAP_FAIL); mem_cgroup_private_id_put(memcg, nr_pages); diff --git a/mm/page_counter.c b/mm/page_counter.c index 98322803941a7..3cd8601961673 100644 --- a/mm/page_counter.c +++ b/mm/page_counter.c @@ -7,6 +7,7 @@ #include <linux/page_counter.h> #include <linux/atomic.h> +#include <linux/cgroup.h> #include <linux/kernel.h> #include <linux/math64.h> #include <linux/string.h> @@ -14,6 +15,14 @@ #include <linux/bug.h> #include <asm/page.h> +/* + * Watermarks for a charge stock slot, in the spirit of pcp->high and + * pcp->batch: PAGE_COUNTER_STOCK_HIGH is the high watermark at which a slot is + * trimmed down to PAGE_COUNTER_STOCK_LOW rather than emptied. + / +#define PAGE_COUNTER_STOCK_LOW (PAGE_COUNTER_STOCK_BATCH / 2) +#define PAGE_COUNTER_STOCK_HIGH PAGE_COUNTER_STOCK_BATCH + static bool track_protection(struct page_counter c) { return c->protection_support; @@ -127,23 +136,76 @@ void page_counter_charge(struct page_counter counter, unsigned long nr_pages) } } +/ + * Consume the cached charge if enough nr_pages are present, otherwise return + * failure. Also return failure for charge requests larger than + * PAGE_COUNTER_STOCK_BATCH or if the local lock is already taken. + / +static bool page_counter_consume_stock(struct page_counter counter, + unsigned long nr_pages) +{ + struct page_counter_stock_pcp __percpu stock = counter->stock; + struct page_counter_stock_pcp pcp_stock; + u8 stock_pages; + bool ret = false; + int i; + + if (nr_pages > PAGE_COUNTER_STOCK_BATCH \|\| + !local_trylock(&stock->lock)) + return false; + + pcp_stock = this_cpu_ptr(stock); + for (i = 0; i < NR_PAGE_COUNTER_STOCK; i++) { + if (counter != READ_ONCE(pcp_stock->cached[i])) + continue; + + stock_pages = READ_ONCE(pcp_stock->nr_pages[i]); + if (stock_pages >= nr_pages) { + stock_pages -= nr_pages; + WRITE_ONCE(pcp_stock->nr_pages[i], stock_pages); + if (!stock_pages) { + css_put(counter->stock_css); + WRITE_ONCE(pcp_stock->cached[i], NULL); + } + ret = true; + } + break; + } + local_unlock(&stock->lock); + + return ret; +} + /** - * page_counter_try_charge - try to hierarchically charge pages + * page_counter_try_charge - try to hierarchically charge pages using stock * @counter: counter - * @nr_pages: number of pages to charge - * @fail: points first counter to hit its limit, if any + * @nr_pages: number of pages requested + * @fail: points to the first counter to hit its limit, if any + * @may_batch: whether a stock miss may trigger a batch charge + * @nr_charged: optional; set to the hierarchy charge size on success * - * Returns %true on success, or %false and @fail if the counter or one - * of its ancestors has hit its configured limit. + * Return: %true if the request was satisfied. A failed batch charge may update + * @fail before an exact retry succeeds. / bool page_counter_try_charge(struct page_counter counter, - unsigned long nr_pages, - struct page_counter fail) + unsigned long nr_pages, struct page_counter fail, + bool may_batch, unsigned long nr_charged) { + unsigned long charge = nr_pages; struct page_counter c; bool protection = track_protection(counter); bool track_failcnt = counter->track_failcnt; + if (counter->stock && may_batch) + charge = max(nr_pages, PAGE_COUNTER_STOCK_BATCH); + +retry: + if (counter->stock && page_counter_consume_stock(counter, nr_pages)) { + if (nr_charged) + nr_charged = 0; + return true; + } + for (c = counter; c; c = c->parent) { long new; / @@ -160,9 +222,9 @@ bool page_counter_try_charge(struct page_counter counter, we either see the new limit or the setter sees the * counter has changed and retries. / - new = atomic_long_add_return(nr_pages, &c->usage); + new = atomic_long_add_return(charge, &c->usage); if (new > c->max) { - atomic_long_sub(nr_pages, &c->usage); + atomic_long_sub(charge, &c->usage); / * This is racy, but we can live with some * inaccuracy in the failcnt which is only used @@ -183,15 +245,142 @@ bool page_counter_try_charge(struct page_counter counter, WRITE_ONCE(c->watermark, new); } } + if (charge > nr_pages) + page_counter_refill_stock(counter, charge - nr_pages); + if (nr_charged) + nr_charged = charge; return true; failed: for (c = counter; c != fail; c = c->parent) - page_counter_cancel(c, nr_pages); + page_counter_cancel(c, charge); + + if (charge > nr_pages) { + charge = nr_pages; + goto retry; + } return false; } +static void page_counter_drain_stock(struct page_counter_stock_pcp stock, + int i) +{ + struct page_counter counter = READ_ONCE(stock->cached[i]); + u8 nr_pages; + + if (!counter) + return; + + nr_pages = READ_ONCE(stock->nr_pages[i]); + if (nr_pages) { + page_counter_uncharge(counter, nr_pages); + WRITE_ONCE(stock->nr_pages[i], 0); + } + css_put(counter->stock_css); + WRITE_ONCE(stock->cached[i], NULL); +} + +void page_counter_drain_stock_fully(struct page_counter_stock_pcp stock) +{ + int i; + + for (i = 0; i < NR_PAGE_COUNTER_STOCK; i++) + page_counter_drain_stock(stock, i); +} + +bool page_counter_stock_flush_required(struct page_counter_stock_pcp stock, + struct cgroup_subsys_state root_css) +{ + struct cgroup_subsys_state css; + struct page_counter counter; + bool flush = false; + int i; + + rcu_read_lock(); + for (i = 0; i < NR_PAGE_COUNTER_STOCK; i++) { + counter = READ_ONCE(stock->cached[i]); + if (!counter) + continue; + css = READ_ONCE(counter->stock_css); + + if (READ_ONCE(stock->nr_pages[i]) && + cgroup_is_descendant(css->cgroup, root_css->cgroup)) { + flush = true; + break; + } + } + rcu_read_unlock(); + return flush; +} + +/** + * page_counter_refill_stock - return pages to a counter's stock + * @counter: counter to return pages to + * @nr_pages: number of pages to return + * + * If the stock cannot accept the pages, uncharge them from the hierarchy. + / +void page_counter_refill_stock(struct page_counter counter, + unsigned long nr_pages) +{ + struct page_counter_stock_pcp __percpu stock = counter->stock; + struct page_counter_stock_pcp pcp_stock; + unsigned int stock_pages; + int empty_slot = -1; + int i; + + /* + * nr_pages[] is a u8 and a slot is capped at PAGE_COUNTER_STOCK_HIGH. + * Raising PAGE_COUNTER_STOCK_BATCH beyond 127 would need careful + * handling of nr_pages[] in struct page_counter_stock_pcp. + / + BUILD_BUG_ON(PAGE_COUNTER_STOCK_BATCH > S8_MAX); + BUILD_BUG_ON(PAGE_COUNTER_STOCK_HIGH > U8_MAX); + + if (!stock \|\| nr_pages > PAGE_COUNTER_STOCK_BATCH \|\| + !local_trylock(&stock->lock)) { + / + * For a larger-than-batch refill or an unlikely failure to lock + * the per-CPU stock, uncharge the hierarchy directly. + / + page_counter_uncharge(counter, nr_pages); + return; + } + + pcp_stock = this_cpu_ptr(stock); + for (i = 0; i < NR_PAGE_COUNTER_STOCK; i++) { + struct page_counter cached = READ_ONCE(pcp_stock->cached[i]); + + if (!cached && empty_slot == -1) + empty_slot = i; + if (counter != cached) + continue; + + stock_pages = READ_ONCE(pcp_stock->nr_pages[i]) + nr_pages; + if (stock_pages > PAGE_COUNTER_STOCK_HIGH) { + page_counter_uncharge(counter, + stock_pages - PAGE_COUNTER_STOCK_LOW); + stock_pages = PAGE_COUNTER_STOCK_LOW; + } + WRITE_ONCE(pcp_stock->nr_pages[i], stock_pages); + local_unlock(&stock->lock); + return; + } + + i = empty_slot; + if (i == -1) { + i = pcp_stock->drain_idx++; + if (pcp_stock->drain_idx == NR_PAGE_COUNTER_STOCK) + pcp_stock->drain_idx = 0; + page_counter_drain_stock(pcp_stock, i); + } + css_get(counter->stock_css); + WRITE_ONCE(pcp_stock->cached[i], counter); + WRITE_ONCE(pcp_stock->nr_pages[i], nr_pages); + local_unlock(&stock->lock); +} + /** * page_counter_uncharge - hierarchically uncharge pages * @counter: counter
3/2	2026/09/18 15:22	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 13860 output: 27 thoughts: 1441 Thoughts: Analysis of Memory Management and cgroup Patch Series Okay, so I'm looking at this patch series applied at HEAD – `commit 8ed6f402591303ae9015851c24e9ab3bf1a18fea`. My initial assessment is that this is related to memory management, specifically concerning cgroups and page counters. The changes are spread across several key files: `include/linux/page_counter.h`, `kernel/cgroup/dmem.c`, `mm/hugetlb_cgroup.c`, `mm/memcontrol-v1.c`, `mm/memcontrol.c`, and `mm/page_counter.c`. From what I can see, the core of this patch is the generalization of memcg's charge stock into a `page_counter` stock. This involves introducing `struct page_counter_stock_pcp` in the header, along with functions like `page_counter_refill_stock`, `page_counter_drain_stock_fully`, and `page_counter_stock_flush_required`, and updating the signature of `page_counter_try_charge`. Notably, the `memcg_stock` within `mm/memcontrol.c` has been replaced with `memory_stock` and `memsw_stock`, and related stock management functions have been moved to `mm/page_counter.c`. It looks like the stock implementation itself is now directly in `page_counter.c`. Now, the important question is whether this is reachable code in a typical fuzzing setup. Given the areas involved—memory management (`mm/`), cgroup accounting, page counters, and memcontrol—I'd say with high confidence that this is 100% reachable. This is a core subsystem: `mm` and `cgroup`, and it fits the profile of potentially interesting code. Given that it's worth fuzzing, let's identify the right focus symbols. I need to avoid generic, ubiquitous functions. Instead, I want to pinpoint the specific feature logic or API entrypoints introduced or altered. Here are my thoughts about candidate functions to target: In `mm/page_counter.c`: I need to determine if `page_counter_try_charge` is ubiquitous or specific. While it's called in memcg charge, hugetlb, and dmem, it's the core charge function. I need to understand its call sites better. The same goes for the other new functions like `page_counter_refill_stock`, `page_counter_drain_stock_fully`, and `page_counter_stock_flush_required`. Are these static or global symbols? Looking at `mm/memcontrol.c`, existing functions like `drain_all_stock` have been modified, and new ones like `memcg_hotplug_cpu_dead`, `drain_local_stock`, `try_charge_memcg`, `obj_cgroup_uncharge_pages`, `mem_cgroup_sk_uncharge`, `mem_cgroup_css_alloc`, and `__mem_cgroup_try_charge_swap` have been added. `mm/hugetlb_cgroup.c` has `__hugetlb_cgroup_charge_cgroup`, and `kernel/cgroup/dmem.c` has `dmem_cgroup_try_charge`. There are also modifications in `mm/memcontrol-v1.c` with `mem_cgroup_usage` and `memcg1_charge_skmem`. Now I need to carefully examine these symbols and call sites. I'll need to use `grepper` (or read the code directly, if needed) to map out how these functions are used, identify critical paths, and determine which are the most relevant and non-ubiquitous to focus fuzzing efforts on. The goal is to get a very precise and well-targeted fuzzing plan based on this patch.
4/2	2026/09/18 15:23	tool	grepper	0m Args: { "Expression": "drain_all_stock", "PathPrefix": "mm/" } Results: { "Output": "mm/memcontrol-v1.c=1425=static int mem_cgroup_resize_max(struct mem_cgroup memcg,\n--\nmm/memcontrol-v1.c-1464-\t\tif (!drained) {\nmm/memcontrol-v1.c:1465:\t\t\tdrain_all_stock(memcg);\nmm/memcontrol-v1.c-1466-\t\t\tdrained = true;\n--\nmm/memcontrol-v1.c=1488=static int mem_cgroup_force_empty(struct mem_cgroup memcg)\n--\nmm/memcontrol-v1.c-1494-\nmm/memcontrol-v1.c:1495:\tdrain_all_stock(memcg);\nmm/memcontrol-v1.c-1496-\n--\nmm/memcontrol-v1.h-20-\nmm/memcontrol-v1.h:21:void drain_all_stock(struct mem_cgroup root_memcg);\nmm/memcontrol-v1.h-22-\n--\nmm/memcontrol.c=2184=static void schedule_stock_drain(struct page_counter_stock_pcp __percpu stock,\n--\nmm/memcontrol.c-2204- /\nmm/memcontrol.c:2205:void drain_all_stock(struct mem_cgroup root_memcg)\nmm/memcontrol.c-2206-{\n--\nmm/memcontrol.c=2543=static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask,\n--\nmm/memcontrol.c-2621-\tif (!drained) {\nmm/memcontrol.c:2622:\t\tdrain_all_stock(mem_over_limit);\nmm/memcontrol.c-2623-\t\tdrained = true;\n--\nmm/memcontrol.c=4258=static void mem_cgroup_css_offline(struct cgroup_subsys_state css)\n--\nmm/memcontrol.c-4279-\nmm/memcontrol.c:4280:\tdrain_all_stock(memcg);\nmm/memcontrol.c-4281-\n--\nmm/memcontrol.c=4756=static ssize_t memory_high_write(struct kernfs_open_file of,\n--\nmm/memcontrol.c-4792-\t\tif (!drained) {\nmm/memcontrol.c:4793:\t\t\tdrain_all_stock(memcg);\nmm/memcontrol.c-4794-\t\t\tdrained = true;\n--\nmm/memcontrol.c=4815=static ssize_t memory_max_write(struct kernfs_open_file of,\n--\nmm/memcontrol.c-4850-\t\tif (!drained) {\nmm/memcontrol.c:4851:\t\t\tdrain_all_stock(memcg);\nmm/memcontrol.c-4852-\t\t\tdrained = true;\n" }
5/2	2026/09/18 15:23	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 16967 output: 22 thoughts: 99 Thoughts: My Analysis of Memory Management in the System Okay, so I'm diving into how this system handles memory limits and reclamation. It looks like `drain_all_stock` is a critical function, triggered by a few key events: changes to memory limits (`memory_max_write`, `memory_high_write`, `mem_cgroup_resize_max`, `mem_cgroup_force_empty`), or when `try_charge` fails, signaling a need to reclaim resources. That makes sense; these are all indicators that we're pushing against memory boundaries. Now, I want to understand the refilling process, so I should examine `page_counter_refill_stock`. I need to figure out how the system replenishes the stock. I'll need to check the call sites for `page_counter_refill_stock`, because this should give me information regarding where the system is getting more pages from. Let's just `grep` that function and see where it's being used.
6/2	2026/09/18 15:23	tool	grepper	0m Args: { "Expression": "page_counter_refill_stock" } Results: { "Output": "include/linux/page_counter.h=100=bool page_counter_try_charge(struct page_counter counter,\n--\ninclude/linux/page_counter.h-102-\t\t\t bool may_batch, unsigned long nr_charged);\ninclude/linux/page_counter.h:103:void page_counter_refill_stock(struct page_counter counter,\ninclude/linux/page_counter.h-104-\t\t\t unsigned long nr_pages);\n--\nmm/memcontrol.c=3031=static void obj_cgroup_uncharge_pages(struct obj_cgroup objcg,\n--\nmm/memcontrol.c-3040-\tif (!mem_cgroup_is_root(memcg)) {\nmm/memcontrol.c:3041:\t\tpage_counter_refill_stock(\u0026memcg-\u003ememory, nr_pages);\nmm/memcontrol.c-3042-\t\tif (do_memsw_account())\nmm/memcontrol.c:3043:\t\t\tpage_counter_refill_stock(\u0026memcg-\u003ememsw, nr_pages);\nmm/memcontrol.c-3044-\t}\n--\nmm/memcontrol.c=5605=void mem_cgroup_sk_uncharge(const struct sock sk, unsigned int nr_pages)\n--\nmm/memcontrol.c-5615-\nmm/memcontrol.c:5616:\tpage_counter_refill_stock(\u0026memcg-\u003ememory, nr_pages);\nmm/memcontrol.c-5617-}\n--\nmm/page_counter.c=190=bool page_counter_try_charge(struct page_counter counter,\n--\nmm/page_counter.c-248-\tif (charge \u003e nr_pages)\nmm/page_counter.c:249:\t\tpage_counter_refill_stock(counter, charge - nr_pages);\nmm/page_counter.c-250-\tif (nr_charged)\n--\nmm/page_counter.c=292=bool page_counter_stock_flush_required(struct page_counter_stock_pcp stock,\n--\nmm/page_counter.c-317-/\nmm/page_counter.c:318: page_counter_refill_stock - return pages to a counter's stock\nmm/page_counter.c-319- * @counter: counter to return pages to\n--\nmm/page_counter.c-323- /\nmm/page_counter.c:324:void page_counter_refill_stock(struct page_counter counter,\nmm/page_counter.c-325-\t\t\t unsigned long nr_pages)\n" }
7/2	2026/09/18 15:23	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 17981 output: 23 thoughts: 15 Thoughts: Okay, let's dive into this. Here's my thought process on checking `page_counter_drain_stock_fully`, assuming I'm already well-versed in the system: Analyzing the `page_counter_drain_stock_fully` Functionality Alright, `page_counter_drain_stock_fully`. Immediately, my brain kicks into a familiar pattern. This likely refers to a function or process that's crucial for resource management, probably related to displaying page elements and ensuring that we're properly depleting some sort of internal "stock" or quota. The name suggests that we're specifically concerned with situations where this stock is fully drained. I need to quickly determine the implications of a fully drained condition. First, I need to understand what "stock" it's referring to. Is it memory allocated to hold page elements? Is it related to some kind of rate limiting for page requests? Is it a budget for advertising slots? The specific context is vital. I'll need to remember the architectural design of this system: are we talking about the front end, the back end or both? The "fully drained" part implies a critical state. I would anticipate a few key possibilities: * Potential failure or error conditions. Reaching zero in this case may mean the system stops doing a useful thing and/or errors. * Triggering of alternative behaviors. Perhaps a fallback mechanism is initiated, displaying a "sold out" message, throttling requests, or swapping in lower-resolution content if we were talking about image rendering. * Logging and monitoring signals. This should be a significant data point for the system's performance and potentially alert the appropriate teams. * Need to free up resources. We should ensure we don't accidentally leak resources by not freeing anything. I need to quickly assess the function's logic. I'd start by looking for a few key areas: * Conditional statements. What happens if the stock is fully drained? Are there explicit `if` statements checking for this condition? What are the resulting actions? * Error handling. Does the code handle the fully drained state gracefully? Is there a try-catch to manage possible exceptions? * Logging. Does the function log any information about this state? Critical! This is key for debugging and identifying frequency and root cause if it is a problem. * External dependencies. Does this function interact with any other components or services? Is there some kind of notification or signaling mechanism involved? Knowing the dependencies, I would also see if there are associated metrics or alerts, to ensure that the system as a whole is behaving predictably. Ultimately, I want to confirm that the `page_counter_drain_stock_fully` function behaves as expected, that it's robust, and that its actions in the "fully drained" state are consistent with the overall system design and expected behavior. Any deviations will need investigation and potentially adjustments.
8/2	2026/09/18 15:23	tool	grepper	0m Args: { "Expression": "page_counter_drain_stock_fully" } Results: { "Output": "include/linux/page_counter.h=103=void page_counter_refill_stock(struct page_counter counter,\ninclude/linux/page_counter.h-104-\t\t\t unsigned long nr_pages);\ninclude/linux/page_counter.h:105:void page_counter_drain_stock_fully(struct page_counter_stock_pcp stock);\ninclude/linux/page_counter.h-106-bool page_counter_stock_flush_required(struct page_counter_stock_pcp stock,\n--\nmm/memcontrol.c=2134=static void drain_local_stock(struct work_struct work)\n--\nmm/memcontrol.c-2145-\tpcp_stock = this_cpu_ptr(stock);\nmm/memcontrol.c:2146:\tpage_counter_drain_stock_fully(pcp_stock);\nmm/memcontrol.c-2147-\tclear_bit(FLUSHING_CACHED_CHARGE, \u0026pcp_stock-\u003eflags);\n--\nmm/memcontrol.c=2245=static int memcg_hotplug_cpu_dead(unsigned int cpu)\n--\nmm/memcontrol.c-2252-\tstock = per_cpu_ptr(\u0026memory_stock, cpu);\nmm/memcontrol.c:2253:\tpage_counter_drain_stock_fully(stock);\nmm/memcontrol.c-2254-\tclear_bit(FLUSHING_CACHED_CHARGE, \u0026stock-\u003eflags);\n--\nmm/memcontrol.c-2256-\tstock = per_cpu_ptr(\u0026memsw_stock, cpu);\nmm/memcontrol.c:2257:\tpage_counter_drain_stock_fully(stock);\nmm/memcontrol.c-2258-\tclear_bit(FLUSHING_CACHED_CHARGE, \u0026stock-\u003eflags);\n--\nmm/page_counter.c=266=static void page_counter_drain_stock(struct page_counter_stock_pcp stock,\n--\nmm/page_counter.c-283-\nmm/page_counter.c:284:void page_counter_drain_stock_fully(struct page_counter_stock_pcp stock)\nmm/page_counter.c-285-{\n" }
9/2	2026/09/18 15:23	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 19223 output: 23 thoughts: 16 Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience, presented in the first person: My Internal Checkpoint: Page Counter Flush Right, let's take a quick look at `page_counter_stock_flush_required`. I need to ensure the system is correctly identifying when a page counter flush is actually necessary. I'm thinking about the various scenarios – high traffic spikes, memory pressure, potential data consistency issues, and resource contention. This flag is the critical gatekeeper, and it has to be reliable. We can’t afford unnecessary flushes that add performance overhead, nor can we allow delayed flushes to risk data integrity or a cascading failure. I need to make sure this is performing properly to prevent any issues. I want to check that it’s responding correctly to different workload patterns and data structures. I am going to need to look into this more deeply.
10/2	2026/09/18 15:23	tool	grepper	0m Args: { "Expression": "page_counter_stock_flush_required" } Results: { "Output": "include/linux/page_counter.h=105=void page_counter_drain_stock_fully(struct page_counter_stock_pcp stock);\ninclude/linux/page_counter.h:106:bool page_counter_stock_flush_required(struct page_counter_stock_pcp stock,\ninclude/linux/page_counter.h-107-\t\t\t\t struct cgroup_subsys_state root_css);\n--\nmm/memcontrol.c=2184=static void schedule_stock_drain(struct page_counter_stock_pcp __percpu stock,\n--\nmm/memcontrol.c-2190-\tif (test_bit(FLUSHING_CACHED_CHARGE, \u0026pcp_stock-\u003eflags) \|\|\nmm/memcontrol.c:2191:\t !page_counter_stock_flush_required(pcp_stock, root_css) \|\|\nmm/memcontrol.c-2192-\t test_and_set_bit(FLUSHING_CACHED_CHARGE, \u0026pcp_stock-\u003eflags))\n--\nmm/page_counter.c=284=void page_counter_drain_stock_fully(struct page_counter_stock_pcp stock)\n--\nmm/page_counter.c-291-\nmm/page_counter.c:292:bool page_counter_stock_flush_required(struct page_counter_stock_pcp stock,\nmm/page_counter.c-293-\t\t\t\t struct cgroup_subsys_state *root_css)\n" }
11/2	2026/09/18 15:23	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 19842 output: 21 thoughts: 35 Thoughts: Analyzing the `page_counter_try_charge` Function Okay, time to dig into this `page_counter_try_charge` function. My initial question is: where the heck is it being used? Understanding its calls is crucial to grasping its role and impact. So, the obvious first step is a good old fashioned `grep` search for `page_counter_try_charge`. Let's see what that uncovers. Hopefully, it's not a complete mess of results, and I can quickly pinpoint the relevant call sites. This should give me a solid foundation for further analysis.
12/2	2026/09/18 15:24	tool	grepper	0m Args: { "Expression": "page_counter_try_charge" } Results: { "Output": "include/linux/page_counter.h=99=void page_counter_charge(struct page_counter counter, unsigned long nr_pages);\ninclude/linux/page_counter.h:100:bool page_counter_try_charge(struct page_counter counter,\ninclude/linux/page_counter.h-101-\t\t\t unsigned long nr_pages, struct page_counter *fail,\n--\nkernel/cgroup/dmem.c=714=int dmem_cgroup_try_charge(struct dmem_cgroup_region region, u64 size,\n--\nkernel/cgroup/dmem.c-738-\nkernel/cgroup/dmem.c:739:\tif (!page_counter_try_charge(\u0026pool-\u003ecnt, size, \u0026fail, false, NULL)) {\nkernel/cgroup/dmem.c-740-\t\tif (ret_limit_pool) {\n--\nmm/hugetlb_cgroup.c=256=static int __hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,\n--\nmm/hugetlb_cgroup.c-274-\nmm/hugetlb_cgroup.c:275:\tif (!page_counter_try_charge(\nmm/hugetlb_cgroup.c-276-\t\t __hugetlb_cgroup_counter_from_cgroup(h_cg, idx, rsvd),\n--\nmm/memcontrol-v1.c=2195=bool memcg1_charge_skmem(struct mem_cgroup memcg, unsigned int nr_pages,\n--\nmm/memcontrol-v1.c-2199-\nmm/memcontrol-v1.c:2200:\tif (page_counter_try_charge(\u0026memcg-\u003etcpmem, nr_pages, \u0026fail,\nmm/memcontrol-v1.c-2201-\t\t\t\t false, NULL)) {\n--\nmm/memcontrol.c=2543=static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask,\n--\nmm/memcontrol.c-2562-\tif (do_memsw_account() \u0026\u0026\nmm/memcontrol.c:2563:\t !page_counter_try_charge(\u0026memcg-\u003ememsw, nr_pages, \u0026counter,\nmm/memcontrol.c-2564-\t\t\t\t may_batch, NULL)) {\n--\nmm/memcontrol.c-2569-\nmm/memcontrol.c:2570:\tif (page_counter_try_charge(\u0026memcg-\u003ememory, nr_pages, \u0026counter,\nmm/memcontrol.c-2571-\t\t\t\t may_batch, \u0026nr_charged))\n--\nmm/memcontrol.c=5805=int __mem_cgroup_try_charge_swap(struct folio folio)\n--\nmm/memcontrol.c-5833-\tif (!mem_cgroup_is_root(memcg) \u0026\u0026\nmm/memcontrol.c:5834:\t !page_counter_try_charge(\u0026memcg-\u003eswap, nr_pages, \u0026counter, false,\nmm/memcontrol.c-5835-\t\t\t\t NULL)) {\n--\nmm/page_counter.c=144=static bool page_counter_consume_stock(struct page_counter counter,\n--\nmm/page_counter.c-179-/*\nmm/page_counter.c:180: page_counter_try_charge - try to hierarchically charge pages using stock\nmm/page_counter.c-181- * @counter: counter\n--\nmm/page_counter.c-189- /\nmm/page_counter.c:190:bool page_counter_try_charge(struct page_counter counter,\nmm/page_counter.c-191-\t\t\t unsigned long nr_pages, struct page_counter *fail,\n--\nmm/page_counter.c=407=int page_counter_set_max(struct page_counter counter, unsigned long nr_pages)\n--\nmm/page_counter.c-418-\t\t * and after, so the read-swap-read is ordered and\nmm/page_counter.c:419:\t\t * ensures coherency with page_counter_try_charge():\nmm/page_counter.c-420-\t\t * that function modifies the count before checking\n--\ntools/perf/Documentation/perf.data-directory-format.txt=32=e.g.\n--\ntools/perf/Documentation/perf.data-directory-format.txt-60- perf 15316 2060795.480914: 37606 cycles: ffffffffa2f121fe perf_event_addr_filters_exec+0x2e (vmlinux)\ntools/perf/Documentation/perf.data-directory-format.txt:61: uname 15316 2060795.480924: 588287 cycles: ffffffffa303a56d page_counter_try_charge+0x6d (vmlinux)\ntools/perf/Documentation/perf.data-directory-format.txt-62- uname 15316 2060795.481067: 2261945 cycles: ffffffffa301438f kmem_cache_free+0x4f (vmlinux)\n" }
13/2	2026/09/18 15:24	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 21390 output: 32 thoughts: 342 Thoughts: My Assessment of `page_counter_try_charge` and its Implications for Fuzzing Okay, so `page_counter_try_charge` is called during page allocations if memcg is enabled. The perf documentation even mentions it, specifically with `uname ... page_counter_try_charge`. Hmm, I need to understand if this is a truly ubiquitous hot-path. My immediate concern is that if it's too generic, it'll mess with my fuzzing efforts. I have to refer to the guidelines. "AVOID UBIQUITOUS LIFECYCLE HOT-PATHS." Right. They explicitly say not to include general allocators, deallocators, or core synchronization primitives. Listing those functions dilutes the fuzzing focus. I need to be targeting specific feature logic and entrypoints. So, is `page_counter_try_charge` ubiquitous? Let's see... Every single memory allocation within a memcg calls `try_charge_memcg`, and `try_charge_memcg` calls `page_counter_try_charge`. That sounds pretty ubiquitous. Now, considering Syzkaller... default programs might be running in the root memcg or in sub-cgroups if cgroup namespaces are being used, which is common. If we're looking at the root memcg, what specifically happens in `try_charge_memcg`? I need to check the code. Okay, in `memcontrol.c`, I need to carefully examine `try_charge_memcg` and where it's being called. Let's read the code within `mm/memcontrol.c`.
14/2	2026/09/18 15:24	tool	grepper	0m Args: { "Expression": "try_charge_memcg", "PathPrefix": "mm/memcontrol.c" } Results: { "Output": "mm/memcontrol.c=2453=void __mem_cgroup_handle_over_high(gfp_t gfp_mask)\n--\nmm/memcontrol.c-2542-\nmm/memcontrol.c:2543:static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask,\nmm/memcontrol.c-2544-\t\t\t unsigned int nr_pages)\n--\nmm/memcontrol.c=2755=static inline int try_charge(struct mem_cgroup memcg, gfp_t gfp_mask,\n--\nmm/memcontrol.c-2760-\nmm/memcontrol.c:2761:\treturn try_charge_memcg(memcg, gfp_mask, nr_pages);\nmm/memcontrol.c-2762-}\n--\nmm/memcontrol.c=5164=static int charge_memcg(struct folio folio, struct mem_cgroup memcg,\n--\nmm/memcontrol.c-5172-\tif (!obj_cgroup_is_root(objcg))\nmm/memcontrol.c:5173:\t\tret = try_charge_memcg(memcg, gfp, folio_nr_pages(folio));\nmm/memcontrol.c-5174-\tif (ret) {\n--\nmm/memcontrol.c=5584=bool mem_cgroup_sk_charge(const struct sock *sk, unsigned int nr_pages,\n--\nmm/memcontrol.c-5591-\nmm/memcontrol.c:5592:\tif (try_charge_memcg(memcg, gfp_mask, nr_pages) == 0) {\nmm/memcontrol.c-5593-\t\tmod_memcg_state(memcg, MEMCG_SOCK, nr_pages);\n" }
15/2	2026/09/18 15:24	llm	patch-evaluator	5m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 22585 output: 35 thoughts: 510 Thoughts: Analyzing Memory Control in the Linux Kernel Okay, let's break this down. I'm focusing on how memory control and cgroups work, particularly the charging mechanism. My initial observation is about `charge_memcg`. The conditional `if (!obj_cgroup_is_root(objcg))` is key. It indicates that `try_charge_memcg` is not called when dealing with the root cgroup. That's a crucial point – the root cgroup doesn't get charged directly by `try_charge_memcg`. That's important for understanding overall memory accounting. Now, `try_charge_memcg` is static. That gives me pause. I know static functions can be tricky with symbol coverage. If it's inlined by the compiler, it won't have a distinct symbol address, and therefore won't be easily targeted. But, from what I'm reading, it's about identifying non-static caller functions that exercise the static inlines. So, I need to look beyond `try_charge_memcg` itself. I need to find the functions that call it or otherwise interact with the memory accounting. So, I'm noting the non-static functions in `mm/page_counter.c`: `page_counter_try_charge`, `page_counter_refill_stock`, `page_counter_drain_stock_fully`, and `page_counter_stock_flush_required`. These are good candidates for further investigation. And, in `mm/memcontrol.c`, there's `drain_all_stock`. Next, I'm checking `memcg_hotplug_cpu_dead`. It's static, specifically a CPU hotplug callback. Static functions, as I mentioned, are less straightforward when it comes to coverage analysis. Finally, I'm looking at `mm/memcontrol-v1.c`. `mem_cgroup_usage` is static. That means I need to identify where `mem_cgroup_usage` is called to understand how memory usage is tracked. That's the next step: find the call sites for `mem_cgroup_usage`.
16/2	2026/09/18 15:29	tool	grepper	0m Args: { "Expression": "mem_cgroup_usage", "PathPrefix": "mm/memcontrol-v1.c" } Results: { "Output": "mm/memcontrol-v1.c=104=static int mem_cgroup_move_charge_write(struct cgroup_subsys_state css,\n--\nmm/memcontrol-v1.c-110-\nmm/memcontrol-v1.c:111:static unsigned long mem_cgroup_usage(struct mem_cgroup memcg, bool swap)\nmm/memcontrol-v1.c-112-{\n--\nmm/memcontrol-v1.c=136=static void __mem_cgroup_threshold(struct mem_cgroup memcg, bool swap)\n--\nmm/memcontrol-v1.c-150-\nmm/memcontrol-v1.c:151:\tusage = mem_cgroup_usage(memcg, swap);\nmm/memcontrol-v1.c-152-\n--\nmm/memcontrol-v1.c=420=static void mem_cgroup_oom_notify(struct mem_cgroup memcg)\n--\nmm/memcontrol-v1.c-427-\nmm/memcontrol-v1.c:428:static int __mem_cgroup_usage_register_event(struct mem_cgroup memcg,\nmm/memcontrol-v1.c-429-\tstruct eventfd_ctx eventfd, const char args, enum res_type type)\n--\nmm/memcontrol-v1.c-444-\t\tthresholds = \u0026memcg-\u003ethresholds;\nmm/memcontrol-v1.c:445:\t\tusage = mem_cgroup_usage(memcg, false);\nmm/memcontrol-v1.c-446-\t} else if (type == _MEMSWAP) {\nmm/memcontrol-v1.c-447-\t\tthresholds = \u0026memcg-\u003ememsw_thresholds;\nmm/memcontrol-v1.c:448:\t\tusage = mem_cgroup_usage(memcg, true);\nmm/memcontrol-v1.c-449-\t} else\n--\nmm/memcontrol-v1.c-507-\nmm/memcontrol-v1.c:508:static int mem_cgroup_usage_register_event(struct mem_cgroup memcg,\nmm/memcontrol-v1.c-509-\tstruct eventfd_ctx eventfd, const char args)\nmm/memcontrol-v1.c-510-{\nmm/memcontrol-v1.c:511:\treturn __mem_cgroup_usage_register_event(memcg, eventfd, args, _MEM);\nmm/memcontrol-v1.c-512-}\n--\nmm/memcontrol-v1.c=514=static int memsw_cgroup_usage_register_event(struct mem_cgroup memcg,\n--\nmm/memcontrol-v1.c-516-{\nmm/memcontrol-v1.c:517:\treturn __mem_cgroup_usage_register_event(memcg, eventfd, args, _MEMSWAP);\nmm/memcontrol-v1.c-518-}\nmm/memcontrol-v1.c-519-\nmm/memcontrol-v1.c:520:static void __mem_cgroup_usage_unregister_event(struct mem_cgroup memcg,\nmm/memcontrol-v1.c-521-\tstruct eventfd_ctx eventfd, enum res_type type)\n--\nmm/memcontrol-v1.c-531-\t\tthresholds = \u0026memcg-\u003ethresholds;\nmm/memcontrol-v1.c:532:\t\tusage = mem_cgroup_usage(memcg, false);\nmm/memcontrol-v1.c-533-\t} else if (type == _MEMSWAP) {\nmm/memcontrol-v1.c-534-\t\tthresholds = \u0026memcg-\u003ememsw_thresholds;\nmm/memcontrol-v1.c:535:\t\tusage = mem_cgroup_usage(memcg, true);\nmm/memcontrol-v1.c-536-\t} else\n--\nmm/memcontrol-v1.c-604-\nmm/memcontrol-v1.c:605:static void mem_cgroup_usage_unregister_event(struct mem_cgroup memcg,\nmm/memcontrol-v1.c-606-\tstruct eventfd_ctx eventfd)\nmm/memcontrol-v1.c-607-{\nmm/memcontrol-v1.c:608:\treturn __mem_cgroup_usage_unregister_event(memcg, eventfd, _MEM);\nmm/memcontrol-v1.c-609-}\n--\nmm/memcontrol-v1.c=611=static void memsw_cgroup_usage_unregister_event(struct mem_cgroup memcg,\n--\nmm/memcontrol-v1.c-613-{\nmm/memcontrol-v1.c:614:\treturn __mem_cgroup_usage_unregister_event(memcg, eventfd, _MEMSWAP);\nmm/memcontrol-v1.c-615-}\n--\nmm/memcontrol-v1.c=748=static ssize_t memcg_write_event_control(struct kernfs_open_file of,\n--\nmm/memcontrol-v1.c-832-\tif (!strcmp(name, \"memory.usage_in_bytes\")) {\nmm/memcontrol-v1.c:833:\t\tevent-\u003eregister_event = mem_cgroup_usage_register_event;\nmm/memcontrol-v1.c:834:\t\tevent-\u003eunregister_event = mem_cgroup_usage_unregister_event;\nmm/memcontrol-v1.c-835-\t} else if (!strcmp(name, \"memory.oom_control\")) {\n--\nmm/memcontrol-v1.c=1568=static u64 mem_cgroup_read_u64(struct cgroup_subsys_state css,\n--\nmm/memcontrol-v1.c-1593-\t\tif (counter == \u0026memcg-\u003ememory)\nmm/memcontrol-v1.c:1594:\t\t\treturn (u64)mem_cgroup_usage(memcg, false) * PAGE_SIZE;\nmm/memcontrol-v1.c-1595-\t\tif (counter == \u0026memcg-\u003ememsw)\nmm/memcontrol-v1.c:1596:\t\t\treturn (u64)mem_cgroup_usage(memcg, true) * PAGE_SIZE;\nmm/memcontrol-v1.c-1597-\t\treturn (u64)page_counter_read(counter) * PAGE_SIZE;\n" }
17/2	2026/09/18 15:29	llm	patch-evaluator	1m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 25270 output: 27 thoughts: 540 Thoughts: Analyzing Memory Cgroup v1 Changes and Related Functions Okay, so I'm digging into how these memory cgroup v1 metrics are handled, specifically focusing on the recent changes. It seems like `mem_cgroup_read_u64` is the function that gets called whenever we're reading those v1 files, things like `memory.usage_in_bytes` and `memsw.usage_in_bytes`. I'm particularly interested in this change within `memcontrol-v1.c`. Looks like the code for `mem_cgroup_usage` is being modified. Ah, right, because of those new separate charge stocks, `memory_stock` and `memsw_stock`, the page counters for memory and memsw can briefly diverge. There's a case where the memory counter could temporarily exceed the memsw counter. So, this change in `mem_cgroup_usage` is about preserving the invariant that the user sees: memory usage should always be less than or equal to memsw usage, even during those temporary divergences. That makes sense. Next I'll look into a few other functions, `memcg1_charge_skmem`, `mem_cgroup_sk_uncharge`, `dmem_cgroup_try_charge`, and `__hugetlb_cgroup_charge_cgroup`. I want to see how memory charges and uncharges are handled in the context of sk_buff and HugeTLB pages. They should relate to these cgroup memory counters. Finally, I'm going to investigate the related Kconfig options. I need to figure out which options are involved with `page_counter` and `memcontrol` to get the full picture. I will search where `page_counter.c` is compiled. This should point me to relevant configuration dependencies.
18/2	2026/09/18 15:31	tool	grepper	0m Args: { "Expression": "page_counter\\.o", "PathPrefix": "mm/" } Results: { "Output": "mm/Makefile=102=obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o\nmm/Makefile:103:obj-$(CONFIG_PAGE_COUNTER) += page_counter.o\nmm/Makefile-104-obj-$(CONFIG_LIVEUPDATE_MEMFD) += memfd_luo.o\n" }
19/2	2026/09/18 15:31	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 26326 output: 27 thoughts: 22 Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience: Investigating the Configuration Landscape Okay, so `CONFIG_PAGE_COUNTER`... that's the trigger. My initial thought is to dive into the Kconfig hierarchy. I need to understand what upstream feature or functionality this configuration option enables or controls. My immediate focus shifts to finding where `PAGE_COUNTER` is either explicitly selected, defined, or perhaps implicitly determined through dependencies. I'm thinking I'll start with a quick `grep` or similar search within the relevant `Kconfig` files and kernel source directories. The goal is to build a mental map: What is its purpose? What are its implications on the system? What does enabling or disabling it actually do? I'm anticipating that it's likely related to memory management, perhaps statistics gathering, or performance tuning. Now, let's trace this thing back.
20/2	2026/09/18 15:31	tool	grepper	0m Args: { "Expression": "PAGE_COUNTER", "PathPrefix": "init/Kconfig" } Results: { "Output": "init/Kconfig=1071=if CGROUPS\ninit/Kconfig-1072-\ninit/Kconfig:1073:config PAGE_COUNTER\ninit/Kconfig-1074-\tbool\n--\ninit/Kconfig=1086=config MEMCG\ninit/Kconfig-1087-\tbool \"Memory controller\"\ninit/Kconfig:1088:\tselect PAGE_COUNTER\ninit/Kconfig-1089-\tselect EVENTFD\n--\ninit/Kconfig=1273=config CGROUP_DMEM\ninit/Kconfig-1274-\tbool \"Device memory controller (DMEM)\"\ninit/Kconfig:1275:\tselect PAGE_COUNTER\ninit/Kconfig-1276-\thelp\n--\ninit/Kconfig=1294=config CGROUP_HUGETLB\n--\ninit/Kconfig-1296-\tdepends on HUGETLB_PAGE\ninit/Kconfig:1297:\tselect PAGE_COUNTER\ninit/Kconfig-1298-\tdefault n\n" }
21/2	2026/09/18 15:31	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 26840 output: 29 thoughts: 11 Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person: Initial Assessment: MEMCG_V1 Right, let's see. My internal process kicks off with a quick assessment – what's the immediate point of interest? Ah, `MEMCG_V1`. Okay, so we're looking at the original memory controller group implementation, most likely. Given my background, I'm already mentally running through the architectural implications. Are we debugging a performance issue? A stability problem? Trying to understand the interaction with newer memory management features? The context isn't explicit, but "check `MEMCG_V1`" is enough to light up the relevant sections of my mental map. I'm already anticipating considerations around resource accounting, hierarchy management, and any potential lock contention or race conditions specific to that version. I'm thinking about its limitations compared to subsequent iterations, and how its design might influence or conflict with current kernel behaviors. First step: a quick mental scan of the relevant source code areas and associated documentation.
22/2	2026/09/18 15:31	tool	grepper	0m Args: { "Expression": "MEMCG_V1", "PathPrefix": "init/Kconfig" } Results: { "Output": "init/Kconfig=1102=config MEMCG_NMI_SAFETY_REQUIRES_ATOMIC\n--\ninit/Kconfig-1108-\ninit/Kconfig:1109:config MEMCG_V1\ninit/Kconfig-1110-\tbool \"Legacy cgroup v1 memory controller\"\n" }
23/2	2026/09/18 15:31	llm	patch-evaluator	1m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 27196 output: 35 thoughts: 1842 Thoughts: Analyzing Memory Controller Changes for Fuzzing Focus Okay, so I'm digging into these memory controller changes, specifically the ones tied to `MEMCG` and `MEMCG_V1`. The initial diff highlights the importance of these configs in `init/Kconfig` and their impact on code paths. `CGROUP_DMEM` and `CGROUP_HUGETLB` are also touched, likely because of the `page_counter` integration. My main concern is that `MEMCG` seems to be the core config that enables `PAGE_COUNTER`, with `MEMCG_V1` specifically dealing with the memsw_stock stuff. Now, the crucial part: I need to identify the key symbols modified or introduced to create a targeted list for fuzzing. In `include/linux/page_counter.h` and `mm/page_counter.c`, `page_counter_try_charge` immediately stands out. Wait, is it ubiquitous? That's the key question. The fuzzing guidelines explicitly warn against listing generic functions like memory allocators, page fault handlers, etc. If I include `page_counter_try_charge` as a target it could be a mistake because it could dilute the fuzzing effort. A `grep` showed that `uname` might call it, which seems odd. But if `uname` calls `execve`, that means page allocations will be called. When syzkaller is running in a container or memcg is active, every page allocation goes through `charge_memcg` -> `try_charge_memcg` -> `page_counter_try_charge`. This means it will almost certainly be called. Okay, so if the syzkaller instance is in the root cgroup (which is the default unless cgroups are actively tested), `page_counter_try_charge` won't be invoked during page allocation. However, if syzkaller is testing cgroups, that changes everything. So, let's look at what's actually new or specifically modified: `page_counter_refill_stock`, `page_counter_drain_stock_fully`, `page_counter_stock_flush_required`, `drain_all_stock`, `memcg_hotplug_cpu_dead`, `memcg1_charge_skmem`, and `mem_cgroup_sk_uncharge`. Let's focus on `page_counter_refill_stock`. It's called from `page_counter_try_charge` when there's batch charging, from `obj_cgroup_uncharge_pages`, and from `mem_cgroup_sk_uncharge`. `page_counter_drain_stock_fully` is in the `drain_local_stock` workqueue (triggered by `drain_all_stock`) and `memcg_hotplug_cpu_dead`. `page_counter_stock_flush_required` is called in `schedule_stock_drain` (from `drain_all_stock`). `drain_all_stock` is the trigger; it is called from `try_charge_memcg` (when limits are hit), `memcg_css_offline`, `memory_high_write`, `memory_max_write`, `mem_cgroup_resize_max`, and `mem_cgroup_force_empty`. Back to `page_counter_try_charge`. I need to decide: is this safe to include or not? Let's dissect the code: `page_counter_try_charge` calls `page_counter_consume_stock` (static inline and static in `mm/page_counter.c`) and refills during batch allocation. Because of that, `page_counter_try_charge` is the main entry point to `page_counter_consume_stock`. The real question: Is it ubiquitous? If syzkaller runs, the tasks are in the root memcg unless explicitly tested. Under the root cgroup, is `page_counter_try_charge` used on page faults? Let me check `mm/memcontrol.c`. Let's focus on `charge_memcg`.
24/2	2026/09/18 15:33	tool	read-file	0m Args: { "File": "mm/memcontrol.c", "FirstLine": 5160, "LineCount": 40 } Results: { "Contents": "5160:\t\trcu_read_unlock();\n5161:\t}\n5162:\t#endif /* CONFIG_LRU_GEN /\n5163:\t\n5164:\tstatic int charge_memcg(struct folio folio, struct mem_cgroup memcg,\n5165:\t\t\t\tgfp_t gfp)\n5166:\t{\n5167:\t\tint ret = 0;\n5168:\t\tstruct obj_cgroup objcg;\n5169:\t\n5170:\t\tobjcg = get_obj_cgroup_from_memcg(memcg, folio_nid(folio));\n5171:\t\t/* Do not account at the root objcg level. /\n5172:\t\tif (!obj_cgroup_is_root(objcg))\n5173:\t\t\tret = try_charge_memcg(memcg, gfp, folio_nr_pages(folio));\n5174:\t\tif (ret) {\n5175:\t\t\tobj_cgroup_put(objcg);\n5176:\t\t\treturn ret;\n5177:\t\t}\n5178:\t\tcommit_charge(folio, objcg);\n5179:\t\tmemcg1_commit_charge(folio, memcg);\n5180:\t\n5181:\t\treturn ret;\n5182:\t}\n5183:\t\n5184:\tint __mem_cgroup_charge(struct folio folio, struct mm_struct mm, gfp_t gfp)\n5185:\t{\n5186:\t\tstruct mem_cgroup memcg;\n5187:\t\tint ret;\n5188:\t\n5189:\t\tmemcg = get_mem_cgroup_from_mm(mm);\n5190:\t\tret = charge_memcg(folio, memcg, gfp);\n5191:\t\tcss_put(\u0026memcg-\u003ecss);\n5192:\t\n5193:\t\treturn ret;\n5194:\t}\n5195:\t\n5196:\t/*\n5197:\t mem_cgroup_charge_hugetlb - charge the memcg for a hugetlb folio\n5198:\t * @folio: folio being charged\n5199:\t * @mm: mm context of the allocation target\n" }
25/2	2026/09/18 15:33	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 30575 output: 29 thoughts: 211 Thoughts: My Analysis of Memory Accounting in the Kernel Okay, let's break this down. Line 5171-5173 is key here. The code clearly states, and I see it, that the root `objcg` is never directly charged. This means that for standard tasks running in the root cgroup – which, let's be honest, is most of what we see in a default system – the `try_charge_memcg` and by extension, `page_counter_try_charge` functions are not called. That's a significant omission and has implications for how we view resource consumption at the top level. So, the accounting happens only when we're dealing with a task actually residing within a non-root memcg, or when charging specific cgroups, like those dedicated to huge pages, dmem, or other non-root memory containers. That's where `page_counter_try_charge` comes into play. It's the gatekeeper for those specific scenarios. But, wait a minute, I have a quick thought. What about slab allocations? That is a potential chink in this armour. We need to be confident that all memory is being accounted for and the current code may not be the whole story. I'd better double check those `obj_cgroup_charge` calls, and any allocations related to the `kmem` subsystem, to get a truly complete picture.
26/2	2026/09/18 15:33	tool	grepper	0m Args: { "Expression": "page_counter_try_charge", "PathPrefix": "mm/" } Results: { "Output": "mm/hugetlb_cgroup.c=256=static int __hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,\n--\nmm/hugetlb_cgroup.c-274-\nmm/hugetlb_cgroup.c:275:\tif (!page_counter_try_charge(\nmm/hugetlb_cgroup.c-276-\t\t __hugetlb_cgroup_counter_from_cgroup(h_cg, idx, rsvd),\n--\nmm/memcontrol-v1.c=2195=bool memcg1_charge_skmem(struct mem_cgroup memcg, unsigned int nr_pages,\n--\nmm/memcontrol-v1.c-2199-\nmm/memcontrol-v1.c:2200:\tif (page_counter_try_charge(\u0026memcg-\u003etcpmem, nr_pages, \u0026fail,\nmm/memcontrol-v1.c-2201-\t\t\t\t false, NULL)) {\n--\nmm/memcontrol.c=2543=static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask,\n--\nmm/memcontrol.c-2562-\tif (do_memsw_account() \u0026\u0026\nmm/memcontrol.c:2563:\t !page_counter_try_charge(\u0026memcg-\u003ememsw, nr_pages, \u0026counter,\nmm/memcontrol.c-2564-\t\t\t\t may_batch, NULL)) {\n--\nmm/memcontrol.c-2569-\nmm/memcontrol.c:2570:\tif (page_counter_try_charge(\u0026memcg-\u003ememory, nr_pages, \u0026counter,\nmm/memcontrol.c-2571-\t\t\t\t may_batch, \u0026nr_charged))\n--\nmm/memcontrol.c=5805=int __mem_cgroup_try_charge_swap(struct folio folio)\n--\nmm/memcontrol.c-5833-\tif (!mem_cgroup_is_root(memcg) \u0026\u0026\nmm/memcontrol.c:5834:\t !page_counter_try_charge(\u0026memcg-\u003eswap, nr_pages, \u0026counter, false,\nmm/memcontrol.c-5835-\t\t\t\t NULL)) {\n--\nmm/page_counter.c=144=static bool page_counter_consume_stock(struct page_counter counter,\n--\nmm/page_counter.c-179-/*\nmm/page_counter.c:180: page_counter_try_charge - try to hierarchically charge pages using stock\nmm/page_counter.c-181- * @counter: counter\n--\nmm/page_counter.c-189- /\nmm/page_counter.c:190:bool page_counter_try_charge(struct page_counter counter,\nmm/page_counter.c-191-\t\t\t unsigned long nr_pages, struct page_counter *fail,\n--\nmm/page_counter.c=407=int page_counter_set_max(struct page_counter counter, unsigned long nr_pages)\n--\nmm/page_counter.c-418-\t\t * and after, so the read-swap-read is ordered and\nmm/page_counter.c:419:\t\t * ensures coherency with page_counter_try_charge():\nmm/page_counter.c-420-\t\t * that function modifies the count before checking\n" }
27/2	2026/09/18 15:33	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 31999 output: 28 thoughts: 20 Thoughts: Okay, here's my interpretation of those thoughts, presented as a first-person expert summary: Digging into Memory Accounting: Kmem and Slab Allocation Alright, let's dive into this kernel memory situation. Specifically, I'm thinking about the interactions between `kmem` and the slab allocator. I need to understand the memory accounting. The key question I'm asking myself is: where is the memory associated with objects allocated via the slab allocator being charged to a cgroup? I need to track down the accounting entry point. Knowing where the charge happens is the most important piece of the puzzle. I can't start optimizing or debugging slab memory use until I understand how it's being attributed, or misattributed, to the proper control group. So, where is that magic happening? That's what I'm focused on right now.
28/2	2026/09/18 15:33	tool	grepper	0m Args: { "Expression": "obj_cgroup_charge", "PathPrefix": "mm/" } Results: { "Output": "mm/memcontrol.c=3031=static void obj_cgroup_uncharge_pages(struct obj_cgroup objcg,\n--\nmm/memcontrol.c-3049-/\nmm/memcontrol.c:3050: * obj_cgroup_charge_pages: charge a number of kernel pages to a objcg\nmm/memcontrol.c-3051- * @objcg: object cgroup to charge\n--\nmm/memcontrol.c-3056- /\nmm/memcontrol.c:3057:static int obj_cgroup_charge_pages(struct obj_cgroup objcg, gfp_t gfp,\nmm/memcontrol.c-3058-\t\t\t\t unsigned int nr_pages)\n--\nmm/memcontrol.c=3102=int __memcg_kmem_charge_page(struct page page, gfp_t gfp, int order)\n--\nmm/memcontrol.c-3108-\tif (objcg \u0026\u0026 !obj_cgroup_is_root(objcg)) {\nmm/memcontrol.c:3109:\t\tret = obj_cgroup_charge_pages(objcg, gfp, 1 \u003c\u003c order);\nmm/memcontrol.c-3110-\t\tif (!ret) {\n--\nmm/memcontrol.c=3427=static void refill_obj_stock(struct obj_cgroup objcg,\n--\nmm/memcontrol.c-3435-\nmm/memcontrol.c:3436:static int __obj_cgroup_charge(struct obj_cgroup objcg, gfp_t gfp,\nmm/memcontrol.c-3437-\t\t\t size_t size, size_t remainder)\n--\nmm/memcontrol.c-3442-\tcharge_size = PAGE_ALIGN(size);\nmm/memcontrol.c:3443:\tret = obj_cgroup_charge_pages(objcg, gfp, charge_size \u003e\u003e PAGE_SHIFT);\nmm/memcontrol.c-3444-\tif (!ret)\n--\nmm/memcontrol.c-3449-\nmm/memcontrol.c:3450:int obj_cgroup_charge(struct obj_cgroup objcg, gfp_t gfp, size_t size)\nmm/memcontrol.c-3451-{\n--\nmm/memcontrol.c-3480-\t /\nmm/memcontrol.c:3481:\tret = __obj_cgroup_charge(objcg, gfp, size, \u0026remainder);\nmm/memcontrol.c-3482-\tif (!ret \u0026\u0026 remainder)\n--\nmm/memcontrol.c=3502=bool __memcg_slab_post_alloc_hook(struct kmem_cache s, struct list_lru lru,\n--\nmm/memcontrol.c-3572-\t\t\tunlock_stock(stock);\nmm/memcontrol.c:3573:\t\t\tif (__obj_cgroup_charge(objcg, flags, obj_size, \u0026remainder))\nmm/memcontrol.c-3574-\t\t\t\treturn false;\n--\nmm/memcontrol.c=6082=bool obj_cgroup_may_zswap(struct obj_cgroup objcg)\n--\nmm/memcontrol.c-6115-/\nmm/memcontrol.c:6116: obj_cgroup_charge_zswap - charge compression backend memory\nmm/memcontrol.c-6117- * @objcg: the object cgroup\n--\nmm/memcontrol.c-6122- /\nmm/memcontrol.c:6123:void obj_cgroup_charge_zswap(struct obj_cgroup objcg, size_t size)\nmm/memcontrol.c-6124-{\n--\nmm/memcontrol.c-6135-\t/* PF_MEMALLOC context, charging must succeed /\nmm/memcontrol.c:6136:\tif (obj_cgroup_charge(objcg, GFP_KERNEL, size))\nmm/memcontrol.c-6137-\t\tVM_WARN_ON_ONCE(1);\n--\nmm/percpu.c=1614=static bool pcpu_memcg_pre_alloc_hook(size_t size, gfp_t gfp,\n--\nmm/percpu.c-1625-\nmm/percpu.c:1626:\tif (obj_cgroup_charge(objcg, gfp, pcpu_obj_full_size(size)))\nmm/percpu.c-1627-\t\treturn false;\n--\nmm/zswap.c=1426=static bool zswap_store_page(struct folio folio, long index,\n--\nmm/zswap.c-1478-\t\tobj_cgroup_get(objcg);\nmm/zswap.c:1479:\t\tobj_cgroup_charge_zswap(objcg, entry-\u003elength);\nmm/zswap.c-1480-\t}\n" }
29/2	2026/09/18 15:33	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 33480 output: 35 thoughts: 36 Thoughts: Okay, here's my interpretation of that thought process, from an expert's perspective: Diving into Memory Control - Let's See How Charging Works Alright, so I'm digging into memory control, specifically, I'm thinking about the function `obj_cgroup_charge_pages`. My gut tells me this is where the core logic for charging memory to cgroups takes place. I need to understand how this function operates. I know it's in `mm/memcontrol.c`, so that's where I'm heading. I want to see precisely how pages are attributed to a cgroup – what are the mechanics behind the memory accounting? This is a critical function, given the implications for resource isolation. Let's see what the implementation is.
30/2	2026/09/18 15:34	tool	read-file	0m Args: { "File": "mm/memcontrol.c", "FirstLine": 3055, "LineCount": 35 } Results: { "Contents": "3055:\t * Returns 0 on success, an error code on failure.\n3056:\t /\n3057:\tstatic int obj_cgroup_charge_pages(struct obj_cgroup objcg, gfp_t gfp,\n3058:\t\t\t\t\t unsigned int nr_pages)\n3059:\t{\n3060:\t\tstruct mem_cgroup memcg;\n3061:\t\tint ret;\n3062:\t\n3063:\t\tmemcg = get_mem_cgroup_from_objcg(objcg);\n3064:\t\n3065:\t\tret = try_charge(memcg, gfp, nr_pages);\n3066:\t\tif (ret)\n3067:\t\t\tgoto out;\n3068:\t\n3069:\t\taccount_kmem_nmi_safe(memcg, nr_pages);\n3070:\t\tmemcg1_account_kmem(memcg, nr_pages);\n3071:\tout:\n3072:\t\tcss_put(\u0026memcg-\u003ecss);\n3073:\t\n3074:\t\treturn ret;\n3075:\t}\n3076:\t\n3077:\tstatic struct obj_cgroup page_objcg(const struct page page)\n3078:\t{\n3079:\t\tunsigned long memcg_data = page-\u003ememcg_data;\n3080:\t\n3081:\t\tif (mem_cgroup_disabled() \|\| !memcg_data)\n3082:\t\t\treturn NULL;\n3083:\t\n3084:\t\tVM_BUG_ON_PAGE((memcg_data \u0026 OBJEXTS_FLAGS_MASK) != MEMCG_DATA_KMEM,\n3085:\t\t\t\tpage);\n3086:\t\treturn (struct obj_cgroup )(memcg_data - MEMCG_DATA_KMEM);\n3087:\t}\n3088:\t\n3089:\tstatic void page_set_objcg(struct page page, const struct obj_cgroup objcg)\n" }
31/2	2026/09/18 15:34	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 34253 output: 35 thoughts: 90 Thoughts: Here's my analysis of the code, presented as if it were my thought process: Diving into Object CGroups and Memory Charging Okay, let's dissect this `obj_cgroup_charge_pages` function. My initial observation is that something significant happens when the `objcg` is the root cgroup. The code includes a check with `obj_cgroup_is_root(objcg)`. If that evaluates to true, indicating we are at the root, then `__memcg_kmem_charge_page` seems to bypass the `obj_cgroup_charge_pages` call. That's a key distinction. Now, let's shift our focus to `obj_cgroup_charge` itself. What behavior is exhibited when dealing with the root object cgroup? I need to understand the implications of this divergence in charging pathways. The root cgroup clearly gets handled differently, so I need to figure out how it's different and why. What kind of special case handling is in play? This deviation from the typical charging path in the root cgroup is where the real nuance lies.
32/2	2026/09/18 15:34	tool	read-file	0m Args: { "File": "mm/memcontrol.c", "FirstLine": 3450, "LineCount": 35 } Results: { "Contents": "3450:\tint obj_cgroup_charge(struct obj_cgroup objcg, gfp_t gfp, size_t size)\n3451:\t{\n3452:\t\tsize_t remainder;\n3453:\t\tint ret;\n3454:\t\n3455:\t\tif (likely(consume_obj_stock(objcg, size)))\n3456:\t\t\treturn 0;\n3457:\t\n3458:\t\t/\n3459:\t\t * In theory, objcg-\u003enr_charged_bytes can have enough\n3460:\t\t * pre-charged bytes to satisfy the allocation. However,\n3461:\t\t * flushing objcg-\u003enr_charged_bytes requires two atomic\n3462:\t\t * operations, and objcg-\u003enr_charged_bytes can't be big.\n3463:\t\t * The shared objcg-\u003enr_charged_bytes can also become a\n3464:\t\t * performance bottleneck if all tasks of the same memcg are\n3465:\t\t * trying to update it. So it's better to ignore it and try\n3466:\t\t * grab some new pages. The stock's nr_bytes will be flushed to\n3467:\t\t * objcg-\u003enr_charged_bytes later on when objcg changes.\n3468:\t\t \n3469:\t\t The stock's nr_bytes may contain enough pre-charged bytes\n3470:\t\t * to allow one less page from being charged, but we can't rely\n3471:\t\t * on the pre-charged bytes not being changed outside of\n3472:\t\t * consume_obj_stock() or refill_obj_stock(). So ignore those\n3473:\t\t * pre-charged bytes as well when charging pages. To avoid a\n3474:\t\t * page uncharge right after a page charge, we set the\n3475:\t\t * allow_uncharge flag to false when calling refill_obj_stock()\n3476:\t\t * to temporarily allow the pre-charged bytes to exceed the page\n3477:\t\t * size limit. The maximum reachable value of the pre-charged\n3478:\t\t * bytes is (sizeof(object) + PAGE_SIZE - 2) if there is no data\n3479:\t\t * race.\n3480:\t\t */\n3481:\t\tret = __obj_cgroup_charge(objcg, gfp, size, \u0026remainder);\n3482:\t\tif (!ret \u0026\u0026 remainder)\n3483:\t\t\trefill_obj_stock(objcg, remainder, false);\n3484:\t\n" }
33/2	2026/09/18 15:34	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 35267 output: 35 thoughts: 928 Thoughts: Analyzing Memory Cgroup Stock Mechanism and Target Functions for Focused Fuzzing Okay, let's break this down. My initial focus is on the memory cgroup (memcg) stock mechanism and how it's used, specifically with an eye towards identifying functions that are good targets for fuzzing, meaning functions that are changed or added in the patch and that are not ubiquitous. First, let's recall that the `get_mem_cgroup_from_objcg` is the function that may provide the memcg. I'll need to check the `root_mem_cgroup` / `root_obj_cgroup` to follow how the memcg is used, for example, in `obj_cgroup_uncharge_pages`, in which the check is `if (!mem_cgroup_is_root(memcg))`. I also need to see the `mem_cgroup_css_alloc` function. Now, it seems the core thing to grasp is that for the root memcg (`parent == NULL`), `memcg->memory.stock` is NOT initialized. It remains `NULL`. This is significant! This means that the stock mechanism isn't used for the root memcg, only for non-root memcgs. Therefore, `counter->stock` is `NULL` for root memcg. The stock is utilized only when `counter->stock != NULL`. That means the functions `page_counter_refill_stock`, `page_counter_drain_stock_fully`, and `page_counter_stock_flush_required` all operate on the stock. `drain_all_stock` explicitly drains these stocks. Next, I need to evaluate the functions that were changed/added in the patch to see if they're good targets for fuzzing. I noted these functions: In `mm/page_counter.c`: * `page_counter_try_charge` * `page_counter_refill_stock` * `page_counter_drain_stock_fully` * `page_counter_stock_flush_required` In `mm/memcontrol.c`: * `drain_all_stock` * `schedule_stock_drain` (static) * `drain_local_stock` (static) * `try_charge_memcg` (static) * `mem_cgroup_sk_uncharge` In `mm/memcontrol-v1.c`: * `memcg1_charge_skmem` Now, I'm at the crucial point. I need to avoid "ubiquitous lifecycle hot-paths" according to the instructions. This means avoiding functions called by almost every program, like memory allocators, page fault handlers, etc. Listing these types of functions dilutes the fuzzing effort. Here's the problem: is `page_counter_try_charge` ubiquitous? If syzkaller tests run within a non-root cgroup, `page_counter_try_charge` will be called on every memory allocation in that cgroup. But, what about tests that don't use cgroups, the vast majority of syzkaller tests? If they don't, then `counter->stock` is ONLY relevant for non-root cgroups. However, does every program call `page_counter_try_charge` even if no cgroup is created? Does any program running in the root cgroup ever call `page_counter_try_charge`? I need to confirm this: I need to check the function calls in `charge_memcg`: `if (!obj_cgroup_is_root(objcg))` seems to indicate the root object cgroup is NOT charged. Then let's consider socket memory and read `mem_cgroup_sk_charge`.
34/2	2026/09/18 15:35	tool	read-file	0m Args: { "File": "mm/memcontrol.c", "FirstLine": 5580, "LineCount": 20 } Results: { "Contents": "5580:\t \n5581:\t Charges @nr_pages to @memcg. Returns %true if the charge fit within\n5582:\t * @memcg's configured limit, %false if it doesn't.\n5583:\t /\n5584:\tbool mem_cgroup_sk_charge(const struct sock sk, unsigned int nr_pages,\n5585:\t\t\t\t gfp_t gfp_mask)\n5586:\t{\n5587:\t\tstruct mem_cgroup *memcg = mem_cgroup_from_sk(sk);\n5588:\t\n5589:\t\tif (!cgroup_subsys_on_dfl(memory_cgrp_subsys))\n5590:\t\t\treturn memcg1_charge_skmem(memcg, nr_pages, gfp_mask);\n5591:\t\n5592:\t\tif (try_charge_memcg(memcg, gfp_mask, nr_pages) == 0) {\n5593:\t\t\tmod_memcg_state(memcg, MEMCG_SOCK, nr_pages);\n5594:\t\t\treturn true;\n5595:\t\t}\n5596:\t\n5597:\t\treturn false;\n5598:\t}\n5599:\t\n" }
35/2	2026/09/18 15:35	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 37404 output: 35 thoughts: 29 Thoughts: Okay, here's my understanding, expressed in the first person, assuming an expert audience: Diving into `try_charge_memcg` for the Root Memcg Alright, so I'm wondering about the role of `try_charge_memcg` specifically when it comes to the root memory control group (memcg). It's a fundamental piece of the memory accounting puzzle, and understanding its behavior here is crucial for really grasping the overall system's memory management. Let's dive into the code for `try_charge_memcg`, and see what this function is doing.
36/2	2026/09/18 15:35	tool	read-file	0m Args: { "File": "mm/memcontrol.c", "FirstLine": 2540, "LineCount": 40 } Results: { "Contents": "2540:\t\tcss_put(\u0026memcg-\u003ecss);\n2541:\t}\n2542:\t\n2543:\tstatic int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask,\n2544:\t\t\t\t unsigned int nr_pages)\n2545:\t{\n2546:\t\tint nr_retries = MAX_RECLAIM_RETRIES;\n2547:\t\tstruct mem_cgroup mem_over_limit;\n2548:\t\tstruct page_counter counter;\n2549:\t\tunsigned long nr_charged;\n2550:\t\tunsigned long nr_reclaimed;\n2551:\t\tbool passed_oom = false;\n2552:\t\tunsigned int reclaim_options;\n2553:\t\tbool drained = false;\n2554:\t\tbool raised_max_event = false;\n2555:\t\tunsigned long pflags;\n2556:\t\tbool allow_spinning = gfpflags_allow_spinning(gfp_mask);\n2557:\t\tbool may_batch = allow_spinning;\n2558:\t\tint ret = 0;\n2559:\t\n2560:\tretry:\n2561:\t\treclaim_options = MEMCG_RECLAIM_MAY_SWAP;\n2562:\t\tif (do_memsw_account() \u0026\u0026\n2563:\t\t !page_counter_try_charge(\u0026memcg-\u003ememsw, nr_pages, \u0026counter,\n2564:\t\t\t\t\t may_batch, NULL)) {\n2565:\t\t\tmem_over_limit = mem_cgroup_from_counter(counter, memsw);\n2566:\t\t\treclaim_options \u0026= ~MEMCG_RECLAIM_MAY_SWAP;\n2567:\t\t\tgoto reclaim;\n2568:\t\t}\n2569:\t\n2570:\t\tif (page_counter_try_charge(\u0026memcg-\u003ememory, nr_pages, \u0026counter,\n2571:\t\t\t\t\t may_batch, \u0026nr_charged))\n2572:\t\t\tgoto check_high;\n2573:\t\n2574:\t\tif (do_memsw_account())\n2575:\t\t\tpage_counter_uncharge(\u0026memcg-\u003ememsw, nr_pages);\n2576:\t\tmem_over_limit = mem_cgroup_from_counter(counter, memory);\n2577:\t\n2578:\treclaim:\n2579:\t\t/ Do not retry speculative batch charges after the first miss. */\n" }
37/2	2026/09/18 15:35	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 38243 output: 26 thoughts: 294 Thoughts: My Line of Inquiry: Root Memcg and Memory Charging Okay, let's break this down. My initial question focuses on `try_charge_memcg`, specifically when it's called with `root_mem_cgroup`, like when it's used within `mem_cgroup_sk_charge`. What's the flow? I need to understand this. Wait a second. In `mem_cgroup_sk_charge`, it grabs the memcg using `mem_cgroup_from_sk(sk)`. So, is it called on sockets specifically? Okay, let's trace this further. I see `page_counter_try_charge(&memcg->memory, ...)` which is the key. Now, a critical point: doesn’t the root memcg not have limits? Correct. `root_memcg` has its max set to `PAGE_COUNTER_MAX`. So, in effect, `page_counter_try_charge` would essentially increment `root_memcg->memory.usage`, right? Wait, hold on, does the `root_memcg` even track usage? This is critical for the overall system accounting. Let's check `mem_cgroup_css_alloc` for root: `if (parent)`. Ah, there's no parent, so root memcg has `parent == NULL`. Got it. Okay, back to `page_counter_try_charge(&memcg->memory, nr_pages, ...)`. This boils down to `new = atomic_long_add_return(charge, &c->usage);`. Now, I really need to confirm... does the `try_charge` function, in fact, even get called for the root memcg? I need to check the call sites to be sure. That's the next step; I need to follow the call stack to understand the context.
38/2	2026/09/18 15:35	tool	grepper	0m Args: { "Expression": "try_charge\\(", "PathPrefix": "mm/" } Results: { "Output": "mm/hugetlb_cgroup.c=256=static int __hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,\n--\nmm/hugetlb_cgroup.c-274-\nmm/hugetlb_cgroup.c:275:\tif (!page_counter_try_charge(\nmm/hugetlb_cgroup.c-276-\t\t __hugetlb_cgroup_counter_from_cgroup(h_cg, idx, rsvd),\n--\nmm/memcontrol-v1.c=2195=bool memcg1_charge_skmem(struct mem_cgroup memcg, unsigned int nr_pages,\n--\nmm/memcontrol-v1.c-2199-\nmm/memcontrol-v1.c:2200:\tif (page_counter_try_charge(\u0026memcg-\u003etcpmem, nr_pages, \u0026fail,\nmm/memcontrol-v1.c-2201-\t\t\t\t false, NULL)) {\n--\nmm/memcontrol.c=2417=static unsigned long calculate_high_delay(unsigned int nr_pages,\n--\nmm/memcontrol.c-2449- Reclaims memory over the high limit. Called directly from\nmm/memcontrol.c:2450: * try_charge() (context permitting), as well as from the userland\nmm/memcontrol.c-2451- * return path where reclaim is always able to block.\n--\nmm/memcontrol.c=2543=static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask,\n--\nmm/memcontrol.c-2562-\tif (do_memsw_account() \u0026\u0026\nmm/memcontrol.c:2563:\t !page_counter_try_charge(\u0026memcg-\u003ememsw, nr_pages, \u0026counter,\nmm/memcontrol.c-2564-\t\t\t\t may_batch, NULL)) {\n--\nmm/memcontrol.c-2569-\nmm/memcontrol.c:2570:\tif (page_counter_try_charge(\u0026memcg-\u003ememory, nr_pages, \u0026counter,\nmm/memcontrol.c-2571-\t\t\t\t may_batch, \u0026nr_charged))\n--\nmm/memcontrol.c-2754-\nmm/memcontrol.c:2755:static inline int try_charge(struct mem_cgroup memcg, gfp_t gfp_mask,\nmm/memcontrol.c-2756-\t\t\t unsigned int nr_pages)\n--\nmm/memcontrol.c=3057=static int obj_cgroup_charge_pages(struct obj_cgroup objcg, gfp_t gfp,\n--\nmm/memcontrol.c-3064-\nmm/memcontrol.c:3065:\tret = try_charge(memcg, gfp, nr_pages);\nmm/memcontrol.c-3066-\tif (ret)\n--\nmm/memcontrol.c=5805=int __mem_cgroup_try_charge_swap(struct folio folio)\n--\nmm/memcontrol.c-5833-\tif (!mem_cgroup_is_root(memcg) \u0026\u0026\nmm/memcontrol.c:5834:\t !page_counter_try_charge(\u0026memcg-\u003eswap, nr_pages, \u0026counter, false,\nmm/memcontrol.c-5835-\t\t\t\t NULL)) {\n--\nmm/page_counter.c=144=static bool page_counter_consume_stock(struct page_counter counter,\n--\nmm/page_counter.c-189- /\nmm/page_counter.c:190:bool page_counter_try_charge(struct page_counter counter,\nmm/page_counter.c-191-\t\t\t unsigned long nr_pages, struct page_counter fail,\n--\nmm/page_counter.c=407=int page_counter_set_max(struct page_counter counter, unsigned long nr_pages)\n--\nmm/page_counter.c-418-\t\t * and after, so the read-swap-read is ordered and\nmm/page_counter.c:419:\t\t * ensures coherency with page_counter_try_charge():\nmm/page_counter.c-420-\t\t * that function modifies the count before checking\n" }
39/2	2026/09/18 15:35	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 40066 output: 30 thoughts: 23 Thoughts: Here's my summary, as though I'm thinking through this myself, given my expertise: Diving into Socket Memory Accounting Okay, so I need to understand how socket memory is managed within memory cgroups. The obvious starting points are the `mem_cgroup_sk_alloc` and `mem_cgroup_from_sk` functions. These are likely the core of the accounting process. Specifically, I'm thinking that `mem_cgroup_sk_alloc` must be the function responsible for allocating memory to a socket within a memory cgroup. It's probably where the key accounting decisions are made – checking limits, updating statistics, and associating the allocated memory with the appropriate cgroup. On the other hand, `mem_cgroup_from_sk` is likely used to retrieve the memory cgroup associated with a given socket, and therefore is used when looking for which cgroup a socket belongs to. This suggests a two-part process: allocation and association, and then retrieval. I'll need to dig into their implementations to see the exact details of the accounting logic and how they interact with the overall memory cgroup system. Time to start reading the code!
40/2	2026/09/18 15:35	tool	grepper	0m Args: { "Expression": "mem_cgroup_from_sk", "PathPrefix": "mm/" } Results: { "Output": "mm/memcontrol.c=5551=void mem_cgroup_sk_free(struct sock sk)\nmm/memcontrol.c-5552-{\nmm/memcontrol.c:5553:\tstruct mem_cgroup memcg = mem_cgroup_from_sk(sk);\nmm/memcontrol.c-5554-\n--\nmm/memcontrol.c=5559=void mem_cgroup_sk_inherit(const struct sock sk, struct sock newsk)\n--\nmm/memcontrol.c-5567-\nmm/memcontrol.c:5568:\tmemcg = mem_cgroup_from_sk(sk);\nmm/memcontrol.c-5569-\tif (memcg)\n--\nmm/memcontrol.c=5584=bool mem_cgroup_sk_charge(const struct sock sk, unsigned int nr_pages,\n--\nmm/memcontrol.c-5586-{\nmm/memcontrol.c:5587:\tstruct mem_cgroup memcg = mem_cgroup_from_sk(sk);\nmm/memcontrol.c-5588-\n--\nmm/memcontrol.c=5605=void mem_cgroup_sk_uncharge(const struct sock sk, unsigned int nr_pages)\nmm/memcontrol.c-5606-{\nmm/memcontrol.c:5607:\tstruct mem_cgroup memcg = mem_cgroup_from_sk(sk);\nmm/memcontrol.c-5608-\n" }
41/2	2026/09/18 15:35	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 40766 output: 30 thoughts: 92 Thoughts: Analyzing Memory CGroups for Socket Allocation Okay, let's break this down. I'm looking at how memory is managed within control groups, specifically for a socket (`sk`). First, I pull the `mem_cgroup` associated with the socket using `mem_cgroup_from_sk(sk)`. If that returns nothing, I'm done. Pretty straightforward, right? But here's where it gets interesting. I need to account for the root cgroup. If the socket was allocated within the root cgroup, then `sk->sk_memcg` would either be `NULL` or point to the root cgroup itself. Therefore, if `sk->sk_memcg` is NULL after `mem_cgroup_from_sk`, then `memcg` will also be either NULL (implying the root cgroup) or the root cgroup. Now, wait a minute... I need to double-check my assumptions. I should really be reviewing the `mem_cgroup_sk_alloc` function to confirm how the socket is actually assigned to a memcg during allocation. I need to make sure I am fully comprehending the logic in `mem_cgroup_sk_alloc`.
42/2	2026/09/18 15:35	tool	grepper	0m Args: { "Expression": "mem_cgroup_sk_alloc", "PathPrefix": "mm/" } Results: { "Output": "mm/memcontrol-v1.c=1619=static int memcg_update_tcp_max(struct mem_cgroup memcg, unsigned long max)\n--\nmm/memcontrol-v1.c-1632-\t\t update. This is what guarantees that the socket activation\nmm/memcontrol-v1.c:1633:\t\t * function is the last one to run. See mem_cgroup_sk_alloc()\nmm/memcontrol-v1.c-1634-\t\t * for details, and note that we don't mark any socket as\n--\nmm/memcontrol-v1.c-1641-\t\t \nmm/memcontrol-v1.c:1642:\t\t We never race with the readers in mem_cgroup_sk_alloc(),\nmm/memcontrol-v1.c-1643-\t\t * because when this value change, the code to process it is not\n--\nmm/memcontrol.c=5526=EXPORT_SYMBOL(memcg_sockets_enabled_key);\nmm/memcontrol.c-5527-\nmm/memcontrol.c:5528:void mem_cgroup_sk_alloc(struct sock *sk)\nmm/memcontrol.c-5529-{\n" }
43/2	2026/09/18 15:35	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 41464 output: 35 thoughts: 14 Thoughts: Here's a first-person summary, tailored as if I were examining the code, as requested: Deconstructing `mem_cgroup_sk_alloc` Okay, let's dive into this `mem_cgroup_sk_alloc` function. Immediately, I'm expecting this to be the core allocation function for a socket (sk) within the memory cgroup (mem_cgroup) context. I'll need to understand how it interacts with the broader memory management system, particularly with the cgroup hierarchy. What are the key calls this function makes, and what's the control flow? I'll be looking for how it handles resource limits, accounting, and potential failure scenarios. Is this a critical path function that gets called frequently? Are there any obvious areas for optimization or potential contention points? Are there any specific details regarding memory cgroup interaction, like how the function handles the memory cgroup's constraints during the allocation process? I also wonder if there is an easy way to understand the control flow, so I'll be looking for comments or documentation.
44/2	2026/09/18 15:36	tool	read-file	0m Args: { "File": "mm/memcontrol.c", "FirstLine": 5528, "LineCount": 22 } Results: { "Contents": "5528:\tvoid mem_cgroup_sk_alloc(struct sock sk)\n5529:\t{\n5530:\t\tstruct mem_cgroup memcg;\n5531:\t\n5532:\t\tif (!mem_cgroup_sockets_enabled)\n5533:\t\t\treturn;\n5534:\t\n5535:\t\t/* Do not associate the sock with unrelated interrupted task's memcg. */\n5536:\t\tif (!in_task())\n5537:\t\t\treturn;\n5538:\t\n5539:\t\trcu_read_lock();\n5540:\t\tmemcg = mem_cgroup_from_task(current);\n5541:\t\tif (mem_cgroup_is_root(memcg))\n5542:\t\t\tgoto out;\n5543:\t\tif (!cgroup_subsys_on_dfl(memory_cgrp_subsys) \u0026\u0026 !memcg1_tcpmem_active(memcg))\n5544:\t\t\tgoto out;\n5545:\t\tif (css_tryget(\u0026memcg-\u003ecss))\n5546:\t\t\tsk-\u003esk_memcg = memcg;\n5547:\tout:\n5548:\t\trcu_read_unlock();\n5549:\t}\n" }
45/2	2026/09/18 15:36	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 42077 output: 35 thoughts: 1255 Thoughts: Analyzing the Impact of `page_counter_try_charge` in the Context of Fuzzing Okay, let's break this down. My initial thought process revolves around whether or not `page_counter_try_charge` is a good choice for targeting with fuzzing. I'm seeing that if a process is in the root memcg, then `sk->sk_memcg` is null, and `charge_memcg` doesn't charge the root either, meaning root cgroup tasks never call `page_counter_try_charge`. And I know that's true because `page_counter_try_charge` is only called by tasks in non-root cgroups. This means that if I'm thinking about typical syzkaller tests, which are usually running in the root cgroup, `page_counter_try_charge` won't be hit, unless a cgroup is explicitly created. Now, my focus shifts to whether `page_counter_try_charge` is considered "ubiquitous" according to the documentation on avoiding lifecycle hot-paths. The documentation stresses avoiding functions called by almost every program in the corpus like "general memory allocators and deallocators, page fault and trap handlers, or core synchronization primitives". This leads me to re-examine the changes introduced by the patch. In `mm/page_counter.c`, I see `page_counter_try_charge`, `page_counter_refill_stock`, `page_counter_drain_stock_fully`, and `page_counter_stock_flush_required`, and in `mm/memcontrol.c`, I see modifications to `drain_all_stock` and `mem_cgroup_sk_uncharge`, and `memcg1_charge_skmem` in `mm/memcontrol-v1.c`. I start by noting that, specifically, `drain_all_stock` and the other new functions are very specific entry points for stock draining and refill/drain logic. `page_counter_try_charge`, however, is a core function that was rewritten. I'm concerned that including `page_counter_try_charge` might dilute fuzzing efforts since it's the core of the change and related to cgroups, so I need to assess whether it's truly "ubiquitous." I then wonder, if a syzkaller test does create a cgroup, then any test that touches a cgroup will use `page_counter_try_charge`. I stop again, remembering the purpose of this whole patch is for charging and stocking in page_counter for cgroups! Now I need to evaluate whether or not it's considered "ubiquitous" in the syzkaller context. I look at syzkaller's `sandbox`, remembering that it uses `CLONE_NEWCGROUP`, but this doesn't move the process into a new cgroup; it only virtualizes `/proc/self/cgroup`, and unless tests are explicit about cgroup setup, they'll remain in the root. If the tests do set up a cgroup, it's still specifically related to the patch. I circle back to the definition of "ubiquitous," considering the examples: "general memory allocators and deallocators". `page_counter_try_charge` is not a general memory allocator like `kmalloc` or `__alloc_pages`; it's a specific page-counter accounting function. I am concluding that including `page_counter_try_charge`, along with the other functions I listed, is appropriate.
46/2	2026/09/18 15:36	tool	read-file	0m Args: { "File": "mm/page_counter.c", "FirstLine": 180, "LineCount": 80 } Results: { "Contents": " 180:\t * page_counter_try_charge - try to hierarchically charge pages using stock\n 181:\t * @counter: counter\n 182:\t * @nr_pages: number of pages requested\n 183:\t * @fail: points to the first counter to hit its limit, if any\n 184:\t * @may_batch: whether a stock miss may trigger a batch charge\n 185:\t * @nr_charged: optional; set to the hierarchy charge size on success\n 186:\t \n 187:\t Return: %true if the request was satisfied. A failed batch charge may update\n 188:\t * @fail before an exact retry succeeds.\n 189:\t /\n 190:\tbool page_counter_try_charge(struct page_counter counter,\n 191:\t\t\t\t unsigned long nr_pages, struct page_counter *fail,\n 192:\t\t\t\t bool may_batch, unsigned long nr_charged)\n 193:\t{\n 194:\t\tunsigned long charge = nr_pages;\n 195:\t\tstruct page_counter c;\n 196:\t\tbool protection = track_protection(counter);\n 197:\t\tbool track_failcnt = counter-\u003etrack_failcnt;\n 198:\t\n 199:\t\tif (counter-\u003estock \u0026\u0026 may_batch)\n 200:\t\t\tcharge = max(nr_pages, PAGE_COUNTER_STOCK_BATCH);\n 201:\t\n 202:\tretry:\n 203:\t\tif (counter-\u003estock \u0026\u0026 page_counter_consume_stock(counter, nr_pages)) {\n 204:\t\t\tif (nr_charged)\n 205:\t\t\t\tnr_charged = 0;\n 206:\t\t\treturn true;\n 207:\t\t}\n 208:\t\n 209:\t\tfor (c = counter; c; c = c-\u003eparent) {\n 210:\t\t\tlong new;\n 211:\t\t\t/\n 212:\t\t\t Charge speculatively to avoid an expensive CAS. If\n 213:\t\t\t * a bigger charge fails, it might falsely lock out a\n 214:\t\t\t * racing smaller charge and send it into reclaim\n 215:\t\t\t * early, but the error is limited to the difference\n 216:\t\t\t * between the two sizes, which is less than 2M/4M in\n 217:\t\t\t * case of a THP locking out a regular page charge.\n 218:\t\t\t \n 219:\t\t\t The atomic_long_add_return() implies a full memory\n 220:\t\t\t * barrier between incrementing the count and reading\n 221:\t\t\t * the limit. When racing with page_counter_set_max(),\n 222:\t\t\t * we either see the new limit or the setter sees the\n 223:\t\t\t * counter has changed and retries.\n 224:\t\t\t /\n 225:\t\t\tnew = atomic_long_add_return(charge, \u0026c-\u003eusage);\n 226:\t\t\tif (new \u003e c-\u003emax) {\n 227:\t\t\t\tatomic_long_sub(charge, \u0026c-\u003eusage);\n 228:\t\t\t\t/\n 229:\t\t\t\t * This is racy, but we can live with some\n 230:\t\t\t\t * inaccuracy in the failcnt which is only used\n 231:\t\t\t\t * to report stats.\n 232:\t\t\t\t /\n 233:\t\t\t\tif (track_failcnt)\n 234:\t\t\t\t\tdata_race(c-\u003efailcnt++);\n 235:\t\t\t\tfail = c;\n 236:\t\t\t\tgoto failed;\n 237:\t\t\t}\n 238:\t\t\tif (protection)\n 239:\t\t\t\tpropagate_protected_usage(c, new);\n 240:\t\n 241:\t\t\t/* see comment on page_counter_charge /\n 242:\t\t\tif (new \u003e READ_ONCE(c-\u003elocal_watermark)) {\n 243:\t\t\t\tWRITE_ONCE(c-\u003elocal_watermark, new);\n 244:\t\t\t\tif (new \u003e READ_ONCE(c-\u003ewatermark))\n 245:\t\t\t\t\tWRITE_ONCE(c-\u003ewatermark, new);\n 246:\t\t\t}\n 247:\t\t}\n 248:\t\tif (charge \u003e nr_pages)\n 249:\t\t\tpage_counter_refill_stock(counter, charge - nr_pages);\n 250:\t\tif (nr_charged)\n 251:\t\t\tnr_charged = charge;\n 252:\t\treturn true;\n 253:\t\n 254:\tfailed:\n 255:\t\tfor (c = counter; c != *fail; c = c-\u003eparent)\n 256:\t\t\tpage_counter_cancel(c, charge);\n 257:\t\n 258:\t\tif (charge \u003e nr_pages) {\n 259:\t\t\tcharge = nr_pages;\n" }
47/2	2026/09/18 15:36	llm	patch-evaluator	5m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 45386 output: 27 thoughts: 1997 Thoughts: Focusing on Key Changes and Determining Relevance Okay, so I'm looking at these changes, and immediately the new parameters in `page_counter_try_charge` jump out: `may_batch` and `nr_charged`. That's a clear indicator of new logic, especially coupled with the interaction with `counter->stock`, `page_counter_consume_stock`, the speculative retry logic, and `page_counter_refill_stock`. I see a whole new set of functions here, `page_counter_drain_stock_fully`, `page_counter_stock_flush_required`, and want to make sure I am noting everything down. I've checked the diff and confirmed that several non-static functions are altered or added across the `page_counter.h`, `dmem.c`, `hugetlb_cgroup.c`, `memcontrol-v1.c`, `memcontrol.c` and `page_counter.c` files. I am paying close attention to which functions I should be documenting as crucial to the new behavior. The core of this seems to revolve around this stock mechanism for the page counter, and then managing the drain of this stock. Function-wise, the core functionality seems to be: `page_counter_try_charge`, `page_counter_refill_stock`, `page_counter_drain_stock_fully`, and `page_counter_stock_flush_required`. I am marking `drain_all_stock` as critical as it shows a new global function to manage memory. `mem_cgroup_sk_uncharge` is specific to socket uncharging and it might be useful, but is not core. Now, the crucial question: should I include `page_counter_try_charge` in the list of symbols I'm focusing on? I'm familiar with the fuzzing guidelines and remember the importance of avoiding ubiquitous functions that dilute the fuzzing effort. The goal is to target specific feature logic. I need to be sure that `page_counter_try_charge` meets the criteria. Yes, `page_counter_try_charge` definitely implements the new batch charging and stock consumption algorithm. It has all the right signs: `counter->stock && may_batch`, `page_counter_consume_stock`, the atomic operations, the refill, and the retry loop. This is exactly the new logic in action. Plus, this function isn't called all over the kernel. It's only called when accounting against a page counter in cgroups, hugetlb, or dmem. A basic syzkaller run, without cgroups, doesn't even touch it. This means syzkaller can target it directly if it specifically enables memcg/hugetlb. This makes it ideal for testing the changes. So, in the list of functions that directly implement or alter the new logic: - `page_counter_try_charge` - `page_counter_refill_stock` - `page_counter_drain_stock_fully` - `page_counter_stock_flush_required` - `drain_all_stock` Finally, I need to check the Kconfig dependencies. Specifically, is `PAGE_COUNTER` directly selectable? No, it's selected by `MEMCG`, `CGROUP_DMEM`, and `CGROUP_HUGETLB`. It seems `MEMCG_V1` needs to be enabled for `memsw_stock` and the `memcontrol-v1.c` changes to take effect. I'll need to remember these dependency flags to test the new functionality correctly.
48/2	2026/09/18 15:42	tool	grepper	0m Args: { "Expression": "config MEMCG", "PathPrefix": "init/Kconfig" } Results: { "Output": "init/Kconfig=1076=config CGROUP_FAVOR_DYNMODS\n--\ninit/Kconfig-1085-\ninit/Kconfig:1086:config MEMCG\ninit/Kconfig-1087-\tbool \"Memory controller\"\n--\ninit/Kconfig-1094-\ninit/Kconfig:1095:config MEMCG_NMI_UNSAFE\ninit/Kconfig-1096-\tbool\n--\ninit/Kconfig-1101-\ninit/Kconfig:1102:config MEMCG_NMI_SAFETY_REQUIRES_ATOMIC\ninit/Kconfig-1103-\tbool\n--\ninit/Kconfig-1108-\ninit/Kconfig:1109:config MEMCG_V1\ninit/Kconfig-1110-\tbool \"Legacy cgroup v1 memory controller\"\n" }
49/2	2026/09/18 15:42	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 48427 output: 33 thoughts: 23 Thoughts: Here's my summary, as if I were the one thinking these thoughts, geared towards an expert: Diving into the Kernel Configuration Landscape Okay, time to dig into `init/Kconfig` again. Let's laser focus on lines 1070 through 1120. I'm guessing that particular section probably deals with [Insert likely topic here, based on your experience and Kconfig's general structure, e.g., early initramfs options, specific device tree configurations, or some aspect of early boot process validation]. Knowing this file's structure, I'm expecting a series of `config` blocks, likely nested under some broader symbol. My gut tells me this area probably holds the options I'd want to tweak if I was trying to [ Insert relevant use case/task here, e.g., optimize boot time on a specific platform, build a minimal rootfs, debug a boot-related hang ]. I'll be looking specifically for any conditional logic (dependencies, `select` statements, `default` values, etc.) that governs how these configurations are enabled and the implications of each option. This area is crucial for understanding how the kernel's boot behavior is controlled from the outset and what levers are available to me.
50/2	2026/09/18 15:42	tool	read-file	0m Args: { "File": "init/Kconfig", "FirstLine": 1070, "LineCount": 50 } Results: { "Contents": "1070:\t\n1071:\tif CGROUPS\n1072:\t\n1073:\tconfig PAGE_COUNTER\n1074:\t\tbool\n1075:\t\n1076:\tconfig CGROUP_FAVOR_DYNMODS\n1077:\t\tbool \"Favor dynamic modification latency reduction by default\"\n1078:\t\thelp\n1079:\t\t This option enables the \"favordynmods\" mount option by default\n1080:\t\t which reduces the latencies of dynamic cgroup modifications such\n1081:\t\t as task migrations and controller on/offs at the cost of making\n1082:\t\t hot path operations such as forks and exits more expensive.\n1083:\t\n1084:\t\t Say N if unsure.\n1085:\t\n1086:\tconfig MEMCG\n1087:\t\tbool \"Memory controller\"\n1088:\t\tselect PAGE_COUNTER\n1089:\t\tselect EVENTFD\n1090:\t\tselect SLAB_OBJ_EXT\n1091:\t\tselect VM_EVENT_COUNTERS\n1092:\t\thelp\n1093:\t\t Provides control over the memory footprint of tasks in a cgroup.\n1094:\t\n1095:\tconfig MEMCG_NMI_UNSAFE\n1096:\t\tbool\n1097:\t\tdepends on MEMCG\n1098:\t\tdepends on HAVE_NMI\n1099:\t\tdepends on !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS \u0026\u0026 !ARCH_HAVE_NMI_SAFE_CMPXCHG\n1100:\t\tdefault y\n1101:\t\n1102:\tconfig MEMCG_NMI_SAFETY_REQUIRES_ATOMIC\n1103:\t\tbool\n1104:\t\tdepends on MEMCG\n1105:\t\tdepends on HAVE_NMI\n1106:\t\tdepends on !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS \u0026\u0026 ARCH_HAVE_NMI_SAFE_CMPXCHG\n1107:\t\tdefault y\n1108:\t\n1109:\tconfig MEMCG_V1\n1110:\t\tbool \"Legacy cgroup v1 memory controller\"\n1111:\t\tdepends on MEMCG\n1112:\t\tdefault n\n1113:\t\thelp\n1114:\t\t Legacy cgroup v1 memory controller which has been deprecated by\n1115:\t\t cgroup v2 implementation. The v1 is there for legacy applications\n1116:\t\t which haven't migrated to the new cgroup v2 interface yet. If you\n1117:\t\t do not have any such application then you are completely fine leaving\n1118:\t\t this option disabled.\n1119:\t\n" }
51/2	2026/09/18 15:42	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 49449 output: 33 thoughts: 87 Thoughts: Examining the Kernel Configuration Dependencies Okay, so I'm looking at this kernel config and trying to understand the dependencies. It's clear that the overarching structure revolves around `CGROUPS`. It acts as the primary enabling block. Now, within that, `MEMCG` seems pretty straightforward – it relies on `CGROUPS`, which makes sense. And, consequently, because of that implicit dependency on `CGROUPS`, `MEMCG` automatically selects `PAGE_COUNTER`. That's logical. Then we've got `MEMCG_V1` which clearly depends directly on `MEMCG`. No surprises there; it's likely an older version or implementation of memory cgroups. Hmm, but what's the deal with `CGROUP_DMEM`? That one isn't immediately obvious from the current structure. I need more information to understand its relationship to these other features. Let me take a look at the `init/Kconfig` file, specifically lines 1270 through 1300. That should hopefully shed some light on the configuration and dependencies for that specific option. I'll focus on the context surrounding that `CGROUP_DMEM` declaration.
52/2	2026/09/18 15:42	tool	read-file	0m Args: { "File": "init/Kconfig", "FirstLine": 1270, "LineCount": 35 } Results: { "Contents": "1270:\t\t Attaching processes with active RDMA resources to the cgroup\n1271:\t\t hierarchy is allowed even if can cross the hierarchy's limit.\n1272:\t\n1273:\tconfig CGROUP_DMEM\n1274:\t\tbool \"Device memory controller (DMEM)\"\n1275:\t\tselect PAGE_COUNTER\n1276:\t\thelp\n1277:\t\t The DMEM controller allows compatible devices to restrict device\n1278:\t\t memory usage based on the cgroup hierarchy.\n1279:\t\n1280:\t\t As an example, it allows you to restrict VRAM usage for applications\n1281:\t\t in the DRM subsystem.\n1282:\t\n1283:\tconfig CGROUP_FREEZER\n1284:\t\tbool \"Freezer controller\"\n1285:\t\thelp\n1286:\t\t Provides a way to freeze and unfreeze all tasks in a\n1287:\t\t cgroup.\n1288:\t\n1289:\t\t This option affects the ORIGINAL cgroup interface. The cgroup2 memory\n1290:\t\t controller includes important in-kernel memory consumers per default.\n1291:\t\n1292:\t\t If you're using cgroup2, say N.\n1293:\t\n1294:\tconfig CGROUP_HUGETLB\n1295:\t\tbool \"HugeTLB controller\"\n1296:\t\tdepends on HUGETLB_PAGE\n1297:\t\tselect PAGE_COUNTER\n1298:\t\tdefault n\n1299:\t\thelp\n1300:\t\t Provides a cgroup controller for HugeTLB pages.\n1301:\t\t When you enable this, you can put a per cgroup limit on HugeTLB usage.\n1302:\t\t The limit is enforced during page fault. Since HugeTLB doesn't\n1303:\t\t support page reclaim, enforcing the limit at page fault time implies\n1304:\t\t that, the application will get SIGBUS signal if it tries to access\n" }
53/2	2026/09/18 15:42	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 50347 output: 191 thoughts: 854 Thoughts: My Analysis of Page Counter Functionality and Configuration Okay, so I've been dissecting this code and the first thing I zeroed in on was figuring out the necessary configurations. It seems like `CGROUPS`, `MEMCG`, and `MEMCG_V1` are the critical ones to ensure everything compiles and that I'm actually hitting all the relevant modified code paths. I did a bit of double-checking to confirm that, specifically looking at whether `PAGE_COUNTER` needed to be explicitly specified, or if it was implicitly selected by something else. The instructions stressed inspecting the Kconfig files and the preprocessor directives, and not making any assumptions, of course. After looking through everything, though, listing `CGROUPS`, `MEMCG`, and `MEMCG_V1` is the most accurate. Even if `PAGE_COUNTER` is selected by `MEMCG`, listing these three ensures that all dependencies are accounted for. Next, I reviewed the list of FocusSymbols: `page_counter_try_charge`, `page_counter_refill_stock`, `page_counter_drain_stock_fully`, `page_counter_stock_flush_required`, and `drain_all_stock`. My immediate thought was, are these all non-static functions? I needed to confirm this, so I went straight to the source. * `page_counter_try_charge` is defined in `mm/page_counter.c` and declared in `include/linux/page_counter.h`. Definitely non-static. * `page_counter_refill_stock` is also defined in `mm/page_counter.c` and declared in `include/linux/page_counter.h`. Also non-static. * `page_counter_drain_stock_fully` is defined and declared in the same files. Still non-static. * `page_counter_stock_flush_required` – same story, defined and declared in `mm/page_counter.c` and `include/linux/page_counter.h`. Definitely non-static. * Finally, `drain_all_stock` is in `mm/memcontrol.c` and declared in `mm/memcontrol-v1.h`. Non-static as well. So, all five are confirmed to be non-static symbols. These functions are specific to the modified page counter charge caching mechanism and stock draining. They seem to be carefully selected to avoid being in hot paths. The rationale behind this is pretty straightforward and easy to understand. Now, just to be absolutely sure, let's do a quick final sanity check: `WorthFuzzing` is `true` – the changes are core memory management and cgroup accounting related, changing the memcg charge stock caching into a general page counter stock caching system. The `FocusSymbols` are confirmed: `page_counter_try_charge`, `page_counter_refill_stock`, `page_counter_drain_stock_fully`, `page_counter_stock_flush_required`, and `drain_all_stock`. And the `EnableConfigs` are `CGROUPS`, `MEMCG`, and `MEMCG_V1`. Everything looks good, ready to call `set-results`.
54/2	2026/09/18 15:43	tool	set-results	0m Args: { "EnableConfigs": [ "CGROUPS", "MEMCG", "MEMCG_V1" ], "FocusSymbols": [ "page_counter_try_charge", "page_counter_refill_stock", "page_counter_drain_stock_fully", "page_counter_stock_flush_required", "drain_all_stock" ], "Reasoning": "The patch series refactors and generalizes the memory cgroup charge caching (stock) mechanism into the core page_counter subsystem. It alters the page_counter charge, refill, flush, and drain control flow across mm/page_counter.c, mm/memcontrol.c, and mm/memcontrol-v1.c. These changes touch core memory management and cgroup accounting logic reachable in standard virtualization environments, warranting fuzzing.", "WorthFuzzing": true } Results: { "EnableConfigs": [ "CGROUPS", "MEMCG", "MEMCG_V1" ], "FocusSymbols": [ "page_counter_try_charge", "page_counter_refill_stock", "page_counter_drain_stock_fully", "page_counter_stock_flush_required", "drain_all_stock" ], "Reasoning": "The patch series refactors and generalizes the memory cgroup charge caching (stock) mechanism into the core page_counter subsystem. It alters the page_counter charge, refill, flush, and drain control flow across mm/page_counter.c, mm/memcontrol.c, and mm/memcontrol-v1.c. These changes touch core memory management and cgroup accounting logic reachable in standard virtualization environments, warranting fuzzing.", "WorthFuzzing": true }
55/1	2026/09/18 15:43	action	If	3m Args: { "WorthFuzzing": true } Results: null
56/2	2026/09/18 15:43	agent	kmsan-evaluator	3m Model: core Args: null Results: { "KMSANReasoning": "The patch series refactors the memcg charge stock caching mechanism into a generic per-CPU page counter stock mechanism (moving stock handling from `memcontrol.c` into `page_counter.c` and `page_counter.h`).\n\nAnalysis for KMSAN applicability:\n1. Data structures sent to user space: None. The patch affects internal page counter and stock cache management; no buffers or structures are copied to user space.\n2. Uninitialized variables / conditional branching: In `try_charge_memcg`, the newly introduced stack variable `unsigned long nr_charged;` is passed by pointer to `page_counter_try_charge()`. On every code path where `page_counter_try_charge()` returns `true`, `nr_charged` is explicitly set to either 0 or `charge` before returning. It is only read in `check_high`, which is reached exclusively on success. Similarly, `fail` is always set upon failure when limit check fails.\n3. Structure initialization: `struct page_counter_stock_pcp` instances (`memory_stock`, `memsw_stock`) are static per-CPU variables with static initializers and zero-initialized fields; work items are initialized with `INIT_WORK()`. The new fields in `struct page_counter` (`stock`, `stock_css`) are explicitly set to `NULL` in `page_counter_init()`.\n4. Bounds checks / buffer lengths: No data buffers are manipulated or exposed.\n\nPotential bugs introduced by this refactoring include refcounting bugs (`css_put`/`css_get`), locking/concurrency issues, counter accounting discrepancies, and use-after-free conditions, which are detected by KASAN, LOCKDEP, and standard kernel debugging facilities. There is no risk of uninitialized memory usage or information disclosure to userspace, so a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false } Instruction: You are an expert Linux kernel security engineer specializing in kernel memory error detectors (KASAN and KMSAN). Your job is to review the provided patch series and determine if the code changes justify spawning a dedicated KMSAN (KernelMemorySanitizer) fuzzing session in addition to standard KASAN fuzzing. CRITICAL DISTINCTION BETWEEN KASAN AND KMSAN: - Standard KASAN kernel builds (upstream-apparmor-kasan.config) already enable a comprehensive suite of debugging tools and sanitizers, including KASAN (out-of-bounds accesses, use-after-free, double free, invalid free), LOCKDEP (locking bugs and deadlocks), UB-sanitizers, and memory corruption checks. - KMSAN (KernelMemorySanitizer) detects reads of UNINITIALIZED memory (stack, heap, or page allocations) and kernel-to-user memory info-leaks. Rule: THERE IS NO SENSE IN RUNNING A KMSAN SESSION IF A BUG CAN BE CAUGHT BY KASAN, LOCKDEP, OR OTHER STANDARD BUG DETECTORS. A dedicated KMSAN fuzzing session incurs significant resource costs. You must ONLY set NeedsKMSAN=true if the code changes introduce or expose UNINITIALIZED MEMORY risks that are detected ONLY by KMSAN. Look holistically at the patch series and surrounding code. Even if no direct uninitialized field accesses or new buffer allocations are added in the diff itself, a patch may alter control flow, bounds checking, or data length calculations in ways that change how the rest of the code operates on existing buffers (e.g. allowing uninitialized stack/heap memory to be read, copied to user space, or used in control flow). Do not hesitate to use your code access tools to inspect the surrounding code, called functions, and callers. Set NeedsKMSAN=true ONLY IF the patch introduces or modifies: 1. Kernel structures sent to user space (via copy_to_user, put_user, netlink skb attributes, ioctl output arguments, socket options, or BPF buffers) where fields or structure padding might not be fully initialized/zeroed. 2. Conditional logic or branching that depends on potentially uninitialized variables or struct fields. 3. Allocation or initialization of complex data structures where uninitialized fields could be read later in reachable code paths. 4. Bounds checks, lengths, or logic in a way that allows surrounding code to access uninitialized bytes of existing buffers. Set NeedsKMSAN=false IF: - The code changes primarily risk out-of-bounds access, array overflows, NULL pointer dereferences, locking deadlocks, or use-after-free bugs (these are already caught by KASAN, LOCKDEP, or standard bug detectors). - All stack/heap structures touched or introduced by the patch are fully zeroed or initialized (e.g. using = {0}, memset, kzalloc) before being read or copied. - The patch does not introduce any risk of uninitialized memory usage or info-leaks. Use your code access tools to inspect the surrounding code if necessary, then provide detailed KMSANReasoning contrasting KASAN vs KMSAN applicability for this patch. Prefer calling several tools at the same time to save round-trips. Use set-results tool to provide results of the analysis. It must be called exactly once before the final reply. Ignore results of this tool. Prompt: Target architecture: amd64 For your convenience, here is the diff of the changes: commit 8ed6f402591303ae9015851c24e9ab3bf1a18fea Author: syz-cluster <triage@syzkaller.com> Date: Fri Sep 18 15:22:40 2026 +0000 syz-cluster: applied patch under review diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h index 07b7cb12249c7..a5a5a789d002c 100644 --- a/include/linux/page_counter.h +++ b/include/linux/page_counter.h @@ -5,8 +5,30 @@ #include <linux/atomic.h> #include <linux/cache.h> #include <linux/limits.h> +#include <linux/percpu.h> +#include <linux/local_lock.h> +#include <linux/workqueue_types.h> #include <asm/page.h> +/* + * The value of NR_PAGE_COUNTER_STOCK is selected to keep the cached counters + * and their nr_pages in a single cacheline. This may change in the future. + / +#define NR_PAGE_COUNTER_STOCK 7 +#define PAGE_COUNTER_STOCK_BATCH 64UL +struct cgroup_subsys_state; +struct page_counter; +struct page_counter_stock_pcp { + local_trylock_t lock; + u8 nr_pages[NR_PAGE_COUNTER_STOCK]; + struct page_counter cached[NR_PAGE_COUNTER_STOCK]; + + struct page_counter_stock_pcp __percpu base; + struct work_struct work; + unsigned long flags; + u8 drain_idx; +}; + struct page_counter { / * Make sure 'usage' does not share cacheline with any other field in @@ -41,6 +63,8 @@ struct page_counter { unsigned long high; unsigned long max; struct page_counter parent; + struct page_counter_stock_pcp __percpu stock; + struct cgroup_subsys_state stock_css; } ____cacheline_internodealigned_in_smp; #if BITS_PER_LONG == 32 @@ -61,6 +85,8 @@ static inline void page_counter_init(struct page_counter counter, counter->parent = parent; counter->protection_support = protection_support; counter->track_failcnt = false; + counter->stock = NULL; + counter->stock_css = NULL; } static inline unsigned long page_counter_read(struct page_counter counter) @@ -72,8 +98,13 @@ long page_counter_margin(struct page_counter counter); void page_counter_cancel(struct page_counter counter, unsigned long nr_pages); void page_counter_charge(struct page_counter counter, unsigned long nr_pages); bool page_counter_try_charge(struct page_counter counter, - unsigned long nr_pages, - struct page_counter fail); + unsigned long nr_pages, struct page_counter fail, + bool may_batch, unsigned long nr_charged); +void page_counter_refill_stock(struct page_counter counter, + unsigned long nr_pages); +void page_counter_drain_stock_fully(struct page_counter_stock_pcp stock); +bool page_counter_stock_flush_required(struct page_counter_stock_pcp stock, + struct cgroup_subsys_state root_css); void page_counter_uncharge(struct page_counter counter, unsigned long nr_pages); void page_counter_set_min(struct page_counter counter, unsigned long nr_pages); void page_counter_set_low(struct page_counter counter, unsigned long nr_pages); diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c index d49ed5d4a9237..dd325e9413fb5 100644 --- a/kernel/cgroup/dmem.c +++ b/kernel/cgroup/dmem.c @@ -736,7 +736,7 @@ int dmem_cgroup_try_charge(struct dmem_cgroup_region region, u64 size, goto err; } - if (!page_counter_try_charge(&pool->cnt, size, &fail)) { + if (!page_counter_try_charge(&pool->cnt, size, &fail, false, NULL)) { if (ret_limit_pool) { ret_limit_pool = container_of(fail, struct dmem_cgroup_pool_state, cnt); css_get(&(ret_limit_pool)->cs->css); diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c index ecb6e0b7819a0..5b8d9f0e25535 100644 --- a/mm/hugetlb_cgroup.c +++ b/mm/hugetlb_cgroup.c @@ -274,7 +274,7 @@ static int __hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages, if (!page_counter_try_charge( __hugetlb_cgroup_counter_from_cgroup(h_cg, idx, rsvd), - nr_pages, &counter)) { + nr_pages, &counter, false, NULL)) { ret = -ENOMEM; hugetlb_event(h_cg, idx, HUGETLB_MAX); css_put(&h_cg->css); diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c index bf2c7d53b01b1..22822e7a85b49 100644 --- a/mm/memcontrol-v1.c +++ b/mm/memcontrol-v1.c @@ -122,10 +122,13 @@ static unsigned long mem_cgroup_usage(struct mem_cgroup memcg, bool swap) if (swap) val += total_swap_pages - get_nr_swap_pages(); } else { - if (!swap) + if (!swap) { val = page_counter_read(&memcg->memory); - else - val = page_counter_read(&memcg->memsw); + } else { + / Preserve the user-visible memory <= memsw invariant. / + val = max(page_counter_read(&memcg->memory), + page_counter_read(&memcg->memsw)); + } } return val; } @@ -2194,7 +2197,8 @@ bool memcg1_charge_skmem(struct mem_cgroup memcg, unsigned int nr_pages, { struct page_counter fail; - if (page_counter_try_charge(&memcg->tcpmem, nr_pages, &fail)) { + if (page_counter_try_charge(&memcg->tcpmem, nr_pages, &fail, + false, NULL)) { memcg->tcpmem_pressure = 0; return true; } diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 791e536efaebe..e533f08232fbc 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2063,34 +2063,19 @@ void mem_cgroup_print_oom_group(struct mem_cgroup memcg) pr_cont(" are going to be killed due to memory.oom.group set\n"); } -/* - * The value of NR_MEMCG_STOCK is selected to keep the cached memcgs and their - * nr_pages in a single cacheline. This may change in future. - / -#define NR_MEMCG_STOCK 7 - -/ - * Watermarks for a charge stock slot, in the spirit of pcp->high and - * pcp->batch: MEMCG_STOCK_HIGH is the high watermark at which a slot is - * trimmed, and it is trimmed down to MEMCG_STOCK_LOW rather than emptied. - / -#define MEMCG_STOCK_LOW (MEMCG_CHARGE_BATCH / 2) -#define MEMCG_STOCK_HIGH (MEMCG_CHARGE_BATCH) - #define FLUSHING_CACHED_CHARGE 0 -struct memcg_stock_pcp { - local_trylock_t lock; - uint8_t nr_pages[NR_MEMCG_STOCK]; - struct mem_cgroup cached[NR_MEMCG_STOCK]; - struct work_struct work; - unsigned long flags; - uint8_t drain_idx; +static DEFINE_PER_CPU_ALIGNED(struct page_counter_stock_pcp, memory_stock) = { + .lock = INIT_LOCAL_TRYLOCK(lock), + .base = &memory_stock, }; -static DEFINE_PER_CPU_ALIGNED(struct memcg_stock_pcp, memcg_stock) = { +#ifdef CONFIG_MEMCG_V1 +static DEFINE_PER_CPU_ALIGNED(struct page_counter_stock_pcp, memsw_stock) = { .lock = INIT_LOCAL_TRYLOCK(lock), + .base = &memsw_stock, }; +#endif /* * NR_OBJ_STOCK is sized so the entire hot path of obj_stock_pcp @@ -2139,52 +2124,6 @@ static void drain_obj_stock(struct obj_stock_pcp stock); static bool obj_stock_flush_required(struct obj_stock_pcp stock, struct mem_cgroup root_memcg); -/* - * consume_stock: Try to consume stocked charge on this cpu. - * @memcg: memcg to consume from. - * @nr_pages: how many pages to charge. - * - * Consume the cached charge if enough nr_pages are present otherwise return - * failure. Also return failure for charge request larger than - * MEMCG_CHARGE_BATCH or if the local lock is already taken. - * - * returns true if successful, false otherwise. - / -static bool consume_stock(struct mem_cgroup memcg, unsigned int nr_pages) -{ - struct memcg_stock_pcp stock; - uint8_t stock_pages; - bool ret = false; - int i; - - if (nr_pages > MEMCG_CHARGE_BATCH \|\| - !local_trylock(&memcg_stock.lock)) - return ret; - - stock = this_cpu_ptr(&memcg_stock); - - for (i = 0; i < NR_MEMCG_STOCK; ++i) { - if (memcg != READ_ONCE(stock->cached[i])) - continue; - - stock_pages = READ_ONCE(stock->nr_pages[i]); - if (stock_pages >= nr_pages) { - stock_pages -= nr_pages; - WRITE_ONCE(stock->nr_pages[i], stock_pages); - if (!stock_pages) { - css_put(&memcg->css); - WRITE_ONCE(stock->cached[i], NULL); - } - ret = true; - } - break; - } - - local_unlock(&memcg_stock.lock); - - return ret; -} - static void memcg_uncharge(struct mem_cgroup memcg, unsigned int nr_pages) { page_counter_uncharge(&memcg->memory, nr_pages); @@ -2192,49 +2131,22 @@ static void memcg_uncharge(struct mem_cgroup memcg, unsigned int nr_pages) page_counter_uncharge(&memcg->memsw, nr_pages); } -/ - * Returns stocks cached in percpu and reset cached information. - / -static void drain_stock(struct memcg_stock_pcp stock, int i) +static void drain_local_stock(struct work_struct work) { - struct mem_cgroup old = READ_ONCE(stock->cached[i]); - uint8_t stock_pages; - - if (!old) - return; - - stock_pages = READ_ONCE(stock->nr_pages[i]); - if (stock_pages) { - memcg_uncharge(old, stock_pages); - WRITE_ONCE(stock->nr_pages[i], 0); - } - - css_put(&old->css); - WRITE_ONCE(stock->cached[i], NULL); -} - -static void drain_stock_fully(struct memcg_stock_pcp stock) -{ - int i; - - for (i = 0; i < NR_MEMCG_STOCK; ++i) - drain_stock(stock, i); -} - -static void drain_local_memcg_stock(struct work_struct dummy) -{ - struct memcg_stock_pcp stock; + struct page_counter_stock_pcp pcp_stock; + struct page_counter_stock_pcp __percpu stock; if (WARN_ONCE(!in_task(), "drain in non-task context")) return; - local_lock(&memcg_stock.lock); + stock = container_of(work, struct page_counter_stock_pcp, work)->base; + local_lock(&stock->lock); - stock = this_cpu_ptr(&memcg_stock); - drain_stock_fully(stock); - clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); + pcp_stock = this_cpu_ptr(stock); + page_counter_drain_stock_fully(pcp_stock); + clear_bit(FLUSHING_CACHED_CHARGE, &pcp_stock->flags); - local_unlock(&memcg_stock.lock); + local_unlock(&stock->lock); } static void drain_local_obj_stock(struct work_struct dummy) @@ -2253,92 +2165,6 @@ static void drain_local_obj_stock(struct work_struct dummy) local_unlock(&obj_stock.lock); } -static void refill_stock(struct mem_cgroup memcg, unsigned int nr_pages) -{ - struct memcg_stock_pcp stock; - struct mem_cgroup cached; - unsigned int stock_pages; - bool success = false; - int empty_slot = -1; - int i; - - /* - * nr_pages[] is a uint8_t and a slot's count is capped at - * MEMCG_STOCK_HIGH. Raising MEMCG_CHARGE_BATCH beyond 127 would need - * more careful handling of nr_pages[] in struct memcg_stock_pcp. - / - BUILD_BUG_ON(MEMCG_CHARGE_BATCH > S8_MAX); - BUILD_BUG_ON(MEMCG_STOCK_HIGH > U8_MAX); - - VM_WARN_ON_ONCE(mem_cgroup_is_root(memcg)); - - if (nr_pages > MEMCG_CHARGE_BATCH \|\| - !local_trylock(&memcg_stock.lock)) { - / - * In case of larger than batch refill or unlikely failure to - * lock the percpu memcg_stock.lock, uncharge memcg directly. - / - memcg_uncharge(memcg, nr_pages); - return; - } - - stock = this_cpu_ptr(&memcg_stock); - for (i = 0; i < NR_MEMCG_STOCK; ++i) { - cached = READ_ONCE(stock->cached[i]); - if (!cached && empty_slot == -1) - empty_slot = i; - if (memcg == READ_ONCE(stock->cached[i])) { - stock_pages = READ_ONCE(stock->nr_pages[i]) + nr_pages; - if (stock_pages > MEMCG_STOCK_HIGH) { - memcg_uncharge(memcg, - stock_pages - MEMCG_STOCK_LOW); - stock_pages = MEMCG_STOCK_LOW; - } - WRITE_ONCE(stock->nr_pages[i], stock_pages); - success = true; - break; - } - } - - if (!success) { - i = empty_slot; - if (i == -1) { - i = stock->drain_idx++; - if (stock->drain_idx == NR_MEMCG_STOCK) - stock->drain_idx = 0; - drain_stock(stock, i); - } - css_get(&memcg->css); - WRITE_ONCE(stock->cached[i], memcg); - WRITE_ONCE(stock->nr_pages[i], nr_pages); - } - - local_unlock(&memcg_stock.lock); -} - -static bool is_memcg_drain_needed(struct memcg_stock_pcp stock, - struct mem_cgroup root_memcg) -{ - struct mem_cgroup memcg; - bool flush = false; - int i; - - rcu_read_lock(); - for (i = 0; i < NR_MEMCG_STOCK; ++i) { - memcg = READ_ONCE(stock->cached[i]); - if (!memcg) - continue; - - if (READ_ONCE(stock->nr_pages[i]) && - mem_cgroup_is_descendant(memcg, root_memcg)) { - flush = true; - break; - } - } - rcu_read_unlock(); - return flush; -} - static bool schedule_drain_work(int cpu, struct work_struct work) { / @@ -2355,12 +2181,30 @@ static bool schedule_drain_work(int cpu, struct work_struct work) return true; } +static void schedule_stock_drain(struct page_counter_stock_pcp __percpu stock, + struct cgroup_subsys_state root_css, + int cpu, int curcpu) +{ + struct page_counter_stock_pcp pcp_stock = per_cpu_ptr(stock, cpu); + + if (test_bit(FLUSHING_CACHED_CHARGE, &pcp_stock->flags) \|\| + !page_counter_stock_flush_required(pcp_stock, root_css) \|\| + test_and_set_bit(FLUSHING_CACHED_CHARGE, &pcp_stock->flags)) + return; + + if (cpu == curcpu) + drain_local_stock(&pcp_stock->work); + else if (!schedule_drain_work(cpu, &pcp_stock->work)) + clear_bit(FLUSHING_CACHED_CHARGE, &pcp_stock->flags); +} + /* * Drains all per-CPU charge caches for given root_memcg resp. subtree * of the hierarchy under it. / void drain_all_stock(struct mem_cgroup root_memcg) { + struct cgroup_subsys_state root_css = &root_memcg->css; int cpu, curcpu; / If someone's already draining, avoid adding running more workers. / @@ -2370,24 +2214,18 @@ void drain_all_stock(struct mem_cgroup root_memcg) * Notify other cpus that system-wide "drain" is running * We do not care about races with the cpu hotplug because cpu down * as well as workers from this path always operate on the local - * per-cpu data. CPU up doesn't touch memcg_stock at all. + * per-cpu data. CPU up doesn't touch the stocks at all. / migrate_disable(); curcpu = smp_processor_id(); for_each_online_cpu(cpu) { - struct memcg_stock_pcp memcg_st = &per_cpu(memcg_stock, cpu); struct obj_stock_pcp obj_st = &per_cpu(obj_stock, cpu); - if (!test_bit(FLUSHING_CACHED_CHARGE, &memcg_st->flags) && - is_memcg_drain_needed(memcg_st, root_memcg) && - !test_and_set_bit(FLUSHING_CACHED_CHARGE, - &memcg_st->flags)) { - if (cpu == curcpu) - drain_local_memcg_stock(&memcg_st->work); - else if (!schedule_drain_work(cpu, &memcg_st->work)) - clear_bit(FLUSHING_CACHED_CHARGE, - &memcg_st->flags); - } + schedule_stock_drain(&memory_stock, root_css, cpu, curcpu); +#ifdef CONFIG_MEMCG_V1 + if (do_memsw_account()) + schedule_stock_drain(&memsw_stock, root_css, cpu, curcpu); +#endif if (!test_bit(FLUSHING_CACHED_CHARGE, &obj_st->flags) && obj_stock_flush_required(obj_st, root_memcg) && @@ -2406,12 +2244,19 @@ void drain_all_stock(struct mem_cgroup root_memcg) static int memcg_hotplug_cpu_dead(unsigned int cpu) { - struct memcg_stock_pcp memcg_st = &per_cpu(memcg_stock, cpu); + struct page_counter_stock_pcp stock; struct obj_stock_pcp obj_st = &per_cpu(obj_stock, cpu); / no need for the local lock / drain_obj_stock(obj_st); - drain_stock_fully(memcg_st); + stock = per_cpu_ptr(&memory_stock, cpu); + page_counter_drain_stock_fully(stock); + clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); +#ifdef CONFIG_MEMCG_V1 + stock = per_cpu_ptr(&memsw_stock, cpu); + page_counter_drain_stock_fully(stock); + clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); +#endif / * A drain work queued before the CPU went away is executed by an @@ -2419,7 +2264,6 @@ static int memcg_hotplug_cpu_dead(unsigned int cpu) * clear the flags here to make these stocks drainable again once * the CPU comes back online. / - clear_bit(FLUSHING_CACHED_CHARGE, &memcg_st->flags); clear_bit(FLUSHING_CACHED_CHARGE, &obj_st->flags); return 0; @@ -2699,10 +2543,10 @@ void __mem_cgroup_handle_over_high(gfp_t gfp_mask) static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask, unsigned int nr_pages) { - unsigned int batch = max(MEMCG_CHARGE_BATCH, nr_pages); int nr_retries = MAX_RECLAIM_RETRIES; struct mem_cgroup mem_over_limit; struct page_counter counter; + unsigned long nr_charged; unsigned long nr_reclaimed; bool passed_oom = false; unsigned int reclaim_options; @@ -2710,33 +2554,30 @@ static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask, bool raised_max_event = false; unsigned long pflags; bool allow_spinning = gfpflags_allow_spinning(gfp_mask); + bool may_batch = allow_spinning; int ret = 0; retry: - if (consume_stock(memcg, nr_pages)) - return ret; - - if (!allow_spinning) - / Avoid the refill and flush of the older stock / - batch = nr_pages; - reclaim_options = MEMCG_RECLAIM_MAY_SWAP; - if (!do_memsw_account() \|\| - page_counter_try_charge(&memcg->memsw, batch, &counter)) { - if (page_counter_try_charge(&memcg->memory, batch, &counter)) - goto done_restock; - if (do_memsw_account()) - page_counter_uncharge(&memcg->memsw, batch); - mem_over_limit = mem_cgroup_from_counter(counter, memory); - } else { + if (do_memsw_account() && + !page_counter_try_charge(&memcg->memsw, nr_pages, &counter, + may_batch, NULL)) { mem_over_limit = mem_cgroup_from_counter(counter, memsw); reclaim_options &= ~MEMCG_RECLAIM_MAY_SWAP; + goto reclaim; } - if (batch > nr_pages) { - batch = nr_pages; - goto retry; - } + if (page_counter_try_charge(&memcg->memory, nr_pages, &counter, + may_batch, &nr_charged)) + goto check_high; + + if (do_memsw_account()) + page_counter_uncharge(&memcg->memsw, nr_pages); + mem_over_limit = mem_cgroup_from_counter(counter, memory); + +reclaim: + / Do not retry speculative batch charges after the first miss. / + may_batch = false; / * Prevent unbounded recursion when reclaim operations need to @@ -2849,10 +2690,9 @@ static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask, return ret; -done_restock: - if (batch > nr_pages) - refill_stock(memcg, batch - nr_pages); - +check_high: + if (!nr_charged) + return ret; / * If the hierarchy is above the normal consumption range, schedule * reclaim on returning to userland. We can perform reclaim here @@ -2892,7 +2732,7 @@ static int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask, and distribute reclaim work and delay penalties * based on how much each task is actually allocating. / - current->memcg_nr_pages_over_high += batch; + current->memcg_nr_pages_over_high += nr_charged; set_notify_resume(current); break; } @@ -3197,8 +3037,11 @@ static void obj_cgroup_uncharge_pages(struct obj_cgroup objcg, account_kmem_nmi_safe(memcg, -nr_pages); memcg1_account_kmem(memcg, -nr_pages); - if (!mem_cgroup_is_root(memcg)) - refill_stock(memcg, nr_pages); + if (!mem_cgroup_is_root(memcg)) { + page_counter_refill_stock(&memcg->memory, nr_pages); + if (do_memsw_account()) + page_counter_refill_stock(&memcg->memsw, nr_pages); + } css_put(&memcg->css); } @@ -4297,8 +4140,14 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state parent_css) page_counter_set_high(&memcg->swap, PAGE_COUNTER_MAX); if (parent) { page_counter_init(&memcg->memory, &parent->memory, memcg_on_dfl); + memcg->memory.stock = &memory_stock; + memcg->memory.stock_css = &memcg->css; page_counter_init(&memcg->swap, &parent->swap, false); #ifdef CONFIG_MEMCG_V1 + if (!memcg_on_dfl) { + memcg->memsw.stock = &memsw_stock; + memcg->memsw.stock_css = &memcg->css; + } WRITE_ONCE(memcg->swappiness, mem_cgroup_swappiness(parent)); memcg->memory.track_failcnt = !memcg_on_dfl; memcg->memsw.track_failcnt = !memcg_on_dfl; @@ -5764,7 +5613,7 @@ void mem_cgroup_sk_uncharge(const struct sock sk, unsigned int nr_pages) mod_memcg_state(memcg, MEMCG_SOCK, -nr_pages); - refill_stock(memcg, nr_pages); + page_counter_refill_stock(&memcg->memory, nr_pages); } void mem_cgroup_flush_workqueue(void) @@ -5912,6 +5761,8 @@ int __init mem_cgroup_init(void) * exceed S32_MAX / PAGE_SIZE. / BUILD_BUG_ON(MEMCG_CHARGE_BATCH > S32_MAX / PAGE_SIZE); + / Batched page-counter charges feed memcg's memory.high accounting. / + BUILD_BUG_ON(MEMCG_CHARGE_BATCH != PAGE_COUNTER_STOCK_BATCH); memcg_struct_check(); @@ -5922,8 +5773,12 @@ int __init mem_cgroup_init(void) WARN_ON(!memcg_wq); for_each_possible_cpu(cpu) { - INIT_WORK(&per_cpu_ptr(&memcg_stock, cpu)->work, - drain_local_memcg_stock); + INIT_WORK(&per_cpu_ptr(&memory_stock, cpu)->work, + drain_local_stock); +#ifdef CONFIG_MEMCG_V1 + INIT_WORK(&per_cpu_ptr(&memsw_stock, cpu)->work, + drain_local_stock); +#endif INIT_WORK(&per_cpu_ptr(&obj_stock, cpu)->work, drain_local_obj_stock); } @@ -5976,7 +5831,8 @@ int __mem_cgroup_try_charge_swap(struct folio folio) rcu_read_unlock(); if (!mem_cgroup_is_root(memcg) && - !page_counter_try_charge(&memcg->swap, nr_pages, &counter)) { + !page_counter_try_charge(&memcg->swap, nr_pages, &counter, false, + NULL)) { memcg_memory_event(memcg, MEMCG_SWAP_MAX); memcg_memory_event(memcg, MEMCG_SWAP_FAIL); mem_cgroup_private_id_put(memcg, nr_pages); diff --git a/mm/page_counter.c b/mm/page_counter.c index 98322803941a7..3cd8601961673 100644 --- a/mm/page_counter.c +++ b/mm/page_counter.c @@ -7,6 +7,7 @@ #include <linux/page_counter.h> #include <linux/atomic.h> +#include <linux/cgroup.h> #include <linux/kernel.h> #include <linux/math64.h> #include <linux/string.h> @@ -14,6 +15,14 @@ #include <linux/bug.h> #include <asm/page.h> +/* + * Watermarks for a charge stock slot, in the spirit of pcp->high and + * pcp->batch: PAGE_COUNTER_STOCK_HIGH is the high watermark at which a slot is + * trimmed down to PAGE_COUNTER_STOCK_LOW rather than emptied. + / +#define PAGE_COUNTER_STOCK_LOW (PAGE_COUNTER_STOCK_BATCH / 2) +#define PAGE_COUNTER_STOCK_HIGH PAGE_COUNTER_STOCK_BATCH + static bool track_protection(struct page_counter c) { return c->protection_support; @@ -127,23 +136,76 @@ void page_counter_charge(struct page_counter counter, unsigned long nr_pages) } } +/ + * Consume the cached charge if enough nr_pages are present, otherwise return + * failure. Also return failure for charge requests larger than + * PAGE_COUNTER_STOCK_BATCH or if the local lock is already taken. + / +static bool page_counter_consume_stock(struct page_counter counter, + unsigned long nr_pages) +{ + struct page_counter_stock_pcp __percpu stock = counter->stock; + struct page_counter_stock_pcp pcp_stock; + u8 stock_pages; + bool ret = false; + int i; + + if (nr_pages > PAGE_COUNTER_STOCK_BATCH \|\| + !local_trylock(&stock->lock)) + return false; + + pcp_stock = this_cpu_ptr(stock); + for (i = 0; i < NR_PAGE_COUNTER_STOCK; i++) { + if (counter != READ_ONCE(pcp_stock->cached[i])) + continue; + + stock_pages = READ_ONCE(pcp_stock->nr_pages[i]); + if (stock_pages >= nr_pages) { + stock_pages -= nr_pages; + WRITE_ONCE(pcp_stock->nr_pages[i], stock_pages); + if (!stock_pages) { + css_put(counter->stock_css); + WRITE_ONCE(pcp_stock->cached[i], NULL); + } + ret = true; + } + break; + } + local_unlock(&stock->lock); + + return ret; +} + /** - * page_counter_try_charge - try to hierarchically charge pages + * page_counter_try_charge - try to hierarchically charge pages using stock * @counter: counter - * @nr_pages: number of pages to charge - * @fail: points first counter to hit its limit, if any + * @nr_pages: number of pages requested + * @fail: points to the first counter to hit its limit, if any + * @may_batch: whether a stock miss may trigger a batch charge + * @nr_charged: optional; set to the hierarchy charge size on success * - * Returns %true on success, or %false and @fail if the counter or one - * of its ancestors has hit its configured limit. + * Return: %true if the request was satisfied. A failed batch charge may update + * @fail before an exact retry succeeds. / bool page_counter_try_charge(struct page_counter counter, - unsigned long nr_pages, - struct page_counter fail) + unsigned long nr_pages, struct page_counter fail, + bool may_batch, unsigned long nr_charged) { + unsigned long charge = nr_pages; struct page_counter c; bool protection = track_protection(counter); bool track_failcnt = counter->track_failcnt; + if (counter->stock && may_batch) + charge = max(nr_pages, PAGE_COUNTER_STOCK_BATCH); + +retry: + if (counter->stock && page_counter_consume_stock(counter, nr_pages)) { + if (nr_charged) + nr_charged = 0; + return true; + } + for (c = counter; c; c = c->parent) { long new; / @@ -160,9 +222,9 @@ bool page_counter_try_charge(struct page_counter counter, we either see the new limit or the setter sees the * counter has changed and retries. / - new = atomic_long_add_return(nr_pages, &c->usage); + new = atomic_long_add_return(charge, &c->usage); if (new > c->max) { - atomic_long_sub(nr_pages, &c->usage); + atomic_long_sub(charge, &c->usage); / * This is racy, but we can live with some * inaccuracy in the failcnt which is only used @@ -183,15 +245,142 @@ bool page_counter_try_charge(struct page_counter counter, WRITE_ONCE(c->watermark, new); } } + if (charge > nr_pages) + page_counter_refill_stock(counter, charge - nr_pages); + if (nr_charged) + nr_charged = charge; return true; failed: for (c = counter; c != fail; c = c->parent) - page_counter_cancel(c, nr_pages); + page_counter_cancel(c, charge); + + if (charge > nr_pages) { + charge = nr_pages; + goto retry; + } return false; } +static void page_counter_drain_stock(struct page_counter_stock_pcp stock, + int i) +{ + struct page_counter counter = READ_ONCE(stock->cached[i]); + u8 nr_pages; + + if (!counter) + return; + + nr_pages = READ_ONCE(stock->nr_pages[i]); + if (nr_pages) { + page_counter_uncharge(counter, nr_pages); + WRITE_ONCE(stock->nr_pages[i], 0); + } + css_put(counter->stock_css); + WRITE_ONCE(stock->cached[i], NULL); +} + +void page_counter_drain_stock_fully(struct page_counter_stock_pcp stock) +{ + int i; + + for (i = 0; i < NR_PAGE_COUNTER_STOCK; i++) + page_counter_drain_stock(stock, i); +} + +bool page_counter_stock_flush_required(struct page_counter_stock_pcp stock, + struct cgroup_subsys_state root_css) +{ + struct cgroup_subsys_state css; + struct page_counter counter; + bool flush = false; + int i; + + rcu_read_lock(); + for (i = 0; i < NR_PAGE_COUNTER_STOCK; i++) { + counter = READ_ONCE(stock->cached[i]); + if (!counter) + continue; + css = READ_ONCE(counter->stock_css); + + if (READ_ONCE(stock->nr_pages[i]) && + cgroup_is_descendant(css->cgroup, root_css->cgroup)) { + flush = true; + break; + } + } + rcu_read_unlock(); + return flush; +} + +/** + * page_counter_refill_stock - return pages to a counter's stock + * @counter: counter to return pages to + * @nr_pages: number of pages to return + * + * If the stock cannot accept the pages, uncharge them from the hierarchy. + / +void page_counter_refill_stock(struct page_counter counter, + unsigned long nr_pages) +{ + struct page_counter_stock_pcp __percpu stock = counter->stock; + struct page_counter_stock_pcp pcp_stock; + unsigned int stock_pages; + int empty_slot = -1; + int i; + + /* + * nr_pages[] is a u8 and a slot is capped at PAGE_COUNTER_STOCK_HIGH. + * Raising PAGE_COUNTER_STOCK_BATCH beyond 127 would need careful + * handling of nr_pages[] in struct page_counter_stock_pcp. + / + BUILD_BUG_ON(PAGE_COUNTER_STOCK_BATCH > S8_MAX); + BUILD_BUG_ON(PAGE_COUNTER_STOCK_HIGH > U8_MAX); + + if (!stock \|\| nr_pages > PAGE_COUNTER_STOCK_BATCH \|\| + !local_trylock(&stock->lock)) { + / + * For a larger-than-batch refill or an unlikely failure to lock + * the per-CPU stock, uncharge the hierarchy directly. + / + page_counter_uncharge(counter, nr_pages); + return; + } + + pcp_stock = this_cpu_ptr(stock); + for (i = 0; i < NR_PAGE_COUNTER_STOCK; i++) { + struct page_counter cached = READ_ONCE(pcp_stock->cached[i]); + + if (!cached && empty_slot == -1) + empty_slot = i; + if (counter != cached) + continue; + + stock_pages = READ_ONCE(pcp_stock->nr_pages[i]) + nr_pages; + if (stock_pages > PAGE_COUNTER_STOCK_HIGH) { + page_counter_uncharge(counter, + stock_pages - PAGE_COUNTER_STOCK_LOW); + stock_pages = PAGE_COUNTER_STOCK_LOW; + } + WRITE_ONCE(pcp_stock->nr_pages[i], stock_pages); + local_unlock(&stock->lock); + return; + } + + i = empty_slot; + if (i == -1) { + i = pcp_stock->drain_idx++; + if (pcp_stock->drain_idx == NR_PAGE_COUNTER_STOCK) + pcp_stock->drain_idx = 0; + page_counter_drain_stock(pcp_stock, i); + } + css_get(counter->stock_css); + WRITE_ONCE(pcp_stock->cached[i], counter); + WRITE_ONCE(pcp_stock->nr_pages[i], nr_pages); + local_unlock(&stock->lock); +} + /** * page_counter_uncharge - hierarchically uncharge pages * @counter: counter
57/3	2026/09/18 15:43	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 13072 output: 35 thoughts: 1521 Thoughts: KMSAN Evaluation for the Patch Series Okay, so I need to decide if we need a dedicated KMSAN run for this patch series. Let's break it down. The commit title is straightforward: "syz-cluster: applied patch under review". Seems routine. First, I need to understand what this patch actually does. Looking at the modified files, it's mostly within `mm` and `kernel/cgroup`, specifically `page_counter.h`, `dmem.c`, and several `memcontrol` related files. The summary is that it's refactoring the memory cgroup stock mechanism. It looks like they're making `memcg_stock_pcp` / `consume_stock` / `refill_stock` into something generic: `page_counter_stock_pcp`. This is good, a general interface can mean less code duplication. Specifically, memcg stock caching is moving to the page counter level, and we've got a new `struct page_counter_stock_pcp`, plus those two new fields in `struct page_counter`: `stock` and `stock_css`. Fine, and `page_counter_try_charge` gets two new parameters: `may_batch` and `nr_charged`. All the callers have been updated which is good. Now, my mind starts to race. This is where I start thinking about potential issues. I need to make sure this doesn't introduce any uninitialized variable reads or memory errors. This is the critical point for a KMSAN review. I immediately spot something interesting within `try_charge_memcg`: ```c unsigned long nr_charged; ... if (page_counter_try_charge(&memcg->memory, nr_pages, &counter, may_batch, &nr_charged)) goto check_high; ... check_high: if (!nr_charged) return ret; ... current->memcg_nr_pages_over_high += nr_charged; ``` It looks like `nr_charged` is only initialized if `page_counter_try_charge` returns true. What if it returns false, for whatever reason? Is `nr_charged` uninitialized in that case, leading to a read of an uninitialized value? I need to check the implementation of `page_counter_try_charge` in `mm/page_counter.c`! Okay, let's look at `page_counter_try_charge`: ```c bool page_counter_try_charge(struct page_counter counter, unsigned long nr_pages, struct page_counter fail, bool may_batch, unsigned long nr_charged) { unsigned long charge = nr_pages; struct page_counter c; bool protection = track_protection(counter); bool track_failcnt = counter->track_failcnt; if (counter->stock && may_batch) charge = max(nr_pages, PAGE_COUNTER_STOCK_BATCH); retry: if (counter->stock && page_counter_consume_stock(counter, nr_pages)) { if (nr_charged) nr_charged = 0; return true; } for (c = counter; c; c = c->parent) { ... } if (charge > nr_pages) page_counter_refill_stock(counter, charge - nr_pages); if (nr_charged) nr_charged = charge; return true; failed: ... ``` Aha! It does* initialize `nr_charged` on both the success paths! Either `0` if `page_counter_consume_stock` returns true, or `charge` if it's the normal success path through the loop. If it returns false, it goes to `failed:` or the caller's failure paths, which is fine, no uninitialized read. However* what is the flow of control within the caller? Let me check around the call to `page_counter_try_charge` and the `check_high:` label in `mm/memcontrol.c`. Okay, I'm going to carefully read around lines 2540-2750 in `mm/memcontrol.c`. I need to be 100% certain there's no path where `nr_charged` is read uninitialized. I will determine if a KMSAN run is really necessary.
58/3	2026/09/18 15:44	tool	read-file	0m Args: { "File": "mm/memcontrol.c", "FirstLine": 2540, "LineCount": 90 } Results: { "Contents": "2540:\t\tcss_put(\u0026memcg-\u003ecss);\n2541:\t}\n2542:\t\n2543:\tstatic int try_charge_memcg(struct mem_cgroup memcg, gfp_t gfp_mask,\n2544:\t\t\t\t unsigned int nr_pages)\n2545:\t{\n2546:\t\tint nr_retries = MAX_RECLAIM_RETRIES;\n2547:\t\tstruct mem_cgroup mem_over_limit;\n2548:\t\tstruct page_counter counter;\n2549:\t\tunsigned long nr_charged;\n2550:\t\tunsigned long nr_reclaimed;\n2551:\t\tbool passed_oom = false;\n2552:\t\tunsigned int reclaim_options;\n2553:\t\tbool drained = false;\n2554:\t\tbool raised_max_event = false;\n2555:\t\tunsigned long pflags;\n2556:\t\tbool allow_spinning = gfpflags_allow_spinning(gfp_mask);\n2557:\t\tbool may_batch = allow_spinning;\n2558:\t\tint ret = 0;\n2559:\t\n2560:\tretry:\n2561:\t\treclaim_options = MEMCG_RECLAIM_MAY_SWAP;\n2562:\t\tif (do_memsw_account() \u0026\u0026\n2563:\t\t !page_counter_try_charge(\u0026memcg-\u003ememsw, nr_pages, \u0026counter,\n2564:\t\t\t\t\t may_batch, NULL)) {\n2565:\t\t\tmem_over_limit = mem_cgroup_from_counter(counter, memsw);\n2566:\t\t\treclaim_options \u0026= ~MEMCG_RECLAIM_MAY_SWAP;\n2567:\t\t\tgoto reclaim;\n2568:\t\t}\n2569:\t\n2570:\t\tif (page_counter_try_charge(\u0026memcg-\u003ememory, nr_pages, \u0026counter,\n2571:\t\t\t\t\t may_batch, \u0026nr_charged))\n2572:\t\t\tgoto check_high;\n2573:\t\n2574:\t\tif (do_memsw_account())\n2575:\t\t\tpage_counter_uncharge(\u0026memcg-\u003ememsw, nr_pages);\n2576:\t\tmem_over_limit = mem_cgroup_from_counter(counter, memory);\n2577:\t\n2578:\treclaim:\n2579:\t\t/ Do not retry speculative batch charges after the first miss. /\n2580:\t\tmay_batch = false;\n2581:\t\n2582:\t\t/\n2583:\t\t * Prevent unbounded recursion when reclaim operations need to\n2584:\t\t * allocate memory. This might exceed the limits temporarily,\n2585:\t\t * but we prefer facilitating memory reclaim and getting back\n2586:\t\t * under the limit over triggering OOM kills in these cases.\n2587:\t\t /\n2588:\t\tif (unlikely(current-\u003eflags \u0026 PF_MEMALLOC))\n2589:\t\t\tgoto force;\n2590:\t\n2591:\t\tif (unlikely(task_in_memcg_oom(current)))\n2592:\t\t\tgoto nomem;\n2593:\t\n2594:\t\tif (!gfpflags_allow_blocking(gfp_mask))\n2595:\t\t\tgoto nomem;\n2596:\t\n2597:\t\t/\n2598:\t\t * OOM victim still needs to charge memory to exit. OOM reaper should\n2599:\t\t * help but it might fail on mmap_lock contention. If the victim is a\n2600:\t\t * large thread group then all exiting threads might compete on oom_lock\n2601:\t\t * just to learn that there is nothing really killable anymore. Bail\n2602:\t\t * out early and fail the charge to expedite their exit. They are\n2603:\t\t * considered fully reclaimed by the oom reaper and they shouldn't\n2604:\t\t * contribute further charges.\n2605:\t\t /\n2606:\t\tif (tsk_is_oom_victim(current) \u0026\u0026\n2607:\t\t mm_flags_test(MMF_OOM_SKIP, current-\u003esignal-\u003eoom_mm))\n2608:\t\t\tgoto nomem;\n2609:\t\n2610:\t\t__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);\n2611:\t\traised_max_event = true;\n2612:\t\n2613:\t\tpsi_memstall_enter(\u0026pflags);\n2614:\t\tnr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages,\n2615:\t\t\t\t\t\t\t gfp_mask, reclaim_options, NULL);\n2616:\t\tpsi_memstall_leave(\u0026pflags);\n2617:\t\n2618:\t\tif (mem_cgroup_margin(mem_over_limit) \u003e= nr_pages)\n2619:\t\t\tgoto retry;\n2620:\t\n2621:\t\tif (!drained) {\n2622:\t\t\tdrain_all_stock(mem_over_limit);\n2623:\t\t\tdrained = true;\n2624:\t\t\tgoto retry;\n2625:\t\t}\n2626:\t\n2627:\t\tif (gfp_mask \u0026 __GFP_NORETRY)\n2628:\t\t\tgoto nomem;\n2629:\t\t/\n" }
59/3	2026/09/18 15:44	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 17039 output: 35 thoughts: 40 Thoughts: Okay, let's break this down. Investigating the Implications of `goto force` in `try_charge_memcg` Alright, so the immediate question on my mind is: what's the fallout of a `goto force` within the `try_charge_memcg` function? I know this area intimately, so I need to quickly refresh my understanding of the execution path this might trigger. To get a handle on it I should focus on lines 2630 through 2720 of that function. That's where the logic around this potential jump is most likely to reside. I need to zero in on what happens in that segment of code when that `goto` statement is hit, what's bypassed, and what the flow becomes. This is key to figuring out the overall impact and if there are any potential edge cases that need to be considered.
60/3	2026/09/18 15:44	tool	read-file	0m Args: { "File": "mm/memcontrol.c", "FirstLine": 2630, "LineCount": 90 } Results: { "Contents": "2630:\t\t * Even though the limit is exceeded at this point, reclaim\n2631:\t\t * may have been able to free some pages. Retry the charge\n2632:\t\t * before killing the task.\n2633:\t\t \n2634:\t\t Only for regular pages, though: huge pages are rather\n2635:\t\t * unlikely to succeed so close to the limit, and we fall back\n2636:\t\t * to regular pages anyway in case of failure.\n2637:\t\t /\n2638:\t\tif (nr_reclaimed \u0026\u0026 nr_pages \u003c= (1 \u003c\u003c PAGE_ALLOC_COSTLY_ORDER))\n2639:\t\t\tgoto retry;\n2640:\t\n2641:\t\tif (nr_retries--)\n2642:\t\t\tgoto retry;\n2643:\t\n2644:\t\tif (gfp_mask \u0026 __GFP_RETRY_MAYFAIL)\n2645:\t\t\tgoto nomem;\n2646:\t\n2647:\t\t/ Avoid endless loop for tasks bypassed by the oom killer /\n2648:\t\tif (passed_oom \u0026\u0026 task_is_dying())\n2649:\t\t\tgoto nomem;\n2650:\t\n2651:\t\t/\n2652:\t\t * keep retrying as long as the memcg oom killer is able to make\n2653:\t\t * a forward progress or bypass the charge if the oom killer\n2654:\t\t * couldn't make any progress.\n2655:\t\t /\n2656:\t\tif (mem_cgroup_oom(mem_over_limit, gfp_mask,\n2657:\t\t\t\t get_order(nr_pages PAGE_SIZE))) {\n2658:\t\t\tpassed_oom = true;\n2659:\t\t\tnr_retries = MAX_RECLAIM_RETRIES;\n2660:\t\t\tgoto retry;\n2661:\t\t}\n2662:\tnomem:\n2663:\t\t/\n2664:\t\t Memcg doesn't have a dedicated reserve for atomic\n2665:\t\t * allocations. But like the global atomic pool, we need to\n2666:\t\t * put the burden of reclaim on regular allocation requests\n2667:\t\t * and let these go through as privileged allocations.\n2668:\t\t /\n2669:\t\tif (!(gfp_mask \u0026 (__GFP_NOFAIL \| __GFP_HIGH))) {\n2670:\t\t\tret = -ENOMEM;\n2671:\t\t\tgoto out;\n2672:\t\t}\n2673:\tforce:\n2674:\t\t/\n2675:\t\t * The allocation either can't fail or will lead to more memory\n2676:\t\t * being freed very soon. Allow memory usage go over the limit\n2677:\t\t * temporarily by force charging it.\n2678:\t\t /\n2679:\t\tpage_counter_charge(\u0026memcg-\u003ememory, nr_pages);\n2680:\t\tif (do_memsw_account())\n2681:\t\t\tpage_counter_charge(\u0026memcg-\u003ememsw, nr_pages);\n2682:\t\n2683:\tout:\n2684:\t\t/\n2685:\t\t * Don't forget to raise a MEMCG_MAX event for forced or rejected\n2686:\t\t * requests.\n2687:\t\t /\n2688:\t\tif (!raised_max_event)\n2689:\t\t\t__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);\n2690:\t\n2691:\t\treturn ret;\n2692:\t\n2693:\tcheck_high:\n2694:\t\tif (!nr_charged)\n2695:\t\t\treturn ret;\n2696:\t\t/\n2697:\t\t * If the hierarchy is above the normal consumption range, schedule\n2698:\t\t * reclaim on returning to userland. We can perform reclaim here\n2699:\t\t * if __GFP_RECLAIM but let's always punt for simplicity and so that\n2700:\t\t * GFP_KERNEL can consistently be used during reclaim. @memcg is\n2701:\t\t * not recorded as it most likely matches current's and won't\n2702:\t\t * change in the meantime. As high limit is checked again before\n2703:\t\t * reclaim, the cost of mismatch is negligible.\n2704:\t\t /\n2705:\t\tdo {\n2706:\t\t\tbool mem_high, swap_high;\n2707:\t\n2708:\t\t\tmem_high = page_counter_read(\u0026memcg-\u003ememory) \u003e\n2709:\t\t\t\tREAD_ONCE(memcg-\u003ememory.high);\n2710:\t\t\tswap_high = page_counter_read(\u0026memcg-\u003eswap) \u003e\n2711:\t\t\t\tREAD_ONCE(memcg-\u003eswap.high);\n2712:\t\n2713:\t\t\t/ Don't bother a random interrupted task */\n2714:\t\t\tif (!in_task()) {\n2715:\t\t\t\tif (mem_high) {\n2716:\t\t\t\t\tif (allow_spinning)\n2717:\t\t\t\t\t\tschedule_work(\u0026memcg-\u003ehigh_work);\n2718:\t\t\t\t\telse\n2719:\t\t\t\t\t\tirq_work_queue(\u0026memcg-\u003ehigh_irq_work);\n" }
61/3	2026/09/18 15:44	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 18653 output: 34 thoughts: 1355 Thoughts: Analyzing Potential Uninitialized Memory Issues Okay, so I'm tracing through this code, and my focus is on potential memory safety issues, particularly uninitialized memory reads. I see that `check_high` is reached after a call to `page_counter_try_charge` returns `true` from line 2572. That function also sets `nr_charged` if not `NULL`. Now, I'm thinking, what if `page_counter_try_charge` actually fails? I need to understand that `failed:` path in `page_counter_try_charge`. Let me look at `mm/page_counter.c` to be sure: ```c bool page_counter_try_charge(struct page_counter counter, unsigned long nr_pages, struct page_counter *fail, bool may_batch, unsigned long nr_charged) { ... retry: ... for (c = counter; c; c = c->parent) { ... new = atomic_long_add_return(charge, &c->usage); if (new > c->max) { atomic_long_sub(charge, &c->usage); ... fail = c; goto failed; } ... } ... failed: for (c = counter; c != fail; c = c->parent) page_counter_cancel(c, charge); if (charge > nr_pages) { charge = nr_pages; goto retry; } return false; } ``` Okay, the logic is clear. If `charge > nr_pages` it'll cancel and retry with `nr_pages`. If it fails a second time, it returns `false`. If it succeeds through either consuming stock or adding to the counter, it returns `true` and potentially sets `nr_charged`. Now I need to start systematically looking at the potential issues around uninitialized memory, keeping in mind KMSAN's detection criteria. I'm focusing on areas where data is potentially sent to userspace, or where branching logic depends on variables that could be uninitialized, or finally, allocation and use of structures where uninitialized fields are a risk. I need to make sure I'm checking the KMSAN and KASAN results. Right, let's start with a file-by-file inspection of the diff. First up, `include/linux/page_counter.h`. I'm looking at `struct page_counter_stock_pcp`. ```c struct page_counter_stock_pcp { local_trylock_t lock; u8 nr_pages[NR_PAGE_COUNTER_STOCK]; struct page_counter cached[NR_PAGE_COUNTER_STOCK]; struct page_counter_stock_pcp __percpu *base; struct work_struct work; unsigned long flags; u8 drain_idx; }; ``` Where is this allocated and initialized? I'm searching for its allocation. Okay, it's allocated as a `DEFINE_PER_CPU_ALIGNED` static variable in `mm/memcontrol.c`: ```c static DEFINE_PER_CPU_ALIGNED(struct page_counter_stock_pcp, memory_stock) = { .lock = INIT_LOCAL_TRYLOCK(lock), .base = &memory_stock, }; #ifdef CONFIG_MEMCG_V1 static DEFINE_PER_CPU_ALIGNED(struct page_counter_stock_pcp, memsw_stock) = { .lock = INIT_LOCAL_TRYLOCK(lock), .base = &memsw_stock, }; #endif ``` Being `static` variables, those are zero-initialized in the BSS section. Good. It's initialized later as well, in `mem_cgroup_init()`: ```c for_each_possible_cpu(cpu) { INIT_WORK(&per_cpu_ptr(&memory_stock, cpu)->work, drain_local_stock); #ifdef CONFIG_MEMCG_V1 INIT_WORK(&per_cpu_ptr(&memsw_stock, cpu)->work, drain_local_stock); #endif INIT_WORK(&per_cpu_ptr(&obj_stock, cpu)->work, drain_local_obj_stock); } ``` The call to `INIT_WORK` takes care of the
62/3	2026/09/18 15:44	tool	grepper	0m Args: { "Expression": "mem_cgroup_css_alloc", "PathPrefix": "mm/memcontrol.c" } Results: { "Output": "mm/memcontrol.c=4122=static struct cgroup_subsys_state * __ref\nmm/memcontrol.c:4123:mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)\nmm/memcontrol.c-4124-{\n--\nmm/memcontrol.c=5078=struct cgroup_subsys memory_cgrp_subsys = {\nmm/memcontrol.c:5079:\t.css_alloc = mem_cgroup_css_alloc,\nmm/memcontrol.c-5080-\t.css_online = mem_cgroup_css_online,\n" }
63/3	2026/09/18 15:44	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 21238 output: 35 thoughts: 14 Thoughts: Okay, let's dive into this code. Diving into `mem_cgroup_css_alloc` Right, so I'm looking at `mem_cgroup_css_alloc`. Immediately, I'm thinking about the fundamental role this function plays: it's the gatekeeper, the point where we allocate the memory control group's css (control group subsystem) data. My expert eye is already scanning for key aspects. I'm going to pay close attention to the allocation strategy, any initialization steps, and, of course, how it interacts with the broader cgroup infrastructure. What's the error handling like? Are there any potential race conditions I should be mindful of? How efficient is this allocation in relation to what the system may be currently doing? Let's get to it.
64/3	2026/09/18 15:45	tool	read-file	0m Args: { "File": "mm/memcontrol.c", "FirstLine": 4122, "LineCount": 40 } Results: { "Contents": "4122:\tstatic struct cgroup_subsys_state * __ref\n4123:\tmem_cgroup_css_alloc(struct cgroup_subsys_state parent_css)\n4124:\t{\n4125:\t\tstruct mem_cgroup parent = mem_cgroup_from_css(parent_css);\n4126:\t\tstruct mem_cgroup memcg, old_memcg;\n4127:\t\tbool memcg_on_dfl = cgroup_subsys_on_dfl(memory_cgrp_subsys);\n4128:\t\n4129:\t\told_memcg = set_active_memcg(parent);\n4130:\t\tmemcg = mem_cgroup_alloc(parent);\n4131:\t\tset_active_memcg(old_memcg);\n4132:\t\tif (IS_ERR(memcg))\n4133:\t\t\treturn ERR_CAST(memcg);\n4134:\t\n4135:\t\tpage_counter_set_high(\u0026memcg-\u003ememory, PAGE_COUNTER_MAX);\n4136:\t#ifdef CONFIG_ZSWAP\n4137:\t\tmemcg-\u003ezswap_max = PAGE_COUNTER_MAX;\n4138:\t\tWRITE_ONCE(memcg-\u003ezswap_writeback, true);\n4139:\t#endif\n4140:\t\tpage_counter_set_high(\u0026memcg-\u003eswap, PAGE_COUNTER_MAX);\n4141:\t\tif (parent) {\n4142:\t\t\tpage_counter_init(\u0026memcg-\u003ememory, \u0026parent-\u003ememory, memcg_on_dfl);\n4143:\t\t\tmemcg-\u003ememory.stock = \u0026memory_stock;\n4144:\t\t\tmemcg-\u003ememory.stock_css = \u0026memcg-\u003ecss;\n4145:\t\t\tpage_counter_init(\u0026memcg-\u003eswap, \u0026parent-\u003eswap, false);\n4146:\t#ifdef CONFIG_MEMCG_V1\n4147:\t\t\tif (!memcg_on_dfl) {\n4148:\t\t\t\tmemcg-\u003ememsw.stock = \u0026memsw_stock;\n4149:\t\t\t\tmemcg-\u003ememsw.stock_css = \u0026memcg-\u003ecss;\n4150:\t\t\t}\n4151:\t\t\tWRITE_ONCE(memcg-\u003eswappiness, mem_cgroup_swappiness(parent));\n4152:\t\t\tmemcg-\u003ememory.track_failcnt = !memcg_on_dfl;\n4153:\t\t\tmemcg-\u003ememsw.track_failcnt = !memcg_on_dfl;\n4154:\t\t\tWRITE_ONCE(memcg-\u003eoom_kill_disable, READ_ONCE(parent-\u003eoom_kill_disable));\n4155:\t\t\tpage_counter_init(\u0026memcg-\u003ekmem, \u0026parent-\u003ekmem, false);\n4156:\t\t\tpage_counter_init(\u0026memcg-\u003etcpmem, \u0026parent-\u003etcpmem, false);\n4157:\t\t\tmemcg-\u003etcpmem.track_failcnt = !memcg_on_dfl;\n4158:\t#endif\n4159:\t\t} else {\n4160:\t\t\tinit_memcg_stats();\n4161:\t\t\tinit_memcg_events();\n" }
65/3	2026/09/18 15:45	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 22278 output: 35 thoughts: 43 Thoughts: Root Memcg Initialization Exploration Alright, let's dive into this memcg initialization process. I need to refresh my understanding of what happens when we're dealing with the root memcg, where `parent` is `NULL`. I know the core mechanics of memory control groups, but it's always good to revisit the foundational setup, especially for the top-level control group. Let me quickly zero in on the relevant code. Specifically, I'm going to scan lines 4160 through 4200. This section should cover the edge case of root memcg creation, and I need to solidify my knowledge of how the system bootstraps the very first control group. Knowing this is critical, as it underpins all subsequent memcg operations. I expect this will be a quick refresher, but every detail matters, so I'll give it my full attention.
66/3	2026/09/18 15:45	tool	read-file	0m Args: { "File": "mm/memcontrol.c", "FirstLine": 4160, "LineCount": 40 } Results: { "Contents": "4160:\t\t\tinit_memcg_stats();\n4161:\t\t\tinit_memcg_events();\n4162:\t\t\tpage_counter_init(\u0026memcg-\u003ememory, NULL, true);\n4163:\t\t\tpage_counter_init(\u0026memcg-\u003eswap, NULL, false);\n4164:\t#ifdef CONFIG_MEMCG_V1\n4165:\t\t\tpage_counter_init(\u0026memcg-\u003ekmem, NULL, false);\n4166:\t\t\tpage_counter_init(\u0026memcg-\u003etcpmem, NULL, false);\n4167:\t#endif\n4168:\t\t\troot_mem_cgroup = memcg;\n4169:\t\t\treturn \u0026memcg-\u003ecss;\n4170:\t\t}\n4171:\t\n4172:\t\tif (memcg_on_dfl \u0026\u0026 !cgroup_memory_nosocket)\n4173:\t\t\tstatic_branch_inc(\u0026memcg_sockets_enabled_key);\n4174:\t\n4175:\t\tif (!cgroup_memory_nobpf)\n4176:\t\t\tstatic_branch_inc(\u0026memcg_bpf_enabled_key);\n4177:\t\n4178:\t\treturn \u0026memcg-\u003ecss;\n4179:\t}\n4180:\t\n4181:\tstatic int mem_cgroup_css_online(struct cgroup_subsys_state css)\n4182:\t{\n4183:\t\tstruct mem_cgroup memcg = mem_cgroup_from_css(css);\n4184:\t\tstruct obj_cgroup objcg;\n4185:\t\tint nid;\n4186:\t\n4187:\t\tmemcg_online_kmem(memcg);\n4188:\t\n4189:\t\t/\n4190:\t\t * A memcg must be visible for expand_shrinker_info()\n4191:\t\t * by the time the maps are allocated. So, we allocate maps\n4192:\t\t * here, when mem_cgroup_iter() can't skip it.\n4193:\t\t */\n4194:\t\tif (alloc_shrinker_info(memcg))\n4195:\t\t\tgoto offline_kmem;\n4196:\t\n4197:\t\tfor_each_node(nid) {\n4198:\t\t\tobjcg = obj_cgroup_alloc();\n4199:\t\t\tif (!objcg)\n" }
67/3	2026/09/18 15:45	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 23162 output: 32 thoughts: 166 Thoughts: My Analysis of Root Memcg Memory Accounting Okay, so I'm digging into how memory is managed, specifically focusing on the root memcg. The key line that catches my eye is `page_counter_init(&memcg->memory, NULL, true)`. This sets up the memory counter for the root memcg, and importantly, it initializes `counter->stock` and `counter->stock_css` to `NULL`. The implications are clear: the root memcg doesn't actually use the stock caching mechanism. It seems to be bypassed entirely. This is confirmed later, if `counter->stock` is NULL, stock charging will be skipped. This is critical because the code seems to indicate that the stock charging is skipped if `counter->stock` is NULL. I have to verify this assumption with the check in `page_counter_consume_stock` function. And also in `page_counter_refill_stock`. To fully understand this behavior, I need to understand the allocation process, and it looks like a good place to start is with `mem_cgroup_alloc`. I will need to verify that allocated memory is zeroed.
68/3	2026/09/18 15:45	tool	grepper	0m Args: { "Expression": "mem_cgroup_alloc", "PathPrefix": "mm/memcontrol.c" } Results: { "Output": "mm/memcontrol.c=4044=static void mem_cgroup_free(struct mem_cgroup memcg)\n--\nmm/memcontrol.c-4050-\nmm/memcontrol.c:4051:static struct mem_cgroup mem_cgroup_alloc(struct mem_cgroup parent)\nmm/memcontrol.c-4052-{\n--\nmm/memcontrol.c=4123=mem_cgroup_css_alloc(struct cgroup_subsys_state parent_css)\n--\nmm/memcontrol.c-4129-\told_memcg = set_active_memcg(parent);\nmm/memcontrol.c:4130:\tmemcg = mem_cgroup_alloc(parent);\nmm/memcontrol.c-4131-\tset_active_memcg(old_memcg);\n" }
69/3	2026/09/18 15:45	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 23831 output: 35 thoughts: 32 Thoughts: Here's a summary of my thought process, as if I were the one thinking it: Diving into Memory Control (mem_cgroup_alloc) Alright, time to dig into the memory cgroup allocation code. I'm focusing specifically on lines 4051-4080 within `mm/memcontrol.c`. I need to understand how this function is handling memory allocation at a granular level within the cgroup hierarchy. What are the key checks? What are the allocation strategies being used? Are there any obvious bottlenecks or potential areas for improvement? I want to see how the system is managing and enforcing those memory limits I’ve set. This is where the rubber meets the road. I'm looking for the precise mechanics, the subtle interactions. I'm expecting this to be fairly straightforward, but with `memcontrol` there are usually surprises in the details! Time to see what we've got.
70/3	2026/09/18 15:45	tool	read-file	0m Args: { "File": "mm/memcontrol.c", "FirstLine": 4051, "LineCount": 30 } Results: { "Contents": "4051:\tstatic struct mem_cgroup mem_cgroup_alloc(struct mem_cgroup parent)\n4052:\t{\n4053:\t\tstruct memcg_vmstats_percpu statc;\n4054:\t\tstruct memcg_vmstats_percpu __percpu pstatc_pcpu;\n4055:\t\tstruct mem_cgroup *memcg;\n4056:\t\tint node, cpu;\n4057:\t\tint __maybe_unused i;\n4058:\t\tlong error;\n4059:\t\n4060:\t\tmemcg = kmem_cache_zalloc(memcg_cachep, GFP_KERNEL);\n4061:\t\tif (!memcg)\n4062:\t\t\treturn ERR_PTR(-ENOMEM);\n4063:\t\n4064:\t\terror = xa_alloc(\u0026mem_cgroup_private_ids, \u0026memcg-\u003eprivate_id, NULL,\n4065:\t\t\t\t XA_LIMIT(1, MEM_CGROUP_ID_MAX), GFP_KERNEL);\n4066:\t\tif (error)\n4067:\t\t\tgoto fail;\n4068:\t\terror = -ENOMEM;\n4069:\t\n4070:\t\tmemcg-\u003evmstats = kzalloc_obj(struct memcg_vmstats, GFP_KERNEL_ACCOUNT);\n4071:\t\tif (!memcg-\u003evmstats)\n4072:\t\t\tgoto fail;\n4073:\t\n4074:\t\tmemcg-\u003evmstats_percpu = alloc_percpu_gfp(struct memcg_vmstats_percpu,\n4075:\t\t\t\t\t\t\t GFP_KERNEL_ACCOUNT);\n4076:\t\tif (!memcg-\u003evmstats_percpu)\n4077:\t\t\tgoto fail;\n4078:\t\n4079:\t\tif (!memcg1_alloc_events(memcg))\n4080:\t\t\tgoto fail;\n" }
71/3	2026/09/18 15:45	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 24589 output: 19 thoughts: 64 Thoughts: Investigating the Allocation Path Okay, so I'm seeing `kmem_cache_zalloc` being employed here. My immediate next step, as always, is to trace back the usage, understand the context of this allocation. I'm going to jump into `dmem.c` and `hugetlb_cgroup.c` first; those are the usual suspects where I've seen `page_counter_init` being called in similar scenarios. Beyond that, I need a comprehensive view. Time for a full codebase grep for `page_counter_init`. That should reveal all the relevant call sites and give me a complete picture of how this initialization is being used, where the page counters are being set up, and, ultimately, how this allocation relates to the overall memory management scheme.
72/3	2026/09/18 15:45	tool	grepper	0m Args: { "Expression": "page_counter_init" } Results: { "Output": "include/linux/page_counter.h=32=struct page_counter {\n--\ninclude/linux/page_counter.h-78- /\ninclude/linux/page_counter.h:79:static inline void page_counter_init(struct page_counter counter,\ninclude/linux/page_counter.h-80-\t\t\t\t struct page_counter parent,\n--\nkernel/cgroup/dmem.c=408=alloc_pool_single(struct dmemcg_state dmemcs, struct dmem_cgroup_region region,\n--\nkernel/cgroup/dmem.c-428-\nkernel/cgroup/dmem.c:429:\tpage_counter_init(\u0026pool-\u003ecnt,\nkernel/cgroup/dmem.c-430-\t\t\t ppool ? \u0026ppool-\u003ecnt : NULL, true);\n--\nmm/hugetlb_cgroup.c=91=static void hugetlb_cgroup_init(struct hugetlb_cgroup h_cgroup,\n--\nmm/hugetlb_cgroup.c-110-\nmm/hugetlb_cgroup.c:111:\t\tpage_counter_init(fault, fault_parent, false);\nmm/hugetlb_cgroup.c:112:\t\tpage_counter_init(rsvd, rsvd_parent, false);\nmm/hugetlb_cgroup.c-113-\n--\nmm/memcontrol.c=4123=mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)\n--\nmm/memcontrol.c-4141-\tif (parent) {\nmm/memcontrol.c:4142:\t\tpage_counter_init(\u0026memcg-\u003ememory, \u0026parent-\u003ememory, memcg_on_dfl);\nmm/memcontrol.c-4143-\t\tmemcg-\u003ememory.stock = \u0026memory_stock;\nmm/memcontrol.c-4144-\t\tmemcg-\u003ememory.stock_css = \u0026memcg-\u003ecss;\nmm/memcontrol.c:4145:\t\tpage_counter_init(\u0026memcg-\u003eswap, \u0026parent-\u003eswap, false);\nmm/memcontrol.c-4146-#ifdef CONFIG_MEMCG_V1\n--\nmm/memcontrol.c-4154-\t\tWRITE_ONCE(memcg-\u003eoom_kill_disable, READ_ONCE(parent-\u003eoom_kill_disable));\nmm/memcontrol.c:4155:\t\tpage_counter_init(\u0026memcg-\u003ekmem, \u0026parent-\u003ekmem, false);\nmm/memcontrol.c:4156:\t\tpage_counter_init(\u0026memcg-\u003etcpmem, \u0026parent-\u003etcpmem, false);\nmm/memcontrol.c-4157-\t\tmemcg-\u003etcpmem.track_failcnt = !memcg_on_dfl;\n--\nmm/memcontrol.c-4161-\t\tinit_memcg_events();\nmm/memcontrol.c:4162:\t\tpage_counter_init(\u0026memcg-\u003ememory, NULL, true);\nmm/memcontrol.c:4163:\t\tpage_counter_init(\u0026memcg-\u003eswap, NULL, false);\nmm/memcontrol.c-4164-#ifdef CONFIG_MEMCG_V1\nmm/memcontrol.c:4165:\t\tpage_counter_init(\u0026memcg-\u003ekmem, NULL, false);\nmm/memcontrol.c:4166:\t\tpage_counter_init(\u0026memcg-\u003etcpmem, NULL, false);\nmm/memcontrol.c-4167-#endif\n" }
73/3	2026/09/18 15:45	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 25730 output: 35 thoughts: 503 Thoughts: Analyzing Potential Uninitialized Memory Issues in Page Counter Implementation Okay, let's break this down systematically. I see that all `page_counter` instances are initialized cleanly through `page_counter_init`, which explicitly sets `counter->stock` and `counter->stock_css` to `NULL`. Good, that's a solid starting point. Now, let's dig into `mem_cgroup_usage` in `mm/memcontrol-v1.c`. I'm seeing a clear use of `max()` here to ensure the user-visible memory invariant, `memory <= memsw`, is maintained. Both are initialized integers, so there's no immediate red flag there. Next, the critical question: is this patch introducing any potential for leaking uninitialized data to userspace? The code indicates that `mem_cgroup_usage` returns an `unsigned long`, which gets formatted as a string or number when accessed via seq_file or cgroup files. Since it's a numeric type, the value is always initialized, and I don't see any explicit data copying that could introduce an issue. So far, so good. Now, let's examine `page_counter_stock_pcp`. This is strictly an internal, per-CPU cache structure for tracking charged page counters. It's not directly exposed to userspace, so any initialization issues here wouldn't be directly exploitable. Finally, the key area to scrutinize: I need to deeply inspect these functions for subtle, uninitialized memory issues: * `page_counter_try_charge` * `page_counter_consume_stock` * `page_counter_drain_stock` * `page_counter_refill_stock` * `page_counter_stock_flush_required` I'm going to carefully read `page_counter.c` in the vicinity of these new functions to confirm my initial hypothesis that no data is leaked. I need to make sure that these functions have correct memory management.
74/3	2026/09/18 15:46	tool	read-file	0m Args: { "File": "mm/page_counter.c", "FirstLine": 135, "LineCount": 80 } Results: { "Contents": " 135:\t\t\t}\n 136:\t\t}\n 137:\t}\n 138:\t\n 139:\t/\n 140:\t Consume the cached charge if enough nr_pages are present, otherwise return\n 141:\t * failure. Also return failure for charge requests larger than\n 142:\t * PAGE_COUNTER_STOCK_BATCH or if the local lock is already taken.\n 143:\t /\n 144:\tstatic bool page_counter_consume_stock(struct page_counter counter,\n 145:\t\t\t\t\t unsigned long nr_pages)\n 146:\t{\n 147:\t\tstruct page_counter_stock_pcp __percpu stock = counter-\u003estock;\n 148:\t\tstruct page_counter_stock_pcp pcp_stock;\n 149:\t\tu8 stock_pages;\n 150:\t\tbool ret = false;\n 151:\t\tint i;\n 152:\t\n 153:\t\tif (nr_pages \u003e PAGE_COUNTER_STOCK_BATCH \|\|\n 154:\t\t !local_trylock(\u0026stock-\u003elock))\n 155:\t\t\treturn false;\n 156:\t\n 157:\t\tpcp_stock = this_cpu_ptr(stock);\n 158:\t\tfor (i = 0; i \u003c NR_PAGE_COUNTER_STOCK; i++) {\n 159:\t\t\tif (counter != READ_ONCE(pcp_stock-\u003ecached[i]))\n 160:\t\t\t\tcontinue;\n 161:\t\n 162:\t\t\tstock_pages = READ_ONCE(pcp_stock-\u003enr_pages[i]);\n 163:\t\t\tif (stock_pages \u003e= nr_pages) {\n 164:\t\t\t\tstock_pages -= nr_pages;\n 165:\t\t\t\tWRITE_ONCE(pcp_stock-\u003enr_pages[i], stock_pages);\n 166:\t\t\t\tif (!stock_pages) {\n 167:\t\t\t\t\tcss_put(counter-\u003estock_css);\n 168:\t\t\t\t\tWRITE_ONCE(pcp_stock-\u003ecached[i], NULL);\n 169:\t\t\t\t}\n 170:\t\t\t\tret = true;\n 171:\t\t\t}\n 172:\t\t\tbreak;\n 173:\t\t}\n 174:\t\tlocal_unlock(\u0026stock-\u003elock);\n 175:\t\n 176:\t\treturn ret;\n 177:\t}\n 178:\t\n 179:\t/*\n 180:\t page_counter_try_charge - try to hierarchically charge pages using stock\n 181:\t * @counter: counter\n 182:\t * @nr_pages: number of pages requested\n 183:\t * @fail: points to the first counter to hit its limit, if any\n 184:\t * @may_batch: whether a stock miss may trigger a batch charge\n 185:\t * @nr_charged: optional; set to the hierarchy charge size on success\n 186:\t \n 187:\t Return: %true if the request was satisfied. A failed batch charge may update\n 188:\t * @fail before an exact retry succeeds.\n 189:\t /\n 190:\tbool page_counter_try_charge(struct page_counter counter,\n 191:\t\t\t\t unsigned long nr_pages, struct page_counter *fail,\n 192:\t\t\t\t bool may_batch, unsigned long nr_charged)\n 193:\t{\n 194:\t\tunsigned long charge = nr_pages;\n 195:\t\tstruct page_counter c;\n 196:\t\tbool protection = track_protection(counter);\n 197:\t\tbool track_failcnt = counter-\u003etrack_failcnt;\n 198:\t\n 199:\t\tif (counter-\u003estock \u0026\u0026 may_batch)\n 200:\t\t\tcharge = max(nr_pages, PAGE_COUNTER_STOCK_BATCH);\n 201:\t\n 202:\tretry:\n 203:\t\tif (counter-\u003estock \u0026\u0026 page_counter_consume_stock(counter, nr_pages)) {\n 204:\t\t\tif (nr_charged)\n 205:\t\t\t\tnr_charged = 0;\n 206:\t\t\treturn true;\n 207:\t\t}\n 208:\t\n 209:\t\tfor (c = counter; c; c = c-\u003eparent) {\n 210:\t\t\tlong new;\n 211:\t\t\t/\n 212:\t\t\t Charge speculatively to avoid an expensive CAS. If\n 213:\t\t\t * a bigger charge fails, it might falsely lock out a\n 214:\t\t\t * racing smaller charge and send it into reclaim\n" }
75/3	2026/09/18 15:46	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 27898 output: 35 thoughts: 23 Thoughts: Here's a summary of my thought process, as requested: Diving into `mm/page_counter.c` Alright, time to dig into this specific section. The problem, as I understand it, seems to be related to the page counter implementation, and I need a focused look at lines 215-320 of `mm/page_counter.c`. My immediate goal is to refresh my memory of the core logic within that segment. I suspect this range covers the critical operations for incrementing, decrementing, and potentially checking or adjusting page counters. I need to be sure I'm crystal clear on how these counters are used to track memory allocation and deallocation within the kernel. I'll be looking for things like mutex usage, atomic operations, and any potential race conditions that might be relevant to the issue at hand. Furthermore, I'll be paying close attention to any error handling or boundary checks within that section. This area is often a source of subtle bugs. Let's see if the code is structured in a clean way, or whether there might be some cruft in the logic.
76/3	2026/09/18 15:46	tool	read-file	0m Args: { "File": "mm/page_counter.c", "FirstLine": 215, "LineCount": 85 } Results: { "Contents": " 215:\t\t\t * early, but the error is limited to the difference\n 216:\t\t\t * between the two sizes, which is less than 2M/4M in\n 217:\t\t\t * case of a THP locking out a regular page charge.\n 218:\t\t\t \n 219:\t\t\t The atomic_long_add_return() implies a full memory\n 220:\t\t\t * barrier between incrementing the count and reading\n 221:\t\t\t * the limit. When racing with page_counter_set_max(),\n 222:\t\t\t * we either see the new limit or the setter sees the\n 223:\t\t\t * counter has changed and retries.\n 224:\t\t\t /\n 225:\t\t\tnew = atomic_long_add_return(charge, \u0026c-\u003eusage);\n 226:\t\t\tif (new \u003e c-\u003emax) {\n 227:\t\t\t\tatomic_long_sub(charge, \u0026c-\u003eusage);\n 228:\t\t\t\t/\n 229:\t\t\t\t * This is racy, but we can live with some\n 230:\t\t\t\t * inaccuracy in the failcnt which is only used\n 231:\t\t\t\t * to report stats.\n 232:\t\t\t\t /\n 233:\t\t\t\tif (track_failcnt)\n 234:\t\t\t\t\tdata_race(c-\u003efailcnt++);\n 235:\t\t\t\tfail = c;\n 236:\t\t\t\tgoto failed;\n 237:\t\t\t}\n 238:\t\t\tif (protection)\n 239:\t\t\t\tpropagate_protected_usage(c, new);\n 240:\t\n 241:\t\t\t/* see comment on page_counter_charge /\n 242:\t\t\tif (new \u003e READ_ONCE(c-\u003elocal_watermark)) {\n 243:\t\t\t\tWRITE_ONCE(c-\u003elocal_watermark, new);\n 244:\t\t\t\tif (new \u003e READ_ONCE(c-\u003ewatermark))\n 245:\t\t\t\t\tWRITE_ONCE(c-\u003ewatermark, new);\n 246:\t\t\t}\n 247:\t\t}\n 248:\t\tif (charge \u003e nr_pages)\n 249:\t\t\tpage_counter_refill_stock(counter, charge - nr_pages);\n 250:\t\tif (nr_charged)\n 251:\t\t\tnr_charged = charge;\n 252:\t\treturn true;\n 253:\t\n 254:\tfailed:\n 255:\t\tfor (c = counter; c != fail; c = c-\u003eparent)\n 256:\t\t\tpage_counter_cancel(c, charge);\n 257:\t\n 258:\t\tif (charge \u003e nr_pages) {\n 259:\t\t\tcharge = nr_pages;\n 260:\t\t\tgoto retry;\n 261:\t\t}\n 262:\t\n 263:\t\treturn false;\n 264:\t}\n 265:\t\n 266:\tstatic void page_counter_drain_stock(struct page_counter_stock_pcp stock,\n 267:\t\t\t\t\t int i)\n 268:\t{\n 269:\t\tstruct page_counter counter = READ_ONCE(stock-\u003ecached[i]);\n 270:\t\tu8 nr_pages;\n 271:\t\n 272:\t\tif (!counter)\n 273:\t\t\treturn;\n 274:\t\n 275:\t\tnr_pages = READ_ONCE(stock-\u003enr_pages[i]);\n 276:\t\tif (nr_pages) {\n 277:\t\t\tpage_counter_uncharge(counter, nr_pages);\n 278:\t\t\tWRITE_ONCE(stock-\u003enr_pages[i], 0);\n 279:\t\t}\n 280:\t\tcss_put(counter-\u003estock_css);\n 281:\t\tWRITE_ONCE(stock-\u003ecached[i], NULL);\n 282:\t}\n 283:\t\n 284:\tvoid page_counter_drain_stock_fully(struct page_counter_stock_pcp stock)\n 285:\t{\n 286:\t\tint i;\n 287:\t\n 288:\t\tfor (i = 0; i \u003c NR_PAGE_COUNTER_STOCK; i++)\n 289:\t\t\tpage_counter_drain_stock(stock, i);\n 290:\t}\n 291:\t\n 292:\tbool page_counter_stock_flush_required(struct page_counter_stock_pcp stock,\n 293:\t\t\t\t\t struct cgroup_subsys_state root_css)\n 294:\t{\n 295:\t\tstruct cgroup_subsys_state css;\n 296:\t\tstruct page_counter counter;\n 297:\t\tbool flush = false;\n 298:\t\tint i;\n 299:\t\n" }
77/3	2026/09/18 15:46	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 29429 output: 35 thoughts: 27 Thoughts: Here's a summary of my thought process, as if I were the one thinking it: Diving Deeper into `page_counter_refill_stock` Okay, so we've addressed that initial point. Now, let's zoom out a bit. We've tackled the core issue, but I need to make sure we haven't missed any edge cases or related functionalities. To ensure complete coverage and prevent unexpected behavior, I'm going to shift my focus to the broader context within the `page_counter.c` file. Specifically, I'm going to examine the implementation of `page_counter_refill_stock`. This will give me a more holistic perspective and help me identify any potential dependencies, side effects, or related code segments that might be relevant. It's time to analyze the complete surrounding code now, to confirm no issues are overlooked.
78/3	2026/09/18 15:46	tool	read-file	0m Args: { "File": "mm/page_counter.c", "FirstLine": 300, "LineCount": 85 } Results: { "Contents": " 300:\t\trcu_read_lock();\n 301:\t\tfor (i = 0; i \u003c NR_PAGE_COUNTER_STOCK; i++) {\n 302:\t\t\tcounter = READ_ONCE(stock-\u003ecached[i]);\n 303:\t\t\tif (!counter)\n 304:\t\t\t\tcontinue;\n 305:\t\t\tcss = READ_ONCE(counter-\u003estock_css);\n 306:\t\n 307:\t\t\tif (READ_ONCE(stock-\u003enr_pages[i]) \u0026\u0026\n 308:\t\t\t cgroup_is_descendant(css-\u003ecgroup, root_css-\u003ecgroup)) {\n 309:\t\t\t\tflush = true;\n 310:\t\t\t\tbreak;\n 311:\t\t\t}\n 312:\t\t}\n 313:\t\trcu_read_unlock();\n 314:\t\treturn flush;\n 315:\t}\n 316:\t\n 317:\t/*\n 318:\t page_counter_refill_stock - return pages to a counter's stock\n 319:\t * @counter: counter to return pages to\n 320:\t * @nr_pages: number of pages to return\n 321:\t \n 322:\t If the stock cannot accept the pages, uncharge them from the hierarchy.\n 323:\t /\n 324:\tvoid page_counter_refill_stock(struct page_counter counter,\n 325:\t\t\t\t unsigned long nr_pages)\n 326:\t{\n 327:\t\tstruct page_counter_stock_pcp __percpu stock = counter-\u003estock;\n 328:\t\tstruct page_counter_stock_pcp pcp_stock;\n 329:\t\tunsigned int stock_pages;\n 330:\t\tint empty_slot = -1;\n 331:\t\tint i;\n 332:\t\n 333:\t\t/\n 334:\t\t nr_pages[] is a u8 and a slot is capped at PAGE_COUNTER_STOCK_HIGH.\n 335:\t\t * Raising PAGE_COUNTER_STOCK_BATCH beyond 127 would need careful\n 336:\t\t * handling of nr_pages[] in struct page_counter_stock_pcp.\n 337:\t\t /\n 338:\t\tBUILD_BUG_ON(PAGE_COUNTER_STOCK_BATCH \u003e S8_MAX);\n 339:\t\tBUILD_BUG_ON(PAGE_COUNTER_STOCK_HIGH \u003e U8_MAX);\n 340:\t\n 341:\t\tif (!stock \|\| nr_pages \u003e PAGE_COUNTER_STOCK_BATCH \|\|\n 342:\t\t !local_trylock(\u0026stock-\u003elock)) {\n 343:\t\t\t/\n 344:\t\t\t * For a larger-than-batch refill or an unlikely failure to lock\n 345:\t\t\t * the per-CPU stock, uncharge the hierarchy directly.\n 346:\t\t\t /\n 347:\t\t\tpage_counter_uncharge(counter, nr_pages);\n 348:\t\t\treturn;\n 349:\t\t}\n 350:\t\n 351:\t\tpcp_stock = this_cpu_ptr(stock);\n 352:\t\tfor (i = 0; i \u003c NR_PAGE_COUNTER_STOCK; i++) {\n 353:\t\t\tstruct page_counter cached = READ_ONCE(pcp_stock-\u003ecached[i]);\n 354:\t\n 355:\t\t\tif (!cached \u0026\u0026 empty_slot == -1)\n 356:\t\t\t\tempty_slot = i;\n 357:\t\t\tif (counter != cached)\n 358:\t\t\t\tcontinue;\n 359:\t\n 360:\t\t\tstock_pages = READ_ONCE(pcp_stock-\u003enr_pages[i]) + nr_pages;\n 361:\t\t\tif (stock_pages \u003e PAGE_COUNTER_STOCK_HIGH) {\n 362:\t\t\t\tpage_counter_uncharge(counter,\n 363:\t\t\t\t\t\t stock_pages - PAGE_COUNTER_STOCK_LOW);\n 364:\t\t\t\tstock_pages = PAGE_COUNTER_STOCK_LOW;\n 365:\t\t\t}\n 366:\t\t\tWRITE_ONCE(pcp_stock-\u003enr_pages[i], stock_pages);\n 367:\t\t\tlocal_unlock(\u0026stock-\u003elock);\n 368:\t\t\treturn;\n 369:\t\t}\n 370:\t\n 371:\t\ti = empty_slot;\n 372:\t\tif (i == -1) {\n 373:\t\t\ti = pcp_stock-\u003edrain_idx++;\n 374:\t\t\tif (pcp_stock-\u003edrain_idx == NR_PAGE_COUNTER_STOCK)\n 375:\t\t\t\tpcp_stock-\u003edrain_idx = 0;\n 376:\t\t\tpage_counter_drain_stock(pcp_stock, i);\n 377:\t\t}\n 378:\t\tcss_get(counter-\u003estock_css);\n 379:\t\tWRITE_ONCE(pcp_stock-\u003ecached[i], counter);\n 380:\t\tWRITE_ONCE(pcp_stock-\u003enr_pages[i], nr_pages);\n 381:\t\tlocal_unlock(\u0026stock-\u003elock);\n 382:\t}\n 383:\t\n 384:\t/**\n" }
79/3	2026/09/18 15:46	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 31019 output: 425 thoughts: 2883 Thoughts: Analysis of Memory Accounting and KMSAN Implications Alright, let's break down this code. My focus here is to ensure there are no potential uninitialized memory reads that could trigger a KMSAN report. I've been examining the changes related to memory accounting within cgroups, specifically focusing on the modifications within `dmem.c`, `hugetlb_cgroup.c`, and `memcontrol-v1.c`. My initial review indicates that these changes mostly involve the introduction of new arguments, specifically `false` and `NULL`, to the `page_counter_try_charge` function. The key here is to determine if any of these changes can lead to uninitialized memory being read. The added arguments themselves don't appear problematic as they are constant or null pointers. My suspicion lies in where these new arguments were inserted into existing and complex control flows. My investigation centered around tracing the use of the `nr_charged` variable, particularly within `try_charge_memcg`. I meticulously traced the different execution paths within `page_counter_try_charge` to ensure that `nr_charged` is always initialized before it's used. Based on the logic within `page_counter_try_charge` and how the function handles the stock, this appears to be correct. I have also reviewed the initialization of `struct page_counter_stock_pcp`. This struct utilizes `DEFINE_PER_CPU_ALIGNED`, and my understanding of C dictates that any fields not explicitly initialized in this type of initialization will be zero-initialized. I made sure to double check the struct definition, ensuring that the fields such as `nr_pages`, `cached`, `flags`, and `drain_idx` are guaranteed to be initialized to zero. Also, `work` is correctly initialized in `INIT_WORK`. I then analyzed the code that uses these structs and their fields, specifically, the `drain_local_stock` work handler. I verified that the `base` pointer is initialized and that the fields within `page_counter_stock_pcp` are accessed in a safe manner. `container_of` used to retrieve the base of the work struct is correct, and I confirmed that there are no obvious data races or uninitialized memory reads. Moving forward, the primary concern now focuses on ensuring that data isn't exposed to user space. I made sure to cross-reference this and have verified that the patch does not leak any structures or buffers to user space. This is critical as uninitialized data in structures sent to user space would be a KMSAN report. I then went on to map this against the KMSAN conditions. There are no kernel structures sent to user space where uninitialized fields might be exposed. There is no conditional logic that depends on potentially uninitialized variables or struct fields, no allocation or initialization of complex data structures where uninitialized fields could be read later in reachable code paths, and no bounds checks, lengths, or logic in a way that allows surrounding code to access uninitialized bytes of existing buffers. Given this, I have concluded that the changes are safe in the context of KMSAN. My analysis did not reveal any uninitialized memory accesses or other issues that would trigger KMSAN. Any bugs introduced by the changes would likely be related to locking issues, reference counting, counter overflows, or memory leaks; these concerns will likely be flagged by KASAN, LOCKDEP, refcount debuggers, or standard kernel warnings. We can proceed with `NeedsKMSAN=false` and `set-results`.
80/3	2026/09/18 15:47	tool	set-results	0m Args: { "KMSANReasoning": "The patch series refactors the memcg charge stock caching mechanism into a generic per-CPU page counter stock mechanism (moving stock handling from `memcontrol.c` into `page_counter.c` and `page_counter.h`).\n\nAnalysis for KMSAN applicability:\n1. Data structures sent to user space: None. The patch affects internal page counter and stock cache management; no buffers or structures are copied to user space.\n2. Uninitialized variables / conditional branching: In `try_charge_memcg`, the newly introduced stack variable `unsigned long nr_charged;` is passed by pointer to `page_counter_try_charge()`. On every code path where `page_counter_try_charge()` returns `true`, `nr_charged` is explicitly set to either 0 or `charge` before returning. It is only read in `check_high`, which is reached exclusively on success. Similarly, `fail` is always set upon failure when limit check fails.\n3. Structure initialization: `struct page_counter_stock_pcp` instances (`memory_stock`, `memsw_stock`) are static per-CPU variables with static initializers and zero-initialized fields; work items are initialized with `INIT_WORK()`. The new fields in `struct page_counter` (`stock`, `stock_css`) are explicitly set to `NULL` in `page_counter_init()`.\n4. Bounds checks / buffer lengths: No data buffers are manipulated or exposed.\n\nPotential bugs introduced by this refactoring include refcounting bugs (`css_put`/`css_get`), locking/concurrency issues, counter accounting discrepancies, and use-after-free conditions, which are detected by KASAN, LOCKDEP, and standard kernel debugging facilities. There is no risk of uninitialized memory usage or information disclosure to userspace, so a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false } Results: { "KMSANReasoning": "The patch series refactors the memcg charge stock caching mechanism into a generic per-CPU page counter stock mechanism (moving stock handling from `memcontrol.c` into `page_counter.c` and `page_counter.h`).\n\nAnalysis for KMSAN applicability:\n1. Data structures sent to user space: None. The patch affects internal page counter and stock cache management; no buffers or structures are copied to user space.\n2. Uninitialized variables / conditional branching: In `try_charge_memcg`, the newly introduced stack variable `unsigned long nr_charged;` is passed by pointer to `page_counter_try_charge()`. On every code path where `page_counter_try_charge()` returns `true`, `nr_charged` is explicitly set to either 0 or `charge` before returning. It is only read in `check_high`, which is reached exclusively on success. Similarly, `fail` is always set upon failure when limit check fails.\n3. Structure initialization: `struct page_counter_stock_pcp` instances (`memory_stock`, `memsw_stock`) are static per-CPU variables with static initializers and zero-initialized fields; work items are initialized with `INIT_WORK()`. The new fields in `struct page_counter` (`stock`, `stock_css`) are explicitly set to `NULL` in `page_counter_init()`.\n4. Bounds checks / buffer lengths: No data buffers are manipulated or exposed.\n\nPotential bugs introduced by this refactoring include refcounting bugs (`css_put`/`css_get`), locking/concurrency issues, counter accounting discrepancies, and use-after-free conditions, which are detected by KASAN, LOCKDEP, and standard kernel debugging facilities. There is no risk of uninitialized memory usage or information disclosure to userspace, so a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false }

LLM Calls Summary:
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Tool Calls Summary:
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