AI Trajectory

Trajectory: (Expand/Collapse All)
Seq	Timestamp	Type	Name	Duration
0/0	2026/11/03 19:55	flow	patch-triage	25m Args: null Results: { "EnableConfigs": [ "MEMCG", "CGROUPS" ], "FocusSymbols": [ "memcg_shrinker_unit_alloc", "set_shrinker_bit", "reparent_shrinker_deferred", "alloc_shrinker_info", "free_shrinker_info", "shrink_slab", "__list_lru_init", "memcg_list_lru_alloc" ], "KMSANReasoning": "The patch refactors memory cgroup shrinker info management by replacing the custom RCU-managed dynamic array `shrinker_info` in `struct mem_cgroup_per_node` with an XArray (`shrinker_units`), allocating `shrinker_info_unit` structures on demand rather than eagerly sizing them.\n\nEvaluation of KMSAN vs KASAN applicability:\n1. No uninitialized memory exposure to userspace: The shrinker tracking structures are strictly internal to the kernel's memory management subsystem (page reclaim and list_lru). No structures or buffers modified by this patch are copied to userspace via `copy_to_user`, ioctl, netlink, or socket interfaces.\n2. Complete initialization of allocated structures: All `struct shrinker_info_unit` objects are allocated via `kmem_cache_alloc_node` using `gfp \| __GFP_ZERO`, ensuring that both the `nr_deferred` array and the `map` bitmap are fully zeroed before insertion into the XArray or use in reclaim logic. The per-node XArray is initialized using `xa_init_flags`. All local stack variables and control structures (`struct shrink_control`, `XA_STATE`) are fully initialized before use.\n3. Relevant bug classes: The potential failure modes of this patch are concurrency/synchronization issues (e.g. lockless iteration over XArray vs destruction, IRQ-safe locking), use-after-free, memory leaks, or NULL pointer dereferences. These are covered by KASAN, LOCKDEP, and standard kernel debugging facilities.\n\nBecause no uninitialized memory reads or information leaks are introduced or exposed, a dedicated KMSAN session is not justified.", "NeedsKMSAN": false, "Reasoning": "The patch refactors the memcg slab shrinker tracking mechanism from a flat RCU-allocated array to a lazily-allocated XArray per nodeinfo. It alters memory reclaim iteration (shrink_slab/shrink_slab_memcg), introduces a new WARN_ON_ONCE() assertion in set_shrinker_bit(), modifies deferred reclaim reparenting, and changes list_lru allocation logic. These changes affect core memory management and are fully reachable in virtualized environments via cgroup and memory pressure workloads.", "WorthFuzzing": true }
1/1	2026/11/03 19:55	action	read-patch-diff	0m Args: null Results: { "PatchDiff": "commit b9a5154a739313cf76c33e4e804f9fc2493dba9b\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Tue Nov 3 19:55:47 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h\nindex 69e1bcc67c588d..ea2c0990059479 100644\n--- a/include/linux/memcontrol.h\n+++ b/include/linux/memcontrol.h\n@@ -24,6 +24,7 @@\n #include \u003clinux/page-flags.h\u003e\n #include \u003clinux/shrinker.h\u003e\n #include \u003clinux/irq_work_types.h\u003e\n+#include \u003clinux/xarray.h\u003e\n \n struct mem_cgroup;\n struct obj_cgroup;\n@@ -83,14 +84,14 @@ struct mem_cgroup_reclaim_iter {\n * per-node information in memory controller.\n /\n struct mem_cgroup_per_node {\n-\t/ Set when the memcg is created, then only read. /\n+\t/ Set when the memcg is created, then mostly read. /\n \t__cacheline_group_begin_aligned(memcg_pn_read_mostly);\n \tstruct mem_cgroup\tmemcg;\t\t/* Back pointer, we cannot /\n \t\t\t\t\t\t/ use container_of\t /\n \n \tstruct lruvec_stats_percpu __percpu\tlruvec_stats_percpu;\n \tstruct lruvec_stats\t\t\tlruvec_stats;\n-\tstruct shrinker_info __rcu\tshrinker_info;\n+\tstruct xarray\t\t\tshrinker_units;\n \tstruct obj_cgroup __rcu\t\tobjcg;\n \n \t__cacheline_group_end_aligned(memcg_pn_read_mostly);\n@@ -1719,6 +1720,8 @@ static inline u64 mem_cgroup_get_socket_pressure(const struct mem_cgroup memcg)\n \n void shrinker_unit_cache_init(void);\n int alloc_shrinker_info(struct mem_cgroup memcg);\n+int memcg_shrinker_unit_alloc(struct mem_cgroup memcg, int shrinker_id,\n+\t\t\t gfp_t gfp);\n void free_shrinker_info(struct mem_cgroup memcg);\n void set_shrinker_bit(struct mem_cgroup memcg, int nid, int shrinker_id);\n void reparent_shrinker_deferred(struct mem_cgroup memcg);\ndiff --git a/include/linux/shrinker.h b/include/linux/shrinker.h\nindex 1a00be90d93a9f..2eae68a7ff6c5d 100644\n--- a/include/linux/shrinker.h\n+++ b/include/linux/shrinker.h\n@@ -18,12 +18,6 @@ struct shrinker_info_unit {\n \tDECLARE_BITMAP(map, SHRINKER_UNIT_BITS);\n };\n \n-struct shrinker_info {\n-\tstruct rcu_head rcu;\n-\tint map_nr_max;\n-\tstruct shrinker_info_unit unit[];\n-};\n-\n /\n This struct is used to pass information from page reclaim to the shrinkers.\n * We consolidate the values for easier extension later.\ndiff --git a/mm/list_lru.c b/mm/list_lru.c\nindex d1d256822ccc73..4be22c5238f98a 100644\n--- a/mm/list_lru.c\n+++ b/mm/list_lru.c\n@@ -597,6 +597,12 @@ static int __memcg_list_lru_alloc(struct mem_cgroup memcg,\n \t\t\tparent = parent_mem_cgroup(pos);\n \t\t}\n \n+\t\tif (!css_is_dying(\u0026pos-\u003ecss) \u0026\u0026\n+\t\t memcg_shrinker_unit_alloc(pos, lru_shrinker_id(lru), gfp)) {\n+\t\t\tkfree(mlru);\n+\t\t\treturn -ENOMEM;\n+\t\t}\n+\n \t\tif (!mlru) {\n \t\t\tmlru = memcg_init_list_lru_one(lru, gfp);\n \t\t\tif (!mlru)\n@@ -666,18 +672,20 @@ int __list_lru_init(struct list_lru lru, bool memcg_aware, struct shrinker shr\n \tint i;\n \n #ifdef CONFIG_MEMCG\n+\tif (mem_cgroup_disabled() \|\| mem_cgroup_kmem_disabled())\n+\t\tmemcg_aware = false;\n+\n \t/\n \t * If the shrinker fell back to being non-memcg-aware (e.g. with\n-\t * cgroup.memory=nokmem), its id was never assigned and holds a\n-\t * stale 0. Don't let set_shrinker_bit() act on it.\n+\t * cgroup.memory=nokmem), its id is not valid. Don't let\n+\t * set_shrinker_bit() act on it, nor on a list that is not\n+\t * per-memcg: such a list gets no shrinker units.\n \t /\n-\tif (shrinker \u0026\u0026 (shrinker-\u003eflags \u0026 SHRINKER_MEMCG_AWARE))\n+\tif (shrinker \u0026\u0026 memcg_aware \u0026\u0026\n+\t (shrinker-\u003eflags \u0026 SHRINKER_MEMCG_AWARE))\n \t\tlru-\u003eshrinker_id = shrinker-\u003eid;\n \telse\n \t\tlru-\u003eshrinker_id = -1;\n-\n-\tif (mem_cgroup_disabled() \|\| mem_cgroup_kmem_disabled())\n-\t\tmemcg_aware = false;\n #endif\n \n \tlru-\u003enode = kzalloc_objs(lru-\u003enode, nr_node_ids);\ndiff --git a/mm/memcontrol.c b/mm/memcontrol.c\nindex a05d9a8baa1b6b..1a582be5a75bbb 100644\n--- a/mm/memcontrol.c\n+++ b/mm/memcontrol.c\n@@ -4219,6 +4219,7 @@ static bool alloc_mem_cgroup_per_node_info(struct mem_cgroup memcg, int node)\n \tINIT_LIST_HEAD(\u0026pn-\u003eobjcg_list);\n \n \tlruvec_init(\u0026pn-\u003elruvec);\n+\txa_init_flags(\u0026pn-\u003eshrinker_units, XA_FLAGS_LOCK_IRQ);\n \tpn-\u003ememcg = memcg;\n \n \tmemcg-\u003enodeinfo[node] = pn;\n@@ -4385,11 +4386,6 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state css)\n \n \tmemcg_online_kmem(memcg);\n \n-\t/\n-\t A memcg must be visible for expand_shrinker_info()\n-\t * by the time the maps are allocated. So, we allocate maps\n-\t * here, when mem_cgroup_iter() can't skip it.\n-\t /\n \tif (alloc_shrinker_info(memcg))\n \t\tgoto offline_kmem;\n \n@@ -5925,7 +5921,7 @@ static void __init memcg_struct_check(void)\n \tCACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup_per_node,\n \t\t\t\t memcg_pn_read_mostly, lruvec_stats);\n \tCACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup_per_node,\n-\t\t\t\t memcg_pn_read_mostly, shrinker_info);\n+\t\t\t\t memcg_pn_read_mostly, shrinker_units);\n \tCACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup_per_node,\n \t\t\t\t memcg_pn_read_mostly, objcg);\n \ndiff --git a/mm/shrinker.c b/mm/shrinker.c\nindex 4fb424e721bca0..3d55a1ed1f986d 100644\n--- a/mm/shrinker.c\n+++ b/mm/shrinker.c\n@@ -19,213 +19,146 @@ void __init shrinker_unit_cache_init(void)\n \tshrinker_unit_cachep = KMEM_CACHE(shrinker_info_unit, SLAB_PANIC);\n }\n \n-static inline int shrinker_unit_size(int nr_items)\n+static inline int shrinker_id_to_index(int shrinker_id)\n {\n-\treturn (DIV_ROUND_UP(nr_items, SHRINKER_UNIT_BITS) sizeof(struct shrinker_info_unit ));\n+\treturn shrinker_id / SHRINKER_UNIT_BITS;\n }\n \n-static inline void shrinker_unit_free(struct shrinker_info info, int start)\n+static inline int shrinker_id_to_offset(int shrinker_id)\n {\n-\tstruct shrinker_info_unit *unit;\n-\tint nr, i;\n-\n-\tif (!info)\n-\t\treturn;\n-\n-\tunit = info-\u003eunit;\n-\tnr = DIV_ROUND_UP(info-\u003emap_nr_max, SHRINKER_UNIT_BITS);\n+\treturn shrinker_id % SHRINKER_UNIT_BITS;\n+}\n \n-\tfor (i = start; i \u003c nr; i++) {\n-\t\tif (!unit[i])\n-\t\t\tbreak;\n+static inline int calc_shrinker_id(int index, int offset)\n+{\n+\treturn index SHRINKER_UNIT_BITS + offset;\n+}\n \n-\t\tkmem_cache_free(shrinker_unit_cachep, unit[i]);\n-\t\tunit[i] = NULL;\n-\t}\n+static struct shrinker_info_unit shrinker_unit_get(struct mem_cgroup memcg,\n+\t\t\t\t\t\t int nid, int shrinker_id)\n+{\n+\treturn xa_load(\u0026memcg-\u003enodeinfo[nid]-\u003eshrinker_units,\n+\t\t shrinker_id_to_index(shrinker_id));\n }\n \n-static inline int shrinker_unit_alloc(struct shrinker_info new,\n-\t\t\t\t struct shrinker_info old, int nid)\n+/\n+ Installs run with the caller's gfp, possibly under the i_pages lock, which\n+ * is taken from interrupts: hence the irq-safe lock and xas_nomem().\n+ /\n+static int shrinker_unit_install(struct mem_cgroup memcg, int nid, int index,\n+\t\t\t\t gfp_t gfp)\n {\n+\tXA_STATE(xas, \u0026memcg-\u003enodeinfo[nid]-\u003eshrinker_units, index);\n \tstruct shrinker_info_unit unit;\n-\tint nr = DIV_ROUND_UP(new-\u003emap_nr_max, SHRINKER_UNIT_BITS);\n-\tint start = old ? DIV_ROUND_UP(old-\u003emap_nr_max, SHRINKER_UNIT_BITS) : 0;\n-\tint i;\n-\n-\tfor (i = start; i \u003c nr; i++) {\n-\t\tunit = kmem_cache_alloc_node(shrinker_unit_cachep,\n-\t\t\t\t\t GFP_KERNEL \| __GFP_ZERO, nid);\n-\t\tif (!unit) {\n-\t\t\tshrinker_unit_free(new, start);\n-\t\t\treturn -ENOMEM;\n-\t\t}\n-\n-\t\tnew-\u003eunit[i] = unit;\n-\t}\n+\tunsigned long flags;\n \n-\treturn 0;\n-}\n+\tif (xa_load(xas.xa, index))\n+\t\treturn 0;\n \n-static void __free_shrinker_info(struct mem_cgroup memcg)\n-{\n-\tstruct mem_cgroup_per_node pn;\n-\tstruct shrinker_info info;\n-\tint nid;\n+\tunit = kmem_cache_alloc_node(shrinker_unit_cachep, gfp \| __GFP_ZERO,\n+\t\t\t\t nid);\n+\tif (!unit)\n+\t\treturn -ENOMEM;\n \n-\tlockdep_assert_held(\u0026shrinker_mutex);\n+\tdo {\n+\t\txas_lock_irqsave(\u0026xas, flags);\n+\t\tif (!xas_load(\u0026xas)) {\n+\t\t\txas_store(\u0026xas, unit);\n+\t\t\tif (!xas_error(\u0026xas))\n+\t\t\t\tunit = NULL;\n+\t\t}\n+\t\txas_unlock_irqrestore(\u0026xas, flags);\n+\t} while (xas_nomem(\u0026xas, gfp));\n \n-\tfor_each_node(nid) {\n-\t\tpn = memcg-\u003enodeinfo[nid];\n-\t\tinfo = rcu_dereference_protected(pn-\u003eshrinker_info, true);\n-\t\tshrinker_unit_free(info, 0);\n-\t\tkvfree(info);\n-\t\trcu_assign_pointer(pn-\u003eshrinker_info, NULL);\n-\t}\n-}\n+\tif (unit)\n+\t\tkmem_cache_free(shrinker_unit_cachep, unit);\n \n-void free_shrinker_info(struct mem_cgroup memcg)\n-{\n-\tmutex_lock(\u0026shrinker_mutex);\n-\t__free_shrinker_info(memcg);\n-\tmutex_unlock(\u0026shrinker_mutex);\n+\treturn xas_error(\u0026xas);\n }\n \n-int alloc_shrinker_info(struct mem_cgroup memcg)\n+static int shrinker_units_install(struct mem_cgroup memcg, int start, int end)\n {\n-\tint nid, ret = 0;\n-\tint array_size = 0;\n+\tint nid, index, ret;\n \n-\tmutex_lock(\u0026shrinker_mutex);\n-\tarray_size = shrinker_unit_size(shrinker_nr_max);\n \tfor_each_node(nid) {\n-\t\tstruct shrinker_info info = kvzalloc_node(sizeof(info) + array_size,\n-\t\t\t\t\t\t\t GFP_KERNEL, nid);\n-\t\tif (!info)\n-\t\t\tgoto err;\n-\t\tinfo-\u003emap_nr_max = shrinker_nr_max;\n-\t\tif (shrinker_unit_alloc(info, NULL, nid)) {\n-\t\t\tkvfree(info);\n-\t\t\tgoto err;\n+\t\tfor (index = start; index \u003c end; index++) {\n+\t\t\tret = shrinker_unit_install(memcg, nid, index,\n+\t\t\t\t\t\t GFP_KERNEL);\n+\t\t\tif (ret)\n+\t\t\t\treturn ret;\n \t\t}\n-\t\trcu_assign_pointer(memcg-\u003enodeinfo[nid]-\u003eshrinker_info, info);\n \t}\n-\tmutex_unlock(\u0026shrinker_mutex);\n-\n-\treturn ret;\n \n-err:\n-\t__free_shrinker_info(memcg);\n-\tmutex_unlock(\u0026shrinker_mutex);\n-\treturn -ENOMEM;\n-}\n-\n-static struct shrinker_info shrinker_info_protected(struct mem_cgroup memcg,\n-\t\t\t\t\t\t int nid)\n-{\n-\treturn rcu_dereference_protected(memcg-\u003enodeinfo[nid]-\u003eshrinker_info,\n-\t\t\t\t\t lockdep_is_held(\u0026shrinker_mutex));\n+\treturn 0;\n }\n \n-static int expand_one_shrinker_info(struct mem_cgroup memcg, int new_size,\n-\t\t\t\t int old_size, int new_nr_max)\n+void free_shrinker_info(struct mem_cgroup memcg)\n {\n-\tstruct shrinker_info new, old;\n-\tstruct mem_cgroup_per_node pn;\n+\tstruct shrinker_info_unit unit;\n+\tunsigned long index;\n \tint nid;\n \n \tfor_each_node(nid) {\n-\t\tpn = memcg-\u003enodeinfo[nid];\n-\t\told = shrinker_info_protected(memcg, nid);\n-\t\t/ Not yet online memcg /\n-\t\tif (!old)\n-\t\t\treturn 0;\n-\n-\t\t/ Already expanded this shrinker_info /\n-\t\tif (new_nr_max \u003c= old-\u003emap_nr_max)\n-\t\t\tcontinue;\n+\t\tstruct xarray units = \u0026memcg-\u003enodeinfo[nid]-\u003eshrinker_units;\n \n-\t\tnew = kvzalloc_node(sizeof(new) + new_size, GFP_KERNEL, nid);\n-\t\tif (!new)\n-\t\t\treturn -ENOMEM;\n+\t\txa_for_each(units, index, unit)\n+\t\t\tkmem_cache_free(shrinker_unit_cachep, unit);\n+\t\txa_destroy(units);\n+\t}\n+}\n \n-\t\tnew-\u003emap_nr_max = new_nr_max;\n+/\n+ * Global reclaim keeps the deferred work of memcg-aware shrinkers in the\n+ * root's units, and root has no list_lru allocation to install them from.\n+ /\n+int alloc_shrinker_info(struct mem_cgroup memcg)\n+{\n+\tint ret;\n \n-\t\tmemcpy(new-\u003eunit, old-\u003eunit, old_size);\n-\t\tif (shrinker_unit_alloc(new, old, nid)) {\n-\t\t\tkvfree(new);\n-\t\t\treturn -ENOMEM;\n-\t\t}\n+\tif (!mem_cgroup_is_root(memcg))\n+\t\treturn 0;\n \n-\t\trcu_assign_pointer(pn-\u003eshrinker_info, new);\n-\t\tkvfree_rcu(old, rcu);\n-\t}\n+\tmutex_lock(\u0026shrinker_mutex);\n+\tret = shrinker_units_install(memcg, 0,\n+\t\t\t\t shrinker_id_to_index(shrinker_nr_max));\n+\tif (ret)\n+\t\tfree_shrinker_info(memcg);\n+\tmutex_unlock(\u0026shrinker_mutex);\n \n-\treturn 0;\n+\treturn ret;\n }\n \n static int expand_shrinker_info(int new_id)\n {\n-\tint ret = 0;\n \tint new_nr_max = round_up(new_id + 1, SHRINKER_UNIT_BITS);\n-\tint new_size, old_size = 0;\n-\tstruct mem_cgroup memcg;\n-\n-\tif (!root_mem_cgroup)\n-\t\tgoto out;\n+\tint ret = 0;\n \n \tlockdep_assert_held(\u0026shrinker_mutex);\n \n-\tnew_size = shrinker_unit_size(new_nr_max);\n-\told_size = shrinker_unit_size(shrinker_nr_max);\n-\n-\tmemcg = mem_cgroup_iter(NULL, NULL, NULL);\n-\tdo {\n-\t\tret = expand_one_shrinker_info(memcg, new_size, old_size,\n-\t\t\t\t\t new_nr_max);\n-\t\tif (ret) {\n-\t\t\tmem_cgroup_iter_break(NULL, memcg);\n-\t\t\tgoto out;\n-\t\t}\n-\t} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);\n-out:\n+\tif (root_mem_cgroup)\n+\t\tret = shrinker_units_install(root_mem_cgroup,\n+\t\t\t\t\t shrinker_id_to_index(shrinker_nr_max),\n+\t\t\t\t\t shrinker_id_to_index(new_nr_max));\n \tif (!ret)\n \t\tshrinker_nr_max = new_nr_max;\n \n \treturn ret;\n }\n \n-static inline int shrinker_id_to_index(int shrinker_id)\n-{\n-\treturn shrinker_id / SHRINKER_UNIT_BITS;\n-}\n-\n-static inline int shrinker_id_to_offset(int shrinker_id)\n+void set_shrinker_bit(struct mem_cgroup memcg, int nid, int shrinker_id)\n {\n-\treturn shrinker_id % SHRINKER_UNIT_BITS;\n-}\n+\tstruct shrinker_info_unit unit;\n \n-static inline int calc_shrinker_id(int index, int offset)\n-{\n-\treturn index SHRINKER_UNIT_BITS + offset;\n-}\n+\tif (shrinker_id \u003c 0 \|\| !memcg \|\| mem_cgroup_is_root(memcg))\n+\t\treturn;\n \n-void set_shrinker_bit(struct mem_cgroup memcg, int nid, int shrinker_id)\n-{\n-\tif (shrinker_id \u003e= 0 \u0026\u0026 memcg \u0026\u0026 !mem_cgroup_is_root(memcg)) {\n-\t\tstruct shrinker_info info;\n+\tunit = shrinker_unit_get(memcg, nid, shrinker_id);\n+\tif (WARN_ON_ONCE(!unit))\n+\t\treturn;\n \n-\t\trcu_read_lock();\n-\t\tinfo = rcu_dereference(memcg-\u003enodeinfo[nid]-\u003eshrinker_info);\n-\t\tif (!WARN_ON_ONCE(shrinker_id \u003e= info-\u003emap_nr_max)) {\n-\t\t\tstruct shrinker_info_unit unit;\n-\n-\t\t\tunit = info-\u003eunit[shrinker_id_to_index(shrinker_id)];\n-\t\t\t/ Pairs with smp mb in shrink_slab() /\n-\t\t\tsmp_mb__before_atomic();\n-\t\t\tset_bit(shrinker_id_to_offset(shrinker_id), unit-\u003emap);\n-\t\t}\n-\t\trcu_read_unlock();\n-\t}\n+\t/ Pairs with smp mb in shrink_slab() /\n+\tsmp_mb__before_atomic();\n+\tset_bit(shrinker_id_to_offset(shrinker_id), unit-\u003emap);\n }\n \n static DEFINE_IDR(shrinker_idr);\n@@ -270,59 +203,73 @@ static void shrinker_memcg_remove(struct shrinker shrinker)\n static long xchg_nr_deferred_memcg(int nid, struct shrinker shrinker,\n \t\t\t\t struct mem_cgroup memcg)\n {\n-\tstruct shrinker_info info;\n \tstruct shrinker_info_unit unit;\n-\tlong nr_deferred;\n \n-\trcu_read_lock();\n-\tinfo = rcu_dereference(memcg-\u003enodeinfo[nid]-\u003eshrinker_info);\n-\tunit = info-\u003eunit[shrinker_id_to_index(shrinker-\u003eid)];\n-\tnr_deferred = atomic_long_xchg(\u0026unit-\u003enr_deferred[shrinker_id_to_offset(shrinker-\u003eid)], 0);\n-\trcu_read_unlock();\n+\tunit = shrinker_unit_get(memcg, nid, shrinker-\u003eid);\n+\t/* No unit: this memcg never held objects of this shrinker. /\n+\tif (!unit)\n+\t\treturn 0;\n \n-\treturn nr_deferred;\n+\treturn atomic_long_xchg(\u0026unit-\u003enr_deferred[shrinker_id_to_offset(shrinker-\u003eid)], 0);\n }\n \n static long add_nr_deferred_memcg(long nr, int nid, struct shrinker shrinker,\n \t\t\t\t struct mem_cgroup memcg)\n {\n-\tstruct shrinker_info info;\n \tstruct shrinker_info_unit unit;\n-\tlong nr_deferred;\n \n-\trcu_read_lock();\n-\tinfo = rcu_dereference(memcg-\u003enodeinfo[nid]-\u003eshrinker_info);\n-\tunit = info-\u003eunit[shrinker_id_to_index(shrinker-\u003eid)];\n-\tnr_deferred =\n-\t\tatomic_long_add_return(nr, \u0026unit-\u003enr_deferred[shrinker_id_to_offset(shrinker-\u003eid)]);\n-\trcu_read_unlock();\n+\tunit = shrinker_unit_get(memcg, nid, shrinker-\u003eid);\n+\tif (!unit)\n+\t\treturn 0;\n \n-\treturn nr_deferred;\n+\treturn atomic_long_add_return(nr, \u0026unit-\u003enr_deferred[shrinker_id_to_offset(shrinker-\u003eid)]);\n+}\n+\n+/\n+ * Called before @memcg gets a list on a list_lru of shrinker @shrinker_id:\n+ * a map bit is only ever set on a memcg that has such a list.\n+ /\n+int memcg_shrinker_unit_alloc(struct mem_cgroup memcg, int shrinker_id,\n+\t\t\t gfp_t gfp)\n+{\n+\tint nid, ret;\n+\n+\tif (shrinker_id \u003c 0 \|\| mem_cgroup_is_root(memcg))\n+\t\treturn 0;\n+\n+\tfor_each_node(nid) {\n+\t\tret = shrinker_unit_install(memcg, nid,\n+\t\t\t\t\t shrinker_id_to_index(shrinker_id),\n+\t\t\t\t\t gfp);\n+\t\tif (ret)\n+\t\t\treturn ret;\n+\t}\n+\n+\treturn 0;\n }\n \n void reparent_shrinker_deferred(struct mem_cgroup memcg)\n {\n-\tint nid, index, offset;\n-\tlong nr;\n \tstruct mem_cgroup parent = parent_mem_cgroup(memcg);\n-\tstruct shrinker_info child_info, parent_info;\n \tstruct shrinker_info_unit child_unit, parent_unit;\n+\tunsigned long index;\n+\tint nid, offset;\n+\tlong nr;\n \n-\t/* Prevent from concurrent shrinker_info expand /\n-\tmutex_lock(\u0026shrinker_mutex);\n \tfor_each_node(nid) {\n-\t\tchild_info = shrinker_info_protected(memcg, nid);\n-\t\tparent_info = shrinker_info_protected(parent, nid);\n-\t\tfor (index = 0; index \u003c shrinker_id_to_index(child_info-\u003emap_nr_max); index++) {\n-\t\t\tchild_unit = child_info-\u003eunit[index];\n-\t\t\tparent_unit = parent_info-\u003eunit[index];\n+\t\tstruct xarray parent_units = \u0026parent-\u003enodeinfo[nid]-\u003eshrinker_units;\n+\n+\t\txa_for_each(\u0026memcg-\u003enodeinfo[nid]-\u003eshrinker_units, index, child_unit) {\n+\t\t\tparent_unit = xa_load(parent_units, index);\n+\t\t\t/* Installed but never listed: nothing deferred in it. /\n+\t\t\tif (!parent_unit)\n+\t\t\t\tcontinue;\n \t\t\tfor (offset = 0; offset \u003c SHRINKER_UNIT_BITS; offset++) {\n \t\t\t\tnr = atomic_long_read(\u0026child_unit-\u003enr_deferred[offset]);\n \t\t\t\tatomic_long_add(nr, \u0026parent_unit-\u003enr_deferred[offset]);\n \t\t\t}\n \t\t}\n \t}\n-\tmutex_unlock(\u0026shrinker_mutex);\n }\n #else\n static int shrinker_memcg_alloc(struct shrinker shrinker)\n@@ -485,9 +432,9 @@ static unsigned long do_shrink_slab(struct shrink_control shrinkctl,\n static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,\n \t\t\tstruct mem_cgroup memcg, int priority)\n {\n-\tstruct shrinker_info info;\n-\tunsigned long ret, freed = 0;\n-\tint offset, index = 0;\n+\tstruct shrinker_info_unit unit;\n+\tunsigned long index, ret, freed = 0;\n+\tint offset;\n \n \tif (!mem_cgroup_online(memcg))\n \t\treturn 0;\n@@ -495,51 +442,17 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,\n \t/\n \t lockless algorithm of memcg shrink.\n \t \n-\t The shrinker_info may be freed asynchronously via RCU in the\n-\t * expand_one_shrinker_info(), so the rcu_read_lock() needs to be used\n-\t * to ensure the existence of the shrinker_info.\n-\t \n-\t The shrinker_info_unit is never freed unless its corresponding memcg\n-\t * is destroyed. Here we already hold the refcount of memcg, so the\n-\t * memcg will not be destroyed, and of course shrinker_info_unit will\n-\t * not be freed.\n+\t * A unit is only freed together with its memcg, and the caller holds\n+\t * a reference to the memcg, so the units found by xa_for_each() stay\n+\t * valid without the RCU lock and do_shrink_slab() may sleep.\n \t \n-\t So in the memcg shrink:\n-\t * step 1: use rcu_read_lock() to guarantee existence of the\n-\t * shrinker_info.\n-\t * step 2: after getting shrinker_info_unit we can safely release the\n-\t * RCU lock.\n-\t * step 3: traverse the bitmap and calculate shrinker_id\n-\t * step 4: use rcu_read_lock() to guarantee existence of the shrinker.\n-\t * step 5: use shrinker_id to find the shrinker, then use\n-\t * shrinker_try_get() to guarantee existence of the shrinker,\n-\t * then we can release the RCU lock to do do_shrink_slab() that\n-\t * may sleep.\n-\t * step 6: do shrinker_put() paired with step 5 to put the refcount,\n-\t * if the refcount reaches 0, then wake up the waiter in\n-\t * shrinker_free() by calling complete().\n-\t * Note: here is different from the global shrink, we don't\n-\t * need to acquire the RCU lock to guarantee existence of\n-\t * the shrinker, because we don't need to use this\n-\t * shrinker to traverse the next shrinker in the bitmap.\n-\t * step 7: we have already exited the read-side of rcu critical section\n-\t * before calling do_shrink_slab(), the shrinker_info may be\n-\t * released in expand_one_shrinker_info(), so go back to step 1\n-\t * to reacquire the shrinker_info.\n+\t * The shrinker is found by id under the RCU lock, and\n+\t * shrinker_try_get() pins it before the lock is dropped;\n+\t * shrinker_put() wakes up the waiter in shrinker_free() by calling\n+\t * complete() when the last reference goes. The next shrinker comes\n+\t * from the bitmap, not from this shrinker, so nothing else is needed.\n \t /\n-again:\n-\trcu_read_lock();\n-\tinfo = rcu_dereference(memcg-\u003enodeinfo[nid]-\u003eshrinker_info);\n-\tif (unlikely(!info))\n-\t\tgoto unlock;\n-\n-\tif (index \u003c shrinker_id_to_index(info-\u003emap_nr_max)) {\n-\t\tstruct shrinker_info_unit unit;\n-\n-\t\tunit = info-\u003eunit[index];\n-\n-\t\trcu_read_unlock();\n-\n+\txa_for_each(\u0026memcg-\u003enodeinfo[nid]-\u003eshrinker_units, index, unit) {\n \t\tfor_each_set_bit(offset, unit-\u003emap, SHRINKER_UNIT_BITS) {\n \t\t\tstruct shrink_control sc = {\n \t\t\t\t.gfp_mask = gfp_mask,\n@@ -594,12 +507,8 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,\n \t\t\tfreed += ret;\n \t\t\tshrinker_put(shrinker);\n \t\t}\n-\n-\t\tindex++;\n-\t\tgoto again;\n \t}\n-unlock:\n-\trcu_read_unlock();\n+\n \treturn freed;\n }\n #else /* !CONFIG_MEMCG */\n" }
2/1	2026/11/03 19:55	agent	patch-evaluator	22m Model: core Args: null Results: { "EnableConfigs": [ "MEMCG", "CGROUPS" ], "FocusSymbols": [ "memcg_shrinker_unit_alloc", "set_shrinker_bit", "reparent_shrinker_deferred", "alloc_shrinker_info", "free_shrinker_info", "shrink_slab", "__list_lru_init", "memcg_list_lru_alloc" ], "Reasoning": "The patch refactors the memcg slab shrinker tracking mechanism from a flat RCU-allocated array to a lazily-allocated XArray per nodeinfo. It alters memory reclaim iteration (shrink_slab/shrink_slab_memcg), introduces a new WARN_ON_ONCE() assertion in set_shrinker_bit(), modifies deferred reclaim reparenting, and changes list_lru allocation logic. These changes affect core memory management and are fully reachable in virtualized environments via cgroup and memory pressure workloads.", "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 b9a5154a739313cf76c33e4e804f9fc2493dba9b Author: syz-cluster <triage@syzkaller.com> Date: Tue Nov 3 19:55:47 2026 +0000 syz-cluster: applied patch under review diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 69e1bcc67c588d..ea2c0990059479 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -24,6 +24,7 @@ #include <linux/page-flags.h> #include <linux/shrinker.h> #include <linux/irq_work_types.h> +#include <linux/xarray.h> struct mem_cgroup; struct obj_cgroup; @@ -83,14 +84,14 @@ struct mem_cgroup_reclaim_iter { * per-node information in memory controller. / struct mem_cgroup_per_node { - / Set when the memcg is created, then only read. / + / Set when the memcg is created, then mostly read. / __cacheline_group_begin_aligned(memcg_pn_read_mostly); struct mem_cgroup memcg; /* Back pointer, we cannot / / use container_of / struct lruvec_stats_percpu __percpu lruvec_stats_percpu; struct lruvec_stats lruvec_stats; - struct shrinker_info __rcu shrinker_info; + struct xarray shrinker_units; struct obj_cgroup __rcu objcg; __cacheline_group_end_aligned(memcg_pn_read_mostly); @@ -1719,6 +1720,8 @@ static inline u64 mem_cgroup_get_socket_pressure(const struct mem_cgroup memcg) void shrinker_unit_cache_init(void); int alloc_shrinker_info(struct mem_cgroup memcg); +int memcg_shrinker_unit_alloc(struct mem_cgroup memcg, int shrinker_id, + gfp_t gfp); void free_shrinker_info(struct mem_cgroup memcg); void set_shrinker_bit(struct mem_cgroup memcg, int nid, int shrinker_id); void reparent_shrinker_deferred(struct mem_cgroup memcg); diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h index 1a00be90d93a9f..2eae68a7ff6c5d 100644 --- a/include/linux/shrinker.h +++ b/include/linux/shrinker.h @@ -18,12 +18,6 @@ struct shrinker_info_unit { DECLARE_BITMAP(map, SHRINKER_UNIT_BITS); }; -struct shrinker_info { - struct rcu_head rcu; - int map_nr_max; - struct shrinker_info_unit unit[]; -}; - /* * This struct is used to pass information from page reclaim to the shrinkers. * We consolidate the values for easier extension later. diff --git a/mm/list_lru.c b/mm/list_lru.c index d1d256822ccc73..4be22c5238f98a 100644 --- a/mm/list_lru.c +++ b/mm/list_lru.c @@ -597,6 +597,12 @@ static int __memcg_list_lru_alloc(struct mem_cgroup memcg, parent = parent_mem_cgroup(pos); } + if (!css_is_dying(&pos->css) && + memcg_shrinker_unit_alloc(pos, lru_shrinker_id(lru), gfp)) { + kfree(mlru); + return -ENOMEM; + } + if (!mlru) { mlru = memcg_init_list_lru_one(lru, gfp); if (!mlru) @@ -666,18 +672,20 @@ int __list_lru_init(struct list_lru lru, bool memcg_aware, struct shrinker shr int i; #ifdef CONFIG_MEMCG + if (mem_cgroup_disabled() \|\| mem_cgroup_kmem_disabled()) + memcg_aware = false; + / * If the shrinker fell back to being non-memcg-aware (e.g. with - * cgroup.memory=nokmem), its id was never assigned and holds a - * stale 0. Don't let set_shrinker_bit() act on it. + * cgroup.memory=nokmem), its id is not valid. Don't let + * set_shrinker_bit() act on it, nor on a list that is not + * per-memcg: such a list gets no shrinker units. / - if (shrinker && (shrinker->flags & SHRINKER_MEMCG_AWARE)) + if (shrinker && memcg_aware && + (shrinker->flags & SHRINKER_MEMCG_AWARE)) lru->shrinker_id = shrinker->id; else lru->shrinker_id = -1; - - if (mem_cgroup_disabled() \|\| mem_cgroup_kmem_disabled()) - memcg_aware = false; #endif lru->node = kzalloc_objs(lru->node, nr_node_ids); diff --git a/mm/memcontrol.c b/mm/memcontrol.c index a05d9a8baa1b6b..1a582be5a75bbb 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4219,6 +4219,7 @@ static bool alloc_mem_cgroup_per_node_info(struct mem_cgroup memcg, int node) INIT_LIST_HEAD(&pn->objcg_list); lruvec_init(&pn->lruvec); + xa_init_flags(&pn->shrinker_units, XA_FLAGS_LOCK_IRQ); pn->memcg = memcg; memcg->nodeinfo[node] = pn; @@ -4385,11 +4386,6 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state css) memcg_online_kmem(memcg); - /* - * A memcg must be visible for expand_shrinker_info() - * by the time the maps are allocated. So, we allocate maps - * here, when mem_cgroup_iter() can't skip it. - / if (alloc_shrinker_info(memcg)) goto offline_kmem; @@ -5925,7 +5921,7 @@ static void __init memcg_struct_check(void) CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup_per_node, memcg_pn_read_mostly, lruvec_stats); CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup_per_node, - memcg_pn_read_mostly, shrinker_info); + memcg_pn_read_mostly, shrinker_units); CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup_per_node, memcg_pn_read_mostly, objcg); diff --git a/mm/shrinker.c b/mm/shrinker.c index 4fb424e721bca0..3d55a1ed1f986d 100644 --- a/mm/shrinker.c +++ b/mm/shrinker.c @@ -19,213 +19,146 @@ void __init shrinker_unit_cache_init(void) shrinker_unit_cachep = KMEM_CACHE(shrinker_info_unit, SLAB_PANIC); } -static inline int shrinker_unit_size(int nr_items) +static inline int shrinker_id_to_index(int shrinker_id) { - return (DIV_ROUND_UP(nr_items, SHRINKER_UNIT_BITS) sizeof(struct shrinker_info_unit )); + return shrinker_id / SHRINKER_UNIT_BITS; } -static inline void shrinker_unit_free(struct shrinker_info info, int start) +static inline int shrinker_id_to_offset(int shrinker_id) { - struct shrinker_info_unit *unit; - int nr, i; - - if (!info) - return; - - unit = info->unit; - nr = DIV_ROUND_UP(info->map_nr_max, SHRINKER_UNIT_BITS); + return shrinker_id % SHRINKER_UNIT_BITS; +} - for (i = start; i < nr; i++) { - if (!unit[i]) - break; +static inline int calc_shrinker_id(int index, int offset) +{ + return index SHRINKER_UNIT_BITS + offset; +} - kmem_cache_free(shrinker_unit_cachep, unit[i]); - unit[i] = NULL; - } +static struct shrinker_info_unit shrinker_unit_get(struct mem_cgroup memcg, + int nid, int shrinker_id) +{ + return xa_load(&memcg->nodeinfo[nid]->shrinker_units, + shrinker_id_to_index(shrinker_id)); } -static inline int shrinker_unit_alloc(struct shrinker_info new, - struct shrinker_info old, int nid) +/* + * Installs run with the caller's gfp, possibly under the i_pages lock, which + * is taken from interrupts: hence the irq-safe lock and xas_nomem(). + / +static int shrinker_unit_install(struct mem_cgroup memcg, int nid, int index, + gfp_t gfp) { + XA_STATE(xas, &memcg->nodeinfo[nid]->shrinker_units, index); struct shrinker_info_unit unit; - int nr = DIV_ROUND_UP(new->map_nr_max, SHRINKER_UNIT_BITS); - int start = old ? DIV_ROUND_UP(old->map_nr_max, SHRINKER_UNIT_BITS) : 0; - int i; - - for (i = start; i < nr; i++) { - unit = kmem_cache_alloc_node(shrinker_unit_cachep, - GFP_KERNEL \| __GFP_ZERO, nid); - if (!unit) { - shrinker_unit_free(new, start); - return -ENOMEM; - } - - new->unit[i] = unit; - } + unsigned long flags; - return 0; -} + if (xa_load(xas.xa, index)) + return 0; -static void __free_shrinker_info(struct mem_cgroup memcg) -{ - struct mem_cgroup_per_node pn; - struct shrinker_info info; - int nid; + unit = kmem_cache_alloc_node(shrinker_unit_cachep, gfp \| __GFP_ZERO, + nid); + if (!unit) + return -ENOMEM; - lockdep_assert_held(&shrinker_mutex); + do { + xas_lock_irqsave(&xas, flags); + if (!xas_load(&xas)) { + xas_store(&xas, unit); + if (!xas_error(&xas)) + unit = NULL; + } + xas_unlock_irqrestore(&xas, flags); + } while (xas_nomem(&xas, gfp)); - for_each_node(nid) { - pn = memcg->nodeinfo[nid]; - info = rcu_dereference_protected(pn->shrinker_info, true); - shrinker_unit_free(info, 0); - kvfree(info); - rcu_assign_pointer(pn->shrinker_info, NULL); - } -} + if (unit) + kmem_cache_free(shrinker_unit_cachep, unit); -void free_shrinker_info(struct mem_cgroup memcg) -{ - mutex_lock(&shrinker_mutex); - __free_shrinker_info(memcg); - mutex_unlock(&shrinker_mutex); + return xas_error(&xas); } -int alloc_shrinker_info(struct mem_cgroup memcg) +static int shrinker_units_install(struct mem_cgroup memcg, int start, int end) { - int nid, ret = 0; - int array_size = 0; + int nid, index, ret; - mutex_lock(&shrinker_mutex); - array_size = shrinker_unit_size(shrinker_nr_max); for_each_node(nid) { - struct shrinker_info info = kvzalloc_node(sizeof(info) + array_size, - GFP_KERNEL, nid); - if (!info) - goto err; - info->map_nr_max = shrinker_nr_max; - if (shrinker_unit_alloc(info, NULL, nid)) { - kvfree(info); - goto err; + for (index = start; index < end; index++) { + ret = shrinker_unit_install(memcg, nid, index, + GFP_KERNEL); + if (ret) + return ret; } - rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info); } - mutex_unlock(&shrinker_mutex); - - return ret; -err: - __free_shrinker_info(memcg); - mutex_unlock(&shrinker_mutex); - return -ENOMEM; -} - -static struct shrinker_info shrinker_info_protected(struct mem_cgroup memcg, - int nid) -{ - return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info, - lockdep_is_held(&shrinker_mutex)); + return 0; } -static int expand_one_shrinker_info(struct mem_cgroup memcg, int new_size, - int old_size, int new_nr_max) +void free_shrinker_info(struct mem_cgroup memcg) { - struct shrinker_info new, old; - struct mem_cgroup_per_node pn; + struct shrinker_info_unit unit; + unsigned long index; int nid; for_each_node(nid) { - pn = memcg->nodeinfo[nid]; - old = shrinker_info_protected(memcg, nid); - / Not yet online memcg / - if (!old) - return 0; - - / Already expanded this shrinker_info / - if (new_nr_max <= old->map_nr_max) - continue; + struct xarray units = &memcg->nodeinfo[nid]->shrinker_units; - new = kvzalloc_node(sizeof(new) + new_size, GFP_KERNEL, nid); - if (!new) - return -ENOMEM; + xa_for_each(units, index, unit) + kmem_cache_free(shrinker_unit_cachep, unit); + xa_destroy(units); + } +} - new->map_nr_max = new_nr_max; +/ + * Global reclaim keeps the deferred work of memcg-aware shrinkers in the + * root's units, and root has no list_lru allocation to install them from. + / +int alloc_shrinker_info(struct mem_cgroup memcg) +{ + int ret; - memcpy(new->unit, old->unit, old_size); - if (shrinker_unit_alloc(new, old, nid)) { - kvfree(new); - return -ENOMEM; - } + if (!mem_cgroup_is_root(memcg)) + return 0; - rcu_assign_pointer(pn->shrinker_info, new); - kvfree_rcu(old, rcu); - } + mutex_lock(&shrinker_mutex); + ret = shrinker_units_install(memcg, 0, + shrinker_id_to_index(shrinker_nr_max)); + if (ret) + free_shrinker_info(memcg); + mutex_unlock(&shrinker_mutex); - return 0; + return ret; } static int expand_shrinker_info(int new_id) { - int ret = 0; int new_nr_max = round_up(new_id + 1, SHRINKER_UNIT_BITS); - int new_size, old_size = 0; - struct mem_cgroup memcg; - - if (!root_mem_cgroup) - goto out; + int ret = 0; lockdep_assert_held(&shrinker_mutex); - new_size = shrinker_unit_size(new_nr_max); - old_size = shrinker_unit_size(shrinker_nr_max); - - memcg = mem_cgroup_iter(NULL, NULL, NULL); - do { - ret = expand_one_shrinker_info(memcg, new_size, old_size, - new_nr_max); - if (ret) { - mem_cgroup_iter_break(NULL, memcg); - goto out; - } - } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL); -out: + if (root_mem_cgroup) + ret = shrinker_units_install(root_mem_cgroup, + shrinker_id_to_index(shrinker_nr_max), + shrinker_id_to_index(new_nr_max)); if (!ret) shrinker_nr_max = new_nr_max; return ret; } -static inline int shrinker_id_to_index(int shrinker_id) -{ - return shrinker_id / SHRINKER_UNIT_BITS; -} - -static inline int shrinker_id_to_offset(int shrinker_id) +void set_shrinker_bit(struct mem_cgroup memcg, int nid, int shrinker_id) { - return shrinker_id % SHRINKER_UNIT_BITS; -} + struct shrinker_info_unit unit; -static inline int calc_shrinker_id(int index, int offset) -{ - return index SHRINKER_UNIT_BITS + offset; -} + if (shrinker_id < 0 \|\| !memcg \|\| mem_cgroup_is_root(memcg)) + return; -void set_shrinker_bit(struct mem_cgroup memcg, int nid, int shrinker_id) -{ - if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) { - struct shrinker_info info; + unit = shrinker_unit_get(memcg, nid, shrinker_id); + if (WARN_ON_ONCE(!unit)) + return; - rcu_read_lock(); - info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info); - if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) { - struct shrinker_info_unit unit; - - unit = info->unit[shrinker_id_to_index(shrinker_id)]; - / Pairs with smp mb in shrink_slab() / - smp_mb__before_atomic(); - set_bit(shrinker_id_to_offset(shrinker_id), unit->map); - } - rcu_read_unlock(); - } + / Pairs with smp mb in shrink_slab() / + smp_mb__before_atomic(); + set_bit(shrinker_id_to_offset(shrinker_id), unit->map); } static DEFINE_IDR(shrinker_idr); @@ -270,59 +203,73 @@ static void shrinker_memcg_remove(struct shrinker shrinker) static long xchg_nr_deferred_memcg(int nid, struct shrinker shrinker, struct mem_cgroup memcg) { - struct shrinker_info info; struct shrinker_info_unit unit; - long nr_deferred; - rcu_read_lock(); - info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info); - unit = info->unit[shrinker_id_to_index(shrinker->id)]; - nr_deferred = atomic_long_xchg(&unit->nr_deferred[shrinker_id_to_offset(shrinker->id)], 0); - rcu_read_unlock(); + unit = shrinker_unit_get(memcg, nid, shrinker->id); + /* No unit: this memcg never held objects of this shrinker. / + if (!unit) + return 0; - return nr_deferred; + return atomic_long_xchg(&unit->nr_deferred[shrinker_id_to_offset(shrinker->id)], 0); } static long add_nr_deferred_memcg(long nr, int nid, struct shrinker shrinker, struct mem_cgroup memcg) { - struct shrinker_info info; struct shrinker_info_unit unit; - long nr_deferred; - rcu_read_lock(); - info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info); - unit = info->unit[shrinker_id_to_index(shrinker->id)]; - nr_deferred = - atomic_long_add_return(nr, &unit->nr_deferred[shrinker_id_to_offset(shrinker->id)]); - rcu_read_unlock(); + unit = shrinker_unit_get(memcg, nid, shrinker->id); + if (!unit) + return 0; - return nr_deferred; + return atomic_long_add_return(nr, &unit->nr_deferred[shrinker_id_to_offset(shrinker->id)]); +} + +/ + * Called before @memcg gets a list on a list_lru of shrinker @shrinker_id: + * a map bit is only ever set on a memcg that has such a list. + / +int memcg_shrinker_unit_alloc(struct mem_cgroup memcg, int shrinker_id, + gfp_t gfp) +{ + int nid, ret; + + if (shrinker_id < 0 \|\| mem_cgroup_is_root(memcg)) + return 0; + + for_each_node(nid) { + ret = shrinker_unit_install(memcg, nid, + shrinker_id_to_index(shrinker_id), + gfp); + if (ret) + return ret; + } + + return 0; } void reparent_shrinker_deferred(struct mem_cgroup memcg) { - int nid, index, offset; - long nr; struct mem_cgroup parent = parent_mem_cgroup(memcg); - struct shrinker_info child_info, parent_info; struct shrinker_info_unit child_unit, parent_unit; + unsigned long index; + int nid, offset; + long nr; - /* Prevent from concurrent shrinker_info expand / - mutex_lock(&shrinker_mutex); for_each_node(nid) { - child_info = shrinker_info_protected(memcg, nid); - parent_info = shrinker_info_protected(parent, nid); - for (index = 0; index < shrinker_id_to_index(child_info->map_nr_max); index++) { - child_unit = child_info->unit[index]; - parent_unit = parent_info->unit[index]; + struct xarray parent_units = &parent->nodeinfo[nid]->shrinker_units; + + xa_for_each(&memcg->nodeinfo[nid]->shrinker_units, index, child_unit) { + parent_unit = xa_load(parent_units, index); + /* Installed but never listed: nothing deferred in it. / + if (!parent_unit) + continue; for (offset = 0; offset < SHRINKER_UNIT_BITS; offset++) { nr = atomic_long_read(&child_unit->nr_deferred[offset]); atomic_long_add(nr, &parent_unit->nr_deferred[offset]); } } } - mutex_unlock(&shrinker_mutex); } #else static int shrinker_memcg_alloc(struct shrinker shrinker) @@ -485,9 +432,9 @@ static unsigned long do_shrink_slab(struct shrink_control shrinkctl, static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, struct mem_cgroup memcg, int priority) { - struct shrinker_info info; - unsigned long ret, freed = 0; - int offset, index = 0; + struct shrinker_info_unit unit; + unsigned long index, ret, freed = 0; + int offset; if (!mem_cgroup_online(memcg)) return 0; @@ -495,51 +442,17 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, /* * lockless algorithm of memcg shrink. * - * The shrinker_info may be freed asynchronously via RCU in the - * expand_one_shrinker_info(), so the rcu_read_lock() needs to be used - * to ensure the existence of the shrinker_info. - * - * The shrinker_info_unit is never freed unless its corresponding memcg - * is destroyed. Here we already hold the refcount of memcg, so the - * memcg will not be destroyed, and of course shrinker_info_unit will - * not be freed. + * A unit is only freed together with its memcg, and the caller holds + * a reference to the memcg, so the units found by xa_for_each() stay + * valid without the RCU lock and do_shrink_slab() may sleep. * - * So in the memcg shrink: - * step 1: use rcu_read_lock() to guarantee existence of the - * shrinker_info. - * step 2: after getting shrinker_info_unit we can safely release the - * RCU lock. - * step 3: traverse the bitmap and calculate shrinker_id - * step 4: use rcu_read_lock() to guarantee existence of the shrinker. - * step 5: use shrinker_id to find the shrinker, then use - * shrinker_try_get() to guarantee existence of the shrinker, - * then we can release the RCU lock to do do_shrink_slab() that - * may sleep. - * step 6: do shrinker_put() paired with step 5 to put the refcount, - * if the refcount reaches 0, then wake up the waiter in - * shrinker_free() by calling complete(). - * Note: here is different from the global shrink, we don't - * need to acquire the RCU lock to guarantee existence of - * the shrinker, because we don't need to use this - * shrinker to traverse the next shrinker in the bitmap. - * step 7: we have already exited the read-side of rcu critical section - * before calling do_shrink_slab(), the shrinker_info may be - * released in expand_one_shrinker_info(), so go back to step 1 - * to reacquire the shrinker_info. + * The shrinker is found by id under the RCU lock, and + * shrinker_try_get() pins it before the lock is dropped; + * shrinker_put() wakes up the waiter in shrinker_free() by calling + * complete() when the last reference goes. The next shrinker comes + * from the bitmap, not from this shrinker, so nothing else is needed. / -again: - rcu_read_lock(); - info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info); - if (unlikely(!info)) - goto unlock; - - if (index < shrinker_id_to_index(info->map_nr_max)) { - struct shrinker_info_unit unit; - - unit = info->unit[index]; - - rcu_read_unlock(); - + xa_for_each(&memcg->nodeinfo[nid]->shrinker_units, index, unit) { for_each_set_bit(offset, unit->map, SHRINKER_UNIT_BITS) { struct shrink_control sc = { .gfp_mask = gfp_mask, @@ -594,12 +507,8 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, freed += ret; shrinker_put(shrinker); } - - index++; - goto again; } -unlock: - rcu_read_unlock(); + return freed; } #else /* !CONFIG_MEMCG */
3/2	2026/11/03 19:55	llm	patch-evaluator	6m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 10705 output: 43 thoughts: 718 Thoughts: Analyzing the memcg Shrinker Info Refactor Okay, so this patch is touching `memcontrol.h`, `shrinker.h`, `list_lru.c`, `memcontrol.c`, and `shrinker.c`. Immediately, my spidey-sense is tingling because this suggests a fairly significant refactor of the cgroup (specifically memcg) shrinker info mechanism. Let's dig in. Previously, `mem_cgroup_per_node` held a `struct shrinker_info __rcu shrinker_info` which was dynamically managed with `expand_shrinker_info` and reallocations on shrinker registration. Now, it looks like they're ditching that approach. Instead, they're using an xarray: `struct xarray shrinker_units;` initialized with `XA_FLAGS_LOCK_IRQ`. Interesting... This is allocated on-demand via `memcg_shrinker_unit_alloc`, specifically when `__memcg_list_lru_alloc` runs. I'll need to remember that. Okay, so `shrink_slab_memcg` is using `xa_for_each` to iterate. And I'm seeing `set_shrinker_bit` now calls `shrinker_unit_get` with a `WARN_ON_ONCE(!unit)`. I wonder why that warning is there. It's a key observation. I also see functions like `reparent_shrinker_deferred`, `alloc_shrinker_info`, `free_shrinker_info`, `xchg_nr_deferred_memcg`, and `add_nr_deferred_memcg` that seem related. Hmm... The major question here is about the `xa_for_each` in `shrink_slab_memcg`! I'm noticing that it doesn't* appear to hold an RCU read lock or any other explicit lock. Wait a minute! The comment says "A unit is only freed together with its memcg, and the caller holds a reference to the memcg, so the units found by xa_for_each() stay valid without the RCU lock and do_shrink_slab() may sleep." Okay, that makes sense. The memcg reference guarantees that the units stay valid. However, I need to verify that `xa_for_each` can safely iterate while another thread is modifying the xarray, specifically with `memcg_shrinker_unit_alloc` / `shrinker_unit_install` inserting into the xarray. Does `xa_for_each` require RCU read lock or xa_lock? Wait, let's look at how `xa_for_each` is defined. Aha! It iterates with `xa_find` and `xa_find_after`. And from past experience, I remember that `xa_find` and `xa_find_after` do use `rcu_read_lock()` internally! Good. That should be safe! Wait! But what about the case where `xa_for_each` yields between iterations, or, if `do_shrink_slab` sleeps? Index is incremented between iterations so `xa_find_after` is called. Okay, I need to check `xa_find` and `xa_find_after` in the xarray code base more carefully. Let's use grep to double-check.
4/2	2026/11/03 20:01	tool	grepper	0m Args: { "Expression": "xa_find_after", "PathPrefixes": [ "include/linux/xarray.h", "lib/xarray.c" ] } Results: { "Output": "include/linux/xarray.h=363=void xa_find(struct xarray xa, unsigned long index,\ninclude/linux/xarray.h-364-\t\tunsigned long max, xa_mark_t) __attribute__((nonnull(2)));\ninclude/linux/xarray.h:365:void xa_find_after(struct xarray xa, unsigned long index,\ninclude/linux/xarray.h-366-\t\tunsigned long max, xa_mark_t) __attribute__((nonnull(2)));\n--\ninclude/linux/xarray.h=422=static inline bool xa_marked(const struct xarray xa, xa_mark_t mark)\n--\ninclude/linux/xarray.h-454-\t entry;\t\t\t\t\t\t\t\\\ninclude/linux/xarray.h:455:\t entry = xa_find_after(xa, \u0026index, last, XA_PRESENT))\ninclude/linux/xarray.h-456-\n--\ninclude/linux/xarray.h-532-\tfor (index = 0, entry = xa_find(xa, \u0026index, ULONG_MAX, filter); \\\ninclude/linux/xarray.h:533:\t entry; entry = xa_find_after(xa, \u0026index, ULONG_MAX, filter))\ninclude/linux/xarray.h-534-\n--\nlib/xarray.c=2213=static bool xas_sibling(struct xa_state xas)\n--\nlib/xarray.c-2225-/*\nlib/xarray.c:2226: xa_find_after() - Search the XArray for a present entry.\nlib/xarray.c-2227- * @xa: XArray.\n--\nlib/xarray.c-2241- /\nlib/xarray.c:2242:void xa_find_after(struct xarray xa, unsigned long indexp,\nlib/xarray.c-2243-\t\t\tunsigned long max, xa_mark_t filter)\n--\nlib/xarray.c-2270-}\nlib/xarray.c:2271:EXPORT_SYMBOL(xa_find_after);\nlib/xarray.c-2272-\n" }
5/2	2026/11/03 20:01	llm	patch-evaluator	5m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 12764 output: 52 thoughts: 1950 Thoughts: Analysis of Memcg and Shrinker Code Changes Okay, so I'm looking at this patch and immediately, my spidey-sense is tingling. Diving into `mm/shrinker.c` and `mm/list_lru.c`, it's clear this touches critical areas: memcg and slab shrinker handling. This is right in the heart of memory management, which means it's absolutely reachable in standard QEMU setups – Cgroups, memory reclamation, slab shrinkers, and `list_lru` are all active during pretty much any memory pressure or filesystem operation. Good, good, we've got a reachable target. Then I see it: `WARN_ON_ONCE(!unit)` in `set_shrinker_bit`. My ears perked up. This is a classic potential race condition or use-after-free scenario. What if a shrinker bit is set before the shrinker unit is fully allocated? Or during some reparenting madness? Thinking about it, the `reparent_shrinker_deferred` function just jumps out screaming "potential bug!". If `parent_unit` is NULL, the deferred count gets dropped. Now what about that whole `root_mem_cgroup` setup? Doesn't the root already have those shrinker units preallocated? But what if the parent isn't root, is an intermediate cgroup? If an intermediate cgroup never had objects of that shrinker, `parent_unit` is NULL! Deferred count gone. It feels like this is screaming for a race condition, leak, or locking issue. Also, I see `__memcg_list_lru_alloc` has a check on `css_is_dying` and can skip `memcg_shrinker_unit_alloc`. What if a `set_shrinker_bit` is called on a dying css after that? Triggering the `WARN_ON_ONCE`. This screams "syzkaller candidate." New `WARN_ON_ONCE`! Race conditions! Leaks! It's all there. Alright, let's apply the fuzzing rules. First, reachability is key. This code is reachable – we're good. Second, these are new or modified assertions in reachable code. Definitely worth fuzzing! It's definitely worth fuzzing given it's memory management, locking, and data structures. So, let's nail down what to focus on. Let's see: `include/linux/memcontrol.h`, `include/linux/shrinker.h`, `mm/list_lru.c`, `mm/memcontrol.c`, and `mm/shrinker.c` have all been touched. Now let's check the function level: It looks like a bunch of static inline and static functions have been changed, but also functions like: `free_shrinker_info`, `alloc_shrinker_info`, `memcg_shrinker_unit_alloc`, `set_shrinker_bit`, and `reparent_shrinker_deferred`. I need to check how they're called. We need to focus the fuzzing on those entry points. I will use `grepper` to see where `alloc_shrinker_info`, `free_shrinker_info`, `memcg_shrinker_unit_alloc`, `set_shrinker_bit`, `reparent_shrinker_deferred`, `shrink_slab_memcg` or `__memcg_list_lru_alloc` are called.
6/2	2026/11/03 20:07	tool	grepper	0m Args: { "Expression": "memcg_shrinker_unit_alloc\|reparent_shrinker_deferred\|free_shrinker_info\|alloc_shrinker_info\|set_shrinker_bit" } Results: { "Output": "include/linux/memcontrol.h=1721=void shrinker_unit_cache_init(void);\ninclude/linux/memcontrol.h:1722:int alloc_shrinker_info(struct mem_cgroup memcg);\ninclude/linux/memcontrol.h:1723:int memcg_shrinker_unit_alloc(struct mem_cgroup memcg, int shrinker_id,\ninclude/linux/memcontrol.h-1724-\t\t\t gfp_t gfp);\ninclude/linux/memcontrol.h:1725:void free_shrinker_info(struct mem_cgroup memcg);\ninclude/linux/memcontrol.h:1726:void set_shrinker_bit(struct mem_cgroup memcg, int nid, int shrinker_id);\ninclude/linux/memcontrol.h:1727:void reparent_shrinker_deferred(struct mem_cgroup memcg);\ninclude/linux/memcontrol.h-1728-\n--\ninclude/linux/memcontrol.h=1755=static inline void mem_cgroup_sk_uncharge(const struct sock sk,\n--\ninclude/linux/memcontrol.h-1759-\ninclude/linux/memcontrol.h:1760:static inline void set_shrinker_bit(struct mem_cgroup memcg,\ninclude/linux/memcontrol.h-1761-\t\t\t\t int nid, int shrinker_id)\n--\nmm/list_lru.c=190=bool __list_lru_add(struct list_lru lru, struct list_lru_one l,\n--\nmm/list_lru.c-201-\t\tif (!l-\u003enr_items++)\nmm/list_lru.c:202:\t\t\tset_shrinker_bit(memcg, nid, lru_shrinker_id(lru));\nmm/list_lru.c-203-\t\tatomic_long_inc(\u0026lru-\u003enode[nid].nr_items);\n--\nmm/list_lru.c=501=static void memcg_reparent_list_lru_one(struct list_lru lru, int nid,\n--\nmm/list_lru.c-515-\t\tdst-\u003enr_items += src-\u003enr_items;\nmm/list_lru.c:516:\t\tset_shrinker_bit(dst_memcg, nid, lru_shrinker_id(lru));\nmm/list_lru.c-517-\t}\n--\nmm/list_lru.c=574=static int __memcg_list_lru_alloc(struct mem_cgroup memcg,\n--\nmm/list_lru.c-600-\t\tif (!css_is_dying(\u0026pos-\u003ecss) \u0026\u0026\nmm/list_lru.c:601:\t\t memcg_shrinker_unit_alloc(pos, lru_shrinker_id(lru), gfp)) {\nmm/list_lru.c-602-\t\t\tkfree(mlru);\n--\nmm/list_lru.c=670=int __list_lru_init(struct list_lru lru, bool memcg_aware, struct shrinker shrinker)\n--\nmm/list_lru.c-680-\t cgroup.memory=nokmem), its id is not valid. Don't let\nmm/list_lru.c:681:\t * set_shrinker_bit() act on it, nor on a list that is not\nmm/list_lru.c-682-\t * per-memcg: such a list gets no shrinker units.\n--\nmm/memcontrol.c=4381=static int mem_cgroup_css_online(struct cgroup_subsys_state css)\n--\nmm/memcontrol.c-4388-\nmm/memcontrol.c:4389:\tif (alloc_shrinker_info(memcg))\nmm/memcontrol.c-4390-\t\tgoto offline_kmem;\n--\nmm/memcontrol.c-4446-\t}\nmm/memcontrol.c:4447:\tfree_shrinker_info(memcg);\nmm/memcontrol.c-4448-offline_kmem:\n--\nmm/memcontrol.c=4454=static void mem_cgroup_css_offline(struct cgroup_subsys_state css)\n--\nmm/memcontrol.c-4471-\tmemcg_reparent_objcgs(memcg);\nmm/memcontrol.c:4472:\treparent_shrinker_deferred(memcg);\nmm/memcontrol.c-4473-\twb_memcg_offline(memcg);\n--\nmm/memcontrol.c=4489=static void mem_cgroup_css_free(struct cgroup_subsys_state css)\n--\nmm/memcontrol.c-4509-\tcancel_work_sync(\u0026memcg-\u003ehigh_work);\nmm/memcontrol.c:4510:\tfree_shrinker_info(memcg);\nmm/memcontrol.c-4511-\tmem_cgroup_free(memcg);\n--\nmm/shrinker.c=79=static int shrinker_units_install(struct mem_cgroup memcg, int start, int end)\n--\nmm/shrinker.c-94-\nmm/shrinker.c:95:void free_shrinker_info(struct mem_cgroup memcg)\nmm/shrinker.c-96-{\n--\nmm/shrinker.c-113- /\nmm/shrinker.c:114:int alloc_shrinker_info(struct mem_cgroup memcg)\nmm/shrinker.c-115-{\n--\nmm/shrinker.c-124-\tif (ret)\nmm/shrinker.c:125:\t\tfree_shrinker_info(memcg);\nmm/shrinker.c-126-\tmutex_unlock(\u0026shrinker_mutex);\n--\nmm/shrinker.c=131=static int expand_shrinker_info(int new_id)\n--\nmm/shrinker.c-147-\nmm/shrinker.c:148:void set_shrinker_bit(struct mem_cgroup memcg, int nid, int shrinker_id)\nmm/shrinker.c-149-{\n--\nmm/shrinker.c=216=static long add_nr_deferred_memcg(long nr, int nid, struct shrinker shrinker,\n--\nmm/shrinker.c-231- /\nmm/shrinker.c:232:int memcg_shrinker_unit_alloc(struct mem_cgroup memcg, int shrinker_id,\nmm/shrinker.c-233-\t\t\t gfp_t gfp)\n--\nmm/shrinker.c-250-\nmm/shrinker.c:251:void reparent_shrinker_deferred(struct mem_cgroup memcg)\nmm/shrinker.c-252-{\n--\nmm/shrinker.c=432=static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,\n--\nmm/shrinker.c-492-\t\t\t\t * The memory barrier here pairs with the barrier in\nmm/shrinker.c:493:\t\t\t\t * set_shrinker_bit():\nmm/shrinker.c-494-\t\t\t\t *\n--\nmm/shrinker.c-504-\t\t\t\telse\nmm/shrinker.c:505:\t\t\t\t\tset_shrinker_bit(memcg, nid, shrinker_id);\nmm/shrinker.c-506-\t\t\t}\n" }
7/2	2026/11/03 20:07	llm	patch-evaluator	6m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 17458 output: 29 thoughts: 81 Thoughts: Okay, let's break this down. Slab Shrinker Investigations Right, so I'm diving into the slab shrinker mechanism here. I need to understand the lifecycle of these units and how memory is managed. My initial focus is on the key functions involved in the allocation and deallocation process. I'm seeing a sequence of functions that, at a glance, appear to be related to memory shrinker bit setting, memcg unit allocation, potentially deferred reparenting within the shrinker, freeing shrinker information structures, and the initial allocation of those same structures, as well as the initialization of a list LRU. Let's start by mapping them: `set_shrinker_bit`, `memcg_shrinker_unit_alloc`, `reparent_shrinker_deferred`, `free_shrinker_info`, `alloc_shrinker_info`, and `__list_lru_init`. My immediate question is, how does this all relate to actually shrinking the slab cache within a memcg? I need to trace the calling path. Now, the key function to watch is `shrink_slab_memcg`, as I suspect that it is where the work actually gets done. I need to find its callers.
8/2	2026/11/03 20:13	tool	grepper	0m Args: { "Expression": "shrink_slab_memcg", "PathPrefixes": [ "mm/" ] } Results: { "Output": "mm/shrinker.c=332=static unsigned long do_shrink_slab(struct shrink_control shrinkctl,\n--\nmm/shrinker.c-431-#ifdef CONFIG_MEMCG\nmm/shrinker.c:432:static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,\nmm/shrinker.c-433-\t\t\tstruct mem_cgroup memcg, int priority)\n--\nmm/shrinker.c-494-\t\t\t\t \nmm/shrinker.c:495:\t\t\t\t list_lru_add() shrink_slab_memcg()\nmm/shrinker.c-496-\t\t\t\t * list_add_tail() clear_bit()\n--\nmm/shrinker.c-514-#else /* !CONFIG_MEMCG /\nmm/shrinker.c:515:static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,\nmm/shrinker.c-516-\t\t\tstruct mem_cgroup memcg, int priority)\n--\nmm/shrinker.c=542=unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,\n--\nmm/shrinker.c-555-\tif (!mem_cgroup_disabled() \u0026\u0026 !mem_cgroup_is_root(memcg))\nmm/shrinker.c:556:\t\treturn shrink_slab_memcg(gfp_mask, nid, memcg, priority);\nmm/shrinker.c-557-\n" }
9/2	2026/11/03 20:13	llm	patch-evaluator	4m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 18222 output: 42 thoughts: 745 Thoughts: Focusing on the Relevant Symbols Okay, so `shrink_slab` calls `shrink_slab_memcg`, and initially, I was going down the wrong path thinking `shrink_slab` itself might be the focus. But, hang on. `shrink_slab` is called during memory reclaim, and that's a ubiquitous function. Memory reclaim is called by so many other components in the system; it's not specific to the actual changes. The guidelines for FocusSymbols specifically tell me to avoid these hot-path, general functions like reclaimers and allocators. Right, so `shrink_slab` is out. Now, let me shift gears. The real question is: What are the specific functions that this patch is touching directly? The guideline says to target specific feature logic and entrypoints. Here's the list I've identified from the code: 1. `memcg_shrinker_unit_alloc` (new, good!) 2. `reparent_shrinker_deferred` 3. `set_shrinker_bit` 4. `free_shrinker_info` 5. `alloc_shrinker_info` 6. `__list_lru_init` That's a much more targeted set. Now, I have to be careful about static functions. I see `shrink_slab_memcg` is static and called by the less-targeted `shrink_slab`. The compiler might or might not inline that; it depends on the build. There are a few other static functions in `mm/shrinker.c` that are also modified, such as `expand_shrinker_info`, `xchg_nr_deferred_memcg`, `add_nr_deferred_memcg`, `shrinker_unit_install`, `shrinker_units_install`, `shrinker_unit_get`. So, the key is to determine if those are inlined. `set_shrinker_bit`, `memcg_shrinker_unit_alloc`, `reparent_shrinker_deferred`, `alloc_shrinker_info`, `free_shrinker_info`, and `__list_lru_init` are non-static and exported. Let me also check which functions call `xchg_nr_deferred_memcg` and `add_nr_deferred_memcg` to confirm if the static function is important. I'll use grep for that.
10/2	2026/11/03 20:17	tool	grepper	0m Args: { "Expression": "xchg_nr_deferred_memcg\|add_nr_deferred_memcg", "PathPrefixes": [ "mm/" ] } Results: { "Output": "mm/shrinker.c=192=static void shrinker_memcg_remove(struct shrinker shrinker)\n--\nmm/shrinker.c-202-\nmm/shrinker.c:203:static long xchg_nr_deferred_memcg(int nid, struct shrinker shrinker,\nmm/shrinker.c-204-\t\t\t\t struct mem_cgroup memcg)\n--\nmm/shrinker.c-215-\nmm/shrinker.c:216:static long add_nr_deferred_memcg(long nr, int nid, struct shrinker shrinker,\nmm/shrinker.c-217-\t\t\t\t struct mem_cgroup memcg)\n--\nmm/shrinker.c=280=static void shrinker_memcg_remove(struct shrinker shrinker)\n--\nmm/shrinker.c-283-\nmm/shrinker.c:284:static long xchg_nr_deferred_memcg(int nid, struct shrinker shrinker,\nmm/shrinker.c-285-\t\t\t\t struct mem_cgroup memcg)\n--\nmm/shrinker.c-289-\nmm/shrinker.c:290:static long add_nr_deferred_memcg(long nr, int nid, struct shrinker shrinker,\nmm/shrinker.c-291-\t\t\t\t struct mem_cgroup memcg)\n--\nmm/shrinker.c=297=static long xchg_nr_deferred(struct shrinker shrinker,\n--\nmm/shrinker.c-306-\t (shrinker-\u003eflags \u0026 SHRINKER_MEMCG_AWARE))\nmm/shrinker.c:307:\t\treturn xchg_nr_deferred_memcg(nid, shrinker,\nmm/shrinker.c-308-\t\t\t\t\t sc-\u003ememcg);\n--\nmm/shrinker.c=314=static long add_nr_deferred(long nr, struct shrinker shrinker,\n--\nmm/shrinker.c-323-\t (shrinker-\u003eflags \u0026 SHRINKER_MEMCG_AWARE))\nmm/shrinker.c:324:\t\treturn add_nr_deferred_memcg(nr, nid, shrinker,\nmm/shrinker.c-325-\t\t\t\t\t sc-\u003ememcg);\n" }
11/2	2026/11/03 20:17	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 20127 output: 28 thoughts: 16 Thoughts: Okay, let's dive into this code. Investigating the `do_shrink_slab` Callers Alright, my immediate thought is, before I even start digging into the intricacies of `do_shrink_slab` itself, I need to understand its context. Where is this function being invoked? Knowing the call sites will give me crucial clues about its purpose and how it fits into the larger picture of the slab allocator. I need to trace back from that function definition and see which other parts of the system are actually using this `do_shrink_slab` function. Understanding the calling contexts will give me the best insight into its actual function.
12/2	2026/11/03 20:17	tool	grepper	0m Args: { "Expression": "do_shrink_slab", "PathPrefixes": [ "mm/" ] } Results: { "Output": "mm/shrinker.c=314=static long add_nr_deferred(long nr, struct shrinker shrinker,\n--\nmm/shrinker.c-331-\nmm/shrinker.c:332:static unsigned long do_shrink_slab(struct shrink_control shrinkctl,\nmm/shrinker.c-333-\t\t\t\t struct shrinker shrinker, int priority)\n--\nmm/shrinker.c=432=static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,\n--\nmm/shrinker.c-446-\t a reference to the memcg, so the units found by xa_for_each() stay\nmm/shrinker.c:447:\t * valid without the RCU lock and do_shrink_slab() may sleep.\nmm/shrinker.c-448-\t \n--\nmm/shrinker.c-481-\nmm/shrinker.c:482:\t\t\tret = do_shrink_slab(\u0026sc, shrinker, priority);\nmm/shrinker.c-483-\t\t\tif (ret == SHRINK_EMPTY) {\n--\nmm/shrinker.c-497-\t\t\t\t \u003cMB\u003e \u003cMB\u003e\nmm/shrinker.c:498:\t\t\t\t * set_bit() do_shrink_slab()\nmm/shrinker.c-499-\t\t\t\t /\nmm/shrinker.c-500-\t\t\t\tsmp_mb__after_atomic();\nmm/shrinker.c:501:\t\t\t\tret = do_shrink_slab(\u0026sc, shrinker, priority);\nmm/shrinker.c-502-\t\t\t\tif (ret == SHRINK_EMPTY)\n--\nmm/shrinker.c=542=unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup memcg,\n--\nmm/shrinker.c-569-\t * then the existence of the shrinker can also be guaranteed,\nmm/shrinker.c:570:\t * so we can release the RCU lock to do do_shrink_slab() that\nmm/shrinker.c-571-\t * may sleep.\n--\nmm/shrinker.c-591-\nmm/shrinker.c:592:\t\tret = do_shrink_slab(\u0026sc, shrinker, priority);\nmm/shrinker.c-593-\t\tif (ret == SHRINK_EMPTY)\n" }
13/2	2026/11/03 20:17	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 20918 output: 53 thoughts: 57 Thoughts: Okay, let's break this down. Investigating Configuration Dependencies Alright, time to get to the core of this. I need to figure out the specific `CONFIG_` options that are enabling this particular bit of code. I'm going to start by tracing through the dependencies. My first stop is `include/linux/memcontrol.h`. This is where I'm betting the crucial definitions or declarations related to the memory control mechanisms lie. I'll be looking specifically for conditional compilation directives, the `#ifdef` blocks, that guard either `shrinker_units` or `alloc_shrinker_info`. Those will give me the key to unlocking which configuration options are relevant and, by extension, why this code is even active in the first place. This should be a quick jump.
14/2	2026/11/03 20:17	tool	grepper	0m Args: { "Expression": "CONFIG_MEMCG", "PathPrefixes": [ "mm/shrinker.c", "mm/list_lru.c", "include/linux/memcontrol.h" ] } Results: { "Output": "include/linux/memcontrol.h=62=struct mem_cgroup_reclaim_cookie {\n--\ninclude/linux/memcontrol.h-66-\ninclude/linux/memcontrol.h:67:#ifdef CONFIG_MEMCG\ninclude/linux/memcontrol.h-68-\n--\ninclude/linux/memcontrol.h=86=struct mem_cgroup_per_node {\n--\ninclude/linux/memcontrol.h-111-\tstruct mem_cgroup_reclaim_iter\titer;\ninclude/linux/memcontrol.h:112:#ifdef CONFIG_MEMCG_NMI_SAFETY_REQUIRES_ATOMIC\ninclude/linux/memcontrol.h-113-\t/* slab stats for nmi context /\n--\ninclude/linux/memcontrol.h=198=struct mem_cgroup {\n--\ninclude/linux/memcontrol.h-229-\ninclude/linux/memcontrol.h:230:#ifdef CONFIG_MEMCG_NMI_SAFETY_REQUIRES_ATOMIC\ninclude/linux/memcontrol.h-231-\t/ MEMCG_KMEM for nmi context /\n--\ninclude/linux/memcontrol.h-271-\ninclude/linux/memcontrol.h:272:#ifdef CONFIG_MEMCG_V1\ninclude/linux/memcontrol.h-273-\t/ v1 only. Not grouped: v1 is legacy, sorting it is not worth it. /\n--\ninclude/linux/memcontrol.h-308-\tint swappiness;\ninclude/linux/memcontrol.h:309:#endif / CONFIG_MEMCG_V1 /\ninclude/linux/memcontrol.h-310-\n--\ninclude/linux/memcontrol.h=361=enum page_memcg_data_flags {\n--\ninclude/linux/memcontrol.h-372-\ninclude/linux/memcontrol.h:373:#else / CONFIG_MEMCG /\ninclude/linux/memcontrol.h-374-\n--\ninclude/linux/memcontrol.h-377-\ninclude/linux/memcontrol.h:378:#endif / CONFIG_MEMCG /\ninclude/linux/memcontrol.h-379-\ninclude/linux/memcontrol.h=380=enum objext_flags {\n--\ninclude/linux/memcontrol.h-393-\ninclude/linux/memcontrol.h:394:#ifdef CONFIG_MEMCG\ninclude/linux/memcontrol.h-395-/\n--\ninclude/linux/memcontrol.h=1081=extern int mem_cgroup_init(void);\ninclude/linux/memcontrol.h:1082:#else /* CONFIG_MEMCG /\ninclude/linux/memcontrol.h-1083-\n--\ninclude/linux/memcontrol.h=1517=static inline int mem_cgroup_init(void) { return 0; }\ninclude/linux/memcontrol.h:1518:#endif / CONFIG_MEMCG /\ninclude/linux/memcontrol.h-1519-\n--\ninclude/linux/memcontrol.h=1539=static inline struct lruvec lruvec_live_lock_irq(struct lruvec lruvec)\ninclude/linux/memcontrol.h-1540-{\ninclude/linux/memcontrol.h:1541:#ifdef CONFIG_MEMCG\ninclude/linux/memcontrol.h-1542-\tstruct pglist_data pgdat = lruvec_pgdat(lruvec);\n--\ninclude/linux/memcontrol.h=1674=struct sock;\ninclude/linux/memcontrol.h:1675:#ifdef CONFIG_MEMCG\ninclude/linux/memcontrol.h-1676-extern struct static_key_false memcg_sockets_enabled_key;\n--\ninclude/linux/memcontrol.h=1765=static inline int shrinker_id(struct shrinker shrinker)\n--\ninclude/linux/memcontrol.h-1770-\ninclude/linux/memcontrol.h:1771:#ifdef CONFIG_MEMCG\ninclude/linux/memcontrol.h-1772-bool mem_cgroup_kmem_disabled(void);\n--\ninclude/linux/memcontrol.h=1933=static inline bool memcg_is_dying(struct mem_cgroup memcg)\n--\ninclude/linux/memcontrol.h-1936-}\ninclude/linux/memcontrol.h:1937:#endif /* CONFIG_MEMCG /\ninclude/linux/memcontrol.h-1938-\ninclude/linux/memcontrol.h:1939:#if defined(CONFIG_MEMCG) \u0026\u0026 defined(CONFIG_LRU_GEN)\ninclude/linux/memcontrol.h-1940-void mem_cgroup_calculate_protection_path(struct mem_cgroup root,\n--\ninclude/linux/memcontrol.h=1943=static inline void mem_cgroup_calculate_protection_path(struct mem_cgroup root,\n--\ninclude/linux/memcontrol.h-1948-\ninclude/linux/memcontrol.h:1949:#if defined(CONFIG_MEMCG) \u0026\u0026 defined(CONFIG_ZSWAP)\ninclude/linux/memcontrol.h-1950-bool obj_cgroup_may_zswap(struct obj_cgroup objcg);\n--\ninclude/linux/memcontrol.h=1967=static inline bool mem_cgroup_zswap_writeback_enabled(const struct mem_cgroup memcg)\n--\ninclude/linux/memcontrol.h-1976-\ninclude/linux/memcontrol.h:1977:#ifdef CONFIG_MEMCG_V1\ninclude/linux/memcontrol.h-1978-bool mem_cgroup_oom_synchronize(bool wait);\n--\ninclude/linux/memcontrol.h=1991=static inline void mem_cgroup_exit_user_fault(void)\n--\ninclude/linux/memcontrol.h-1996-\ninclude/linux/memcontrol.h:1997:#else / CONFIG_MEMCG_V1 /\ninclude/linux/memcontrol.h-1998-static inline bool task_in_memcg_oom(const struct task_struct p)\n--\ninclude/linux/memcontrol.h=2012=static inline void mem_cgroup_exit_user_fault(void)\n--\ninclude/linux/memcontrol.h-2015-\ninclude/linux/memcontrol.h:2016:#endif /* CONFIG_MEMCG_V1 /\ninclude/linux/memcontrol.h-2017-\ninclude/linux/memcontrol.h:2018:#if defined(CONFIG_MEMCG_V1) \u0026\u0026 defined(CONFIG_SWAP)\ninclude/linux/memcontrol.h-2019-\n--\nmm/list_lru.c=29=static inline void unlock_list_lru(struct list_lru_one l, bool irq_off,\n--\nmm/list_lru.c-39-\nmm/list_lru.c:40:#ifdef CONFIG_MEMCG\nmm/list_lru.c-41-static LIST_HEAD(memcg_list_lrus);\n--\nmm/list_lru.c=141=lock_list_lru_of_memcg(struct list_lru lru, int nid,\n--\nmm/list_lru.c-150-}\nmm/list_lru.c:151:#endif / CONFIG_MEMCG /\nmm/list_lru.c-152-\n--\nmm/list_lru.c=413=unsigned long list_lru_walk_node(struct list_lru lru, int nid,\n--\nmm/list_lru.c-421-\nmm/list_lru.c:422:#ifdef CONFIG_MEMCG\nmm/list_lru.c-423-\tif (nr_to_walk \u003e 0 \u0026\u0026 list_lru_memcg_aware(lru)) {\n--\nmm/list_lru.c=451=static void init_one_lru(struct list_lru lru, struct list_lru_one l)\n--\nmm/list_lru.c-461-\nmm/list_lru.c:462:#ifdef CONFIG_MEMCG\nmm/list_lru.c-463-static struct list_lru_memcg memcg_init_list_lru_one(struct list_lru lru, gfp_t gfp)\n--\nmm/list_lru.c=665=static void memcg_destroy_list_lru(struct list_lru lru)\n--\nmm/list_lru.c-667-}\nmm/list_lru.c:668:#endif /* CONFIG_MEMCG /\nmm/list_lru.c-669-\nmm/list_lru.c=670=int __list_lru_init(struct list_lru lru, bool memcg_aware, struct shrinker shrinker)\n--\nmm/list_lru.c-673-\nmm/list_lru.c:674:#ifdef CONFIG_MEMCG\nmm/list_lru.c-675-\tif (mem_cgroup_disabled() \|\| mem_cgroup_kmem_disabled())\n--\nmm/list_lru.c=705=void list_lru_destroy(struct list_lru lru)\n--\nmm/list_lru.c-716-\nmm/list_lru.c:717:#ifdef CONFIG_MEMCG\nmm/list_lru.c-718-\tlru-\u003eshrinker_id = -1;\n--\nmm/shrinker.c=11=DEFINE_MUTEX(shrinker_mutex);\nmm/shrinker.c-12-\nmm/shrinker.c:13:#ifdef CONFIG_MEMCG\nmm/shrinker.c-14-static int shrinker_nr_max;\n--\nmm/shrinker.c=290=static long add_nr_deferred_memcg(long nr, int nid, struct shrinker shrinker,\n--\nmm/shrinker.c-294-}\nmm/shrinker.c:295:#endif / CONFIG_MEMCG /\nmm/shrinker.c-296-\n--\nmm/shrinker.c=332=static unsigned long do_shrink_slab(struct shrink_control shrinkctl,\n--\nmm/shrinker.c-430-\nmm/shrinker.c:431:#ifdef CONFIG_MEMCG\nmm/shrinker.c-432-static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,\n--\nmm/shrinker.c-513-}\nmm/shrinker.c:514:#else /* !CONFIG_MEMCG /\nmm/shrinker.c-515-static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,\n--\nmm/shrinker.c-519-}\nmm/shrinker.c:520:#endif / CONFIG_MEMCG /\nmm/shrinker.c-521-\n--\nmm/shrinker.c=606=struct shrinker shrinker_alloc(unsigned int flags, const char fmt, ...)\n--\nmm/shrinker.c-644-\t - non-memcg-aware shrinkers\nmm/shrinker.c:645:\t * - !CONFIG_MEMCG\nmm/shrinker.c-646-\t * - memcg is disabled by kernel command line\n" }
15/2	2026/11/03 20:17	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 24073 output: 37 thoughts: 27 Thoughts: Here's my thought process, summarized as you requested: Investigating the MEMCG Kconfig Definition Okay, time to dig into the kernel configuration. I need to understand how `MEMCG` is defined, especially since I'm seeing something unexpected in its behavior. The most logical place to start is the Kconfig files. I'm going to jump into the `init/Kconfig` directory first. That's usually where the top-level options reside, and `MEMCG` is fundamental enough that it likely has a general definition there. If it's not there, or if the definition is more granular or specific to memory management details, I'll switch over to `mm/Kconfig`. That's the other obvious spot for such a critical memory-related configuration option. This should give me the foundation I need to properly interpret how it affects the system.
16/2	2026/11/03 20:18	tool	grepper	0m Args: { "Expression": "config MEMCG\\b", "PathPrefixes": [ "init/Kconfig", "mm/Kconfig" ] } Results: { "Output": "init/Kconfig=871=config CGROUP_FAVOR_DYNMODS\n--\ninit/Kconfig-880-\ninit/Kconfig:881:config MEMCG\ninit/Kconfig-882-\tbool \"Memory controller\"\n" }
17/2	2026/11/03 20:18	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 24396 output: 32 thoughts: 17 Thoughts: Okay, let's dive into this. Here's my thought process on the matter: Navigating the Kernel Configuration Landscape Right, I need to understand this aspect of the kernel configuration. I'm going to take a look at the `init/Kconfig` file, specifically around line 881. It seems like that area likely holds the relevant configuration option or a related definition I'm interested in. I'm hoping to get a clearer picture of how this feature is defined and handled within the build system. Let's see what Kconfig has to say.
18/2	2026/11/03 20:18	tool	read-file	0m Args: { "File": "init/Kconfig", "FirstLine": 880, "LineCount": 20 } Results: { "Contents": " 880:\t\n 881:\tconfig MEMCG\n 882:\t\tbool \"Memory controller\"\n 883:\t\tselect PAGE_COUNTER\n 884:\t\tselect EVENTFD\n 885:\t\tselect SLAB_OBJ_EXT\n 886:\t\tselect VM_EVENT_COUNTERS\n 887:\t\thelp\n 888:\t\t Provides control over the memory footprint of tasks in a cgroup.\n 889:\t\n 890:\tconfig MEMCG_NMI_UNSAFE\n 891:\t\tbool\n 892:\t\tdepends on MEMCG\n 893:\t\tdepends on HAVE_NMI\n 894:\t\tdepends on !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS \u0026\u0026 !ARCH_HAVE_NMI_SAFE_CMPXCHG\n 895:\t\tdefault y\n 896:\t\n 897:\tconfig MEMCG_NMI_SAFETY_REQUIRES_ATOMIC\n 898:\t\tbool\n 899:\t\tdepends on MEMCG\n" }
19/2	2026/11/03 20:18	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 24839 output: 32 thoughts: 34 Thoughts: Here's my take on the thought process: Diving into the Kernel Configuration for Memory Control Groups Okay, so I need to find where the `MEMCG` configuration option lives in the kernel. I already know it's related to control groups, so logically, I should start by looking under `menuconfig CGROUPS`. That's the most likely place to start. Now, let's get specific. I seem to recall something about it being near the beginning of the cgroup options in the `init/Kconfig` file. Specifically, lines 860-880 sound like a good starting point. I should be able to quickly navigate to that section and confirm my assumption or adjust my search if necessary. This should give me the base I'm looking for to understand how to control `MEMCG` functionality.
20/2	2026/11/03 20:18	tool	read-file	0m Args: { "File": "init/Kconfig", "FirstLine": 860, "LineCount": 25 } Results: { "Contents": " 860:\t\t\t- Documentation/scheduler/sched-design-CFS.rst\t(CFS)\n 861:\t\t\t- Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation\n 862:\t\t\t\t\t\t and resource control)\n 863:\t\n 864:\t\t Say N if unsure.\n 865:\t\n 866:\tif CGROUPS\n 867:\t\n 868:\tconfig PAGE_COUNTER\n 869:\t\tbool\n 870:\t\n 871:\tconfig CGROUP_FAVOR_DYNMODS\n 872:\t\tbool \"Favor dynamic modification latency reduction by default\"\n 873:\t\thelp\n 874:\t\t This option enables the \"favordynmods\" mount option by default\n 875:\t\t which reduces the latencies of dynamic cgroup modifications such\n 876:\t\t as task migrations and controller on/offs at the cost of making\n 877:\t\t hot path operations such as forks and exits more expensive.\n 878:\t\n 879:\t\t Say N if unsure.\n 880:\t\n 881:\tconfig MEMCG\n 882:\t\tbool \"Memory controller\"\n 883:\t\tselect PAGE_COUNTER\n 884:\t\tselect EVENTFD\n" }
21/2	2026/11/03 20:18	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 25424 output: 31 thoughts: 82 Thoughts: Okay, here's my breakdown of what I'm looking at: Kernel Configuration Dependencies for Memory Management Alright, so I'm diving into this kernel configuration space and first off, I'm noting that `CGROUPS` and `MEMCG` are baseline, almost assumed to be required. Now, I need to make sure I'm not missing anything crucial. I'm going to quickly check for any other dependencies floating around. Given that `CONFIG_MEMCG` is, as I suspected, nested under `if CGROUPS`, so that's expected behavior, and good to confirm. But, I need to make sure I haven't missed anything specific to the shrinker or the `list_lru` mechanisms. Given the likely importance, I'm going to check the `mm/Makefile` to see if there are any makefile directives that call out needed configurations or specific objects. I suspect that anything truly essential for the core memory management stuff will be right there in that file.
22/2	2026/11/03 20:18	tool	grepper	0m Args: { "Expression": "list_lru\|shrinker", "PathPrefixes": [ "mm/Makefile" ] } Results: { "Output": "mm/Makefile=51=obj-y\t\t\t:= filemap.o mempool.o oom_kill.o fadvise.o \\\nmm/Makefile-52-\t\t\t maccess.o page-writeback.o folio-compat.o \\\nmm/Makefile:53:\t\t\t readahead.o folio.o truncate.o vmscan.o shrinker.o \\\nmm/Makefile-54-\t\t\t shmem.o util.o mmzone.o vmstat.o backing-dev.o \\\n--\nmm/Makefile-56-\t\t\t compaction.o show_mem.o \\\nmm/Makefile:57:\t\t\t interval_tree.o list_lru.o workingset.o \\\nmm/Makefile-58-\t\t\t debug.o gup.o mmap_lock.o vma_init.o char-mem.o \\\n--\nmm/Makefile=146=obj-$(CONFIG_GENERIC_IOREMAP) += ioremap.o\nmm/Makefile:147:obj-$(CONFIG_SHRINKER_DEBUG) += shrinker_debug.o\nmm/Makefile-148-obj-$(CONFIG_EXECMEM) += execmem.o\n" }
23/2	2026/11/03 20:18	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 26042 output: 37 thoughts: 132 Thoughts: Investigating Memory Management Configuration Okay, so I'm looking at `shrinker.o` and `list_lru.o` – they're part of `obj-y` in the build system. Naturally, under `CONFIG_MEMCG`, the code that deals with memory cgroups and the list_lru structures are compiled. I need to make sure I'm considering all the relevant configurations here. Let's see... what about `MEMCG_KMEM`? Does that even exist as a configuration option? I'll need to check. Okay, let's dive into `mm/list_lru.c`. I see a conditional statement there: `if (mem_cgroup_disabled() \|\| mem_cgroup_kmem_disabled())`. That looks promising. It seems `mem_cgroup_kmem_disabled()` is the key. Let's do a quick `grep` to see where else that is used to get the full picture.
24/2	2026/11/03 20:18	tool	grepper	0m Args: { "Expression": "mem_cgroup_kmem_disabled", "PathPrefixes": [ "mm/", "include/" ] } Results: { "Output": "include/linux/memcontrol.h=1765=static inline int shrinker_id(struct shrinker shrinker)\n--\ninclude/linux/memcontrol.h-1771-#ifdef CONFIG_MEMCG\ninclude/linux/memcontrol.h:1772:bool mem_cgroup_kmem_disabled(void);\ninclude/linux/memcontrol.h-1773-int __memcg_kmem_charge_page(struct page page, gfp_t gfp, int order);\n--\ninclude/linux/memcontrol.h=1857=static inline bool memcg_is_dying(struct mem_cgroup memcg)\n--\ninclude/linux/memcontrol.h-1862-#else\ninclude/linux/memcontrol.h:1863:static inline bool mem_cgroup_kmem_disabled(void)\ninclude/linux/memcontrol.h-1864-{\n--\nmm/list_lru.c=670=int __list_lru_init(struct list_lru lru, bool memcg_aware, struct shrinker shrinker)\n--\nmm/list_lru.c-674-#ifdef CONFIG_MEMCG\nmm/list_lru.c:675:\tif (mem_cgroup_disabled() \|\| mem_cgroup_kmem_disabled())\nmm/list_lru.c-676-\t\tmemcg_aware = false;\n--\nmm/memcontrol.c=133=static DEFINE_SPINLOCK(objcg_lock);\nmm/memcontrol.c-134-\nmm/memcontrol.c:135:bool mem_cgroup_kmem_disabled(void)\nmm/memcontrol.c-136-{\n--\nmm/memcontrol.c=3810=static void memcg_online_kmem(struct mem_cgroup memcg)\nmm/memcontrol.c-3811-{\nmm/memcontrol.c:3812:\tif (mem_cgroup_kmem_disabled())\nmm/memcontrol.c-3813-\t\treturn;\n--\nmm/memcontrol.c=3823=static void memcg_offline_kmem(struct mem_cgroup memcg)\n--\nmm/memcontrol.c-3826-\nmm/memcontrol.c:3827:\tif (mem_cgroup_kmem_disabled())\nmm/memcontrol.c-3828-\t\treturn;\n--\nmm/percpu-internal.h=90=static inline bool need_pcpuobj_ext(void)\n--\nmm/percpu-internal.h-93-\t\treturn true;\nmm/percpu-internal.h:94:\tif (!mem_cgroup_kmem_disabled())\nmm/percpu-internal.h-95-\t\treturn true;\n--\nmm/percpu-internal.h=153=static inline size_t pcpu_obj_full_size(size_t size)\n--\nmm/percpu-internal.h-157-#ifdef CONFIG_MEMCG\nmm/percpu-internal.h:158:\tif (!mem_cgroup_kmem_disabled())\nmm/percpu-internal.h-159-\t\textra_size += size / PCPU_MIN_ALLOC_SIZE sizeof(struct obj_cgroup );\n--\nmm/shrinker.c=166=static int shrinker_memcg_alloc(struct shrinker shrinker)\n--\nmm/shrinker.c-173-\t\treturn -ENOSYS;\nmm/shrinker.c:174:\tif (mem_cgroup_kmem_disabled() \u0026\u0026 !(shrinker-\u003eflags \u0026 SHRINKER_NONSLAB))\nmm/shrinker.c-175-\t\treturn -ENOSYS;\n--\nmm/slab.h=574=static inline bool need_kmalloc_no_objext(void)\n--\nmm/slab.h-578-\nmm/slab.h:579:\tif (!mem_cgroup_kmem_disabled() \u0026\u0026\nmm/slab.h-580-\t\t\t(KMALLOC_NORMAL == KMALLOC_RECLAIM))\n--\nmm/slab_common.c=318=struct kmem_cache __kmem_cache_create_args(const char name,\n--\nmm/slab_common.c-365-\t /\nmm/slab_common.c:366:\tif (!mem_cgroup_kmem_disabled())\nmm/slab_common.c-367-\t\tflags \|= SLAB_MAY_ACCOUNT;\n--\nmm/slab_common.c=972=new_kmalloc_cache(int idx, enum kmalloc_cache_type type)\n--\nmm/slab_common.c-981-\t} else if (IS_ENABLED(CONFIG_MEMCG) \u0026\u0026 (type == KMALLOC_CGROUP)) {\nmm/slab_common.c:982:\t\tif (mem_cgroup_kmem_disabled()) {\nmm/slab_common.c-983-\t\t\tkmalloc_caches[type][idx] = kmalloc_caches[KMALLOC_NORMAL][idx];\n--\nmm/slab_common.c-1010-\t /\nmm/slab_common.c:1011:\tif (!mem_cgroup_kmem_disabled()) {\nmm/slab_common.c-1012-\t\tif (type == KMALLOC_NORMAL \u0026\u0026 KMALLOC_RECLAIM != KMALLOC_NORMAL)\n" }
25/2	2026/11/03 20:18	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 27770 output: 29 thoughts: 512 Thoughts: Analyzing MemCG Shrinker Unit Allocation Changes Alright, let's break this down. The code involves changes related to `mem_cgroup_kmem_disabled()`, which is a runtime check. It looks like it's enabled by default, given `CONFIG_MEMCG` is enabled, which in turn means `CGROUPS` is also. That's good to know for context. Now, let's determine the relevant FocusSymbols. I need to be precise here. I have to avoid the common, ubiquitous functions – things like generic allocators and deallocators, page fault handlers, and core synchronization primitives. Instead, I need to pinpoint the specific feature logic and entry points. And, a note to myself, I need to remember the inline functions in headers, and concentrate on the non-static functions in the `.c` files that use them, to avoid those ubiquitous wrappers. So, here's what I've identified as the functions directly affected or added by this patch: * `memcg_shrinker_unit_alloc`: This is new – a non-static function in `mm/shrinker.c`. That's important; it's specific to allocating shrinker units for a memcg. I'll flag it. * `set_shrinker_bit`: This is also non-static in `mm/shrinker.c`. It's been rewritten to use an xarray, which is a key structural change. The added `WARN_ON_ONCE(!unit)` is an interesting assertion too; I should probably keep an eye on how it triggers. * `reparent_shrinker_deferred`: Again, non-static, rewritten for xarray in `mm/shrinker.c`. Another direct implementation change. * `alloc_shrinker_info`: This one in `mm/shrinker.c` is rewritten too, and crucial; it installs units on the root memcg. I'll need to think about the implications of that for the overall memcg structure. * `free_shrinker_info`: And, also in `mm/shrinker.c`, it's rewritten to handle freeing units from the xarray. This is directly related to the allocation. * `__list_lru_init`: This in `mm/list_lru.c` has its logic modified for shrinker ID assignment. That's a relatively focused change, and relevant. * `shrink_slab`: This calls `shrink_slab_memcg`, which was heavily refactored from an RCU array to an `xa_for_each`. Hmm, is `shrink_slab` non-ubiquitous? I'll need to check the callers of `shrink_slab` to make sure it's not a generic function used everywhere. That seems important, so I will prioritize that.
26/2	2026/11/03 20:18	tool	grepper	0m Args: { "Expression": "\\bshrink_slab\\(", "PathPrefixes": [ "mm/" ] } Results: { "Output": "mm/internal.h=1421=static inline bool pte_needs_soft_dirty_wp(struct vm_area_struct vma, pte_t pte)\n--\nmm/internal.h-1426-/ shrinker related functions /\nmm/internal.h:1427:unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup memcg,\nmm/internal.h-1428-\t\t\t int priority);\n--\nmm/page_isolation.c=173=static int set_migratetype_isolate(struct page page, enum pb_isolate_mode mode,\n--\nmm/page_isolation.c-192-\t\t/\nmm/page_isolation.c:193:\t\t * FIXME: Now, memory hotplug doesn't call shrink_slab() by\nmm/page_isolation.c-194-\t\t * itself. We just check MOVABLE pages.\n--\nmm/shrinker.c=148=void set_shrinker_bit(struct mem_cgroup memcg, int nid, int shrinker_id)\n--\nmm/shrinker.c-158-\nmm/shrinker.c:159:\t/ Pairs with smp mb in shrink_slab() /\nmm/shrinker.c-160-\tsmp_mb__before_atomic();\n--\nmm/shrinker.c=515=static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,\n--\nmm/shrinker.c-541- /\nmm/shrinker.c:542:unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup memcg,\nmm/shrinker.c-543-\t\t\t int priority)\n--\nmm/vmscan.c=481=static unsigned long drop_slab_node(int nid)\n--\nmm/vmscan.c-487-\tdo {\nmm/vmscan.c:488:\t\tfreed += shrink_slab(GFP_KERNEL, nid, memcg, 0);\nmm/vmscan.c-489-\t} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);\n--\nmm/vmscan.c=5292=static int shrink_one(struct lruvec lruvec, struct scan_control sc)\n--\nmm/vmscan.c-5319-\nmm/vmscan.c:5320:\tshrink_slab(sc-\u003egfp_mask, pgdat-\u003enode_id, memcg, sc-\u003epriority);\nmm/vmscan.c-5321-\n--\nmm/vmscan.c=6378=static void shrink_node_memcgs(pg_data_t pgdat, struct scan_control *sc)\n--\nmm/vmscan.c-6439-\nmm/vmscan.c:6440:\t\tshrink_slab(sc-\u003egfp_mask, pgdat-\u003enode_id, memcg,\nmm/vmscan.c-6441-\t\t\t sc-\u003epriority);\n" }
27/2	2026/11/03 20:18	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 29699 output: 39 thoughts: 400 Thoughts: Analyzing Slab Reclaim and Related Functions Okay, so I'm digging into how slab shrinking works, specifically during reclaim, both triggered by `drop_caches` and the kernel's own memory management. My initial thought was whether `shrink_slab` or `shrink_slab_memcg` would be the best FocusSymbol for what I'm looking at. `shrink_slab` is the non-static entry point, but let's double-check how things are called. The key thing is `shrink_slab_memcg` is only called by `shrink_slab`. Given the compiler optimization, the static nature shouldn't matter, though let's confirm: ah, it is static! I need to decide which function to target. Should it be just `shrink_slab`, or should I include both? It's probably better to go with just `shrink_slab` for now. But wait, let's zoom out and consider all the functions that were changed related to this: besides the ones related to `shrink_slab`, I need to look at: * `memcg_shrinker_unit_alloc` * `set_shrinker_bit` * `reparent_shrinker_deferred` * `alloc_shrinker_info` * `free_shrinker_info` * `shrink_slab` * `__list_lru_init` Now, I need to understand how these relate to each other. Specifically, I'm thinking about `memcg_shrinker_unit_alloc`. Let's see if that's called from anywhere else in `mm/list_lru.c`. Okay, `__memcg_list_lru_alloc` does call `memcg_shrinker_unit_alloc`. Then, what calls `__memcg_list_lru_alloc`? That's what I need to track down next using grepper.
28/2	2026/11/03 20:18	tool	grepper	0m Args: { "Expression": "__memcg_list_lru_alloc", "PathPrefixes": [ "mm/list_lru.c" ] } Results: { "Output": "mm/list_lru.c=566=static inline bool memcg_list_lru_allocated(struct mem_cgroup memcg,\n--\nmm/list_lru.c-573-\nmm/list_lru.c:574:static int __memcg_list_lru_alloc(struct mem_cgroup memcg,\nmm/list_lru.c-575-\t\t\t\t struct list_lru lru, gfp_t gfp)\n--\nmm/list_lru.c=629=int memcg_list_lru_alloc(struct mem_cgroup memcg, struct list_lru lru,\n--\nmm/list_lru.c-633-\t\treturn 0;\nmm/list_lru.c:634:\treturn __memcg_list_lru_alloc(memcg, lru, gfp);\nmm/list_lru.c-635-}\n--\nmm/list_lru.c=637=int folio_memcg_list_lru_alloc(struct folio folio, struct list_lru *lru,\n--\nmm/list_lru.c-655-\tmemcg = get_mem_cgroup_from_folio(folio);\nmm/list_lru.c:656:\tres = __memcg_list_lru_alloc(memcg, lru, gfp);\nmm/list_lru.c-657-\tmem_cgroup_put(memcg);\n" }
29/2	2026/11/03 20:18	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 30951 output: 224 thoughts: 972 Thoughts: Analyzing Shrirnker Unit Refactoring in Memory Management Okay, so I'm looking at this patch and my initial thought is, it looks like `__memcg_list_lru_alloc` is being called by both `memcg_list_lru_alloc` and `folio_memcg_list_lru_alloc`. I remember that `memcg_list_lru_alloc` is used by list_lru users like dcache and icache, so that's a good starting point. Now, let's take a look at `memcg_shrinker_unit_alloc`, which is a non-static function. I've got a set of focus symbols here: `memcg_shrinker_unit_alloc`, `set_shrinker_bit`, `reparent_shrinker_deferred`, `alloc_shrinker_info`, `free_shrinker_info`, `shrink_slab`, `__list_lru_init`, and `memcg_list_lru_alloc`. I need to figure out how these fit into the bigger picture. Are there other relevant functions in `mm/shrinker.c` or elsewhere? Let's check. Alright, I see these in `mm/shrinker.c`: `shrinker_alloc`, `shrinker_free`, and `shrinker_register`. Hmm, did the patch modify `shrinker_alloc` or `shrinker_free`? Nope, it didn't touch those. Instead, I'm seeing changes in: `shrinker_unit_cache_init`, `shrinker_id_to_index`, `shrinker_id_to_offset`, `calc_shrinker_id`, `shrinker_unit_get`, `shrinker_unit_install`, `shrinker_units_install`, `free_shrinker_info`, `alloc_shrinker_info`, `expand_shrinker_info`, `set_shrinker_bit`, `xchg_nr_deferred_memcg`, `add_nr_deferred_memcg`, `memcg_shrinker_unit_alloc`, `reparent_shrinker_deferred`, and `shrink_slab_memcg`. Now the big question is, are these functions reachable through something like syzkaller? The answer is yes. Syzkaller is exercising cgroups, creating, attaching tasks, allocating slab objects accounted to cgroups (like dentries and inodes), setting memory limits, dropping caches, triggering memory reclamation, and destroying cgroups. It covers all these paths: -Creating / initializing memcg: `alloc_shrinker_info`, `alloc_mem_cgroup_per_node_info` -Allocating list_lru items in memcg: `memcg_list_lru_alloc`, `__memcg_list_lru_alloc`, `memcg_shrinker_unit_alloc`, `set_shrinker_bit` -Freeing / offline memcg: `reparent_shrinker_deferred`, `free_shrinker_info` -Memory pressure / slab reclamation: `shrink_slab`, `shrink_slab_memcg` The key is that this patch is converting the shrinker info representation in `struct mem_cgroup_per_node` from an RCU array (`struct shrinker_info`) to an XArray (`struct xarray shrinker_units`). It's lazily allocating units on-demand during `memcg_shrinker_unit_alloc()` instead of upfront or expanding. And it's also adding a new `WARN_ON_ONCE(!unit)` in `set_shrinker_bit()`. This is changing the synchronization, lazy allocation, iteration using `xa_for_each()`, and deferred reparenting logic across memcg and slab shrinker subsystems. The relevant kernel configs are `MEMCG` and `CGROUPS`, which are definitely enabled. This makes total sense. I've got a concise explanation of the changes: refactoring shrinker units from an RCU flat array to a lazy per-cgroup XArray, adding runtime assertions in `set_shrinker_bit`, and updating slab reclaim and deferred reparenting paths in the core memory management. Time to call `set-results`.
30/2	2026/11/03 20:18	tool	set-results	0m Args: { "EnableConfigs": [ "MEMCG", "CGROUPS" ], "FocusSymbols": [ "memcg_shrinker_unit_alloc", "set_shrinker_bit", "reparent_shrinker_deferred", "alloc_shrinker_info", "free_shrinker_info", "shrink_slab", "__list_lru_init", "memcg_list_lru_alloc" ], "Reasoning": "The patch refactors the memcg slab shrinker tracking mechanism from a flat RCU-allocated array to a lazily-allocated XArray per nodeinfo. It alters memory reclaim iteration (shrink_slab/shrink_slab_memcg), introduces a new WARN_ON_ONCE() assertion in set_shrinker_bit(), modifies deferred reclaim reparenting, and changes list_lru allocation logic. These changes affect core memory management and are fully reachable in virtualized environments via cgroup and memory pressure workloads.", "WorthFuzzing": true } Results: { "EnableConfigs": [ "MEMCG", "CGROUPS" ], "FocusSymbols": [ "memcg_shrinker_unit_alloc", "set_shrinker_bit", "reparent_shrinker_deferred", "alloc_shrinker_info", "free_shrinker_info", "shrink_slab", "__list_lru_init", "memcg_list_lru_alloc" ], "Reasoning": "The patch refactors the memcg slab shrinker tracking mechanism from a flat RCU-allocated array to a lazily-allocated XArray per nodeinfo. It alters memory reclaim iteration (shrink_slab/shrink_slab_memcg), introduces a new WARN_ON_ONCE() assertion in set_shrinker_bit(), modifies deferred reclaim reparenting, and changes list_lru allocation logic. These changes affect core memory management and are fully reachable in virtualized environments via cgroup and memory pressure workloads.", "WorthFuzzing": true }
31/1	2026/11/03 20:18	action	If	2m Args: { "WorthFuzzing": true } Results: null
32/2	2026/11/03 20:18	agent	kmsan-evaluator	2m Model: core Args: null Results: { "KMSANReasoning": "The patch refactors memory cgroup shrinker info management by replacing the custom RCU-managed dynamic array `shrinker_info` in `struct mem_cgroup_per_node` with an XArray (`shrinker_units`), allocating `shrinker_info_unit` structures on demand rather than eagerly sizing them.\n\nEvaluation of KMSAN vs KASAN applicability:\n1. No uninitialized memory exposure to userspace: The shrinker tracking structures are strictly internal to the kernel's memory management subsystem (page reclaim and list_lru). No structures or buffers modified by this patch are copied to userspace via `copy_to_user`, ioctl, netlink, or socket interfaces.\n2. Complete initialization of allocated structures: All `struct shrinker_info_unit` objects are allocated via `kmem_cache_alloc_node` using `gfp \| __GFP_ZERO`, ensuring that both the `nr_deferred` array and the `map` bitmap are fully zeroed before insertion into the XArray or use in reclaim logic. The per-node XArray is initialized using `xa_init_flags`. All local stack variables and control structures (`struct shrink_control`, `XA_STATE`) are fully initialized before use.\n3. Relevant bug classes: The potential failure modes of this patch are concurrency/synchronization issues (e.g. lockless iteration over XArray vs destruction, IRQ-safe locking), use-after-free, memory leaks, or NULL pointer dereferences. These are covered by KASAN, LOCKDEP, and standard kernel debugging facilities.\n\nBecause no uninitialized memory reads or information leaks are introduced or exposed, a dedicated KMSAN session is not justified.", "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 b9a5154a739313cf76c33e4e804f9fc2493dba9b Author: syz-cluster <triage@syzkaller.com> Date: Tue Nov 3 19:55:47 2026 +0000 syz-cluster: applied patch under review diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 69e1bcc67c588d..ea2c0990059479 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -24,6 +24,7 @@ #include <linux/page-flags.h> #include <linux/shrinker.h> #include <linux/irq_work_types.h> +#include <linux/xarray.h> struct mem_cgroup; struct obj_cgroup; @@ -83,14 +84,14 @@ struct mem_cgroup_reclaim_iter { * per-node information in memory controller. / struct mem_cgroup_per_node { - / Set when the memcg is created, then only read. / + / Set when the memcg is created, then mostly read. / __cacheline_group_begin_aligned(memcg_pn_read_mostly); struct mem_cgroup memcg; /* Back pointer, we cannot / / use container_of / struct lruvec_stats_percpu __percpu lruvec_stats_percpu; struct lruvec_stats lruvec_stats; - struct shrinker_info __rcu shrinker_info; + struct xarray shrinker_units; struct obj_cgroup __rcu objcg; __cacheline_group_end_aligned(memcg_pn_read_mostly); @@ -1719,6 +1720,8 @@ static inline u64 mem_cgroup_get_socket_pressure(const struct mem_cgroup memcg) void shrinker_unit_cache_init(void); int alloc_shrinker_info(struct mem_cgroup memcg); +int memcg_shrinker_unit_alloc(struct mem_cgroup memcg, int shrinker_id, + gfp_t gfp); void free_shrinker_info(struct mem_cgroup memcg); void set_shrinker_bit(struct mem_cgroup memcg, int nid, int shrinker_id); void reparent_shrinker_deferred(struct mem_cgroup memcg); diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h index 1a00be90d93a9f..2eae68a7ff6c5d 100644 --- a/include/linux/shrinker.h +++ b/include/linux/shrinker.h @@ -18,12 +18,6 @@ struct shrinker_info_unit { DECLARE_BITMAP(map, SHRINKER_UNIT_BITS); }; -struct shrinker_info { - struct rcu_head rcu; - int map_nr_max; - struct shrinker_info_unit unit[]; -}; - /* * This struct is used to pass information from page reclaim to the shrinkers. * We consolidate the values for easier extension later. diff --git a/mm/list_lru.c b/mm/list_lru.c index d1d256822ccc73..4be22c5238f98a 100644 --- a/mm/list_lru.c +++ b/mm/list_lru.c @@ -597,6 +597,12 @@ static int __memcg_list_lru_alloc(struct mem_cgroup memcg, parent = parent_mem_cgroup(pos); } + if (!css_is_dying(&pos->css) && + memcg_shrinker_unit_alloc(pos, lru_shrinker_id(lru), gfp)) { + kfree(mlru); + return -ENOMEM; + } + if (!mlru) { mlru = memcg_init_list_lru_one(lru, gfp); if (!mlru) @@ -666,18 +672,20 @@ int __list_lru_init(struct list_lru lru, bool memcg_aware, struct shrinker shr int i; #ifdef CONFIG_MEMCG + if (mem_cgroup_disabled() \|\| mem_cgroup_kmem_disabled()) + memcg_aware = false; + / * If the shrinker fell back to being non-memcg-aware (e.g. with - * cgroup.memory=nokmem), its id was never assigned and holds a - * stale 0. Don't let set_shrinker_bit() act on it. + * cgroup.memory=nokmem), its id is not valid. Don't let + * set_shrinker_bit() act on it, nor on a list that is not + * per-memcg: such a list gets no shrinker units. / - if (shrinker && (shrinker->flags & SHRINKER_MEMCG_AWARE)) + if (shrinker && memcg_aware && + (shrinker->flags & SHRINKER_MEMCG_AWARE)) lru->shrinker_id = shrinker->id; else lru->shrinker_id = -1; - - if (mem_cgroup_disabled() \|\| mem_cgroup_kmem_disabled()) - memcg_aware = false; #endif lru->node = kzalloc_objs(lru->node, nr_node_ids); diff --git a/mm/memcontrol.c b/mm/memcontrol.c index a05d9a8baa1b6b..1a582be5a75bbb 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4219,6 +4219,7 @@ static bool alloc_mem_cgroup_per_node_info(struct mem_cgroup memcg, int node) INIT_LIST_HEAD(&pn->objcg_list); lruvec_init(&pn->lruvec); + xa_init_flags(&pn->shrinker_units, XA_FLAGS_LOCK_IRQ); pn->memcg = memcg; memcg->nodeinfo[node] = pn; @@ -4385,11 +4386,6 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state css) memcg_online_kmem(memcg); - /* - * A memcg must be visible for expand_shrinker_info() - * by the time the maps are allocated. So, we allocate maps - * here, when mem_cgroup_iter() can't skip it. - / if (alloc_shrinker_info(memcg)) goto offline_kmem; @@ -5925,7 +5921,7 @@ static void __init memcg_struct_check(void) CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup_per_node, memcg_pn_read_mostly, lruvec_stats); CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup_per_node, - memcg_pn_read_mostly, shrinker_info); + memcg_pn_read_mostly, shrinker_units); CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup_per_node, memcg_pn_read_mostly, objcg); diff --git a/mm/shrinker.c b/mm/shrinker.c index 4fb424e721bca0..3d55a1ed1f986d 100644 --- a/mm/shrinker.c +++ b/mm/shrinker.c @@ -19,213 +19,146 @@ void __init shrinker_unit_cache_init(void) shrinker_unit_cachep = KMEM_CACHE(shrinker_info_unit, SLAB_PANIC); } -static inline int shrinker_unit_size(int nr_items) +static inline int shrinker_id_to_index(int shrinker_id) { - return (DIV_ROUND_UP(nr_items, SHRINKER_UNIT_BITS) sizeof(struct shrinker_info_unit )); + return shrinker_id / SHRINKER_UNIT_BITS; } -static inline void shrinker_unit_free(struct shrinker_info info, int start) +static inline int shrinker_id_to_offset(int shrinker_id) { - struct shrinker_info_unit *unit; - int nr, i; - - if (!info) - return; - - unit = info->unit; - nr = DIV_ROUND_UP(info->map_nr_max, SHRINKER_UNIT_BITS); + return shrinker_id % SHRINKER_UNIT_BITS; +} - for (i = start; i < nr; i++) { - if (!unit[i]) - break; +static inline int calc_shrinker_id(int index, int offset) +{ + return index SHRINKER_UNIT_BITS + offset; +} - kmem_cache_free(shrinker_unit_cachep, unit[i]); - unit[i] = NULL; - } +static struct shrinker_info_unit shrinker_unit_get(struct mem_cgroup memcg, + int nid, int shrinker_id) +{ + return xa_load(&memcg->nodeinfo[nid]->shrinker_units, + shrinker_id_to_index(shrinker_id)); } -static inline int shrinker_unit_alloc(struct shrinker_info new, - struct shrinker_info old, int nid) +/* + * Installs run with the caller's gfp, possibly under the i_pages lock, which + * is taken from interrupts: hence the irq-safe lock and xas_nomem(). + / +static int shrinker_unit_install(struct mem_cgroup memcg, int nid, int index, + gfp_t gfp) { + XA_STATE(xas, &memcg->nodeinfo[nid]->shrinker_units, index); struct shrinker_info_unit unit; - int nr = DIV_ROUND_UP(new->map_nr_max, SHRINKER_UNIT_BITS); - int start = old ? DIV_ROUND_UP(old->map_nr_max, SHRINKER_UNIT_BITS) : 0; - int i; - - for (i = start; i < nr; i++) { - unit = kmem_cache_alloc_node(shrinker_unit_cachep, - GFP_KERNEL \| __GFP_ZERO, nid); - if (!unit) { - shrinker_unit_free(new, start); - return -ENOMEM; - } - - new->unit[i] = unit; - } + unsigned long flags; - return 0; -} + if (xa_load(xas.xa, index)) + return 0; -static void __free_shrinker_info(struct mem_cgroup memcg) -{ - struct mem_cgroup_per_node pn; - struct shrinker_info info; - int nid; + unit = kmem_cache_alloc_node(shrinker_unit_cachep, gfp \| __GFP_ZERO, + nid); + if (!unit) + return -ENOMEM; - lockdep_assert_held(&shrinker_mutex); + do { + xas_lock_irqsave(&xas, flags); + if (!xas_load(&xas)) { + xas_store(&xas, unit); + if (!xas_error(&xas)) + unit = NULL; + } + xas_unlock_irqrestore(&xas, flags); + } while (xas_nomem(&xas, gfp)); - for_each_node(nid) { - pn = memcg->nodeinfo[nid]; - info = rcu_dereference_protected(pn->shrinker_info, true); - shrinker_unit_free(info, 0); - kvfree(info); - rcu_assign_pointer(pn->shrinker_info, NULL); - } -} + if (unit) + kmem_cache_free(shrinker_unit_cachep, unit); -void free_shrinker_info(struct mem_cgroup memcg) -{ - mutex_lock(&shrinker_mutex); - __free_shrinker_info(memcg); - mutex_unlock(&shrinker_mutex); + return xas_error(&xas); } -int alloc_shrinker_info(struct mem_cgroup memcg) +static int shrinker_units_install(struct mem_cgroup memcg, int start, int end) { - int nid, ret = 0; - int array_size = 0; + int nid, index, ret; - mutex_lock(&shrinker_mutex); - array_size = shrinker_unit_size(shrinker_nr_max); for_each_node(nid) { - struct shrinker_info info = kvzalloc_node(sizeof(info) + array_size, - GFP_KERNEL, nid); - if (!info) - goto err; - info->map_nr_max = shrinker_nr_max; - if (shrinker_unit_alloc(info, NULL, nid)) { - kvfree(info); - goto err; + for (index = start; index < end; index++) { + ret = shrinker_unit_install(memcg, nid, index, + GFP_KERNEL); + if (ret) + return ret; } - rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info); } - mutex_unlock(&shrinker_mutex); - - return ret; -err: - __free_shrinker_info(memcg); - mutex_unlock(&shrinker_mutex); - return -ENOMEM; -} - -static struct shrinker_info shrinker_info_protected(struct mem_cgroup memcg, - int nid) -{ - return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info, - lockdep_is_held(&shrinker_mutex)); + return 0; } -static int expand_one_shrinker_info(struct mem_cgroup memcg, int new_size, - int old_size, int new_nr_max) +void free_shrinker_info(struct mem_cgroup memcg) { - struct shrinker_info new, old; - struct mem_cgroup_per_node pn; + struct shrinker_info_unit unit; + unsigned long index; int nid; for_each_node(nid) { - pn = memcg->nodeinfo[nid]; - old = shrinker_info_protected(memcg, nid); - / Not yet online memcg / - if (!old) - return 0; - - / Already expanded this shrinker_info / - if (new_nr_max <= old->map_nr_max) - continue; + struct xarray units = &memcg->nodeinfo[nid]->shrinker_units; - new = kvzalloc_node(sizeof(new) + new_size, GFP_KERNEL, nid); - if (!new) - return -ENOMEM; + xa_for_each(units, index, unit) + kmem_cache_free(shrinker_unit_cachep, unit); + xa_destroy(units); + } +} - new->map_nr_max = new_nr_max; +/ + * Global reclaim keeps the deferred work of memcg-aware shrinkers in the + * root's units, and root has no list_lru allocation to install them from. + / +int alloc_shrinker_info(struct mem_cgroup memcg) +{ + int ret; - memcpy(new->unit, old->unit, old_size); - if (shrinker_unit_alloc(new, old, nid)) { - kvfree(new); - return -ENOMEM; - } + if (!mem_cgroup_is_root(memcg)) + return 0; - rcu_assign_pointer(pn->shrinker_info, new); - kvfree_rcu(old, rcu); - } + mutex_lock(&shrinker_mutex); + ret = shrinker_units_install(memcg, 0, + shrinker_id_to_index(shrinker_nr_max)); + if (ret) + free_shrinker_info(memcg); + mutex_unlock(&shrinker_mutex); - return 0; + return ret; } static int expand_shrinker_info(int new_id) { - int ret = 0; int new_nr_max = round_up(new_id + 1, SHRINKER_UNIT_BITS); - int new_size, old_size = 0; - struct mem_cgroup memcg; - - if (!root_mem_cgroup) - goto out; + int ret = 0; lockdep_assert_held(&shrinker_mutex); - new_size = shrinker_unit_size(new_nr_max); - old_size = shrinker_unit_size(shrinker_nr_max); - - memcg = mem_cgroup_iter(NULL, NULL, NULL); - do { - ret = expand_one_shrinker_info(memcg, new_size, old_size, - new_nr_max); - if (ret) { - mem_cgroup_iter_break(NULL, memcg); - goto out; - } - } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL); -out: + if (root_mem_cgroup) + ret = shrinker_units_install(root_mem_cgroup, + shrinker_id_to_index(shrinker_nr_max), + shrinker_id_to_index(new_nr_max)); if (!ret) shrinker_nr_max = new_nr_max; return ret; } -static inline int shrinker_id_to_index(int shrinker_id) -{ - return shrinker_id / SHRINKER_UNIT_BITS; -} - -static inline int shrinker_id_to_offset(int shrinker_id) +void set_shrinker_bit(struct mem_cgroup memcg, int nid, int shrinker_id) { - return shrinker_id % SHRINKER_UNIT_BITS; -} + struct shrinker_info_unit unit; -static inline int calc_shrinker_id(int index, int offset) -{ - return index SHRINKER_UNIT_BITS + offset; -} + if (shrinker_id < 0 \|\| !memcg \|\| mem_cgroup_is_root(memcg)) + return; -void set_shrinker_bit(struct mem_cgroup memcg, int nid, int shrinker_id) -{ - if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) { - struct shrinker_info info; + unit = shrinker_unit_get(memcg, nid, shrinker_id); + if (WARN_ON_ONCE(!unit)) + return; - rcu_read_lock(); - info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info); - if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) { - struct shrinker_info_unit unit; - - unit = info->unit[shrinker_id_to_index(shrinker_id)]; - / Pairs with smp mb in shrink_slab() / - smp_mb__before_atomic(); - set_bit(shrinker_id_to_offset(shrinker_id), unit->map); - } - rcu_read_unlock(); - } + / Pairs with smp mb in shrink_slab() / + smp_mb__before_atomic(); + set_bit(shrinker_id_to_offset(shrinker_id), unit->map); } static DEFINE_IDR(shrinker_idr); @@ -270,59 +203,73 @@ static void shrinker_memcg_remove(struct shrinker shrinker) static long xchg_nr_deferred_memcg(int nid, struct shrinker shrinker, struct mem_cgroup memcg) { - struct shrinker_info info; struct shrinker_info_unit unit; - long nr_deferred; - rcu_read_lock(); - info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info); - unit = info->unit[shrinker_id_to_index(shrinker->id)]; - nr_deferred = atomic_long_xchg(&unit->nr_deferred[shrinker_id_to_offset(shrinker->id)], 0); - rcu_read_unlock(); + unit = shrinker_unit_get(memcg, nid, shrinker->id); + /* No unit: this memcg never held objects of this shrinker. / + if (!unit) + return 0; - return nr_deferred; + return atomic_long_xchg(&unit->nr_deferred[shrinker_id_to_offset(shrinker->id)], 0); } static long add_nr_deferred_memcg(long nr, int nid, struct shrinker shrinker, struct mem_cgroup memcg) { - struct shrinker_info info; struct shrinker_info_unit unit; - long nr_deferred; - rcu_read_lock(); - info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info); - unit = info->unit[shrinker_id_to_index(shrinker->id)]; - nr_deferred = - atomic_long_add_return(nr, &unit->nr_deferred[shrinker_id_to_offset(shrinker->id)]); - rcu_read_unlock(); + unit = shrinker_unit_get(memcg, nid, shrinker->id); + if (!unit) + return 0; - return nr_deferred; + return atomic_long_add_return(nr, &unit->nr_deferred[shrinker_id_to_offset(shrinker->id)]); +} + +/ + * Called before @memcg gets a list on a list_lru of shrinker @shrinker_id: + * a map bit is only ever set on a memcg that has such a list. + / +int memcg_shrinker_unit_alloc(struct mem_cgroup memcg, int shrinker_id, + gfp_t gfp) +{ + int nid, ret; + + if (shrinker_id < 0 \|\| mem_cgroup_is_root(memcg)) + return 0; + + for_each_node(nid) { + ret = shrinker_unit_install(memcg, nid, + shrinker_id_to_index(shrinker_id), + gfp); + if (ret) + return ret; + } + + return 0; } void reparent_shrinker_deferred(struct mem_cgroup memcg) { - int nid, index, offset; - long nr; struct mem_cgroup parent = parent_mem_cgroup(memcg); - struct shrinker_info child_info, parent_info; struct shrinker_info_unit child_unit, parent_unit; + unsigned long index; + int nid, offset; + long nr; - /* Prevent from concurrent shrinker_info expand / - mutex_lock(&shrinker_mutex); for_each_node(nid) { - child_info = shrinker_info_protected(memcg, nid); - parent_info = shrinker_info_protected(parent, nid); - for (index = 0; index < shrinker_id_to_index(child_info->map_nr_max); index++) { - child_unit = child_info->unit[index]; - parent_unit = parent_info->unit[index]; + struct xarray parent_units = &parent->nodeinfo[nid]->shrinker_units; + + xa_for_each(&memcg->nodeinfo[nid]->shrinker_units, index, child_unit) { + parent_unit = xa_load(parent_units, index); + /* Installed but never listed: nothing deferred in it. / + if (!parent_unit) + continue; for (offset = 0; offset < SHRINKER_UNIT_BITS; offset++) { nr = atomic_long_read(&child_unit->nr_deferred[offset]); atomic_long_add(nr, &parent_unit->nr_deferred[offset]); } } } - mutex_unlock(&shrinker_mutex); } #else static int shrinker_memcg_alloc(struct shrinker shrinker) @@ -485,9 +432,9 @@ static unsigned long do_shrink_slab(struct shrink_control shrinkctl, static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, struct mem_cgroup memcg, int priority) { - struct shrinker_info info; - unsigned long ret, freed = 0; - int offset, index = 0; + struct shrinker_info_unit unit; + unsigned long index, ret, freed = 0; + int offset; if (!mem_cgroup_online(memcg)) return 0; @@ -495,51 +442,17 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, /* * lockless algorithm of memcg shrink. * - * The shrinker_info may be freed asynchronously via RCU in the - * expand_one_shrinker_info(), so the rcu_read_lock() needs to be used - * to ensure the existence of the shrinker_info. - * - * The shrinker_info_unit is never freed unless its corresponding memcg - * is destroyed. Here we already hold the refcount of memcg, so the - * memcg will not be destroyed, and of course shrinker_info_unit will - * not be freed. + * A unit is only freed together with its memcg, and the caller holds + * a reference to the memcg, so the units found by xa_for_each() stay + * valid without the RCU lock and do_shrink_slab() may sleep. * - * So in the memcg shrink: - * step 1: use rcu_read_lock() to guarantee existence of the - * shrinker_info. - * step 2: after getting shrinker_info_unit we can safely release the - * RCU lock. - * step 3: traverse the bitmap and calculate shrinker_id - * step 4: use rcu_read_lock() to guarantee existence of the shrinker. - * step 5: use shrinker_id to find the shrinker, then use - * shrinker_try_get() to guarantee existence of the shrinker, - * then we can release the RCU lock to do do_shrink_slab() that - * may sleep. - * step 6: do shrinker_put() paired with step 5 to put the refcount, - * if the refcount reaches 0, then wake up the waiter in - * shrinker_free() by calling complete(). - * Note: here is different from the global shrink, we don't - * need to acquire the RCU lock to guarantee existence of - * the shrinker, because we don't need to use this - * shrinker to traverse the next shrinker in the bitmap. - * step 7: we have already exited the read-side of rcu critical section - * before calling do_shrink_slab(), the shrinker_info may be - * released in expand_one_shrinker_info(), so go back to step 1 - * to reacquire the shrinker_info. + * The shrinker is found by id under the RCU lock, and + * shrinker_try_get() pins it before the lock is dropped; + * shrinker_put() wakes up the waiter in shrinker_free() by calling + * complete() when the last reference goes. The next shrinker comes + * from the bitmap, not from this shrinker, so nothing else is needed. / -again: - rcu_read_lock(); - info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info); - if (unlikely(!info)) - goto unlock; - - if (index < shrinker_id_to_index(info->map_nr_max)) { - struct shrinker_info_unit unit; - - unit = info->unit[index]; - - rcu_read_unlock(); - + xa_for_each(&memcg->nodeinfo[nid]->shrinker_units, index, unit) { for_each_set_bit(offset, unit->map, SHRINKER_UNIT_BITS) { struct shrink_control sc = { .gfp_mask = gfp_mask, @@ -594,12 +507,8 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, freed += ret; shrinker_put(shrinker); } - - index++; - goto again; } -unlock: - rcu_read_unlock(); + return freed; } #else /* !CONFIG_MEMCG */
33/3	2026/11/03 20:18	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 9917 output: 37 thoughts: 442 Thoughts: KMSAN Fuzzing Session Justification Okay, so I'm looking at this patch series and the key question is: does it warrant setting up a dedicated KMSAN fuzzing session? Let's break it down and see. First, I need to thoroughly understand what this patch actually does. I need to dive into the changes, analyze them, and, critically, identify the memory allocation, access, and initialization patterns. The end goal here is to pinpoint any potential uninitialized memory risks. That's where KMSAN can really shine. Alright, let's start reading the patch. From what I can tell, it's about converting the `struct shrinker_info` in `struct mem_cgroup_per_node` from an array managed under RCU to an xarray called `shrinker_units`. Now, let me look at the code. In `include/linux/memcontrol.h`, it's clear: `struct shrinker_info __rcu shrinker_info;` is being replaced by `struct xarray shrinker_units;`. In `mm/memcontrol.c`, I see `xa_init_flags(&pn->shrinker_units, XA_FLAGS_LOCK_IRQ);` being used in `alloc_mem_cgroup_per_node_info`. This is initializing the xarray. Over in `mm/list_lru.c`, it looks like `memcg_shrinker_unit_alloc` is being called dynamically during list_lru allocation. Interesting. Now, the juicy part: `mm/shrinker.c`. This is where the `shrinker_info_unit` allocation happens. I see that `unit = kmem_cache_alloc_node(shrinker_unit_cachep, gfp \| __GFP_ZERO, nid);`. The important thing here is that it's being allocated with `__GFP_ZERO`! That's good, right? It means the memory should be zeroed out. Oh, and `shrinker_unit_cachep = KMEM_CACHE(shrinker_info_unit, SLAB_PANIC);`. Let's dig into `struct shrinker_info_unit` to confirm. It has `DECLARE_BITMAP(map, SHRINKER_UNIT_BITS); atomic_long_t nr_deferred[SHRINKER_UNIT_BITS]; ...`. I need to look at `include/linux/shrinker.h` to see the complete definition of this `struct shrinker_info_unit`. From what I see so far, with that `__GFP_ZERO` allocation, it seems less likely, at first glance*, that there would be any immediate uninitialized memory issues. However, given that this patch involves low-level memory management and data structures, and the potential for off-by-one errors with bitmaps and atomic variables, it is still a prime candidate for a dedicated KMSAN fuzzing session. I will need to delve deeper.
34/3	2026/11/03 20:18	tool	grepper	0m Args: { "Expression": "struct shrinker_info_unit \\{", "PathPrefixes": [ "include/linux/shrinker.h" ] } Results: { "Output": "include/linux/shrinker.h-15- */\ninclude/linux/shrinker.h:16:struct shrinker_info_unit {\ninclude/linux/shrinker.h-17-\tatomic_long_t nr_deferred[SHRINKER_UNIT_BITS];\n" }
35/3	2026/11/03 20:18	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 11116 output: 35 thoughts: 20 Thoughts: Here's a summary of my thought process, keeping in mind my deep understanding of the Linux kernel: Delving into the Shrinker Header Alright, let's dive into the core of the shrinker mechanism. I need to refresh my understanding of how this works at a fundamental level. I'm going to jump straight into `include/linux/shrinker.h`, specifically around line 16. I want to see the core data structures and likely the key function prototypes that define the shrinker API. This header file is the Rosetta Stone for understanding how the kernel manages memory pressure and reclaims resources. I expect to find the definition of the `shrinker_t` structure, probably alongside the function signatures for the `count_objects` and `scan_objects` methods. I'm really looking for the core interface – the contract that all shrinker implementations must adhere to. This includes the parameters passed in, the return types, and the expected behavior in different memory scenarios. Specifically I'll be looking for any hints about how the shrinker framework interacts with the page cache, swap, and NUMA. Understanding this API is paramount to diagnosing memory bottlenecks and performance issues. I expect to be able to build a mental map of how the system functions in a very short order.
36/3	2026/11/03 20:18	tool	read-file	0m Args: { "File": "include/linux/shrinker.h", "FirstLine": 15, "LineCount": 25 } Results: { "Contents": " 15:\t /\n 16:\tstruct shrinker_info_unit {\n 17:\t\tatomic_long_t nr_deferred[SHRINKER_UNIT_BITS];\n 18:\t\tDECLARE_BITMAP(map, SHRINKER_UNIT_BITS);\n 19:\t};\n 20:\t\n 21:\t/\n 22:\t * This struct is used to pass information from page reclaim to the shrinkers.\n 23:\t * We consolidate the values for easier extension later.\n 24:\t \n 25:\t The 'gfpmask' refers to the allocation we are currently trying to\n 26:\t * fulfil.\n 27:\t /\n 28:\tstruct shrink_control {\n 29:\t\tgfp_t gfp_mask;\n 30:\t\n 31:\t\t/ current node being shrunk (for NUMA aware shrinkers) /\n 32:\t\tint nid;\n 33:\t\n 34:\t\t/\n 35:\t\t * How many objects scan_objects should scan and try to reclaim.\n 36:\t\t * This is reset before every call, so it is safe for callees\n 37:\t\t * to modify.\n 38:\t\t */\n 39:\t\tunsigned long nr_to_scan;\n" }
37/3	2026/11/03 20:18	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 11765 output: 34 thoughts: 779 Thoughts: Analyzing Memory Management within the `memcg` context Okay, let's break this down systematically. I'm focusing on the allocation and freeing of the `shrinker_info_unit` structure. First, I see that the `unit` is allocated using `kmem_cache_alloc_node` with `__GFP_ZERO`, meaning its memory is explicitly zeroed out. That's good. When it is freed, it's done via `kmem_cache_free`, and also destroyed via the `free_shrinker_info` function, which iterates through a node's xarray and frees each `unit`. Now, the `reparent_shrinker_deferred` function catches my eye. It looks like it's dealing with reparenting memory cgroups. It iterates through the children units, and adds to the parent units. But wait... what happens if `parent` is `NULL`? If the parent is `NULL`, then there's a serious potential for a null pointer dereference, which could lead to a crash. This raises a red flag; should we add a check here? Is this situation even possible? I need to look into when this function is called. But wait, no it doesn't. If `parent` is `NULL` then a crash. Now, let's shift focus to `shrink_slab_memcg`. The function `shrink_slab_memcg` is using a designated initializer called `sc`. It seems that the fields have been explicitly initialized. Overall, it looks like there are some potential race conditions and null pointer dereferences that need to be addressed.
38/3	2026/11/03 20:19	tool	grepper	0m Args: { "Expression": "struct shrink_control sc = \\{", "PathPrefixes": [ "mm/shrinker.c" ] } Results: { "Output": "mm/shrinker.c=432=static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,\n--\nmm/shrinker.c-456-\t\tfor_each_set_bit(offset, unit-\u003emap, SHRINKER_UNIT_BITS) {\nmm/shrinker.c:457:\t\t\tstruct shrink_control sc = {\nmm/shrinker.c-458-\t\t\t\t.gfp_mask = gfp_mask,\n--\nmm/shrinker.c=542=unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,\n--\nmm/shrinker.c-580-\tlist_for_each_entry_rcu(shrinker, \u0026shrinker_list, list) {\nmm/shrinker.c:581:\t\tstruct shrink_control sc = {\nmm/shrinker.c-582-\t\t\t.gfp_mask = gfp_mask,\n" }
39/3	2026/11/03 20:19	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 13174 output: 34 thoughts: 22 Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience: Diving into the Shrinker Alright, time to troubleshoot this memory issue. I'm going to start by zeroing in on a likely culprit: the memory shrinker code. Specifically, let's pull up `mm/shrinker.c` and take a look at the code between lines 450 and 480. I suspect something within that section is behaving unexpectedly, or maybe it's interacting in an unanticipated way with another part of the system. I have a hunch about what might be going on there, but it's important to start with the evidence. Let's see what's happening within those lines and see if my intuition holds any weight. This section might be where a critical decision is made or where a resource is mismanaged. The goal here is to carefully evaluate the logic and data flow within that specific range, looking for clues about the root cause of this memory behavior.
40/3	2026/11/03 20:19	tool	read-file	0m Args: { "File": "mm/shrinker.c", "FirstLine": 455, "LineCount": 40 } Results: { "Contents": " 455:\t\txa_for_each(\u0026memcg-\u003enodeinfo[nid]-\u003eshrinker_units, index, unit) {\n 456:\t\t\tfor_each_set_bit(offset, unit-\u003emap, SHRINKER_UNIT_BITS) {\n 457:\t\t\t\tstruct shrink_control sc = {\n 458:\t\t\t\t\t.gfp_mask = gfp_mask,\n 459:\t\t\t\t\t.nid = nid,\n 460:\t\t\t\t\t.memcg = memcg,\n 461:\t\t\t\t};\n 462:\t\t\t\tstruct shrinker shrinker;\n 463:\t\t\t\tint shrinker_id = calc_shrinker_id(index, offset);\n 464:\t\n 465:\t\t\t\trcu_read_lock();\n 466:\t\t\t\tshrinker = idr_find(\u0026shrinker_idr, shrinker_id);\n 467:\t\t\t\tif (unlikely(!shrinker \|\| !shrinker_try_get(shrinker))) {\n 468:\t\t\t\t\tclear_bit(offset, unit-\u003emap);\n 469:\t\t\t\t\trcu_read_unlock();\n 470:\t\t\t\t\tcontinue;\n 471:\t\t\t\t}\n 472:\t\t\t\trcu_read_unlock();\n 473:\t\n 474:\t\t\t\t/ Call non-slab shrinkers even though kmem is disabled /\n 475:\t\t\t\tif (!memcg_kmem_online() \u0026\u0026\n 476:\t\t\t\t !(shrinker-\u003eflags \u0026 SHRINKER_NONSLAB)) {\n 477:\t\t\t\t\tclear_bit(offset, unit-\u003emap);\n 478:\t\t\t\t\tshrinker_put(shrinker);\n 479:\t\t\t\t\tcontinue;\n 480:\t\t\t\t}\n 481:\t\n 482:\t\t\t\tret = do_shrink_slab(\u0026sc, shrinker, priority);\n 483:\t\t\t\tif (ret == SHRINK_EMPTY) {\n 484:\t\t\t\t\tclear_bit(offset, unit-\u003emap);\n 485:\t\t\t\t\t/\n 486:\t\t\t\t\t * After the shrinker reported that it had no objects to\n 487:\t\t\t\t\t * free, but before we cleared the corresponding bit in\n 488:\t\t\t\t\t * the memcg shrinker map, a new object might have been\n 489:\t\t\t\t\t * added. To make sure, we have the bit set in this\n 490:\t\t\t\t\t * case, we invoke the shrinker one more time and reset\n 491:\t\t\t\t\t * the bit if it reports that it is not empty anymore.\n 492:\t\t\t\t\t * The memory barrier here pairs with the barrier in\n 493:\t\t\t\t\t * set_shrinker_bit():\n 494:\t\t\t\t\t *\n" }
41/3	2026/11/03 20:19	llm	kmsan-evaluator	1m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 14103 output: 383 thoughts: 2851 Thoughts: KMSAN Assessment: No Uninitialized Memory Risks Okay, here's my assessment of this patch. It looks like we're replacing the old RCU-managed dynamic array with an XArray (`shrinker_units`) to manage `shrinker_info_unit` instances per memcg, and I need to determine if this requires KMSAN. `sc` was already there prior to the patch. The core of this hinges on whether the changes introduce any uninitialized memory usage that could lead to information leaks or other vulnerabilities. First, I examined whether any kernel structures are exposed to userspace via the various methods, like `copy_to_user`. Nope, the `shrinker_units` mechanism is entirely internal to memory cgroup tracking. No user-space data transfer here. Next, I meticulously went through the code, function by function: `shrinker_unit_install`, `shrinker_units_install`, `free_shrinker_info`, `alloc_shrinker_info`, `expand_shrinker_info`, `memcg_shrinker_unit_alloc`, `reparent_shrinker_deferred`, and `__memcg_list_lru_alloc`. I carefully traced the initialization of all variables, especially the allocation of `shrinker_info_unit` structures and XArray initialization. Specifically, I checked for uninitialized variables, conditional logic depending on uninitialized data, and any potential access to uninitialized bytes in the allocated structures. `flags`, `unit`, `xas` and `ret` are all checked to be initialized. I made sure that `shrinker_info_unit` allocations use `kmem_cache_alloc_node` with `__GFP_ZERO` and that `pn->shrinker_units` is initialized with `xa_init_flags(&pn->shrinker_units, XA_FLAGS_LOCK_IRQ)`. I verified that all local variables, stacks, etc. were also fully initialized. Then, I focused on potential allocation of complex data structures and the introduction of uninitialized fields that could be read later. I made sure that all allocations were zeroed using the right flags. No uninitialized fields. I looked for bounds check issues. Nothing that would introduce a risk of accessing uninitialized memory. The potential issues I did identify are related to concurrency (RCU vs. XArray locking, race conditions, etc.), memory allocation failures, and potential null pointer dereferences. I noted that these kinds of concurrency, memory allocation, and NULL pointer related issues are problems detected by KASAN/LOCKDEP/KMEMLEAK. These aren't KMSAN issues. I then went back to first principles: is there an uninitialized memory risk that only KMSAN would detect? The answer is a resounding no. The new `shrinker_info_unit` objects are explicitly zeroed during allocation. The XArrays are initialized. No uninitialized memory is ever exposed to user space. The primary risks are standard kernel bugs - locking issues, null dereferences, and so on. Therefore, since standard bug detectors like KASAN, LOCKDEP, and KMEMLEAK are sufficient for this patch, there is no need for KMSAN. The reasoning is clear: no uninitialized memory, no information leaks, no need for KMSAN. I'll set NeedsKMSAN to false and move on.
42/3	2026/11/03 20:21	tool	set-results	0m Args: { "KMSANReasoning": "The patch refactors memory cgroup shrinker info management by replacing the custom RCU-managed dynamic array `shrinker_info` in `struct mem_cgroup_per_node` with an XArray (`shrinker_units`), allocating `shrinker_info_unit` structures on demand rather than eagerly sizing them.\n\nEvaluation of KMSAN vs KASAN applicability:\n1. No uninitialized memory exposure to userspace: The shrinker tracking structures are strictly internal to the kernel's memory management subsystem (page reclaim and list_lru). No structures or buffers modified by this patch are copied to userspace via `copy_to_user`, ioctl, netlink, or socket interfaces.\n2. Complete initialization of allocated structures: All `struct shrinker_info_unit` objects are allocated via `kmem_cache_alloc_node` using `gfp \| __GFP_ZERO`, ensuring that both the `nr_deferred` array and the `map` bitmap are fully zeroed before insertion into the XArray or use in reclaim logic. The per-node XArray is initialized using `xa_init_flags`. All local stack variables and control structures (`struct shrink_control`, `XA_STATE`) are fully initialized before use.\n3. Relevant bug classes: The potential failure modes of this patch are concurrency/synchronization issues (e.g. lockless iteration over XArray vs destruction, IRQ-safe locking), use-after-free, memory leaks, or NULL pointer dereferences. These are covered by KASAN, LOCKDEP, and standard kernel debugging facilities.\n\nBecause no uninitialized memory reads or information leaks are introduced or exposed, a dedicated KMSAN session is not justified.", "NeedsKMSAN": false } Results: { "KMSANReasoning": "The patch refactors memory cgroup shrinker info management by replacing the custom RCU-managed dynamic array `shrinker_info` in `struct mem_cgroup_per_node` with an XArray (`shrinker_units`), allocating `shrinker_info_unit` structures on demand rather than eagerly sizing them.\n\nEvaluation of KMSAN vs KASAN applicability:\n1. No uninitialized memory exposure to userspace: The shrinker tracking structures are strictly internal to the kernel's memory management subsystem (page reclaim and list_lru). No structures or buffers modified by this patch are copied to userspace via `copy_to_user`, ioctl, netlink, or socket interfaces.\n2. Complete initialization of allocated structures: All `struct shrinker_info_unit` objects are allocated via `kmem_cache_alloc_node` using `gfp \| __GFP_ZERO`, ensuring that both the `nr_deferred` array and the `map` bitmap are fully zeroed before insertion into the XArray or use in reclaim logic. The per-node XArray is initialized using `xa_init_flags`. All local stack variables and control structures (`struct shrink_control`, `XA_STATE`) are fully initialized before use.\n3. Relevant bug classes: The potential failure modes of this patch are concurrency/synchronization issues (e.g. lockless iteration over XArray vs destruction, IRQ-safe locking), use-after-free, memory leaks, or NULL pointer dereferences. These are covered by KASAN, LOCKDEP, and standard kernel debugging facilities.\n\nBecause no uninitialized memory reads or information leaks are introduced or exposed, a dedicated KMSAN session is not justified.", "NeedsKMSAN": false }

LLM Calls Summary:
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Tool Calls Summary:
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