AI Trajectory

null

{
  "EnableConfigs": [
    "CGROUPS",
    "MEMCG"
  ],
  "FocusSymbols": [
    "__memcg_memory_event",
    "mem_cgroup_sk_charge",
    "__mem_cgroup_charge",
    "mem_cgroup_charge_hugetlb",
    "mem_cgroup_swapin_charge_folio"
  ],
  "KMSANReasoning": "The patch modifies the control flow in `try_charge_memcg()` within `mm/memcontrol.c` so that the `MEMCG_MAX` event (`__memcg_memory_event`) is recorded earlier whenever a memory cgroup limit is exceeded, ensuring it is accounted even if the allocation bails out early (e.g. non-blocking GFP masks or OOM scenarios).\n\nAll variables involved (`mem_over_limit`, `allow_spinning`, `raised_max_event`) are explicitly initialized before use. The patch does not introduce or modify any memory copying to userspace, buffer length/bounds calculations, memory allocations, or struct initializations that could result in uninitialized memory reads or information leaks.\n\nTherefore, this change does not introduce any uninitialized memory risks that would require dedicated KMSAN fuzzing; standard KASAN/LOCKDEP test configurations are appropriate.",
  "NeedsKMSAN": false,
  "Reasoning": "The patch changes the memory controller (memcg) charging path in try_charge_memcg() to raise MEMCG_MAX memory events immediately when the page counter exceeds the limit, before any early bail-outs (such as non-blocking allocations, OOM tasks, or exiting OOM victims). This functionally affects memory event counting and notifications for memory.events and memory.events.local.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 96fe8df56a28ddb7912b73355d66b60f22cb76a3\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Thu Aug 27 23:37:36 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/mm/memcontrol.c b/mm/memcontrol.c\nindex 1271d390b617e..3904fe9a7b2e9 100644\n--- a/mm/memcontrol.c\n+++ b/mm/memcontrol.c\n@@ -2683,6 +2683,11 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,\n \t\tgoto retry;\n \t}\n \n+\tif (!raised_max_event) {\n+\t\t__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);\n+\t\traised_max_event = true;\n+\t}\n+\n \t/*\n \t * Prevent unbounded recursion when reclaim operations need to\n \t * allocate memory. This might exceed the limits temporarily,\n@@ -2711,9 +2716,6 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,\n \t    mm_flags_test(MMF_OOM_SKIP, current-\u003esignal-\u003eoom_mm))\n \t\tgoto nomem;\n \n-\t__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);\n-\traised_max_event = true;\n-\n \tpsi_memstall_enter(\u0026pflags);\n \tnr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages,\n \t\t\t\t\t\t    gfp_mask, reclaim_options, NULL);\n@@ -2773,13 +2775,6 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,\n \tif (!(gfp_mask \u0026 (__GFP_NOFAIL | __GFP_HIGH)))\n \t\treturn -ENOMEM;\n force:\n-\t/*\n-\t * If the allocation has to be enforced, don't forget to raise\n-\t * a MEMCG_MAX event.\n-\t */\n-\tif (!raised_max_event)\n-\t\t__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);\n-\n \t/*\n \t * The allocation either can't fail or will lead to more memory\n \t * being freed very soon.  Allow memory usage go over the limit\n"
}

core

null

{
  "EnableConfigs": [
    "CGROUPS",
    "MEMCG"
  ],
  "FocusSymbols": [
    "__memcg_memory_event",
    "mem_cgroup_sk_charge",
    "__mem_cgroup_charge",
    "mem_cgroup_charge_hugetlb",
    "mem_cgroup_swapin_charge_folio"
  ],
  "Reasoning": "The patch changes the memory controller (memcg) charging path in try_charge_memcg() to raise MEMCG_MAX memory events immediately when the page counter exceeds the limit, before any early bail-outs (such as non-blocking allocations, OOM tasks, or exiting OOM victims). This functionally affects memory event counting and notifications for memory.events and memory.events.local.",
  "WorthFuzzing": true
}

You are an expert Linux kernel maintainer.
Your job is to review a provided patch series and determine
if it makes functional changes to the kernel that should be fuzzed.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on your internal knowledge of the kernel. You must actively
use your code access tools to examine the actual source code and confirm any assumptions.

Return WorthFuzzing=false if the patch only contains:
- Modifications to Documentation/, Kconfig files, or code comments.
- Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints.
- Changes to numeric constants or macros that do not functionally alter execution flow.
- Code paths that are impossible to reach in virtualized environments like GCE or QEMU,
  even when utilizing software-emulated hardware (e.g., usb gadget, mac80211_hwsim).
- Code in vendor-specific PCIe switch, SmartNIC, or GPU drivers (e.g., mlxsw, pds_core, qed,
  ionic, amdgpu) that require physical PCIe hardware cards not emulated in standard QEMU.
- Driver .remove, .shutdown, or pci_unregister_driver teardown callbacks (e.g., igb_remove)
  that are executed only during PCI hot-unplug or sysfs driver unbind operations.

If it modifies reachable core kernel logic, drivers, or architectures, use your code search
tools to verify the code can be executed, then return WorthFuzzing=true.

When returning WorthFuzzing=true, you MUST ALSO:
1. Extract any specific kernel functions that should be heavily fuzzed into FocusSymbols.
   Avoid listing generic hot-path functions to prevent skewed test distributions.
   Prefer non-static, non-inlined API entrypoint functions over internal static helper functions
   (which are inlined by the compiler and do not have distinct symbol addresses).
2. Identify any specific CONFIG_ options required to properly test this new/modified feature.
   Go and look into the Kconfig files and check for ifdefs around the code, do not make assumptions.
   Also check "depends on" lines in Kconfig to include any non-standard parent subsystem configs
   needed for Kbuild to compile the code statically into vmlinux. List them in the EnableConfigs
   output array, and DO NOT add a '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.

For your convenience, here is the diff of the changes:
commit 96fe8df56a28ddb7912b73355d66b60f22cb76a3
Author: syz-cluster <triage@syzkaller.com>
Date:   Thu Aug 27 23:37:36 2026 +0000

    syz-cluster: applied patch under review

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1271d390b617e..3904fe9a7b2e9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2683,6 +2683,11 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 		goto retry;
 	}
 
+	if (!raised_max_event) {
+		__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);
+		raised_max_event = true;
+	}
+
 	/*
 	 * Prevent unbounded recursion when reclaim operations need to
 	 * allocate memory. This might exceed the limits temporarily,
@@ -2711,9 +2716,6 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	    mm_flags_test(MMF_OOM_SKIP, current->signal->oom_mm))
 		goto nomem;
 
-	__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);
-	raised_max_event = true;
-
 	psi_memstall_enter(&pflags);
 	nr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages,
 						    gfp_mask, reclaim_options, NULL);
@@ -2773,13 +2775,6 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	if (!(gfp_mask & (__GFP_NOFAIL | __GFP_HIGH)))
 		return -ENOMEM;
 force:
-	/*
-	 * If the allocation has to be enforced, don't forget to raise
-	 * a MEMCG_MAX event.
-	 */
-	if (!raised_max_event)
-		__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);
-
 	/*
 	 * The allocation either can't fail or will lead to more memory
 	 * being freed very soon.  Allow memory usage go over the limit

gemini-3.7-flash

null

null

							input: 2457
							output: 36
							thoughts: 48
						

Okay, let's dive in.

**Inspecting the Code Changes**

Right, so the first thing I need to do is get a good handle on this patch. It looks like it's touching `mm/memcontrol.c`, specifically the `try_charge_memcg` function. My spidey-sense is already tingling a bit; anything related to memory control and charging is critical, and a change here warrants careful attention. I need to understand this change within its broader context. I'm going to carefully review the surrounding code in `mm/memcontrol.c` before I even try to understand what *this* change does. Getting the lay of the land will give me the proper framework.

{
  "File": "mm/memcontrol.c",
  "FirstLine": 2660,
  "LineCount": 100
}

{
  "Contents": "2660:\tretry:\n2661:\t\tif (consume_stock(memcg, nr_pages))\n2662:\t\t\treturn 0;\n2663:\t\n2664:\t\tif (!allow_spinning)\n2665:\t\t\t/* Avoid the refill and flush of the older stock */\n2666:\t\t\tbatch = nr_pages;\n2667:\t\n2668:\t\treclaim_options = MEMCG_RECLAIM_MAY_SWAP;\n2669:\t\tif (!do_memsw_account() ||\n2670:\t\t    page_counter_try_charge(\u0026memcg-\u003ememsw, batch, \u0026counter)) {\n2671:\t\t\tif (page_counter_try_charge(\u0026memcg-\u003ememory, batch, \u0026counter))\n2672:\t\t\t\tgoto done_restock;\n2673:\t\t\tif (do_memsw_account())\n2674:\t\t\t\tpage_counter_uncharge(\u0026memcg-\u003ememsw, batch);\n2675:\t\t\tmem_over_limit = mem_cgroup_from_counter(counter, memory);\n2676:\t\t} else {\n2677:\t\t\tmem_over_limit = mem_cgroup_from_counter(counter, memsw);\n2678:\t\t\treclaim_options \u0026= ~MEMCG_RECLAIM_MAY_SWAP;\n2679:\t\t}\n2680:\t\n2681:\t\tif (batch \u003e nr_pages) {\n2682:\t\t\tbatch = nr_pages;\n2683:\t\t\tgoto retry;\n2684:\t\t}\n2685:\t\n2686:\t\tif (!raised_max_event) {\n2687:\t\t\t__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);\n2688:\t\t\traised_max_event = true;\n2689:\t\t}\n2690:\t\n2691:\t\t/*\n2692:\t\t * Prevent unbounded recursion when reclaim operations need to\n2693:\t\t * allocate memory. This might exceed the limits temporarily,\n2694:\t\t * but we prefer facilitating memory reclaim and getting back\n2695:\t\t * under the limit over triggering OOM kills in these cases.\n2696:\t\t */\n2697:\t\tif (unlikely(current-\u003eflags \u0026 PF_MEMALLOC))\n2698:\t\t\tgoto force;\n2699:\t\n2700:\t\tif (unlikely(task_in_memcg_oom(current)))\n2701:\t\t\tgoto nomem;\n2702:\t\n2703:\t\tif (!gfpflags_allow_blocking(gfp_mask))\n2704:\t\t\tgoto nomem;\n2705:\t\n2706:\t\t/*\n2707:\t\t * OOM victim still needs to charge memory to exit. OOM reaper should\n2708:\t\t * help but it might fail on mmap_lock contention. If the victim is a\n2709:\t\t * large thread group then all exiting threads might compete on oom_lock\n2710:\t\t * just to learn that there is nothing really killable anymore. Bail\n2711:\t\t * out early and fail the charge to expedite their exit. They are\n2712:\t\t * considered fully reclaimed by the oom reaper and they shouldn't\n2713:\t\t * contribute further charges.\n2714:\t\t */\n2715:\t\tif (tsk_is_oom_victim(current) \u0026\u0026\n2716:\t\t    mm_flags_test(MMF_OOM_SKIP, current-\u003esignal-\u003eoom_mm))\n2717:\t\t\tgoto nomem;\n2718:\t\n2719:\t\tpsi_memstall_enter(\u0026pflags);\n2720:\t\tnr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages,\n2721:\t\t\t\t\t\t\t    gfp_mask, reclaim_options, NULL);\n2722:\t\tpsi_memstall_leave(\u0026pflags);\n2723:\t\n2724:\t\tif (mem_cgroup_margin(mem_over_limit) \u003e= nr_pages)\n2725:\t\t\tgoto retry;\n2726:\t\n2727:\t\tif (!drained) {\n2728:\t\t\tdrain_all_stock(mem_over_limit);\n2729:\t\t\tdrained = true;\n2730:\t\t\tgoto retry;\n2731:\t\t}\n2732:\t\n2733:\t\tif (gfp_mask \u0026 __GFP_NORETRY)\n2734:\t\t\tgoto nomem;\n2735:\t\t/*\n2736:\t\t * Even though the limit is exceeded at this point, reclaim\n2737:\t\t * may have been able to free some pages.  Retry the charge\n2738:\t\t * before killing the task.\n2739:\t\t *\n2740:\t\t * Only for regular pages, though: huge pages are rather\n2741:\t\t * unlikely to succeed so close to the limit, and we fall back\n2742:\t\t * to regular pages anyway in case of failure.\n2743:\t\t */\n2744:\t\tif (nr_reclaimed \u0026\u0026 nr_pages \u003c= (1 \u003c\u003c PAGE_ALLOC_COSTLY_ORDER))\n2745:\t\t\tgoto retry;\n2746:\t\n2747:\t\tif (nr_retries--)\n2748:\t\t\tgoto retry;\n2749:\t\n2750:\t\tif (gfp_mask \u0026 __GFP_RETRY_MAYFAIL)\n2751:\t\t\tgoto nomem;\n2752:\t\n2753:\t\t/* Avoid endless loop for tasks bypassed by the oom killer */\n2754:\t\tif (passed_oom \u0026\u0026 task_is_dying())\n2755:\t\t\tgoto nomem;\n2756:\t\n2757:\t\t/*\n2758:\t\t * keep retrying as long as the memcg oom killer is able to make\n2759:\t\t * a forward progress or bypass the charge if the oom killer\n"
}

gemini-3.7-flash

null

null

							input: 4216
							output: 31
							thoughts: 36
						

**Analyzing the Commit**

Okay, let's dive in. First, I need to understand exactly what this commit is attempting to achieve. I'll start by examining the commit itself – what files were changed, added, or deleted? That's the baseline. Then, I'll leverage the power of the `git log` to provide more context. Knowing the specific commit hash, I can start with a targeted `git log` command. Maybe I can quickly find a helpful message there, or perhaps I'll need to expand my search. Knowing the state of things before the commit is just as, if not more, important, so I'll probably look to see what the *previous* commit did. The log will tell the story.

{
  "Expression": "raised_max_event",
  "PathPrefix": "mm/memcontrol.c"
}

{
  "Output": "mm/memcontrol.c=2645=static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,\n--\nmm/memcontrol.c-2655-\tbool drained = false;\nmm/memcontrol.c:2656:\tbool raised_max_event = false;\nmm/memcontrol.c-2657-\tunsigned long pflags;\n--\nmm/memcontrol.c-2685-\nmm/memcontrol.c:2686:\tif (!raised_max_event) {\nmm/memcontrol.c-2687-\t\t__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);\nmm/memcontrol.c:2688:\t\traised_max_event = true;\nmm/memcontrol.c-2689-\t}\n"
}

gemini-3.7-flash

null

null

							input: 4665
							output: 29
							thoughts: 448
						

**Analyzing the Memcg Memory Charge Change**

Okay, let's dive into this patch. I need to understand the implications of this change to `try_charge_memcg`. Previously, when a memory charge failed – say, a limit was hit – the logic flow was pretty specific: it checked several conditions before potentially raising a memory event. Essentially, it had several "early exits" that prevented raising the event. It checked if `PF_MEMALLOC` was set, if the task was in OOM state, if the GFP flags allowed blocking, and if it should skip the OOM killer. Only if *none* of those conditions were met did it call `__memcg_memory_event` and set `raised_max_event` before attempting to free memory. There was also a redundant call to the event handler in the `force:` label.

Now, this patch seems to be significantly altering that. It's moving that crucial `__memcg_memory_event` call *up* in the call chain. It's now being called unconditionally, right at the start of `try_charge_memcg`, whenever the page counter charge fails (and the `batch` count matches the attempted allocation size). Critically, it *also* removes the redundant call from `force:`. So, essentially, we now get the `__memcg_memory_event` firing every time a page charge fails.

I need to understand the ramifications of this shift. Specifically, what's the purpose of `__memcg_memory_event`? Let's take a look at its definition and see what's changed and what the implications are. This unconditional trigger could potentially impact the system's reaction to memory pressure, especially given the various early exit conditions it bypassed before. I need to be sure that the new behavior doesn't introduce unwanted side effects or regressions.

{
  "Expression": "__memcg_memory_event",
  "PathPrefix": "mm/"
}

{
  "Output": "mm/memcontrol.c=1880=unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)\n--\nmm/memcontrol.c-1898-\nmm/memcontrol.c:1899:void __memcg_memory_event(struct mem_cgroup *memcg,\nmm/memcontrol.c-1900-\t\t\t  enum memcg_memory_event event, bool allow_spinning)\n--\nmm/memcontrol.c-1927-}\nmm/memcontrol.c:1928:EXPORT_SYMBOL_GPL(__memcg_memory_event);\nmm/memcontrol.c-1929-\n--\nmm/memcontrol.c=2645=static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,\n--\nmm/memcontrol.c-2686-\tif (!raised_max_event) {\nmm/memcontrol.c:2687:\t\t__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);\nmm/memcontrol.c-2688-\t\traised_max_event = true;\n"
}

gemini-3.7-flash

null

null

							input: 5834
							output: 35
							thoughts: 22
						

Here's my summary, as though I'm thinking through this process:

**Diving into memcg_memory_event**

Alright, time to dig into `__memcg_memory_event` within `mm/memcontrol.c`. I know this function is pivotal for handling memory events within the memory cgroup (memcg) framework. My focus here is going to be on understanding *how* these events are triggered, *what* information is being tracked, and ultimately, *how* this contributes to the broader resource management strategy of the kernel for memory. Specifically, I need to look closely at the scenarios that are calling this function. Are we talking page faults? Memory reclaim? OOM situations? I need to understand the trigger events. From there I'll be able to trace how these events are recorded. What stats are updated? Are there any significant side effects or cascading changes triggered by the event handling? What locks are in play here? I need to quickly ascertain the lock order to rule out any potential deadlocks. I need to keep in mind, of course, the implications of this within the context of the larger memcg architecture. How does this event interplay with other memcg components, like the controllers for memory usage, swapping, and so on? I should anticipate this being complex but hopefully well-structured. Let's see how they've handled the locking, accounting, and any potential race conditions. Time to get started!

{
  "File": "mm/memcontrol.c",
  "FirstLine": 1895,
  "LineCount": 40
}

{
  "Contents": "1895:\t\t}\n1896:\t\treturn max;\n1897:\t}\n1898:\t\n1899:\tvoid __memcg_memory_event(struct mem_cgroup *memcg,\n1900:\t\t\t\t  enum memcg_memory_event event, bool allow_spinning)\n1901:\t{\n1902:\t\tbool swap_event = event == MEMCG_SWAP_HIGH || event == MEMCG_SWAP_MAX ||\n1903:\t\t\t\t  event == MEMCG_SWAP_FAIL;\n1904:\t\n1905:\t\t/* For now only MEMCG_MAX can happen with !allow_spinning context. */\n1906:\t\tVM_WARN_ON_ONCE(!allow_spinning \u0026\u0026 event != MEMCG_MAX);\n1907:\t\n1908:\t\tatomic_long_inc(\u0026memcg-\u003ememory_events_local[event]);\n1909:\t\tif (!swap_event \u0026\u0026 allow_spinning)\n1910:\t\t\tcgroup_file_notify(\u0026memcg-\u003eevents_local_file);\n1911:\t\n1912:\t\tdo {\n1913:\t\t\tatomic_long_inc(\u0026memcg-\u003ememory_events[event]);\n1914:\t\t\tif (allow_spinning) {\n1915:\t\t\t\tif (swap_event)\n1916:\t\t\t\t\tcgroup_file_notify(\u0026memcg-\u003eswap_events_file);\n1917:\t\t\t\telse\n1918:\t\t\t\t\tcgroup_file_notify(\u0026memcg-\u003eevents_file);\n1919:\t\t\t}\n1920:\t\n1921:\t\t\tif (!cgroup_subsys_on_dfl(memory_cgrp_subsys))\n1922:\t\t\t\tbreak;\n1923:\t\t\tif (cgrp_dfl_root.flags \u0026 CGRP_ROOT_MEMORY_LOCAL_EVENTS)\n1924:\t\t\t\tbreak;\n1925:\t\t} while ((memcg = parent_mem_cgroup(memcg)) \u0026\u0026\n1926:\t\t\t !mem_cgroup_is_root(memcg));\n1927:\t}\n1928:\tEXPORT_SYMBOL_GPL(__memcg_memory_event);\n1929:\t\n1930:\tstatic bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,\n1931:\t\t\t\t\t     int order)\n1932:\t{\n1933:\t\tstruct oom_control oc = {\n1934:\t\t\t.zonelist = NULL,\n"
}

gemini-3.7-flash

null

null

							input: 6845
							output: 32
							thoughts: 38
						

Okay, let's dive into this code.

**Investigating `try_charge_memcg`**

Right, so I need to understand this `try_charge_memcg` function. I'm going to start by figuring out where it's called from – what are its callers? Understanding the call stack will give me context on its role within the larger memory management framework. Once I have that context, I'll then zero in on the specific functional changes made related to its usage. Knowing the changes will allow me to understand the implications of the change, and the rationale behind it. Basically, I want to understand what's different, and why. Okay, let's start with `try_charge_memcg`.

{
  "Expression": "try_charge_memcg",
  "PathPrefix": "mm/memcontrol.c"
}

{
  "Output": "mm/memcontrol.c=2555=void __mem_cgroup_handle_over_high(gfp_t gfp_mask)\n--\nmm/memcontrol.c-2644-\nmm/memcontrol.c:2645:static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,\nmm/memcontrol.c-2646-\t\t\t    unsigned int nr_pages)\n--\nmm/memcontrol.c=2849=static inline int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,\n--\nmm/memcontrol.c-2854-\nmm/memcontrol.c:2855:\treturn try_charge_memcg(memcg, gfp_mask, nr_pages);\nmm/memcontrol.c-2856-}\n--\nmm/memcontrol.c=3148=static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,\n--\nmm/memcontrol.c-3155-\nmm/memcontrol.c:3156:\tret = try_charge_memcg(memcg, gfp, nr_pages);\nmm/memcontrol.c-3157-\tif (ret)\n--\nmm/memcontrol.c=5196=static int charge_memcg(struct folio *folio, struct mem_cgroup *memcg,\n--\nmm/memcontrol.c-5204-\tif (!obj_cgroup_is_root(objcg))\nmm/memcontrol.c:5205:\t\tret = try_charge_memcg(memcg, gfp, folio_nr_pages(folio));\nmm/memcontrol.c-5206-\tif (ret) {\n--\nmm/memcontrol.c=5616=bool mem_cgroup_sk_charge(const struct sock *sk, unsigned int nr_pages,\n--\nmm/memcontrol.c-5623-\nmm/memcontrol.c:5624:\tif (try_charge_memcg(memcg, gfp_mask, nr_pages) == 0) {\nmm/memcontrol.c-5625-\t\tmod_memcg_state(memcg, MEMCG_SOCK, nr_pages);\n"
}

gemini-3.7-flash

null

null

							input: 7649
							output: 24
							thoughts: 27
						

Okay, let's dive into this. Here's how I'd approach this task, as if these were my internal thoughts:

**Analyzing `mm/memcontrol.c` Configuration**

Alright, I need to figure out the configuration dependencies and requirements for `mm/memcontrol.c`. My first instinct is to check the related `Makefile` in the `mm/` directory. That's usually the best place to find the build rules, dependencies, and any conditional compilation flags. The Makefile should shed light on the necessary kernel features, other modules or options, and any specific configurations needed to include or enable this particular memory control component. I'm expecting to find references to `CONFIG_` options, or perhaps even indirect dependencies on other modules that are *required* for the memory controller to function properly within the bigger memory management context. Let's see what that Makefile has to say... I'm looking for clues!

{
  "Expression": "memcontrol",
  "PathPrefix": "mm/"
}

{
  "Output": "mm/Makefile=27=KCOV_INSTRUMENT_kmemleak.o := n\nmm/Makefile:28:KCOV_INSTRUMENT_memcontrol.o := n\nmm/Makefile:29:KCOV_INSTRUMENT_memcontrol-v1.o := n\nmm/Makefile-30-KCOV_INSTRUMENT_mmzone.o := n\n--\nmm/Makefile=103=obj-$(CONFIG_LIVEUPDATE_MEMFD) += memfd_luo.o\nmm/Makefile:104:obj-$(CONFIG_MEMCG_V1) += memcontrol-v1.o\nmm/Makefile:105:obj-$(CONFIG_MEMCG) += memcontrol.o vmpressure.o\nmm/Makefile-106-ifdef CONFIG_BPF_SYSCALL\nmm/Makefile:107:obj-$(CONFIG_MEMCG) += bpf_memcontrol.o\nmm/Makefile-108-endif\n--\nmm/backing-dev.c=580=static void wb_exit(struct bdi_writeback *wb)\n--\nmm/backing-dev.c-588-\nmm/backing-dev.c:589:#include \u003clinux/memcontrol.h\u003e\nmm/backing-dev.c-590-\n--\nmm/bpf_memcontrol.c-7-\nmm/bpf_memcontrol.c:8:#include \u003clinux/memcontrol.h\u003e\nmm/bpf_memcontrol.c-9-#include \u003clinux/bpf.h\u003e\n--\nmm/bpf_memcontrol.c=162=__bpf_kfunc_end_defs();\nmm/bpf_memcontrol.c-163-\nmm/bpf_memcontrol.c:164:BTF_KFUNCS_START(bpf_memcontrol_kfuncs)\nmm/bpf_memcontrol.c-165-BTF_ID_FLAGS(func, bpf_get_root_mem_cgroup, KF_ACQUIRE | KF_RET_NULL)\n--\nmm/bpf_memcontrol.c=173=BTF_ID_FLAGS(func, bpf_mem_cgroup_flush_stats, KF_SLEEPABLE)\nmm/bpf_memcontrol.c-174-\nmm/bpf_memcontrol.c:175:BTF_KFUNCS_END(bpf_memcontrol_kfuncs)\nmm/bpf_memcontrol.c-176-\nmm/bpf_memcontrol.c:177:static const struct btf_kfunc_id_set bpf_memcontrol_kfunc_set = {\nmm/bpf_memcontrol.c-178-\t.owner          = THIS_MODULE,\nmm/bpf_memcontrol.c:179:\t.set            = \u0026bpf_memcontrol_kfuncs,\nmm/bpf_memcontrol.c-180-};\nmm/bpf_memcontrol.c-181-\nmm/bpf_memcontrol.c:182:static int __init bpf_memcontrol_init(void)\nmm/bpf_memcontrol.c-183-{\n--\nmm/bpf_memcontrol.c-186-\terr = register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC,\nmm/bpf_memcontrol.c:187:\t\t\t\t\t\u0026bpf_memcontrol_kfunc_set);\nmm/bpf_memcontrol.c-188-\tif (err)\nmm/bpf_memcontrol.c:189:\t\tpr_warn(\"error while registering bpf memcontrol kfuncs: %d\", err);\nmm/bpf_memcontrol.c-190-\n--\nmm/bpf_memcontrol.c-192-}\nmm/bpf_memcontrol.c:193:late_initcall(bpf_memcontrol_init);\n--\nmm/damon/core.c-10-#include \u003clinux/kthread.h\u003e\nmm/damon/core.c:11:#include \u003clinux/memcontrol.h\u003e\nmm/damon/core.c-12-#include \u003clinux/mm.h\u003e\n--\nmm/debug.c-11-#include \u003clinux/trace_events.h\u003e\nmm/debug.c:12:#include \u003clinux/memcontrol.h\u003e\nmm/debug.c-13-#include \u003ctrace/events/mmflags.h\u003e\n--\nmm/filemap.c-37-#include \u003clinux/hugetlb.h\u003e\nmm/filemap.c:38:#include \u003clinux/memcontrol.h\u003e\nmm/filemap.c-39-#include \u003clinux/shmem_fs.h\u003e\n--\nmm/folio.c-28-#include \u003clinux/backing-dev.h\u003e\nmm/folio.c:29:#include \u003clinux/memcontrol.h\u003e\nmm/folio.c-30-#include \u003clinux/gfp.h\u003e\n--\nmm/hwpoison-inject.c-10-#include \u003clinux/page-flags.h\u003e\nmm/hwpoison-inject.c:11:#include \u003clinux/memcontrol.h\u003e\nmm/hwpoison-inject.c-12-#include \"internal.h\"\n--\nmm/list_lru.c-13-#include \u003clinux/mutex.h\u003e\nmm/list_lru.c:14:#include \u003clinux/memcontrol.h\u003e\nmm/list_lru.c-15-#include \"slab.h\"\n--\nmm/memcontrol-v1.c-2-\nmm/memcontrol-v1.c:3:#include \u003clinux/memcontrol.h\u003e\nmm/memcontrol-v1.c-4-#include \u003clinux/swap.h\u003e\n--\nmm/memcontrol-v1.c-17-#include \"swap_table.h\"\nmm/memcontrol-v1.c:18:#include \"memcontrol-v1.h\"\nmm/memcontrol-v1.c-19-\n--\nmm/memcontrol-v1.h-6-#include \u003clinux/cgroup-defs.h\u003e\nmm/memcontrol-v1.h:7:#include \u003clinux/memcontrol.h\u003e\nmm/memcontrol-v1.h-8-\n--\nmm/memcontrol.c-1-// SPDX-License-Identifier: GPL-2.0-or-later\nmm/memcontrol.c:2:/* memcontrol.c - Memory Controller\nmm/memcontrol.c-3- *\n--\nmm/memcontrol.c-29-#include \u003clinux/page_counter.h\u003e\nmm/memcontrol.c:30:#include \u003clinux/memcontrol.h\u003e\nmm/memcontrol.c-31-#include \u003clinux/cgroup.h\u003e\n--\nmm/memcontrol.c-70-#include \"slab.h\"\nmm/memcontrol.c:71:#include \"memcontrol-v1.h\"\nmm/memcontrol.c-72-\n--\nmm/memory.c-60-#include \u003clinux/writeback.h\u003e\nmm/memory.c:61:#include \u003clinux/memcontrol.h\u003e\nmm/memory.c-62-#include \u003clinux/mmu_notifier.h\u003e\n--\nmm/mlock.c-24-#include \u003clinux/hugetlb.h\u003e\nmm/mlock.c:25:#include \u003clinux/memcontrol.h\u003e\nmm/mlock.c-26-#include \u003clinux/mm_inline.h\u003e\n--\nmm/mmap_lock.c-6-#include \u003clinux/cgroup.h\u003e\nmm/mmap_lock.c:7:#include \u003clinux/memcontrol.h\u003e\nmm/mmap_lock.c-8-#include \u003clinux/mmap_lock.h\u003e\n--\nmm/oom_kill.c-35-#include \u003clinux/notifier.h\u003e\nmm/oom_kill.c:36:#include \u003clinux/memcontrol.h\u003e\nmm/oom_kill.c-37-#include \u003clinux/mempolicy.h\u003e\n--\nmm/page_alloc.c-48-#include \u003clinux/page_table_check.h\u003e\nmm/page_alloc.c:49:#include \u003clinux/memcontrol.h\u003e\nmm/page_alloc.c-50-#include \u003clinux/ftrace.h\u003e\n--\nmm/page_owner.c-12-#include \u003clinux/seq_file.h\u003e\nmm/page_owner.c:13:#include \u003clinux/memcontrol.h\u003e\nmm/page_owner.c-14-#include \u003clinux/sched/clock.h\u003e\n--\nmm/percpu-internal.h-6-#include \u003clinux/percpu.h\u003e\nmm/percpu-internal.h:7:#include \u003clinux/memcontrol.h\u003e\nmm/percpu-internal.h-8-\n--\nmm/percpu.c-88-#include \u003clinux/sched/mm.h\u003e\nmm/percpu.c:89:#include \u003clinux/memcontrol.h\u003e\nmm/percpu.c-90-\n--\nmm/rmap.c-66-#include \u003clinux/export.h\u003e\nmm/rmap.c:67:#include \u003clinux/memcontrol.h\u003e\nmm/rmap.c-68-#include \u003clinux/mmu_notifier.h\u003e\n--\nmm/shrinker.c-1-// SPDX-License-Identifier: GPL-2.0\nmm/shrinker.c:2:#include \u003clinux/memcontrol.h\u003e\nmm/shrinker.c-3-#include \u003clinux/rwsem.h\u003e\n--\nmm/shrinker_debug.c-6-#include \u003clinux/shrinker.h\u003e\nmm/shrinker_debug.c:7:#include \u003clinux/memcontrol.h\u003e\nmm/shrinker_debug.c-8-\n--\nmm/slab.h-10-#include \u003clinux/sched/mm.h\u003e\nmm/slab.h:11:#include \u003clinux/memcontrol.h\u003e\nmm/slab.h-12-#include \u003clinux/kfence.h\u003e\n--\nmm/slab_common.c-28-#include \u003casm/page.h\u003e\nmm/slab_common.c:29:#include \u003clinux/memcontrol.h\u003e\nmm/slab_common.c-30-#include \u003clinux/stackdepot.h\u003e\n--\nmm/slub.c-43-#include \u003clinux/prefetch.h\u003e\nmm/slub.c:44:#include \u003clinux/memcontrol.h\u003e\nmm/slub.c-45-#include \u003clinux/random.h\u003e\n--\nmm/swap.h-6-#include \u003clinux/mm.h\u003e /* for PAGE_SHIFT */\nmm/swap.h:7:#include \u003clinux/memcontrol.h\u003e /* for mem_cgroup_swappiness() */\nmm/swap.h-8-#include \u003clinux/swap.h\u003e /* for MAX_SWAPFILES_SHIFT, struct swap_info_struct */\n--\nmm/swapfile.c-34-#include \u003clinux/syscalls.h\u003e\nmm/swapfile.c:35:#include \u003clinux/memcontrol.h\u003e\nmm/swapfile.c-36-#include \u003clinux/poll.h\u003e\n--\nmm/vmalloc.c-33-#include \u003clinux/compiler.h\u003e\nmm/vmalloc.c:34:#include \u003clinux/memcontrol.h\u003e\nmm/vmalloc.c-35-#include \u003clinux/llist.h\u003e\n--\nmm/vmpressure.c-11- * Tree-mode (cgroup v1 userspace eventfd) bookkeeping lives in\nmm/vmpressure.c:12: * mm/memcontrol-v1.c; this file holds the shared code and the in-kernel\nmm/vmpressure.c-13- * (tree=false) socket-pressure path that runs on cgroup v2.\n--\nmm/vmscan.c-40-#include \u003clinux/freezer.h\u003e\nmm/vmscan.c:41:#include \u003clinux/memcontrol.h\u003e\nmm/vmscan.c-42-#include \u003clinux/migrate.h\u003e\n--\nmm/workingset.c-7-\nmm/workingset.c:8:#include \u003clinux/memcontrol.h\u003e\nmm/workingset.c-9-#include \u003clinux/mm_inline.h\u003e\n"
}

gemini-3.7-flash

null

null

							input: 10879
							output: 25
							thoughts: 10
						

Okay, here's my attempt at summarizing that thought process, tailored for an expert audience:

**Checking Kconfig for MEMCG**

Alright, let's get down to brass tacks. First, I need to make sure I'm on solid ground with memory cgroups. I'm going to quickly check the Kconfig files. This is standard operating procedure. I need to confirm whether `CONFIG_MEMCG` is enabled or at least configurable, and what its current state is. This immediately tells me if I even *have* memory cgroups support compiled in, or if I need to dig into build configurations to enable it. I might also check for associated options that control its behavior, like nested cgroups or any specific resource limits defined. No point in wasting time if I'm not even working with a kernel that supports the functionality I need. Quickly checking Kconfig provides a fast sanity check before proceeding further.

{
  "Expression": "config MEMCG",
  "PathPrefix": "init/"
}

{
  "Output": "init/Kconfig=1075=config CGROUP_FAVOR_DYNMODS\n--\ninit/Kconfig-1084-\ninit/Kconfig:1085:config MEMCG\ninit/Kconfig-1086-\tbool \"Memory controller\"\n--\ninit/Kconfig-1093-\ninit/Kconfig:1094:config MEMCG_NMI_UNSAFE\ninit/Kconfig-1095-\tbool\n--\ninit/Kconfig-1100-\ninit/Kconfig:1101:config MEMCG_NMI_SAFETY_REQUIRES_ATOMIC\ninit/Kconfig-1102-\tbool\n--\ninit/Kconfig-1107-\ninit/Kconfig:1108:config MEMCG_V1\ninit/Kconfig-1109-\tbool \"Legacy cgroup v1 memory controller\"\n"
}

gemini-3.7-flash

null

null

							input: 11333
							output: 33
							thoughts: 17
						

Here's my attempt at summarizing the thought process, tailored for an expert audience:

**Diving into `init/Kconfig`**

Okay, time to get my hands dirty. I need to understand the configuration logic, specifically within the initialization phase of this system. Let's start by zeroing in on `init/Kconfig`, that's the obvious place to begin dissecting the build-time options and dependencies. I'm going to look at it around line 1085, that's generally where I'd expect to find either a core component or a more specialized module declaration. Hopefully, that will give me some insight to work with. I'm anticipating some critical definitions in this section, I need to see how the early boot process is shaped by the config.

{
  "File": "init/Kconfig",
  "FirstLine": 1080,
  "LineCount": 40
}

{
  "Contents": "1080:\t\t  as task migrations and controller on/offs at the cost of making\n1081:\t\t  hot path operations such as forks and exits more expensive.\n1082:\t\n1083:\t\t  Say N if unsure.\n1084:\t\n1085:\tconfig MEMCG\n1086:\t\tbool \"Memory controller\"\n1087:\t\tselect PAGE_COUNTER\n1088:\t\tselect EVENTFD\n1089:\t\tselect SLAB_OBJ_EXT\n1090:\t\tselect VM_EVENT_COUNTERS\n1091:\t\thelp\n1092:\t\t  Provides control over the memory footprint of tasks in a cgroup.\n1093:\t\n1094:\tconfig MEMCG_NMI_UNSAFE\n1095:\t\tbool\n1096:\t\tdepends on MEMCG\n1097:\t\tdepends on HAVE_NMI\n1098:\t\tdepends on !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS \u0026\u0026 !ARCH_HAVE_NMI_SAFE_CMPXCHG\n1099:\t\tdefault y\n1100:\t\n1101:\tconfig MEMCG_NMI_SAFETY_REQUIRES_ATOMIC\n1102:\t\tbool\n1103:\t\tdepends on MEMCG\n1104:\t\tdepends on HAVE_NMI\n1105:\t\tdepends on !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS \u0026\u0026 ARCH_HAVE_NMI_SAFE_CMPXCHG\n1106:\t\tdefault y\n1107:\t\n1108:\tconfig MEMCG_V1\n1109:\t\tbool \"Legacy cgroup v1 memory controller\"\n1110:\t\tdepends on MEMCG\n1111:\t\tdefault n\n1112:\t\thelp\n1113:\t\t  Legacy cgroup v1 memory controller which has been deprecated by\n1114:\t\t  cgroup v2 implementation. The v1 is there for legacy applications\n1115:\t\t  which haven't migrated to the new cgroup v2 interface yet. If you\n1116:\t\t  do not have any such application then you are completely fine leaving\n1117:\t\t  this option disabled.\n1118:\t\n1119:\t\t  Please note that feature set of the legacy memory controller is likely\n"
}

gemini-3.7-flash

null

null

							input: 12132
							output: 33
							thoughts: 41
						

Here's my summary, as though I'm thinking through this process:

**Diving into the Kernel Configuration Dependencies**

Okay, so I need to figure out the dependencies for `config MEMCG` – that’s line 1085 in `init/Kconfig`. Time to get the lay of the land. I'll quickly scan the surrounding lines, specifically from 1060 to 1085, to understand what's influencing its configuration. This usually reveals the relevant `depends on` statements and any associated conditional logic within that segment of the Kconfig file. I'm expecting to see conditions related to other kernel features, architecture-specific flags, or perhaps some preprocessor macros that are relevant to memory control groups. Let's see what the dependencies are!

{
  "File": "init/Kconfig",
  "FirstLine": 1060,
  "LineCount": 30
}

{
  "Contents": "1060:\t\t  This option adds support for grouping sets of processes together, for\n1061:\t\t  use with process control subsystems such as Cpusets, CFS, memory\n1062:\t\t  controls or device isolation.\n1063:\t\t  See\n1064:\t\t\t- Documentation/scheduler/sched-design-CFS.rst\t(CFS)\n1065:\t\t\t- Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation\n1066:\t\t\t\t\t\t  and resource control)\n1067:\t\n1068:\t\t  Say N if unsure.\n1069:\t\n1070:\tif CGROUPS\n1071:\t\n1072:\tconfig PAGE_COUNTER\n1073:\t\tbool\n1074:\t\n1075:\tconfig CGROUP_FAVOR_DYNMODS\n1076:\t\tbool \"Favor dynamic modification latency reduction by default\"\n1077:\t\thelp\n1078:\t\t  This option enables the \"favordynmods\" mount option by default\n1079:\t\t  which reduces the latencies of dynamic cgroup modifications such\n1080:\t\t  as task migrations and controller on/offs at the cost of making\n1081:\t\t  hot path operations such as forks and exits more expensive.\n1082:\t\n1083:\t\t  Say N if unsure.\n1084:\t\n1085:\tconfig MEMCG\n1086:\t\tbool \"Memory controller\"\n1087:\t\tselect PAGE_COUNTER\n1088:\t\tselect EVENTFD\n1089:\t\tselect SLAB_OBJ_EXT\n"
}

gemini-3.7-flash

null

null

							input: 12793
							output: 35
							thoughts: 1137
						

**Analyzing the memcg Patch: A Deep Dive**

Okay, so we're looking at a patch concerning `CGROUPS` and `MEMCG`, specifically within the `try_charge_memcg` function. My initial thought is to figure out precisely what this patch is changing. It appears to be related to how we handle `memory.max` events.

My understanding is that previously, when a non-blocking allocation (e.g., `GFP_ATOMIC`, `GFP_NOWAIT`) hit the `memory.max` limit, the code would jump to `nomem` before triggering the `__memcg_memory_event` call. This meant that the "max" counter in `memory.events` wasn't being incremented, which seems like a bug. Similarly, tasks in OOM or exiting OOM victims also wouldn't trigger the event.

The patch's core change is moving the `__memcg_memory_event` call *above* these bail-out checks. This is significant because it guarantees that *any* failed charge against `memory.max` (or `memory.swap.max`) will now correctly increment the "max" counter in `memory.events` (and `events.local`). This should ensure proper notification to listeners via inotify/epoll on cgroup v2. This seems to correct a clear bug and improve monitoring of memcg events.

The next question is whether this merits fuzzing. Given my expertise, I'll apply the criteria: this patch modifies core kernel logic (specifically, memory management within `memcg`). It's directly reachable in standard virtualized environments. Therefore, it satisfies the conditions for being worth fuzzing.

I need to confirm something though.
The code passes `allow_spinning` to `__memcg_memory_event`. I'll look into it.
The code uses `gfpflags_allow_blocking(gfp_mask) && !(current->flags & PF_MEMALLOC)` to determine the value of this flag.
I should confirm its usage to ensure that it's safe to call the memcg event from atomic contexts.

{
  "File": "mm/memcontrol.c",
  "FirstLine": 2640,
  "LineCount": 30
}

{
  "Contents": "2640:\t\n2641:\tout:\n2642:\t\tcss_put(\u0026memcg-\u003ecss);\n2643:\t}\n2644:\t\n2645:\tstatic int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,\n2646:\t\t\t\t    unsigned int nr_pages)\n2647:\t{\n2648:\t\tunsigned int batch = max(MEMCG_CHARGE_BATCH, nr_pages);\n2649:\t\tint nr_retries = MAX_RECLAIM_RETRIES;\n2650:\t\tstruct mem_cgroup *mem_over_limit;\n2651:\t\tstruct page_counter *counter;\n2652:\t\tunsigned long nr_reclaimed;\n2653:\t\tbool passed_oom = false;\n2654:\t\tunsigned int reclaim_options;\n2655:\t\tbool drained = false;\n2656:\t\tbool raised_max_event = false;\n2657:\t\tunsigned long pflags;\n2658:\t\tbool allow_spinning = gfpflags_allow_spinning(gfp_mask);\n2659:\t\n2660:\tretry:\n2661:\t\tif (consume_stock(memcg, nr_pages))\n2662:\t\t\treturn 0;\n2663:\t\n2664:\t\tif (!allow_spinning)\n2665:\t\t\t/* Avoid the refill and flush of the older stock */\n2666:\t\t\tbatch = nr_pages;\n2667:\t\n2668:\t\treclaim_options = MEMCG_RECLAIM_MAY_SWAP;\n2669:\t\tif (!do_memsw_account() ||\n"
}

gemini-3.7-flash

null

null

							input: 14864
							output: 25
							thoughts: 531
						

**Fuzzing Target Identification: Memory Control in the Linux Kernel**

Okay, let's break this down. I've got a section of kernel code related to memory control (`mm/memcontrol.c`) that's clearly interesting from a fuzzing perspective. The key is how memory limits are handled and reported through the `memcg` mechanism. I can see the code focuses on event tracking and notifications related to hitting those limits, and I note that it affects several key areas: memcg charging, event reporting, cgroup file notifications. Given the critical nature of these functions, finding a vulnerability here would have significant consequences. I can also trigger this logic in standard environments like QEMU or GCE without special hardware.

My first thought, is that `WorthFuzzing = true`, so I need to find the `FocusSymbols`. I need to figure out the right entrypoints for a fuzzer to target. I'll need to identify the relevant API entrypoints – specifically, any non-static, non-inlined functions that are involved in this code path. I will need to trace back from this core function and find out how to trigger it. I'll look for functions in `mm/memcontrol.c` or exported functions that call `try_charge_memcg` or similar functions that trigger memcg charging.

{
  "Expression": "try_charge",
  "PathPrefix": "mm/"
}

{
  "Output": "mm/hugetlb_cgroup.c=256=static int __hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,\n--\nmm/hugetlb_cgroup.c-274-\nmm/hugetlb_cgroup.c:275:\tif (!page_counter_try_charge(\nmm/hugetlb_cgroup.c-276-\t\t    __hugetlb_cgroup_counter_from_cgroup(h_cg, idx, rsvd),\n--\nmm/memcontrol-v1.c=2541=bool memcg1_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages,\n--\nmm/memcontrol-v1.c-2545-\nmm/memcontrol-v1.c:2546:\tif (page_counter_try_charge(\u0026memcg-\u003etcpmem, nr_pages, \u0026fail)) {\nmm/memcontrol-v1.c-2547-\t\tmemcg-\u003etcpmem_pressure = 0;\n--\nmm/memcontrol.c=2518=static unsigned long calculate_high_delay(struct mem_cgroup *memcg,\n--\nmm/memcontrol.c-2551- * Reclaims memory over the high limit. Called directly from\nmm/memcontrol.c:2552: * try_charge() (context permitting), as well as from the userland\nmm/memcontrol.c-2553- * return path where reclaim is always able to block.\n--\nmm/memcontrol.c=2555=void __mem_cgroup_handle_over_high(gfp_t gfp_mask)\n--\nmm/memcontrol.c-2644-\nmm/memcontrol.c:2645:static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,\nmm/memcontrol.c-2646-\t\t\t    unsigned int nr_pages)\n--\nmm/memcontrol.c-2669-\tif (!do_memsw_account() ||\nmm/memcontrol.c:2670:\t    page_counter_try_charge(\u0026memcg-\u003ememsw, batch, \u0026counter)) {\nmm/memcontrol.c:2671:\t\tif (page_counter_try_charge(\u0026memcg-\u003ememory, batch, \u0026counter))\nmm/memcontrol.c-2672-\t\t\tgoto done_restock;\n--\nmm/memcontrol.c-2848-\nmm/memcontrol.c:2849:static inline int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,\nmm/memcontrol.c-2850-\t\t\t     unsigned int nr_pages)\n--\nmm/memcontrol.c-2854-\nmm/memcontrol.c:2855:\treturn try_charge_memcg(memcg, gfp_mask, nr_pages);\nmm/memcontrol.c-2856-}\n--\nmm/memcontrol.c=3148=static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,\n--\nmm/memcontrol.c-3155-\nmm/memcontrol.c:3156:\tret = try_charge_memcg(memcg, gfp, nr_pages);\nmm/memcontrol.c-3157-\tif (ret)\n--\nmm/memcontrol.c=5196=static int charge_memcg(struct folio *folio, struct mem_cgroup *memcg,\n--\nmm/memcontrol.c-5204-\tif (!obj_cgroup_is_root(objcg))\nmm/memcontrol.c:5205:\t\tret = try_charge_memcg(memcg, gfp, folio_nr_pages(folio));\nmm/memcontrol.c-5206-\tif (ret) {\n--\nmm/memcontrol.c=5616=bool mem_cgroup_sk_charge(const struct sock *sk, unsigned int nr_pages,\n--\nmm/memcontrol.c-5623-\nmm/memcontrol.c:5624:\tif (try_charge_memcg(memcg, gfp_mask, nr_pages) == 0) {\nmm/memcontrol.c-5625-\t\tmod_memcg_state(memcg, MEMCG_SOCK, nr_pages);\n--\nmm/memcontrol.c=5682=int __init mem_cgroup_init(void)\n--\nmm/memcontrol.c-5719-/**\nmm/memcontrol.c:5720: * __mem_cgroup_try_charge_swap - try charging swap space for a folio\nmm/memcontrol.c-5721- * @folio: folio being added to swap\n--\nmm/memcontrol.c-5726- */\nmm/memcontrol.c:5727:int __mem_cgroup_try_charge_swap(struct folio *folio)\nmm/memcontrol.c-5728-{\n--\nmm/memcontrol.c-5755-\tif (!mem_cgroup_is_root(memcg) \u0026\u0026\nmm/memcontrol.c:5756:\t    !page_counter_try_charge(\u0026memcg-\u003eswap, nr_pages, \u0026counter)) {\nmm/memcontrol.c-5757-\t\tmemcg_memory_event(memcg, MEMCG_SWAP_MAX);\n--\nmm/page_counter.c=76=void page_counter_charge(struct page_counter *counter, unsigned long nr_pages)\n--\nmm/page_counter.c-109-/**\nmm/page_counter.c:110: * page_counter_try_charge - try to hierarchically charge pages\nmm/page_counter.c-111- * @counter: counter\n--\nmm/page_counter.c-117- */\nmm/page_counter.c:118:bool page_counter_try_charge(struct page_counter *counter,\nmm/page_counter.c-119-\t\t\t     unsigned long nr_pages,\n--\nmm/page_counter.c=197=int page_counter_set_max(struct page_counter *counter, unsigned long nr_pages)\n--\nmm/page_counter.c-208-\t\t * and after, so the read-swap-read is ordered and\nmm/page_counter.c:209:\t\t * ensures coherency with page_counter_try_charge():\nmm/page_counter.c-210-\t\t * that function modifies the count before checking\n--\nmm/swapfile.c=1740=int folio_alloc_swap(struct folio *folio)\n--\nmm/swapfile.c-1777-\t/* Need to call this even if allocation failed, for MEMCG_SWAP_FAIL. */\nmm/swapfile.c:1778:\tif (unlikely(mem_cgroup_try_charge_swap(folio)))\nmm/swapfile.c-1779-\t\tswap_cache_del_folio(folio);\n"
}

gemini-3.7-flash

null

null

							input: 17459
							output: 30
							thoughts: 134
						

**Analyzing Memory Control Group Charge Functions**

Alright, let's dive into this. I need to understand how memory charges are handled within the memory control group framework. My immediate focus is on the functions that directly invoke `try_charge_memcg`.

It looks like the key players are: `mem_cgroup_sk_charge`, `charge_memcg`, `obj_cgroup_charge_pages`, and that intriguing `__memcg_memory_event`. I'll want to pay particularly close attention to how that last one is modified at its callsite.

`charge_memcg` seems to be central, being called by a few important others like `mem_cgroup_charge` and `mem_cgroup_swapin_charge_folio`. Now, let's specifically examine the `mem_cgroup_charge` function and its callers within `mm/memcontrol.c`. That should give me a pretty good understanding of where the core memory charging logic resides. Time to crack open the code.

{
  "Expression": "charge_memcg",
  "PathPrefix": "mm/memcontrol.c"
}

{
  "Output": "mm/memcontrol.c=2555=void __mem_cgroup_handle_over_high(gfp_t gfp_mask)\n--\nmm/memcontrol.c-2644-\nmm/memcontrol.c:2645:static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,\nmm/memcontrol.c-2646-\t\t\t    unsigned int nr_pages)\n--\nmm/memcontrol.c=2849=static inline int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,\n--\nmm/memcontrol.c-2854-\nmm/memcontrol.c:2855:\treturn try_charge_memcg(memcg, gfp_mask, nr_pages);\nmm/memcontrol.c-2856-}\n--\nmm/memcontrol.c=3148=static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,\n--\nmm/memcontrol.c-3155-\nmm/memcontrol.c:3156:\tret = try_charge_memcg(memcg, gfp, nr_pages);\nmm/memcontrol.c-3157-\tif (ret)\n--\nmm/memcontrol.c=5181=void mem_cgroup_calculate_protection(struct mem_cgroup *root,\n--\nmm/memcontrol.c-5195-\nmm/memcontrol.c:5196:static int charge_memcg(struct folio *folio, struct mem_cgroup *memcg,\nmm/memcontrol.c-5197-\t\t\tgfp_t gfp)\n--\nmm/memcontrol.c-5204-\tif (!obj_cgroup_is_root(objcg))\nmm/memcontrol.c:5205:\t\tret = try_charge_memcg(memcg, gfp, folio_nr_pages(folio));\nmm/memcontrol.c-5206-\tif (ret) {\n--\nmm/memcontrol.c=5216=int __mem_cgroup_charge(struct folio *folio, struct mm_struct *mm, gfp_t gfp)\n--\nmm/memcontrol.c-5221-\tmemcg = get_mem_cgroup_from_mm(mm);\nmm/memcontrol.c:5222:\tret = charge_memcg(folio, memcg, gfp);\nmm/memcontrol.c-5223-\tcss_put(\u0026memcg-\u003ecss);\n--\nmm/memcontrol.c=5240=int mem_cgroup_charge_hugetlb(struct folio *folio, gfp_t gfp)\n--\nmm/memcontrol.c-5253-\nmm/memcontrol.c:5254:\tif (charge_memcg(folio, memcg, gfp))\nmm/memcontrol.c-5255-\t\tret = -ENOMEM;\n--\nmm/memcontrol.c=5274=int mem_cgroup_swapin_charge_folio(struct folio *folio, unsigned short id,\n--\nmm/memcontrol.c-5288-\nmm/memcontrol.c:5289:\tret = charge_memcg(folio, memcg, gfp);\nmm/memcontrol.c-5290-\n--\nmm/memcontrol.c=5616=bool mem_cgroup_sk_charge(const struct sock *sk, unsigned int nr_pages,\n--\nmm/memcontrol.c-5623-\nmm/memcontrol.c:5624:\tif (try_charge_memcg(memcg, gfp_mask, nr_pages) == 0) {\nmm/memcontrol.c-5625-\t\tmod_memcg_state(memcg, MEMCG_SOCK, nr_pages);\n"
}

gemini-3.7-flash

null

null

							input: 18811
							output: 178
							thoughts: 632
						

**My Analysis of Memory Controller Functionality for Fuzzing**

Alright, let's break this down. My goal is to identify the key kernel functions impacted by this change, especially those relevant for fuzzing, keeping in mind the need to avoid generic functions and prioritize non-static, non-inlined entry points.

I'm starting by looking at the specific functions mentioned: `__mem_cgroup_charge`, `mem_cgroup_charge_hugetlb`, `mem_cgroup_swapin_charge_folio`, and `mem_cgroup_sk_charge`, along with `__memcg_memory_event`. I'm verifying that `__memcg_memory_event` is indeed non-static and exported.

The core of the matter seems to be in `try_charge_memcg`, where the patch affects when `__memcg_memory_event` gets called. This makes it a direct target, and, by extension, the other charge functions too, so I'll include them in my FocusSymbols.

Now, let's examine dependencies. I'm checking `Kconfig` for the `MEMCG` configuration, since this is in the memory control module. I found it, and it depends on `CGROUPS`. I need to ensure that no other configs are needed. Looking at `init/Kconfig` again, it looks like `MEMCG` selects `PAGE_COUNTER`, `EVENTFD`, `SLAB_OBJ_EXT`, and `VM_EVENT_COUNTERS` but these are all selected and should not require any further consideration.

So, in summary, I'm setting the `WorthFuzzing` flag to true, and my `FocusSymbols` are `__memcg_memory_event`, `mem_cgroup_sk_charge`, `__mem_cgroup_charge`, `mem_cgroup_charge_hugetlb`, and `mem_cgroup_swapin_charge_folio`. The `EnableConfigs` are `CGROUPS` and `MEMCG`. My reasoning centers on the change in event reporting behavior in the memory controller during charging against `memory.max` in non-blocking or OOM scenarios. This impacts function reachability and functional impact, which makes this worthwhile for fuzzing.

Finally, I will run the set-results tool for a sanity check.

{
  "EnableConfigs": [
    "CGROUPS",
    "MEMCG"
  ],
  "FocusSymbols": [
    "__memcg_memory_event",
    "mem_cgroup_sk_charge",
    "__mem_cgroup_charge",
    "mem_cgroup_charge_hugetlb",
    "mem_cgroup_swapin_charge_folio"
  ],
  "Reasoning": "The patch changes the memory controller (memcg) charging path in try_charge_memcg() to raise MEMCG_MAX memory events immediately when the page counter exceeds the limit, before any early bail-outs (such as non-blocking allocations, OOM tasks, or exiting OOM victims). This functionally affects memory event counting and notifications for memory.events and memory.events.local.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "CGROUPS",
    "MEMCG"
  ],
  "FocusSymbols": [
    "__memcg_memory_event",
    "mem_cgroup_sk_charge",
    "__mem_cgroup_charge",
    "mem_cgroup_charge_hugetlb",
    "mem_cgroup_swapin_charge_folio"
  ],
  "Reasoning": "The patch changes the memory controller (memcg) charging path in try_charge_memcg() to raise MEMCG_MAX memory events immediately when the page counter exceeds the limit, before any early bail-outs (such as non-blocking allocations, OOM tasks, or exiting OOM victims). This functionally affects memory event counting and notifications for memory.events and memory.events.local.",
  "WorthFuzzing": true
}

{
  "WorthFuzzing": true
}

null

core

null

{
  "KMSANReasoning": "The patch modifies the control flow in `try_charge_memcg()` within `mm/memcontrol.c` so that the `MEMCG_MAX` event (`__memcg_memory_event`) is recorded earlier whenever a memory cgroup limit is exceeded, ensuring it is accounted even if the allocation bails out early (e.g. non-blocking GFP masks or OOM scenarios).\n\nAll variables involved (`mem_over_limit`, `allow_spinning`, `raised_max_event`) are explicitly initialized before use. The patch does not introduce or modify any memory copying to userspace, buffer length/bounds calculations, memory allocations, or struct initializations that could result in uninitialized memory reads or information leaks.\n\nTherefore, this change does not introduce any uninitialized memory risks that would require dedicated KMSAN fuzzing; standard KASAN/LOCKDEP test configurations are appropriate.",
  "NeedsKMSAN": false
}

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.

For your convenience, here is the diff of the changes:
commit 96fe8df56a28ddb7912b73355d66b60f22cb76a3
Author: syz-cluster <triage@syzkaller.com>
Date:   Thu Aug 27 23:37:36 2026 +0000

    syz-cluster: applied patch under review

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1271d390b617e..3904fe9a7b2e9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2683,6 +2683,11 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 		goto retry;
 	}
 
+	if (!raised_max_event) {
+		__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);
+		raised_max_event = true;
+	}
+
 	/*
 	 * Prevent unbounded recursion when reclaim operations need to
 	 * allocate memory. This might exceed the limits temporarily,
@@ -2711,9 +2716,6 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	    mm_flags_test(MMF_OOM_SKIP, current->signal->oom_mm))
 		goto nomem;
 
-	__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);
-	raised_max_event = true;
-
 	psi_memstall_enter(&pflags);
 	nr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages,
 						    gfp_mask, reclaim_options, NULL);
@@ -2773,13 +2775,6 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	if (!(gfp_mask & (__GFP_NOFAIL | __GFP_HIGH)))
 		return -ENOMEM;
 force:
-	/*
-	 * If the allocation has to be enforced, don't forget to raise
-	 * a MEMCG_MAX event.
-	 */
-	if (!raised_max_event)
-		__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);
-
 	/*
 	 * The allocation either can't fail or will lead to more memory
 	 * being freed very soon.  Allow memory usage go over the limit

gemini-3.7-flash

null

null

							input: 2454
							output: 36
							thoughts: 44
						

Okay, here's my interpretation of those directives, structured as a first-person account of the thought process:

**Diving into `mm/memcontrol.c`**

Alright, time to get my hands dirty. I'm going to take a look at the diff and surrounding code within `mm/memcontrol.c`. This suggests there's some change or bug report I need to understand, and this file is the focal point. Specifically, I'm thinking I'll want to use `read-file`, likely around line 2680. That line number will give me a good initial point to examine the context of the change or issue. This is my go-to approach – context first, then the specific modification, helps me get the full picture of what's happening.

{
  "File": "mm/memcontrol.c",
  "FirstLine": 2660,
  "LineCount": 100
}

{
  "Contents": "2660:\tretry:\n2661:\t\tif (consume_stock(memcg, nr_pages))\n2662:\t\t\treturn 0;\n2663:\t\n2664:\t\tif (!allow_spinning)\n2665:\t\t\t/* Avoid the refill and flush of the older stock */\n2666:\t\t\tbatch = nr_pages;\n2667:\t\n2668:\t\treclaim_options = MEMCG_RECLAIM_MAY_SWAP;\n2669:\t\tif (!do_memsw_account() ||\n2670:\t\t    page_counter_try_charge(\u0026memcg-\u003ememsw, batch, \u0026counter)) {\n2671:\t\t\tif (page_counter_try_charge(\u0026memcg-\u003ememory, batch, \u0026counter))\n2672:\t\t\t\tgoto done_restock;\n2673:\t\t\tif (do_memsw_account())\n2674:\t\t\t\tpage_counter_uncharge(\u0026memcg-\u003ememsw, batch);\n2675:\t\t\tmem_over_limit = mem_cgroup_from_counter(counter, memory);\n2676:\t\t} else {\n2677:\t\t\tmem_over_limit = mem_cgroup_from_counter(counter, memsw);\n2678:\t\t\treclaim_options \u0026= ~MEMCG_RECLAIM_MAY_SWAP;\n2679:\t\t}\n2680:\t\n2681:\t\tif (batch \u003e nr_pages) {\n2682:\t\t\tbatch = nr_pages;\n2683:\t\t\tgoto retry;\n2684:\t\t}\n2685:\t\n2686:\t\tif (!raised_max_event) {\n2687:\t\t\t__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);\n2688:\t\t\traised_max_event = true;\n2689:\t\t}\n2690:\t\n2691:\t\t/*\n2692:\t\t * Prevent unbounded recursion when reclaim operations need to\n2693:\t\t * allocate memory. This might exceed the limits temporarily,\n2694:\t\t * but we prefer facilitating memory reclaim and getting back\n2695:\t\t * under the limit over triggering OOM kills in these cases.\n2696:\t\t */\n2697:\t\tif (unlikely(current-\u003eflags \u0026 PF_MEMALLOC))\n2698:\t\t\tgoto force;\n2699:\t\n2700:\t\tif (unlikely(task_in_memcg_oom(current)))\n2701:\t\t\tgoto nomem;\n2702:\t\n2703:\t\tif (!gfpflags_allow_blocking(gfp_mask))\n2704:\t\t\tgoto nomem;\n2705:\t\n2706:\t\t/*\n2707:\t\t * OOM victim still needs to charge memory to exit. OOM reaper should\n2708:\t\t * help but it might fail on mmap_lock contention. If the victim is a\n2709:\t\t * large thread group then all exiting threads might compete on oom_lock\n2710:\t\t * just to learn that there is nothing really killable anymore. Bail\n2711:\t\t * out early and fail the charge to expedite their exit. They are\n2712:\t\t * considered fully reclaimed by the oom reaper and they shouldn't\n2713:\t\t * contribute further charges.\n2714:\t\t */\n2715:\t\tif (tsk_is_oom_victim(current) \u0026\u0026\n2716:\t\t    mm_flags_test(MMF_OOM_SKIP, current-\u003esignal-\u003eoom_mm))\n2717:\t\t\tgoto nomem;\n2718:\t\n2719:\t\tpsi_memstall_enter(\u0026pflags);\n2720:\t\tnr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages,\n2721:\t\t\t\t\t\t\t    gfp_mask, reclaim_options, NULL);\n2722:\t\tpsi_memstall_leave(\u0026pflags);\n2723:\t\n2724:\t\tif (mem_cgroup_margin(mem_over_limit) \u003e= nr_pages)\n2725:\t\t\tgoto retry;\n2726:\t\n2727:\t\tif (!drained) {\n2728:\t\t\tdrain_all_stock(mem_over_limit);\n2729:\t\t\tdrained = true;\n2730:\t\t\tgoto retry;\n2731:\t\t}\n2732:\t\n2733:\t\tif (gfp_mask \u0026 __GFP_NORETRY)\n2734:\t\t\tgoto nomem;\n2735:\t\t/*\n2736:\t\t * Even though the limit is exceeded at this point, reclaim\n2737:\t\t * may have been able to free some pages.  Retry the charge\n2738:\t\t * before killing the task.\n2739:\t\t *\n2740:\t\t * Only for regular pages, though: huge pages are rather\n2741:\t\t * unlikely to succeed so close to the limit, and we fall back\n2742:\t\t * to regular pages anyway in case of failure.\n2743:\t\t */\n2744:\t\tif (nr_reclaimed \u0026\u0026 nr_pages \u003c= (1 \u003c\u003c PAGE_ALLOC_COSTLY_ORDER))\n2745:\t\t\tgoto retry;\n2746:\t\n2747:\t\tif (nr_retries--)\n2748:\t\t\tgoto retry;\n2749:\t\n2750:\t\tif (gfp_mask \u0026 __GFP_RETRY_MAYFAIL)\n2751:\t\t\tgoto nomem;\n2752:\t\n2753:\t\t/* Avoid endless loop for tasks bypassed by the oom killer */\n2754:\t\tif (passed_oom \u0026\u0026 task_is_dying())\n2755:\t\t\tgoto nomem;\n2756:\t\n2757:\t\t/*\n2758:\t\t * keep retrying as long as the memcg oom killer is able to make\n2759:\t\t * a forward progress or bypass the charge if the oom killer\n"
}

gemini-3.7-flash

null

null

							input: 4228
							output: 35
							thoughts: 31
						

Here's my take on the thought process, as requested:

**Deconstructing try_charge_memcg: A Deeper Dive**

Okay, so I need to get a handle on the changes in `try_charge_memcg`. The previous commit introduced something, and I've got to understand the implications. The best way to do that, as always, is to follow the code. First, let's look at where `try_charge_memcg` is used in the rest of the code, in this context. Then I'll need to go back and examine the function's definition itself, the function signature and the internals. Context is king here; understanding *how* it's being used is just as vital as understanding *what* it does. From there I'll be able to see the modifications and why they were made. I'm expecting this will involve looking at memory accounting, resource limiting, and how this particular function fits into the overall memory management scheme within the cgroup hierarchy. Right, let's get to it.

{
  "File": "mm/memcontrol.c",
  "FirstLine": 2635,
  "LineCount": 40
}

{
  "Contents": "2635:\t\t * need to account for any ill-begotten jiffies to pay them off later.\n2636:\t\t */\n2637:\t\tpsi_memstall_enter(\u0026pflags);\n2638:\t\tschedule_timeout_killable(penalty_jiffies);\n2639:\t\tpsi_memstall_leave(\u0026pflags);\n2640:\t\n2641:\tout:\n2642:\t\tcss_put(\u0026memcg-\u003ecss);\n2643:\t}\n2644:\t\n2645:\tstatic int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,\n2646:\t\t\t\t    unsigned int nr_pages)\n2647:\t{\n2648:\t\tunsigned int batch = max(MEMCG_CHARGE_BATCH, nr_pages);\n2649:\t\tint nr_retries = MAX_RECLAIM_RETRIES;\n2650:\t\tstruct mem_cgroup *mem_over_limit;\n2651:\t\tstruct page_counter *counter;\n2652:\t\tunsigned long nr_reclaimed;\n2653:\t\tbool passed_oom = false;\n2654:\t\tunsigned int reclaim_options;\n2655:\t\tbool drained = false;\n2656:\t\tbool raised_max_event = false;\n2657:\t\tunsigned long pflags;\n2658:\t\tbool allow_spinning = gfpflags_allow_spinning(gfp_mask);\n2659:\t\n2660:\tretry:\n2661:\t\tif (consume_stock(memcg, nr_pages))\n2662:\t\t\treturn 0;\n2663:\t\n2664:\t\tif (!allow_spinning)\n2665:\t\t\t/* Avoid the refill and flush of the older stock */\n2666:\t\t\tbatch = nr_pages;\n2667:\t\n2668:\t\treclaim_options = MEMCG_RECLAIM_MAY_SWAP;\n2669:\t\tif (!do_memsw_account() ||\n2670:\t\t    page_counter_try_charge(\u0026memcg-\u003ememsw, batch, \u0026counter)) {\n2671:\t\t\tif (page_counter_try_charge(\u0026memcg-\u003ememory, batch, \u0026counter))\n2672:\t\t\t\tgoto done_restock;\n2673:\t\t\tif (do_memsw_account())\n2674:\t\t\t\tpage_counter_uncharge(\u0026memcg-\u003ememsw, batch);\n"
}

gemini-3.7-flash

null

null

							input: 5155
							output: 22
							thoughts: 221
						

**Analyzing the Memory Charge Patch**

Okay, let's dive into this patch. I need to understand the change in `try_charge_memcg`. It seems the crucial part lies in the order of operations concerning memory events. Previously, the `__memcg_memory_event(mem_over_limit, MEMCG_MAX, allow_spinning);` call, along with the `raised_max_event = true;` flag, was situated *after* the `psi_memstall_enter` and within the `force:` block. Now, the patch has shifted this crucial check and call significantly earlier, immediately after the `if (batch > nr_pages) ...` condition. This is placed before the `if (unlikely(current->flags & PF_MEMALLOC))` and, importantly, before all those `nomem` checks – the ones dealing with `task_in_memcg_oom`, whether blocking is allowed with `!gfpflags_allow_blocking`, and so on. They also took out the duplicate call in `force:`. This is interesting; it suggests a subtle but potentially important change in how the system handles memory overcommit scenarios.

Now, I want to confirm what this early call to `__memcg_memory_event` actually does. Let's see... I'll just grep for `__memcg_memory_event` and check the definition. I need to be sure exactly what's happening.

{
  "Expression": "void __memcg_memory_event"
}

{
  "Output": "include/linux/memcontrol.h=997=static inline void count_memcg_event_mm(struct mm_struct *mm,\n--\ninclude/linux/memcontrol.h-1002-\ninclude/linux/memcontrol.h:1003:void __memcg_memory_event(struct mem_cgroup *memcg,\ninclude/linux/memcontrol.h-1004-\t\t\t  enum memcg_memory_event event, bool allow_spinning);\n--\nmm/memcontrol.c=1880=unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)\n--\nmm/memcontrol.c-1898-\nmm/memcontrol.c:1899:void __memcg_memory_event(struct mem_cgroup *memcg,\nmm/memcontrol.c-1900-\t\t\t  enum memcg_memory_event event, bool allow_spinning)\n"
}

gemini-3.7-flash

null

null

							input: 5940
							output: 35
							thoughts: 19
						

Here's my attempt at summarizing the thought process, tailored for an expert audience:

**Diving into `mm/memcontrol.c`**

Okay, let's zero in on `mm/memcontrol.c` near line 1899. I need to refresh my understanding of how this specific area of memory control is working. I'm probably looking at some core memory management function or data structure interaction within the memory cgroup implementation. I'm expecting to find details around how memory accounting is done, possibly relating to a specific memory resource or event. Given the line number, it's likely dealing with some level of memory allocation, deallocation or tracking. Let's see if this involves page faults, swapping, or perhaps memory limits. Time to dig in and see what's actually going on.

{
  "File": "mm/memcontrol.c",
  "FirstLine": 1895,
  "LineCount": 25
}

{
  "Contents": "1895:\t\t}\n1896:\t\treturn max;\n1897:\t}\n1898:\t\n1899:\tvoid __memcg_memory_event(struct mem_cgroup *memcg,\n1900:\t\t\t\t  enum memcg_memory_event event, bool allow_spinning)\n1901:\t{\n1902:\t\tbool swap_event = event == MEMCG_SWAP_HIGH || event == MEMCG_SWAP_MAX ||\n1903:\t\t\t\t  event == MEMCG_SWAP_FAIL;\n1904:\t\n1905:\t\t/* For now only MEMCG_MAX can happen with !allow_spinning context. */\n1906:\t\tVM_WARN_ON_ONCE(!allow_spinning \u0026\u0026 event != MEMCG_MAX);\n1907:\t\n1908:\t\tatomic_long_inc(\u0026memcg-\u003ememory_events_local[event]);\n1909:\t\tif (!swap_event \u0026\u0026 allow_spinning)\n1910:\t\t\tcgroup_file_notify(\u0026memcg-\u003eevents_local_file);\n1911:\t\n1912:\t\tdo {\n1913:\t\t\tatomic_long_inc(\u0026memcg-\u003ememory_events[event]);\n1914:\t\t\tif (allow_spinning) {\n1915:\t\t\t\tif (swap_event)\n1916:\t\t\t\t\tcgroup_file_notify(\u0026memcg-\u003eswap_events_file);\n1917:\t\t\t\telse\n1918:\t\t\t\t\tcgroup_file_notify(\u0026memcg-\u003eevents_file);\n1919:\t\t\t}\n"
}

gemini-3.7-flash

null

null

							input: 6572
							output: 210
							thoughts: 562
						

**KMSAN/KASAN Analysis of the Patch: try_charge_memcg()**

Okay, let's break this down. My initial impression is that this patch, which modifies `mm/memcontrol.c:try_charge_memcg()`, seems straightforward. The change is centered around when the `MEMCG_MAX` memory event is raised within the function, specifically when a charging failure occurs and we're over the memory limit (`mem_over_limit`). Essentially, it moves the event notification earlier in the execution path, before the code bails out to `nomem` or jumps to `force:`. Previously, certain conditions would bypass the event.

My primary concern, as always, is memory safety, so I'm running through my KMSAN/KASAN checklist.

First, *what does it touch*? It's primarily about control flow and event raising. It looks like `raised_max_event` is a local boolean, initialized to `false`. `mem_over_limit` is set in the `if` statement right above the relevant lines. `allow_spinning` is initialized at function entry. So, from the initial look, everything seems initialized as expected.

Then, *does this patch introduce any memory safety risks*? I'm checking for all the classic KMSAN concerns:

*   **Uninitialized memory reads:** Nope. `raised_max_event`, `mem_over_limit` and `allow_spinning` are all initialized before use.
*   **Kernel structures with uninitialized padding sent to userspace:** Doesn't seem relevant here. No structures are being passed to userspace.
*   **Conditional logic based on uninitialized variables:** No. Control flow relies on initialized variables like `mem_over_limit`.
*   **Memory allocation/initialization bugs related to uninitialized fields:** Not a factor. The change is at an earlier point, and doesn't introduce any new structures that are used or initialized.
*   **Buffer indexing/bounds changes exposing uninitialized bytes:** Not in play here.

I've gone through those core points. There is nothing in this patch that exposes uninitialized memory at all, or that introduces new uninitialized variables.

Just to be thorough, I'll go through my four-point review:

1.  **Kernel structures sent to userspace with potentially uninitialized fields:** Still no.
2.  **Conditional logic depending on uninitialized variables:** No.
3.  **Allocation or initialization of complex data structures with potential uninitialized fields:** Nothing new here.
4.  **Bounds checks, lengths, or logic that could allow access to uninitialized bytes:** No, this does not have anything to do with that.

So, *my conclusion?* This is all KASAN territory. KMSAN is not needed here. Standard KASAN/LOCKDEP builds should be sufficient to verify memory safety and the lock handling. There's nothing in this patch that introduces uninitialized memory usage or potential information leaks.
**NeedsKMSAN = false.**

{
  "KMSANReasoning": "The patch modifies the control flow in `try_charge_memcg()` within `mm/memcontrol.c` so that the `MEMCG_MAX` event (`__memcg_memory_event`) is recorded earlier whenever a memory cgroup limit is exceeded, ensuring it is accounted even if the allocation bails out early (e.g. non-blocking GFP masks or OOM scenarios).\n\nAll variables involved (`mem_over_limit`, `allow_spinning`, `raised_max_event`) are explicitly initialized before use. The patch does not introduce or modify any memory copying to userspace, buffer length/bounds calculations, memory allocations, or struct initializations that could result in uninitialized memory reads or information leaks.\n\nTherefore, this change does not introduce any uninitialized memory risks that would require dedicated KMSAN fuzzing; standard KASAN/LOCKDEP test configurations are appropriate.",
  "NeedsKMSAN": false
}

{
  "KMSANReasoning": "The patch modifies the control flow in `try_charge_memcg()` within `mm/memcontrol.c` so that the `MEMCG_MAX` event (`__memcg_memory_event`) is recorded earlier whenever a memory cgroup limit is exceeded, ensuring it is accounted even if the allocation bails out early (e.g. non-blocking GFP masks or OOM scenarios).\n\nAll variables involved (`mem_over_limit`, `allow_spinning`, `raised_max_event`) are explicitly initialized before use. The patch does not introduce or modify any memory copying to userspace, buffer length/bounds calculations, memory allocations, or struct initializations that could result in uninitialized memory reads or information leaks.\n\nTherefore, this change does not introduce any uninitialized memory risks that would require dedicated KMSAN fuzzing; standard KASAN/LOCKDEP test configurations are appropriate.",
  "NeedsKMSAN": false
}