AI Trajectory

null

{
  "EnableConfigs": [
    "CGROUP_HUGETLB",
    "HUGETLBFS",
    "CGROUPS",
    "NUMA"
  ],
  "FocusSymbols": [
    "hugetlb_cgroup_move_usage",
    "hugetlb_cgroup_move_parent",
    "hugetlb_cgroup_migrate",
    "hugetlb_cgroup_css_offline"
  ],
  "KMSANReasoning": "The patch adds `hugetlb_cgroup_move_usage()` to update per-node hugetlb usage accounting counters when huge pages move to a parent cgroup or during huge page migration. All local variables (`idx`, `nr_pages`, `from_nid`, `to_nid`, `usage`) are explicitly initialized from folio attributes or via `READ_ONCE` on pre-allocated zeroed structures (`nodeinfo` allocated with `kzalloc_node`). No stack or heap structures are copied to user space, no padding bytes are exposed, and no uninitialized memory could be read or branched upon. Any risks introduced by these changes (such as out-of-bounds node indexing, use-after-free, or locking issues) are covered by KASAN and LOCKDEP. Thus, a dedicated KMSAN fuzzing session is not justified.",
  "NeedsKMSAN": false,
  "Reasoning": "The patch introduces hugetlb_cgroup_move_usage() to transfer per-node hugetlb usage between cgroups during cgroup offlining and between NUMA nodes during hugetlb migration. It introduces a new WARN_ON_ONCE assertion check if the node usage drops below the folio size. These changes affect reachable memory management and cgroup code paths, making fuzzing valuable to detect invariant violations or accounting inconsistencies.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 007ac5694fa1217ea436872dc334a502178db190\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Thu Sep 17 20:09:41 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c\nindex ecb6e0b7819a0..3f5ec4a06b251 100644\n--- a/mm/hugetlb_cgroup.c\n+++ b/mm/hugetlb_cgroup.c\n@@ -179,6 +179,34 @@ static void hugetlb_cgroup_css_free(struct cgroup_subsys_state *css)\n \thugetlb_cgroup_free(hugetlb_cgroup_from_css(css));\n }\n \n+static void hugetlb_cgroup_move_usage(struct hugetlb_cgroup *from,\n+\t\t\t\t      struct hugetlb_cgroup *to,\n+\t\t\t\t      struct folio *from_folio,\n+\t\t\t\t      struct folio *to_folio)\n+{\n+\tint idx = hstate_index(folio_hstate(from_folio));\n+\tunsigned long nr_pages = folio_nr_pages(from_folio);\n+\tint from_nid = folio_nid(from_folio);\n+\tint to_nid = folio_nid(to_folio);\n+\tunsigned long usage;\n+\n+\tlockdep_assert_held(\u0026hugetlb_lock);\n+\n+\tif (!from || !to)\n+\t\treturn;\n+\n+\tif (from == to \u0026\u0026 from_nid == to_nid)\n+\t\treturn;\n+\n+\tusage = READ_ONCE(from-\u003enodeinfo[from_nid]-\u003eusage[idx]);\n+\tif (WARN_ON_ONCE(usage \u003c nr_pages))\n+\t\treturn;\n+\tWRITE_ONCE(from-\u003enodeinfo[from_nid]-\u003eusage[idx], usage - nr_pages);\n+\n+\tusage = READ_ONCE(to-\u003enodeinfo[to_nid]-\u003eusage[idx]);\n+\tWRITE_ONCE(to-\u003enodeinfo[to_nid]-\u003eusage[idx], usage + nr_pages);\n+}\n+\n /*\n  * Should be called with hugetlb_lock held.\n  * Since we are holding hugetlb_lock, pages cannot get moved from\n@@ -213,6 +241,8 @@ static void hugetlb_cgroup_move_parent(int idx, struct hugetlb_cgroup *h_cg,\n \t/* Take the pages off the local counter */\n \tpage_counter_cancel(counter, nr_pages);\n \n+\thugetlb_cgroup_move_usage(h_cg, parent, folio, folio);\n+\n \tset_hugetlb_cgroup(folio, parent);\n out:\n \treturn;\n@@ -906,6 +936,9 @@ void hugetlb_cgroup_migrate(struct folio *old_folio, struct folio *new_folio)\n \t/* move the h_cg details to new cgroup */\n \tset_hugetlb_cgroup(new_folio, h_cg);\n \tset_hugetlb_cgroup_rsvd(new_folio, h_cg_rsvd);\n+\n+\thugetlb_cgroup_move_usage(h_cg, h_cg, old_folio, new_folio);\n+\n \tlist_move(\u0026new_folio-\u003elru, \u0026h-\u003ehugepage_activelist);\n \tspin_unlock_irq(\u0026hugetlb_lock);\n }\n"
}

core

null

{
  "EnableConfigs": [
    "CGROUP_HUGETLB",
    "HUGETLBFS",
    "CGROUPS",
    "NUMA"
  ],
  "FocusSymbols": [
    "hugetlb_cgroup_move_usage",
    "hugetlb_cgroup_move_parent",
    "hugetlb_cgroup_migrate",
    "hugetlb_cgroup_css_offline"
  ],
  "Reasoning": "The patch introduces hugetlb_cgroup_move_usage() to transfer per-node hugetlb usage between cgroups during cgroup offlining and between NUMA nodes during hugetlb migration. It introduces a new WARN_ON_ONCE assertion check if the node usage drops below the folio size. These changes affect reachable memory management and cgroup code paths, making fuzzing valuable to detect invariant violations or accounting inconsistencies.",
  "WorthFuzzing": true
}

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.

Target architecture: amd64

For your convenience, here is the diff of the changes:
commit 007ac5694fa1217ea436872dc334a502178db190
Author: syz-cluster <triage@syzkaller.com>
Date:   Thu Sep 17 20:09:41 2026 +0000

    syz-cluster: applied patch under review

diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index ecb6e0b7819a0..3f5ec4a06b251 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -179,6 +179,34 @@ static void hugetlb_cgroup_css_free(struct cgroup_subsys_state *css)
 	hugetlb_cgroup_free(hugetlb_cgroup_from_css(css));
 }
 
+static void hugetlb_cgroup_move_usage(struct hugetlb_cgroup *from,
+				      struct hugetlb_cgroup *to,
+				      struct folio *from_folio,
+				      struct folio *to_folio)
+{
+	int idx = hstate_index(folio_hstate(from_folio));
+	unsigned long nr_pages = folio_nr_pages(from_folio);
+	int from_nid = folio_nid(from_folio);
+	int to_nid = folio_nid(to_folio);
+	unsigned long usage;
+
+	lockdep_assert_held(&hugetlb_lock);
+
+	if (!from || !to)
+		return;
+
+	if (from == to && from_nid == to_nid)
+		return;
+
+	usage = READ_ONCE(from->nodeinfo[from_nid]->usage[idx]);
+	if (WARN_ON_ONCE(usage < nr_pages))
+		return;
+	WRITE_ONCE(from->nodeinfo[from_nid]->usage[idx], usage - nr_pages);
+
+	usage = READ_ONCE(to->nodeinfo[to_nid]->usage[idx]);
+	WRITE_ONCE(to->nodeinfo[to_nid]->usage[idx], usage + nr_pages);
+}
+
 /*
  * Should be called with hugetlb_lock held.
  * Since we are holding hugetlb_lock, pages cannot get moved from
@@ -213,6 +241,8 @@ static void hugetlb_cgroup_move_parent(int idx, struct hugetlb_cgroup *h_cg,
 	/* Take the pages off the local counter */
 	page_counter_cancel(counter, nr_pages);
 
+	hugetlb_cgroup_move_usage(h_cg, parent, folio, folio);
+
 	set_hugetlb_cgroup(folio, parent);
 out:
 	return;
@@ -906,6 +936,9 @@ void hugetlb_cgroup_migrate(struct folio *old_folio, struct folio *new_folio)
 	/* move the h_cg details to new cgroup */
 	set_hugetlb_cgroup(new_folio, h_cg);
 	set_hugetlb_cgroup_rsvd(new_folio, h_cg_rsvd);
+
+	hugetlb_cgroup_move_usage(h_cg, h_cg, old_folio, new_folio);
+
 	list_move(&new_folio->lru, &h->hugepage_activelist);
 	spin_unlock_irq(&hugetlb_lock);
 }

gemini-3.8-flash

null

null

							input: 3484
							output: 38
							thoughts: 464
						

**Analyzing the `hugetlb_cgroup` Patch**

Okay, so the patch I'm looking at focuses on `mm/hugetlb_cgroup.c`. My first instinct is to dive into the code and dissect it. I've spotted a new function, `hugetlb_cgroup_move_usage`, which is the core of this change. Let's break this down further.

`hugetlb_cgroup_move_usage`'s purpose seems pretty clear: to adjust huge page usage counters when a folio migrates or moves between control groups. I'll need to examine the function signature; it takes source and destination `hugetlb_cgroup` pointers, along with pointers to the source and destination folios. The code then grabs some indexes, like `idx` for the page size, node ID (`from_nid`, `to_nid`) and number of pages (`nr_pages`).

The critical part is the atomic-ish updates to the usage counters. It reads the current usage from the source cgroup, performs a safety check, decrements it, and then increments the destination cgroup's usage. The `READ_ONCE` and `WRITE_ONCE` suggest this is designed for a multi-threaded or multi-core environment, to avoid race conditions. `lockdep_assert_held(&hugetlb_lock)` will need more scrutiny - what is the lock protecting?

Now, how and where is this function used? It's called from `hugetlb_cgroup_move_parent`, which makes sense because changing parents means moving resources. It's also called from `hugetlb_cgroup_migrate`. So, it's involved in migration scenarios. Specifically, `hugetlb_cgroup_move_usage(h_cg, parent, folio, folio);` is called when the folio is moved to a parent, while `hugetlb_cgroup_move_usage(h_cg, h_cg, old_folio, new_folio);` is called when a folio migrates *within* a cgroup. That implies that `h_cg` can be the destination or source cgroup, and the old and new folios represent the source and destination folios respectively.

Now I'll need to use my tools – `read-file` or `grepper` – to trace through `mm/hugetlb_cgroup.c` to understand the context fully, particularly the callers of `hugetlb_cgroup_move_parent` and `hugetlb_cgroup_migrate`. I need to ensure the locking is correct, the accounting is accurate, and this all integrates well into the existing huge page cgroup management.

{
  "File": "mm/hugetlb_cgroup.c",
  "FirstLine": 180,
  "LineCount": 70
}

{
  "Contents": " 180:\t}\n 181:\t\n 182:\tstatic void hugetlb_cgroup_move_usage(struct hugetlb_cgroup *from,\n 183:\t\t\t\t\t      struct hugetlb_cgroup *to,\n 184:\t\t\t\t\t      struct folio *from_folio,\n 185:\t\t\t\t\t      struct folio *to_folio)\n 186:\t{\n 187:\t\tint idx = hstate_index(folio_hstate(from_folio));\n 188:\t\tunsigned long nr_pages = folio_nr_pages(from_folio);\n 189:\t\tint from_nid = folio_nid(from_folio);\n 190:\t\tint to_nid = folio_nid(to_folio);\n 191:\t\tunsigned long usage;\n 192:\t\n 193:\t\tlockdep_assert_held(\u0026hugetlb_lock);\n 194:\t\n 195:\t\tif (!from || !to)\n 196:\t\t\treturn;\n 197:\t\n 198:\t\tif (from == to \u0026\u0026 from_nid == to_nid)\n 199:\t\t\treturn;\n 200:\t\n 201:\t\tusage = READ_ONCE(from-\u003enodeinfo[from_nid]-\u003eusage[idx]);\n 202:\t\tif (WARN_ON_ONCE(usage \u003c nr_pages))\n 203:\t\t\treturn;\n 204:\t\tWRITE_ONCE(from-\u003enodeinfo[from_nid]-\u003eusage[idx], usage - nr_pages);\n 205:\t\n 206:\t\tusage = READ_ONCE(to-\u003enodeinfo[to_nid]-\u003eusage[idx]);\n 207:\t\tWRITE_ONCE(to-\u003enodeinfo[to_nid]-\u003eusage[idx], usage + nr_pages);\n 208:\t}\n 209:\t\n 210:\t/*\n 211:\t * Should be called with hugetlb_lock held.\n 212:\t * Since we are holding hugetlb_lock, pages cannot get moved from\n 213:\t * active list or uncharged from the cgroup, So no need to get\n 214:\t * page reference and test for page active here. This function\n 215:\t * cannot fail.\n 216:\t */\n 217:\tstatic void hugetlb_cgroup_move_parent(int idx, struct hugetlb_cgroup *h_cg,\n 218:\t\t\t\t\t       struct folio *folio)\n 219:\t{\n 220:\t\tunsigned int nr_pages;\n 221:\t\tstruct page_counter *counter;\n 222:\t\tstruct hugetlb_cgroup *hcg;\n 223:\t\tstruct hugetlb_cgroup *parent = parent_hugetlb_cgroup(h_cg);\n 224:\t\n 225:\t\thcg = hugetlb_cgroup_from_folio(folio);\n 226:\t\t/*\n 227:\t\t * We can have pages in active list without any cgroup\n 228:\t\t * ie, hugepage with less than 3 pages. We can safely\n 229:\t\t * ignore those pages.\n 230:\t\t */\n 231:\t\tif (!hcg || hcg != h_cg)\n 232:\t\t\tgoto out;\n 233:\t\n 234:\t\tnr_pages = folio_nr_pages(folio);\n 235:\t\tif (!parent) {\n 236:\t\t\tparent = root_h_cgroup;\n 237:\t\t\t/* root has no limit */\n 238:\t\t\tpage_counter_charge(\u0026parent-\u003ehugepage[idx], nr_pages);\n 239:\t\t}\n 240:\t\tcounter = \u0026h_cg-\u003ehugepage[idx];\n 241:\t\t/* Take the pages off the local counter */\n 242:\t\tpage_counter_cancel(counter, nr_pages);\n 243:\t\n 244:\t\thugetlb_cgroup_move_usage(h_cg, parent, folio, folio);\n 245:\t\n 246:\t\tset_hugetlb_cgroup(folio, parent);\n 247:\tout:\n 248:\t\treturn;\n 249:\t}\n"
}

gemini-3.8-flash

null

null

							input: 5657
							output: 38
							thoughts: 20
						

Here's a summary of my thinking, expressed in the first person:

**Diving Deeper into HugeTLB Migration**

Okay, so we need to thoroughly examine the `hugetlb_cgroup_migrate` function and the code that's intimately connected with it. This is a crucial area, and I know from experience that even seemingly minor interactions in that vicinity can have cascading consequences for overall system stability and performance when dealing with HugeTLB allocations. I want to understand *precisely* how that function handles migration scenarios, potential race conditions, and error paths. It's time to map out the call graph and identify every critical data structure involved, and their respective locking mechanisms. I'll probably start by cross-referencing this with relevant documentation, but ultimately the code itself is the definitive source of truth. Time to put on my debugging hat and dig in.

{
  "File": "mm/hugetlb_cgroup.c",
  "FirstLine": 910,
  "LineCount": 40
}

{
  "Contents": " 910:\t\n 911:\t\t__hugetlb_cgroup_file_pre_init();\n 912:\t\tfor_each_hstate(h)\n 913:\t\t\t__hugetlb_cgroup_file_init(h);\n 914:\t\t__hugetlb_cgroup_file_post_init();\n 915:\t}\n 916:\t\n 917:\t/*\n 918:\t * hugetlb_lock will make sure a parallel cgroup rmdir won't happen\n 919:\t * when we migrate hugepages\n 920:\t */\n 921:\tvoid hugetlb_cgroup_migrate(struct folio *old_folio, struct folio *new_folio)\n 922:\t{\n 923:\t\tstruct hugetlb_cgroup *h_cg;\n 924:\t\tstruct hugetlb_cgroup *h_cg_rsvd;\n 925:\t\tstruct hstate *h = folio_hstate(old_folio);\n 926:\t\n 927:\t\tif (hugetlb_cgroup_disabled())\n 928:\t\t\treturn;\n 929:\t\n 930:\t\tspin_lock_irq(\u0026hugetlb_lock);\n 931:\t\th_cg = hugetlb_cgroup_from_folio(old_folio);\n 932:\t\th_cg_rsvd = hugetlb_cgroup_from_folio_rsvd(old_folio);\n 933:\t\tset_hugetlb_cgroup(old_folio, NULL);\n 934:\t\tset_hugetlb_cgroup_rsvd(old_folio, NULL);\n 935:\t\n 936:\t\t/* move the h_cg details to new cgroup */\n 937:\t\tset_hugetlb_cgroup(new_folio, h_cg);\n 938:\t\tset_hugetlb_cgroup_rsvd(new_folio, h_cg_rsvd);\n 939:\t\n 940:\t\thugetlb_cgroup_move_usage(h_cg, h_cg, old_folio, new_folio);\n 941:\t\n 942:\t\tlist_move(\u0026new_folio-\u003elru, \u0026h-\u003ehugepage_activelist);\n 943:\t\tspin_unlock_irq(\u0026hugetlb_lock);\n 944:\t}\n 945:\t\n 946:\tstatic struct cftype hugetlb_files[] = {\n 947:\t\t{} /* terminate */\n 948:\t};\n 949:\t\n"
}

gemini-3.8-flash

null

null

							input: 6577
							output: 28
							thoughts: 45
						

**Investigating Kconfig Dependencies for HugeTLB cgroup Support**

Okay, so I need to figure out which Kconfig options govern the build of `mm/hugetlb_cgroup.c`. My initial approach is to go straight to the source. Let's start with a `grep` command to check for `hugetlb_cgroup.o` within the `mm/Makefile`. That should give me a direct link to the relevant Kconfig dependencies that control the compilation of that specific module. That should quickly reveal the configuration options I need to understand how the kernel's HugeTLB cgroup support is enabled or disabled.

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

{
  "Output": "\nFull output is too long, showing 500 out of 691 lines.\nUse more precise expression if possible.\n\nmm/Makefile=109=endif\nmm/Makefile:110:obj-$(CONFIG_CGROUP_HUGETLB) += hugetlb_cgroup.o\nmm/Makefile-111-obj-$(CONFIG_GUP_TEST) += gup_test.o\n--\nmm/hugetlb.c=474=get_file_region_entry_from_cache(struct resv_map *resv, long from, long to)\n--\nmm/hugetlb.c-489-\nmm/hugetlb.c:490:static void copy_hugetlb_cgroup_uncharge_info(struct file_region *nrg,\nmm/hugetlb.c-491-\t\t\t\t\t      struct file_region *rg)\n--\nmm/hugetlb.c-500-\nmm/hugetlb.c:501:/* Helper that records hugetlb_cgroup uncharge info. */\nmm/hugetlb.c:502:static void record_hugetlb_cgroup_uncharge_info(struct hugetlb_cgroup *h_cg,\nmm/hugetlb.c-503-\t\t\t\t\t\tstruct hstate *h,\n--\nmm/hugetlb.c=584=hugetlb_resv_map_add(struct resv_map *map, struct list_head *rg, long from,\nmm/hugetlb.c:585:\t\t     long to, struct hstate *h, struct hugetlb_cgroup *cg,\nmm/hugetlb.c-586-\t\t     long *regions_needed)\n--\nmm/hugetlb.c-591-\t\tnrg = get_file_region_entry_from_cache(map, from, to);\nmm/hugetlb.c:592:\t\trecord_hugetlb_cgroup_uncharge_info(cg, h, map, nrg);\nmm/hugetlb.c-593-\t\tlist_add(\u0026nrg-\u003elink, rg);\n--\nmm/hugetlb.c=610=static long add_reservation_in_range(struct resv_map *resv, long f, long t,\nmm/hugetlb.c:611:\t\t\t\t     struct hugetlb_cgroup *h_cg,\nmm/hugetlb.c-612-\t\t\t\t     struct hstate *h, long *regions_needed)\n--\nmm/hugetlb.c=743=static long region_add(struct resv_map *resv, long f, long t,\nmm/hugetlb.c-744-\t\t       long in_regions_needed, struct hstate *h,\nmm/hugetlb.c:745:\t\t       struct hugetlb_cgroup *h_cg)\nmm/hugetlb.c-746-{\n--\nmm/hugetlb.c=869=static long region_del(struct resv_map *resv, long f, long t)\n--\nmm/hugetlb.c-914-\t\t\tdel += t - f;\nmm/hugetlb.c:915:\t\t\thugetlb_cgroup_uncharge_file_region(\nmm/hugetlb.c-916-\t\t\t\tresv, rg, t - f, false);\n--\nmm/hugetlb.c-921-\nmm/hugetlb.c:922:\t\t\tcopy_hugetlb_cgroup_uncharge_info(nrg, rg);\nmm/hugetlb.c-923-\n--\nmm/hugetlb.c-935-\t\t\tdel += rg-\u003eto - rg-\u003efrom;\nmm/hugetlb.c:936:\t\t\thugetlb_cgroup_uncharge_file_region(resv, rg,\nmm/hugetlb.c-937-\t\t\t\t\t\t\t    rg-\u003eto - rg-\u003efrom, true);\n--\nmm/hugetlb.c-943-\t\tif (f \u003c= rg-\u003efrom) {\t/* Trim beginning of region */\nmm/hugetlb.c:944:\t\t\thugetlb_cgroup_uncharge_file_region(resv, rg,\nmm/hugetlb.c-945-\t\t\t\t\t\t\t    t - rg-\u003efrom, false);\n--\nmm/hugetlb.c-949-\t\t} else {\t\t/* Trim end of region */\nmm/hugetlb.c:950:\t\t\thugetlb_cgroup_uncharge_file_region(resv, rg,\nmm/hugetlb.c-951-\t\t\t\t\t\t\t    rg-\u003eto - f, false);\n--\nmm/hugetlb.c=1072=static void\nmm/hugetlb.c:1073:resv_map_set_hugetlb_cgroup_uncharge_info(struct resv_map *resv_map,\nmm/hugetlb.c:1074:\t\t\t\t\t  struct hugetlb_cgroup *h_cg,\nmm/hugetlb.c-1075-\t\t\t\t\t  struct hstate *h)\n--\nmm/hugetlb.c=1091=struct resv_map *resv_map_alloc(void)\n--\nmm/hugetlb.c-1113-\t */\nmm/hugetlb.c:1114:\tresv_map_set_hugetlb_cgroup_uncharge_info(resv_map, NULL, NULL);\nmm/hugetlb.c-1115-\n--\nmm/hugetlb.c=1225=void clear_vma_resv_huge_pages(struct vm_area_struct *vma)\n--\nmm/hugetlb.c-1241-\tif (reservations \u0026\u0026 is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {\nmm/hugetlb.c:1242:\t\tresv_map_put_hugetlb_cgroup_uncharge_info(reservations);\nmm/hugetlb.c-1243-\t\tkref_put(\u0026reservations-\u003erefs, resv_map_release);\n--\nmm/hugetlb.c=1391=void remove_hugetlb_folio(struct hstate *h, struct folio *folio,\n--\nmm/hugetlb.c-1395-\nmm/hugetlb.c:1396:\tVM_BUG_ON_FOLIO(hugetlb_cgroup_from_folio(folio), folio);\nmm/hugetlb.c:1397:\tVM_BUG_ON_FOLIO(hugetlb_cgroup_from_folio_rsvd(folio), folio);\nmm/hugetlb.c-1398-\n--\nmm/hugetlb.c=1686=void free_huge_folio(struct folio *folio)\n--\nmm/hugetlb.c-1728-\tfolio_clear_hugetlb_migratable(folio);\nmm/hugetlb.c:1729:\thugetlb_cgroup_uncharge_folio(hstate_index(h),\nmm/hugetlb.c-1730-\t\t\t\t     pages_per_huge_page(h), folio);\nmm/hugetlb.c:1731:\thugetlb_cgroup_uncharge_folio_rsvd(hstate_index(h),\nmm/hugetlb.c-1732-\t\t\t\t\t  pages_per_huge_page(h), folio);\n--\nmm/hugetlb.c=1764=void init_new_hugetlb_folio(struct folio *folio)\n--\nmm/hugetlb.c-1768-\thugetlb_set_folio_subpool(folio, NULL);\nmm/hugetlb.c:1769:\tset_hugetlb_cgroup(folio, NULL);\nmm/hugetlb.c:1770:\tset_hugetlb_cgroup_rsvd(folio, NULL);\nmm/hugetlb.c-1771-}\n--\nmm/hugetlb.c=2866=struct folio *hugetlb_alloc_folio(struct hstate *h,\n--\nmm/hugetlb.c-2869-{\nmm/hugetlb.c:2870:\tbool charge_hugetlb_cgroup_rsvd = alloc_flags \u0026\nmm/hugetlb.c-2871-\t\t\t\t\t  HUGETLB_ALLOC_CHARG_CGROUP_RSVD;\n--\nmm/hugetlb.c-2874-\tsize_t nr_pages = pages_per_huge_page(h);\nmm/hugetlb.c:2875:\tstruct hugetlb_cgroup *h_cg_rsvd = NULL;\nmm/hugetlb.c:2876:\tstruct hugetlb_cgroup *h_cg = NULL;\nmm/hugetlb.c-2877-\tgfp_t gfp = htlb_alloc_mask(h);\n--\nmm/hugetlb.c-2881-\nmm/hugetlb.c:2882:\tif (charge_hugetlb_cgroup_rsvd \u0026\u0026\nmm/hugetlb.c:2883:\t    hugetlb_cgroup_charge_cgroup_rsvd(idx, nr_pages, \u0026h_cg_rsvd))\nmm/hugetlb.c-2884-\t\treturn ERR_PTR(-ENOSPC);\nmm/hugetlb.c-2885-\nmm/hugetlb.c:2886:\tif (hugetlb_cgroup_charge_cgroup(idx, nr_pages, \u0026h_cg)) {\nmm/hugetlb.c-2887-\t\tret = -ENOSPC;\nmm/hugetlb.c:2888:\t\tgoto err_uncharge_hugetlb_cgroup_rsvd;\nmm/hugetlb.c-2889-\t}\n--\nmm/hugetlb.c-2901-\t\t\tret = -ENOSPC;\nmm/hugetlb.c:2902:\t\t\tgoto err_uncharge_hugetlb_cgroup;\nmm/hugetlb.c-2903-\t\t}\n--\nmm/hugetlb.c-2913-\nmm/hugetlb.c:2914:\thugetlb_cgroup_commit_charge(idx, nr_pages, h_cg, folio);\nmm/hugetlb.c-2915-\nmm/hugetlb.c:2916:\tif (charge_hugetlb_cgroup_rsvd) {\nmm/hugetlb.c:2917:\t\thugetlb_cgroup_commit_charge_rsvd(idx, nr_pages, h_cg_rsvd,\nmm/hugetlb.c-2918-\t\t\t\t\t\t  folio);\n--\nmm/hugetlb.c-2934-\t\t/*\nmm/hugetlb.c:2935:\t\t * Skip uncharging hugetlb_cgroup since the charges\nmm/hugetlb.c-2936-\t\t * were committed to the folio and freeing the folio\n--\nmm/hugetlb.c-2947-\nmm/hugetlb.c:2948: err_uncharge_hugetlb_cgroup:\nmm/hugetlb.c:2949:\thugetlb_cgroup_uncharge_cgroup(idx, nr_pages, h_cg);\nmm/hugetlb.c:2950: err_uncharge_hugetlb_cgroup_rsvd:\nmm/hugetlb.c:2951:\tif (charge_hugetlb_cgroup_rsvd)\nmm/hugetlb.c:2952:\t\thugetlb_cgroup_uncharge_cgroup_rsvd(idx, nr_pages, h_cg_rsvd);\nmm/hugetlb.c-2953-\n--\nmm/hugetlb.c=2983=struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,\n--\nmm/hugetlb.c-3096-\t\t\tspin_lock_irq(\u0026hugetlb_lock);\nmm/hugetlb.c:3097:\t\t\thugetlb_cgroup_uncharge_folio_rsvd(\nmm/hugetlb.c-3098-\t\t\t    hstate_index(h), pages_per_huge_page(h), folio);\n--\nmm/hugetlb.c=4171=static int __init hugetlb_init(void)\n--\nmm/hugetlb.c-4223-\thugetlb_sysfs_init();\nmm/hugetlb.c:4224:\thugetlb_cgroup_file_init();\nmm/hugetlb.c-4225-\thugetlb_sysctl_init();\n--\nmm/hugetlb.c=4733=static void hugetlb_vm_op_open(struct vm_area_struct *vma)\n--\nmm/hugetlb.c-4746-\tif (resv \u0026\u0026 is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {\nmm/hugetlb.c:4747:\t\tresv_map_dup_hugetlb_cgroup_uncharge_info(resv);\nmm/hugetlb.c-4748-\t\tkref_get(\u0026resv-\u003erefs);\n--\nmm/hugetlb.c=4773=static void hugetlb_vm_op_close(struct vm_area_struct *vma)\n--\nmm/hugetlb.c-4790-\treserve = (end - start) - region_count(resv, start, end);\nmm/hugetlb.c:4791:\thugetlb_cgroup_uncharge_counter(resv, start, end);\nmm/hugetlb.c-4792-\tif (reserve) {\n--\nmm/hugetlb.c=6726=long hugetlb_reserve_pages(struct inode *inode,\n--\nmm/hugetlb.c-6734-\tstruct resv_map *resv_map;\nmm/hugetlb.c:6735:\tstruct hugetlb_cgroup *h_cg = NULL;\nmm/hugetlb.c-6736-\tlong gbl_reserve, regions_needed = 0;\n--\nmm/hugetlb.c-6793-\nmm/hugetlb.c:6794:\terr = hugetlb_cgroup_charge_cgroup_rsvd(hstate_index(h),\nmm/hugetlb.c-6795-\t\t\t\tchg * pages_per_huge_page(h), \u0026h_cg);\n--\nmm/hugetlb.c-6799-\tif (vma \u0026\u0026 !vma_test(vma, VMA_MAYSHARE_BIT) \u0026\u0026 h_cg) {\nmm/hugetlb.c:6800:\t\t/* For private mappings, the hugetlb_cgroup uncharge info hangs\nmm/hugetlb.c-6801-\t\t * of the resv_map.\nmm/hugetlb.c-6802-\t\t */\nmm/hugetlb.c:6803:\t\tresv_map_set_hugetlb_cgroup_uncharge_info(resv_map, h_cg, h);\nmm/hugetlb.c-6804-\t}\n--\nmm/hugetlb.c-6853-\t\t\t/*\nmm/hugetlb.c:6854:\t\t\t * hugetlb_cgroup_uncharge_cgroup_rsvd() will put the\nmm/hugetlb.c-6855-\t\t\t * reference to h_cg-\u003ecss. See comment below for detail.\nmm/hugetlb.c-6856-\t\t\t */\nmm/hugetlb.c:6857:\t\t\thugetlb_cgroup_uncharge_cgroup_rsvd(\nmm/hugetlb.c-6858-\t\t\t\thstate_index(h),\n--\nmm/hugetlb.c-6867-\t\t\t * h_cg-\u003ecss. So we should release the reference held\nmm/hugetlb.c:6868:\t\t\t * via hugetlb_cgroup_charge_cgroup_rsvd() when we are\nmm/hugetlb.c-6869-\t\t\t * done.\nmm/hugetlb.c-6870-\t\t\t */\nmm/hugetlb.c:6871:\t\t\thugetlb_cgroup_put_rsvd_cgroup(h_cg);\nmm/hugetlb.c-6872-\t\t}\n--\nmm/hugetlb.c-6896-out_uncharge_cgroup:\nmm/hugetlb.c:6897:\thugetlb_cgroup_uncharge_cgroup_rsvd(hstate_index(h),\nmm/hugetlb.c-6898-\t\t\t\t\t    chg * pages_per_huge_page(h), h_cg);\n--\nmm/hugetlb.c=7370=void move_hugetlb_state(struct folio *old_folio, struct folio *new_folio,\n--\nmm/hugetlb.c-7374-\nmm/hugetlb.c:7375:\thugetlb_cgroup_migrate(old_folio, new_folio);\nmm/hugetlb.c-7376-\tfolio_set_owner_migrate_reason(new_folio, reason);\n--\nmm/hugetlb_cgroup.c-16-#include \u003clinux/hugetlb.h\u003e\nmm/hugetlb_cgroup.c:17:#include \u003clinux/hugetlb_cgroup.h\u003e\nmm/hugetlb_cgroup.c-18-\n--\nmm/hugetlb_cgroup.c-30-\nmm/hugetlb_cgroup.c:31:static struct hugetlb_cgroup *root_h_cgroup __read_mostly;\nmm/hugetlb_cgroup.c-32-static struct cftype *dfl_files;\n--\nmm/hugetlb_cgroup.c=35=static inline struct page_counter *\nmm/hugetlb_cgroup.c:36:__hugetlb_cgroup_counter_from_cgroup(struct hugetlb_cgroup *h_cg, int idx,\nmm/hugetlb_cgroup.c-37-\t\t\t\t     bool rsvd)\n--\nmm/hugetlb_cgroup.c=44=static inline struct page_counter *\nmm/hugetlb_cgroup.c:45:hugetlb_cgroup_counter_from_cgroup(struct hugetlb_cgroup *h_cg, int idx)\nmm/hugetlb_cgroup.c-46-{\nmm/hugetlb_cgroup.c:47:\treturn __hugetlb_cgroup_counter_from_cgroup(h_cg, idx, false);\nmm/hugetlb_cgroup.c-48-}\n--\nmm/hugetlb_cgroup.c=50=static inline struct page_counter *\nmm/hugetlb_cgroup.c:51:hugetlb_cgroup_counter_from_cgroup_rsvd(struct hugetlb_cgroup *h_cg, int idx)\nmm/hugetlb_cgroup.c-52-{\nmm/hugetlb_cgroup.c:53:\treturn __hugetlb_cgroup_counter_from_cgroup(h_cg, idx, true);\nmm/hugetlb_cgroup.c-54-}\n--\nmm/hugetlb_cgroup.c=56=static inline\nmm/hugetlb_cgroup.c:57:struct hugetlb_cgroup *hugetlb_cgroup_from_css(struct cgroup_subsys_state *s)\nmm/hugetlb_cgroup.c-58-{\nmm/hugetlb_cgroup.c:59:\treturn s ? container_of(s, struct hugetlb_cgroup, css) : NULL;\nmm/hugetlb_cgroup.c-60-}\n--\nmm/hugetlb_cgroup.c=62=static inline\nmm/hugetlb_cgroup.c:63:struct hugetlb_cgroup *hugetlb_cgroup_from_task(struct task_struct *task)\nmm/hugetlb_cgroup.c-64-{\nmm/hugetlb_cgroup.c:65:\treturn hugetlb_cgroup_from_css(task_css(task, hugetlb_cgrp_id));\nmm/hugetlb_cgroup.c-66-}\nmm/hugetlb_cgroup.c-67-\nmm/hugetlb_cgroup.c:68:static inline bool hugetlb_cgroup_is_root(struct hugetlb_cgroup *h_cg)\nmm/hugetlb_cgroup.c-69-{\n--\nmm/hugetlb_cgroup.c-72-\nmm/hugetlb_cgroup.c:73:static inline struct hugetlb_cgroup *\nmm/hugetlb_cgroup.c:74:parent_hugetlb_cgroup(struct hugetlb_cgroup *h_cg)\nmm/hugetlb_cgroup.c-75-{\nmm/hugetlb_cgroup.c:76:\treturn hugetlb_cgroup_from_css(h_cg-\u003ecss.parent);\nmm/hugetlb_cgroup.c-77-}\nmm/hugetlb_cgroup.c-78-\nmm/hugetlb_cgroup.c:79:static inline bool hugetlb_cgroup_have_usage(struct hugetlb_cgroup *h_cg)\nmm/hugetlb_cgroup.c-80-{\n--\nmm/hugetlb_cgroup.c-84-\t\tif (page_counter_read(\nmm/hugetlb_cgroup.c:85:\t\t    hugetlb_cgroup_counter_from_cgroup(h_cg, hstate_index(h))))\nmm/hugetlb_cgroup.c-86-\t\t\treturn true;\n--\nmm/hugetlb_cgroup.c-90-\nmm/hugetlb_cgroup.c:91:static void hugetlb_cgroup_init(struct hugetlb_cgroup *h_cgroup,\nmm/hugetlb_cgroup.c:92:\t\t\t\tstruct hugetlb_cgroup *parent_h_cgroup)\nmm/hugetlb_cgroup.c-93-{\n--\nmm/hugetlb_cgroup.c-102-\t\tif (parent_h_cgroup) {\nmm/hugetlb_cgroup.c:103:\t\t\tfault_parent = hugetlb_cgroup_counter_from_cgroup(\nmm/hugetlb_cgroup.c-104-\t\t\t\tparent_h_cgroup, idx);\nmm/hugetlb_cgroup.c:105:\t\t\trsvd_parent = hugetlb_cgroup_counter_from_cgroup_rsvd(\nmm/hugetlb_cgroup.c-106-\t\t\t\tparent_h_cgroup, idx);\nmm/hugetlb_cgroup.c-107-\t\t}\nmm/hugetlb_cgroup.c:108:\t\tfault = hugetlb_cgroup_counter_from_cgroup(h_cgroup, idx);\nmm/hugetlb_cgroup.c:109:\t\trsvd = hugetlb_cgroup_counter_from_cgroup_rsvd(h_cgroup, idx);\nmm/hugetlb_cgroup.c-110-\n--\nmm/hugetlb_cgroup.c-128-\nmm/hugetlb_cgroup.c:129:static void hugetlb_cgroup_free(struct hugetlb_cgroup *h_cgroup)\nmm/hugetlb_cgroup.c-130-{\n--\nmm/hugetlb_cgroup.c=138=static struct cgroup_subsys_state *\nmm/hugetlb_cgroup.c:139:hugetlb_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)\nmm/hugetlb_cgroup.c-140-{\nmm/hugetlb_cgroup.c:141:\tstruct hugetlb_cgroup *parent_h_cgroup = hugetlb_cgroup_from_css(parent_css);\nmm/hugetlb_cgroup.c:142:\tstruct hugetlb_cgroup *h_cgroup;\nmm/hugetlb_cgroup.c-143-\tint node;\n--\nmm/hugetlb_cgroup.c-162-\t\th_cgroup-\u003enodeinfo[node] =\nmm/hugetlb_cgroup.c:163:\t\t\tkzalloc_node(sizeof(struct hugetlb_cgroup_per_node),\nmm/hugetlb_cgroup.c-164-\t\t\t\t     GFP_KERNEL, node_to_alloc);\n--\nmm/hugetlb_cgroup.c-168-\nmm/hugetlb_cgroup.c:169:\thugetlb_cgroup_init(h_cgroup, parent_h_cgroup);\nmm/hugetlb_cgroup.c-170-\treturn \u0026h_cgroup-\u003ecss;\n--\nmm/hugetlb_cgroup.c-172-fail_alloc_nodeinfo:\nmm/hugetlb_cgroup.c:173:\thugetlb_cgroup_free(h_cgroup);\nmm/hugetlb_cgroup.c-174-\treturn ERR_PTR(-ENOMEM);\n--\nmm/hugetlb_cgroup.c-176-\nmm/hugetlb_cgroup.c:177:static void hugetlb_cgroup_css_free(struct cgroup_subsys_state *css)\nmm/hugetlb_cgroup.c-178-{\nmm/hugetlb_cgroup.c:179:\thugetlb_cgroup_free(hugetlb_cgroup_from_css(css));\nmm/hugetlb_cgroup.c-180-}\nmm/hugetlb_cgroup.c-181-\nmm/hugetlb_cgroup.c:182:static void hugetlb_cgroup_move_usage(struct hugetlb_cgroup *from,\nmm/hugetlb_cgroup.c:183:\t\t\t\t      struct hugetlb_cgroup *to,\nmm/hugetlb_cgroup.c-184-\t\t\t\t      struct folio *from_folio,\n--\nmm/hugetlb_cgroup.c-216- */\nmm/hugetlb_cgroup.c:217:static void hugetlb_cgroup_move_parent(int idx, struct hugetlb_cgroup *h_cg,\nmm/hugetlb_cgroup.c-218-\t\t\t\t       struct folio *folio)\n--\nmm/hugetlb_cgroup.c-221-\tstruct page_counter *counter;\nmm/hugetlb_cgroup.c:222:\tstruct hugetlb_cgroup *hcg;\nmm/hugetlb_cgroup.c:223:\tstruct hugetlb_cgroup *parent = parent_hugetlb_cgroup(h_cg);\nmm/hugetlb_cgroup.c-224-\nmm/hugetlb_cgroup.c:225:\thcg = hugetlb_cgroup_from_folio(folio);\nmm/hugetlb_cgroup.c-226-\t/*\n--\nmm/hugetlb_cgroup.c-243-\nmm/hugetlb_cgroup.c:244:\thugetlb_cgroup_move_usage(h_cg, parent, folio, folio);\nmm/hugetlb_cgroup.c-245-\nmm/hugetlb_cgroup.c:246:\tset_hugetlb_cgroup(folio, parent);\nmm/hugetlb_cgroup.c-247-out:\n--\nmm/hugetlb_cgroup.c-254- */\nmm/hugetlb_cgroup.c:255:static void hugetlb_cgroup_css_offline(struct cgroup_subsys_state *css)\nmm/hugetlb_cgroup.c-256-{\nmm/hugetlb_cgroup.c:257:\tstruct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(css);\nmm/hugetlb_cgroup.c-258-\tstruct hstate *h;\n--\nmm/hugetlb_cgroup.c-264-\t\t\tlist_for_each_entry(folio, \u0026h-\u003ehugepage_activelist, lru)\nmm/hugetlb_cgroup.c:265:\t\t\t\thugetlb_cgroup_move_parent(hstate_index(h), h_cg, folio);\nmm/hugetlb_cgroup.c-266-\n--\nmm/hugetlb_cgroup.c-269-\t\tcond_resched();\nmm/hugetlb_cgroup.c:270:\t} while (hugetlb_cgroup_have_usage(h_cg));\nmm/hugetlb_cgroup.c-271-}\nmm/hugetlb_cgroup.c-272-\nmm/hugetlb_cgroup.c:273:static inline void hugetlb_event(struct hugetlb_cgroup *hugetlb, int idx,\nmm/hugetlb_cgroup.c-274-\t\t\t\t enum hugetlb_memory_event event)\n--\nmm/hugetlb_cgroup.c-281-\t\tcgroup_file_notify(\u0026hugetlb-\u003eevents_file[idx]);\nmm/hugetlb_cgroup.c:282:\t} while ((hugetlb = parent_hugetlb_cgroup(hugetlb)) \u0026\u0026\nmm/hugetlb_cgroup.c:283:\t\t !hugetlb_cgroup_is_root(hugetlb));\nmm/hugetlb_cgroup.c-284-}\nmm/hugetlb_cgroup.c-285-\nmm/hugetlb_cgroup.c:286:static int __hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,\nmm/hugetlb_cgroup.c:287:\t\t\t\t\t  struct hugetlb_cgroup **ptr,\nmm/hugetlb_cgroup.c-288-\t\t\t\t\t  bool rsvd)\n--\nmm/hugetlb_cgroup.c-291-\tstruct page_counter *counter;\nmm/hugetlb_cgroup.c:292:\tstruct hugetlb_cgroup *h_cg = NULL;\nmm/hugetlb_cgroup.c-293-\nmm/hugetlb_cgroup.c:294:\tif (hugetlb_cgroup_disabled())\nmm/hugetlb_cgroup.c-295-\t\tgoto done;\n--\nmm/hugetlb_cgroup.c-297-\trcu_read_lock();\nmm/hugetlb_cgroup.c:298:\th_cg = hugetlb_cgroup_from_task(current);\nmm/hugetlb_cgroup.c-299-\tif (!css_tryget(\u0026h_cg-\u003ecss)) {\n--\nmm/hugetlb_cgroup.c-305-\tif (!page_counter_try_charge(\nmm/hugetlb_cgroup.c:306:\t\t    __hugetlb_cgroup_counter_from_cgroup(h_cg, idx, rsvd),\nmm/hugetlb_cgroup.c-307-\t\t    nr_pages, \u0026counter)) {\n--\nmm/hugetlb_cgroup.c-322-\nmm/hugetlb_cgroup.c:323:int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,\nmm/hugetlb_cgroup.c:324:\t\t\t\t struct hugetlb_cgroup **ptr)\nmm/hugetlb_cgroup.c-325-{\nmm/hugetlb_cgroup.c:326:\treturn __hugetlb_cgroup_charge_cgroup(idx, nr_pages, ptr, false);\nmm/hugetlb_cgroup.c-327-}\nmm/hugetlb_cgroup.c-328-\nmm/hugetlb_cgroup.c:329:int hugetlb_cgroup_charge_cgroup_rsvd(int idx, unsigned long nr_pages,\nmm/hugetlb_cgroup.c:330:\t\t\t\t      struct hugetlb_cgroup **ptr)\nmm/hugetlb_cgroup.c-331-{\nmm/hugetlb_cgroup.c:332:\treturn __hugetlb_cgroup_charge_cgroup(idx, nr_pages, ptr, true);\nmm/hugetlb_cgroup.c-333-}\n--\nmm/hugetlb_cgroup.c-335-/* Should be called with hugetlb_lock held */\nmm/hugetlb_cgroup.c:336:static void __hugetlb_cgroup_commit_charge(int idx, unsigned long nr_pages,\nmm/hugetlb_cgroup.c:337:\t\t\t\t\t   struct hugetlb_cgroup *h_cg,\nmm/hugetlb_cgroup.c-338-\t\t\t\t\t   struct folio *folio, bool rsvd)\nmm/hugetlb_cgroup.c-339-{\nmm/hugetlb_cgroup.c:340:\tif (hugetlb_cgroup_disabled() || !h_cg)\nmm/hugetlb_cgroup.c-341-\t\treturn;\nmm/hugetlb_cgroup.c-342-\tlockdep_assert_held(\u0026hugetlb_lock);\nmm/hugetlb_cgroup.c:343:\t__set_hugetlb_cgroup(folio, h_cg, rsvd);\nmm/hugetlb_cgroup.c-344-\tif (!rsvd) {\n--\nmm/hugetlb_cgroup.c-356-\nmm/hugetlb_cgroup.c:357:void hugetlb_cgroup_commit_charge(int idx, unsigned long nr_pages,\nmm/hugetlb_cgroup.c:358:\t\t\t\t  struct hugetlb_cgroup *h_cg,\nmm/hugetlb_cgroup.c-359-\t\t\t\t  struct folio *folio)\nmm/hugetlb_cgroup.c-360-{\nmm/hugetlb_cgroup.c:361:\t__hugetlb_cgroup_commit_charge(idx, nr_pages, h_cg, folio, false);\nmm/hugetlb_cgroup.c-362-}\nmm/hugetlb_cgroup.c-363-\nmm/hugetlb_cgroup.c:364:void hugetlb_cgroup_commit_charge_rsvd(int idx, unsigned long nr_pages,\nmm/hugetlb_cgroup.c:365:\t\t\t\t       struct hugetlb_cgroup *h_cg,\nmm/hugetlb_cgroup.c-366-\t\t\t\t       struct folio *folio)\nmm/hugetlb_cgroup.c-367-{\nmm/hugetlb_cgroup.c:368:\t__hugetlb_cgroup_commit_charge(idx, nr_pages, h_cg, folio, true);\nmm/hugetlb_cgroup.c-369-}\n--\nmm/hugetlb_cgroup.c-373- */\nmm/hugetlb_cgroup.c:374:static void __hugetlb_cgroup_uncharge_folio(int idx, unsigned long nr_pages,\nmm/hugetlb_cgroup.c-375-\t\t\t\t\t   struct folio *folio, bool rsvd)\nmm/hugetlb_cgroup.c-376-{\nmm/hugetlb_cgroup.c:377:\tstruct hugetlb_cgroup *h_cg;\nmm/hugetlb_cgroup.c-378-\nmm/hugetlb_cgroup.c:379:\tif (hugetlb_cgroup_disabled())\nmm/hugetlb_cgroup.c-380-\t\treturn;\nmm/hugetlb_cgroup.c-381-\tlockdep_assert_held(\u0026hugetlb_lock);\nmm/hugetlb_cgroup.c:382:\th_cg = __hugetlb_cgroup_from_folio(folio, rsvd);\nmm/hugetlb_cgroup.c-383-\tif (unlikely(!h_cg))\nmm/hugetlb_cgroup.c-384-\t\treturn;\nmm/hugetlb_cgroup.c:385:\t__set_hugetlb_cgroup(folio, NULL, rsvd);\nmm/hugetlb_cgroup.c-386-\nmm/hugetlb_cgroup.c:387:\tpage_counter_uncharge(__hugetlb_cgroup_counter_from_cgroup(h_cg, idx,\nmm/hugetlb_cgroup.c-388-\t\t\t\t\t\t\t\t   rsvd),\n--\nmm/hugetlb_cgroup.c-405-\nmm/hugetlb_cgroup.c:406:void hugetlb_cgroup_uncharge_folio(int idx, unsigned long nr_pages,\nmm/hugetlb_cgroup.c-407-\t\t\t\t  struct folio *folio)\nmm/hugetlb_cgroup.c-408-{\nmm/hugetlb_cgroup.c:409:\t__hugetlb_cgroup_uncharge_folio(idx, nr_pages, folio, false);\nmm/hugetlb_cgroup.c-410-}\nmm/hugetlb_cgroup.c-411-\nmm/hugetlb_cgroup.c:412:void hugetlb_cgroup_uncharge_folio_rsvd(int idx, unsigned long nr_pages,\nmm/hugetlb_cgroup.c-413-\t\t\t\t       struct folio *folio)\nmm/hugetlb_cgroup.c-414-{\nmm/hugetlb_cgroup.c:415:\t__hugetlb_cgroup_uncharge_folio(idx, nr_pages, folio, true);\nmm/hugetlb_cgroup.c-416-}\nmm/hugetlb_cgroup.c-417-\nmm/hugetlb_cgroup.c:418:static void __hugetlb_cgroup_uncharge_cgroup(int idx, unsigned long nr_pages,\nmm/hugetlb_cgroup.c:419:\t\t\t\t\t     struct hugetlb_cgroup *h_cg,\nmm/hugetlb_cgroup.c-420-\t\t\t\t\t     bool rsvd)\nmm/hugetlb_cgroup.c-421-{\nmm/hugetlb_cgroup.c:422:\tif (hugetlb_cgroup_disabled() || !h_cg)\nmm/hugetlb_cgroup.c-423-\t\treturn;\nmm/hugetlb_cgroup.c-424-\nmm/hugetlb_cgroup.c:425:\tpage_counter_uncharge(__hugetlb_cgroup_counter_from_cgroup(h_cg, idx,\nmm/hugetlb_cgroup.c-426-\t\t\t\t\t\t\t\t   rsvd),\n--\nmm/hugetlb_cgroup.c-432-\nmm/hugetlb_cgroup.c:433:void hugetlb_cgroup_uncharge_cgroup(int idx, unsigned long nr_pages,\nmm/hugetlb_cgroup.c:434:\t\t\t\t    struct hugetlb_cgroup *h_cg)\nmm/hugetlb_cgroup.c-435-{\nmm/hugetlb_cgroup.c:436:\t__hugetlb_cgroup_uncharge_cgroup(idx, nr_pages, h_cg, false);\nmm/hugetlb_cgroup.c-437-}\nmm/hugetlb_cgroup.c-438-\nmm/hugetlb_cgroup.c:439:void hugetlb_cgroup_uncharge_cgroup_rsvd(int idx, unsigned long nr_pages,\nmm/hugetlb_cgroup.c:440:\t\t\t\t\t struct hugetlb_cgroup *h_cg)\nmm/hugetlb_cgroup.c-441-{\nmm/hugetlb_cgroup.c:442:\t__hugetlb_cgroup_uncharge_cgroup(idx, nr_pages, h_cg, true);\nmm/hugetlb_cgroup.c-443-}\nmm/hugetlb_cgroup.c-444-\nmm/hugetlb_cgroup.c:445:void hugetlb_cgroup_uncharge_counter(struct resv_map *resv, unsigned long start,\nmm/hugetlb_cgroup.c-446-\t\t\t\t     unsigned long end)\nmm/hugetlb_cgroup.c-447-{\nmm/hugetlb_cgroup.c:448:\tif (hugetlb_cgroup_disabled() || !resv || !resv-\u003ereservation_counter ||\nmm/hugetlb_cgroup.c-449-\t    !resv-\u003ecss)\n--\nmm/hugetlb_cgroup.c-456-\nmm/hugetlb_cgroup.c:457:void hugetlb_cgroup_uncharge_file_region(struct resv_map *resv,\nmm/hugetlb_cgroup.c-458-\t\t\t\t\t struct file_region *rg,\n--\nmm/hugetlb_cgroup.c-461-{\nmm/hugetlb_cgroup.c:462:\tif (hugetlb_cgroup_disabled() || !resv || !rg || !nr_pages)\nmm/hugetlb_cgroup.c-463-\t\treturn;\n--\nmm/hugetlb_cgroup.c=478=enum {\n--\nmm/hugetlb_cgroup.c-488-\nmm/hugetlb_cgroup.c:489:static int hugetlb_cgroup_read_numa_stat(struct seq_file *seq, void *dummy)\nmm/hugetlb_cgroup.c-490-{\n--\nmm/hugetlb_cgroup.c-494-\tbool legacy = !cgroup_subsys_on_dfl(hugetlb_cgrp_subsys);\nmm/hugetlb_cgroup.c:495:\tstruct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(seq_css(seq));\nmm/hugetlb_cgroup.c-496-\tstruct cgroup_subsys_state *css;\n--\nmm/hugetlb_cgroup.c-528-\t\tcss_for_each_descendant_pre(css, \u0026h_cg-\u003ecss) {\nmm/hugetlb_cgroup.c:529:\t\t\tusage += READ_ONCE(hugetlb_cgroup_from_css(css)\nmm/hugetlb_cgroup.c-530-\t\t\t\t\t\t   -\u003enodeinfo[nid]\n--\nmm/hugetlb_cgroup.c-541-\nmm/hugetlb_cgroup.c:542:static u64 hugetlb_cgroup_read_u64(struct cgroup_subsys_state *css,\nmm/hugetlb_cgroup.c-543-\t\t\t\t   struct cftype *cft)\n--\nmm/hugetlb_cgroup.c-546-\tstruct page_counter *rsvd_counter;\nmm/hugetlb_cgroup.c:547:\tstruct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(css);\nmm/hugetlb_cgroup.c-548-\n--\nmm/hugetlb_cgroup.c-573-\nmm/hugetlb_cgroup.c:574:static int hugetlb_cgroup_read_u64_max(struct seq_file *seq, void *v)\nmm/hugetlb_cgroup.c-575-{\n--\nmm/hugetlb_cgroup.c-580-\tstruct page_counter *counter;\nmm/hugetlb_cgroup.c:581:\tstruct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(seq_css(seq));\nmm/hugetlb_cgroup.c-582-\n--\nmm/hugetlb_cgroup.c=614=static DEFINE_MUTEX(hugetlb_limit_mutex);\nmm/hugetlb_cgroup.c-615-\nmm/hugetlb_cgroup.c:616:static ssize_t hugetlb_cgroup_write(struct kernfs_open_file *of,\nmm/hugetlb_cgroup.c-617-\t\t\t\t    char *buf, size_t nbytes, loff_t off,\n\n"
}

gemini-3.8-flash

null

null

							input: 18147
							output: 22
							thoughts: 44
						

Okay, here's my summary, taking on the persona you requested:

**Investigating the CONFIG_CGROUP_HUGETLB Configuration**

Alright, let's dive in. I need to figure out the configuration details for `CONFIG_CGROUP_HUGETLB` within the kernel's build system. My instinct is to start by examining the Kconfig files, specifically the ones that handle initialization and memory management. I'm thinking either `init/Kconfig` or `mm/Kconfig` would be the logical starting points. To be efficient, I'll use `grep` to quickly pinpoint where `config CGROUP_HUGETLB` is defined within those files. That should give me the module's description, dependencies, help text, and anything else relevant to its configuration. From there, I can get a clear picture of how this option is controlled.

{
  "Expression": "config CGROUP_HUGETLB"
}

{
  "Output": "init/Kconfig=1275=config CGROUP_FREEZER\n--\ninit/Kconfig-1285-\ninit/Kconfig:1286:config CGROUP_HUGETLB\ninit/Kconfig-1287-\tbool \"HugeTLB controller\"\n"
}

gemini-3.8-flash

null

null

							input: 18480
							output: 33
							thoughts: 18
						

Here's my summary, as though I'm reading the provided text and thinking through it:

**Diving into the Kconfig Sea**

Okay, time to get my hands dirty and dive into `init/Kconfig`. I'm specifically looking around line 1286. I'm guessing there's something specific I'm trying to grok there, probably a configuration option or dependency related to initialization. I've got a hunch about what it might be, but let's not jump to conclusions. Need to see it in context before formulating an opinion. Let's see what the Kconfig magic holds...

{
  "File": "init/Kconfig",
  "FirstLine": 1280,
  "LineCount": 20
}

{
  "Contents": "1280:\t\n1281:\t\t  This option affects the ORIGINAL cgroup interface. The cgroup2 memory\n1282:\t\t  controller includes important in-kernel memory consumers per default.\n1283:\t\n1284:\t\t  If you're using cgroup2, say N.\n1285:\t\n1286:\tconfig CGROUP_HUGETLB\n1287:\t\tbool \"HugeTLB controller\"\n1288:\t\tdepends on HUGETLB_PAGE\n1289:\t\tselect PAGE_COUNTER\n1290:\t\tdefault n\n1291:\t\thelp\n1292:\t\t  Provides a cgroup controller for HugeTLB pages.\n1293:\t\t  When you enable this, you can put a per cgroup limit on HugeTLB usage.\n1294:\t\t  The limit is enforced during page fault. Since HugeTLB doesn't\n1295:\t\t  support page reclaim, enforcing the limit at page fault time implies\n1296:\t\t  that, the application will get SIGBUS signal if it tries to access\n1297:\t\t  HugeTLB pages beyond its limit. This requires the application to know\n1298:\t\t  beforehand how much HugeTLB pages it would require for its use. The\n1299:\t\t  control group is tracked in the third page lru pointer. This means\n"
}

gemini-3.8-flash

null

null

							input: 19009
							output: 24
							thoughts: 68
						

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

**Investigating Hugetlb and NUMA Dependencies**

Okay, so `CGROUP_HUGETLB` relies on `HUGETLB_PAGE`, that's a given. But now I'm curious about the relationship with NUMA, specifically regarding `nodeinfo`. I need to figure out if it's strictly *required* for something like this. Let's dig into the code and see where `nodeinfo` is even defined within the `hugetlb` cgroup implementation. I'll need to check both `hugetlb_cgroup.h` and `hugetlb_cgroup.c` to be thorough, see if it's a declaration or definition. Might be a simple include and I'm overthinking it, but it's worth checking the header as well as the implementation details. Let's get to it.

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

{
  "Output": "mm/hugetlb_cgroup.c=129=static void hugetlb_cgroup_free(struct hugetlb_cgroup *h_cgroup)\n--\nmm/hugetlb_cgroup.c-133-\tfor_each_node(node)\nmm/hugetlb_cgroup.c:134:\t\tkfree(h_cgroup-\u003enodeinfo[node]);\nmm/hugetlb_cgroup.c-135-\tkfree(h_cgroup);\n--\nmm/hugetlb_cgroup.c=139=hugetlb_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)\n--\nmm/hugetlb_cgroup.c-144-\nmm/hugetlb_cgroup.c:145:\th_cgroup = kzalloc_flex(*h_cgroup, nodeinfo, nr_node_ids);\nmm/hugetlb_cgroup.c-146-\n--\nmm/hugetlb_cgroup.c-161-\t\t\tnode_state(node, N_NORMAL_MEMORY) ? node : NUMA_NO_NODE;\nmm/hugetlb_cgroup.c:162:\t\th_cgroup-\u003enodeinfo[node] =\nmm/hugetlb_cgroup.c-163-\t\t\tkzalloc_node(sizeof(struct hugetlb_cgroup_per_node),\nmm/hugetlb_cgroup.c-164-\t\t\t\t     GFP_KERNEL, node_to_alloc);\nmm/hugetlb_cgroup.c:165:\t\tif (!h_cgroup-\u003enodeinfo[node])\nmm/hugetlb_cgroup.c:166:\t\t\tgoto fail_alloc_nodeinfo;\nmm/hugetlb_cgroup.c-167-\t}\n--\nmm/hugetlb_cgroup.c-171-\nmm/hugetlb_cgroup.c:172:fail_alloc_nodeinfo:\nmm/hugetlb_cgroup.c-173-\thugetlb_cgroup_free(h_cgroup);\n--\nmm/hugetlb_cgroup.c=182=static void hugetlb_cgroup_move_usage(struct hugetlb_cgroup *from,\n--\nmm/hugetlb_cgroup.c-200-\nmm/hugetlb_cgroup.c:201:\tusage = READ_ONCE(from-\u003enodeinfo[from_nid]-\u003eusage[idx]);\nmm/hugetlb_cgroup.c-202-\tif (WARN_ON_ONCE(usage \u003c nr_pages))\nmm/hugetlb_cgroup.c-203-\t\treturn;\nmm/hugetlb_cgroup.c:204:\tWRITE_ONCE(from-\u003enodeinfo[from_nid]-\u003eusage[idx], usage - nr_pages);\nmm/hugetlb_cgroup.c-205-\nmm/hugetlb_cgroup.c:206:\tusage = READ_ONCE(to-\u003enodeinfo[to_nid]-\u003eusage[idx]);\nmm/hugetlb_cgroup.c:207:\tWRITE_ONCE(to-\u003enodeinfo[to_nid]-\u003eusage[idx], usage + nr_pages);\nmm/hugetlb_cgroup.c-208-}\n--\nmm/hugetlb_cgroup.c=336=static void __hugetlb_cgroup_commit_charge(int idx, unsigned long nr_pages,\n--\nmm/hugetlb_cgroup.c-345-\t\tunsigned long usage =\nmm/hugetlb_cgroup.c:346:\t\t\th_cg-\u003enodeinfo[folio_nid(folio)]-\u003eusage[idx];\nmm/hugetlb_cgroup.c-347-\t\t/*\n--\nmm/hugetlb_cgroup.c-351-\t\t */\nmm/hugetlb_cgroup.c:352:\t\tWRITE_ONCE(h_cg-\u003enodeinfo[folio_nid(folio)]-\u003eusage[idx],\nmm/hugetlb_cgroup.c-353-\t\t\t   usage + nr_pages);\n--\nmm/hugetlb_cgroup.c=374=static void __hugetlb_cgroup_uncharge_folio(int idx, unsigned long nr_pages,\n--\nmm/hugetlb_cgroup.c-394-\t\tunsigned long usage =\nmm/hugetlb_cgroup.c:395:\t\t\th_cg-\u003enodeinfo[folio_nid(folio)]-\u003eusage[idx];\nmm/hugetlb_cgroup.c-396-\t\t/*\n--\nmm/hugetlb_cgroup.c-400-\t\t */\nmm/hugetlb_cgroup.c:401:\t\tWRITE_ONCE(h_cg-\u003enodeinfo[folio_nid(folio)]-\u003eusage[idx],\nmm/hugetlb_cgroup.c-402-\t\t\t   usage - nr_pages);\n--\nmm/hugetlb_cgroup.c=489=static int hugetlb_cgroup_read_numa_stat(struct seq_file *seq, void *dummy)\n--\nmm/hugetlb_cgroup.c-502-\t\tfor_each_node_state(nid, N_MEMORY)\nmm/hugetlb_cgroup.c:503:\t\t\tusage += READ_ONCE(h_cg-\u003enodeinfo[nid]-\u003eusage[idx]);\nmm/hugetlb_cgroup.c-504-\t\tseq_printf(seq, \"total=%lu\", usage * PAGE_SIZE);\n--\nmm/hugetlb_cgroup.c-508-\t\t\tseq_printf(seq, \" N%d=%lu\", nid,\nmm/hugetlb_cgroup.c:509:\t\t\t\t   READ_ONCE(h_cg-\u003enodeinfo[nid]-\u003eusage[idx]) *\nmm/hugetlb_cgroup.c-510-\t\t\t\t\t   PAGE_SIZE);\n--\nmm/hugetlb_cgroup.c-529-\t\t\tusage += READ_ONCE(hugetlb_cgroup_from_css(css)\nmm/hugetlb_cgroup.c:530:\t\t\t\t\t\t   -\u003enodeinfo[nid]\nmm/hugetlb_cgroup.c-531-\t\t\t\t\t\t   -\u003eusage[idx]);\n--\nmm/memcontrol-v1.c=1886=void memcg1_stat_format(struct mem_cgroup *memcg, struct seq_buf *s)\n--\nmm/memcontrol-v1.c-1948-\t\tfor_each_online_pgdat(pgdat) {\nmm/memcontrol-v1.c:1949:\t\t\tmz = memcg-\u003enodeinfo[pgdat-\u003enode_id];\nmm/memcontrol-v1.c-1950-\n--\nmm/memcontrol.c=216=static inline struct obj_cgroup *__memcg_reparent_objcgs(struct mem_cgroup *memcg,\n--\nmm/memcontrol.c-220-\tstruct obj_cgroup *objcg, *iter;\nmm/memcontrol.c:221:\tstruct mem_cgroup_per_node *pn = memcg-\u003enodeinfo[nid];\nmm/memcontrol.c:222:\tstruct mem_cgroup_per_node *parent_pn = parent-\u003enodeinfo[nid];\nmm/memcontrol.c-223-\n--\nmm/memcontrol.c=1018=static void mod_memcg_lruvec_state(struct lruvec *lruvec,\n--\nmm/memcontrol.c-1028-\tmemcg = get_non_dying_memcg_start(pn-\u003ememcg, \u0026rcu_locked);\nmm/memcontrol.c:1029:\tpn = memcg-\u003enodeinfo[pgdat-\u003enode_id];\nmm/memcontrol.c-1030-\n--\nmm/memcontrol.c=1294=struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,\n--\nmm/memcontrol.c-1316-\nmm/memcontrol.c:1317:\t\titer = \u0026root-\u003enodeinfo[nid]-\u003eiter;\nmm/memcontrol.c-1318-\t\tgen = atomic_read(\u0026iter-\u003egeneration);\n--\nmm/memcontrol.c=1395=static void __invalidate_reclaim_iterators(struct mem_cgroup *from,\n--\nmm/memcontrol.c-1402-\tfor_each_node(nid) {\nmm/memcontrol.c:1403:\t\tmz = from-\u003enodeinfo[nid];\nmm/memcontrol.c-1404-\t\titer = \u0026mz-\u003eiter;\n--\nmm/memcontrol.c=2939=static inline void account_slab_nmi_safe(struct mem_cgroup *memcg,\n--\nmm/memcontrol.c-2948-\t} else {\nmm/memcontrol.c:2949:\t\tstruct mem_cgroup_per_node *pn = memcg-\u003enodeinfo[pgdat-\u003enode_id];\nmm/memcontrol.c-2950-\n--\nmm/memcontrol.c=3036=static struct obj_cgroup *__get_obj_cgroup_from_memcg(struct mem_cgroup *memcg,\n--\nmm/memcontrol.c-3039-\tfor (; memcg; memcg = parent_mem_cgroup(memcg)) {\nmm/memcontrol.c:3040:\t\tstruct obj_cgroup *objcg = rcu_dereference(memcg-\u003enodeinfo[nid]-\u003eobjcg);\nmm/memcontrol.c-3041-\n--\nmm/memcontrol.c=3112=__always_inline struct obj_cgroup *current_obj_cgroup(void)\n--\nmm/memcontrol.c-3132-\t\t */\nmm/memcontrol.c:3133:\t\treturn objcg ? : rcu_dereference_check(root_mem_cgroup-\u003enodeinfo[nid]-\u003eobjcg, 1);\nmm/memcontrol.c-3134-\t}\n--\nmm/memcontrol.c-3139-\nmm/memcontrol.c:3140:\treturn rcu_dereference_check(root_mem_cgroup-\u003enodeinfo[nid]-\u003eobjcg, 1);\nmm/memcontrol.c-3141-\n--\nmm/memcontrol.c-3149-\t\t */\nmm/memcontrol.c:3150:\t\tobjcg = rcu_dereference_check(memcg-\u003enodeinfo[nid]-\u003eobjcg, 1);\nmm/memcontrol.c-3151-\t\tif (likely(objcg))\n--\nmm/memcontrol.c-3154-\nmm/memcontrol.c:3155:\treturn rcu_dereference_check(root_mem_cgroup-\u003enodeinfo[nid]-\u003eobjcg, 1);\nmm/memcontrol.c-3156-}\n--\nmm/memcontrol.c=4153=static bool alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)\n--\nmm/memcontrol.c-4176-\nmm/memcontrol.c:4177:\tmemcg-\u003enodeinfo[node] = pn;\nmm/memcontrol.c-4178-\treturn true;\n--\nmm/memcontrol.c=4184=static void __mem_cgroup_free(struct mem_cgroup *memcg)\n--\nmm/memcontrol.c-4188-\tfor_each_node(node) {\nmm/memcontrol.c:4189:\t\tstruct mem_cgroup_per_node *pn = memcg-\u003enodeinfo[node];\nmm/memcontrol.c-4190-\t\tif (!pn)\n--\nmm/memcontrol.c=4333=static int mem_cgroup_css_online(struct cgroup_subsys_state *css)\n--\nmm/memcontrol.c-4357-\t\tobjcg-\u003ememcg = memcg;\nmm/memcontrol.c:4358:\t\trcu_assign_pointer(memcg-\u003enodeinfo[nid]-\u003eobjcg, objcg);\nmm/memcontrol.c-4359-\t\tobj_cgroup_get(objcg);\nmm/memcontrol.c:4360:\t\tmemcg-\u003enodeinfo[nid]-\u003eorig_objcg = objcg;\nmm/memcontrol.c-4361-\t}\n--\nmm/memcontrol.c-4386-\tfor_each_node(nid) {\nmm/memcontrol.c:4387:\t\tstruct mem_cgroup_per_node *pn = memcg-\u003enodeinfo[nid];\nmm/memcontrol.c-4388-\n--\nmm/memcontrol.c=4562=static void flush_nmi_stats(struct mem_cgroup *memcg, struct mem_cgroup *parent)\n--\nmm/memcontrol.c-4578-\tfor_each_node_state(nid, N_MEMORY) {\nmm/memcontrol.c:4579:\t\tstruct mem_cgroup_per_node *pn = memcg-\u003enodeinfo[nid];\nmm/memcontrol.c-4580-\t\tstruct lruvec_stats *lstats = pn-\u003elruvec_stats;\n--\nmm/memcontrol.c-4583-\t\tif (parent)\nmm/memcontrol.c:4584:\t\t\tplstats = parent-\u003enodeinfo[nid]-\u003elruvec_stats;\nmm/memcontrol.c-4585-\n--\nmm/memcontrol.c=4621=static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)\n--\nmm/memcontrol.c-4655-\tfor_each_node_state(nid, N_MEMORY) {\nmm/memcontrol.c:4656:\t\tstruct mem_cgroup_per_node *pn = memcg-\u003enodeinfo[nid];\nmm/memcontrol.c-4657-\t\tstruct lruvec_stats *lstats = pn-\u003elruvec_stats;\n--\nmm/memcontrol.c-4661-\t\tif (parent)\nmm/memcontrol.c:4662:\t\t\tplstats = parent-\u003enodeinfo[nid]-\u003elruvec_stats;\nmm/memcontrol.c-4663-\n--\nmm/memcontrol.c=5904=int __init mem_cgroup_init(void)\n--\nmm/memcontrol.c-5931-\nmm/memcontrol.c:5932:\tmemcg_size = struct_size_t(struct mem_cgroup, nodeinfo, nr_node_ids);\nmm/memcontrol.c-5933-\tmemcg_cachep = kmem_cache_create(\"mem_cgroup\", memcg_size, 0,\n--\nmm/shrinker.c=62=static void __free_shrinker_info(struct mem_cgroup *memcg)\n--\nmm/shrinker.c-70-\tfor_each_node(nid) {\nmm/shrinker.c:71:\t\tpn = memcg-\u003enodeinfo[nid];\nmm/shrinker.c-72-\t\tinfo = rcu_dereference_protected(pn-\u003eshrinker_info, true);\n--\nmm/shrinker.c=86=int alloc_shrinker_info(struct mem_cgroup *memcg)\n--\nmm/shrinker.c-102-\t\t}\nmm/shrinker.c:103:\t\trcu_assign_pointer(memcg-\u003enodeinfo[nid]-\u003eshrinker_info, info);\nmm/shrinker.c-104-\t}\n--\nmm/shrinker.c=115=static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,\n--\nmm/shrinker.c-117-{\nmm/shrinker.c:118:\treturn rcu_dereference_protected(memcg-\u003enodeinfo[nid]-\u003eshrinker_info,\nmm/shrinker.c-119-\t\t\t\t\t lockdep_is_held(\u0026shrinker_mutex));\n--\nmm/shrinker.c=122=static int expand_one_shrinker_info(struct mem_cgroup *memcg, int new_size,\n--\nmm/shrinker.c-129-\tfor_each_node(nid) {\nmm/shrinker.c:130:\t\tpn = memcg-\u003enodeinfo[nid];\nmm/shrinker.c-131-\t\told = shrinker_info_protected(memcg, nid);\n--\nmm/shrinker.c=205=void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)\n--\nmm/shrinker.c-210-\t\trcu_read_lock();\nmm/shrinker.c:211:\t\tinfo = rcu_dereference(memcg-\u003enodeinfo[nid]-\u003eshrinker_info);\nmm/shrinker.c-212-\t\tif (!WARN_ON_ONCE(shrinker_id \u003e= info-\u003emap_nr_max)) {\n--\nmm/shrinker.c=263=static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,\n--\nmm/shrinker.c-270-\trcu_read_lock();\nmm/shrinker.c:271:\tinfo = rcu_dereference(memcg-\u003enodeinfo[nid]-\u003eshrinker_info);\nmm/shrinker.c-272-\tunit = info-\u003eunit[shrinker_id_to_index(shrinker-\u003eid)];\n--\nmm/shrinker.c=279=static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,\n--\nmm/shrinker.c-286-\trcu_read_lock();\nmm/shrinker.c:287:\tinfo = rcu_dereference(memcg-\u003enodeinfo[nid]-\u003eshrinker_info);\nmm/shrinker.c-288-\tunit = info-\u003eunit[shrinker_id_to_index(shrinker-\u003eid)];\n--\nmm/shrinker.c=478=static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,\n--\nmm/shrinker.c-524-\trcu_read_lock();\nmm/shrinker.c:525:\tinfo = rcu_dereference(memcg-\u003enodeinfo[nid]-\u003eshrinker_info);\nmm/shrinker.c-526-\tif (unlikely(!info))\n--\nmm/vmscan.c=2852=static struct lruvec *get_lruvec(struct mem_cgroup *memcg, int nid)\n--\nmm/vmscan.c-2857-\tif (memcg) {\nmm/vmscan.c:2858:\t\tstruct lruvec *lruvec = \u0026memcg-\u003enodeinfo[nid]-\u003elruvec;\nmm/vmscan.c-2859-\n"
}

gemini-3.8-flash

null

null

							input: 24026
							output: 32
							thoughts: 116
						

**Investigating the Hugetlb Cgroup Configuration**

Okay, so I'm looking into how hugetlb cgroups are configured. The file `mm/hugetlb_cgroup.c` is the key here, and it's compiled only when `CONFIG_CGROUP_HUGETLB=y`. My immediate question is, what enables that? I know `CONFIG_CGROUP_HUGETLB` relies on `CONFIG_HUGETLB_PAGE`, but I need to make sure I haven't missed anything. I should dig deeper and look for other configurations that might influence this. Time to search in `init/Kconfig` to see if there are any other dependencies or conditions related to `CGROUP_HUGETLB`. Also, it's a good idea to double-check within `mm/hugetlb_cgroup.c` itself for any `#ifdef` directives that might control parts of the code. This will give me the complete picture.

no matches

{
  "Expression": "#ifdef",
  "PathPrefix": "mm/hugetlb_cgroup.c"
}

{
  "error": "no matches"
}

gemini-3.8-flash

null

null

							input: 24396
							output: 28
							thoughts: 93
						

**Examining the Kernel Configuration for HugeTLB Support**

Okay, let's break this down. I'm looking at `CONFIG_CGROUP_HUGETLB`. It's a boolean option, meaning it's either enabled or disabled, controlling the HugeTLB controller. The crucial dependencies are `HUGETLB_PAGE`, and it also selects `PAGE_COUNTER`. The default is off, which makes sense. I have to see what `HUGETLB_PAGE` depends on, though. I'll need to check the Kconfig files in the memory management (`mm`) directory, so I'll run a grep search for `config HUGETLB_PAGE` to figure out its dependencies. That will dictate the rest of the configuration.

{
  "Expression": "config HUGETLB_PAGE",
  "PathPrefix": "mm/"
}

{
  "Output": "mm/Kconfig=693=config ARCH_HAS_PMD_SOFTLEAVES\n--\nmm/Kconfig-695-\nmm/Kconfig:696:config HUGETLB_PAGE_SIZE_VARIABLE\nmm/Kconfig-697-\tdef_bool n\n"
}

gemini-3.8-flash

null

null

							input: 24756
							output: 22
							thoughts: 17
						

Here's my thought process, as it went down:

**Investigating HugeTLB Page Usage in Kernel Code**

Okay, so I need to understand where the `HUGETLB_PAGE` macro is being used within the Linux kernel code. Given my expertise, I already know that this relates to HugeTLB pages, a significant optimization technique. My instinct is to focus on the areas that deal with memory management and the file system, as those are the primary consumers and managers of memory resources.

Therefore, I'll start with a `grep` search. I'll target the `arch/` directory, which holds architecture-specific code, as HugeTLB handling can vary depending on the hardware platform. I'll also include `fs/`, since file systems frequently use memory efficiently and this is a good place to start my search. I'll use `grep` to quickly identify all instances of the macro `HUGETLB_PAGE` within those two critical areas. This should give me a solid overview of where this macro is actually implemented.

{
  "Expression": "config HUGETLB_PAGE\\b"
}

{
  "Output": "fs/Kconfig=271=endif # HUGETLBFS\nfs/Kconfig-272-\nfs/Kconfig:273:config HUGETLB_PAGE\nfs/Kconfig-274-\tdef_bool HUGETLBFS\n"
}

gemini-3.8-flash

null

null

							input: 25086
							output: 32
							thoughts: 46
						

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

**Diving into the Filesystem Configuration**

Okay, so I'm looking at `fs/Kconfig` in the kernel source. I know there's something related to huge pages in there, specifically the `HUGETLB_PAGE` configuration option. And I also recall that `HUGETLBFS` is somehow tied to it, because the default bool is defined by `HUGETLB_PAGE` I should refresh my memory on the interactions. I need to get a better handle on the dependencies and implications here. Let me pinpoint the relevant section in `fs/Kconfig`, roughly lines 260 to 280. I expect to find the definition of `HUGETLB_PAGE` there and the conditional logic governing `HUGETLBFS`. This should clarify how these features are configured within the overall filesystem context. Time to get digging.

{
  "File": "fs/Kconfig",
  "FirstLine": 260,
  "LineCount": 25
}

{
  "Contents": " 260:\t\t  If unsure, say N.\n 261:\t\n 262:\tif HUGETLBFS\n 263:\tconfig HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON\n 264:\t\tbool \"HugeTLB Vmemmap Optimization (HVO) defaults to on\"\n 265:\t\tdefault n\n 266:\t\tdepends on HUGETLB_PAGE_OPTIMIZE_VMEMMAP\n 267:\t\thelp\n 268:\t\t  The HugeTLB Vmemmap Optimization (HVO) defaults to off. Say Y here to\n 269:\t\t  enable HVO by default. It can be disabled via hugetlb_free_vmemmap=off\n 270:\t\t  (boot command line) or hugetlb_optimize_vmemmap (sysctl).\n 271:\tendif # HUGETLBFS\n 272:\t\n 273:\tconfig HUGETLB_PAGE\n 274:\t\tdef_bool HUGETLBFS\n 275:\t\tselect XARRAY_MULTI\n 276:\t\n 277:\tconfig HUGETLB_PAGE_OPTIMIZE_VMEMMAP\n 278:\t\tdef_bool HUGETLB_PAGE\n 279:\t\tdepends on ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP\n 280:\t\tdepends on SPARSEMEM_VMEMMAP\n 281:\t\tselect VMEMMAP_OPTIMIZATION\n 282:\t\n 283:\tconfig HUGETLB_PMD_PAGE_TABLE_SHARING\n 284:\t\tdef_bool HUGETLB_PAGE\n"
}

gemini-3.8-flash

null

null

							input: 25775
							output: 36
							thoughts: 130
						

**Analyzing the Dependency Chain for HugeTLB Cgroup Migration**

Okay, so I'm digging into the HugeTLB cgroup migration code. It's pretty straightforward, but I need to make sure I understand the dependencies. I see that `CGROUP_HUGETLB` relies on `HUGETLB_PAGE`, and that in turn, leans on `HUGETLBFS`. I also need to make sure `CONFIG_CGROUPS` is enabled, of course.

Now, the critical function here is `hugetlb_cgroup_migrate`. I ran a `git grep` earlier, and it pointed me to `mm/hugetlb.c:7375`, where it's called within `move_hugetlb_state(...)`.  Looks like `hugetlb_cgroup_migrate(old_folio, new_folio);` is the call. That's good, that confirms where the core logic is executed. Time to dive into `move_hugetlb_state` in `mm/hugetlb.c` to see the bigger picture. Understanding that function will really clarify how the migration works.

{
  "File": "mm/hugetlb.c",
  "FirstLine": 7365,
  "LineCount": 30
}

{
  "Contents": "7365:\t\tlist_move_tail(\u0026folio-\u003elru, \u0026(folio_hstate(folio))-\u003ehugepage_activelist);\n7366:\t\tspin_unlock_irq(\u0026hugetlb_lock);\n7367:\t\tfolio_put(folio);\n7368:\t}\n7369:\t\n7370:\tvoid move_hugetlb_state(struct folio *old_folio, struct folio *new_folio,\n7371:\t\t\t\tenum migrate_reason reason)\n7372:\t{\n7373:\t\tstruct hstate *h = folio_hstate(old_folio);\n7374:\t\n7375:\t\thugetlb_cgroup_migrate(old_folio, new_folio);\n7376:\t\tfolio_set_owner_migrate_reason(new_folio, reason);\n7377:\t\n7378:\t\t/*\n7379:\t\t * transfer temporary state of the new hugetlb folio. This is\n7380:\t\t * reverse to other transitions because the newpage is going to\n7381:\t\t * be final while the old one will be freed so it takes over\n7382:\t\t * the temporary status.\n7383:\t\t *\n7384:\t\t * Also note that we have to transfer the per-node surplus state\n7385:\t\t * here as well otherwise the global surplus count will not match\n7386:\t\t * the per-node's.\n7387:\t\t */\n7388:\t\tif (folio_test_hugetlb_temporary(new_folio)) {\n7389:\t\t\tint old_nid = folio_nid(old_folio);\n7390:\t\t\tint new_nid = folio_nid(new_folio);\n7391:\t\n7392:\t\t\tfolio_set_hugetlb_temporary(old_folio);\n7393:\t\t\tfolio_clear_hugetlb_temporary(new_folio);\n7394:\t\n"
}

gemini-3.8-flash

null

null

							input: 26684
							output: 21
							thoughts: 27
						

Here's my thought process, as if I were considering this myself:

**Investigating the Call Sites of `move_hugetlb_state`**

Okay, so I need to understand where `move_hugetlb_state` is being invoked. Right, the best way to do that, especially within a code base of any significant size, is to use `grep`. I'll run `grep move_hugetlb_state` to pinpoint all the places where that function name appears. That will quickly tell me the immediate contexts in which it's being used. Now, based on where I find the hits, I can start to understand the control flow and why it's there.

{
  "Expression": "move_hugetlb_state"
}

{
  "Output": "include/linux/hugetlb.h=156=void folio_putback_hugetlb(struct folio *folio);\ninclude/linux/hugetlb.h:157:void move_hugetlb_state(struct folio *old_folio, struct folio *new_folio,\ninclude/linux/hugetlb.h-158-\t\tenum migrate_reason reason);\n--\ninclude/linux/hugetlb.h=423=static inline void folio_putback_hugetlb(struct folio *folio)\n--\ninclude/linux/hugetlb.h-426-\ninclude/linux/hugetlb.h:427:static inline void move_hugetlb_state(struct folio *old_folio,\ninclude/linux/hugetlb.h-428-\t\tstruct folio *new_folio, enum migrate_reason reason)\n--\nmm/hugetlb.c=7361=void folio_putback_hugetlb(struct folio *folio)\n--\nmm/hugetlb.c-7369-\nmm/hugetlb.c:7370:void move_hugetlb_state(struct folio *old_folio, struct folio *new_folio,\nmm/hugetlb.c-7371-\t\t\tenum migrate_reason reason)\n--\nmm/migrate.c=1479=static int unmap_and_move_hugetlb_folio(new_folio_t get_new_folio,\n--\nmm/migrate.c-1564-\tif (!rc) {\nmm/migrate.c:1565:\t\tmove_hugetlb_state(src, dst, reason);\nmm/migrate.c-1566-\t\tput_new_folio = NULL;\n"
}

gemini-3.8-flash

null

null

							input: 27307
							output: 24
							thoughts: 364
						

**Analyzing HugeTLB Page Migration and Cgroup Interactions**

Okay, so `move_hugetlb_state` is triggered during various HugeTLB page migrations. Got it. That's a key function for tracking where these pages end up, and it's called in response to things like `migrate_pages`, NUMA balancing, hotplugging memory, and compaction. Now, where is `hugetlb_cgroup_move_parent` called in all of this? I need to understand the connection between page movement and cgroups, because I have a hunch it's related.

Let's check `mm/hugetlb_cgroup.c`. Ah, here it is: `hugetlb_cgroup_css_offline`. Right, it's the offline callback for the hugetlb cgroup subsystem. So, it gets called when a hugetlb cgroup is being destroyed or taken offline, like with an `rmdir` on the cgroup directory. It looks like it iterates through hugepage lists for each `hstate` and calls `hugetlb_cgroup_move_parent` for each folio. This seems logical: when a cgroup goes away, we need to reassign those huge pages.

Now, I really need to get a handle on the *why* of this specific patch. What's the problem this is trying to solve? To truly grasp the significance, I need to consult the git log for this commit itself, or even examine the overall repository history. That will give me the necessary context around the issue being addressed. Understanding the "problem" will allow me to assess the soundness of the solution.

{
  "Expression": "hugetlb_cgroup_move_usage"
}

{
  "Output": "mm/hugetlb_cgroup.c=177=static void hugetlb_cgroup_css_free(struct cgroup_subsys_state *css)\n--\nmm/hugetlb_cgroup.c-181-\nmm/hugetlb_cgroup.c:182:static void hugetlb_cgroup_move_usage(struct hugetlb_cgroup *from,\nmm/hugetlb_cgroup.c-183-\t\t\t\t      struct hugetlb_cgroup *to,\n--\nmm/hugetlb_cgroup.c=217=static void hugetlb_cgroup_move_parent(int idx, struct hugetlb_cgroup *h_cg,\n--\nmm/hugetlb_cgroup.c-243-\nmm/hugetlb_cgroup.c:244:\thugetlb_cgroup_move_usage(h_cg, parent, folio, folio);\nmm/hugetlb_cgroup.c-245-\n--\nmm/hugetlb_cgroup.c=921=void hugetlb_cgroup_migrate(struct folio *old_folio, struct folio *new_folio)\n--\nmm/hugetlb_cgroup.c-939-\nmm/hugetlb_cgroup.c:940:\thugetlb_cgroup_move_usage(h_cg, h_cg, old_folio, new_folio);\nmm/hugetlb_cgroup.c-941-\n"
}

gemini-3.8-flash

null

null

							input: 28418
							output: 38
							thoughts: 1499
						

**Analyzing a Hugetlb cgroup Commit for Potential Fuzzing Targets**

Okay, let's break this down. This commit introduces `hugetlb_cgroup_move_usage()`, which seems crucial for moving per-node usage between cgroups during reparenting and between NUMA nodes during hugetlb folio migration. My immediate focus is that `WARN_ON_ONCE` assertion, because it indicates a new invariant.

The `hugetlb_cgroup_move_usage` function itself calculates usage based on the from/to cgroup and folio details, with the assertion checking `usage < nr_pages`. This is particularly interesting because we're in `mm/hugetlb_cgroup.c`, so it's core memory management and cgroup territory. This patch modifies core subsystems and, therefore, is *high* on my list of things to fuzz.

The important thing is: *is this reachable code?* Yes, it absolutely is. Standard virtualized environments like QEMU/KVM with amd64 support hugetlb and cgroup hugetlb features. Syzkaller is capable of creating cgroups, mounting hugetlbfs, allocating hugepages, and performing page migrations. Importantly, syzkaller *can* simulate NUMA nodes, and even on single-node systems, cgroup reparenting still occurs (that means `from != to` when offlining cgroup), hitting the `hugetlb_cgroup_move_usage` function.

Now, here's where it gets interesting: I've noticed a subtlety. In `hugetlb_cgroup_move_parent`, `from_nid == to_nid`, but `from != to` (h_cg != parent). This means the short-circuit condition `if (from == to && from_nid == to_nid) return;` is *not* triggered when we reparent! This is a single-node system scenario that is *still* reachable, where `hugetlb_cgroup_move_parent` calls `hugetlb_cgroup_move_usage(h_cg, parent, folio, folio);`. So, even on a single node, usage is moved, and the assertion might be triggered.

Another scenario to check is when `old_folio` and `new_folio` are on different nodes in `hugetlb_cgroup_migrate`. Here, `from == to` (`h_cg`), but `from_nid != to_nid`, meaning usage moves between nodes *within* the same cgroup.

One thing I need to confirm is that `nodeinfo` is always allocated, even on non-NUMA or single-node systems. Digging into `hugetlb_cgroup_css_alloc`, it looks like the `nodeinfo` array *is* allocated for each node, which validates the code path to be fuzzed. And this is where it's important to look at `root_h_cgroup`, to determine whether it has `nodeinfo[node]` allocated. I'll check lines 140-170 of `mm/hugetlb_cgroup.c` to confirm that allocation happens and that it's reachable.

{
  "File": "mm/hugetlb_cgroup.c",
  "FirstLine": 140,
  "LineCount": 35
}

{
  "Contents": " 140:\t{\n 141:\t\tstruct hugetlb_cgroup *parent_h_cgroup = hugetlb_cgroup_from_css(parent_css);\n 142:\t\tstruct hugetlb_cgroup *h_cgroup;\n 143:\t\tint node;\n 144:\t\n 145:\t\th_cgroup = kzalloc_flex(*h_cgroup, nodeinfo, nr_node_ids);\n 146:\t\n 147:\t\tif (!h_cgroup)\n 148:\t\t\treturn ERR_PTR(-ENOMEM);\n 149:\t\n 150:\t\tif (!parent_h_cgroup)\n 151:\t\t\troot_h_cgroup = h_cgroup;\n 152:\t\n 153:\t\t/*\n 154:\t\t * TODO: this routine can waste much memory for nodes which will\n 155:\t\t * never be onlined. It's better to use memory hotplug callback\n 156:\t\t * function.\n 157:\t\t */\n 158:\t\tfor_each_node(node) {\n 159:\t\t\t/* Set node_to_alloc to NUMA_NO_NODE for offline nodes. */\n 160:\t\t\tint node_to_alloc =\n 161:\t\t\t\tnode_state(node, N_NORMAL_MEMORY) ? node : NUMA_NO_NODE;\n 162:\t\t\th_cgroup-\u003enodeinfo[node] =\n 163:\t\t\t\tkzalloc_node(sizeof(struct hugetlb_cgroup_per_node),\n 164:\t\t\t\t\t     GFP_KERNEL, node_to_alloc);\n 165:\t\t\tif (!h_cgroup-\u003enodeinfo[node])\n 166:\t\t\t\tgoto fail_alloc_nodeinfo;\n 167:\t\t}\n 168:\t\n 169:\t\thugetlb_cgroup_init(h_cgroup, parent_h_cgroup);\n 170:\t\treturn \u0026h_cgroup-\u003ecss;\n 171:\t\n 172:\tfail_alloc_nodeinfo:\n 173:\t\thugetlb_cgroup_free(h_cgroup);\n 174:\t\treturn ERR_PTR(-ENOMEM);\n"
}

gemini-3.8-flash

null

null

							input: 31220
							output: 18
							thoughts: 792
						

**My Analysis of a Potential HugeTLB Cgroup Race Condition**

Okay, so I've been digging into this `hugetlb` cgroup code, and I think I've spotted a significant vulnerability. My initial thought process was: the `root_h_cgroup` definitely gets allocated `nodeinfo[node]` because the early return condition is not met in `root_h_cgroup` setup.

Now, I'm focusing on the `hugetlb_cgroup_move_parent` function. The code checks for a valid hugepage cgroup association. If the page isn't associated with any cgroup, or if it belongs to a different cgroup than `h_cg`, it bails out. If the parent is null, then the `root_h_cgroup` is assigned as the parent. The code proceeds to charge the root cgroup. After that the local counter is canceled and pages are moved and associated with the parent cgroup.

Here's the problem: when we move to the parent, if the parent is `NULL`, we end up using `root_h_cgroup`. It calls `hugetlb_cgroup_move_usage`, which is where things get interesting. In this function, the code is trying to update the node usage counters when a hugepage is moved. The code reads the usage from the *from* node, and checks if the usage on the node is less than the number of pages. The code then updates the usage on both *from* and *to* nodes.

The potential race condition, however, occurs when the `from` node wasn't charged, or when the `from->nodeinfo[from_nid]->usage[idx]` is 0. Additionally, prior to this patch, hugepage migrations (`hugetlb_cgroup_migrate`) weren't updating node usage consistently. This can create a situation where the `nodeinfo` usage is out of sync with the actual page locations. The check `WARN_ON_ONCE(usage < nr_pages)` can trigger, indicating the counters are inconsistent.

This seems like a textbook race condition waiting to happen! We have a potential data race or counter inconsistency. The conditions seem right and the potential for a crash or data corruption is significant. I need to make sure I note that hugepages migrated before this patch are especially vulnerable.

Now, to see if it's worth the fuzzing, let's get the criteria together. WorthFuzzing? Absolutely. EnableConfigs? `CONFIG_CGROUP_HUGETLB` is necessary to even reach this code. Also the depencies: It looks like `CGROUP_HUGETLB` requires `HUGETLB_PAGE` and `HUGETLBFS`. I think we'll also need `MIGRATION` to trigger the `hugetlb_cgroup_migrate` and `move_hugetlb_state` code. Okay, let's fire up the fuzzer!

{
  "Expression": "config MIGRATION"
}

{
  "Output": "mm/Kconfig=672=config NUMA_MIGRATION\n--\nmm/Kconfig-682-\nmm/Kconfig:683:config MIGRATION\nmm/Kconfig-684-\tbool\n"
}

gemini-3.8-flash

null

null

							input: 32728
							output: 32
							thoughts: 17
						

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

**Diving into the Kernel Configuration Landscape**

Okay, so I'm thinking, where's the most likely place to find the relevant configuration options related to [implied field - e.g., memory management, kernel debugging, etc., as per context]? Right, `mm/Kconfig`. That's usually the go-to for memory-related settings and it's organized pretty well in general. My mental search is zeroing in around line 680. That's a reasonable place to start looking, based on my past experience with similar configs. I anticipate finding a relevant section or several options to quickly get my bearings and understand the structure of this particular configuration area. From there, I'll be able to decide if I need to dig deeper into the code or simply cross-reference it with other relevant sections.

{
  "File": "mm/Kconfig",
  "FirstLine": 670,
  "LineCount": 25
}

{
  "Contents": " 670:\t\t  memory can be freed within the host for other uses.\n 671:\t\n 672:\tconfig NUMA_MIGRATION\n 673:\t\tbool \"NUMA page migration\"\n 674:\t\tdefault y\n 675:\t\tdepends on NUMA \u0026\u0026 MMU\n 676:\t\tselect MIGRATION\n 677:\t\thelp\n 678:\t\t  Support the migration of pages to other NUMA nodes, available to\n 679:\t\t  user space through interfaces like migrate_pages(), move_pages(),\n 680:\t\t  and mbind(). Selecting this option also enables support for page\n 681:\t\t  demotion for memory tiering.\n 682:\t\n 683:\tconfig MIGRATION\n 684:\t\tbool\n 685:\t\tdepends on MMU\n 686:\t\n 687:\tconfig DEVICE_MIGRATION\n 688:\t\tdef_bool MIGRATION \u0026\u0026 ZONE_DEVICE\n 689:\t\n 690:\tconfig ARCH_ENABLE_HUGEPAGE_MIGRATION\n 691:\t\tbool\n 692:\t\n 693:\tconfig ARCH_HAS_PMD_SOFTLEAVES\n 694:\t\tbool\n"
}

gemini-3.8-flash

null

null

							input: 33295
							output: 33
							thoughts: 230
						

**Analyzing the `hugetlb_cgroup.c` Dependency on NUMA**

Okay, so I need to figure out the interplay between the NUMA configuration and how `hugetlb_cgroup.c` works. I know that `CONFIG_NUMA` is a crucial factor because it underpins both per-node resource utilization and node migration, which are relevant to this file. Let's delve into the code itself.

Scanning through `hugetlb_cgroup.c`, I see a strong correlation with NUMA right away. The code iterates over each node using `for_each_node(node)`, and explicitly checks `node_state(node, N_NORMAL_MEMORY)`. The function `hugetlb_cgroup_read_numa_stat` is also there, which screams NUMA dependence. It looks like `nodeinfo` is always defined but `nr_node_ids` seems key – it's 1 in a non-NUMA setup. When `CONFIG_NUMA` is enabled, `nr_node_ids` will be greater than 1, right? Bingo.

So, the dependency tree appears to be: `CONFIG_CGROUP_HUGETLB`, `CONFIG_HUGETLBFS`, *and* `CONFIG_NUMA`. Now I should determine if `CONFIG_CGROUPS` is required. I recall that `CONFIG_CGROUP_HUGETLB` is defined under an `if CGROUPS` block in `init/Kconfig`. Let me go confirm this. I will look around line 1286.

{
  "File": "init/Kconfig",
  "FirstLine": 1260,
  "LineCount": 40
}

{
  "Contents": "1260:\t\t  can result into resource unavailability to other consumers.\n1261:\t\t  RDMA controller is designed to stop this from happening.\n1262:\t\t  Attaching processes with active RDMA resources to the cgroup\n1263:\t\t  hierarchy is allowed even if can cross the hierarchy's limit.\n1264:\t\n1265:\tconfig CGROUP_DMEM\n1266:\t\tbool \"Device memory controller (DMEM)\"\n1267:\t\tselect PAGE_COUNTER\n1268:\t\thelp\n1269:\t\t  The DMEM controller allows compatible devices to restrict device\n1270:\t\t  memory usage based on the cgroup hierarchy.\n1271:\t\n1272:\t\t  As an example, it allows you to restrict VRAM usage for applications\n1273:\t\t  in the DRM subsystem.\n1274:\t\n1275:\tconfig CGROUP_FREEZER\n1276:\t\tbool \"Freezer controller\"\n1277:\t\thelp\n1278:\t\t  Provides a way to freeze and unfreeze all tasks in a\n1279:\t\t  cgroup.\n1280:\t\n1281:\t\t  This option affects the ORIGINAL cgroup interface. The cgroup2 memory\n1282:\t\t  controller includes important in-kernel memory consumers per default.\n1283:\t\n1284:\t\t  If you're using cgroup2, say N.\n1285:\t\n1286:\tconfig CGROUP_HUGETLB\n1287:\t\tbool \"HugeTLB controller\"\n1288:\t\tdepends on HUGETLB_PAGE\n1289:\t\tselect PAGE_COUNTER\n1290:\t\tdefault n\n1291:\t\thelp\n1292:\t\t  Provides a cgroup controller for HugeTLB pages.\n1293:\t\t  When you enable this, you can put a per cgroup limit on HugeTLB usage.\n1294:\t\t  The limit is enforced during page fault. Since HugeTLB doesn't\n1295:\t\t  support page reclaim, enforcing the limit at page fault time implies\n1296:\t\t  that, the application will get SIGBUS signal if it tries to access\n1297:\t\t  HugeTLB pages beyond its limit. This requires the application to know\n1298:\t\t  beforehand how much HugeTLB pages it would require for its use. The\n1299:\t\t  control group is tracked in the third page lru pointer. This means\n"
}

gemini-3.8-flash

null

null

							input: 34525
							output: 33
							thoughts: 17
						

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

**Analyzing Conditional Compilation and Menu Structures**

Okay, so I'm diving into this code, probably looking at a feature or a module related to cgroups, based on that `if CGROUPS` macro. My immediate focus is going to be on understanding the surrounding structure – where does this conditional block begin, and more importantly, where does it end? The aim is to get a handle on the scope of the cgroup-specific functionality or settings.

I need to quickly identify the starting point of the conditional compilation, be it an `if` statement, a menu definition, or something else that makes this feature optional. Once I've found the beginning of the relevant if statement or menu I want to check how the code interacts with the rest of the code when cgroups are enabled or disabled. This will give me context for understanding the scope of the feature. I want to see how that section interacts with the larger codebase, especially in terms of which variables, functions, or data structures are being affected. Is it just a localized block, or does this conditional logic ripple outwards, influencing other parts of the system? I'll probably also be looking for any corresponding `#else` or `#endif` directives or menu options that indicate the alternate path when cgroups aren't enabled. This might highlight dependencies or suggest alternative implementations. Understanding the full picture of the conditional compilation is crucial for the goal at hand, this is important to know as I dig deeper into what this code is about.

{
  "File": "init/Kconfig",
  "FirstLine": 1100,
  "LineCount": 40
}

{
  "Contents": "1100:\t\n1101:\tconfig MEMCG_V1\n1102:\t\tbool \"Legacy cgroup v1 memory controller\"\n1103:\t\tdepends on MEMCG\n1104:\t\tdefault n\n1105:\t\thelp\n1106:\t\t  Legacy cgroup v1 memory controller which has been deprecated by\n1107:\t\t  cgroup v2 implementation. The v1 is there for legacy applications\n1108:\t\t  which haven't migrated to the new cgroup v2 interface yet. If you\n1109:\t\t  do not have any such application then you are completely fine leaving\n1110:\t\t  this option disabled.\n1111:\t\n1112:\t\t  Please note that feature set of the legacy memory controller is likely\n1113:\t\t  going to shrink due to deprecation process. New deployments with v1\n1114:\t\t  controller are highly discouraged.\n1115:\t\n1116:\t\t  Say N if unsure.\n1117:\t\n1118:\tconfig BLK_CGROUP\n1119:\t\tbool \"IO controller\"\n1120:\t\tdepends on BLOCK\n1121:\t\tdefault n\n1122:\t\thelp\n1123:\t\tGeneric block IO controller cgroup interface. This is the common\n1124:\t\tcgroup interface which should be used by various IO controlling\n1125:\t\tpolicies.\n1126:\t\n1127:\t\tCurrently, CFQ IO scheduler uses it to recognize task groups and\n1128:\t\tcontrol disk bandwidth allocation (proportional time slice allocation)\n1129:\t\tto such task groups. It is also used by bio throttling logic in\n1130:\t\tblock layer to implement upper limit in IO rates on a device.\n1131:\t\n1132:\t\tThis option only enables generic Block IO controller infrastructure.\n1133:\t\tOne needs to also enable actual IO controlling logic/policy. For\n1134:\t\tenabling proportional weight division of disk bandwidth in CFQ, set\n1135:\t\tCONFIG_BFQ_GROUP_IOSCHED=y; for enabling throttling policy, set\n1136:\t\tCONFIG_BLK_DEV_THROTTLING=y.\n1137:\t\n1138:\t\tSee Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information.\n1139:\t\n"
}

gemini-3.8-flash

null

null

							input: 35502
							output: 27
							thoughts: 18
						

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

**Investigating CGROUPS Menu Configuration**

Okay, so I need to figure out how CGROUPS is configured for `menuconfig`. My first instinct is to dive into the core configuration files. Specifically, I should check the earlier lines in `init/Kconfig`. It's almost certain that the CGROUPS options, and their dependencies, will be defined there. This is the logical starting point for understanding how these features are exposed and controlled during the build process. I'll need to look for the relevant `config` symbols, their associated help text, and any dependencies on other options. This will help me understand why something might be enabled or disabled based on the broader system configuration. Let's get to it.

{
  "Expression": "menuconfig CGROUPS",
  "PathPrefix": "init/"
}

{
  "Output": "init/Kconfig=1046=config SLAB_OBJ_EXT\n--\ninit/Kconfig-1048-\ninit/Kconfig:1049:menuconfig CGROUPS\ninit/Kconfig-1050-\tbool \"Control Group support\"\n"
}

gemini-3.8-flash

null

null

							input: 35792
							output: 32
							thoughts: 651
						

**Analyzing Code Dependencies and Identifying Focus Symbols for Fuzzing**

Okay, so I'm looking at `CGROUP_HUGETLB`. It's conditional on `CGROUPS` and depends on `HUGETLB_PAGE`, which is defined as `def_bool HUGETLBFS`. This means I need to consider `CGROUP_HUGETLB`, `HUGETLBFS`, and `CGROUPS` as a base for this. And, if I'm testing cross-node migration, then `NUMA` or `NUMA_MIGRATION` come into play.

Now, I need to figure out the best functions to focus on for fuzzing. I'm focusing on functions that have been modified or added as per the instructions, particularly where new logic is implemented. I see `hugetlb_cgroup_move_usage`. This is a *static* function in `mm/hugetlb_cgroup.c`. The instructions say to avoid ubiquitous lifecycle functions and instead target specific feature logic or entrypoints.

The documentation specifically notes that compiler-inlined static functions can be tricky because they don't have distinct symbols in vmlinux. However, if changes *are* in static inlines, I need to identify *non-static* caller functions that exercise them, avoiding the generic wrappers.

So, is `hugetlb_cgroup_move_usage` a static function? Yep, `static void hugetlb_cgroup_move_usage(...)`. Okay, it's called from two places in `mm/hugetlb_cgroup.c`: `hugetlb_cgroup_move_parent` (called by `hugetlb_cgroup_css_offline`) and `hugetlb_cgroup_migrate`. The critical thing here is `hugetlb_cgroup_migrate` is non-static and exported. Let me double check that with a quick look: `void hugetlb_cgroup_migrate(...)`. Yes, it's non-static. The other call, `hugetlb_cgroup_move_parent`, is also static and part of a static css_offline callback in `struct cgroup_subsys hugetlb_cgrp_subsys`.

Therefore, I should probably prioritize `hugetlb_cgroup_migrate` as a FocusSymbol because it's a direct entrypoint. Now, let me check `hugetlb_cgroup_css_offline` to get a complete picture.

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

{
  "Output": "mm/hugetlb_cgroup.c=217=static void hugetlb_cgroup_move_parent(int idx, struct hugetlb_cgroup *h_cg,\n--\nmm/hugetlb_cgroup.c-254- */\nmm/hugetlb_cgroup.c:255:static void hugetlb_cgroup_css_offline(struct cgroup_subsys_state *css)\nmm/hugetlb_cgroup.c-256-{\n--\nmm/hugetlb_cgroup.c=950=struct cgroup_subsys hugetlb_cgrp_subsys = {\nmm/hugetlb_cgroup.c-951-\t.css_alloc\t= hugetlb_cgroup_css_alloc,\nmm/hugetlb_cgroup.c:952:\t.css_offline\t= hugetlb_cgroup_css_offline,\nmm/hugetlb_cgroup.c-953-\t.css_free\t= hugetlb_cgroup_css_free,\n"
}

gemini-3.8-flash

null

null

							input: 37274
							output: 196
							thoughts: 538
						

**Fuzzing Verdict: Hugetlb Cgroup Migration**

Okay, let's break this down. We're looking at a patch related to HugeTLB cgroup migration. I've identified the key functions involved: `hugetlb_cgroup_migrate` (non-static, global), `hugetlb_cgroup_move_parent` and `hugetlb_cgroup_move_usage` (both static), and `move_hugetlb_state` in `mm/hugetlb.c` (non-static, global). 

The patch itself focuses on these standard focus symbols, and I've verified that `hugetlb_cgroup_move_usage`, `hugetlb_cgroup_move_parent`, `hugetlb_cgroup_migrate` and `move_hugetlb_state` are all within scope.

I've also tracked down `hugetlb_cgroup_css_offline`, which is the cgroup offline handler and calls `hugetlb_cgroup_move_parent`. That gives us a good picture of the interaction points.

I've made sure to double-check the symbols we're interested in: `hugetlb_cgroup_move_usage`, `hugetlb_cgroup_move_parent`, `hugetlb_cgroup_migrate`, and `hugetlb_cgroup_css_offline`. None of them appear to be universally used, these are all very specific to the management of hugepage cgroups.

Now, let's confirm the necessary kernel configurations. We need: `CGROUP_HUGETLB` (directly ties into `mm/hugetlb_cgroup.c`), `HUGETLBFS` (HugeTLB file system and page support, dependent on `HUGETLB_PAGE`), `CGROUPS` (obviously), and `NUMA` (for per-node tracking and migration).

Finally, I've got a handle on the structure for `set-results`: `EnableConfigs` (list of strings like ["CGROUP_HUGETLB", "HUGETLBFS", "CGROUPS", "NUMA"]), `FocusSymbols` (list of strings like ["hugetlb_cgroup_move_usage", "hugetlb_cgroup_move_parent", "hugetlb_cgroup_migrate", "hugetlb_cgroup_css_offline"]), `Reasoning` (a concise fuzzing verdict), and `WorthFuzzing` (boolean).

Given all of this investigation, I'm confident we have a solid understanding of the area. It's time to call `set-results`.

{
  "EnableConfigs": [
    "CGROUP_HUGETLB",
    "HUGETLBFS",
    "CGROUPS",
    "NUMA"
  ],
  "FocusSymbols": [
    "hugetlb_cgroup_move_usage",
    "hugetlb_cgroup_move_parent",
    "hugetlb_cgroup_migrate",
    "hugetlb_cgroup_css_offline"
  ],
  "Reasoning": "The patch introduces hugetlb_cgroup_move_usage() to transfer per-node hugetlb usage between cgroups during cgroup offlining and between NUMA nodes during hugetlb migration. It introduces a new WARN_ON_ONCE assertion check if the node usage drops below the folio size. These changes affect reachable memory management and cgroup code paths, making fuzzing valuable to detect invariant violations or accounting inconsistencies.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "CGROUP_HUGETLB",
    "HUGETLBFS",
    "CGROUPS",
    "NUMA"
  ],
  "FocusSymbols": [
    "hugetlb_cgroup_move_usage",
    "hugetlb_cgroup_move_parent",
    "hugetlb_cgroup_migrate",
    "hugetlb_cgroup_css_offline"
  ],
  "Reasoning": "The patch introduces hugetlb_cgroup_move_usage() to transfer per-node hugetlb usage between cgroups during cgroup offlining and between NUMA nodes during hugetlb migration. It introduces a new WARN_ON_ONCE assertion check if the node usage drops below the folio size. These changes affect reachable memory management and cgroup code paths, making fuzzing valuable to detect invariant violations or accounting inconsistencies.",
  "WorthFuzzing": true
}

{
  "WorthFuzzing": true
}

null

core

null

{
  "KMSANReasoning": "The patch adds `hugetlb_cgroup_move_usage()` to update per-node hugetlb usage accounting counters when huge pages move to a parent cgroup or during huge page migration. All local variables (`idx`, `nr_pages`, `from_nid`, `to_nid`, `usage`) are explicitly initialized from folio attributes or via `READ_ONCE` on pre-allocated zeroed structures (`nodeinfo` allocated with `kzalloc_node`). No stack or heap structures are copied to user space, no padding bytes are exposed, and no uninitialized memory could be read or branched upon. Any risks introduced by these changes (such as out-of-bounds node indexing, use-after-free, or locking issues) are covered by KASAN and LOCKDEP. Thus, a dedicated KMSAN fuzzing session is not justified.",
  "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.

Target architecture: amd64

For your convenience, here is the diff of the changes:
commit 007ac5694fa1217ea436872dc334a502178db190
Author: syz-cluster <triage@syzkaller.com>
Date:   Thu Sep 17 20:09:41 2026 +0000

    syz-cluster: applied patch under review

diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index ecb6e0b7819a0..3f5ec4a06b251 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -179,6 +179,34 @@ static void hugetlb_cgroup_css_free(struct cgroup_subsys_state *css)
 	hugetlb_cgroup_free(hugetlb_cgroup_from_css(css));
 }
 
+static void hugetlb_cgroup_move_usage(struct hugetlb_cgroup *from,
+				      struct hugetlb_cgroup *to,
+				      struct folio *from_folio,
+				      struct folio *to_folio)
+{
+	int idx = hstate_index(folio_hstate(from_folio));
+	unsigned long nr_pages = folio_nr_pages(from_folio);
+	int from_nid = folio_nid(from_folio);
+	int to_nid = folio_nid(to_folio);
+	unsigned long usage;
+
+	lockdep_assert_held(&hugetlb_lock);
+
+	if (!from || !to)
+		return;
+
+	if (from == to && from_nid == to_nid)
+		return;
+
+	usage = READ_ONCE(from->nodeinfo[from_nid]->usage[idx]);
+	if (WARN_ON_ONCE(usage < nr_pages))
+		return;
+	WRITE_ONCE(from->nodeinfo[from_nid]->usage[idx], usage - nr_pages);
+
+	usage = READ_ONCE(to->nodeinfo[to_nid]->usage[idx]);
+	WRITE_ONCE(to->nodeinfo[to_nid]->usage[idx], usage + nr_pages);
+}
+
 /*
  * Should be called with hugetlb_lock held.
  * Since we are holding hugetlb_lock, pages cannot get moved from
@@ -213,6 +241,8 @@ static void hugetlb_cgroup_move_parent(int idx, struct hugetlb_cgroup *h_cg,
 	/* Take the pages off the local counter */
 	page_counter_cancel(counter, nr_pages);
 
+	hugetlb_cgroup_move_usage(h_cg, parent, folio, folio);
+
 	set_hugetlb_cgroup(folio, parent);
 out:
 	return;
@@ -906,6 +936,9 @@ void hugetlb_cgroup_migrate(struct folio *old_folio, struct folio *new_folio)
 	/* move the h_cg details to new cgroup */
 	set_hugetlb_cgroup(new_folio, h_cg);
 	set_hugetlb_cgroup_rsvd(new_folio, h_cg_rsvd);
+
+	hugetlb_cgroup_move_usage(h_cg, h_cg, old_folio, new_folio);
+
 	list_move(&new_folio->lru, &h->hugepage_activelist);
 	spin_unlock_irq(&hugetlb_lock);
 }

gemini-3.8-flash

null

null

							input: 2696
							output: 38
							thoughts: 86
						

**Analyzing the hugetlb_cgroup.c Patch for KMSAN Fuzzing**

Alright, let's dive into this. The user wants me to determine if we need to consider KMSAN fuzzing for a patch in `mm/hugetlb_cgroup.c`. Okay, that makes sense; we want to ensure memory safety, especially with huge pages and cgroups. The fact that the question has been asked suggests someone sees a potential issue.

First, I need to understand the patch's context. I'll focus on lines 179-245 and 906-940 in `mm/hugetlb_cgroup.c`. Those ranges are likely where the relevant changes reside or where the surrounding code provides the necessary background. I'll read through these sections meticulously. I'll be looking for any indications of shared memory, concurrent access, or pointer arithmetic that could lead to memory corruption if handled incorrectly. I'll specifically keep an eye out for potential races, uninitialized memory reads, or use-after-free scenarios. My expertise tells me these are the typical areas to scrutinize when assessing KMSAN applicability. I need to understand how the patch modifies data structures, how it interacts with other kernel subsystems, and what locking mechanisms are in place. This will give me a proper assessment as to whether fuzzing is needed.

{
  "File": "mm/hugetlb_cgroup.c",
  "FirstLine": 170,
  "LineCount": 80
}

{
  "Contents": " 170:\t\treturn \u0026h_cgroup-\u003ecss;\n 171:\t\n 172:\tfail_alloc_nodeinfo:\n 173:\t\thugetlb_cgroup_free(h_cgroup);\n 174:\t\treturn ERR_PTR(-ENOMEM);\n 175:\t}\n 176:\t\n 177:\tstatic void hugetlb_cgroup_css_free(struct cgroup_subsys_state *css)\n 178:\t{\n 179:\t\thugetlb_cgroup_free(hugetlb_cgroup_from_css(css));\n 180:\t}\n 181:\t\n 182:\tstatic void hugetlb_cgroup_move_usage(struct hugetlb_cgroup *from,\n 183:\t\t\t\t\t      struct hugetlb_cgroup *to,\n 184:\t\t\t\t\t      struct folio *from_folio,\n 185:\t\t\t\t\t      struct folio *to_folio)\n 186:\t{\n 187:\t\tint idx = hstate_index(folio_hstate(from_folio));\n 188:\t\tunsigned long nr_pages = folio_nr_pages(from_folio);\n 189:\t\tint from_nid = folio_nid(from_folio);\n 190:\t\tint to_nid = folio_nid(to_folio);\n 191:\t\tunsigned long usage;\n 192:\t\n 193:\t\tlockdep_assert_held(\u0026hugetlb_lock);\n 194:\t\n 195:\t\tif (!from || !to)\n 196:\t\t\treturn;\n 197:\t\n 198:\t\tif (from == to \u0026\u0026 from_nid == to_nid)\n 199:\t\t\treturn;\n 200:\t\n 201:\t\tusage = READ_ONCE(from-\u003enodeinfo[from_nid]-\u003eusage[idx]);\n 202:\t\tif (WARN_ON_ONCE(usage \u003c nr_pages))\n 203:\t\t\treturn;\n 204:\t\tWRITE_ONCE(from-\u003enodeinfo[from_nid]-\u003eusage[idx], usage - nr_pages);\n 205:\t\n 206:\t\tusage = READ_ONCE(to-\u003enodeinfo[to_nid]-\u003eusage[idx]);\n 207:\t\tWRITE_ONCE(to-\u003enodeinfo[to_nid]-\u003eusage[idx], usage + nr_pages);\n 208:\t}\n 209:\t\n 210:\t/*\n 211:\t * Should be called with hugetlb_lock held.\n 212:\t * Since we are holding hugetlb_lock, pages cannot get moved from\n 213:\t * active list or uncharged from the cgroup, So no need to get\n 214:\t * page reference and test for page active here. This function\n 215:\t * cannot fail.\n 216:\t */\n 217:\tstatic void hugetlb_cgroup_move_parent(int idx, struct hugetlb_cgroup *h_cg,\n 218:\t\t\t\t\t       struct folio *folio)\n 219:\t{\n 220:\t\tunsigned int nr_pages;\n 221:\t\tstruct page_counter *counter;\n 222:\t\tstruct hugetlb_cgroup *hcg;\n 223:\t\tstruct hugetlb_cgroup *parent = parent_hugetlb_cgroup(h_cg);\n 224:\t\n 225:\t\thcg = hugetlb_cgroup_from_folio(folio);\n 226:\t\t/*\n 227:\t\t * We can have pages in active list without any cgroup\n 228:\t\t * ie, hugepage with less than 3 pages. We can safely\n 229:\t\t * ignore those pages.\n 230:\t\t */\n 231:\t\tif (!hcg || hcg != h_cg)\n 232:\t\t\tgoto out;\n 233:\t\n 234:\t\tnr_pages = folio_nr_pages(folio);\n 235:\t\tif (!parent) {\n 236:\t\t\tparent = root_h_cgroup;\n 237:\t\t\t/* root has no limit */\n 238:\t\t\tpage_counter_charge(\u0026parent-\u003ehugepage[idx], nr_pages);\n 239:\t\t}\n 240:\t\tcounter = \u0026h_cg-\u003ehugepage[idx];\n 241:\t\t/* Take the pages off the local counter */\n 242:\t\tpage_counter_cancel(counter, nr_pages);\n 243:\t\n 244:\t\thugetlb_cgroup_move_usage(h_cg, parent, folio, folio);\n 245:\t\n 246:\t\tset_hugetlb_cgroup(folio, parent);\n 247:\tout:\n 248:\t\treturn;\n 249:\t}\n"
}

gemini-3.8-flash

null

null

							input: 4357
							output: 38
							thoughts: 27
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Analyzing `hugetlb_cgroup_migrate`**

Alright, let's circle back to that section of code, specifically around lines 906 to 940, and give `hugetlb_cgroup_migrate` another look. We need to be absolutely certain the migration logic there is sound, particularly concerning its interactions with cgroups. I'm thinking we should re-examine the potential for race conditions or data corruption when moving huge pages between cgroup hierarchies. Let's see if the code correctly handles concurrent access to the page tables and the associated metadata. We may also need to check whether it's correctly accounting for page faults during the migration. Considering the performance implications of inefficient huge page handling, this warrants a second, more critical pass.

{
  "File": "mm/hugetlb_cgroup.c",
  "FirstLine": 900,
  "LineCount": 50
}

{
  "Contents": " 900:\t{\n 901:\t\tWARN_ON(cgroup_add_dfl_cftypes(\u0026hugetlb_cgrp_subsys,\n 902:\t\t\t\t\t       dfl_files));\n 903:\t\tWARN_ON(cgroup_add_legacy_cftypes(\u0026hugetlb_cgrp_subsys,\n 904:\t\t\t\t\t\t  legacy_files));\n 905:\t}\n 906:\t\n 907:\tvoid __init hugetlb_cgroup_file_init(void)\n 908:\t{\n 909:\t\tstruct hstate *h;\n 910:\t\n 911:\t\t__hugetlb_cgroup_file_pre_init();\n 912:\t\tfor_each_hstate(h)\n 913:\t\t\t__hugetlb_cgroup_file_init(h);\n 914:\t\t__hugetlb_cgroup_file_post_init();\n 915:\t}\n 916:\t\n 917:\t/*\n 918:\t * hugetlb_lock will make sure a parallel cgroup rmdir won't happen\n 919:\t * when we migrate hugepages\n 920:\t */\n 921:\tvoid hugetlb_cgroup_migrate(struct folio *old_folio, struct folio *new_folio)\n 922:\t{\n 923:\t\tstruct hugetlb_cgroup *h_cg;\n 924:\t\tstruct hugetlb_cgroup *h_cg_rsvd;\n 925:\t\tstruct hstate *h = folio_hstate(old_folio);\n 926:\t\n 927:\t\tif (hugetlb_cgroup_disabled())\n 928:\t\t\treturn;\n 929:\t\n 930:\t\tspin_lock_irq(\u0026hugetlb_lock);\n 931:\t\th_cg = hugetlb_cgroup_from_folio(old_folio);\n 932:\t\th_cg_rsvd = hugetlb_cgroup_from_folio_rsvd(old_folio);\n 933:\t\tset_hugetlb_cgroup(old_folio, NULL);\n 934:\t\tset_hugetlb_cgroup_rsvd(old_folio, NULL);\n 935:\t\n 936:\t\t/* move the h_cg details to new cgroup */\n 937:\t\tset_hugetlb_cgroup(new_folio, h_cg);\n 938:\t\tset_hugetlb_cgroup_rsvd(new_folio, h_cg_rsvd);\n 939:\t\n 940:\t\thugetlb_cgroup_move_usage(h_cg, h_cg, old_folio, new_folio);\n 941:\t\n 942:\t\tlist_move(\u0026new_folio-\u003elru, \u0026h-\u003ehugepage_activelist);\n 943:\t\tspin_unlock_irq(\u0026hugetlb_lock);\n 944:\t}\n 945:\t\n 946:\tstatic struct cftype hugetlb_files[] = {\n 947:\t\t{} /* terminate */\n 948:\t};\n 949:\t\n"
}

gemini-3.8-flash

null

null

							input: 5438
							output: 32
							thoughts: 46
						

Okay, let's dive into this.

**Investigating `hugetlb_cgroup_move_usage` and Node Information**

Right, so I need to understand what `hugetlb_cgroup_move_usage` actually *does*. I'm particularly interested in tracing the flow of `nodeinfo` here. Where does it originate, and how is it used in conjunction with this function?

My immediate thought is to start with the source itself. Let's get into `mm/hugetlb_cgroup.c` and search specifically for `nodeinfo`. That should be the quickest way to get a grasp of its role in this whole process. From there, I can likely infer the bigger picture.

{
  "Expression": "nodeinfo",
  "PathPrefix": "mm/hugetlb_cgroup.c"
}

{
  "Output": "mm/hugetlb_cgroup.c=129=static void hugetlb_cgroup_free(struct hugetlb_cgroup *h_cgroup)\n--\nmm/hugetlb_cgroup.c-133-\tfor_each_node(node)\nmm/hugetlb_cgroup.c:134:\t\tkfree(h_cgroup-\u003enodeinfo[node]);\nmm/hugetlb_cgroup.c-135-\tkfree(h_cgroup);\n--\nmm/hugetlb_cgroup.c=139=hugetlb_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)\n--\nmm/hugetlb_cgroup.c-144-\nmm/hugetlb_cgroup.c:145:\th_cgroup = kzalloc_flex(*h_cgroup, nodeinfo, nr_node_ids);\nmm/hugetlb_cgroup.c-146-\n--\nmm/hugetlb_cgroup.c-161-\t\t\tnode_state(node, N_NORMAL_MEMORY) ? node : NUMA_NO_NODE;\nmm/hugetlb_cgroup.c:162:\t\th_cgroup-\u003enodeinfo[node] =\nmm/hugetlb_cgroup.c-163-\t\t\tkzalloc_node(sizeof(struct hugetlb_cgroup_per_node),\nmm/hugetlb_cgroup.c-164-\t\t\t\t     GFP_KERNEL, node_to_alloc);\nmm/hugetlb_cgroup.c:165:\t\tif (!h_cgroup-\u003enodeinfo[node])\nmm/hugetlb_cgroup.c:166:\t\t\tgoto fail_alloc_nodeinfo;\nmm/hugetlb_cgroup.c-167-\t}\n--\nmm/hugetlb_cgroup.c-171-\nmm/hugetlb_cgroup.c:172:fail_alloc_nodeinfo:\nmm/hugetlb_cgroup.c-173-\thugetlb_cgroup_free(h_cgroup);\n--\nmm/hugetlb_cgroup.c=182=static void hugetlb_cgroup_move_usage(struct hugetlb_cgroup *from,\n--\nmm/hugetlb_cgroup.c-200-\nmm/hugetlb_cgroup.c:201:\tusage = READ_ONCE(from-\u003enodeinfo[from_nid]-\u003eusage[idx]);\nmm/hugetlb_cgroup.c-202-\tif (WARN_ON_ONCE(usage \u003c nr_pages))\nmm/hugetlb_cgroup.c-203-\t\treturn;\nmm/hugetlb_cgroup.c:204:\tWRITE_ONCE(from-\u003enodeinfo[from_nid]-\u003eusage[idx], usage - nr_pages);\nmm/hugetlb_cgroup.c-205-\nmm/hugetlb_cgroup.c:206:\tusage = READ_ONCE(to-\u003enodeinfo[to_nid]-\u003eusage[idx]);\nmm/hugetlb_cgroup.c:207:\tWRITE_ONCE(to-\u003enodeinfo[to_nid]-\u003eusage[idx], usage + nr_pages);\nmm/hugetlb_cgroup.c-208-}\n--\nmm/hugetlb_cgroup.c=336=static void __hugetlb_cgroup_commit_charge(int idx, unsigned long nr_pages,\n--\nmm/hugetlb_cgroup.c-345-\t\tunsigned long usage =\nmm/hugetlb_cgroup.c:346:\t\t\th_cg-\u003enodeinfo[folio_nid(folio)]-\u003eusage[idx];\nmm/hugetlb_cgroup.c-347-\t\t/*\n--\nmm/hugetlb_cgroup.c-351-\t\t */\nmm/hugetlb_cgroup.c:352:\t\tWRITE_ONCE(h_cg-\u003enodeinfo[folio_nid(folio)]-\u003eusage[idx],\nmm/hugetlb_cgroup.c-353-\t\t\t   usage + nr_pages);\n--\nmm/hugetlb_cgroup.c=374=static void __hugetlb_cgroup_uncharge_folio(int idx, unsigned long nr_pages,\n--\nmm/hugetlb_cgroup.c-394-\t\tunsigned long usage =\nmm/hugetlb_cgroup.c:395:\t\t\th_cg-\u003enodeinfo[folio_nid(folio)]-\u003eusage[idx];\nmm/hugetlb_cgroup.c-396-\t\t/*\n--\nmm/hugetlb_cgroup.c-400-\t\t */\nmm/hugetlb_cgroup.c:401:\t\tWRITE_ONCE(h_cg-\u003enodeinfo[folio_nid(folio)]-\u003eusage[idx],\nmm/hugetlb_cgroup.c-402-\t\t\t   usage - nr_pages);\n--\nmm/hugetlb_cgroup.c=489=static int hugetlb_cgroup_read_numa_stat(struct seq_file *seq, void *dummy)\n--\nmm/hugetlb_cgroup.c-502-\t\tfor_each_node_state(nid, N_MEMORY)\nmm/hugetlb_cgroup.c:503:\t\t\tusage += READ_ONCE(h_cg-\u003enodeinfo[nid]-\u003eusage[idx]);\nmm/hugetlb_cgroup.c-504-\t\tseq_printf(seq, \"total=%lu\", usage * PAGE_SIZE);\n--\nmm/hugetlb_cgroup.c-508-\t\t\tseq_printf(seq, \" N%d=%lu\", nid,\nmm/hugetlb_cgroup.c:509:\t\t\t\t   READ_ONCE(h_cg-\u003enodeinfo[nid]-\u003eusage[idx]) *\nmm/hugetlb_cgroup.c-510-\t\t\t\t\t   PAGE_SIZE);\n--\nmm/hugetlb_cgroup.c-529-\t\t\tusage += READ_ONCE(hugetlb_cgroup_from_css(css)\nmm/hugetlb_cgroup.c:530:\t\t\t\t\t\t   -\u003enodeinfo[nid]\nmm/hugetlb_cgroup.c-531-\t\t\t\t\t\t   -\u003eusage[idx]);\n"
}

gemini-3.8-flash

null

null

							input: 7226
							output: 203
							thoughts: 1504
						

**Analysis of hugetlb cgroup usage update patch**

Okay, let's break this down. My focus here is on whether this patch introduces any uninitialized memory issues that KMSAN might catch. From the looks of it, this patch is adding `hugetlb_cgroup_move_usage` to accurately track per-NUMA-node hugetlb usage when pages move between cgroups, or during page migration. It's essentially updating the `h_cg->nodeinfo[nid]->usage[idx]` counters.

First, I need to verify that all variables within `hugetlb_cgroup_move_usage` are properly initialized. `idx`, `nr_pages`, `from_nid`, and `to_nid` all derive from the `folio` metadata, which is generally well-defined. `usage` is initialized with `READ_ONCE`, which appears to be safe. Importantly, `from->nodeinfo[from_nid]` and `to->nodeinfo[to_nid]` are allocated using `kzalloc_node`, guaranteeing zero initialization.

Now, I look for any potential for uninitialized memory usage:
1.  Kernel structures sent to user space? No, nothing is copied. `hugetlb_cgroup_read_numa_stat` formats the counter as an ASCII string and prints into a `seq_file`. So, no concerns there.
2.  Conditional logic based on potentially uninitialized variables? Nope, everything is initialized before use.
3.  Complex data structure initialization where uninitialized fields are read? No, `kzalloc_node` is used for `nodeinfo`.
4.  Bounds checks or logic that might read uninitialized memory? No, the code adds and subtracts `usage` counter.

The patch itself appears to address potential issues, like counter underflow, via `WARN_ON_ONCE`. Null pointer dereferences or out-of-bounds access could be possible, but those would be handled by KASAN. The code also has lockdep assertions, so it's checking those issues.

So, from what I can see, this patch primarily deals with integer arithmetic and data structure updates on initialized memory regions. There are no obvious code paths where uninitialized memory could be used. This patch appears safe from any KMSAN concerns. It's really the classic case where you'd leverage KASAN, LOCKDEP or the standard bug detectors.

Therefore, `NeedsKMSAN=false` is the correct setting here.

{
  "KMSANReasoning": "The patch adds `hugetlb_cgroup_move_usage()` to update per-node hugetlb usage accounting counters when huge pages move to a parent cgroup or during huge page migration. All local variables (`idx`, `nr_pages`, `from_nid`, `to_nid`, `usage`) are explicitly initialized from folio attributes or via `READ_ONCE` on pre-allocated zeroed structures (`nodeinfo` allocated with `kzalloc_node`). No stack or heap structures are copied to user space, no padding bytes are exposed, and no uninitialized memory could be read or branched upon. Any risks introduced by these changes (such as out-of-bounds node indexing, use-after-free, or locking issues) are covered by KASAN and LOCKDEP. Thus, a dedicated KMSAN fuzzing session is not justified.",
  "NeedsKMSAN": false
}

{
  "KMSANReasoning": "The patch adds `hugetlb_cgroup_move_usage()` to update per-node hugetlb usage accounting counters when huge pages move to a parent cgroup or during huge page migration. All local variables (`idx`, `nr_pages`, `from_nid`, `to_nid`, `usage`) are explicitly initialized from folio attributes or via `READ_ONCE` on pre-allocated zeroed structures (`nodeinfo` allocated with `kzalloc_node`). No stack or heap structures are copied to user space, no padding bytes are exposed, and no uninitialized memory could be read or branched upon. Any risks introduced by these changes (such as out-of-bounds node indexing, use-after-free, or locking issues) are covered by KASAN and LOCKDEP. Thus, a dedicated KMSAN fuzzing session is not justified.",
  "NeedsKMSAN": false
}