AI Trajectory

null

{
  "EnableConfigs": [
    "MEM_ALLOC_PROFILING",
    "TRACING"
  ],
  "FocusSymbols": [
    "allocinfo_ioctl",
    "allocinfo_ioctl_toggle_trace",
    "alloc_tag_trace_toggle",
    "__alloc_tag_trace_hit",
    "alloc_tag_trace_mem_alloc",
    "alloc_tag_trace_mem_free"
  ],
  "KMSANReasoning": "The patch series adds tracepoints (alloc_tag_hit, alloc_tag_mem_alloced, alloc_tag_mem_freed) and a new ioctl (ALLOCINFO_IOC_TOGGLE_TRACE) to toggle allocation profiling tracing.\n\nKMSAN vs KASAN applicability analysis:\n1. Kernel-to-userspace data leaks: The patch modifies UAPI struct allocinfo_counter by replacing 1 byte of padding with a trace_on field. In allocinfo_ioctl_get_next(), the output struct is zero-initialized with memset(\u0026params, 0, sizeof(params)) before populating fields. In allocinfo_ioctl_get_at(), the struct is zero-initialized and copied from user before fields are updated. The new trace_on field is explicitly assigned in allocinfo_to_params(). The new ioctl ALLOCINFO_IOC_TOGGLE_TRACE is _IOW (input only) and does not copy any data to userspace.\n2. Uninitialized variable reads / conditional branching: Stack variables such as counters in matches_filter() and allocinfo_ioctl_toggle_trace() are only read after being explicitly fetched (guarded by fetched_counters).\n3. Data structures: The codetag flags field is changed to atomic_t and statically initialized using ATOMIC_INIT(0).\n4. Memory allocation/freeing logic: The hook modifications in page_alloc, SLUB, and percpu only pass pointers to tracepoint callbacks and do not alter memory initialization, sizing, or buffer access.\n\nAny potential bugs introduced by this patch (e.g., concurrency races on static keys or atomic counters, locking interactions) are within the scope of LOCKDEP, KASAN, or standard kernel debug facilities. No uninitialized memory usage or info-leaks are introduced, so a dedicated KMSAN run is not needed.",
  "NeedsKMSAN": false,
  "Reasoning": "The patch introduces memory allocation profiling trace events (alloc_tag_hit, alloc_tag_mem_alloced, alloc_tag_mem_freed) and exposes a new ioctl command ALLOCINFO_IOC_TOGGLE_TRACE on /proc/allocinfo to dynamically enable/disable tracing per allocation tag. It introduces dynamic static branch manipulation, atomic flag updates, input filter validation, and hooks into core alloc/free paths across SLUB, page allocator, and percpu subsystems. This code is reachable from userspace via /proc/allocinfo ioctls and warrants fuzzing for concurrency issues, filter parsing, and static branch toggling behavior.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 9c8e1162b5ec6958cde9fbf00162f239ce0066a8\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Wed Oct 7 22:58:48 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/Documentation/mm/allocation-profiling.rst b/Documentation/mm/allocation-profiling.rst\nindex b11ea77c06736..63b6684663426 100644\n--- a/Documentation/mm/allocation-profiling.rst\n+++ b/Documentation/mm/allocation-profiling.rst\n@@ -129,6 +129,79 @@ To do so:\n - Then, use the following form for your allocations:\n   alloc_hooks_tag(ht-\u003eyour_saved_tag, kmalloc_noprof(...))\n \n+Tracing\n+=======\n+\n+Three trace events are available under `/sys/kernel/tracing/events/alloc_tag` to\n+expose the full call stack and the lifetime of individual allocations:\n+\n+- `alloc_tag_hit`: Fired at the exact call site, before the allocation happens.\n+  Can be used to capture the call stack of the caller.\n+\n+- `alloc_tag_mem_alloced`: Fired once the allocation succeeds. Carries the `ptr`,\n+  `tag` and `bytes` for each allocation.\n+\n+- `alloc_tag_mem_freed`: Fired before memory is freed. Carries the same\n+  `ptr`, `tag` and `bytes` as the matching alloc event.\n+\n+`ptr` identifies the allocation, and its meaning depends on the allocator:\n+\n+- slab and percpu: the address of the object's `codetag_ref`\n+- page allocator: the `struct page` pointer of the head page\n+\n+Events are only emitted for tags that have tracing turned on and while profiling\n+is enabled. When no tag is traced, the hooks are behind a static branch.\n+\n+Enabling Tracing\n+----------------\n+\n+Tracing is toggled on and off per tag with the `ALLOCINFO_IOC_TOGGLE_TRACE`\n+ioctl on `/proc/allocinfo`. It takes the same filter as used by\n+`ALLOCINFO_IOC_GET_AT`; an empty mask selects all tags. Size limits in the\n+filter are checked once, against the tag's size at the time of the call. Tags\n+already in the requested state are skipped and a -ENOENT is returned if no\n+tag matched.\n+\n+Tracing is turned off for a module's tags when the module is unloaded.\n+\n+Memory allocated before a tag was enabled has no alloc event but will still\n+produce a free event. Likewise, memory alive when tag is disabled will not\n+produce a free event. Tools should expect unmatched frees after enabling and\n+missing frees after disabling.\n+\n+Correlating the events\n+----------------------\n+\n+`alloc_tag_hit` and `alloc_tag_mem_alloced` come from different points in the\n+call stack, so they have to be stitched together by the user consuming the\n+events. Here's a typical flow:\n+\n+1. On `alloc_tag_hit`: Capture the stack trace and cache it keyed by `(pid, tag)`.\n+\n+2. On `alloc_tag_mem_alloced`: Look up the cached stack trace by `(pid, tag)`,\n+   then create an active allocation record keyed by `ptr` that holds the stack\n+   trace and `bytes`.\n+\n+3. On `alloc_tag_mem_freed`: Look up the record by `ptr` and retire it.\n+\n+Limitations\n+-----------\n+\n+- For the page allocator, events are generated for the original allocation and\n+  the free only. If the tag reference is split or moved to another folio in\n+  between, no event is generated for that. As a result:\n+\n+  - a free event may carry a `ptr` that never appeared in an alloc event;\n+  - `bytes` in a free event may be smaller than in the matching alloc event.\n+\n+  Tools should correlate on `ptr` but must not assume that freed bytes equal\n+  allocated bytes, or that every free has a matching alloc.\n+\n+- Freeing a non-compound high-order page with `__free_pages()` while another CPU\n+  holds a reference frees the tail pages immediately and the head page later when\n+  the reference is dropped. The free event is emitted at the second point and\n+  reports `PAGE_SIZE` rather than the full size.\n+\n Notes\n =====\n \ndiff --git a/MAINTAINERS b/MAINTAINERS\nindex 5c38da7090db8..751ce786a3788 100644\n--- a/MAINTAINERS\n+++ b/MAINTAINERS\n@@ -17100,6 +17100,7 @@ S:\tMaintained\n F:\tDocumentation/mm/allocation-profiling.rst\n F:\tinclude/linux/alloc_tag.h\n F:\tinclude/linux/pgalloc_tag.h\n+F:\tinclude/trace/events/alloc_tag.h\n F:\tinclude/uapi/linux/alloc_tag.h\n F:\tmm/alloc_tag.c\n F:\ttools/testing/selftests/alloc_tag/\ndiff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h\nindex 7f2d80a597924..94697b28053ad 100644\n--- a/include/linux/alloc_tag.h\n+++ b/include/linux/alloc_tag.h\n@@ -128,12 +128,60 @@ DECLARE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag);\n DECLARE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,\n \t\t\tmem_alloc_profiling_key);\n \n+DECLARE_STATIC_KEY_FALSE(alloc_tag_trace_key);\n+\n static inline bool mem_alloc_profiling_enabled(void)\n {\n \treturn static_branch_maybe(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,\n \t\t\t\t   \u0026mem_alloc_profiling_key);\n }\n \n+static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag)\n+{\n+\tatomic_or(CODETAG_FLAG_INACCURATE, \u0026tag-\u003ect.flags);\n+}\n+\n+static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag)\n+{\n+\treturn !!(atomic_read(\u0026tag-\u003ect.flags) \u0026 CODETAG_FLAG_INACCURATE);\n+}\n+\n+static inline void alloc_tag_set_traced(struct alloc_tag *tag)\n+{\n+\tatomic_or(CODETAG_FLAG_TRACE_ON, \u0026tag-\u003ect.flags);\n+}\n+\n+static inline void alloc_tag_clear_traced(struct alloc_tag *tag)\n+{\n+\tatomic_andnot(CODETAG_FLAG_TRACE_ON, \u0026tag-\u003ect.flags);\n+}\n+\n+static inline bool alloc_tag_is_traced(const struct alloc_tag *tag)\n+{\n+\treturn !!(atomic_read(\u0026tag-\u003ect.flags) \u0026 CODETAG_FLAG_TRACE_ON);\n+}\n+\n+static inline bool alloc_tag_trace_enabled(const struct alloc_tag *tag)\n+{\n+\tif (static_branch_unlikely(\u0026alloc_tag_trace_key))\n+\t\treturn tag \u0026\u0026 alloc_tag_is_traced(tag);\n+\treturn false;\n+}\n+\n+void alloc_tag_trace_mem_alloc(const void *ptr, struct alloc_tag *tag,\n+\t\t\t       size_t bytes);\n+\n+void alloc_tag_trace_mem_free(const void *ptr, struct alloc_tag *tag,\n+\t\t\t      size_t bytes);\n+\n+void __alloc_tag_trace_hit(struct alloc_tag *tag);\n+\n+static __always_inline void alloc_tag_trace_hit(struct alloc_tag *tag)\n+{\n+\tif (alloc_tag_trace_enabled(tag))\n+\t\t__alloc_tag_trace_hit(tag);\n+}\n+\n bool mem_alloc_profiling_permanently_disabled(void);\n \n static inline struct alloc_tag_counters alloc_tag_read(struct alloc_tag *tag)\n@@ -198,13 +246,19 @@ static inline bool alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *t\n \treturn true;\n }\n \n-static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes)\n+static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes,\n+\t\t\t\t const void *ptr)\n {\n-\tif (likely(alloc_tag_ref_set(ref, tag)))\n+\tif (likely(alloc_tag_ref_set(ref, tag))) {\n \t\tthis_cpu_add(tag-\u003ecounters-\u003ebytes, bytes);\n+\n+\t\tif (alloc_tag_trace_enabled(tag))\n+\t\t\t/* Trace successful allocs with their unique ptr */\n+\t\t\talloc_tag_trace_mem_alloc(ptr, tag, bytes);\n+\t}\n }\n \n-static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes)\n+static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes, const void *ptr)\n {\n \tstruct alloc_tag *tag;\n \n@@ -222,17 +276,11 @@ static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes)\n \tthis_cpu_sub(tag-\u003ecounters-\u003ebytes, bytes);\n \tthis_cpu_dec(tag-\u003ecounters-\u003ecalls);\n \n-\tref-\u003ect = NULL;\n-}\n-\n-static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag)\n-{\n-\ttag-\u003ect.flags |= CODETAG_FLAG_INACCURATE;\n-}\n+\tif (alloc_tag_trace_enabled(tag))\n+\t\t/* Trace frees with their unique ptr */\n+\t\talloc_tag_trace_mem_free(ptr, tag, bytes);\n \n-static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag)\n-{\n-\treturn !!(tag-\u003ect.flags \u0026 CODETAG_FLAG_INACCURATE);\n+\tref-\u003ect = NULL;\n }\n \n #define alloc_tag_record(p)\t((p) = current-\u003ealloc_tag)\n@@ -243,25 +291,29 @@ static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag)\n static inline bool mem_alloc_profiling_enabled(void) { return false; }\n static inline bool mem_alloc_profiling_permanently_disabled(void) { return true; }\n static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag,\n-\t\t\t\t size_t bytes) {}\n-static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes) {}\n+\t\t\t\t size_t bytes, const void *ptr) {}\n+static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes,\n+\t\t\t\t const void *ptr) {}\n static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag) {}\n static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag) { return false; }\n+#define alloc_tag_trace_hit(_tag)\t/* NOOP */\n #define alloc_tag_record(p)\tdo {} while (0)\n \n #endif /* CONFIG_MEM_ALLOC_PROFILING */\n \n-#define alloc_hooks_tag(_tag, _do_alloc)\t\t\t\t\\\n-({\t\t\t\t\t\t\t\t\t\\\n-\ttypeof(_do_alloc) _res;\t\t\t\t\t\t\\\n-\tif (mem_alloc_profiling_enabled()) {\t\t\t\t\\\n-\t\tstruct alloc_tag * __maybe_unused _old;\t\t\t\\\n-\t\t_old = alloc_tag_save(_tag);\t\t\t\t\\\n-\t\t_res = _do_alloc;\t\t\t\t\t\\\n-\t\talloc_tag_restore(_tag, _old);\t\t\t\t\\\n-\t} else\t\t\t\t\t\t\t\t\\\n-\t\t_res = _do_alloc;\t\t\t\t\t\\\n-\t_res;\t\t\t\t\t\t\t\t\\\n+#define alloc_hooks_tag(_tag, _do_alloc)\t\t\t\t\t\\\n+({\t\t\t\t\t\t\t\t\t\t\\\n+\ttypeof(_do_alloc) _res;\t\t\t\t\t\t\t\\\n+\tif (mem_alloc_profiling_enabled()) {\t\t\t\t\t\\\n+\t\tstruct alloc_tag * __maybe_unused _old;\t\t\t\t\\\n+\t\t/* Fired here to cleanly capture the caller's stack trace */\t\\\n+\t\talloc_tag_trace_hit(_tag);\t\t\t\t\t\\\n+\t\t_old = alloc_tag_save(_tag);\t\t\t\t\t\\\n+\t\t_res = _do_alloc;\t\t\t\t\t\t\\\n+\t\talloc_tag_restore(_tag, _old);\t\t\t\t\t\\\n+\t} else\t\t\t\t\t\t\t\t\t\\\n+\t\t_res = _do_alloc;\t\t\t\t\t\t\\\n+\t_res;\t\t\t\t\t\t\t\t\t\\\n })\n \n #define alloc_hooks(_do_alloc)\t\t\t\t\t\t\\\ndiff --git a/include/linux/codetag.h b/include/linux/codetag.h\nindex a25a085c2df19..f728295d50c05 100644\n--- a/include/linux/codetag.h\n+++ b/include/linux/codetag.h\n@@ -18,6 +18,7 @@ struct module;\n \n /* codetag flags */\n #define CODETAG_FLAG_INACCURATE\t(1 \u003c\u003c 0)\n+#define CODETAG_FLAG_TRACE_ON\t(1 \u003c\u003c 1)\n \n /*\n  * An instance of this structure is created in a special ELF section at every\n@@ -25,7 +26,7 @@ struct module;\n  * an array of these.\n  */\n struct codetag {\n-\tunsigned int flags;\n+\tatomic_t flags;\n \tunsigned int lineno;\n \tconst char *modname;\n \tconst char *function;\n@@ -71,7 +72,7 @@ struct codetag_iterator {\n \t.function\t= __func__,\t\t\t\\\n \t.filename\t= __FILE__,\t\t\t\\\n \t.lineno\t\t= __LINE__,\t\t\t\\\n-\t.flags\t\t= 0,\t\t\t\t\\\n+\t.flags\t\t= ATOMIC_INIT(0),\t\t\\\n }\n \n void codetag_lock_module_list(struct codetag_type *cttype);\ndiff --git a/include/trace/events/alloc_tag.h b/include/trace/events/alloc_tag.h\nnew file mode 100644\nindex 0000000000000..b79efb7dd25c6\n--- /dev/null\n+++ b/include/trace/events/alloc_tag.h\n@@ -0,0 +1,122 @@\n+/* SPDX-License-Identifier: GPL-2.0 */\n+#undef TRACE_SYSTEM\n+#define TRACE_SYSTEM alloc_tag\n+\n+#if !defined(_TRACE_ALLOC_TAG_H) || defined(TRACE_HEADER_MULTI_READ)\n+#define _TRACE_ALLOC_TAG_H\n+\n+#include \u003clinux/tracepoint.h\u003e\n+\n+/*\n+ * alloc_tag_hit is generated at the exact allocation call site and can be\n+ * used to capture a clean stack trace.\n+ *\n+ * To link this stack trace to the actual allocated memory chunk, tools must\n+ * correlate this event with the resulting alloc_tag_mem_alloced event. Since\n+ * multiple threads can hit the same tag simultaneously, tools must match BOTH\n+ * the `tag` field and the implicitly recorded PID provided by the core\n+ * tracing subsystem.\n+ */\n+TRACE_EVENT(alloc_tag_hit,\n+\tTP_PROTO(struct alloc_tag *tag),\n+\n+\tTP_ARGS(tag),\n+\n+\tTP_STRUCT__entry(__field(struct alloc_tag *, tag)\n+\t\t\t __string(modname, tag-\u003ect.modname ? tag-\u003ect.modname : \"NONE\")\n+\t\t\t __string(filename, tag-\u003ect.filename)\n+\t\t\t __string(function, tag-\u003ect.function)\n+\t\t\t __field(unsigned int, lineno)\n+\t),\n+\n+\tTP_fast_assign(__entry-\u003etag = tag;\n+\t\t       __assign_str(modname);\n+\t\t       __assign_str(filename);\n+\t\t       __assign_str(function);\n+\t\t       __entry-\u003elineno = tag-\u003ect.lineno;\n+\t),\n+\n+\tTP_printk(\"tag %p, module: %s, filename: %s, function %s, lineno %u\",\n+\t\t  __entry-\u003etag,\n+\t\t  __get_str(modname),\n+\t\t  __get_str(filename),\n+\t\t  __get_str(function),\n+\t\t  __entry-\u003elineno\n+\t)\n+);\n+\n+/*\n+ * alloc_tag_mem_alloced is generated after memory is successfully allocated.\n+ * It captures the exact byte size.\n+ *\n+ * The `ptr` value identifies the memory chunk for tracking its lifecycle\n+ * (e.g., matching it with alloc_tag_mem_freed).\n+ * - slab and percpu allocators: address of the object's codetag_ref\n+ * - page allocator: the head struct page of the allocation\n+ *\n+ * Because the kernel isolates active allocations within the task struct\n+ * (current-\u003ealloc_tag), this event will always share the same implicit PID as\n+ * its corresponding alloc_tag_hit event. Tools should use the combination\n+ * PID + `tag` to correlate them.\n+ */\n+TRACE_EVENT(alloc_tag_mem_alloced,\n+\tTP_PROTO(const void *ptr, struct alloc_tag *tag, size_t bytes),\n+\n+\tTP_ARGS(ptr, tag, bytes),\n+\n+\tTP_STRUCT__entry(__field(const void *, ptr)\n+\t\t\t __field(struct alloc_tag *, tag)\n+\t\t\t __field(size_t, bytes)\n+\t),\n+\n+\tTP_fast_assign(__entry-\u003eptr = ptr;\n+\t\t       __entry-\u003etag = tag;\n+\t\t       __entry-\u003ebytes = bytes;\n+\t),\n+\n+\tTP_printk(\"ptr %p, tag %p, bytes %zu\",\n+\t\t  __entry-\u003eptr,\n+\t\t  __entry-\u003etag,\n+\t\t  __entry-\u003ebytes\n+\t)\n+);\n+\n+/*\n+ * alloc_tag_mem_freed event is generated immediately before memory is\n+ * freed. The `ptr` value matches the one emitted during allocation,\n+ * allowing tools to match it to its corresponding allocation and\n+ * call stack.\n+ *\n+ * Page allocator caveat: Pages can be split or moved to another folio\n+ * after the alloc event with no new events generated for that. As a\n+ * result, a free event may carry a `ptr` that never appeared in an\n+ * alloc event, and the `bytes` may be smaller than in the matching\n+ * alloc event. Tools must not assume alloc bytes == free bytes, nor\n+ * that every free has a matching alloc.\n+ */\n+TRACE_EVENT(alloc_tag_mem_freed,\n+\tTP_PROTO(const void *ptr, struct alloc_tag *tag, size_t bytes),\n+\n+\tTP_ARGS(ptr, tag, bytes),\n+\n+\tTP_STRUCT__entry(__field(const void *, ptr)\n+\t\t\t __field(struct alloc_tag *, tag)\n+\t\t\t __field(size_t, bytes)\n+\t),\n+\n+\tTP_fast_assign(__entry-\u003eptr = ptr;\n+\t\t       __entry-\u003etag = tag;\n+\t\t       __entry-\u003ebytes = bytes;\n+\t),\n+\n+\tTP_printk(\"ptr %p, tag %p, bytes %zu\",\n+\t\t  __entry-\u003eptr,\n+\t\t  __entry-\u003etag,\n+\t\t  __entry-\u003ebytes\n+\t)\n+);\n+\n+#endif /* _TRACE_ALLOC_TAG_H */\n+\n+/* This part must be outside protection */\n+#include \u003ctrace/define_trace.h\u003e\ndiff --git a/include/uapi/linux/alloc_tag.h b/include/uapi/linux/alloc_tag.h\nindex 7d4618bea0434..a96054ac22376 100644\n--- a/include/uapi/linux/alloc_tag.h\n+++ b/include/uapi/linux/alloc_tag.h\n@@ -38,7 +38,8 @@ struct allocinfo_counter {\n \t__u64 bytes;\n \t__u64 calls;\n \t__u8 accurate;\n-\t__u8 pad[7];\n+\t__u8 trace_on;\n+\t__u8 pad[6];\n } __attribute__((aligned(8)));\n \n struct allocinfo_tag_data {\n@@ -54,7 +55,8 @@ enum {\n \tALLOCINFO_FILTER_INACCURATE,\n \tALLOCINFO_FILTER_MIN_SIZE,\n \tALLOCINFO_FILTER_MAX_SIZE,\n-\t__ALLOCINFO_FILTER_LAST = ALLOCINFO_FILTER_MAX_SIZE\n+\tALLOCINFO_FILTER_TRACE_ON,\n+\t__ALLOCINFO_FILTER_LAST = ALLOCINFO_FILTER_TRACE_ON\n };\n \n #define ALLOCINFO_FILTER_MASK_MODNAME\t\t(1 \u003c\u003c ALLOCINFO_FILTER_MODNAME)\n@@ -64,6 +66,7 @@ enum {\n #define ALLOCINFO_FILTER_MASK_INACCURATE\t(1 \u003c\u003c ALLOCINFO_FILTER_INACCURATE)\n #define ALLOCINFO_FILTER_MASK_MIN_SIZE\t\t(1 \u003c\u003c ALLOCINFO_FILTER_MIN_SIZE)\n #define ALLOCINFO_FILTER_MASK_MAX_SIZE\t\t(1 \u003c\u003c ALLOCINFO_FILTER_MAX_SIZE)\n+#define ALLOCINFO_FILTER_MASK_TRACE_ON\t\t(1 \u003c\u003c ALLOCINFO_FILTER_TRACE_ON)\n \n #define ALLOCINFO_FILTER_MASKS \\\n \t((1 \u003c\u003c (__ALLOCINFO_FILTER_LAST + 1)) - 1)\n@@ -75,6 +78,7 @@ struct allocinfo_filter {\n \t__u64 max_size;\n \t/* filter criteria only; see allocinfo_counter.accurate for actual accuracy */\n \t__u64 inaccurate;\n+\t__u64 tracing;\n };\n \n struct allocinfo_get_at {\n@@ -85,9 +89,20 @@ struct allocinfo_get_at {\n \tstruct allocinfo_tag_data data;\n };\n \n+struct allocinfo_toggle_traces {\n+\t/* inputs */\n+\t/*\n+\t * Tags matching the filter are toggled; an empty mask selects all tags.\n+\t * Size criteria are checked once, against the tag's size at call time.\n+\t */\n+\tstruct allocinfo_filter filter;\n+\t__u64 enable;\n+};\n+\n #define _ALLOCINFO_IOC_CONTENT_ID\t0\n #define _ALLOCINFO_IOC_GET_AT\t\t1\n #define _ALLOCINFO_IOC_GET_NEXT\t\t2\n+#define _ALLOCINFO_IOC_TOGGLE_TRACE\t3\n \n #define ALLOCINFO_IOC_BASE\t\t0xA6\n #define ALLOCINFO_IOC_CONTENT_ID\t_IOR(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_CONTENT_ID,\t\\\n@@ -96,5 +111,7 @@ struct allocinfo_get_at {\n \t\t\t\t\t      struct allocinfo_get_at)\n #define ALLOCINFO_IOC_GET_NEXT\t\t_IOR(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_GET_NEXT,\t\\\n \t\t\t\t\t     struct allocinfo_tag_data)\n+#define ALLOCINFO_IOC_TOGGLE_TRACE\t_IOW(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_TOGGLE_TRACE,\t\\\n+\t\t\t\t\t    struct allocinfo_toggle_traces)\n \n #endif /* _UAPI_ALLOC_TAG_H */\ndiff --git a/mm/alloc_tag.c b/mm/alloc_tag.c\nindex 82e2c3448dcf2..8e63f347657b6 100644\n--- a/mm/alloc_tag.c\n+++ b/mm/alloc_tag.c\n@@ -18,6 +18,9 @@\n #include \u003clinux/kmemleak.h\u003e\n #include \u003cuapi/linux/alloc_tag.h\u003e\n \n+#define CREATE_TRACE_POINTS\n+#include \u003ctrace/events/alloc_tag.h\u003e\n+\n #include \"internal.h\"\n #include \"page_alloc.h\"\n \n@@ -54,6 +57,18 @@ EXPORT_SYMBOL(mem_alloc_profiling_key);\n \n DEFINE_STATIC_KEY_FALSE(mem_profiling_compressed);\n \n+DEFINE_STATIC_KEY_FALSE(alloc_tag_trace_key);\n+EXPORT_SYMBOL(alloc_tag_trace_key);\n+\n+static atomic_t alloc_tag_trace_cnt = ATOMIC_INIT(0);\n+\n+/*\n+ * As `codetag_lock_module_list` is a read lock, we need an additional mutex\n+ * to protect against the race conditions involved in the alloc tag trace\n+ * toggle path.\n+ */\n+static DEFINE_MUTEX(alloc_tag_trace_mutex);\n+\n struct alloc_tag_kernel_section kernel_tags = { NULL, 0 };\n unsigned long alloc_tag_ref_mask;\n int alloc_tag_ref_offs;\n@@ -235,6 +250,7 @@ static void allocinfo_to_params(struct codetag *ct,\n \tdata-\u003ecounter.bytes = counters-\u003ebytes;\n \tdata-\u003ecounter.calls = counters-\u003ecalls;\n \tdata-\u003ecounter.accurate = !alloc_tag_is_inaccurate(ct_to_alloc_tag(ct));\n+\tdata-\u003ecounter.trace_on = alloc_tag_is_traced(ct_to_alloc_tag(ct));\n }\n \n /*\n@@ -290,7 +306,7 @@ static bool matches_filter(struct codetag *ct, struct allocinfo_filter *filter,\n \t\treturn false;\n \n \tif (filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_INACCURATE) {\n-\t\tinaccurate = !!(ct-\u003eflags \u0026 CODETAG_FLAG_INACCURATE);\n+\t\tinaccurate = alloc_tag_is_inaccurate(ct_to_alloc_tag(ct));\n \t\tif (inaccurate != !!(filter-\u003einaccurate))\n \t\t\treturn false;\n \t}\n@@ -308,6 +324,30 @@ static bool matches_filter(struct codetag *ct, struct allocinfo_filter *filter,\n \t\t\treturn false;\n \t}\n \n+\tif (filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_TRACE_ON) {\n+\t\tbool tracing = alloc_tag_is_traced(ct_to_alloc_tag(ct));\n+\n+\t\tif (tracing != !!(filter-\u003etracing))\n+\t\t\treturn false;\n+\t}\n+\n+\treturn true;\n+}\n+\n+/*\n+ * Checks that a user supplied filter only uses known fields and that its size\n+ * range, if any, is not inverted.\n+ */\n+static bool allocinfo_filter_valid(const struct allocinfo_filter *filter)\n+{\n+\tif (filter-\u003emask \u0026 ~ALLOCINFO_FILTER_MASKS)\n+\t\treturn false;\n+\n+\tif ((filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_MIN_SIZE) \u0026\u0026\n+\t    (filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_MAX_SIZE) \u0026\u0026\n+\t    filter-\u003emin_size \u003e filter-\u003emax_size)\n+\t\treturn false;\n+\n \treturn true;\n }\n \n@@ -327,12 +367,7 @@ static int allocinfo_ioctl_get_at(struct seq_file *m, void __user *arg)\n \tif (copy_from_user(\u0026params, arg, sizeof(params)))\n \t\treturn -EFAULT;\n \n-\tif (params.filter.mask \u0026 ~ALLOCINFO_FILTER_MASKS)\n-\t\treturn -EINVAL;\n-\n-\tif ((params.filter.mask \u0026 ALLOCINFO_FILTER_MASK_MIN_SIZE) \u0026\u0026\n-\t    (params.filter.mask \u0026 ALLOCINFO_FILTER_MASK_MAX_SIZE) \u0026\u0026\n-\t    params.filter.min_size \u003e params.filter.max_size)\n+\tif (!allocinfo_filter_valid(\u0026params.filter))\n \t\treturn -EINVAL;\n \n \tpriv = m-\u003eprivate;\n@@ -437,6 +472,75 @@ static int allocinfo_ioctl_get_next(struct seq_file *m, void __user *arg)\n \treturn ret;\n }\n \n+static void alloc_tag_trace_toggle(struct alloc_tag *tag, bool enable)\n+{\n+\tif (enable) {\n+\t\tif (alloc_tag_is_traced(tag))\n+\t\t\treturn;\n+\n+\t\talloc_tag_set_traced(tag);\n+\t\tif (atomic_fetch_inc(\u0026alloc_tag_trace_cnt) == 0)\n+\t\t\tstatic_branch_enable(\u0026alloc_tag_trace_key);\n+\t} else {\n+\t\tif (!alloc_tag_is_traced(tag))\n+\t\t\treturn;\n+\n+\t\talloc_tag_clear_traced(tag);\n+\t\tif (atomic_dec_and_test(\u0026alloc_tag_trace_cnt))\n+\t\t\tstatic_branch_disable(\u0026alloc_tag_trace_key);\n+\t}\n+}\n+\n+/*\n+ * Toggles tracing on every allocation tag that matches the user supplied\n+ * filter. An empty filter mask selects all tags, same as for\n+ * ALLOCINFO_IOC_GET_AT. Tags already in the requested state are not an error.\n+ */\n+static int allocinfo_ioctl_toggle_trace(struct seq_file *m, void __user *arg)\n+{\n+\tstruct allocinfo_toggle_traces params;\n+\tstruct codetag_iterator iter;\n+\tstruct codetag *ct;\n+\tstruct alloc_tag_counters counters;\n+\tbool fetched_counters;\n+\tint matches = 0, ret;\n+\n+\tif (!capable(CAP_SYS_ADMIN))\n+\t\treturn -EPERM;\n+\n+\tif (copy_from_user(\u0026params, arg, sizeof(params)))\n+\t\treturn -EFAULT;\n+\n+\tif (!allocinfo_filter_valid(\u0026params.filter))\n+\t\treturn -EINVAL;\n+\n+\tcodetag_lock_module_list(alloc_tag_cttype);\n+\n+\titer = codetag_get_ct_iter(alloc_tag_cttype);\n+\n+\t/* Toggle tracing on all codetags that match */\n+\twhile ((ct = codetag_next_ct(\u0026iter))) {\n+\t\tfetched_counters = false;\n+\t\tif (matches_filter(ct, \u0026params.filter, \u0026counters, \u0026fetched_counters)) {\n+\t\t\tmatches++;\n+\n+\t\t\tmutex_lock(\u0026alloc_tag_trace_mutex);\n+\t\t\talloc_tag_trace_toggle(ct_to_alloc_tag(ct), !!params.enable);\n+\t\t\tmutex_unlock(\u0026alloc_tag_trace_mutex);\n+\t\t}\n+\t}\n+\n+\tif (matches == 0)\n+\t\t/* Nothing matched the filter */\n+\t\tret = -ENOENT;\n+\telse\n+\t\tret = 0;\n+\n+\tcodetag_unlock_module_list(alloc_tag_cttype);\n+\n+\treturn ret;\n+}\n+\n /*\n  * Entry point ioctl function for /proc/allocinfo routing requests to fetch the\n  * layout content ID, seek to a specific tag, or read sequential tags.\n@@ -457,6 +561,9 @@ static long allocinfo_ioctl(struct file *file, unsigned int cmd,\n \tcase ALLOCINFO_IOC_GET_NEXT:\n \t\tret = allocinfo_ioctl_get_next(file-\u003eprivate_data, arg);\n \t\tbreak;\n+\tcase ALLOCINFO_IOC_TOGGLE_TRACE:\n+\t\tret = allocinfo_ioctl_toggle_trace(file-\u003eprivate_data, arg);\n+\t\tbreak;\n \tdefault:\n \t\tret = -ENOIOCTLCMD;\n \t\tbreak;\n@@ -484,6 +591,26 @@ static const struct proc_ops allocinfo_proc_ops = {\n #endif\n };\n \n+void __alloc_tag_trace_hit(struct alloc_tag *tag)\n+{\n+\ttrace_alloc_tag_hit(tag);\n+}\n+EXPORT_SYMBOL(__alloc_tag_trace_hit);\n+\n+void alloc_tag_trace_mem_alloc(const void *ptr, struct alloc_tag *tag,\n+\t\t\t       size_t bytes)\n+{\n+\ttrace_alloc_tag_mem_alloced(ptr, tag, bytes);\n+}\n+EXPORT_SYMBOL(alloc_tag_trace_mem_alloc);\n+\n+void alloc_tag_trace_mem_free(const void *ptr, struct alloc_tag *tag,\n+\t\t\t      size_t bytes)\n+{\n+\ttrace_alloc_tag_mem_freed(ptr, tag, bytes);\n+}\n+EXPORT_SYMBOL(alloc_tag_trace_mem_free);\n+\n size_t alloc_tag_top_users(struct codetag_bytes *tags, size_t count, bool can_sleep)\n {\n \tstruct codetag_iterator iter;\n@@ -1003,6 +1130,24 @@ static int load_module(struct module *mod, struct codetag *start, struct codetag\n \treturn 0;\n }\n \n+static void unload_module(struct module *mod, struct codetag *start, struct codetag *stop)\n+{\n+\tstruct alloc_tag *start_tag = ct_to_alloc_tag(start);\n+\tstruct alloc_tag *stop_tag = ct_to_alloc_tag(stop);\n+\tstruct alloc_tag *tag;\n+\n+\t/*\n+\t * Turn tracing off for the tags of the module being unloaded. Without\n+\t * this, `alloc_tag_trace_cnt` would never reach zero and tracing would\n+\t * stay enabled forever.\n+\t *\n+\t * `alloc_tag_trace_mutex` is not needed here as this code path is\n+\t * protected by a `down_write(\u0026cttype-\u003emod_lock)`.\n+\t */\n+\tfor (tag = start_tag; tag \u003c stop_tag; tag++)\n+\t\talloc_tag_trace_toggle(tag, false);\n+}\n+\n static void replace_module(struct module *mod, struct module *new_mod)\n {\n \tMA_STATE(mas, \u0026mod_area_mt, 0, module_tags.size);\n@@ -1329,6 +1474,7 @@ static int __init alloc_tag_init(void)\n \t\t.alloc_section_mem\t= reserve_module_tags,\n \t\t.free_section_mem\t= release_module_tags,\n \t\t.module_load\t\t= load_module,\n+\t\t.module_unload\t\t= unload_module,\n \t\t.module_replaced\t= replace_module,\n #endif\n \t};\ndiff --git a/mm/page_alloc.c b/mm/page_alloc.c\nindex 7682aecc2c075..5e3e411d4ffe0 100644\n--- a/mm/page_alloc.c\n+++ b/mm/page_alloc.c\n@@ -1239,7 +1239,7 @@ void __pgalloc_tag_add(struct page *page, struct task_struct *task,\n \tunion codetag_ref ref;\n \n \tif (likely(get_page_tag_ref(page, \u0026ref, \u0026handle))) {\n-\t\talloc_tag_add(\u0026ref, task-\u003ealloc_tag, PAGE_SIZE * nr);\n+\t\talloc_tag_add(\u0026ref, task-\u003ealloc_tag, PAGE_SIZE * nr, page);\n \t\tupdate_page_tag_ref(handle, \u0026ref);\n \t\tput_page_tag_ref(handle);\n \t} else {\n@@ -1268,7 +1268,7 @@ void __pgalloc_tag_sub(struct page *page, unsigned int nr)\n \tunion codetag_ref ref;\n \n \tif (get_page_tag_ref(page, \u0026ref, \u0026handle)) {\n-\t\talloc_tag_sub(\u0026ref, PAGE_SIZE * nr);\n+\t\talloc_tag_sub(\u0026ref, PAGE_SIZE * nr, page);\n \t\tupdate_page_tag_ref(handle, \u0026ref);\n \t\tput_page_tag_ref(handle);\n \t}\ndiff --git a/mm/percpu.c b/mm/percpu.c\nindex 3eff382e565ad..12b6c97d15966 100644\n--- a/mm/percpu.c\n+++ b/mm/percpu.c\n@@ -1695,15 +1695,19 @@ static void pcpu_alloc_tag_alloc_hook(struct pcpu_chunk *chunk, int off,\n \t\t\t\t      size_t size)\n {\n \tif (mem_alloc_profiling_enabled() \u0026\u0026 likely(chunk-\u003eobj_exts)) {\n-\t\talloc_tag_add(\u0026chunk-\u003eobj_exts[off \u003e\u003e PCPU_MIN_ALLOC_SHIFT].tag,\n-\t\t\t      current-\u003ealloc_tag, size);\n+\t\tunion codetag_ref *ref = \u0026chunk-\u003eobj_exts[off \u003e\u003e PCPU_MIN_ALLOC_SHIFT].tag;\n+\n+\t\talloc_tag_add(ref, current-\u003ealloc_tag, size, ref);\n \t}\n }\n \n static void pcpu_alloc_tag_free_hook(struct pcpu_chunk *chunk, int off, size_t size)\n {\n-\tif (mem_alloc_profiling_enabled() \u0026\u0026 likely(chunk-\u003eobj_exts))\n-\t\talloc_tag_sub(\u0026chunk-\u003eobj_exts[off \u003e\u003e PCPU_MIN_ALLOC_SHIFT].tag, size);\n+\tif (mem_alloc_profiling_enabled() \u0026\u0026 likely(chunk-\u003eobj_exts)) {\n+\t\tunion codetag_ref *ref = \u0026chunk-\u003eobj_exts[off \u003e\u003e PCPU_MIN_ALLOC_SHIFT].tag;\n+\n+\t\talloc_tag_sub(ref, size, ref);\n+\t}\n }\n #else\n static void pcpu_alloc_tag_alloc_hook(struct pcpu_chunk *chunk, int off,\ndiff --git a/mm/slub.c b/mm/slub.c\nindex 544cff39762c5..a866576ccb983 100644\n--- a/mm/slub.c\n+++ b/mm/slub.c\n@@ -2404,7 +2404,7 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,\n \t\tobj_ext = slab_obj_ext(s, slab, obj_exts, object);\n \t\tref = slab_obj_ext_codetag_ref(slab, obj_ext);\n \n-\t\talloc_tag_add(ref, current-\u003ealloc_tag, s-\u003esize);\n+\t\talloc_tag_add(ref, current-\u003ealloc_tag, s-\u003esize, ref);\n \n \t\tput_slab_obj_exts(obj_exts);\n \t} else {\n@@ -2444,9 +2444,11 @@ __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p\n \tget_slab_obj_exts(obj_exts);\n \tfor (int i = 0; i \u003c objects; i++) {\n \t\tstruct slabobj_ext *ext;\n+\t\tunion codetag_ref *ref;\n \n \t\text = slab_obj_ext(s, slab, obj_exts, p[i]);\n-\t\talloc_tag_sub(slab_obj_ext_codetag_ref(slab, ext), s-\u003esize);\n+\t\tref = slab_obj_ext_codetag_ref(slab, ext);\n+\t\talloc_tag_sub(ref, s-\u003esize, ref);\n \t}\n \tput_slab_obj_exts(obj_exts);\n }\ndiff --git a/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c b/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c\nindex 74fd64b2370cc..eb52ca1a1dc42 100644\n--- a/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c\n+++ b/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c\n@@ -48,6 +48,11 @@ static inline int __allocinfo_get_next(int dev_fd, struct allocinfo_tag_data *pa\n \treturn ioctl(dev_fd, ALLOCINFO_IOC_GET_NEXT, params);\n }\n \n+static inline int __allocinfo_toggle_trace(int dev_fd, struct allocinfo_toggle_traces *params)\n+{\n+\treturn ioctl(dev_fd, ALLOCINFO_IOC_TOGGLE_TRACE, params);\n+}\n+\n static bool match_entry(const struct allocinfo_tag_data *procfs_entry,\n \t\t\tconst struct allocinfo_tag_data *tag_data,\n \t\t\tbool match_bytes, bool match_calls, bool match_lineno,\n@@ -289,6 +294,8 @@ static int run_filter_test(const struct allocinfo_filter *filter)\n \treturn ret;\n }\n \n+static const char *target_test_function = \"dup_mm\";\n+\n static int test_filename_filter(void)\n {\n \tstruct allocinfo_filter filter;\n@@ -304,11 +311,10 @@ static int test_filename_filter(void)\n static int test_function_filter(void)\n {\n \tstruct allocinfo_filter filter;\n-\tconst char *target_function = \"dup_mm\";\n \n \tmemset(\u0026filter, 0, sizeof(filter));\n \tfilter.mask |= ALLOCINFO_FILTER_MASK_FUNCTION;\n-\tstrncpy(filter.fields.function, target_function, ALLOCINFO_STR_SIZE);\n+\tstrncpy(filter.fields.function, target_test_function, ALLOCINFO_STR_SIZE);\n \n \treturn run_filter_test(\u0026filter);\n }\n@@ -514,11 +520,106 @@ static int test_lineno_filter(void)\n \treturn ret;\n }\n \n+static enum ioctl_ret toggle_trace(struct allocinfo_tag *target_tag,\n+\t\t\t\t   bool enable)\n+{\n+\tint fd;\n+\tstruct allocinfo_toggle_traces toggle_params;\n+\n+\tfd = open(ALLOCINFO_PROC, O_RDONLY);\n+\tif (fd \u003c 0) {\n+\t\tksft_print_msg(\"Failed to open \" ALLOCINFO_PROC \": %s\\n\", strerror(errno));\n+\t\treturn IOCTL_FAILURE;\n+\t}\n+\n+\tmemset(\u0026toggle_params, 0, sizeof(toggle_params));\n+\ttoggle_params.filter.mask = ALLOCINFO_FILTER_MASK_MODNAME | ALLOCINFO_FILTER_MASK_FUNCTION |\n+\t\t\t\t    ALLOCINFO_FILTER_MASK_FILENAME | ALLOCINFO_FILTER_MASK_LINENO;\n+\ttoggle_params.filter.fields = *target_tag;\n+\ttoggle_params.enable = enable;\n+\n+\tif (__allocinfo_toggle_trace(fd, \u0026toggle_params)) {\n+\t\tclose(fd);\n+\t\treturn IOCTL_FAILURE;\n+\t}\n+\n+\tclose(fd);\n+\treturn IOCTL_SUCCESS;\n+}\n+\n+static int test_tracing_toggle_and_filter(void)\n+{\n+\tstruct allocinfo_filter filter = { 0 };\n+\tenum ioctl_ret ioctl_status;\n+\tint ret = KSFT_PASS;\n+\tbool initial_state, target_state;\n+\tstruct allocinfo_tag target_tag;\n+\tstruct allocinfo_tag_data_vec *tags = calloc(1, sizeof(*tags));\n+\n+\tif (!tags) {\n+\t\tksft_print_msg(\"Memory allocation failed.\\n\");\n+\t\treturn KSFT_FAIL;\n+\t}\n+\n+\tfilter.mask |= ALLOCINFO_FILTER_MASK_FUNCTION;\n+\tstrncpy(filter.fields.function, target_test_function, ALLOCINFO_STR_SIZE);\n+\n+\tioctl_status = get_filtered_ioctl_entries(tags, \u0026filter, 0);\n+\tif (ioctl_status != IOCTL_SUCCESS || tags-\u003ecount == 0) {\n+\t\tksft_print_msg(\"Could not retrieve IOCTL entries for %s\\n\", target_test_function);\n+\t\tret = KSFT_SKIP;\n+\t\tgoto exit;\n+\t}\n+\n+\ttarget_tag = tags-\u003etag[0].tag;\n+\tinitial_state = tags-\u003etag[0].counter.trace_on;\n+\ttarget_state = !initial_state;\n+\n+\tioctl_status = toggle_trace(\u0026target_tag, target_state);\n+\tif (ioctl_status != IOCTL_SUCCESS) {\n+\t\tksft_print_msg(\"Failed to toggle tracing\\n\");\n+\t\tret = KSFT_FAIL;\n+\t\tgoto exit;\n+\t}\n+\n+\tfilter.mask |= ALLOCINFO_FILTER_MASK_TRACE_ON;\n+\tfilter.tracing = target_state;\n+\n+\tioctl_status = get_filtered_ioctl_entries(tags, \u0026filter, 0);\n+\tif (ioctl_status != IOCTL_SUCCESS) {\n+\t\tksft_print_msg(\"Error retrieving IOCTL entries with trace filter.\\n\");\n+\t\tret = KSFT_FAIL;\n+\t\tgoto exit_revert;\n+\t}\n+\n+\tif (tags-\u003ecount != 1) {\n+\t\tksft_print_msg(\"Expected exactly 1 entry, but got %llu\\n\", tags-\u003ecount);\n+\t\tret = KSFT_FAIL;\n+\t\tgoto exit_revert;\n+\t}\n+\n+\tif (tags-\u003etag[0].counter.trace_on != target_state) {\n+\t\tksft_print_msg(\"Entry returned by trace filter does not match target state\\n\");\n+\t\tret = KSFT_FAIL;\n+\t}\n+\n+exit_revert:\n+\tioctl_status = toggle_trace(\u0026target_tag, initial_state);\n+\tif (ioctl_status != IOCTL_SUCCESS) {\n+\t\tksft_print_msg(\"Failed to revert tracing to initial state\\n\");\n+\t\tret = KSFT_FAIL;\n+\t}\n+\n+exit:\n+\tfree(tags);\n+\treturn ret;\n+}\n+\n int main(int argc, char *argv[])\n {\n \tint ret;\n \n-\tksft_set_plan(4);\n+\tksft_set_plan(5);\n \n \tret = test_filename_filter();\n \tif (ret == KSFT_SKIP)\n@@ -526,6 +627,12 @@ int main(int argc, char *argv[])\n \telse\n \t\tksft_test_result(ret == KSFT_PASS, \"test_filename_filter\\n\");\n \n+\tret = test_tracing_toggle_and_filter();\n+\tif (ret == KSFT_SKIP)\n+\t\tksft_test_result_skip(\"Skipping test_tracing_toggle_and_filter\\n\");\n+\telse\n+\t\tksft_test_result(ret == KSFT_PASS, \"test_tracing_toggle_and_filter\\n\");\n+\n \tret = test_function_filter();\n \tif (ret == KSFT_SKIP)\n \t\tksft_test_result_skip(\"Skipping test_function_filter\\n\");\n"
}

core

null

{
  "EnableConfigs": [
    "MEM_ALLOC_PROFILING",
    "TRACING"
  ],
  "FocusSymbols": [
    "allocinfo_ioctl",
    "allocinfo_ioctl_toggle_trace",
    "alloc_tag_trace_toggle",
    "__alloc_tag_trace_hit",
    "alloc_tag_trace_mem_alloc",
    "alloc_tag_trace_mem_free"
  ],
  "Reasoning": "The patch introduces memory allocation profiling trace events (alloc_tag_hit, alloc_tag_mem_alloced, alloc_tag_mem_freed) and exposes a new ioctl command ALLOCINFO_IOC_TOGGLE_TRACE on /proc/allocinfo to dynamically enable/disable tracing per allocation tag. It introduces dynamic static branch manipulation, atomic flag updates, input filter validation, and hooks into core alloc/free paths across SLUB, page allocator, and percpu subsystems. This code is reachable from userspace via /proc/allocinfo ioctls and warrants fuzzing for concurrency issues, filter parsing, and static branch toggling behavior.",
  "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 9c8e1162b5ec6958cde9fbf00162f239ce0066a8
Author: syz-cluster <triage@syzkaller.com>
Date:   Wed Oct 7 22:58:48 2026 +0000

    syz-cluster: applied patch under review

diff --git a/Documentation/mm/allocation-profiling.rst b/Documentation/mm/allocation-profiling.rst
index b11ea77c06736..63b6684663426 100644
--- a/Documentation/mm/allocation-profiling.rst
+++ b/Documentation/mm/allocation-profiling.rst
@@ -129,6 +129,79 @@ To do so:
 - Then, use the following form for your allocations:
   alloc_hooks_tag(ht->your_saved_tag, kmalloc_noprof(...))
 
+Tracing
+=======
+
+Three trace events are available under `/sys/kernel/tracing/events/alloc_tag` to
+expose the full call stack and the lifetime of individual allocations:
+
+- `alloc_tag_hit`: Fired at the exact call site, before the allocation happens.
+  Can be used to capture the call stack of the caller.
+
+- `alloc_tag_mem_alloced`: Fired once the allocation succeeds. Carries the `ptr`,
+  `tag` and `bytes` for each allocation.
+
+- `alloc_tag_mem_freed`: Fired before memory is freed. Carries the same
+  `ptr`, `tag` and `bytes` as the matching alloc event.
+
+`ptr` identifies the allocation, and its meaning depends on the allocator:
+
+- slab and percpu: the address of the object's `codetag_ref`
+- page allocator: the `struct page` pointer of the head page
+
+Events are only emitted for tags that have tracing turned on and while profiling
+is enabled. When no tag is traced, the hooks are behind a static branch.
+
+Enabling Tracing
+----------------
+
+Tracing is toggled on and off per tag with the `ALLOCINFO_IOC_TOGGLE_TRACE`
+ioctl on `/proc/allocinfo`. It takes the same filter as used by
+`ALLOCINFO_IOC_GET_AT`; an empty mask selects all tags. Size limits in the
+filter are checked once, against the tag's size at the time of the call. Tags
+already in the requested state are skipped and a -ENOENT is returned if no
+tag matched.
+
+Tracing is turned off for a module's tags when the module is unloaded.
+
+Memory allocated before a tag was enabled has no alloc event but will still
+produce a free event. Likewise, memory alive when tag is disabled will not
+produce a free event. Tools should expect unmatched frees after enabling and
+missing frees after disabling.
+
+Correlating the events
+----------------------
+
+`alloc_tag_hit` and `alloc_tag_mem_alloced` come from different points in the
+call stack, so they have to be stitched together by the user consuming the
+events. Here's a typical flow:
+
+1. On `alloc_tag_hit`: Capture the stack trace and cache it keyed by `(pid, tag)`.
+
+2. On `alloc_tag_mem_alloced`: Look up the cached stack trace by `(pid, tag)`,
+   then create an active allocation record keyed by `ptr` that holds the stack
+   trace and `bytes`.
+
+3. On `alloc_tag_mem_freed`: Look up the record by `ptr` and retire it.
+
+Limitations
+-----------
+
+- For the page allocator, events are generated for the original allocation and
+  the free only. If the tag reference is split or moved to another folio in
+  between, no event is generated for that. As a result:
+
+  - a free event may carry a `ptr` that never appeared in an alloc event;
+  - `bytes` in a free event may be smaller than in the matching alloc event.
+
+  Tools should correlate on `ptr` but must not assume that freed bytes equal
+  allocated bytes, or that every free has a matching alloc.
+
+- Freeing a non-compound high-order page with `__free_pages()` while another CPU
+  holds a reference frees the tail pages immediately and the head page later when
+  the reference is dropped. The free event is emitted at the second point and
+  reports `PAGE_SIZE` rather than the full size.
+
 Notes
 =====
 
diff --git a/MAINTAINERS b/MAINTAINERS
index 5c38da7090db8..751ce786a3788 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17100,6 +17100,7 @@ S:	Maintained
 F:	Documentation/mm/allocation-profiling.rst
 F:	include/linux/alloc_tag.h
 F:	include/linux/pgalloc_tag.h
+F:	include/trace/events/alloc_tag.h
 F:	include/uapi/linux/alloc_tag.h
 F:	mm/alloc_tag.c
 F:	tools/testing/selftests/alloc_tag/
diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
index 7f2d80a597924..94697b28053ad 100644
--- a/include/linux/alloc_tag.h
+++ b/include/linux/alloc_tag.h
@@ -128,12 +128,60 @@ DECLARE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag);
 DECLARE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
 			mem_alloc_profiling_key);
 
+DECLARE_STATIC_KEY_FALSE(alloc_tag_trace_key);
+
 static inline bool mem_alloc_profiling_enabled(void)
 {
 	return static_branch_maybe(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
 				   &mem_alloc_profiling_key);
 }
 
+static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag)
+{
+	atomic_or(CODETAG_FLAG_INACCURATE, &tag->ct.flags);
+}
+
+static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag)
+{
+	return !!(atomic_read(&tag->ct.flags) & CODETAG_FLAG_INACCURATE);
+}
+
+static inline void alloc_tag_set_traced(struct alloc_tag *tag)
+{
+	atomic_or(CODETAG_FLAG_TRACE_ON, &tag->ct.flags);
+}
+
+static inline void alloc_tag_clear_traced(struct alloc_tag *tag)
+{
+	atomic_andnot(CODETAG_FLAG_TRACE_ON, &tag->ct.flags);
+}
+
+static inline bool alloc_tag_is_traced(const struct alloc_tag *tag)
+{
+	return !!(atomic_read(&tag->ct.flags) & CODETAG_FLAG_TRACE_ON);
+}
+
+static inline bool alloc_tag_trace_enabled(const struct alloc_tag *tag)
+{
+	if (static_branch_unlikely(&alloc_tag_trace_key))
+		return tag && alloc_tag_is_traced(tag);
+	return false;
+}
+
+void alloc_tag_trace_mem_alloc(const void *ptr, struct alloc_tag *tag,
+			       size_t bytes);
+
+void alloc_tag_trace_mem_free(const void *ptr, struct alloc_tag *tag,
+			      size_t bytes);
+
+void __alloc_tag_trace_hit(struct alloc_tag *tag);
+
+static __always_inline void alloc_tag_trace_hit(struct alloc_tag *tag)
+{
+	if (alloc_tag_trace_enabled(tag))
+		__alloc_tag_trace_hit(tag);
+}
+
 bool mem_alloc_profiling_permanently_disabled(void);
 
 static inline struct alloc_tag_counters alloc_tag_read(struct alloc_tag *tag)
@@ -198,13 +246,19 @@ static inline bool alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *t
 	return true;
 }
 
-static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes)
+static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes,
+				 const void *ptr)
 {
-	if (likely(alloc_tag_ref_set(ref, tag)))
+	if (likely(alloc_tag_ref_set(ref, tag))) {
 		this_cpu_add(tag->counters->bytes, bytes);
+
+		if (alloc_tag_trace_enabled(tag))
+			/* Trace successful allocs with their unique ptr */
+			alloc_tag_trace_mem_alloc(ptr, tag, bytes);
+	}
 }
 
-static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes)
+static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes, const void *ptr)
 {
 	struct alloc_tag *tag;
 
@@ -222,17 +276,11 @@ static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes)
 	this_cpu_sub(tag->counters->bytes, bytes);
 	this_cpu_dec(tag->counters->calls);
 
-	ref->ct = NULL;
-}
-
-static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag)
-{
-	tag->ct.flags |= CODETAG_FLAG_INACCURATE;
-}
+	if (alloc_tag_trace_enabled(tag))
+		/* Trace frees with their unique ptr */
+		alloc_tag_trace_mem_free(ptr, tag, bytes);
 
-static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag)
-{
-	return !!(tag->ct.flags & CODETAG_FLAG_INACCURATE);
+	ref->ct = NULL;
 }
 
 #define alloc_tag_record(p)	((p) = current->alloc_tag)
@@ -243,25 +291,29 @@ static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag)
 static inline bool mem_alloc_profiling_enabled(void) { return false; }
 static inline bool mem_alloc_profiling_permanently_disabled(void) { return true; }
 static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag,
-				 size_t bytes) {}
-static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes) {}
+				 size_t bytes, const void *ptr) {}
+static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes,
+				 const void *ptr) {}
 static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag) {}
 static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag) { return false; }
+#define alloc_tag_trace_hit(_tag)	/* NOOP */
 #define alloc_tag_record(p)	do {} while (0)
 
 #endif /* CONFIG_MEM_ALLOC_PROFILING */
 
-#define alloc_hooks_tag(_tag, _do_alloc)				\
-({									\
-	typeof(_do_alloc) _res;						\
-	if (mem_alloc_profiling_enabled()) {				\
-		struct alloc_tag * __maybe_unused _old;			\
-		_old = alloc_tag_save(_tag);				\
-		_res = _do_alloc;					\
-		alloc_tag_restore(_tag, _old);				\
-	} else								\
-		_res = _do_alloc;					\
-	_res;								\
+#define alloc_hooks_tag(_tag, _do_alloc)					\
+({										\
+	typeof(_do_alloc) _res;							\
+	if (mem_alloc_profiling_enabled()) {					\
+		struct alloc_tag * __maybe_unused _old;				\
+		/* Fired here to cleanly capture the caller's stack trace */	\
+		alloc_tag_trace_hit(_tag);					\
+		_old = alloc_tag_save(_tag);					\
+		_res = _do_alloc;						\
+		alloc_tag_restore(_tag, _old);					\
+	} else									\
+		_res = _do_alloc;						\
+	_res;									\
 })
 
 #define alloc_hooks(_do_alloc)						\
diff --git a/include/linux/codetag.h b/include/linux/codetag.h
index a25a085c2df19..f728295d50c05 100644
--- a/include/linux/codetag.h
+++ b/include/linux/codetag.h
@@ -18,6 +18,7 @@ struct module;
 
 /* codetag flags */
 #define CODETAG_FLAG_INACCURATE	(1 << 0)
+#define CODETAG_FLAG_TRACE_ON	(1 << 1)
 
 /*
  * An instance of this structure is created in a special ELF section at every
@@ -25,7 +26,7 @@ struct module;
  * an array of these.
  */
 struct codetag {
-	unsigned int flags;
+	atomic_t flags;
 	unsigned int lineno;
 	const char *modname;
 	const char *function;
@@ -71,7 +72,7 @@ struct codetag_iterator {
 	.function	= __func__,			\
 	.filename	= __FILE__,			\
 	.lineno		= __LINE__,			\
-	.flags		= 0,				\
+	.flags		= ATOMIC_INIT(0),		\
 }
 
 void codetag_lock_module_list(struct codetag_type *cttype);
diff --git a/include/trace/events/alloc_tag.h b/include/trace/events/alloc_tag.h
new file mode 100644
index 0000000000000..b79efb7dd25c6
--- /dev/null
+++ b/include/trace/events/alloc_tag.h
@@ -0,0 +1,122 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM alloc_tag
+
+#if !defined(_TRACE_ALLOC_TAG_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_ALLOC_TAG_H
+
+#include <linux/tracepoint.h>
+
+/*
+ * alloc_tag_hit is generated at the exact allocation call site and can be
+ * used to capture a clean stack trace.
+ *
+ * To link this stack trace to the actual allocated memory chunk, tools must
+ * correlate this event with the resulting alloc_tag_mem_alloced event. Since
+ * multiple threads can hit the same tag simultaneously, tools must match BOTH
+ * the `tag` field and the implicitly recorded PID provided by the core
+ * tracing subsystem.
+ */
+TRACE_EVENT(alloc_tag_hit,
+	TP_PROTO(struct alloc_tag *tag),
+
+	TP_ARGS(tag),
+
+	TP_STRUCT__entry(__field(struct alloc_tag *, tag)
+			 __string(modname, tag->ct.modname ? tag->ct.modname : "NONE")
+			 __string(filename, tag->ct.filename)
+			 __string(function, tag->ct.function)
+			 __field(unsigned int, lineno)
+	),
+
+	TP_fast_assign(__entry->tag = tag;
+		       __assign_str(modname);
+		       __assign_str(filename);
+		       __assign_str(function);
+		       __entry->lineno = tag->ct.lineno;
+	),
+
+	TP_printk("tag %p, module: %s, filename: %s, function %s, lineno %u",
+		  __entry->tag,
+		  __get_str(modname),
+		  __get_str(filename),
+		  __get_str(function),
+		  __entry->lineno
+	)
+);
+
+/*
+ * alloc_tag_mem_alloced is generated after memory is successfully allocated.
+ * It captures the exact byte size.
+ *
+ * The `ptr` value identifies the memory chunk for tracking its lifecycle
+ * (e.g., matching it with alloc_tag_mem_freed).
+ * - slab and percpu allocators: address of the object's codetag_ref
+ * - page allocator: the head struct page of the allocation
+ *
+ * Because the kernel isolates active allocations within the task struct
+ * (current->alloc_tag), this event will always share the same implicit PID as
+ * its corresponding alloc_tag_hit event. Tools should use the combination
+ * PID + `tag` to correlate them.
+ */
+TRACE_EVENT(alloc_tag_mem_alloced,
+	TP_PROTO(const void *ptr, struct alloc_tag *tag, size_t bytes),
+
+	TP_ARGS(ptr, tag, bytes),
+
+	TP_STRUCT__entry(__field(const void *, ptr)
+			 __field(struct alloc_tag *, tag)
+			 __field(size_t, bytes)
+	),
+
+	TP_fast_assign(__entry->ptr = ptr;
+		       __entry->tag = tag;
+		       __entry->bytes = bytes;
+	),
+
+	TP_printk("ptr %p, tag %p, bytes %zu",
+		  __entry->ptr,
+		  __entry->tag,
+		  __entry->bytes
+	)
+);
+
+/*
+ * alloc_tag_mem_freed event is generated immediately before memory is
+ * freed. The `ptr` value matches the one emitted during allocation,
+ * allowing tools to match it to its corresponding allocation and
+ * call stack.
+ *
+ * Page allocator caveat: Pages can be split or moved to another folio
+ * after the alloc event with no new events generated for that. As a
+ * result, a free event may carry a `ptr` that never appeared in an
+ * alloc event, and the `bytes` may be smaller than in the matching
+ * alloc event. Tools must not assume alloc bytes == free bytes, nor
+ * that every free has a matching alloc.
+ */
+TRACE_EVENT(alloc_tag_mem_freed,
+	TP_PROTO(const void *ptr, struct alloc_tag *tag, size_t bytes),
+
+	TP_ARGS(ptr, tag, bytes),
+
+	TP_STRUCT__entry(__field(const void *, ptr)
+			 __field(struct alloc_tag *, tag)
+			 __field(size_t, bytes)
+	),
+
+	TP_fast_assign(__entry->ptr = ptr;
+		       __entry->tag = tag;
+		       __entry->bytes = bytes;
+	),
+
+	TP_printk("ptr %p, tag %p, bytes %zu",
+		  __entry->ptr,
+		  __entry->tag,
+		  __entry->bytes
+	)
+);
+
+#endif /* _TRACE_ALLOC_TAG_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/include/uapi/linux/alloc_tag.h b/include/uapi/linux/alloc_tag.h
index 7d4618bea0434..a96054ac22376 100644
--- a/include/uapi/linux/alloc_tag.h
+++ b/include/uapi/linux/alloc_tag.h
@@ -38,7 +38,8 @@ struct allocinfo_counter {
 	__u64 bytes;
 	__u64 calls;
 	__u8 accurate;
-	__u8 pad[7];
+	__u8 trace_on;
+	__u8 pad[6];
 } __attribute__((aligned(8)));
 
 struct allocinfo_tag_data {
@@ -54,7 +55,8 @@ enum {
 	ALLOCINFO_FILTER_INACCURATE,
 	ALLOCINFO_FILTER_MIN_SIZE,
 	ALLOCINFO_FILTER_MAX_SIZE,
-	__ALLOCINFO_FILTER_LAST = ALLOCINFO_FILTER_MAX_SIZE
+	ALLOCINFO_FILTER_TRACE_ON,
+	__ALLOCINFO_FILTER_LAST = ALLOCINFO_FILTER_TRACE_ON
 };
 
 #define ALLOCINFO_FILTER_MASK_MODNAME		(1 << ALLOCINFO_FILTER_MODNAME)
@@ -64,6 +66,7 @@ enum {
 #define ALLOCINFO_FILTER_MASK_INACCURATE	(1 << ALLOCINFO_FILTER_INACCURATE)
 #define ALLOCINFO_FILTER_MASK_MIN_SIZE		(1 << ALLOCINFO_FILTER_MIN_SIZE)
 #define ALLOCINFO_FILTER_MASK_MAX_SIZE		(1 << ALLOCINFO_FILTER_MAX_SIZE)
+#define ALLOCINFO_FILTER_MASK_TRACE_ON		(1 << ALLOCINFO_FILTER_TRACE_ON)
 
 #define ALLOCINFO_FILTER_MASKS \
 	((1 << (__ALLOCINFO_FILTER_LAST + 1)) - 1)
@@ -75,6 +78,7 @@ struct allocinfo_filter {
 	__u64 max_size;
 	/* filter criteria only; see allocinfo_counter.accurate for actual accuracy */
 	__u64 inaccurate;
+	__u64 tracing;
 };
 
 struct allocinfo_get_at {
@@ -85,9 +89,20 @@ struct allocinfo_get_at {
 	struct allocinfo_tag_data data;
 };
 
+struct allocinfo_toggle_traces {
+	/* inputs */
+	/*
+	 * Tags matching the filter are toggled; an empty mask selects all tags.
+	 * Size criteria are checked once, against the tag's size at call time.
+	 */
+	struct allocinfo_filter filter;
+	__u64 enable;
+};
+
 #define _ALLOCINFO_IOC_CONTENT_ID	0
 #define _ALLOCINFO_IOC_GET_AT		1
 #define _ALLOCINFO_IOC_GET_NEXT		2
+#define _ALLOCINFO_IOC_TOGGLE_TRACE	3
 
 #define ALLOCINFO_IOC_BASE		0xA6
 #define ALLOCINFO_IOC_CONTENT_ID	_IOR(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_CONTENT_ID,	\
@@ -96,5 +111,7 @@ struct allocinfo_get_at {
 					      struct allocinfo_get_at)
 #define ALLOCINFO_IOC_GET_NEXT		_IOR(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_GET_NEXT,	\
 					     struct allocinfo_tag_data)
+#define ALLOCINFO_IOC_TOGGLE_TRACE	_IOW(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_TOGGLE_TRACE,	\
+					    struct allocinfo_toggle_traces)
 
 #endif /* _UAPI_ALLOC_TAG_H */
diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
index 82e2c3448dcf2..8e63f347657b6 100644
--- a/mm/alloc_tag.c
+++ b/mm/alloc_tag.c
@@ -18,6 +18,9 @@
 #include <linux/kmemleak.h>
 #include <uapi/linux/alloc_tag.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/alloc_tag.h>
+
 #include "internal.h"
 #include "page_alloc.h"
 
@@ -54,6 +57,18 @@ EXPORT_SYMBOL(mem_alloc_profiling_key);
 
 DEFINE_STATIC_KEY_FALSE(mem_profiling_compressed);
 
+DEFINE_STATIC_KEY_FALSE(alloc_tag_trace_key);
+EXPORT_SYMBOL(alloc_tag_trace_key);
+
+static atomic_t alloc_tag_trace_cnt = ATOMIC_INIT(0);
+
+/*
+ * As `codetag_lock_module_list` is a read lock, we need an additional mutex
+ * to protect against the race conditions involved in the alloc tag trace
+ * toggle path.
+ */
+static DEFINE_MUTEX(alloc_tag_trace_mutex);
+
 struct alloc_tag_kernel_section kernel_tags = { NULL, 0 };
 unsigned long alloc_tag_ref_mask;
 int alloc_tag_ref_offs;
@@ -235,6 +250,7 @@ static void allocinfo_to_params(struct codetag *ct,
 	data->counter.bytes = counters->bytes;
 	data->counter.calls = counters->calls;
 	data->counter.accurate = !alloc_tag_is_inaccurate(ct_to_alloc_tag(ct));
+	data->counter.trace_on = alloc_tag_is_traced(ct_to_alloc_tag(ct));
 }
 
 /*
@@ -290,7 +306,7 @@ static bool matches_filter(struct codetag *ct, struct allocinfo_filter *filter,
 		return false;
 
 	if (filter->mask & ALLOCINFO_FILTER_MASK_INACCURATE) {
-		inaccurate = !!(ct->flags & CODETAG_FLAG_INACCURATE);
+		inaccurate = alloc_tag_is_inaccurate(ct_to_alloc_tag(ct));
 		if (inaccurate != !!(filter->inaccurate))
 			return false;
 	}
@@ -308,6 +324,30 @@ static bool matches_filter(struct codetag *ct, struct allocinfo_filter *filter,
 			return false;
 	}
 
+	if (filter->mask & ALLOCINFO_FILTER_MASK_TRACE_ON) {
+		bool tracing = alloc_tag_is_traced(ct_to_alloc_tag(ct));
+
+		if (tracing != !!(filter->tracing))
+			return false;
+	}
+
+	return true;
+}
+
+/*
+ * Checks that a user supplied filter only uses known fields and that its size
+ * range, if any, is not inverted.
+ */
+static bool allocinfo_filter_valid(const struct allocinfo_filter *filter)
+{
+	if (filter->mask & ~ALLOCINFO_FILTER_MASKS)
+		return false;
+
+	if ((filter->mask & ALLOCINFO_FILTER_MASK_MIN_SIZE) &&
+	    (filter->mask & ALLOCINFO_FILTER_MASK_MAX_SIZE) &&
+	    filter->min_size > filter->max_size)
+		return false;
+
 	return true;
 }
 
@@ -327,12 +367,7 @@ static int allocinfo_ioctl_get_at(struct seq_file *m, void __user *arg)
 	if (copy_from_user(&params, arg, sizeof(params)))
 		return -EFAULT;
 
-	if (params.filter.mask & ~ALLOCINFO_FILTER_MASKS)
-		return -EINVAL;
-
-	if ((params.filter.mask & ALLOCINFO_FILTER_MASK_MIN_SIZE) &&
-	    (params.filter.mask & ALLOCINFO_FILTER_MASK_MAX_SIZE) &&
-	    params.filter.min_size > params.filter.max_size)
+	if (!allocinfo_filter_valid(&params.filter))
 		return -EINVAL;
 
 	priv = m->private;
@@ -437,6 +472,75 @@ static int allocinfo_ioctl_get_next(struct seq_file *m, void __user *arg)
 	return ret;
 }
 
+static void alloc_tag_trace_toggle(struct alloc_tag *tag, bool enable)
+{
+	if (enable) {
+		if (alloc_tag_is_traced(tag))
+			return;
+
+		alloc_tag_set_traced(tag);
+		if (atomic_fetch_inc(&alloc_tag_trace_cnt) == 0)
+			static_branch_enable(&alloc_tag_trace_key);
+	} else {
+		if (!alloc_tag_is_traced(tag))
+			return;
+
+		alloc_tag_clear_traced(tag);
+		if (atomic_dec_and_test(&alloc_tag_trace_cnt))
+			static_branch_disable(&alloc_tag_trace_key);
+	}
+}
+
+/*
+ * Toggles tracing on every allocation tag that matches the user supplied
+ * filter. An empty filter mask selects all tags, same as for
+ * ALLOCINFO_IOC_GET_AT. Tags already in the requested state are not an error.
+ */
+static int allocinfo_ioctl_toggle_trace(struct seq_file *m, void __user *arg)
+{
+	struct allocinfo_toggle_traces params;
+	struct codetag_iterator iter;
+	struct codetag *ct;
+	struct alloc_tag_counters counters;
+	bool fetched_counters;
+	int matches = 0, ret;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (copy_from_user(&params, arg, sizeof(params)))
+		return -EFAULT;
+
+	if (!allocinfo_filter_valid(&params.filter))
+		return -EINVAL;
+
+	codetag_lock_module_list(alloc_tag_cttype);
+
+	iter = codetag_get_ct_iter(alloc_tag_cttype);
+
+	/* Toggle tracing on all codetags that match */
+	while ((ct = codetag_next_ct(&iter))) {
+		fetched_counters = false;
+		if (matches_filter(ct, &params.filter, &counters, &fetched_counters)) {
+			matches++;
+
+			mutex_lock(&alloc_tag_trace_mutex);
+			alloc_tag_trace_toggle(ct_to_alloc_tag(ct), !!params.enable);
+			mutex_unlock(&alloc_tag_trace_mutex);
+		}
+	}
+
+	if (matches == 0)
+		/* Nothing matched the filter */
+		ret = -ENOENT;
+	else
+		ret = 0;
+
+	codetag_unlock_module_list(alloc_tag_cttype);
+
+	return ret;
+}
+
 /*
  * Entry point ioctl function for /proc/allocinfo routing requests to fetch the
  * layout content ID, seek to a specific tag, or read sequential tags.
@@ -457,6 +561,9 @@ static long allocinfo_ioctl(struct file *file, unsigned int cmd,
 	case ALLOCINFO_IOC_GET_NEXT:
 		ret = allocinfo_ioctl_get_next(file->private_data, arg);
 		break;
+	case ALLOCINFO_IOC_TOGGLE_TRACE:
+		ret = allocinfo_ioctl_toggle_trace(file->private_data, arg);
+		break;
 	default:
 		ret = -ENOIOCTLCMD;
 		break;
@@ -484,6 +591,26 @@ static const struct proc_ops allocinfo_proc_ops = {
 #endif
 };
 
+void __alloc_tag_trace_hit(struct alloc_tag *tag)
+{
+	trace_alloc_tag_hit(tag);
+}
+EXPORT_SYMBOL(__alloc_tag_trace_hit);
+
+void alloc_tag_trace_mem_alloc(const void *ptr, struct alloc_tag *tag,
+			       size_t bytes)
+{
+	trace_alloc_tag_mem_alloced(ptr, tag, bytes);
+}
+EXPORT_SYMBOL(alloc_tag_trace_mem_alloc);
+
+void alloc_tag_trace_mem_free(const void *ptr, struct alloc_tag *tag,
+			      size_t bytes)
+{
+	trace_alloc_tag_mem_freed(ptr, tag, bytes);
+}
+EXPORT_SYMBOL(alloc_tag_trace_mem_free);
+
 size_t alloc_tag_top_users(struct codetag_bytes *tags, size_t count, bool can_sleep)
 {
 	struct codetag_iterator iter;
@@ -1003,6 +1130,24 @@ static int load_module(struct module *mod, struct codetag *start, struct codetag
 	return 0;
 }
 
+static void unload_module(struct module *mod, struct codetag *start, struct codetag *stop)
+{
+	struct alloc_tag *start_tag = ct_to_alloc_tag(start);
+	struct alloc_tag *stop_tag = ct_to_alloc_tag(stop);
+	struct alloc_tag *tag;
+
+	/*
+	 * Turn tracing off for the tags of the module being unloaded. Without
+	 * this, `alloc_tag_trace_cnt` would never reach zero and tracing would
+	 * stay enabled forever.
+	 *
+	 * `alloc_tag_trace_mutex` is not needed here as this code path is
+	 * protected by a `down_write(&cttype->mod_lock)`.
+	 */
+	for (tag = start_tag; tag < stop_tag; tag++)
+		alloc_tag_trace_toggle(tag, false);
+}
+
 static void replace_module(struct module *mod, struct module *new_mod)
 {
 	MA_STATE(mas, &mod_area_mt, 0, module_tags.size);
@@ -1329,6 +1474,7 @@ static int __init alloc_tag_init(void)
 		.alloc_section_mem	= reserve_module_tags,
 		.free_section_mem	= release_module_tags,
 		.module_load		= load_module,
+		.module_unload		= unload_module,
 		.module_replaced	= replace_module,
 #endif
 	};
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7682aecc2c075..5e3e411d4ffe0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1239,7 +1239,7 @@ void __pgalloc_tag_add(struct page *page, struct task_struct *task,
 	union codetag_ref ref;
 
 	if (likely(get_page_tag_ref(page, &ref, &handle))) {
-		alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr);
+		alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr, page);
 		update_page_tag_ref(handle, &ref);
 		put_page_tag_ref(handle);
 	} else {
@@ -1268,7 +1268,7 @@ void __pgalloc_tag_sub(struct page *page, unsigned int nr)
 	union codetag_ref ref;
 
 	if (get_page_tag_ref(page, &ref, &handle)) {
-		alloc_tag_sub(&ref, PAGE_SIZE * nr);
+		alloc_tag_sub(&ref, PAGE_SIZE * nr, page);
 		update_page_tag_ref(handle, &ref);
 		put_page_tag_ref(handle);
 	}
diff --git a/mm/percpu.c b/mm/percpu.c
index 3eff382e565ad..12b6c97d15966 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1695,15 +1695,19 @@ static void pcpu_alloc_tag_alloc_hook(struct pcpu_chunk *chunk, int off,
 				      size_t size)
 {
 	if (mem_alloc_profiling_enabled() && likely(chunk->obj_exts)) {
-		alloc_tag_add(&chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag,
-			      current->alloc_tag, size);
+		union codetag_ref *ref = &chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag;
+
+		alloc_tag_add(ref, current->alloc_tag, size, ref);
 	}
 }
 
 static void pcpu_alloc_tag_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
 {
-	if (mem_alloc_profiling_enabled() && likely(chunk->obj_exts))
-		alloc_tag_sub(&chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag, size);
+	if (mem_alloc_profiling_enabled() && likely(chunk->obj_exts)) {
+		union codetag_ref *ref = &chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag;
+
+		alloc_tag_sub(ref, size, ref);
+	}
 }
 #else
 static void pcpu_alloc_tag_alloc_hook(struct pcpu_chunk *chunk, int off,
diff --git a/mm/slub.c b/mm/slub.c
index 544cff39762c5..a866576ccb983 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2404,7 +2404,7 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,
 		obj_ext = slab_obj_ext(s, slab, obj_exts, object);
 		ref = slab_obj_ext_codetag_ref(slab, obj_ext);
 
-		alloc_tag_add(ref, current->alloc_tag, s->size);
+		alloc_tag_add(ref, current->alloc_tag, s->size, ref);
 
 		put_slab_obj_exts(obj_exts);
 	} else {
@@ -2444,9 +2444,11 @@ __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p
 	get_slab_obj_exts(obj_exts);
 	for (int i = 0; i < objects; i++) {
 		struct slabobj_ext *ext;
+		union codetag_ref *ref;
 
 		ext = slab_obj_ext(s, slab, obj_exts, p[i]);
-		alloc_tag_sub(slab_obj_ext_codetag_ref(slab, ext), s->size);
+		ref = slab_obj_ext_codetag_ref(slab, ext);
+		alloc_tag_sub(ref, s->size, ref);
 	}
 	put_slab_obj_exts(obj_exts);
 }
diff --git a/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c b/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c
index 74fd64b2370cc..eb52ca1a1dc42 100644
--- a/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c
+++ b/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c
@@ -48,6 +48,11 @@ static inline int __allocinfo_get_next(int dev_fd, struct allocinfo_tag_data *pa
 	return ioctl(dev_fd, ALLOCINFO_IOC_GET_NEXT, params);
 }
 
+static inline int __allocinfo_toggle_trace(int dev_fd, struct allocinfo_toggle_traces *params)
+{
+	return ioctl(dev_fd, ALLOCINFO_IOC_TOGGLE_TRACE, params);
+}
+
 static bool match_entry(const struct allocinfo_tag_data *procfs_entry,
 			const struct allocinfo_tag_data *tag_data,
 			bool match_bytes, bool match_calls, bool match_lineno,
@@ -289,6 +294,8 @@ static int run_filter_test(const struct allocinfo_filter *filter)
 	return ret;
 }
 
+static const char *target_test_function = "dup_mm";
+
 static int test_filename_filter(void)
 {
 	struct allocinfo_filter filter;
@@ -304,11 +311,10 @@ static int test_filename_filter(void)
 static int test_function_filter(void)
 {
 	struct allocinfo_filter filter;
-	const char *target_function = "dup_mm";
 
 	memset(&filter, 0, sizeof(filter));
 	filter.mask |= ALLOCINFO_FILTER_MASK_FUNCTION;
-	strncpy(filter.fields.function, target_function, ALLOCINFO_STR_SIZE);
+	strncpy(filter.fields.function, target_test_function, ALLOCINFO_STR_SIZE);
 
 	return run_filter_test(&filter);
 }
@@ -514,11 +520,106 @@ static int test_lineno_filter(void)
 	return ret;
 }
 
+static enum ioctl_ret toggle_trace(struct allocinfo_tag *target_tag,
+				   bool enable)
+{
+	int fd;
+	struct allocinfo_toggle_traces toggle_params;
+
+	fd = open(ALLOCINFO_PROC, O_RDONLY);
+	if (fd < 0) {
+		ksft_print_msg("Failed to open " ALLOCINFO_PROC ": %s\n", strerror(errno));
+		return IOCTL_FAILURE;
+	}
+
+	memset(&toggle_params, 0, sizeof(toggle_params));
+	toggle_params.filter.mask = ALLOCINFO_FILTER_MASK_MODNAME | ALLOCINFO_FILTER_MASK_FUNCTION |
+				    ALLOCINFO_FILTER_MASK_FILENAME | ALLOCINFO_FILTER_MASK_LINENO;
+	toggle_params.filter.fields = *target_tag;
+	toggle_params.enable = enable;
+
+	if (__allocinfo_toggle_trace(fd, &toggle_params)) {
+		close(fd);
+		return IOCTL_FAILURE;
+	}
+
+	close(fd);
+	return IOCTL_SUCCESS;
+}
+
+static int test_tracing_toggle_and_filter(void)
+{
+	struct allocinfo_filter filter = { 0 };
+	enum ioctl_ret ioctl_status;
+	int ret = KSFT_PASS;
+	bool initial_state, target_state;
+	struct allocinfo_tag target_tag;
+	struct allocinfo_tag_data_vec *tags = calloc(1, sizeof(*tags));
+
+	if (!tags) {
+		ksft_print_msg("Memory allocation failed.\n");
+		return KSFT_FAIL;
+	}
+
+	filter.mask |= ALLOCINFO_FILTER_MASK_FUNCTION;
+	strncpy(filter.fields.function, target_test_function, ALLOCINFO_STR_SIZE);
+
+	ioctl_status = get_filtered_ioctl_entries(tags, &filter, 0);
+	if (ioctl_status != IOCTL_SUCCESS || tags->count == 0) {
+		ksft_print_msg("Could not retrieve IOCTL entries for %s\n", target_test_function);
+		ret = KSFT_SKIP;
+		goto exit;
+	}
+
+	target_tag = tags->tag[0].tag;
+	initial_state = tags->tag[0].counter.trace_on;
+	target_state = !initial_state;
+
+	ioctl_status = toggle_trace(&target_tag, target_state);
+	if (ioctl_status != IOCTL_SUCCESS) {
+		ksft_print_msg("Failed to toggle tracing\n");
+		ret = KSFT_FAIL;
+		goto exit;
+	}
+
+	filter.mask |= ALLOCINFO_FILTER_MASK_TRACE_ON;
+	filter.tracing = target_state;
+
+	ioctl_status = get_filtered_ioctl_entries(tags, &filter, 0);
+	if (ioctl_status != IOCTL_SUCCESS) {
+		ksft_print_msg("Error retrieving IOCTL entries with trace filter.\n");
+		ret = KSFT_FAIL;
+		goto exit_revert;
+	}
+
+	if (tags->count != 1) {
+		ksft_print_msg("Expected exactly 1 entry, but got %llu\n", tags->count);
+		ret = KSFT_FAIL;
+		goto exit_revert;
+	}
+
+	if (tags->tag[0].counter.trace_on != target_state) {
+		ksft_print_msg("Entry returned by trace filter does not match target state\n");
+		ret = KSFT_FAIL;
+	}
+
+exit_revert:
+	ioctl_status = toggle_trace(&target_tag, initial_state);
+	if (ioctl_status != IOCTL_SUCCESS) {
+		ksft_print_msg("Failed to revert tracing to initial state\n");
+		ret = KSFT_FAIL;
+	}
+
+exit:
+	free(tags);
+	return ret;
+}
+
 int main(int argc, char *argv[])
 {
 	int ret;
 
-	ksft_set_plan(4);
+	ksft_set_plan(5);
 
 	ret = test_filename_filter();
 	if (ret == KSFT_SKIP)
@@ -526,6 +627,12 @@ int main(int argc, char *argv[])
 	else
 		ksft_test_result(ret == KSFT_PASS, "test_filename_filter\n");
 
+	ret = test_tracing_toggle_and_filter();
+	if (ret == KSFT_SKIP)
+		ksft_test_result_skip("Skipping test_tracing_toggle_and_filter\n");
+	else
+		ksft_test_result(ret == KSFT_PASS, "test_tracing_toggle_and_filter\n");
+
 	ret = test_function_filter();
 	if (ret == KSFT_SKIP)
 		ksft_test_result_skip("Skipping test_function_filter\n");

gemini-3.8-flash

null

null

							input: 14555
							output: 41
							thoughts: 716
						

**Analyzing the Patch for Syzkaller Fuzzing Potential**

Okay, let's break this down. My initial assessment is: *does* this patch introduce anything that makes the kernel more susceptible to fuzzing, particularly with syzkaller? Let's go through it systematically.

First, I see documentation and MAINTAINERS updates – that's irrelevant for fuzzing, so moving on. The core of this seems to be around adding allocation tracing. Specifically, it introduces a `static key alloc_tag_trace_key`, various tracing-related functions (`alloc_tag_set_traced`, etc.), and modifies existing functions (`alloc_tag_add`, `alloc_tag_sub`) to incorporate tracing when enabled. It's also adding tracepoints for allocation hits and memory operations. This tracing introduces *new* code paths, and new logic can lead to new bugs.

The changes in `codetag.h` with the `CODETAG_FLAG_TRACE_ON` and the `atomic_t flags` change are standard. The new trace events are good, but I need to see how these are used.

In `uapi/linux/alloc_tag.h`, we're seeing the introduction of IOCTLs, which is interesting.  This potentially means that userspace interaction is *required* to trigger tracing. That’s a significant point. Specifically, `ALLOCINFO_IOC_TOGGLE_TRACE` is a strong indicator of user interaction that we should investigate.  I’ll need to understand how the tracing is toggled and what data can be supplied or observed. I need to understand what this IOCTL does, what the parameters mean, and how to use it.  That's a potential area for fuzzing.

The changes in `mm/alloc_tag.c` include the key tracing variables, the `matches_filter` updates, and the helper functions. The addition of `allocinfo_ioctl_toggle_trace` and the general handling of `ALLOCINFO_IOC_TOGGLE_TRACE` in `allocinfo_ioctl` are *definitely* worth a closer look. I need to understand the filter logic and see if we can manipulate that to cause issues. And the module unload callback toggling tracing off seems like a standard clean-up.

Modifications in `page_alloc.c`, `percpu.c`, and `slub.c` that involve the change in arguments to `alloc_tag_add`/`alloc_tag_sub` are just propagating the changes; not critical in this phase.

Finally, the added selftests will be very useful. I'll need to review them to understand the intended usage of these tracing features.

So, overall, this is *promising* for syzkaller. The introduction of an IOCTL is a big red flag, as it provides a new avenue for userspace interaction and kernel control. I'll need to analyze the IOCTL handler, the filters, and the toggle logic carefully. The selftests could provide good test cases, too. I'm going to grep for `MEM_ALLOC_PROFILING` in the Kconfig to see what prerequisites there are, and then I'll formulate a fuzzing strategy.

{
  "Expression": "config MEM_ALLOC_PROFILING",
  "PathPrefixes": [
    "lib/",
    "mm/",
    "init/"
  ]
}

{
  "Output": "mm/Kconfig.debug=272=config PER_VMA_LOCK_STATS\n--\nmm/Kconfig.debug-283-\nmm/Kconfig.debug:284:config MEM_ALLOC_PROFILING\nmm/Kconfig.debug-285-\tbool \"Enable memory allocation profiling\"\n--\nmm/Kconfig.debug-296-\nmm/Kconfig.debug:297:config MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT\nmm/Kconfig.debug-298-\tbool \"Enable memory allocation profiling by default\"\n--\nmm/Kconfig.debug-301-\nmm/Kconfig.debug:302:config MEM_ALLOC_PROFILING_DEBUG\nmm/Kconfig.debug-303-\tbool \"Memory allocation profiler debugging\"\n"
}

gemini-3.8-flash

null

null

							input: 16198
							output: 34
							thoughts: 23
						

Here's a summary of my thought process, as requested:

**Diving into Debugging Configuration**

Okay, let's get down to brass tacks. I need to understand something about the kernel's debugging configuration, and the likely place to find it is within the Kconfig files. Specifically, I'm thinking about the memory management (`mm`) subsystem, as that's where my current investigation leads me. The `Kconfig.debug` file seems like the logical spot for debugging options related to that. Now, let's zero in on approximately line 284 within that file. I'm going to use a `read-file` tool (or a similar method depending on my current environment) to pull the contents of that section so I can begin to interpret its meaning. I'm anticipating that this will give me the clues I need.

{
  "File": "mm/Kconfig.debug",
  "FirstLine": 280,
  "LineCount": 40
}

{
  "Contents": " 280:\t\t  overhead in the page fault path.\n 281:\t\n 282:\t\t  If in doubt, say N.\n 283:\t\n 284:\tconfig MEM_ALLOC_PROFILING\n 285:\t\tbool \"Enable memory allocation profiling\"\n 286:\t\tdefault n\n 287:\t\tdepends on MMU\n 288:\t\tdepends on PROC_FS\n 289:\t\tselect CODE_TAGGING\n 290:\t\tselect PAGE_EXTENSION\n 291:\t\tselect SLAB_OBJ_EXT\n 292:\t\thelp\n 293:\t\t  Track allocation source code and record total allocation size\n 294:\t\t  initiated at that code location. The mechanism can be used to track\n 295:\t\t  memory leaks with a low performance and memory impact.\n 296:\t\n 297:\tconfig MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT\n 298:\t\tbool \"Enable memory allocation profiling by default\"\n 299:\t\tdefault y\n 300:\t\tdepends on MEM_ALLOC_PROFILING\n 301:\t\n 302:\tconfig MEM_ALLOC_PROFILING_DEBUG\n 303:\t\tbool \"Memory allocation profiler debugging\"\n 304:\t\tdefault n\n 305:\t\tdepends on MEM_ALLOC_PROFILING\n 306:\t\tselect MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT\n 307:\t\thelp\n 308:\t\t  Adds warnings with helpful error messages for memory allocation\n 309:\t\t  profiling.\n"
}

gemini-3.8-flash

null

null

							input: 16845
							output: 30
							thoughts: 22
						

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

**Investigating the Genesis of `/proc/allocinfo`**

Alright, let's dive in. I need to understand the lineage of `/proc/allocinfo`. Specifically, I'm going to track down the code responsible for its creation within the kernel. The obvious starting point is `mm/alloc_tag.c`. That file name suggests a central role in allocation tracking, and `/proc/allocinfo` feels like a natural output for such a subsystem. Time to trace the code and see how this thing gets instantiated and populated. I'm especially interested in the data structures used and the locking involved, to see if there are any obvious bottlenecks or concurrency concerns. Let's see what `mm/alloc_tag.c` has to offer.

{
  "Expression": "allocinfo",
  "PathPrefixes": [
    "mm/alloc_tag.c"
  ]
}

{
  "Output": "\nFull output is too long, showing 200 out of 239 lines.\nUse more precise expression or PathPrefixes if possible.\n\nNumber of matching lines per file (1 files in total):\nmm/alloc_tag.c:76\n\nmm/alloc_tag.c-26-\nmm/alloc_tag.c:27:#define ALLOCINFO_FILE_NAME\t\t\"allocinfo\"\nmm/alloc_tag.c-28-#define MODULE_ALLOC_TAG_VMAP_SIZE\t(100000UL * sizeof(struct alloc_tag))\n--\nmm/alloc_tag.c=74=int alloc_tag_ref_offs;\nmm/alloc_tag.c-75-\nmm/alloc_tag.c:76:struct allocinfo_private {\nmm/alloc_tag.c-77-\tstruct codetag_iterator iter;\n--\nmm/alloc_tag.c-79-\tbool print_header;\nmm/alloc_tag.c:80:\tstruct allocinfo_filter filter;\nmm/alloc_tag.c-81-\t/* ioctl uses a separate iterator not to interfere with reads */\n--\nmm/alloc_tag.c-86-\nmm/alloc_tag.c:87:static void *allocinfo_start(struct seq_file *m, loff_t *pos)\nmm/alloc_tag.c-88-{\nmm/alloc_tag.c:89:\tstruct allocinfo_private *priv;\nmm/alloc_tag.c-90-\tloff_t node = *pos;\nmm/alloc_tag.c-91-\nmm/alloc_tag.c:92:\tpriv = (struct allocinfo_private *)m-\u003eprivate;\nmm/alloc_tag.c-93-\tcodetag_lock_module_list(alloc_tag_cttype);\n--\nmm/alloc_tag.c-103-\nmm/alloc_tag.c:104:static void *allocinfo_next(struct seq_file *m, void *arg, loff_t *pos)\nmm/alloc_tag.c-105-{\nmm/alloc_tag.c:106:\tstruct allocinfo_private *priv = (struct allocinfo_private *)arg;\nmm/alloc_tag.c-107-\tstruct codetag *ct;\n--\nmm/alloc_tag.c-117-\nmm/alloc_tag.c:118:static void allocinfo_stop(struct seq_file *m, void *arg)\nmm/alloc_tag.c-119-{\n--\nmm/alloc_tag.c-122-\nmm/alloc_tag.c:123:static void print_allocinfo_header(struct seq_buf *buf)\nmm/alloc_tag.c-124-{\nmm/alloc_tag.c-125-\t/* Output format version, so we can change it. */\nmm/alloc_tag.c:126:\tseq_buf_printf(buf, \"allocinfo - version: 2.0\\n\");\nmm/alloc_tag.c-127-\tseq_buf_printf(buf, \"#     \u003csize\u003e  \u003ccalls\u003e \u003ctag info\u003e\\n\");\n--\nmm/alloc_tag.c=130=static void alloc_tag_to_text(struct seq_buf *out, struct codetag *ct)\n--\nmm/alloc_tag.c-143-\nmm/alloc_tag.c:144:static int allocinfo_show(struct seq_file *m, void *arg)\nmm/alloc_tag.c-145-{\nmm/alloc_tag.c:146:\tstruct allocinfo_private *priv = (struct allocinfo_private *)arg;\nmm/alloc_tag.c-147-\tchar *bufp;\n--\nmm/alloc_tag.c-152-\tif (priv-\u003eprint_header) {\nmm/alloc_tag.c:153:\t\tprint_allocinfo_header(\u0026buf);\nmm/alloc_tag.c-154-\t\tpriv-\u003eprint_header = false;\n--\nmm/alloc_tag.c-160-\nmm/alloc_tag.c:161:static const struct seq_operations allocinfo_seq_op = {\nmm/alloc_tag.c:162:\t.start\t= allocinfo_start,\nmm/alloc_tag.c:163:\t.next\t= allocinfo_next,\nmm/alloc_tag.c:164:\t.stop\t= allocinfo_stop,\nmm/alloc_tag.c:165:\t.show\t= allocinfo_show,\nmm/alloc_tag.c-166-};\n--\nmm/alloc_tag.c-169- * Initializes seq_file operations and allocates private state when opening\nmm/alloc_tag.c:170: * the /proc/allocinfo procfs entry.\nmm/alloc_tag.c-171- */\nmm/alloc_tag.c:172:static int allocinfo_open(struct inode *inode, struct file *file)\nmm/alloc_tag.c-173-{\n--\nmm/alloc_tag.c-175-\nmm/alloc_tag.c:176:\tret = seq_open_private(file, \u0026allocinfo_seq_op,\nmm/alloc_tag.c:177:\t\t\t       sizeof(struct allocinfo_private));\nmm/alloc_tag.c-178-\tif (!ret) {\nmm/alloc_tag.c-179-\t\tstruct seq_file *m = file-\u003eprivate_data;\nmm/alloc_tag.c:180:\t\tstruct allocinfo_private *priv = m-\u003eprivate;\nmm/alloc_tag.c-181-\n--\nmm/alloc_tag.c-188- * Cleans up the seq_file state and frees up the private state allocated in\nmm/alloc_tag.c:189: * allocinfo_open() when closing the /proc/allocinfo file descriptor.\nmm/alloc_tag.c-190- */\nmm/alloc_tag.c:191:static int allocinfo_release(struct inode *inode, struct file *file)\nmm/alloc_tag.c-192-{\nmm/alloc_tag.c-193-\tstruct seq_file *m = file-\u003eprivate_data;\nmm/alloc_tag.c:194:\tstruct allocinfo_private *priv = m-\u003eprivate;\nmm/alloc_tag.c-195-\n--\nmm/alloc_tag.c-206- */\nmm/alloc_tag.c:207:static const char *allocinfo_str(const char *str)\nmm/alloc_tag.c-208-{\n--\nmm/alloc_tag.c-217-/* Copy a string and trim from the beginning if it's too long */\nmm/alloc_tag.c:218:static void allocinfo_copy_str(char *dest, const char *src)\nmm/alloc_tag.c-219-{\nmm/alloc_tag.c:220:\tstrscpy_pad(dest, allocinfo_str(src), ALLOCINFO_STR_SIZE);\nmm/alloc_tag.c-221-}\n--\nmm/alloc_tag.c-223-/* Compare two strings and only consider the trimmed suffix if s1 is too long */\nmm/alloc_tag.c:224:static int allocinfo_cmp_str(const char *str, const char *template)\nmm/alloc_tag.c-225-{\nmm/alloc_tag.c:226:\treturn strncmp(allocinfo_str(str), template, ALLOCINFO_STR_SIZE);\nmm/alloc_tag.c-227-}\n--\nmm/alloc_tag.c-229-/* Fetch the per-CPU counters */\nmm/alloc_tag.c:230:static inline struct alloc_tag_counters allocinfo_prefetch_counters(struct codetag *ct)\nmm/alloc_tag.c-231-{\n--\nmm/alloc_tag.c-235-/*\nmm/alloc_tag.c:236: * Populates the UAPI allocinfo_tag_data structure with active runtime\nmm/alloc_tag.c-237- * profiling counters extracted from the given kernel codetag.\nmm/alloc_tag.c-238- */\nmm/alloc_tag.c:239:static void allocinfo_to_params(struct codetag *ct,\nmm/alloc_tag.c:240:\t\t\t\tstruct allocinfo_tag_data *data,\nmm/alloc_tag.c-241-\t\t\t\tstruct alloc_tag_counters *counters)\n--\nmm/alloc_tag.c-243-\tif (ct-\u003emodname)\nmm/alloc_tag.c:244:\t\tallocinfo_copy_str(data-\u003etag.modname, ct-\u003emodname);\nmm/alloc_tag.c-245-\telse\nmm/alloc_tag.c-246-\t\tdata-\u003etag.modname[0] = '\\0';\nmm/alloc_tag.c:247:\tallocinfo_copy_str(data-\u003etag.function, ct-\u003efunction);\nmm/alloc_tag.c:248:\tallocinfo_copy_str(data-\u003etag.filename, ct-\u003efilename);\nmm/alloc_tag.c-249-\tdata-\u003etag.lineno = ct-\u003elineno;\n--\nmm/alloc_tag.c-259- */\nmm/alloc_tag.c:260:static int allocinfo_ioctl_get_content_id(struct seq_file *m, void __user *arg)\nmm/alloc_tag.c-261-{\nmm/alloc_tag.c:262:\tstruct allocinfo_content_id params;\nmm/alloc_tag.c-263-\n--\nmm/alloc_tag.c-276- */\nmm/alloc_tag.c:277:static bool matches_filter(struct codetag *ct, struct allocinfo_filter *filter,\nmm/alloc_tag.c-278-\t\t\t   struct alloc_tag_counters *counters,\n--\nmm/alloc_tag.c-291-\t\t\t\treturn false;\nmm/alloc_tag.c:292:\t\t} else if (allocinfo_cmp_str(ct-\u003emodname, filter-\u003efields.modname))\nmm/alloc_tag.c-293-\t\t\treturn false;\n--\nmm/alloc_tag.c-296-\tif ((filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_FUNCTION) \u0026\u0026\nmm/alloc_tag.c:297:\t    ct-\u003efunction \u0026\u0026 allocinfo_cmp_str(ct-\u003efunction, filter-\u003efields.function))\nmm/alloc_tag.c-298-\t\treturn false;\n--\nmm/alloc_tag.c-300-\tif ((filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_FILENAME) \u0026\u0026\nmm/alloc_tag.c:301:\t    ct-\u003efilename \u0026\u0026 allocinfo_cmp_str(ct-\u003efilename, filter-\u003efields.filename))\nmm/alloc_tag.c-302-\t\treturn false;\n--\nmm/alloc_tag.c-315-\t\tif (!*fetched_counters) {\nmm/alloc_tag.c:316:\t\t\t*counters = allocinfo_prefetch_counters(ct);\nmm/alloc_tag.c-317-\t\t\t*fetched_counters = true;\n--\nmm/alloc_tag.c-340- */\nmm/alloc_tag.c:341:static bool allocinfo_filter_valid(const struct allocinfo_filter *filter)\nmm/alloc_tag.c-342-{\n--\nmm/alloc_tag.c-357- */\nmm/alloc_tag.c:358:static int allocinfo_ioctl_get_at(struct seq_file *m, void __user *arg)\nmm/alloc_tag.c-359-{\nmm/alloc_tag.c:360:\tstruct allocinfo_private *priv;\nmm/alloc_tag.c-361-\tstruct codetag *ct;\nmm/alloc_tag.c:362:\tstruct allocinfo_get_at params = {0};\nmm/alloc_tag.c-363-\t__u64 skip_count;\n--\nmm/alloc_tag.c-369-\nmm/alloc_tag.c:370:\tif (!allocinfo_filter_valid(\u0026params.filter))\nmm/alloc_tag.c-371-\t\treturn -EINVAL;\n--\nmm/alloc_tag.c-406-\t\tif (!fetched_counters)\nmm/alloc_tag.c:407:\t\t\tcounters = allocinfo_prefetch_counters(ct);\nmm/alloc_tag.c:408:\t\tallocinfo_to_params(ct, \u0026params.data, \u0026counters);\nmm/alloc_tag.c-409-\t\tpriv-\u003epositioned = true;\n--\nmm/alloc_tag.c-427- */\nmm/alloc_tag.c:428:static int allocinfo_ioctl_get_next(struct seq_file *m, void __user *arg)\nmm/alloc_tag.c-429-{\nmm/alloc_tag.c:430:\tstruct allocinfo_private *priv;\nmm/alloc_tag.c-431-\tstruct codetag *ct;\nmm/alloc_tag.c:432:\tstruct allocinfo_tag_data params;\nmm/alloc_tag.c-433-\tint ret = 0;\n--\nmm/alloc_tag.c-457-\t\tif (!fetched_counters)\nmm/alloc_tag.c:458:\t\t\tcounters = allocinfo_prefetch_counters(ct);\nmm/alloc_tag.c:459:\t\tallocinfo_to_params(ct, \u0026params, \u0026counters);\nmm/alloc_tag.c-460-\t}\n--\nmm/alloc_tag.c=475=static void alloc_tag_trace_toggle(struct alloc_tag *tag, bool enable)\n--\nmm/alloc_tag.c-498- */\nmm/alloc_tag.c:499:static int allocinfo_ioctl_toggle_trace(struct seq_file *m, void __user *arg)\nmm/alloc_tag.c-500-{\nmm/alloc_tag.c:501:\tstruct allocinfo_toggle_traces params;\nmm/alloc_tag.c-502-\tstruct codetag_iterator iter;\n--\nmm/alloc_tag.c-513-\nmm/alloc_tag.c:514:\tif (!allocinfo_filter_valid(\u0026params.filter))\nmm/alloc_tag.c-515-\t\treturn -EINVAL;\n--\nmm/alloc_tag.c-544-/*\nmm/alloc_tag.c:545: * Entry point ioctl function for /proc/allocinfo routing requests to fetch the\nmm/alloc_tag.c-546- * layout content ID, seek to a specific tag, or read sequential tags.\nmm/alloc_tag.c-547- */\nmm/alloc_tag.c:548:static long allocinfo_ioctl(struct file *file, unsigned int cmd,\nmm/alloc_tag.c-549-\t\t\t    unsigned long __arg)\n--\nmm/alloc_tag.c-555-\tcase ALLOCINFO_IOC_CONTENT_ID:\nmm/alloc_tag.c:556:\t\tret = allocinfo_ioctl_get_content_id(file-\u003eprivate_data, arg);\nmm/alloc_tag.c-557-\t\tbreak;\n\n"
}

gemini-3.8-flash

null

null

							input: 20924
							output: 36
							thoughts: 2127
						

**Analysis of `/proc/allocinfo` ioctl `ALLOCINFO_IOC_TOGGLE_TRACE` and Concurrency Concerns**

Okay, so I'm looking at this new `ALLOCINFO_IOC_TOGGLE_TRACE` ioctl in `/proc/allocinfo`. First, I see that it's protected by `CAP_SYS_ADMIN`, which is expected. Syzkaller usually runs with these privileges, so that's fine for testing. The primary function `allocinfo_ioctl_toggle_trace()` calls `alloc_tag_trace_toggle()`.

Now, I'm digging into `alloc_tag_trace_toggle()`. It looks like it enables and disables tracing, using `static_branch_enable` and `static_branch_disable` to modify code, and there's a reference counter, `alloc_tag_trace_cnt`, along with `alloc_tag_is_traced()`. The crucial parts are `alloc_tag_add` and `alloc_tag_sub` which have the `alloc_tag_trace_enabled(tag)` check, and call `alloc_tag_trace_mem_alloc` and `alloc_tag_trace_mem_free` if trace is enabled.

I also see that `alloc_tag_trace_toggle` is called during module unloading (`unload_module`). The interesting thing is that `unload_module` *disables* tracing for tags associated with the module, and it *doesn't* take `alloc_tag_trace_mutex`. The comment says it's protected by `down_write(&cttype->mod_lock)`.

But, when I go back to `allocinfo_ioctl_toggle_trace()`, I see that it *does* use `mutex_lock(&alloc_tag_trace_mutex)` around `alloc_tag_trace_toggle()`. Inside a loop that scans and matches codetags! The loop is guarded by `codetag_lock_module_list()`, which is a `down_read(&cttype->mod_lock)`.

Here's the problem: `unload_module` takes a `down_write`, while `allocinfo_ioctl_toggle_trace` takes a `down_read`. So concurrent access to the module list is protected, which is good. However, what if *multiple* instances of `allocinfo_ioctl_toggle_trace` are running concurrently? They'll all hold `down_read`, and inside the loop, the mutex is locked and unlocked *per matching codetag*. This means, there is a race condition between the `static_branch_enable` and `static_branch_disable`.

So, the concern is this: if one thread enables tracing and another disables it (or *vice versa*), the state of the static branch (and thus the tracing) can become undefined due to the `atomic_fetch_inc(&alloc_tag_trace_cnt)` vs. `atomic_dec_and_test(&alloc_tag_trace_cnt)`. This is especially important because `static_branch_enable` and `static_branch_disable` actually modify code. And, it's possible for a thread to increment `alloc_tag_trace_cnt` to zero, and another thread to decrement to one.

The `unload_module` calls `alloc_tag_trace_toggle` without the mutex, so it is possible for concurrent access to `alloc_tag_trace_cnt`.

We need to confirm if `static_branch_enable` and `static_branch_disable` are internally protected. I know jump labels use their own internal mutex. Additionally, we need to carefully investigate the concurrency implications when the reference counter `alloc_tag_trace_cnt` is zero.

{
  "Expression": "module_unload",
  "PathPrefixes": [
    "lib/",
    "mm/",
    "include/"
  ]
}

{
  "Output": "include/linux/codetag.h=40=struct codetag_type_desc {\n--\ninclude/linux/codetag.h-44-\t\t\t   struct codetag *start, struct codetag *end);\ninclude/linux/codetag.h:45:\tvoid (*module_unload)(struct module *mod,\ninclude/linux/codetag.h-46-\t\t\t      struct codetag *start, struct codetag *end);\n--\nlib/codetag.c=357=void codetag_unload_module(struct module *mod)\n--\nlib/codetag.c-380-\t\tif (found) {\nlib/codetag.c:381:\t\t\tif (cttype-\u003edesc.module_unload)\nlib/codetag.c:382:\t\t\t\tcttype-\u003edesc.module_unload(cmod-\u003emod,\nlib/codetag.c-383-\t\t\t\t\tcmod-\u003erange.start, cmod-\u003erange.stop);\n--\nlib/error-inject.c=108=static void module_load_ei_list(struct module *mod)\n--\nlib/error-inject.c-116-\nlib/error-inject.c:117:static void module_unload_ei_list(struct module *mod)\nlib/error-inject.c-118-{\n--\nlib/error-inject.c=135=static int ei_module_callback(struct notifier_block *nb,\n--\nlib/error-inject.c-142-\telse if (val == MODULE_STATE_GOING)\nlib/error-inject.c:143:\t\tmodule_unload_ei_list(mod);\nlib/error-inject.c-144-\n--\nmm/alloc_tag.c=1467=static int __init alloc_tag_init(void)\n--\nmm/alloc_tag.c-1476-\t\t.module_load\t\t= load_module,\nmm/alloc_tag.c:1477:\t\t.module_unload\t\t= unload_module,\nmm/alloc_tag.c-1478-\t\t.module_replaced\t= replace_module,\n"
}

gemini-3.8-flash

null

null

							input: 24409
							output: 34
							thoughts: 27
						

Here's a summary of my immediate thought process, keeping in mind my expertise:

**Checking `module_unload` Locking in `lib/codetag.c`**

Okay, I need to get a handle on how `module_unload` is protected in this codebase. My instinct tells me that potential race conditions are a high concern there, especially with concurrent module operations. I'm going to jump into `lib/codetag.c`, specifically around line 357. That's a reasonable spot to begin looking for any mutexes, spinlocks, or other synchronization primitives used to guard against conflicts during module unloading. I expect to see some form of locking in place – the complexity will be in _how_ the locking is implemented and whether it's robust enough. I'll need to assess its scope and potential impact on other, possibly related, operations as I scan the code. This is likely a critical area to examine for any potential vulnerabilities or performance bottlenecks.

{
  "File": "lib/codetag.c",
  "FirstLine": 355,
  "LineCount": 40
}

{
  "Contents": " 355:\t}\n 356:\t\n 357:\tvoid codetag_unload_module(struct module *mod)\n 358:\t{\n 359:\t\tstruct codetag_type *cttype;\n 360:\t\n 361:\t\tif (!mod)\n 362:\t\t\treturn;\n 363:\t\n 364:\t\t/* await any module's kfree_rcu() operations to complete */\n 365:\t\tkvfree_rcu_barrier();\n 366:\t\n 367:\t\tmutex_lock(\u0026codetag_lock);\n 368:\t\tlist_for_each_entry(cttype, \u0026codetag_types, link) {\n 369:\t\t\tstruct codetag_module *found = NULL;\n 370:\t\t\tstruct codetag_module *cmod;\n 371:\t\t\tunsigned long mod_id, tmp;\n 372:\t\n 373:\t\t\tdown_write(\u0026cttype-\u003emod_lock);\n 374:\t\t\tidr_for_each_entry_ul(\u0026cttype-\u003emod_idr, cmod, tmp, mod_id) {\n 375:\t\t\t\tif (cmod-\u003emod \u0026\u0026 cmod-\u003emod == mod) {\n 376:\t\t\t\t\tfound = cmod;\n 377:\t\t\t\t\tbreak;\n 378:\t\t\t\t}\n 379:\t\t\t}\n 380:\t\t\tif (found) {\n 381:\t\t\t\tif (cttype-\u003edesc.module_unload)\n 382:\t\t\t\t\tcttype-\u003edesc.module_unload(cmod-\u003emod,\n 383:\t\t\t\t\t\tcmod-\u003erange.start, cmod-\u003erange.stop);\n 384:\t\n 385:\t\t\t\tcttype-\u003ecount -= range_size(cttype, \u0026cmod-\u003erange);\n 386:\t\t\t\tidr_remove(\u0026cttype-\u003emod_idr, mod_id);\n 387:\t\t\t\tkfree(cmod);\n 388:\t\t\t\t++cttype-\u003econtent_id;\n 389:\t\t\t}\n 390:\t\t\tup_write(\u0026cttype-\u003emod_lock);\n 391:\t\t\tif (found \u0026\u0026 cttype-\u003edesc.free_section_mem)\n 392:\t\t\t\tcttype-\u003edesc.free_section_mem(mod, true);\n 393:\t\t}\n 394:\t\tmutex_unlock(\u0026codetag_lock);\n"
}

gemini-3.8-flash

null

null

							input: 25286
							output: 28
							thoughts: 1047
						

**Fuzzing Worthiness Assessment: Allocation Profiling Tracepoints**

Okay, let's break this down. I see a patch that introduces allocation profiling with tracepoints, and the first thing I'm doing is making sure the code is safe and accessible. I've noted the locking order with the `down_write(&cttype->mod_lock)` and the read lock within the `allocinfo_ioctl_toggle_trace` function. This is a common pattern, and I will be looking to confirm this is used in the proper order.

Essentially, this is adding a new feature: tracing memory allocations. I immediately see several key aspects: new trace events (`alloc_tag_hit`, etc.), a new ioctl (`ALLOCINFO_IOC_TOGGLE_TRACE`), and hooks into the core memory allocation paths (slab, percpu, page_alloc). This is a pretty significant change.

Now, let me run through my fuzzing criteria. I need to make a judgment call on whether this is worthy of fuzzing. Based on my analysis:

1.  **Reachability is Key:** This is clearly *reachable*. It's not limited to hardware that is unreachable in normal virtualized environments, and it is going to impact users via the ioctl.
2.  **No Functional Change/Refactoring Claims:** I'm not blindly accepting "no functional change" here. This is *adding* functionality and modifying memory allocation paths.
3.  **New/Modified Assertions:** Not applicable in this code, so far.

Based on the criteria, this *absolutely* falls under the "WorthFuzzing=true" category. Specifically, it touches the "Core Subsystems" – memory management, synchronization, and introduces a new user-facing ioctl. I'm seeing changes to `mm/alloc_tag.c`, `mm/page_alloc.c`, etc. and fast paths for allocation.

Now to the configurations. I need to figure out what config options are required and what FocusSymbols I need to use. I see `CONFIG_MEM_ALLOC_PROFILING`, `CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT`, and `CONFIG_MEM_ALLOC_PROFILING_DEBUG` in `mm/Kconfig.debug`. It looks like `CODE_TAGGING`, `PAGE_EXTENSION`, and `SLAB_OBJ_EXT` are also selected by this config. These are all prerequisites.

Crucially, I need to check the tracing dependency. I see that tracepoints are used (`#include <linux/tracepoint.h>` and `#include <trace/define_trace.h>`). So, is it `CONFIG_TRACING` or `CONFIG_EVENT_TRACING` that enables the tracepoints? I need to check the Makefile, and what module is using these things.

{
  "Expression": "alloc_tag.o",
  "PathPrefixes": [
    "mm/"
  ]
}

{
  "Output": "mm/Makefile=150=obj-$(CONFIG_LAZY_MMU_MODE_KUNIT_TEST) += tests/lazy_mmu_mode_kunit.o\nmm/Makefile:151:obj-$(CONFIG_MEM_ALLOC_PROFILING) += alloc_tag.o\n"
}

gemini-3.8-flash

null

null

							input: 27042
							output: 33
							thoughts: 30
						

Here's my take on the thought process:

**Diving into the Allocation Tagging Implementation**

Okay, so I need to get a handle on what's going on with this allocation tagging stuff. My first instinct is to dive into the core implementation. I'm thinking I'll start with `alloc_tag.c`. That should be the heart of it, right? From there, I'll need to look at the related header file, `trace/events/alloc_tag.h`, to understand how the allocation tagging data structures are defined and how they relate to the tracing infrastructure. Then, I need to be *really* careful and thoroughly review any `#ifdef` preprocessor directives. I know this code has to be flexible enough to handle different configurations and scenarios, so I need to make sure I understand the different conditional compilation paths. Understanding the ifdefs is key because I know that it can be easy to miss code sections. Time to get my hands dirty.

{
  "Expression": "alloc_tag_trace",
  "PathPrefixes": [
    "mm/alloc_tag.c"
  ]
}

{
  "Output": "mm/alloc_tag.c=58=DEFINE_STATIC_KEY_FALSE(mem_profiling_compressed);\nmm/alloc_tag.c-59-\nmm/alloc_tag.c:60:DEFINE_STATIC_KEY_FALSE(alloc_tag_trace_key);\nmm/alloc_tag.c:61:EXPORT_SYMBOL(alloc_tag_trace_key);\nmm/alloc_tag.c-62-\nmm/alloc_tag.c:63:static atomic_t alloc_tag_trace_cnt = ATOMIC_INIT(0);\nmm/alloc_tag.c-64-\n--\nmm/alloc_tag.c-69- */\nmm/alloc_tag.c:70:static DEFINE_MUTEX(alloc_tag_trace_mutex);\nmm/alloc_tag.c-71-\n--\nmm/alloc_tag.c=428=static int allocinfo_ioctl_get_next(struct seq_file *m, void __user *arg)\n--\nmm/alloc_tag.c-474-\nmm/alloc_tag.c:475:static void alloc_tag_trace_toggle(struct alloc_tag *tag, bool enable)\nmm/alloc_tag.c-476-{\n--\nmm/alloc_tag.c-481-\t\talloc_tag_set_traced(tag);\nmm/alloc_tag.c:482:\t\tif (atomic_fetch_inc(\u0026alloc_tag_trace_cnt) == 0)\nmm/alloc_tag.c:483:\t\t\tstatic_branch_enable(\u0026alloc_tag_trace_key);\nmm/alloc_tag.c-484-\t} else {\n--\nmm/alloc_tag.c-488-\t\talloc_tag_clear_traced(tag);\nmm/alloc_tag.c:489:\t\tif (atomic_dec_and_test(\u0026alloc_tag_trace_cnt))\nmm/alloc_tag.c:490:\t\t\tstatic_branch_disable(\u0026alloc_tag_trace_key);\nmm/alloc_tag.c-491-\t}\n--\nmm/alloc_tag.c=499=static int allocinfo_ioctl_toggle_trace(struct seq_file *m, void __user *arg)\n--\nmm/alloc_tag.c-526-\nmm/alloc_tag.c:527:\t\t\tmutex_lock(\u0026alloc_tag_trace_mutex);\nmm/alloc_tag.c:528:\t\t\talloc_tag_trace_toggle(ct_to_alloc_tag(ct), !!params.enable);\nmm/alloc_tag.c:529:\t\t\tmutex_unlock(\u0026alloc_tag_trace_mutex);\nmm/alloc_tag.c-530-\t\t}\n--\nmm/alloc_tag.c=583=static const struct proc_ops allocinfo_proc_ops = {\n--\nmm/alloc_tag.c-593-\nmm/alloc_tag.c:594:void __alloc_tag_trace_hit(struct alloc_tag *tag)\nmm/alloc_tag.c-595-{\n--\nmm/alloc_tag.c-597-}\nmm/alloc_tag.c:598:EXPORT_SYMBOL(__alloc_tag_trace_hit);\nmm/alloc_tag.c-599-\nmm/alloc_tag.c:600:void alloc_tag_trace_mem_alloc(const void *ptr, struct alloc_tag *tag,\nmm/alloc_tag.c-601-\t\t\t       size_t bytes)\n--\nmm/alloc_tag.c-604-}\nmm/alloc_tag.c:605:EXPORT_SYMBOL(alloc_tag_trace_mem_alloc);\nmm/alloc_tag.c-606-\nmm/alloc_tag.c:607:void alloc_tag_trace_mem_free(const void *ptr, struct alloc_tag *tag,\nmm/alloc_tag.c-608-\t\t\t      size_t bytes)\n--\nmm/alloc_tag.c-611-}\nmm/alloc_tag.c:612:EXPORT_SYMBOL(alloc_tag_trace_mem_free);\nmm/alloc_tag.c-613-\n--\nmm/alloc_tag.c=1133=static void unload_module(struct module *mod, struct codetag *start, struct codetag *stop)\n--\nmm/alloc_tag.c-1140-\t * Turn tracing off for the tags of the module being unloaded. Without\nmm/alloc_tag.c:1141:\t * this, `alloc_tag_trace_cnt` would never reach zero and tracing would\nmm/alloc_tag.c-1142-\t * stay enabled forever.\nmm/alloc_tag.c-1143-\t *\nmm/alloc_tag.c:1144:\t * `alloc_tag_trace_mutex` is not needed here as this code path is\nmm/alloc_tag.c-1145-\t * protected by a `down_write(\u0026cttype-\u003emod_lock)`.\n--\nmm/alloc_tag.c-1147-\tfor (tag = start_tag; tag \u003c stop_tag; tag++)\nmm/alloc_tag.c:1148:\t\talloc_tag_trace_toggle(tag, false);\nmm/alloc_tag.c-1149-}\n"
}

gemini-3.8-flash

null

null

							input: 28628
							output: 34
							thoughts: 29
						

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

**Investigating `allocinfo_proc_ops` and `/proc/allocinfo`**

Alright, let's dive in. I need to quickly establish the context around `allocinfo_proc_ops`. My immediate concern is whether or not this structure and its associated functionality are conditionalized in any way. Are there any preprocessor macros or configuration options that could disable it, leaving me with a partial implementation or, worse, a situation where its assumptions are no longer valid? I need to be aware of any scenarios where its availability might be platform-specific or kernel version dependent.

Beyond conditional compilation, I also need to understand how the `/proc/allocinfo` entry is actually brought into existence. I want to trace the code path that leads to its creation, likely involving `proc_create` or a similar function call. This will help me figure out who's responsible for managing the lifecycle of this interface, especially any necessary initialization or cleanup. Is it something that's permanently resident, or does it get dynamically created and destroyed? I also have to consider who has the necessary permissions to access this data - root, a specific group, or user?

{
  "Expression": "allocinfo_proc_ops",
  "PathPrefixes": [
    "mm/alloc_tag.c"
  ]
}

{
  "Output": "mm/alloc_tag.c=576=static long allocinfo_compat_ioctl(struct file *file, unsigned int cmd,\n--\nmm/alloc_tag.c-582-\nmm/alloc_tag.c:583:static const struct proc_ops allocinfo_proc_ops = {\nmm/alloc_tag.c-584-\t.proc_open\t\t= allocinfo_open,\n--\nmm/alloc_tag.c=1467=static int __init alloc_tag_init(void)\n--\nmm/alloc_tag.c-1489-\nmm/alloc_tag.c:1490:\tif (!proc_create(ALLOCINFO_FILE_NAME, 0400, NULL, \u0026allocinfo_proc_ops)) {\nmm/alloc_tag.c-1491-\t\tpr_err(\"Failed to create %s file\\n\", ALLOCINFO_FILE_NAME);\n"
}

gemini-3.8-flash

null

null

							input: 29182
							output: 35
							thoughts: 78
						

Here's my summary, as I see it:

**Diving into `/proc/allocinfo`**

Okay, so I'm digging into how `/proc/allocinfo` works in the kernel, specifically when `CONFIG_MEM_ALLOC_PROFILING` is enabled. It's automatically created under that configuration, which makes sense. I see that `allocinfo_proc_ops` is the key structure here, with those all-important `proc_ioctl` and `proc_compat_ioctl` functions defined. Now, I'm going to start with a deep dive into `allocinfo_compat_ioctl`. I want to figure out what functionality is implemented there.

{
  "File": "mm/alloc_tag.c",
  "FirstLine": 565,
  "LineCount": 25
}

{
  "Contents": " 565:\t\t\tret = allocinfo_ioctl_toggle_trace(file-\u003eprivate_data, arg);\n 566:\t\t\tbreak;\n 567:\t\tdefault:\n 568:\t\t\tret = -ENOIOCTLCMD;\n 569:\t\t\tbreak;\n 570:\t\t}\n 571:\t\n 572:\t\treturn ret;\n 573:\t}\n 574:\t\n 575:\t#ifdef CONFIG_COMPAT\n 576:\tstatic long allocinfo_compat_ioctl(struct file *file, unsigned int cmd,\n 577:\t\t\t\t\t   unsigned long arg)\n 578:\t{\n 579:\t\treturn allocinfo_ioctl(file, cmd, (unsigned long)compat_ptr(arg));\n 580:\t}\n 581:\t#endif\n 582:\t\n 583:\tstatic const struct proc_ops allocinfo_proc_ops = {\n 584:\t\t.proc_open\t\t= allocinfo_open,\n 585:\t\t.proc_read_iter\t\t= seq_read_iter,\n 586:\t\t.proc_lseek\t\t= seq_lseek,\n 587:\t\t.proc_release\t\t= allocinfo_release,\n 588:\t\t.proc_ioctl\t\t= allocinfo_ioctl,\n 589:\t#ifdef CONFIG_COMPAT\n"
}

gemini-3.8-flash

null

null

							input: 29797
							output: 34
							thoughts: 356
						

**Analyzing Memory Allocation Profiling Configuration**

Okay, let's dive into this `CONFIG_MEM_ALLOC_PROFILING` configuration option. First, I need to understand its dependencies. Looking at the Kconfig snippet, it's clear that it hinges on `MMU`, `PROC_FS`, and then selects `CODE_TAGGING`, `PAGE_EXTENSION`, and `SLAB_OBJ_EXT`. Good, that's straightforward. I also see that `CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT` is set to 'y'.

Now, a critical point pops up: what's the relationship with tracing? I need to consider `CONFIG_TRACING` and `CONFIG_EVENT_TRACING`. I suspect there's a dependency there, especially since we're dealing with profiling memory allocations. Let's see if the trace events related to allocation tagging in `trace/events/alloc_tag.h` require `CONFIG_TRACING`. I should probably grep for `TRACE_EVENT` in the Kconfig or Makefiles to see how that macro works. I know that tracepoints generally depend on `CONFIG_TRACEPOINTS`, or `CONFIG_TRACING` and `CONFIG_EVENT_TRACING`.

Ah, here's the tricky part. If `CONFIG_TRACING` isn't enabled, what does the `TRACE_EVENT` macro actually *do*? I'll check `include/linux/tracepoint.h`. Looks like if `CONFIG_TRACEPOINTS` isn't defined, `TRACE_EVENT` just creates empty stub functions. So, even if the tracepoints are *defined*, they won't actually record anything unless `CONFIG_TRACING` or `CONFIG_EVENT_TRACING` is enabled, which routes events to ftrace or tracefs. Alright, I'll go back to `include/linux/tracepoint.h` to confirm the behavior. And, while I'm at it, I'll grep for `TRACEPOINTS` in Kconfig to get a complete picture.

{
  "Expression": "config TRACEPOINTS",
  "PathPrefixes": [
    "init/",
    "kernel/trace/"
  ]
}

{
  "Output": "init/Kconfig=2292=config BINDGEN_VERSION_TEXT\n--\ninit/Kconfig-2300-#\ninit/Kconfig:2301:config TRACEPOINTS\ninit/Kconfig-2302-\tbool\n"
}

gemini-3.8-flash

null

null

							input: 30694
							output: 35
							thoughts: 24
						

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

**Kernel Tracing Configuration - A Quick Check**

Right, let's get down to brass tacks. I'm thinking, before I dive too deep into the issue, a fundamental sanity check is in order. My instinct says to start with the obvious: I need to verify how tracing is configured. My go-to for this kind of low-level configuration is the `Kconfig` files, specifically within the `kernel/trace/` directory. I'm immediately homing in on `kernel/trace/Kconfig`. This is where the magic happens, or doesn't, depending on the current settings.

What I'm really looking for within that file are the crucial flags: `TRACING` and `EVENT_TRACING`. These are the lynchpins, right? If these aren't set, or set incorrectly, then the rest of my investigation is going to be a wild goose chase. So, I need to confirm whether tracing, in general, is enabled, and then I'll look deeper at event tracing specifically. Quick scan of `Kconfig` should quickly confirm these settings. It's the most efficient way to get a bird's-eye view of tracing at this stage. Saves time, prevents misdirection, and allows me to focus on the root of the issue with certainty.

{
  "Expression": "config (TRACING|EVENT_TRACING)",
  "PathPrefixes": [
    "kernel/trace/"
  ]
}

{
  "Output": "kernel/trace/Kconfig=144=config RING_BUFFER\n--\nkernel/trace/Kconfig-148-\nkernel/trace/Kconfig:149:config EVENT_TRACING\nkernel/trace/Kconfig-150-\tselect CONTEXT_SWITCH_TRACER\n--\nkernel/trace/Kconfig=163=config PREEMPTIRQ_TRACEPOINTS\n--\nkernel/trace/Kconfig-178-\nkernel/trace/Kconfig:179:config TRACING\nkernel/trace/Kconfig-180-\tbool\n--\nkernel/trace/Kconfig=190=config GENERIC_TRACER\n--\nkernel/trace/Kconfig-197-#\nkernel/trace/Kconfig:198:config TRACING_SUPPORT\nkernel/trace/Kconfig-199-\tbool\n--\nkernel/trace/Kconfig=707=endchoice\nkernel/trace/Kconfig-708-\nkernel/trace/Kconfig:709:config TRACING_BRANCHES\nkernel/trace/Kconfig-710-\tbool\n--\nkernel/trace/Kconfig=907=config FTRACE_MCOUNT_USE_RECORDMCOUNT\n--\nkernel/trace/Kconfig-913-\nkernel/trace/Kconfig:914:config TRACING_MAP\nkernel/trace/Kconfig-915-\tbool\n"
}

gemini-3.8-flash

null

null

							input: 31387
							output: 242
							thoughts: 3015
						

**Analysis of Memory Allocation Profiling and Tracing for Fuzzing**

Alright, let's break this down. My primary focus is on how best to target this new memory allocation profiling and tracing feature for effective fuzzing. The key configuration options here are `CONFIG_MEM_ALLOC_PROFILING`, which enables the core profiling functionality, and `CONFIG_TRACING` (or `CONFIG_EVENT_TRACING`), which is required for the actual trace events to be active. I also need to keep `CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT` in mind; it dictates whether profiling is enabled at boot, which seems to default to enabled if `MEM_ALLOC_PROFILING` is set. Given this, `MEM_ALLOC_PROFILING` and `TRACING` are my foundational configs for this fuzzing effort, while `MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT` is a secondary consideration for testing various states.

Now, let's get into the *FocusSymbols* aspect, keeping in mind that I need to avoid ubiquitous lifecycle hot-paths, and concentrate on specific feature logic and entrypoints.

The changes primarily reside in `mm/alloc_tag.c`, which includes the new `/proc/allocinfo` ioctl handler. Within that, I need to identify the key functions that implement this new tracing feature:

*   `allocinfo_ioctl` handles `/proc/allocinfo` ioctls, *including* the `ALLOCINFO_IOC_TOGGLE_TRACE` that is newly introduced and needs special attention.
*   `allocinfo_ioctl_toggle_trace` is the function that implements the toggle trace functionality itself.
*   `alloc_tag_trace_toggle` is the helper that toggles the trace state, likely through the `static_branch` mechanism.
*   `__alloc_tag_trace_hit`, `alloc_tag_trace_mem_alloc`, and `alloc_tag_trace_mem_free` are tracepoint-specific functions that are called when *tracing* is enabled via the `alloc_tag_trace_key`. These are *not* ubiquitous because the `alloc_tag_trace_key` is disabled by default, and only enabled by the user via `/proc/allocinfo`. These are excellent targets, since they are very specific to this new feature.

I'm deliberately *excluding* functions like `__pgalloc_tag_add`, `__pgalloc_tag_sub`, `__alloc_tagging_slab_alloc_hook`, and `__alloc_tagging_slab_free_hook`. These are clearly *ubiquitous* lifecycle hooks, and they would contaminate the fuzzing effort.

I've confirmed that `MEM_ALLOC_PROFILING` requires `PROC_FS` and `MMU`, which are standard configurations. I've also verified that `MEM_ALLOC_PROFILING` sets `MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT` to 'y' by default. And that `TRACING` is critical for events.

From a fuzzing perspective, this code is *definitely* worth targeting. I'm looking at testing the new `/proc/allocinfo` ioctl and its interaction with the static branch toggling and memory allocation and deallocation events. The code is *reachable* through a user-space ioctl and memory allocation, which is standard in any environment. I'm thinking of testing *concurrent ioctls*, *static branch manipulation*, *filter validation*, and *potential race conditions* in the tracepoint calls.

My final decision is to concentrate on the following symbols:

*   `allocinfo_ioctl`
*   `allocinfo_ioctl_toggle_trace`
*   `alloc_tag_trace_toggle`
*   `__alloc_tag_trace_hit`
*   `alloc_tag_trace_mem_alloc`
*   `alloc_tag_trace_mem_free`

And for the configs:

*   `MEM_ALLOC_PROFILING`
*   `TRACING`

I'm confident in this setup; I'm setting the results.

{
  "EnableConfigs": [
    "MEM_ALLOC_PROFILING",
    "TRACING"
  ],
  "FocusSymbols": [
    "allocinfo_ioctl",
    "allocinfo_ioctl_toggle_trace",
    "alloc_tag_trace_toggle",
    "__alloc_tag_trace_hit",
    "alloc_tag_trace_mem_alloc",
    "alloc_tag_trace_mem_free"
  ],
  "Reasoning": "The patch introduces memory allocation profiling trace events (alloc_tag_hit, alloc_tag_mem_alloced, alloc_tag_mem_freed) and exposes a new ioctl command ALLOCINFO_IOC_TOGGLE_TRACE on /proc/allocinfo to dynamically enable/disable tracing per allocation tag. It introduces dynamic static branch manipulation, atomic flag updates, input filter validation, and hooks into core alloc/free paths across SLUB, page allocator, and percpu subsystems. This code is reachable from userspace via /proc/allocinfo ioctls and warrants fuzzing for concurrency issues, filter parsing, and static branch toggling behavior.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "MEM_ALLOC_PROFILING",
    "TRACING"
  ],
  "FocusSymbols": [
    "allocinfo_ioctl",
    "allocinfo_ioctl_toggle_trace",
    "alloc_tag_trace_toggle",
    "__alloc_tag_trace_hit",
    "alloc_tag_trace_mem_alloc",
    "alloc_tag_trace_mem_free"
  ],
  "Reasoning": "The patch introduces memory allocation profiling trace events (alloc_tag_hit, alloc_tag_mem_alloced, alloc_tag_mem_freed) and exposes a new ioctl command ALLOCINFO_IOC_TOGGLE_TRACE on /proc/allocinfo to dynamically enable/disable tracing per allocation tag. It introduces dynamic static branch manipulation, atomic flag updates, input filter validation, and hooks into core alloc/free paths across SLUB, page allocator, and percpu subsystems. This code is reachable from userspace via /proc/allocinfo ioctls and warrants fuzzing for concurrency issues, filter parsing, and static branch toggling behavior.",
  "WorthFuzzing": true
}

{
  "WorthFuzzing": true
}

null

core

null

{
  "KMSANReasoning": "The patch series adds tracepoints (alloc_tag_hit, alloc_tag_mem_alloced, alloc_tag_mem_freed) and a new ioctl (ALLOCINFO_IOC_TOGGLE_TRACE) to toggle allocation profiling tracing.\n\nKMSAN vs KASAN applicability analysis:\n1. Kernel-to-userspace data leaks: The patch modifies UAPI struct allocinfo_counter by replacing 1 byte of padding with a trace_on field. In allocinfo_ioctl_get_next(), the output struct is zero-initialized with memset(\u0026params, 0, sizeof(params)) before populating fields. In allocinfo_ioctl_get_at(), the struct is zero-initialized and copied from user before fields are updated. The new trace_on field is explicitly assigned in allocinfo_to_params(). The new ioctl ALLOCINFO_IOC_TOGGLE_TRACE is _IOW (input only) and does not copy any data to userspace.\n2. Uninitialized variable reads / conditional branching: Stack variables such as counters in matches_filter() and allocinfo_ioctl_toggle_trace() are only read after being explicitly fetched (guarded by fetched_counters).\n3. Data structures: The codetag flags field is changed to atomic_t and statically initialized using ATOMIC_INIT(0).\n4. Memory allocation/freeing logic: The hook modifications in page_alloc, SLUB, and percpu only pass pointers to tracepoint callbacks and do not alter memory initialization, sizing, or buffer access.\n\nAny potential bugs introduced by this patch (e.g., concurrency races on static keys or atomic counters, locking interactions) are within the scope of LOCKDEP, KASAN, or standard kernel debug facilities. No uninitialized memory usage or info-leaks are introduced, so a dedicated KMSAN run is not needed.",
  "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 9c8e1162b5ec6958cde9fbf00162f239ce0066a8
Author: syz-cluster <triage@syzkaller.com>
Date:   Wed Oct 7 22:58:48 2026 +0000

    syz-cluster: applied patch under review

diff --git a/Documentation/mm/allocation-profiling.rst b/Documentation/mm/allocation-profiling.rst
index b11ea77c06736..63b6684663426 100644
--- a/Documentation/mm/allocation-profiling.rst
+++ b/Documentation/mm/allocation-profiling.rst
@@ -129,6 +129,79 @@ To do so:
 - Then, use the following form for your allocations:
   alloc_hooks_tag(ht->your_saved_tag, kmalloc_noprof(...))
 
+Tracing
+=======
+
+Three trace events are available under `/sys/kernel/tracing/events/alloc_tag` to
+expose the full call stack and the lifetime of individual allocations:
+
+- `alloc_tag_hit`: Fired at the exact call site, before the allocation happens.
+  Can be used to capture the call stack of the caller.
+
+- `alloc_tag_mem_alloced`: Fired once the allocation succeeds. Carries the `ptr`,
+  `tag` and `bytes` for each allocation.
+
+- `alloc_tag_mem_freed`: Fired before memory is freed. Carries the same
+  `ptr`, `tag` and `bytes` as the matching alloc event.
+
+`ptr` identifies the allocation, and its meaning depends on the allocator:
+
+- slab and percpu: the address of the object's `codetag_ref`
+- page allocator: the `struct page` pointer of the head page
+
+Events are only emitted for tags that have tracing turned on and while profiling
+is enabled. When no tag is traced, the hooks are behind a static branch.
+
+Enabling Tracing
+----------------
+
+Tracing is toggled on and off per tag with the `ALLOCINFO_IOC_TOGGLE_TRACE`
+ioctl on `/proc/allocinfo`. It takes the same filter as used by
+`ALLOCINFO_IOC_GET_AT`; an empty mask selects all tags. Size limits in the
+filter are checked once, against the tag's size at the time of the call. Tags
+already in the requested state are skipped and a -ENOENT is returned if no
+tag matched.
+
+Tracing is turned off for a module's tags when the module is unloaded.
+
+Memory allocated before a tag was enabled has no alloc event but will still
+produce a free event. Likewise, memory alive when tag is disabled will not
+produce a free event. Tools should expect unmatched frees after enabling and
+missing frees after disabling.
+
+Correlating the events
+----------------------
+
+`alloc_tag_hit` and `alloc_tag_mem_alloced` come from different points in the
+call stack, so they have to be stitched together by the user consuming the
+events. Here's a typical flow:
+
+1. On `alloc_tag_hit`: Capture the stack trace and cache it keyed by `(pid, tag)`.
+
+2. On `alloc_tag_mem_alloced`: Look up the cached stack trace by `(pid, tag)`,
+   then create an active allocation record keyed by `ptr` that holds the stack
+   trace and `bytes`.
+
+3. On `alloc_tag_mem_freed`: Look up the record by `ptr` and retire it.
+
+Limitations
+-----------
+
+- For the page allocator, events are generated for the original allocation and
+  the free only. If the tag reference is split or moved to another folio in
+  between, no event is generated for that. As a result:
+
+  - a free event may carry a `ptr` that never appeared in an alloc event;
+  - `bytes` in a free event may be smaller than in the matching alloc event.
+
+  Tools should correlate on `ptr` but must not assume that freed bytes equal
+  allocated bytes, or that every free has a matching alloc.
+
+- Freeing a non-compound high-order page with `__free_pages()` while another CPU
+  holds a reference frees the tail pages immediately and the head page later when
+  the reference is dropped. The free event is emitted at the second point and
+  reports `PAGE_SIZE` rather than the full size.
+
 Notes
 =====
 
diff --git a/MAINTAINERS b/MAINTAINERS
index 5c38da7090db8..751ce786a3788 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17100,6 +17100,7 @@ S:	Maintained
 F:	Documentation/mm/allocation-profiling.rst
 F:	include/linux/alloc_tag.h
 F:	include/linux/pgalloc_tag.h
+F:	include/trace/events/alloc_tag.h
 F:	include/uapi/linux/alloc_tag.h
 F:	mm/alloc_tag.c
 F:	tools/testing/selftests/alloc_tag/
diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
index 7f2d80a597924..94697b28053ad 100644
--- a/include/linux/alloc_tag.h
+++ b/include/linux/alloc_tag.h
@@ -128,12 +128,60 @@ DECLARE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag);
 DECLARE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
 			mem_alloc_profiling_key);
 
+DECLARE_STATIC_KEY_FALSE(alloc_tag_trace_key);
+
 static inline bool mem_alloc_profiling_enabled(void)
 {
 	return static_branch_maybe(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
 				   &mem_alloc_profiling_key);
 }
 
+static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag)
+{
+	atomic_or(CODETAG_FLAG_INACCURATE, &tag->ct.flags);
+}
+
+static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag)
+{
+	return !!(atomic_read(&tag->ct.flags) & CODETAG_FLAG_INACCURATE);
+}
+
+static inline void alloc_tag_set_traced(struct alloc_tag *tag)
+{
+	atomic_or(CODETAG_FLAG_TRACE_ON, &tag->ct.flags);
+}
+
+static inline void alloc_tag_clear_traced(struct alloc_tag *tag)
+{
+	atomic_andnot(CODETAG_FLAG_TRACE_ON, &tag->ct.flags);
+}
+
+static inline bool alloc_tag_is_traced(const struct alloc_tag *tag)
+{
+	return !!(atomic_read(&tag->ct.flags) & CODETAG_FLAG_TRACE_ON);
+}
+
+static inline bool alloc_tag_trace_enabled(const struct alloc_tag *tag)
+{
+	if (static_branch_unlikely(&alloc_tag_trace_key))
+		return tag && alloc_tag_is_traced(tag);
+	return false;
+}
+
+void alloc_tag_trace_mem_alloc(const void *ptr, struct alloc_tag *tag,
+			       size_t bytes);
+
+void alloc_tag_trace_mem_free(const void *ptr, struct alloc_tag *tag,
+			      size_t bytes);
+
+void __alloc_tag_trace_hit(struct alloc_tag *tag);
+
+static __always_inline void alloc_tag_trace_hit(struct alloc_tag *tag)
+{
+	if (alloc_tag_trace_enabled(tag))
+		__alloc_tag_trace_hit(tag);
+}
+
 bool mem_alloc_profiling_permanently_disabled(void);
 
 static inline struct alloc_tag_counters alloc_tag_read(struct alloc_tag *tag)
@@ -198,13 +246,19 @@ static inline bool alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *t
 	return true;
 }
 
-static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes)
+static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes,
+				 const void *ptr)
 {
-	if (likely(alloc_tag_ref_set(ref, tag)))
+	if (likely(alloc_tag_ref_set(ref, tag))) {
 		this_cpu_add(tag->counters->bytes, bytes);
+
+		if (alloc_tag_trace_enabled(tag))
+			/* Trace successful allocs with their unique ptr */
+			alloc_tag_trace_mem_alloc(ptr, tag, bytes);
+	}
 }
 
-static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes)
+static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes, const void *ptr)
 {
 	struct alloc_tag *tag;
 
@@ -222,17 +276,11 @@ static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes)
 	this_cpu_sub(tag->counters->bytes, bytes);
 	this_cpu_dec(tag->counters->calls);
 
-	ref->ct = NULL;
-}
-
-static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag)
-{
-	tag->ct.flags |= CODETAG_FLAG_INACCURATE;
-}
+	if (alloc_tag_trace_enabled(tag))
+		/* Trace frees with their unique ptr */
+		alloc_tag_trace_mem_free(ptr, tag, bytes);
 
-static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag)
-{
-	return !!(tag->ct.flags & CODETAG_FLAG_INACCURATE);
+	ref->ct = NULL;
 }
 
 #define alloc_tag_record(p)	((p) = current->alloc_tag)
@@ -243,25 +291,29 @@ static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag)
 static inline bool mem_alloc_profiling_enabled(void) { return false; }
 static inline bool mem_alloc_profiling_permanently_disabled(void) { return true; }
 static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag,
-				 size_t bytes) {}
-static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes) {}
+				 size_t bytes, const void *ptr) {}
+static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes,
+				 const void *ptr) {}
 static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag) {}
 static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag) { return false; }
+#define alloc_tag_trace_hit(_tag)	/* NOOP */
 #define alloc_tag_record(p)	do {} while (0)
 
 #endif /* CONFIG_MEM_ALLOC_PROFILING */
 
-#define alloc_hooks_tag(_tag, _do_alloc)				\
-({									\
-	typeof(_do_alloc) _res;						\
-	if (mem_alloc_profiling_enabled()) {				\
-		struct alloc_tag * __maybe_unused _old;			\
-		_old = alloc_tag_save(_tag);				\
-		_res = _do_alloc;					\
-		alloc_tag_restore(_tag, _old);				\
-	} else								\
-		_res = _do_alloc;					\
-	_res;								\
+#define alloc_hooks_tag(_tag, _do_alloc)					\
+({										\
+	typeof(_do_alloc) _res;							\
+	if (mem_alloc_profiling_enabled()) {					\
+		struct alloc_tag * __maybe_unused _old;				\
+		/* Fired here to cleanly capture the caller's stack trace */	\
+		alloc_tag_trace_hit(_tag);					\
+		_old = alloc_tag_save(_tag);					\
+		_res = _do_alloc;						\
+		alloc_tag_restore(_tag, _old);					\
+	} else									\
+		_res = _do_alloc;						\
+	_res;									\
 })
 
 #define alloc_hooks(_do_alloc)						\
diff --git a/include/linux/codetag.h b/include/linux/codetag.h
index a25a085c2df19..f728295d50c05 100644
--- a/include/linux/codetag.h
+++ b/include/linux/codetag.h
@@ -18,6 +18,7 @@ struct module;
 
 /* codetag flags */
 #define CODETAG_FLAG_INACCURATE	(1 << 0)
+#define CODETAG_FLAG_TRACE_ON	(1 << 1)
 
 /*
  * An instance of this structure is created in a special ELF section at every
@@ -25,7 +26,7 @@ struct module;
  * an array of these.
  */
 struct codetag {
-	unsigned int flags;
+	atomic_t flags;
 	unsigned int lineno;
 	const char *modname;
 	const char *function;
@@ -71,7 +72,7 @@ struct codetag_iterator {
 	.function	= __func__,			\
 	.filename	= __FILE__,			\
 	.lineno		= __LINE__,			\
-	.flags		= 0,				\
+	.flags		= ATOMIC_INIT(0),		\
 }
 
 void codetag_lock_module_list(struct codetag_type *cttype);
diff --git a/include/trace/events/alloc_tag.h b/include/trace/events/alloc_tag.h
new file mode 100644
index 0000000000000..b79efb7dd25c6
--- /dev/null
+++ b/include/trace/events/alloc_tag.h
@@ -0,0 +1,122 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM alloc_tag
+
+#if !defined(_TRACE_ALLOC_TAG_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_ALLOC_TAG_H
+
+#include <linux/tracepoint.h>
+
+/*
+ * alloc_tag_hit is generated at the exact allocation call site and can be
+ * used to capture a clean stack trace.
+ *
+ * To link this stack trace to the actual allocated memory chunk, tools must
+ * correlate this event with the resulting alloc_tag_mem_alloced event. Since
+ * multiple threads can hit the same tag simultaneously, tools must match BOTH
+ * the `tag` field and the implicitly recorded PID provided by the core
+ * tracing subsystem.
+ */
+TRACE_EVENT(alloc_tag_hit,
+	TP_PROTO(struct alloc_tag *tag),
+
+	TP_ARGS(tag),
+
+	TP_STRUCT__entry(__field(struct alloc_tag *, tag)
+			 __string(modname, tag->ct.modname ? tag->ct.modname : "NONE")
+			 __string(filename, tag->ct.filename)
+			 __string(function, tag->ct.function)
+			 __field(unsigned int, lineno)
+	),
+
+	TP_fast_assign(__entry->tag = tag;
+		       __assign_str(modname);
+		       __assign_str(filename);
+		       __assign_str(function);
+		       __entry->lineno = tag->ct.lineno;
+	),
+
+	TP_printk("tag %p, module: %s, filename: %s, function %s, lineno %u",
+		  __entry->tag,
+		  __get_str(modname),
+		  __get_str(filename),
+		  __get_str(function),
+		  __entry->lineno
+	)
+);
+
+/*
+ * alloc_tag_mem_alloced is generated after memory is successfully allocated.
+ * It captures the exact byte size.
+ *
+ * The `ptr` value identifies the memory chunk for tracking its lifecycle
+ * (e.g., matching it with alloc_tag_mem_freed).
+ * - slab and percpu allocators: address of the object's codetag_ref
+ * - page allocator: the head struct page of the allocation
+ *
+ * Because the kernel isolates active allocations within the task struct
+ * (current->alloc_tag), this event will always share the same implicit PID as
+ * its corresponding alloc_tag_hit event. Tools should use the combination
+ * PID + `tag` to correlate them.
+ */
+TRACE_EVENT(alloc_tag_mem_alloced,
+	TP_PROTO(const void *ptr, struct alloc_tag *tag, size_t bytes),
+
+	TP_ARGS(ptr, tag, bytes),
+
+	TP_STRUCT__entry(__field(const void *, ptr)
+			 __field(struct alloc_tag *, tag)
+			 __field(size_t, bytes)
+	),
+
+	TP_fast_assign(__entry->ptr = ptr;
+		       __entry->tag = tag;
+		       __entry->bytes = bytes;
+	),
+
+	TP_printk("ptr %p, tag %p, bytes %zu",
+		  __entry->ptr,
+		  __entry->tag,
+		  __entry->bytes
+	)
+);
+
+/*
+ * alloc_tag_mem_freed event is generated immediately before memory is
+ * freed. The `ptr` value matches the one emitted during allocation,
+ * allowing tools to match it to its corresponding allocation and
+ * call stack.
+ *
+ * Page allocator caveat: Pages can be split or moved to another folio
+ * after the alloc event with no new events generated for that. As a
+ * result, a free event may carry a `ptr` that never appeared in an
+ * alloc event, and the `bytes` may be smaller than in the matching
+ * alloc event. Tools must not assume alloc bytes == free bytes, nor
+ * that every free has a matching alloc.
+ */
+TRACE_EVENT(alloc_tag_mem_freed,
+	TP_PROTO(const void *ptr, struct alloc_tag *tag, size_t bytes),
+
+	TP_ARGS(ptr, tag, bytes),
+
+	TP_STRUCT__entry(__field(const void *, ptr)
+			 __field(struct alloc_tag *, tag)
+			 __field(size_t, bytes)
+	),
+
+	TP_fast_assign(__entry->ptr = ptr;
+		       __entry->tag = tag;
+		       __entry->bytes = bytes;
+	),
+
+	TP_printk("ptr %p, tag %p, bytes %zu",
+		  __entry->ptr,
+		  __entry->tag,
+		  __entry->bytes
+	)
+);
+
+#endif /* _TRACE_ALLOC_TAG_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/include/uapi/linux/alloc_tag.h b/include/uapi/linux/alloc_tag.h
index 7d4618bea0434..a96054ac22376 100644
--- a/include/uapi/linux/alloc_tag.h
+++ b/include/uapi/linux/alloc_tag.h
@@ -38,7 +38,8 @@ struct allocinfo_counter {
 	__u64 bytes;
 	__u64 calls;
 	__u8 accurate;
-	__u8 pad[7];
+	__u8 trace_on;
+	__u8 pad[6];
 } __attribute__((aligned(8)));
 
 struct allocinfo_tag_data {
@@ -54,7 +55,8 @@ enum {
 	ALLOCINFO_FILTER_INACCURATE,
 	ALLOCINFO_FILTER_MIN_SIZE,
 	ALLOCINFO_FILTER_MAX_SIZE,
-	__ALLOCINFO_FILTER_LAST = ALLOCINFO_FILTER_MAX_SIZE
+	ALLOCINFO_FILTER_TRACE_ON,
+	__ALLOCINFO_FILTER_LAST = ALLOCINFO_FILTER_TRACE_ON
 };
 
 #define ALLOCINFO_FILTER_MASK_MODNAME		(1 << ALLOCINFO_FILTER_MODNAME)
@@ -64,6 +66,7 @@ enum {
 #define ALLOCINFO_FILTER_MASK_INACCURATE	(1 << ALLOCINFO_FILTER_INACCURATE)
 #define ALLOCINFO_FILTER_MASK_MIN_SIZE		(1 << ALLOCINFO_FILTER_MIN_SIZE)
 #define ALLOCINFO_FILTER_MASK_MAX_SIZE		(1 << ALLOCINFO_FILTER_MAX_SIZE)
+#define ALLOCINFO_FILTER_MASK_TRACE_ON		(1 << ALLOCINFO_FILTER_TRACE_ON)
 
 #define ALLOCINFO_FILTER_MASKS \
 	((1 << (__ALLOCINFO_FILTER_LAST + 1)) - 1)
@@ -75,6 +78,7 @@ struct allocinfo_filter {
 	__u64 max_size;
 	/* filter criteria only; see allocinfo_counter.accurate for actual accuracy */
 	__u64 inaccurate;
+	__u64 tracing;
 };
 
 struct allocinfo_get_at {
@@ -85,9 +89,20 @@ struct allocinfo_get_at {
 	struct allocinfo_tag_data data;
 };
 
+struct allocinfo_toggle_traces {
+	/* inputs */
+	/*
+	 * Tags matching the filter are toggled; an empty mask selects all tags.
+	 * Size criteria are checked once, against the tag's size at call time.
+	 */
+	struct allocinfo_filter filter;
+	__u64 enable;
+};
+
 #define _ALLOCINFO_IOC_CONTENT_ID	0
 #define _ALLOCINFO_IOC_GET_AT		1
 #define _ALLOCINFO_IOC_GET_NEXT		2
+#define _ALLOCINFO_IOC_TOGGLE_TRACE	3
 
 #define ALLOCINFO_IOC_BASE		0xA6
 #define ALLOCINFO_IOC_CONTENT_ID	_IOR(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_CONTENT_ID,	\
@@ -96,5 +111,7 @@ struct allocinfo_get_at {
 					      struct allocinfo_get_at)
 #define ALLOCINFO_IOC_GET_NEXT		_IOR(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_GET_NEXT,	\
 					     struct allocinfo_tag_data)
+#define ALLOCINFO_IOC_TOGGLE_TRACE	_IOW(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_TOGGLE_TRACE,	\
+					    struct allocinfo_toggle_traces)
 
 #endif /* _UAPI_ALLOC_TAG_H */
diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
index 82e2c3448dcf2..8e63f347657b6 100644
--- a/mm/alloc_tag.c
+++ b/mm/alloc_tag.c
@@ -18,6 +18,9 @@
 #include <linux/kmemleak.h>
 #include <uapi/linux/alloc_tag.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/alloc_tag.h>
+
 #include "internal.h"
 #include "page_alloc.h"
 
@@ -54,6 +57,18 @@ EXPORT_SYMBOL(mem_alloc_profiling_key);
 
 DEFINE_STATIC_KEY_FALSE(mem_profiling_compressed);
 
+DEFINE_STATIC_KEY_FALSE(alloc_tag_trace_key);
+EXPORT_SYMBOL(alloc_tag_trace_key);
+
+static atomic_t alloc_tag_trace_cnt = ATOMIC_INIT(0);
+
+/*
+ * As `codetag_lock_module_list` is a read lock, we need an additional mutex
+ * to protect against the race conditions involved in the alloc tag trace
+ * toggle path.
+ */
+static DEFINE_MUTEX(alloc_tag_trace_mutex);
+
 struct alloc_tag_kernel_section kernel_tags = { NULL, 0 };
 unsigned long alloc_tag_ref_mask;
 int alloc_tag_ref_offs;
@@ -235,6 +250,7 @@ static void allocinfo_to_params(struct codetag *ct,
 	data->counter.bytes = counters->bytes;
 	data->counter.calls = counters->calls;
 	data->counter.accurate = !alloc_tag_is_inaccurate(ct_to_alloc_tag(ct));
+	data->counter.trace_on = alloc_tag_is_traced(ct_to_alloc_tag(ct));
 }
 
 /*
@@ -290,7 +306,7 @@ static bool matches_filter(struct codetag *ct, struct allocinfo_filter *filter,
 		return false;
 
 	if (filter->mask & ALLOCINFO_FILTER_MASK_INACCURATE) {
-		inaccurate = !!(ct->flags & CODETAG_FLAG_INACCURATE);
+		inaccurate = alloc_tag_is_inaccurate(ct_to_alloc_tag(ct));
 		if (inaccurate != !!(filter->inaccurate))
 			return false;
 	}
@@ -308,6 +324,30 @@ static bool matches_filter(struct codetag *ct, struct allocinfo_filter *filter,
 			return false;
 	}
 
+	if (filter->mask & ALLOCINFO_FILTER_MASK_TRACE_ON) {
+		bool tracing = alloc_tag_is_traced(ct_to_alloc_tag(ct));
+
+		if (tracing != !!(filter->tracing))
+			return false;
+	}
+
+	return true;
+}
+
+/*
+ * Checks that a user supplied filter only uses known fields and that its size
+ * range, if any, is not inverted.
+ */
+static bool allocinfo_filter_valid(const struct allocinfo_filter *filter)
+{
+	if (filter->mask & ~ALLOCINFO_FILTER_MASKS)
+		return false;
+
+	if ((filter->mask & ALLOCINFO_FILTER_MASK_MIN_SIZE) &&
+	    (filter->mask & ALLOCINFO_FILTER_MASK_MAX_SIZE) &&
+	    filter->min_size > filter->max_size)
+		return false;
+
 	return true;
 }
 
@@ -327,12 +367,7 @@ static int allocinfo_ioctl_get_at(struct seq_file *m, void __user *arg)
 	if (copy_from_user(&params, arg, sizeof(params)))
 		return -EFAULT;
 
-	if (params.filter.mask & ~ALLOCINFO_FILTER_MASKS)
-		return -EINVAL;
-
-	if ((params.filter.mask & ALLOCINFO_FILTER_MASK_MIN_SIZE) &&
-	    (params.filter.mask & ALLOCINFO_FILTER_MASK_MAX_SIZE) &&
-	    params.filter.min_size > params.filter.max_size)
+	if (!allocinfo_filter_valid(&params.filter))
 		return -EINVAL;
 
 	priv = m->private;
@@ -437,6 +472,75 @@ static int allocinfo_ioctl_get_next(struct seq_file *m, void __user *arg)
 	return ret;
 }
 
+static void alloc_tag_trace_toggle(struct alloc_tag *tag, bool enable)
+{
+	if (enable) {
+		if (alloc_tag_is_traced(tag))
+			return;
+
+		alloc_tag_set_traced(tag);
+		if (atomic_fetch_inc(&alloc_tag_trace_cnt) == 0)
+			static_branch_enable(&alloc_tag_trace_key);
+	} else {
+		if (!alloc_tag_is_traced(tag))
+			return;
+
+		alloc_tag_clear_traced(tag);
+		if (atomic_dec_and_test(&alloc_tag_trace_cnt))
+			static_branch_disable(&alloc_tag_trace_key);
+	}
+}
+
+/*
+ * Toggles tracing on every allocation tag that matches the user supplied
+ * filter. An empty filter mask selects all tags, same as for
+ * ALLOCINFO_IOC_GET_AT. Tags already in the requested state are not an error.
+ */
+static int allocinfo_ioctl_toggle_trace(struct seq_file *m, void __user *arg)
+{
+	struct allocinfo_toggle_traces params;
+	struct codetag_iterator iter;
+	struct codetag *ct;
+	struct alloc_tag_counters counters;
+	bool fetched_counters;
+	int matches = 0, ret;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (copy_from_user(&params, arg, sizeof(params)))
+		return -EFAULT;
+
+	if (!allocinfo_filter_valid(&params.filter))
+		return -EINVAL;
+
+	codetag_lock_module_list(alloc_tag_cttype);
+
+	iter = codetag_get_ct_iter(alloc_tag_cttype);
+
+	/* Toggle tracing on all codetags that match */
+	while ((ct = codetag_next_ct(&iter))) {
+		fetched_counters = false;
+		if (matches_filter(ct, &params.filter, &counters, &fetched_counters)) {
+			matches++;
+
+			mutex_lock(&alloc_tag_trace_mutex);
+			alloc_tag_trace_toggle(ct_to_alloc_tag(ct), !!params.enable);
+			mutex_unlock(&alloc_tag_trace_mutex);
+		}
+	}
+
+	if (matches == 0)
+		/* Nothing matched the filter */
+		ret = -ENOENT;
+	else
+		ret = 0;
+
+	codetag_unlock_module_list(alloc_tag_cttype);
+
+	return ret;
+}
+
 /*
  * Entry point ioctl function for /proc/allocinfo routing requests to fetch the
  * layout content ID, seek to a specific tag, or read sequential tags.
@@ -457,6 +561,9 @@ static long allocinfo_ioctl(struct file *file, unsigned int cmd,
 	case ALLOCINFO_IOC_GET_NEXT:
 		ret = allocinfo_ioctl_get_next(file->private_data, arg);
 		break;
+	case ALLOCINFO_IOC_TOGGLE_TRACE:
+		ret = allocinfo_ioctl_toggle_trace(file->private_data, arg);
+		break;
 	default:
 		ret = -ENOIOCTLCMD;
 		break;
@@ -484,6 +591,26 @@ static const struct proc_ops allocinfo_proc_ops = {
 #endif
 };
 
+void __alloc_tag_trace_hit(struct alloc_tag *tag)
+{
+	trace_alloc_tag_hit(tag);
+}
+EXPORT_SYMBOL(__alloc_tag_trace_hit);
+
+void alloc_tag_trace_mem_alloc(const void *ptr, struct alloc_tag *tag,
+			       size_t bytes)
+{
+	trace_alloc_tag_mem_alloced(ptr, tag, bytes);
+}
+EXPORT_SYMBOL(alloc_tag_trace_mem_alloc);
+
+void alloc_tag_trace_mem_free(const void *ptr, struct alloc_tag *tag,
+			      size_t bytes)
+{
+	trace_alloc_tag_mem_freed(ptr, tag, bytes);
+}
+EXPORT_SYMBOL(alloc_tag_trace_mem_free);
+
 size_t alloc_tag_top_users(struct codetag_bytes *tags, size_t count, bool can_sleep)
 {
 	struct codetag_iterator iter;
@@ -1003,6 +1130,24 @@ static int load_module(struct module *mod, struct codetag *start, struct codetag
 	return 0;
 }
 
+static void unload_module(struct module *mod, struct codetag *start, struct codetag *stop)
+{
+	struct alloc_tag *start_tag = ct_to_alloc_tag(start);
+	struct alloc_tag *stop_tag = ct_to_alloc_tag(stop);
+	struct alloc_tag *tag;
+
+	/*
+	 * Turn tracing off for the tags of the module being unloaded. Without
+	 * this, `alloc_tag_trace_cnt` would never reach zero and tracing would
+	 * stay enabled forever.
+	 *
+	 * `alloc_tag_trace_mutex` is not needed here as this code path is
+	 * protected by a `down_write(&cttype->mod_lock)`.
+	 */
+	for (tag = start_tag; tag < stop_tag; tag++)
+		alloc_tag_trace_toggle(tag, false);
+}
+
 static void replace_module(struct module *mod, struct module *new_mod)
 {
 	MA_STATE(mas, &mod_area_mt, 0, module_tags.size);
@@ -1329,6 +1474,7 @@ static int __init alloc_tag_init(void)
 		.alloc_section_mem	= reserve_module_tags,
 		.free_section_mem	= release_module_tags,
 		.module_load		= load_module,
+		.module_unload		= unload_module,
 		.module_replaced	= replace_module,
 #endif
 	};
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7682aecc2c075..5e3e411d4ffe0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1239,7 +1239,7 @@ void __pgalloc_tag_add(struct page *page, struct task_struct *task,
 	union codetag_ref ref;
 
 	if (likely(get_page_tag_ref(page, &ref, &handle))) {
-		alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr);
+		alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr, page);
 		update_page_tag_ref(handle, &ref);
 		put_page_tag_ref(handle);
 	} else {
@@ -1268,7 +1268,7 @@ void __pgalloc_tag_sub(struct page *page, unsigned int nr)
 	union codetag_ref ref;
 
 	if (get_page_tag_ref(page, &ref, &handle)) {
-		alloc_tag_sub(&ref, PAGE_SIZE * nr);
+		alloc_tag_sub(&ref, PAGE_SIZE * nr, page);
 		update_page_tag_ref(handle, &ref);
 		put_page_tag_ref(handle);
 	}
diff --git a/mm/percpu.c b/mm/percpu.c
index 3eff382e565ad..12b6c97d15966 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1695,15 +1695,19 @@ static void pcpu_alloc_tag_alloc_hook(struct pcpu_chunk *chunk, int off,
 				      size_t size)
 {
 	if (mem_alloc_profiling_enabled() && likely(chunk->obj_exts)) {
-		alloc_tag_add(&chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag,
-			      current->alloc_tag, size);
+		union codetag_ref *ref = &chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag;
+
+		alloc_tag_add(ref, current->alloc_tag, size, ref);
 	}
 }
 
 static void pcpu_alloc_tag_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
 {
-	if (mem_alloc_profiling_enabled() && likely(chunk->obj_exts))
-		alloc_tag_sub(&chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag, size);
+	if (mem_alloc_profiling_enabled() && likely(chunk->obj_exts)) {
+		union codetag_ref *ref = &chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag;
+
+		alloc_tag_sub(ref, size, ref);
+	}
 }
 #else
 static void pcpu_alloc_tag_alloc_hook(struct pcpu_chunk *chunk, int off,
diff --git a/mm/slub.c b/mm/slub.c
index 544cff39762c5..a866576ccb983 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2404,7 +2404,7 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,
 		obj_ext = slab_obj_ext(s, slab, obj_exts, object);
 		ref = slab_obj_ext_codetag_ref(slab, obj_ext);
 
-		alloc_tag_add(ref, current->alloc_tag, s->size);
+		alloc_tag_add(ref, current->alloc_tag, s->size, ref);
 
 		put_slab_obj_exts(obj_exts);
 	} else {
@@ -2444,9 +2444,11 @@ __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p
 	get_slab_obj_exts(obj_exts);
 	for (int i = 0; i < objects; i++) {
 		struct slabobj_ext *ext;
+		union codetag_ref *ref;
 
 		ext = slab_obj_ext(s, slab, obj_exts, p[i]);
-		alloc_tag_sub(slab_obj_ext_codetag_ref(slab, ext), s->size);
+		ref = slab_obj_ext_codetag_ref(slab, ext);
+		alloc_tag_sub(ref, s->size, ref);
 	}
 	put_slab_obj_exts(obj_exts);
 }
diff --git a/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c b/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c
index 74fd64b2370cc..eb52ca1a1dc42 100644
--- a/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c
+++ b/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c
@@ -48,6 +48,11 @@ static inline int __allocinfo_get_next(int dev_fd, struct allocinfo_tag_data *pa
 	return ioctl(dev_fd, ALLOCINFO_IOC_GET_NEXT, params);
 }
 
+static inline int __allocinfo_toggle_trace(int dev_fd, struct allocinfo_toggle_traces *params)
+{
+	return ioctl(dev_fd, ALLOCINFO_IOC_TOGGLE_TRACE, params);
+}
+
 static bool match_entry(const struct allocinfo_tag_data *procfs_entry,
 			const struct allocinfo_tag_data *tag_data,
 			bool match_bytes, bool match_calls, bool match_lineno,
@@ -289,6 +294,8 @@ static int run_filter_test(const struct allocinfo_filter *filter)
 	return ret;
 }
 
+static const char *target_test_function = "dup_mm";
+
 static int test_filename_filter(void)
 {
 	struct allocinfo_filter filter;
@@ -304,11 +311,10 @@ static int test_filename_filter(void)
 static int test_function_filter(void)
 {
 	struct allocinfo_filter filter;
-	const char *target_function = "dup_mm";
 
 	memset(&filter, 0, sizeof(filter));
 	filter.mask |= ALLOCINFO_FILTER_MASK_FUNCTION;
-	strncpy(filter.fields.function, target_function, ALLOCINFO_STR_SIZE);
+	strncpy(filter.fields.function, target_test_function, ALLOCINFO_STR_SIZE);
 
 	return run_filter_test(&filter);
 }
@@ -514,11 +520,106 @@ static int test_lineno_filter(void)
 	return ret;
 }
 
+static enum ioctl_ret toggle_trace(struct allocinfo_tag *target_tag,
+				   bool enable)
+{
+	int fd;
+	struct allocinfo_toggle_traces toggle_params;
+
+	fd = open(ALLOCINFO_PROC, O_RDONLY);
+	if (fd < 0) {
+		ksft_print_msg("Failed to open " ALLOCINFO_PROC ": %s\n", strerror(errno));
+		return IOCTL_FAILURE;
+	}
+
+	memset(&toggle_params, 0, sizeof(toggle_params));
+	toggle_params.filter.mask = ALLOCINFO_FILTER_MASK_MODNAME | ALLOCINFO_FILTER_MASK_FUNCTION |
+				    ALLOCINFO_FILTER_MASK_FILENAME | ALLOCINFO_FILTER_MASK_LINENO;
+	toggle_params.filter.fields = *target_tag;
+	toggle_params.enable = enable;
+
+	if (__allocinfo_toggle_trace(fd, &toggle_params)) {
+		close(fd);
+		return IOCTL_FAILURE;
+	}
+
+	close(fd);
+	return IOCTL_SUCCESS;
+}
+
+static int test_tracing_toggle_and_filter(void)
+{
+	struct allocinfo_filter filter = { 0 };
+	enum ioctl_ret ioctl_status;
+	int ret = KSFT_PASS;
+	bool initial_state, target_state;
+	struct allocinfo_tag target_tag;
+	struct allocinfo_tag_data_vec *tags = calloc(1, sizeof(*tags));
+
+	if (!tags) {
+		ksft_print_msg("Memory allocation failed.\n");
+		return KSFT_FAIL;
+	}
+
+	filter.mask |= ALLOCINFO_FILTER_MASK_FUNCTION;
+	strncpy(filter.fields.function, target_test_function, ALLOCINFO_STR_SIZE);
+
+	ioctl_status = get_filtered_ioctl_entries(tags, &filter, 0);
+	if (ioctl_status != IOCTL_SUCCESS || tags->count == 0) {
+		ksft_print_msg("Could not retrieve IOCTL entries for %s\n", target_test_function);
+		ret = KSFT_SKIP;
+		goto exit;
+	}
+
+	target_tag = tags->tag[0].tag;
+	initial_state = tags->tag[0].counter.trace_on;
+	target_state = !initial_state;
+
+	ioctl_status = toggle_trace(&target_tag, target_state);
+	if (ioctl_status != IOCTL_SUCCESS) {
+		ksft_print_msg("Failed to toggle tracing\n");
+		ret = KSFT_FAIL;
+		goto exit;
+	}
+
+	filter.mask |= ALLOCINFO_FILTER_MASK_TRACE_ON;
+	filter.tracing = target_state;
+
+	ioctl_status = get_filtered_ioctl_entries(tags, &filter, 0);
+	if (ioctl_status != IOCTL_SUCCESS) {
+		ksft_print_msg("Error retrieving IOCTL entries with trace filter.\n");
+		ret = KSFT_FAIL;
+		goto exit_revert;
+	}
+
+	if (tags->count != 1) {
+		ksft_print_msg("Expected exactly 1 entry, but got %llu\n", tags->count);
+		ret = KSFT_FAIL;
+		goto exit_revert;
+	}
+
+	if (tags->tag[0].counter.trace_on != target_state) {
+		ksft_print_msg("Entry returned by trace filter does not match target state\n");
+		ret = KSFT_FAIL;
+	}
+
+exit_revert:
+	ioctl_status = toggle_trace(&target_tag, initial_state);
+	if (ioctl_status != IOCTL_SUCCESS) {
+		ksft_print_msg("Failed to revert tracing to initial state\n");
+		ret = KSFT_FAIL;
+	}
+
+exit:
+	free(tags);
+	return ret;
+}
+
 int main(int argc, char *argv[])
 {
 	int ret;
 
-	ksft_set_plan(4);
+	ksft_set_plan(5);
 
 	ret = test_filename_filter();
 	if (ret == KSFT_SKIP)
@@ -526,6 +627,12 @@ int main(int argc, char *argv[])
 	else
 		ksft_test_result(ret == KSFT_PASS, "test_filename_filter\n");
 
+	ret = test_tracing_toggle_and_filter();
+	if (ret == KSFT_SKIP)
+		ksft_test_result_skip("Skipping test_tracing_toggle_and_filter\n");
+	else
+		ksft_test_result(ret == KSFT_PASS, "test_tracing_toggle_and_filter\n");
+
 	ret = test_function_filter();
 	if (ret == KSFT_SKIP)
 		ksft_test_result_skip("Skipping test_function_filter\n");

gemini-3.8-flash

null

null

							input: 13767
							output: 34
							thoughts: 1246
						

**KMSAN Evaluation for this Patch Series**

Okay, so I need to decide if this patch series warrants a dedicated KMSAN fuzzing session. The instructions are pretty clear: KMSAN is for detecting uninitialized memory reads, particularly those that KASAN, LOCKDEP, or other standard detectors would miss. I need to be *sure* that the code introduces or exposes UNINITIALIZED MEMORY risks *only* detectable by KMSAN.  Let's break this down.

First, I need to understand the criteria for needing KMSAN: Kernel structures sent to userspace, conditional logic on uninitialized variables, uninitialized fields in complex data structures, or bounds/length checks leading to uninitialized byte access.

Now, let's look at the diff. It seems we're dealing with allocation profiling. Specifically, I'm seeing changes in:

1.  Documentation: This isn't likely the source of KMSAN needs, it's documentation.
2.  `MAINTAINERS`:  Likely not related.
3.  `include/linux/alloc_tag.h`:  Adding `alloc_tag` tracing, helper functions and trace events.  This seems mostly focused on instrumentation and tracking, which is ok, but not a KMSAN flag-raiser by itself.
4.  `include/linux/codetag.h`:  Changes to the `codetag` struct, making `flags` atomic. This looks benign.
5.  `include/trace/events/alloc_tag.h`: Tracepoints.  Again, instrumentation.
6.  `include/uapi/linux/alloc_tag.h`:  **THIS IS WHERE IT GETS INTERESTING.**  In `struct allocinfo_counter`, `trace_on` is replacing a single byte of `pad`.  Critically, `struct allocinfo_counter` is being sent to user space (via ioctl).  And `struct allocinfo_filter` now includes a `tracing` field.  The biggest red flag is `allocinfo_counter` and `trace_on` potentially being uninitialized.
7.  `mm/alloc_tag.c`:  Here's where the data transfer happens. In `allocinfo_to_params`, the `trace_on` field is populated, which is good. However, the comments in the original text are absolutely right to point this out! It copies `data->counter.trace_on = alloc_tag_is_traced(ct_to_alloc_tag(ct));`. This is the important part because we're sending `data->counter` to the user. I need to know how `data` is initialized, and specifically, if `pad` is zeroed.

I need to dig deeper into the code around `allocinfo_to_params` and the ioctls (`allocinfo_ioctl_get_at`, `allocinfo_ioctl_get_next`, `allocinfo_ioctl_toggle_trace`) in `mm/alloc_tag.c`.  I will pay *very* close attention to how `data` is allocated and initialized before it's copied to user space.  Is `pad` zeroed? Are there any potential information leaks regarding uninitialized data?

If I see that `data` is initialized in such a way that the `pad` bytes *could* be uninitialized when sent to user space, then *yes*, a KMSAN session is needed because we're potentially exposing an uninitialized memory read vulnerability to user space. Otherwise, if `pad` is correctly zeroed, then KMSAN is likely not needed.

{
  "Expression": "allocinfo_to_params",
  "PathPrefixes": [
    "mm/alloc_tag.c"
  ]
}

{
  "Output": "mm/alloc_tag.c=230=static inline struct alloc_tag_counters allocinfo_prefetch_counters(struct codetag *ct)\n--\nmm/alloc_tag.c-238- */\nmm/alloc_tag.c:239:static void allocinfo_to_params(struct codetag *ct,\nmm/alloc_tag.c-240-\t\t\t\tstruct allocinfo_tag_data *data,\n--\nmm/alloc_tag.c=358=static int allocinfo_ioctl_get_at(struct seq_file *m, void __user *arg)\n--\nmm/alloc_tag.c-407-\t\t\tcounters = allocinfo_prefetch_counters(ct);\nmm/alloc_tag.c:408:\t\tallocinfo_to_params(ct, \u0026params.data, \u0026counters);\nmm/alloc_tag.c-409-\t\tpriv-\u003epositioned = true;\n--\nmm/alloc_tag.c=428=static int allocinfo_ioctl_get_next(struct seq_file *m, void __user *arg)\n--\nmm/alloc_tag.c-458-\t\t\tcounters = allocinfo_prefetch_counters(ct);\nmm/alloc_tag.c:459:\t\tallocinfo_to_params(ct, \u0026params, \u0026counters);\nmm/alloc_tag.c-460-\t}\n"
}

gemini-3.8-flash

null

null

							input: 16153
							output: 35
							thoughts: 30
						

Okay, here's my interpretation of what's going on in that segment of `mm/alloc_tag.c`, as though it's coming straight from my own thought process.

**Diving into alloc_tag.c: Lines 230-470**

Alright, let's pull up `mm/alloc_tag.c` and zero in on lines 230 to roughly 470. That's a decent chunk of code, so let's try to get the gist of this. I have a feeling this is where the core logic for allocating and managing the allocation tags themselves is housed. I need to refresh my understanding of how this specific module interacts with the larger memory management system. Is it the primary allocator for the tags? Or perhaps it's a specialized allocator on top of the generic one?

Okay, now let's read this. I'm going to quickly skim the code, looking for key function names and data structures. Hopefully, I can pick out the primary data structures that hold the state of the tag allocations. What's the main function to look for to allocate or free a tag? Is there some kind of initialization routine, like an initialization of some sort of free list? I'm anticipating some form of bitfield or a similar compact structure to represent which tags are in use. I also expect to see some form of locking to protect concurrent access. Given the number of lines, this probably isn’t trivial.

I'm also looking for any interactions with the general memory allocator. Is there a call to `kmalloc` or similar? And where does the physical memory actually reside? Is it on a per-CPU basis or global? I want to see if they're using any specific optimizations. There may be some interesting techniques used here to prevent fragmentation. I'd expect that the tag allocations might be designed to be small and efficient, since they're metadata and not actually the data being allocated. I'll focus on how they handle potential out-of-memory scenarios; that's always interesting to me. I should be able to deduce the error handling and allocation strategy.

{
  "File": "mm/alloc_tag.c",
  "FirstLine": 230,
  "LineCount": 80
}

{
  "Contents": " 230:\tstatic inline struct alloc_tag_counters allocinfo_prefetch_counters(struct codetag *ct)\n 231:\t{\n 232:\t\treturn alloc_tag_read(ct_to_alloc_tag(ct));\n 233:\t}\n 234:\t\n 235:\t/*\n 236:\t * Populates the UAPI allocinfo_tag_data structure with active runtime\n 237:\t * profiling counters extracted from the given kernel codetag.\n 238:\t */\n 239:\tstatic void allocinfo_to_params(struct codetag *ct,\n 240:\t\t\t\t\tstruct allocinfo_tag_data *data,\n 241:\t\t\t\t\tstruct alloc_tag_counters *counters)\n 242:\t{\n 243:\t\tif (ct-\u003emodname)\n 244:\t\t\tallocinfo_copy_str(data-\u003etag.modname, ct-\u003emodname);\n 245:\t\telse\n 246:\t\t\tdata-\u003etag.modname[0] = '\\0';\n 247:\t\tallocinfo_copy_str(data-\u003etag.function, ct-\u003efunction);\n 248:\t\tallocinfo_copy_str(data-\u003etag.filename, ct-\u003efilename);\n 249:\t\tdata-\u003etag.lineno = ct-\u003elineno;\n 250:\t\tdata-\u003ecounter.bytes = counters-\u003ebytes;\n 251:\t\tdata-\u003ecounter.calls = counters-\u003ecalls;\n 252:\t\tdata-\u003ecounter.accurate = !alloc_tag_is_inaccurate(ct_to_alloc_tag(ct));\n 253:\t\tdata-\u003ecounter.trace_on = alloc_tag_is_traced(ct_to_alloc_tag(ct));\n 254:\t}\n 255:\t\n 256:\t/*\n 257:\t * Retrieves the unique content ID representing the current allocation tag module\n 258:\t * layout, allowing userspace to detect if modules were loaded / unloaded.\n 259:\t */\n 260:\tstatic int allocinfo_ioctl_get_content_id(struct seq_file *m, void __user *arg)\n 261:\t{\n 262:\t\tstruct allocinfo_content_id params;\n 263:\t\n 264:\t\tcodetag_lock_module_list(alloc_tag_cttype);\n 265:\t\tparams.id = codetag_get_content_id(alloc_tag_cttype);\n 266:\t\tcodetag_unlock_module_list(alloc_tag_cttype);\n 267:\t\tif (copy_to_user(arg, \u0026params, sizeof(params)))\n 268:\t\t\treturn -EFAULT;\n 269:\t\n 270:\t\treturn 0;\n 271:\t}\n 272:\t\n 273:\t/*\n 274:\t * Verifies whether a given codetag satisfies the active filtering criteria by\n 275:\t * matching its characteristics against the specified filter.\n 276:\t */\n 277:\tstatic bool matches_filter(struct codetag *ct, struct allocinfo_filter *filter,\n 278:\t\t\t\t   struct alloc_tag_counters *counters,\n 279:\t\t\t\t   bool *fetched_counters)\n 280:\t{\n 281:\t\tbool inaccurate;\n 282:\t\n 283:\t\tif (!filter || !filter-\u003emask)\n 284:\t\t\treturn true;\n 285:\t\n 286:\t\tif (filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_MODNAME) {\n 287:\t\t\t/* user wants to filter by modname but ct-\u003emodname is NULL */\n 288:\t\t\tif (!ct-\u003emodname) {\n 289:\t\t\t\t/* validate if user was attempting to filter for built-in allocations */\n 290:\t\t\t\tif (filter-\u003efields.modname[0] != '\\0')\n 291:\t\t\t\t\treturn false;\n 292:\t\t\t} else if (allocinfo_cmp_str(ct-\u003emodname, filter-\u003efields.modname))\n 293:\t\t\t\treturn false;\n 294:\t\t}\n 295:\t\n 296:\t\tif ((filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_FUNCTION) \u0026\u0026\n 297:\t\t    ct-\u003efunction \u0026\u0026 allocinfo_cmp_str(ct-\u003efunction, filter-\u003efields.function))\n 298:\t\t\treturn false;\n 299:\t\n 300:\t\tif ((filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_FILENAME) \u0026\u0026\n 301:\t\t    ct-\u003efilename \u0026\u0026 allocinfo_cmp_str(ct-\u003efilename, filter-\u003efields.filename))\n 302:\t\t\treturn false;\n 303:\t\n 304:\t\tif ((filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_LINENO) \u0026\u0026\n 305:\t\t    ct-\u003elineno != filter-\u003efields.lineno)\n 306:\t\t\treturn false;\n 307:\t\n 308:\t\tif (filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_INACCURATE) {\n 309:\t\t\tinaccurate = alloc_tag_is_inaccurate(ct_to_alloc_tag(ct));\n"
}

gemini-3.8-flash

null

null

							input: 17987
							output: 36
							thoughts: 16
						

Okay, here's the summary, formatted as requested:

**Delving Deeper: Lines 350-480**

Right, let's zero in on lines 350 through 480. I need to be precise here; this section likely holds the crux of the argument, or at least a critical piece of the puzzle. I anticipate some nuanced arguments here, possibly a key data set or a complex set of calculations to verify. Considering my expertise in this area, my analysis will need to focus on what those key arguments are. I'm going to look for any hidden assumptions, data manipulation, or logical fallacies. I'll be particularly focused on how this relates to my understanding of the current state of the art in this topic, and how any new information is integrated or challenged. Let's see what gems we can unearth!

{
  "File": "mm/alloc_tag.c",
  "FirstLine": 355,
  "LineCount": 100
}

{
  "Contents": " 355:\t * Seeks the ioctl iterator to the specified 0-indexed tag position, reads its\n 356:\t * profiling data and returns it to userspace.\n 357:\t */\n 358:\tstatic int allocinfo_ioctl_get_at(struct seq_file *m, void __user *arg)\n 359:\t{\n 360:\t\tstruct allocinfo_private *priv;\n 361:\t\tstruct codetag *ct;\n 362:\t\tstruct allocinfo_get_at params = {0};\n 363:\t\t__u64 skip_count;\n 364:\t\tstruct alloc_tag_counters counters;\n 365:\t\tbool fetched_counters;\n 366:\t\n 367:\t\tif (copy_from_user(\u0026params, arg, sizeof(params)))\n 368:\t\t\treturn -EFAULT;\n 369:\t\n 370:\t\tif (!allocinfo_filter_valid(\u0026params.filter))\n 371:\t\t\treturn -EINVAL;\n 372:\t\n 373:\t\tpriv = m-\u003eprivate;\n 374:\t\n 375:\t\tmutex_lock(\u0026priv-\u003eioctl_lock);\n 376:\t\tcodetag_lock_module_list(alloc_tag_cttype);\n 377:\t\n 378:\t\tif (params.pos \u003e= codetag_get_count(alloc_tag_cttype)) {\n 379:\t\t\tcodetag_unlock_module_list(alloc_tag_cttype);\n 380:\t\t\tmutex_unlock(\u0026priv-\u003eioctl_lock);\n 381:\t\t\treturn -ENOENT;\n 382:\t\t}\n 383:\t\n 384:\t\tskip_count = params.pos;\n 385:\t\n 386:\t\tif (params.filter.mask)\n 387:\t\t\tpriv-\u003efilter = params.filter;\n 388:\t\telse\n 389:\t\t\tpriv-\u003efilter.mask = 0;\n 390:\t\n 391:\t\t/* Find the codetag */\n 392:\t\tpriv-\u003eioctl_iter = codetag_get_ct_iter(alloc_tag_cttype);\n 393:\t\tct = codetag_next_ct(\u0026priv-\u003eioctl_iter);\n 394:\t\n 395:\t\twhile (ct) {\n 396:\t\t\tfetched_counters = false;\n 397:\t\t\tif (matches_filter(ct, \u0026priv-\u003efilter, \u0026counters, \u0026fetched_counters)) {\n 398:\t\t\t\tif (skip_count == 0)\n 399:\t\t\t\t\tbreak;\n 400:\t\t\t\tskip_count--;\n 401:\t\t\t}\n 402:\t\t\tct = codetag_next_ct(\u0026priv-\u003eioctl_iter);\n 403:\t\t}\n 404:\t\n 405:\t\tif (ct) {\n 406:\t\t\tif (!fetched_counters)\n 407:\t\t\t\tcounters = allocinfo_prefetch_counters(ct);\n 408:\t\t\tallocinfo_to_params(ct, \u0026params.data, \u0026counters);\n 409:\t\t\tpriv-\u003epositioned = true;\n 410:\t\t}\n 411:\t\n 412:\t\tcodetag_unlock_module_list(alloc_tag_cttype);\n 413:\t\tmutex_unlock(\u0026priv-\u003eioctl_lock);\n 414:\t\n 415:\t\tif (!ct)\n 416:\t\t\treturn -ENOENT;\n 417:\t\n 418:\t\tif (copy_to_user(arg, \u0026params, sizeof(params)))\n 419:\t\t\treturn -EFAULT;\n 420:\t\n 421:\t\treturn 0;\n 422:\t}\n 423:\t\n 424:\t/*\n 425:\t * Advances the ioctl iterator to the next allocation tag in the sequence and\n 426:\t * returns its profiling data to userspace.\n 427:\t */\n 428:\tstatic int allocinfo_ioctl_get_next(struct seq_file *m, void __user *arg)\n 429:\t{\n 430:\t\tstruct allocinfo_private *priv;\n 431:\t\tstruct codetag *ct;\n 432:\t\tstruct allocinfo_tag_data params;\n 433:\t\tint ret = 0;\n 434:\t\tstruct alloc_tag_counters counters;\n 435:\t\tbool fetched_counters;\n 436:\t\n 437:\t\tmemset(\u0026params, 0, sizeof(params));\n 438:\t\tpriv = m-\u003eprivate;\n 439:\t\n 440:\t\tmutex_lock(\u0026priv-\u003eioctl_lock);\n 441:\t\tcodetag_lock_module_list(alloc_tag_cttype);\n 442:\t\n 443:\t\tif (!priv-\u003epositioned) {\n 444:\t\t\tpriv-\u003eioctl_iter = codetag_get_ct_iter(alloc_tag_cttype);\n 445:\t\t\tpriv-\u003epositioned = true;\n 446:\t\t}\n 447:\t\n 448:\t\tct = codetag_next_ct(\u0026priv-\u003eioctl_iter);\n 449:\t\twhile (ct) {\n 450:\t\t\tfetched_counters = false;\n 451:\t\t\tif (matches_filter(ct, \u0026priv-\u003efilter, \u0026counters, \u0026fetched_counters))\n 452:\t\t\t\tbreak;\n 453:\t\t\tct = codetag_next_ct(\u0026priv-\u003eioctl_iter);\n 454:\t\t}\n"
}

gemini-3.8-flash

null

null

							input: 19647
							output: 34
							thoughts: 515
						

**Analyzing the Data Flow in allocinfo_ioctl_get_at**

Okay, let's break this down. First, I'm comparing `allocinfo_ioctl_get_next` and `allocinfo_ioctl_get_at`. In `allocinfo_ioctl_get_next`, we see `memset(&params, 0, sizeof(params));`, which is standard initialization. But in `allocinfo_ioctl_get_at`, it's `struct allocinfo_get_at params = {0};`, same thing. Good, we're zeroing the struct.

Now, the crucial part: in `allocinfo_ioctl_get_at`, `copy_from_user(&params, arg, sizeof(params))` happens *before* any other processing. This means user data completely overwrites `params`. Then, *only if* `ct` is found, the function `allocinfo_to_params(ct, &params.data, &counters);` is called to populate fields.

Hmm, what's `params.data`? That's the key. Back to `copy_from_user`, the user gets to control *every byte* of `params`. If the user populates `params.data.counter.pad` with anything, it will be written back on `copy_to_user`. I was worried about uninitialized kernel data leaks, but wait! Since we *zero* initialized the `params` struct, then `copy_from_user` replaces the zeroed data with user data. So, the only data copied back is either zero, or provided by the user. Excellent!

So, the user-provided data is modified by `allocinfo_to_params`. Let's confirm:

```c
	if (ct->modname)
		allocinfo_copy_str(data->tag.modname, ct->modname);
	else
		data->tag.modname[0] = '\0';
	allocinfo_copy_str(data->tag.function, ct->function);
	allocinfo_copy_str(data->tag.filename, ct->filename);
	data->tag.lineno = ct->lineno;
	data->counter.bytes = counters->bytes;
	data->counter.calls = counters->calls;
	data->counter.accurate = !alloc_tag_is_inaccurate(ct_to_alloc_tag(ct));
	data->counter.trace_on = alloc_tag_is_traced(ct_to_alloc_tag(ct));
```

The user's data isn't *directly* passed back. Instead, `allocinfo_to_params` modifies fields of the user-provided structure, but only *after* the initial zeroing from the declaration and the user data provided through `copy_from_user`. The only thing left to check is the contents of `allocinfo_copy_str`. That's where all the string copies occur. That will be the next place to look for subtle issues.

{
  "Expression": "allocinfo_copy_str",
  "PathPrefixes": [
    "mm/alloc_tag.c"
  ]
}

{
  "Output": "mm/alloc_tag.c=207=static const char *allocinfo_str(const char *str)\n--\nmm/alloc_tag.c-217-/* Copy a string and trim from the beginning if it's too long */\nmm/alloc_tag.c:218:static void allocinfo_copy_str(char *dest, const char *src)\nmm/alloc_tag.c-219-{\n--\nmm/alloc_tag.c=239=static void allocinfo_to_params(struct codetag *ct,\n--\nmm/alloc_tag.c-243-\tif (ct-\u003emodname)\nmm/alloc_tag.c:244:\t\tallocinfo_copy_str(data-\u003etag.modname, ct-\u003emodname);\nmm/alloc_tag.c-245-\telse\nmm/alloc_tag.c-246-\t\tdata-\u003etag.modname[0] = '\\0';\nmm/alloc_tag.c:247:\tallocinfo_copy_str(data-\u003etag.function, ct-\u003efunction);\nmm/alloc_tag.c:248:\tallocinfo_copy_str(data-\u003etag.filename, ct-\u003efilename);\nmm/alloc_tag.c-249-\tdata-\u003etag.lineno = ct-\u003elineno;\n"
}

gemini-3.8-flash

null

null

							input: 21182
							output: 35
							thoughts: 14
						

Here's a first-person summary, keeping in mind the audience is an expert:

**Diving into `allocinfo_copy_str`**

Alright, let's get down to brass tacks. I need to take a look at the `allocinfo_copy_str` implementation. Given the context, I'm probably looking for potential vulnerabilities, performance bottlenecks, or just generally how it's handling memory management. I'm already anticipating the typical suspects: potential buffer overflows, memory leaks if the allocation isn't handled correctly on both success and error paths, and perhaps some inefficiency if the copying method is suboptimal. I'll be focused on how it interacts with the allocator, how it handles null termination, and whether there are any obvious race conditions if it's operating in a multi-threaded environment. Gotta be precise about this. Let's see what's actually under the hood.

{
  "File": "mm/alloc_tag.c",
  "FirstLine": 215,
  "LineCount": 20
}

{
  "Contents": " 215:\t}\n 216:\t\n 217:\t/* Copy a string and trim from the beginning if it's too long */\n 218:\tstatic void allocinfo_copy_str(char *dest, const char *src)\n 219:\t{\n 220:\t\tstrscpy_pad(dest, allocinfo_str(src), ALLOCINFO_STR_SIZE);\n 221:\t}\n 222:\t\n 223:\t/* Compare two strings and only consider the trimmed suffix if s1 is too long */\n 224:\tstatic int allocinfo_cmp_str(const char *str, const char *template)\n 225:\t{\n 226:\t\treturn strncmp(allocinfo_str(str), template, ALLOCINFO_STR_SIZE);\n 227:\t}\n 228:\t\n 229:\t/* Fetch the per-CPU counters */\n 230:\tstatic inline struct alloc_tag_counters allocinfo_prefetch_counters(struct codetag *ct)\n 231:\t{\n 232:\t\treturn alloc_tag_read(ct_to_alloc_tag(ct));\n 233:\t}\n 234:\t\n"
}

gemini-3.8-flash

null

null

							input: 21741
							output: 35
							thoughts: 598
						

**Analyzing Potential Uninitialized Memory Disclosure**

Okay, let's break this down systematically. My initial thought process is to trace where uninitialized memory might be accessible to user space. It starts with `strscpy_pad` zeroing the remaining bytes, and I note the use of `memset` in `allocinfo_ioctl_get_next` to zero out the `params` struct. Similarly, in `allocinfo_ioctl_get_at`, the struct `allocinfo_get_at params = {0};` initialization suggests a clean slate, followed by a `copy_from_user` call. But wait, a partial copy in `copy_from_user` is a failure returning `-EFAULT`. So, no, the `params` data won't contain uninitialized memory, because an incomplete copy would signal an error.

Now, I'm pivoting to `allocinfo_ioctl_toggle_trace`. Here, we have `copy_from_user` populating the stack struct `params`. Critically, this function doesn't *copy back* to userspace; it's an `_IOW` ioctl, so it writes only, or it errors. This indicates that it doesn't read uninitialized memory either, as the `params` struct is initialized by the data from the user space.

Okay, almost there. The variable `counters` in `allocinfo_ioctl_toggle_trace` has me concerned now. I see a while loop with a call to `matches_filter` potentially involving this `counters` variable. I need to be absolutely certain of what this function does. My next step will be to thoroughly examine the `matches_filter` function itself, specifically, within `mm/alloc_tag.c`. I have to read the whole function. I'm going in!

{
  "File": "mm/alloc_tag.c",
  "FirstLine": 275,
  "LineCount": 60
}

{
  "Contents": " 275:\t * matching its characteristics against the specified filter.\n 276:\t */\n 277:\tstatic bool matches_filter(struct codetag *ct, struct allocinfo_filter *filter,\n 278:\t\t\t\t   struct alloc_tag_counters *counters,\n 279:\t\t\t\t   bool *fetched_counters)\n 280:\t{\n 281:\t\tbool inaccurate;\n 282:\t\n 283:\t\tif (!filter || !filter-\u003emask)\n 284:\t\t\treturn true;\n 285:\t\n 286:\t\tif (filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_MODNAME) {\n 287:\t\t\t/* user wants to filter by modname but ct-\u003emodname is NULL */\n 288:\t\t\tif (!ct-\u003emodname) {\n 289:\t\t\t\t/* validate if user was attempting to filter for built-in allocations */\n 290:\t\t\t\tif (filter-\u003efields.modname[0] != '\\0')\n 291:\t\t\t\t\treturn false;\n 292:\t\t\t} else if (allocinfo_cmp_str(ct-\u003emodname, filter-\u003efields.modname))\n 293:\t\t\t\treturn false;\n 294:\t\t}\n 295:\t\n 296:\t\tif ((filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_FUNCTION) \u0026\u0026\n 297:\t\t    ct-\u003efunction \u0026\u0026 allocinfo_cmp_str(ct-\u003efunction, filter-\u003efields.function))\n 298:\t\t\treturn false;\n 299:\t\n 300:\t\tif ((filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_FILENAME) \u0026\u0026\n 301:\t\t    ct-\u003efilename \u0026\u0026 allocinfo_cmp_str(ct-\u003efilename, filter-\u003efields.filename))\n 302:\t\t\treturn false;\n 303:\t\n 304:\t\tif ((filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_LINENO) \u0026\u0026\n 305:\t\t    ct-\u003elineno != filter-\u003efields.lineno)\n 306:\t\t\treturn false;\n 307:\t\n 308:\t\tif (filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_INACCURATE) {\n 309:\t\t\tinaccurate = alloc_tag_is_inaccurate(ct_to_alloc_tag(ct));\n 310:\t\t\tif (inaccurate != !!(filter-\u003einaccurate))\n 311:\t\t\t\treturn false;\n 312:\t\t}\n 313:\t\n 314:\t\tif (filter-\u003emask \u0026 (ALLOCINFO_FILTER_MASK_MIN_SIZE | ALLOCINFO_FILTER_MASK_MAX_SIZE)) {\n 315:\t\t\tif (!*fetched_counters) {\n 316:\t\t\t\t*counters = allocinfo_prefetch_counters(ct);\n 317:\t\t\t\t*fetched_counters = true;\n 318:\t\t\t}\n 319:\t\t\tif ((filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_MIN_SIZE) \u0026\u0026\n 320:\t\t\t    counters-\u003ebytes \u003c filter-\u003emin_size)\n 321:\t\t\t\treturn false;\n 322:\t\t\tif ((filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_MAX_SIZE) \u0026\u0026\n 323:\t\t\t    counters-\u003ebytes \u003e filter-\u003emax_size)\n 324:\t\t\t\treturn false;\n 325:\t\t}\n 326:\t\n 327:\t\tif (filter-\u003emask \u0026 ALLOCINFO_FILTER_MASK_TRACE_ON) {\n 328:\t\t\tbool tracing = alloc_tag_is_traced(ct_to_alloc_tag(ct));\n 329:\t\n 330:\t\t\tif (tracing != !!(filter-\u003etracing))\n 331:\t\t\t\treturn false;\n 332:\t\t}\n 333:\t\n 334:\t\treturn true;\n"
}

gemini-3.8-flash

null

null

							input: 23715
							output: 22
							thoughts: 1761
						

**Code Analysis: Tracing and Tagging**

Alright, let's break this down. First, I focused on how the `counters` variable is used, specifically within the `matches_filter` function and its interactions with `allocinfo_ioctl_toggle_trace`, `allocinfo_ioctl_get_at`, and `allocinfo_ioctl_get_next`. The critical observation here is the potential for uninitialized reads of `counters` *only* if filtering based on minimum or maximum size isn't applied. In the other IOCTL functions, `counters` is consistently initialized via `allocinfo_prefetch_counters()` before being passed around, which is sound.

Now, let's shift gears to the trace events and hooks, starting with `include/trace/events/alloc_tag.h`. The potential issue here is the possible NULL values of strings like `tag->ct.filename` or `tag->ct.function`. The code uses string literals `__FILE__`, `__func__` and module name for `modname`, but not `filename` or `function`.

I checked the definition of the `CODETAG_INIT` macro, which is responsible for the codetag initialization. The relevant fields are initialized with string literals, module names. Therefore, `ct.filename` and `ct.function` are never NULL, unless code changes were made to these core components.

Next, I looked at the `alloc_hooks_tag` macro and the call to `alloc_tag_trace_hit`. I identified that the `alloc_tag_trace_hit` function itself performs a null check on the `tag` pointer through `alloc_tag_trace_enabled`, which should be safe.

Finally, I examined `alloc_tag_add` and `alloc_tag_sub`, which are responsible for updating the allocation counters and triggering trace events. The key question here is whether these functions could receive a `NULL` tag. I checked the code, and found that there are a few call sites from `mm/page_alloc.c`, `mm/percpu.c` and `mm/slub.c`.

I did a quick scan for the callers of these functions to determine whether `tag` could be null, but those function call sites are fine.

{
  "Expression": "alloc_tag_(add|sub)"
}

{
  "Output": "include/linux/alloc_tag.h=187=static inline struct alloc_tag_counters alloc_tag_read(struct alloc_tag *tag)\n--\ninclude/linux/alloc_tag.h-202-#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG\ninclude/linux/alloc_tag.h:203:static inline void alloc_tag_add_check(union codetag_ref *ref, struct alloc_tag *tag)\ninclude/linux/alloc_tag.h-204-{\n--\ninclude/linux/alloc_tag.h-211-\ninclude/linux/alloc_tag.h:212:static inline void alloc_tag_sub_check(union codetag_ref *ref)\ninclude/linux/alloc_tag.h-213-{\n--\ninclude/linux/alloc_tag.h-215-}\ninclude/linux/alloc_tag.h:216:void alloc_tag_add_early_pfn(unsigned long pfn, unsigned int alloc_flags);\ninclude/linux/alloc_tag.h-217-#else\ninclude/linux/alloc_tag.h:218:static inline void alloc_tag_add_check(union codetag_ref *ref, struct alloc_tag *tag) {}\ninclude/linux/alloc_tag.h:219:static inline void alloc_tag_sub_check(union codetag_ref *ref) {}\ninclude/linux/alloc_tag.h:220:static inline void alloc_tag_add_early_pfn(unsigned long pfn, unsigned int alloc_flags) {}\ninclude/linux/alloc_tag.h-221-#endif\n--\ninclude/linux/alloc_tag.h=224=static inline bool __alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *tag)\ninclude/linux/alloc_tag.h-225-{\ninclude/linux/alloc_tag.h:226:\talloc_tag_add_check(ref, tag);\ninclude/linux/alloc_tag.h-227-\tif (!ref || !tag)\n--\ninclude/linux/alloc_tag.h=234=static inline bool alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *tag)\n--\ninclude/linux/alloc_tag.h-248-\ninclude/linux/alloc_tag.h:249:static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes,\ninclude/linux/alloc_tag.h-250-\t\t\t\t const void *ptr)\n--\ninclude/linux/alloc_tag.h-260-\ninclude/linux/alloc_tag.h:261:static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes, const void *ptr)\ninclude/linux/alloc_tag.h-262-{\n--\ninclude/linux/alloc_tag.h-264-\ninclude/linux/alloc_tag.h:265:\talloc_tag_sub_check(ref);\ninclude/linux/alloc_tag.h-266-\tif (!ref || !ref-\u003ect)\n--\ninclude/linux/alloc_tag.h=292=static inline bool mem_alloc_profiling_permanently_disabled(void) { return true; }\ninclude/linux/alloc_tag.h:293:static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag,\ninclude/linux/alloc_tag.h-294-\t\t\t\t size_t bytes, const void *ptr) {}\ninclude/linux/alloc_tag.h:295:static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes,\ninclude/linux/alloc_tag.h-296-\t\t\t\t const void *ptr) {}\n--\ninclude/linux/pgalloc_tag.h=176=static inline struct alloc_tag *__pgalloc_tag_get(struct page *page)\n--\ninclude/linux/pgalloc_tag.h-182-\tif (get_page_tag_ref(page, \u0026ref, \u0026handle)) {\ninclude/linux/pgalloc_tag.h:183:\t\talloc_tag_sub_check(\u0026ref);\ninclude/linux/pgalloc_tag.h-184-\t\tif (ref.ct \u0026\u0026 !is_codetag_empty(\u0026ref))\n--\nmm/alloc_tag.c=1285=static struct pfn_pool *current_pfn_pool __initdata;\nmm/alloc_tag.c-1286-\nmm/alloc_tag.c:1287:static void __init __alloc_tag_add_early_pfn(unsigned long pfn)\nmm/alloc_tag.c-1288-{\n--\nmm/alloc_tag.c-1322-\nmm/alloc_tag.c:1323:typedef void alloc_tag_add_func(unsigned long pfn);\nmm/alloc_tag.c:1324:static alloc_tag_add_func __rcu *alloc_tag_add_early_pfn_ptr __refdata =\nmm/alloc_tag.c:1325:\tRCU_INITIALIZER(__alloc_tag_add_early_pfn);\nmm/alloc_tag.c-1326-\nmm/alloc_tag.c:1327:void alloc_tag_add_early_pfn(unsigned long pfn, unsigned int alloc_flags)\nmm/alloc_tag.c-1328-{\nmm/alloc_tag.c:1329:\talloc_tag_add_func *alloc_tag_add;\nmm/alloc_tag.c-1330-\n--\nmm/alloc_tag.c-1338-\trcu_read_lock();\nmm/alloc_tag.c:1339:\talloc_tag_add = rcu_dereference(alloc_tag_add_early_pfn_ptr);\nmm/alloc_tag.c:1340:\tif (alloc_tag_add)\nmm/alloc_tag.c:1341:\t\talloc_tag_add(pfn);\nmm/alloc_tag.c-1342-\trcu_read_unlock();\n--\nmm/alloc_tag.c=1345=static void __init clear_early_alloc_pfn_tag_refs(void)\n--\nmm/alloc_tag.c-1353-\nmm/alloc_tag.c:1354:\trcu_assign_pointer(alloc_tag_add_early_pfn_ptr, NULL);\nmm/alloc_tag.c:1355:\t/* Make sure we are not racing with __alloc_tag_add_early_pfn() */\nmm/alloc_tag.c-1356-\tsynchronize_rcu();\n--\nmm/page_alloc.c=1234=static noinline\nmm/page_alloc.c:1235:void __pgalloc_tag_add(struct page *page, struct task_struct *task,\nmm/page_alloc.c-1236-\t\t       unsigned int nr, unsigned int alloc_flags)\n--\nmm/page_alloc.c-1241-\tif (likely(get_page_tag_ref(page, \u0026ref, \u0026handle))) {\nmm/page_alloc.c:1242:\t\talloc_tag_add(\u0026ref, task-\u003ealloc_tag, PAGE_SIZE * nr, page);\nmm/page_alloc.c-1243-\t\tupdate_page_tag_ref(handle, \u0026ref);\n--\nmm/page_alloc.c-1249-\t\t */\nmm/page_alloc.c:1250:\t\talloc_tag_add_early_pfn(page_to_pfn(page), alloc_flags);\nmm/page_alloc.c-1251-\t\tif (task-\u003ealloc_tag)\n--\nmm/page_alloc.c-1255-\nmm/page_alloc.c:1256:static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,\nmm/page_alloc.c-1257-\t\t\t\t   unsigned int nr, unsigned int alloc_flags)\n--\nmm/page_alloc.c-1259-\tif (mem_alloc_profiling_enabled())\nmm/page_alloc.c:1260:\t\t__pgalloc_tag_add(page, task, nr, alloc_flags);\nmm/page_alloc.c-1261-}\n--\nmm/page_alloc.c=1264=static noinline\nmm/page_alloc.c:1265:void __pgalloc_tag_sub(struct page *page, unsigned int nr)\nmm/page_alloc.c-1266-{\n--\nmm/page_alloc.c-1270-\tif (get_page_tag_ref(page, \u0026ref, \u0026handle)) {\nmm/page_alloc.c:1271:\t\talloc_tag_sub(\u0026ref, PAGE_SIZE * nr, page);\nmm/page_alloc.c-1272-\t\tupdate_page_tag_ref(handle, \u0026ref);\n--\nmm/page_alloc.c-1276-\nmm/page_alloc.c:1277:static inline void pgalloc_tag_sub(struct page *page, unsigned int nr)\nmm/page_alloc.c-1278-{\nmm/page_alloc.c-1279-\tif (mem_alloc_profiling_enabled())\nmm/page_alloc.c:1280:\t\t__pgalloc_tag_sub(page, nr);\nmm/page_alloc.c-1281-}\n--\nmm/page_alloc.c-1283-/* When tag is not NULL, assuming mem_alloc_profiling_enabled */\nmm/page_alloc.c:1284:static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr)\nmm/page_alloc.c-1285-{\n--\nmm/page_alloc.c-1291-\nmm/page_alloc.c:1292:static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,\nmm/page_alloc.c-1293-\t\t\t\t   unsigned int nr, unsigned int alloc_flags) {}\nmm/page_alloc.c:1294:static inline void pgalloc_tag_sub(struct page *page, unsigned int nr) {}\nmm/page_alloc.c:1295:static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr) {}\nmm/page_alloc.c-1296-\n--\nmm/page_alloc.c=1299=static __always_inline bool __free_pages_prepare(struct page *page,\n--\nmm/page_alloc.c-1336-\t\tpage_table_check_free(page, order);\nmm/page_alloc.c:1337:\t\tpgalloc_tag_sub(page, 1 \u003c\u003c order);\nmm/page_alloc.c-1338-\n--\nmm/page_alloc.c-1402-\tpage_table_check_free(page, order);\nmm/page_alloc.c:1403:\tpgalloc_tag_sub(page, 1 \u003c\u003c order);\nmm/page_alloc.c-1404-\n--\nmm/page_alloc.c=1804=inline void post_alloc_hook(struct page *page, unsigned int order,\n--\nmm/page_alloc.c-1855-\tpage_table_check_alloc(page, order);\nmm/page_alloc.c:1856:\tpgalloc_tag_add(page, current, 1 \u003c\u003c order, alloc_flags);\nmm/page_alloc.c-1857-}\n--\nmm/page_alloc.c=5561=static void ___free_pages(struct page *page, unsigned int order,\n--\nmm/page_alloc.c-5571-\telse if (!head) {\nmm/page_alloc.c:5572:\t\tpgalloc_tag_sub_pages(tag, (1 \u003c\u003c order) - 1);\nmm/page_alloc.c-5573-\t\twhile (order-- \u003e 0) {\n--\nmm/page_alloc.h-55- * Callers must clear_page_tag_ref() before freeing to avoid warnings from\nmm/page_alloc.h:56: * alloc_tag_sub_check().\nmm/page_alloc.h-57- */\n--\nmm/percpu.c=1694=static void pcpu_alloc_tag_alloc_hook(struct pcpu_chunk *chunk, int off,\n--\nmm/percpu.c-1699-\nmm/percpu.c:1700:\t\talloc_tag_add(ref, current-\u003ealloc_tag, size, ref);\nmm/percpu.c-1701-\t}\n--\nmm/percpu.c=1704=static void pcpu_alloc_tag_free_hook(struct pcpu_chunk *chunk, int off, size_t size)\n--\nmm/percpu.c-1708-\nmm/percpu.c:1709:\t\talloc_tag_sub(ref, size, ref);\nmm/percpu.c-1710-\t}\n--\nmm/slub.c=2376=__alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,\n--\nmm/slub.c-2396-\t * If other users appear then mem_alloc_profiling_enabled()\nmm/slub.c:2397:\t * check should be added before alloc_tag_add().\nmm/slub.c-2398-\t */\n--\nmm/slub.c-2406-\nmm/slub.c:2407:\t\talloc_tag_add(ref, current-\u003ealloc_tag, s-\u003esize, ref);\nmm/slub.c-2408-\n--\nmm/slub.c=2431=__alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,\n--\nmm/slub.c-2450-\t\tref = slab_obj_ext_codetag_ref(slab, ext);\nmm/slub.c:2451:\t\talloc_tag_sub(ref, s-\u003esize, ref);\nmm/slub.c-2452-\t}\n--\nmm/slub.c=2847=static void __free_empty_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf,\n--\nmm/slub.c-2851-\t * If the sheaf was created with SLAB_ALLOC_NO_RECURSE flag then its\nmm/slub.c:2852:\t * corresponding extension is NULL and alloc_tag_sub() will throw a\nmm/slub.c-2853-\t * warning, therefore replace NULL with CODETAG_EMPTY to indicate\n"
}

gemini-3.8-flash

null

null

							input: 29721
							output: 26
							thoughts: 905
						

**Memory Safety Analysis of allocinfo Code**

Okay, let's dissect this code for potential memory issues. First, I'm checking the `struct allocinfo_counter`. The `pad` field is six bytes now. I need to make sure this doesn't introduce any uninitialized memory reads or leaks.

Looking at `allocinfo_ioctl_get_next`, `params` is cleared using `memset`, so the `pad` is zeroed.  Then `allocinfo_to_params` sets `data->counter.trace_on`. Since `memset` already zeroed the rest of `pad`, and then the entire `params` structure is copied to user-space, this seems safe.

Now, let's scrutinize `allocinfo_ioctl_get_at`. Here, `params` is initialized to zero, data is copied *from* user-space, updated, and then copied *back* to user-space.  `allocinfo_to_params` initializes any fields that come from the kernel before copying to userspace. So, all data is either user-supplied or explicitly initialized, which looks good and I don't see any kernel information leak.

Next, I'll examine `allocinfo_ioctl_toggle_trace`. Here, data is copied *from* user-space, validated, and no data is copied *to* user-space. Also, uninitialized stack variables aren't being read before use ( `counters` is only read if fetched). This part looks secure too.

Finally, I'm looking at `struct codetag` itself. It looks like it was changed from `unsigned int flags` to `atomic_t flags`. The initialization, which looks like it's done via `CODETAG_INIT`, uses `ATOMIC_INIT(0)`.  These codetags are statically allocated in the codetag sections generated by the compiler. I should verify how these codetags are handled, particularly during module loading and unloading. I'll need to grep for `load_module` and `unload_module` or `module_tags` within `mm/alloc_tag.c` to be completely certain.

{
  "Expression": "unload_module",
  "PathPrefixes": [
    "mm/"
  ]
}

{
  "Output": "mm/alloc_tag.c=1098=static int load_module(struct module *mod, struct codetag *start, struct codetag *stop)\n--\nmm/alloc_tag.c-1132-\nmm/alloc_tag.c:1133:static void unload_module(struct module *mod, struct codetag *start, struct codetag *stop)\nmm/alloc_tag.c-1134-{\n--\nmm/alloc_tag.c=1467=static int __init alloc_tag_init(void)\n--\nmm/alloc_tag.c-1476-\t\t.module_load\t\t= load_module,\nmm/alloc_tag.c:1477:\t\t.module_unload\t\t= unload_module,\nmm/alloc_tag.c-1478-\t\t.module_replaced\t= replace_module,\n"
}

gemini-3.8-flash

null

null

							input: 31332
							output: 30
							thoughts: 31
						

Here's my take on the thought process, tailored for an expert audience:

**Diving into the Codetag Implementation**

Okay, so I need to understand the interaction between module loading and unloading in the context of codetag. My first instinct is to dig into the core implementation. I'll need to examine `lib/codetag.c` – that's where the critical logic for codetag's lifecycle will reside, specifically regarding the handling of modules. I need to get a clear picture of how `module_unload` is designed and how it interacts, or even what its relationship is to something like `codetag_load_module`. I want to identify the fundamental mechanism for how codetag handles the inclusion and removal of dynamic code, and the implications for things like state management, symbol resolution, and potential cleanup tasks. I’m thinking about how dependencies might be handled during unload, and what specific steps occur to remove and free resources. It's time to get my hands dirty.

{
  "Expression": "module_unload",
  "PathPrefixes": [
    "lib/codetag.c"
  ]
}

{
  "Output": "lib/codetag.c=357=void codetag_unload_module(struct module *mod)\n--\nlib/codetag.c-380-\t\tif (found) {\nlib/codetag.c:381:\t\t\tif (cttype-\u003edesc.module_unload)\nlib/codetag.c:382:\t\t\t\tcttype-\u003edesc.module_unload(cmod-\u003emod,\nlib/codetag.c-383-\t\t\t\t\tcmod-\u003erange.start, cmod-\u003erange.stop);\n"
}

gemini-3.8-flash

null

null

							input: 31735
							output: 31
							thoughts: 23
						

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

**Diving into Tag Allocation and Initialization**

Alright, let's get down to brass tacks. I'm going to dig into the `mm/alloc_tag.c` code. Specifically, I need to refresh my memory on the precise mechanisms by which module tags are allocated and initialized during module loading. I'm particularly interested in the finer points of how these tags are integrated with the memory management layer. Understanding the allocation process is, of course, critical for tracking down any memory leaks or incorrect interactions. I know the basics, but I need to scrutinize the initialization sequence to ensure all dependencies are correctly handled and that there aren't any subtle initialization race conditions or potential for undefined behavior. I want to build a rock-solid mental model of what's happening at this low level, before I even start looking at the module loading implementation. That way, any anomalies will jump right out at me.

{
  "Expression": "load_module",
  "PathPrefixes": [
    "mm/alloc_tag.c"
  ]
}

{
  "Output": "mm/alloc_tag.c=1052=static void release_module_tags(struct module *mod, bool used)\n--\nmm/alloc_tag.c-1097-\nmm/alloc_tag.c:1098:static int load_module(struct module *mod, struct codetag *start, struct codetag *stop)\nmm/alloc_tag.c-1099-{\n--\nmm/alloc_tag.c-1132-\nmm/alloc_tag.c:1133:static void unload_module(struct module *mod, struct codetag *start, struct codetag *stop)\nmm/alloc_tag.c-1134-{\n--\nmm/alloc_tag.c=1467=static int __init alloc_tag_init(void)\n--\nmm/alloc_tag.c-1475-\t\t.free_section_mem\t= release_module_tags,\nmm/alloc_tag.c:1476:\t\t.module_load\t\t= load_module,\nmm/alloc_tag.c:1477:\t\t.module_unload\t\t= unload_module,\nmm/alloc_tag.c-1478-\t\t.module_replaced\t= replace_module,\n"
}

gemini-3.8-flash

null

null

							input: 32305
							output: 36
							thoughts: 25
						

Okay, let's dive into this. Here's my summary, framed as my thought process:

**Diving into Allocation Tagging in mm/alloc_tag.c**

Alright, I'm going to focus my attention on `mm/alloc_tag.c` right now, specifically the `load_module` and `unload_module` functions. Given my familiarity with the kernel's memory management and module loading mechanisms, I'm expecting these functions to be crucial for understanding how allocation tagging interacts with the dynamic nature of kernel modules. My initial hypothesis is that these functions likely handle the association and disassociation of allocation tags with specific modules as they are loaded and unloaded. I'll be looking closely at how they ensure that tagged memory is properly tracked and accounted for, preventing potential leaks or inconsistencies when modules come and go. I also anticipate there might be considerations for protecting against tag collisions and ensuring data integrity across module boundaries. Time to dig in and confirm (or refine) that mental model.

{
  "File": "mm/alloc_tag.c",
  "FirstLine": 1095,
  "LineCount": 55
}

{
  "Contents": "1095:\t\tmas_unlock(\u0026mas);\n1096:\t}\n1097:\t\n1098:\tstatic int load_module(struct module *mod, struct codetag *start, struct codetag *stop)\n1099:\t{\n1100:\t\t/* Allocate module alloc_tag percpu counters */\n1101:\t\tstruct alloc_tag *start_tag;\n1102:\t\tstruct alloc_tag *stop_tag;\n1103:\t\tstruct alloc_tag *tag;\n1104:\t\n1105:\t\t/* percpu counters for core allocations are already statically allocated */\n1106:\t\tif (!mod)\n1107:\t\t\treturn 0;\n1108:\t\n1109:\t\tstart_tag = ct_to_alloc_tag(start);\n1110:\t\tstop_tag = ct_to_alloc_tag(stop);\n1111:\t\tfor (tag = start_tag; tag \u003c stop_tag; tag++) {\n1112:\t\t\tWARN_ON(tag-\u003ecounters);\n1113:\t\t\ttag-\u003ecounters = alloc_percpu(struct alloc_tag_counters);\n1114:\t\t\tif (!tag-\u003ecounters) {\n1115:\t\t\t\twhile (--tag \u003e= start_tag) {\n1116:\t\t\t\t\tfree_percpu(tag-\u003ecounters);\n1117:\t\t\t\t\ttag-\u003ecounters = NULL;\n1118:\t\t\t\t}\n1119:\t\t\t\tpr_err(\"Failed to allocate memory for allocation tag percpu counters in the module %s\\n\",\n1120:\t\t\t\t       mod-\u003ename);\n1121:\t\t\t\treturn -ENOMEM;\n1122:\t\t\t}\n1123:\t\n1124:\t\t\t/*\n1125:\t\t\t * Avoid a kmemleak false positive. The pointer to the counters is stored\n1126:\t\t\t * in the alloc_tag section of the module and cannot be directly accessed.\n1127:\t\t\t */\n1128:\t\t\tkmemleak_ignore_percpu(tag-\u003ecounters);\n1129:\t\t}\n1130:\t\treturn 0;\n1131:\t}\n1132:\t\n1133:\tstatic void unload_module(struct module *mod, struct codetag *start, struct codetag *stop)\n1134:\t{\n1135:\t\tstruct alloc_tag *start_tag = ct_to_alloc_tag(start);\n1136:\t\tstruct alloc_tag *stop_tag = ct_to_alloc_tag(stop);\n1137:\t\tstruct alloc_tag *tag;\n1138:\t\n1139:\t\t/*\n1140:\t\t * Turn tracing off for the tags of the module being unloaded. Without\n1141:\t\t * this, `alloc_tag_trace_cnt` would never reach zero and tracing would\n1142:\t\t * stay enabled forever.\n1143:\t\t *\n1144:\t\t * `alloc_tag_trace_mutex` is not needed here as this code path is\n1145:\t\t * protected by a `down_write(\u0026cttype-\u003emod_lock)`.\n1146:\t\t */\n1147:\t\tfor (tag = start_tag; tag \u003c stop_tag; tag++)\n1148:\t\t\talloc_tag_trace_toggle(tag, false);\n1149:\t}\n"
}

gemini-3.8-flash

null

null

							input: 33421
							output: 418
							thoughts: 2374
						

**Analysis of Allocation Tracing Patch for Uninitialized Memory Risks**

Okay, let's break this down. First, I'm examining a patch series focused on extending the kernel's allocation profiling infrastructure. The core additions are tracepoints to track allocation and free events, a new ioctl for toggling tracing, and some minor struct updates. My primary concern, given my expertise, is whether this introduces any potential for uninitialized memory reads or leaks, thus warranting a KMSAN run. I'm going through the code systematically to make sure.

I started by looking at `alloc_tag_trace_toggle`. My initial thought was about concurrency, so I double checked the locks: `mutex_lock(&alloc_tag_trace_mutex)` and `codetag_lock_module_list(alloc_tag_cttype)` and `down_write(&cttype->mod_lock)`.  Those seem solid for protecting against race conditions.  Standard tools like LOCKDEP and KASAN should flag any locking bugs or memory corruption issues.  KMSAN isn't the primary tool to catch concurrency or memory corruption, but uninitialized memory reads.

Next, I looked at the new tracepoints. I focused on the arguments passed, especially any strings. The `alloc_tag_hit` tracepoint uses `__assign_str`, and I made sure that the strings passed (`modname`, `filename`, `function`) are either literals or based on valid module/file/function names, so the risk of passing uninitialized memory is low. Likewise, the `alloc_tag_mem_alloced` and `alloc_tag_mem_freed` tracepoints are straightforward, with scalar arguments: a pointer, a `struct alloc_tag` pointer, and a `size_t` value. Those are all initialized and safe to pass.

I then went through the four KMSAN criteria:

1.  **Kernel structures sent to user space:** I examined the existing ioctls (`allocinfo_ioctl_get_at`, `allocinfo_ioctl_get_next`, `allocinfo_to_params`), and the new one (`ALLOCINFO_IOC_TOGGLE_TRACE`).  `ALLOCINFO_IOC_TOGGLE_TRACE` is input-only (`_IOW`), so there's no data being *returned* to userspace. For `allocinfo_ioctl_get_next`, the `params` struct is explicitly initialized to zero before any fields are set, which is great. In the same vein, `allocinfo_ioctl_get_at` on the stack is initialized, and then filled from userspace. The `trace_on` field is explicitly initialized by `allocinfo_to_params`, so no leaks there. I can see no evidence of uninitialized data leaking to userspace.

2.  **Conditional logic based on uninitialized variables:** I reviewed `matches_filter()` and `allocinfo_ioctl_toggle_trace()`. I verified that all variables used in conditional branching (`counters`, `fetched_counters`) are properly initialized *before* being read, which is a good sign. No risks found here.

3.  **Complex data structures with uninitialized fields:** I checked the `struct codetag` change, where `unsigned int flags` was converted to `atomic_t flags`, and initialized with `ATOMIC_INIT(0)`. No uninitialized fields creeping in with this patch.  I saw nothing new being allocated on the heap or stack with uninitialized memory.

4.  **Bounds checks exposing uninitialized memory:** I looked at `allocinfo_filter_valid` to make sure there are no unintended buffer accesses. I verified there's no way this patch introduces any buffer accesses that could leak uninitialized memory.

Finally, I checked to see if any memory allocation/freeing paths are altered. I examined `alloc_tag_add` and `alloc_tag_sub` in `slub.c`, `page_alloc.c` and `percpu.c`. They're merely hooks for the allocation profiling, passing the raw `ref` or `page` pointer as a parameter to the hooks, so no changes to allocation or freeing itself. This is all good!

So, the conclusion is: **KMSAN is not needed here.** Standard kernel bug detectors like KASAN and LOCKDEP are fully adequate for this patch series.  I'm confident that these changes don't introduce any uninitialized memory risks.  I'll prepare a clear, concise justification outlining why KASAN/LOCKDEP are appropriate and why KMSAN is not.

{
  "KMSANReasoning": "The patch series adds tracepoints (alloc_tag_hit, alloc_tag_mem_alloced, alloc_tag_mem_freed) and a new ioctl (ALLOCINFO_IOC_TOGGLE_TRACE) to toggle allocation profiling tracing.\n\nKMSAN vs KASAN applicability analysis:\n1. Kernel-to-userspace data leaks: The patch modifies UAPI struct allocinfo_counter by replacing 1 byte of padding with a trace_on field. In allocinfo_ioctl_get_next(), the output struct is zero-initialized with memset(\u0026params, 0, sizeof(params)) before populating fields. In allocinfo_ioctl_get_at(), the struct is zero-initialized and copied from user before fields are updated. The new trace_on field is explicitly assigned in allocinfo_to_params(). The new ioctl ALLOCINFO_IOC_TOGGLE_TRACE is _IOW (input only) and does not copy any data to userspace.\n2. Uninitialized variable reads / conditional branching: Stack variables such as counters in matches_filter() and allocinfo_ioctl_toggle_trace() are only read after being explicitly fetched (guarded by fetched_counters).\n3. Data structures: The codetag flags field is changed to atomic_t and statically initialized using ATOMIC_INIT(0).\n4. Memory allocation/freeing logic: The hook modifications in page_alloc, SLUB, and percpu only pass pointers to tracepoint callbacks and do not alter memory initialization, sizing, or buffer access.\n\nAny potential bugs introduced by this patch (e.g., concurrency races on static keys or atomic counters, locking interactions) are within the scope of LOCKDEP, KASAN, or standard kernel debug facilities. No uninitialized memory usage or info-leaks are introduced, so a dedicated KMSAN run is not needed.",
  "NeedsKMSAN": false
}

{
  "KMSANReasoning": "The patch series adds tracepoints (alloc_tag_hit, alloc_tag_mem_alloced, alloc_tag_mem_freed) and a new ioctl (ALLOCINFO_IOC_TOGGLE_TRACE) to toggle allocation profiling tracing.\n\nKMSAN vs KASAN applicability analysis:\n1. Kernel-to-userspace data leaks: The patch modifies UAPI struct allocinfo_counter by replacing 1 byte of padding with a trace_on field. In allocinfo_ioctl_get_next(), the output struct is zero-initialized with memset(\u0026params, 0, sizeof(params)) before populating fields. In allocinfo_ioctl_get_at(), the struct is zero-initialized and copied from user before fields are updated. The new trace_on field is explicitly assigned in allocinfo_to_params(). The new ioctl ALLOCINFO_IOC_TOGGLE_TRACE is _IOW (input only) and does not copy any data to userspace.\n2. Uninitialized variable reads / conditional branching: Stack variables such as counters in matches_filter() and allocinfo_ioctl_toggle_trace() are only read after being explicitly fetched (guarded by fetched_counters).\n3. Data structures: The codetag flags field is changed to atomic_t and statically initialized using ATOMIC_INIT(0).\n4. Memory allocation/freeing logic: The hook modifications in page_alloc, SLUB, and percpu only pass pointers to tracepoint callbacks and do not alter memory initialization, sizing, or buffer access.\n\nAny potential bugs introduced by this patch (e.g., concurrency races on static keys or atomic counters, locking interactions) are within the scope of LOCKDEP, KASAN, or standard kernel debug facilities. No uninitialized memory usage or info-leaks are introduced, so a dedicated KMSAN run is not needed.",
  "NeedsKMSAN": false
}