AI Trajectory

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{
  "EnableConfigs": [
    "MEM_ALLOC_PROFILING",
    "MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT",
    "MEMCG",
    "KFENCE"
  ],
  "FocusSymbols": [
    "alloc_slab_obj_exts",
    "__memcg_slab_post_alloc_hook",
    "__memcg_slab_free_hook",
    "__kfence_free",
    "__kmem_cache_create_args"
  ],
  "Reasoning": "The patch modifies the memory layout and handling of `struct slabobj_ext` in the slab allocator, which is used for memory allocation profiling and memory cgroup accounting. It optimizes the storage of `objcg` and `codetag_ref` pointers. These changes affect core slab allocation and freeing paths, making them highly reachable and functional.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 4a13bfca2427deea41b60eaabb8f8ec9e668853f\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Mon Jul 20 20:20:20 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 5389d241176a8a..d02eb54ee8f2c6 100644\n--- a/Documentation/mm/allocation-profiling.rst\n+++ b/Documentation/mm/allocation-profiling.rst\n@@ -112,3 +112,10 @@ To do so:\n \n - Then, use the following form for your allocations:\n   alloc_hooks_tag(ht-\u003eyour_saved_tag, kmalloc_noprof(...))\n+\n+Notes\n+=====\n+\n+- When a slab object is allocated from KFENCE, its accounting is skipped.\n+  KFENCE allocations are rare and limited to a small number, so this omission\n+  is negligible.\ndiff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h\nindex e1f46a0016fcfd..93869cc35c25bc 100644\n--- a/include/linux/memcontrol.h\n+++ b/include/linux/memcontrol.h\n@@ -1440,19 +1440,6 @@ static inline void mem_cgroup_flush_workqueue(void) { }\n static inline int mem_cgroup_init(void) { return 0; }\n #endif /* CONFIG_MEMCG */\n \n-/*\n- * Extended information for slab objects stored as an array in page-\u003ememcg_data\n- * if MEMCG_DATA_OBJEXTS is set.\n- */\n-struct slabobj_ext {\n-#ifdef CONFIG_MEMCG\n-\tstruct obj_cgroup *objcg;\n-#endif\n-#ifdef CONFIG_MEM_ALLOC_PROFILING\n-\tunion codetag_ref ref;\n-#endif\n-} __aligned(8);\n-\n static inline struct lruvec *parent_lruvec(struct lruvec *lruvec)\n {\n \tstruct mem_cgroup *memcg;\ndiff --git a/include/linux/slab.h b/include/linux/slab.h\nindex 3a14df50766ab0..f9132902c5a6dd 100644\n--- a/include/linux/slab.h\n+++ b/include/linux/slab.h\n@@ -45,6 +45,7 @@ enum _slab_flag_bits {\n #endif\n #ifdef CONFIG_MEMCG\n \t_SLAB_ACCOUNT,\n+\t_SLAB_MAY_ACCOUNT,\n #endif\n #ifdef CONFIG_KASAN_GENERIC\n \t_SLAB_KASAN,\n@@ -204,8 +205,10 @@ enum _slab_flag_bits {\n  */\n #ifdef CONFIG_MEMCG\n # define SLAB_ACCOUNT\t\t__SLAB_FLAG_BIT(_SLAB_ACCOUNT)\n+# define SLAB_MAY_ACCOUNT\t__SLAB_FLAG_BIT(_SLAB_MAY_ACCOUNT)\n #else\n # define SLAB_ACCOUNT\t\t__SLAB_FLAG_UNUSED\n+# define SLAB_MAY_ACCOUNT\t__SLAB_FLAG_UNUSED\n #endif\n \n #ifdef CONFIG_KASAN_GENERIC\ndiff --git a/mm/kfence/core.c b/mm/kfence/core.c\nindex 6577bd76954eb4..897ecf2594fb64 100644\n--- a/mm/kfence/core.c\n+++ b/mm/kfence/core.c\n@@ -640,6 +640,9 @@ static unsigned long kfence_init_pool(void)\n \t\tstruct slab *slab = page_slab(page);\n \t\tslab-\u003eobj_exts = (unsigned long)\u0026kfence_metadata_init[i / 2 - 1].obj_exts |\n \t\t\t\t MEMCG_DATA_OBJEXTS;\n+#ifdef CONFIG_64BIT\n+\t\tslab-\u003eobj_exts_needs_objcg = 1;\n+#endif\n #endif\n \t}\n \n@@ -1249,7 +1252,7 @@ void __kfence_free(void *addr)\n \tstruct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);\n \n #ifdef CONFIG_MEMCG\n-\tKFENCE_WARN_ON(meta-\u003eobj_exts.objcg);\n+\tKFENCE_WARN_ON(slab_obj_ext_objcg(\u0026meta-\u003eobj_exts));\n #endif\n \t/*\n \t * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing\ndiff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c\nindex de2d0f7d62b15e..9867c03ef0ae3d 100644\n--- a/mm/kfence/kfence_test.c\n+++ b/mm/kfence/kfence_test.c\n@@ -295,7 +295,7 @@ static void *test_alloc(struct kunit *test, size_t size, gfp_t gfp, enum allocat\n \t\t\t * memcg accounting works correctly.\n \t\t\t */\n \t\t\tKUNIT_EXPECT_EQ(test, obj_to_index(s, slab, alloc), 0U);\n-\t\t\tKUNIT_EXPECT_EQ(test, objs_per_slab(s, slab), 1);\n+\t\t\tKUNIT_EXPECT_EQ(test, ((unsigned int)slab-\u003eobjects), 1);\n \n \t\t\tif (policy == ALLOCATE_ANY)\n \t\t\t\treturn alloc;\ndiff --git a/mm/memcontrol.c b/mm/memcontrol.c\nindex 6dc4888a90f3fd..aace85fb99f973 100644\n--- a/mm/memcontrol.c\n+++ b/mm/memcontrol.c\n@@ -2865,18 +2865,19 @@ struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p)\n \t */\n \tunsigned long obj_exts;\n \tstruct slabobj_ext *obj_ext;\n-\tunsigned int off;\n+\tstruct obj_cgroup *objcg;\n \n \tobj_exts = slab_obj_exts(slab);\n \tif (!obj_exts)\n \t\treturn NULL;\n \n-\tget_slab_obj_exts(obj_exts);\n-\toff = obj_to_index(slab-\u003eslab_cache, slab, p);\n-\tobj_ext = slab_obj_ext(slab, obj_exts, off);\n-\tif (obj_ext-\u003eobjcg) {\n-\t\tstruct obj_cgroup *objcg = obj_ext-\u003eobjcg;\n+\tif (!slab_needs_objcg(slab))\n+\t\treturn NULL;\n \n+\tget_slab_obj_exts(obj_exts);\n+\tobj_ext = slab_obj_ext(slab-\u003eslab_cache, slab, obj_exts, p);\n+\tobjcg = slab_obj_ext_objcg(obj_ext);\n+\tif (objcg) {\n \t\tput_slab_obj_exts(obj_exts);\n \t\treturn obj_cgroup_memcg(objcg);\n \t}\n@@ -3541,7 +3542,6 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,\n \tsize_t obj_size = obj_full_size(s);\n \tstruct obj_cgroup *objcg;\n \tstruct slab *slab;\n-\tunsigned long off;\n \tsize_t i;\n \n \t/*\n@@ -3583,6 +3583,9 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,\n \n \t\tslab = virt_to_slab(p[i]);\n \n+\t\tif (IS_ENABLED(CONFIG_DEBUG_VM) \u0026\u0026 WARN_ON_ONCE(!slab_needs_objcg(slab)))\n+\t\t\tcontinue;\n+\n \t\tif (!slab_obj_exts(slab) \u0026\u0026\n \t\t    alloc_slab_obj_exts(slab, s, flags, slab_alloc_flags)) {\n \t\t\tcontinue;\n@@ -3616,10 +3619,11 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,\n \n \t\tobj_exts = slab_obj_exts(slab);\n \t\tget_slab_obj_exts(obj_exts);\n-\t\toff = obj_to_index(s, slab, p[i]);\n-\t\tobj_ext = slab_obj_ext(slab, obj_exts, off);\n+\t\tobj_ext = slab_obj_ext(s, slab, obj_exts, p[i]);\n+\n \t\tobj_cgroup_get(objcg);\n-\t\tobj_ext-\u003eobjcg = objcg;\n+\t\tslab_obj_ext_set_objcg(obj_ext, objcg);\n+\n \t\tput_slab_obj_exts(obj_exts);\n \t}\n \n@@ -3635,15 +3639,13 @@ void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,\n \t\tstruct obj_cgroup *objcg;\n \t\tstruct slabobj_ext *obj_ext;\n \t\tstruct obj_stock_pcp *stock;\n-\t\tunsigned int off;\n \n-\t\toff = obj_to_index(s, slab, p[i]);\n-\t\tobj_ext = slab_obj_ext(slab, obj_exts, off);\n-\t\tobjcg = obj_ext-\u003eobjcg;\n+\t\tobj_ext = slab_obj_ext(s, slab, obj_exts, p[i]);\n+\t\tobjcg = slab_obj_ext_objcg(obj_ext);\n \t\tif (!objcg)\n \t\t\tcontinue;\n \n-\t\tobj_ext-\u003eobjcg = NULL;\n+\t\tslab_obj_ext_set_objcg(obj_ext, NULL);\n \n \t\tstock = trylock_stock();\n \t\t__refill_obj_stock(objcg, stock, obj_size, true);\ndiff --git a/mm/slab.h b/mm/slab.h\nindex f5e336b6b6b04c..18c2a807f023ce 100644\n--- a/mm/slab.h\n+++ b/mm/slab.h\n@@ -81,10 +81,11 @@ struct freelist_counters {\n #ifdef CONFIG_64BIT\n \t\t\t\t\t/*\n \t\t\t\t\t * Some optimizations use free bits in 'counters' field\n-\t\t\t\t\t * to save memory. In case -\u003estride field is not available,\n-\t\t\t\t\t * such optimizations are disabled.\n+\t\t\t\t\t * to save memory or CPU. If these free bits are not\n+\t\t\t\t\t * available, such optimizations are disabled.\n \t\t\t\t\t */\n-\t\t\t\t\tunsigned int stride;\n+\t\t\t\t\tunsigned obj_exts_in_object:1;\n+\t\t\t\t\tunsigned obj_exts_needs_objcg:1;\n #endif\n \t\t\t\t};\n \t\t\t};\n@@ -330,12 +331,6 @@ static inline unsigned int obj_to_index(const struct kmem_cache *cache,\n \treturn __obj_to_index(cache, slab_address(slab), obj);\n }\n \n-static inline int objs_per_slab(const struct kmem_cache *cache,\n-\t\t\t\tconst struct slab *slab)\n-{\n-\treturn slab-\u003eobjects;\n-}\n-\n /*\n  * State of the slab allocator.\n  *\n@@ -555,6 +550,93 @@ static inline bool need_kmalloc_no_objext(void)\n \treturn false;\n }\n \n+/*\n+ * Extended information for slab objects stored as a pointer to an array in\n+ * slab-\u003eobj_exts (aliasing page-\u003ememcg_data) if MEMCG_DATA_OBJEXTS is set.\n+ */\n+struct slabobj_ext {\n+\t/*\n+\t * All elements of the union should be pointer-sized to avoid memory\n+\t * waste\n+\t */\n+\tunion {\n+#ifdef CONFIG_MEMCG\n+\t\tstruct obj_cgroup *_objcg;\n+#endif\n+#ifdef CONFIG_MEM_ALLOC_PROFILING\n+\t\tunion codetag_ref _ctref;\n+#endif\n+\t};\n+} __aligned(8);\n+\n+#ifdef CONFIG_MEM_ALLOC_PROFILING\n+DECLARE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,\n+\t\t\t slab_obj_ext_has_codetag_key);\n+\n+static inline bool slab_obj_ext_has_codetag(void)\n+{\n+\treturn static_branch_maybe(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,\n+\t\t\t\t   \u0026slab_obj_ext_has_codetag_key);\n+}\n+#else\n+static inline bool slab_obj_ext_has_codetag(void)\n+{\n+\treturn false;\n+}\n+#endif\n+\n+#ifdef CONFIG_MEMCG\n+static inline bool cache_needs_objcg(struct kmem_cache *cache)\n+{\n+\treturn (cache-\u003eflags \u0026 SLAB_MAY_ACCOUNT);\n+}\n+\n+static inline bool slab_needs_objcg(struct slab *slab)\n+{\n+#ifdef CONFIG_64BIT\n+\treturn slab-\u003eobj_exts_needs_objcg;\n+#else\n+\treturn cache_needs_objcg(slab-\u003eslab_cache);\n+#endif\n+}\n+#else\n+static inline bool cache_needs_objcg(struct kmem_cache *cache)\n+{\n+\treturn false;\n+}\n+\n+static inline bool slab_needs_objcg(struct slab *slab)\n+{\n+\treturn false;\n+}\n+#endif\n+\n+static inline size_t cache_obj_ext_size(struct kmem_cache *s)\n+{\n+\tsize_t sz = 0;\n+\n+\tif (cache_needs_objcg(s))\n+\t\tsz += 1;\n+\n+\tif (slab_obj_ext_has_codetag())\n+\t\tsz += 1;\n+\n+\treturn sizeof(struct slabobj_ext) * sz;\n+}\n+\n+static inline size_t slab_obj_ext_size(struct slab *slab)\n+{\n+\tsize_t sz = 0;\n+\n+\tif (slab_needs_objcg(slab))\n+\t\tsz += 1;\n+\n+\tif (slab_obj_ext_has_codetag())\n+\t\tsz += 1;\n+\n+\treturn sizeof(struct slabobj_ext) * sz;\n+}\n+\n #ifdef CONFIG_SLAB_OBJ_EXT\n \n /*\n@@ -572,7 +654,7 @@ static inline bool need_kmalloc_no_objext(void)\n  * obj_exts = slab_obj_exts(slab);\n  * if (obj_exts) {\n  *         get_slab_obj_exts(obj_exts);\n- *         obj_ext = slab_obj_ext(slab, obj_exts, obj_to_index(s, slab, obj));\n+ *         obj_ext = slab_obj_ext(s, slab, obj_exts, obj);\n  *         // do something with obj_ext\n  *         put_slab_obj_exts(obj_exts);\n  * }\n@@ -610,48 +692,82 @@ static inline void put_slab_obj_exts(unsigned long obj_exts)\n }\n \n #ifdef CONFIG_64BIT\n-static inline void slab_set_stride(struct slab *slab, unsigned int stride)\n-{\n-\tslab-\u003estride = stride;\n-}\n-static inline unsigned int slab_get_stride(struct slab *slab)\n+static inline bool obj_exts_in_object(struct slab *slab)\n {\n-\treturn slab-\u003estride;\n+\t/*\n+\t * Note we cannot rely on the SLAB_OBJ_EXT_IN_OBJ flag here and need to\n+\t * check the per-slab bit. A cache can have SLAB_OBJ_EXT_IN_OBJ set, but\n+\t * allocations within_slab_leftover are preferred. And those may be\n+\t * possible or not depending on the particular slab's size.\n+\t */\n+\treturn slab-\u003eobj_exts_in_object;\n }\n #else\n-static inline void slab_set_stride(struct slab *slab, unsigned int stride)\n+static inline bool obj_exts_in_object(struct slab *slab)\n {\n-\tVM_WARN_ON_ONCE(stride != sizeof(struct slabobj_ext));\n-}\n-static inline unsigned int slab_get_stride(struct slab *slab)\n-{\n-\treturn sizeof(struct slabobj_ext);\n+\treturn false;\n }\n #endif\n \n /*\n  * slab_obj_ext - get the pointer to the slab object extension metadata\n  * associated with an object in a slab.\n+ * @s: cache that the slab blongs to\n  * @slab: a pointer to the slab struct\n  * @obj_exts: a pointer to the object extension vector\n- * @index: an index of the object\n+ * @obj: a pointer to the object\n  *\n  * Returns a pointer to the object extension associated with the object.\n  * Must be called within a section covered by get/put_slab_obj_exts().\n  */\n-static inline struct slabobj_ext *slab_obj_ext(struct slab *slab,\n-\t\t\t\t\t       unsigned long obj_exts,\n-\t\t\t\t\t       unsigned int index)\n+static inline struct slabobj_ext *\n+slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts,\n+\t     const void *obj)\n {\n \tstruct slabobj_ext *obj_ext;\n+\tunsigned int index;\n+\tunsigned int stride;\n \n \tVM_WARN_ON_ONCE(obj_exts != slab_obj_exts(slab));\n \n-\tobj_ext = (struct slabobj_ext *)(obj_exts +\n-\t\t\t\t\t slab_get_stride(slab) * index);\n+\tindex = obj_to_index(s, slab, obj);\n+\n+\tif (!obj_exts_in_object(slab))\n+\t\tstride = slab_obj_ext_size(slab);\n+\telse\n+\t\tstride = s-\u003esize;\n+\n+\tobj_ext = (struct slabobj_ext *)(obj_exts + index * stride);\n+\n \treturn kasan_reset_tag(obj_ext);\n }\n \n+#ifdef CONFIG_MEMCG\n+static inline struct obj_cgroup *slab_obj_ext_objcg(struct slabobj_ext *obj_ext)\n+{\n+\t/* if objcg exists, it comes first, so we don't need to do anything */\n+\treturn obj_ext-\u003e_objcg;\n+}\n+\n+static inline void slab_obj_ext_set_objcg(struct slabobj_ext *obj_ext,\n+\t\t\t\t\t  struct obj_cgroup *objcg)\n+{\n+\t/* if objcg exists, it comes first, so we don't need to do anything */\n+\tobj_ext-\u003e_objcg = objcg;\n+}\n+#endif\n+\n+#ifdef CONFIG_MEM_ALLOC_PROFILING\n+static inline union codetag_ref *\n+slab_obj_ext_codetag_ref(struct slab *slab, struct slabobj_ext *obj_ext)\n+{\n+\tif (slab_needs_objcg(slab))\n+\t\tobj_ext += 1;\n+\n+\treturn \u0026obj_ext-\u003e_ctref;\n+}\n+#endif\n+\n int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,\n \t\t\tgfp_t gfp, unsigned int alloc_flags);\n \n@@ -662,16 +778,17 @@ static inline unsigned long slab_obj_exts(struct slab *slab)\n \treturn 0;\n }\n \n-static inline struct slabobj_ext *slab_obj_ext(struct slab *slab,\n-\t\t\t\t\t       unsigned long obj_exts,\n-\t\t\t\t\t       unsigned int index)\n+static inline struct slabobj_ext *\n+slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts,\n+\t     const void *obj)\n {\n \treturn NULL;\n }\n \n-static inline void slab_set_stride(struct slab *slab, unsigned int stride) { }\n-static inline unsigned int slab_get_stride(struct slab *slab) { return 0; }\n-\n+static inline bool obj_exts_in_object(struct slab *slab)\n+{\n+\treturn false;\n+}\n \n #endif /* CONFIG_SLAB_OBJ_EXT */\n \ndiff --git a/mm/slab_common.c b/mm/slab_common.c\nindex 03ecac12cd865f..4e983e2503387a 100644\n--- a/mm/slab_common.c\n+++ b/mm/slab_common.c\n@@ -52,7 +52,7 @@ struct kmem_cache *kmem_cache;\n \t\tSLAB_OBJ_EXT_IN_OBJ)\n \n #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \\\n-\t\t\t SLAB_CACHE_DMA32 | SLAB_ACCOUNT)\n+\t\t\t SLAB_CACHE_DMA32 | SLAB_ACCOUNT | SLAB_MAY_ACCOUNT)\n \n /*\n  * Merge control. If this is set then no merging of slab caches will occur.\n@@ -359,6 +359,13 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,\n \t\tgoto out_unlock;\n \t}\n \n+\t/*\n+\t * For now we assume any cache can be used with __GFP_ACCOUNT and thus\n+\t * may need to store objcg pointers for objects\n+\t */\n+\tif (!mem_cgroup_kmem_disabled())\n+\t\tflags |= SLAB_MAY_ACCOUNT;\n+\n \t/* Fail closed on bad usersize of useroffset values. */\n \tif (!IS_ENABLED(CONFIG_HARDENED_USERCOPY) ||\n \t    WARN_ON(!args-\u003eusersize \u0026\u0026 args-\u003euseroffset) ||\n@@ -984,11 +991,19 @@ new_kmalloc_cache(int idx, enum kmalloc_cache_type type)\n #endif\n \n \t/*\n-\t * If CONFIG_MEMCG is enabled, disable cache merging for\n-\t * KMALLOC_NORMAL caches.\n+\t * If memcg_kmem is enabled and this is a KMALLOC_NORMAL cache and  not\n+\t * aliased with any other type, make sure it's never merged with any other\n+\t * cache.\n+\t *\n+\t * In other cases the kmalloc cache may end up being used for a\n+\t * __GFP_ACCOUNT allocation so mark it as such\n \t */\n-\tif (IS_ENABLED(CONFIG_MEMCG) \u0026\u0026 (type == KMALLOC_NORMAL))\n-\t\tflags |= SLAB_NO_MERGE;\n+\tif (!mem_cgroup_kmem_disabled()) {\n+\t\tif (type == KMALLOC_NORMAL \u0026\u0026 KMALLOC_RECLAIM != KMALLOC_NORMAL)\n+\t\t\tflags |= SLAB_NO_MERGE;\n+\t\telse\n+\t\t\tflags |= SLAB_MAY_ACCOUNT;\n+\t}\n \n \tif (minalign \u003e ARCH_KMALLOC_MINALIGN) {\n \t\taligned_size = ALIGN(aligned_size, minalign);\ndiff --git a/mm/slub.c b/mm/slub.c\nindex 0337e60db5ace0..e6148b73b92f88 100644\n--- a/mm/slub.c\n+++ b/mm/slub.c\n@@ -213,6 +213,11 @@ DEFINE_STATIC_KEY_FALSE(slub_debug_enabled);\n static DEFINE_STATIC_KEY_FALSE(strict_numa);\n #endif\n \n+#ifdef CONFIG_MEM_ALLOC_PROFILING\n+DEFINE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,\n+\t\t\tslab_obj_ext_has_codetag_key);\n+#endif\n+\n /* Structure holding extra parameters for slab allocations */\n struct slab_alloc_context {\n \tunsigned long caller_addr;\n@@ -803,7 +808,7 @@ static inline bool need_slab_obj_exts(struct kmem_cache *s)\n \n static inline unsigned int obj_exts_size_in_slab(struct slab *slab)\n {\n-\treturn sizeof(struct slabobj_ext) * slab-\u003eobjects;\n+\treturn slab_obj_ext_size(slab) * slab-\u003eobjects;\n }\n \n static inline unsigned long obj_exts_offset_in_slab(struct kmem_cache *s,\n@@ -870,18 +875,6 @@ static inline bool obj_exts_in_slab(struct kmem_cache *s, struct slab *slab)\n #endif\n \n #if defined(CONFIG_SLAB_OBJ_EXT) \u0026\u0026 defined(CONFIG_64BIT)\n-static bool obj_exts_in_object(struct kmem_cache *s, struct slab *slab)\n-{\n-\t/*\n-\t * Note we cannot rely on the SLAB_OBJ_EXT_IN_OBJ flag here and need to\n-\t * check the stride. A cache can have SLAB_OBJ_EXT_IN_OBJ set, but\n-\t * allocations within_slab_leftover are preferred. And those may be\n-\t * possible or not depending on the particular slab's size.\n-\t */\n-\treturn obj_exts_in_slab(s, slab) \u0026\u0026\n-\t       (slab_get_stride(slab) == s-\u003esize);\n-}\n-\n static unsigned int obj_exts_offset_in_object(struct kmem_cache *s)\n {\n \tunsigned int offset = get_info_end(s);\n@@ -896,16 +889,20 @@ static unsigned int obj_exts_offset_in_object(struct kmem_cache *s)\n \n \treturn offset;\n }\n-#else\n-static inline bool obj_exts_in_object(struct kmem_cache *s, struct slab *slab)\n+\n+static inline void slab_set_obj_exts_in_object(struct slab *slab)\n {\n-\treturn false;\n+\tslab-\u003eobj_exts_in_object = 1;\n }\n-\n+#else\n static inline unsigned int obj_exts_offset_in_object(struct kmem_cache *s)\n {\n \treturn 0;\n }\n+\n+static inline void slab_set_obj_exts_in_object(struct slab *slab)\n+{\n+}\n #endif\n \n #ifdef CONFIG_SLUB_DEBUG\n@@ -1206,8 +1203,8 @@ static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p)\n \n \toff += kasan_metadata_size(s, false);\n \n-\tif (obj_exts_in_object(s, slab))\n-\t\toff += sizeof(struct slabobj_ext);\n+\tif (obj_exts_in_object(slab))\n+\t\toff += slab_obj_ext_size(slab);\n \n \tif (off != size_from_object(s))\n \t\t/* Beginning of the filler is the free pointer */\n@@ -1411,8 +1408,8 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p)\n \n \toff += kasan_metadata_size(s, false);\n \n-\tif (obj_exts_in_object(s, slab))\n-\t\toff += sizeof(struct slabobj_ext);\n+\tif (obj_exts_in_object(slab))\n+\t\toff += slab_obj_ext_size(slab);\n \n \tif (size_from_object(s) == off)\n \t\treturn 1;\n@@ -1439,7 +1436,7 @@ slab_pad_check(struct kmem_cache *s, struct slab *slab)\n \tlength = slab_size(slab);\n \tend = start + length;\n \n-\tif (obj_exts_in_slab(s, slab) \u0026\u0026 !obj_exts_in_object(s, slab)) {\n+\tif (obj_exts_in_slab(s, slab) \u0026\u0026 !obj_exts_in_object(slab)) {\n \t\tremainder = length;\n \t\tremainder -= obj_exts_offset_in_slab(s, slab);\n \t\tremainder -= obj_exts_size_in_slab(slab);\n@@ -2070,20 +2067,26 @@ static inline void mark_obj_codetag_empty(const void *obj)\n \tobj_slab = virt_to_slab(obj);\n \tslab_exts = slab_obj_exts(obj_slab);\n \tif (slab_exts) {\n+\t\tstruct slabobj_ext *ext;\n+\t\tunion codetag_ref *ref;\n+\n \t\tget_slab_obj_exts(slab_exts);\n-\t\tunsigned int offs = obj_to_index(obj_slab-\u003eslab_cache,\n-\t\t\t\t\t\t obj_slab, obj);\n-\t\tstruct slabobj_ext *ext = slab_obj_ext(obj_slab,\n-\t\t\t\t\t\t       slab_exts, offs);\n+\t\text = slab_obj_ext(obj_slab-\u003eslab_cache, obj_slab, slab_exts, obj);\n+\t\tref = slab_obj_ext_codetag_ref(obj_slab, ext);\n+\n+\t\tif (is_kfence_address(obj)) {\n+\t\t\tput_slab_obj_exts(slab_exts);\n+\t\t\treturn;\n+\t\t}\n \n-\t\tif (unlikely(is_codetag_empty(\u0026ext-\u003eref))) {\n+\t\tif (unlikely(is_codetag_empty(ref))) {\n \t\t\tput_slab_obj_exts(slab_exts);\n \t\t\treturn;\n \t\t}\n \n \t\t/* codetag should be NULL here */\n-\t\tWARN_ON(ext-\u003eref.ct);\n-\t\tset_codetag_empty(\u0026ext-\u003eref);\n+\t\tWARN_ON(ref-\u003ect);\n+\t\tset_codetag_empty(ref);\n \t\tput_slab_obj_exts(slab_exts);\n \t}\n }\n@@ -2093,19 +2096,29 @@ static inline bool mark_failed_objexts_alloc(struct slab *slab)\n \treturn cmpxchg(\u0026slab-\u003eobj_exts, 0, OBJEXTS_ALLOC_FAIL) == 0;\n }\n \n-static inline void handle_failed_objexts_alloc(unsigned long obj_exts,\n-\t\t\tstruct slabobj_ext *vec, unsigned int objects)\n+static inline void handle_failed_objexts_alloc(struct slab *slab,\n+\t\tunsigned long obj_exts, struct slabobj_ext *vec)\n {\n+\tunsigned int stride;\n+\n+\tif (!mem_alloc_profiling_enabled())\n+\t\treturn;\n+\n \t/*\n \t * If vector previously failed to allocate then we have live\n \t * objects with no tag reference. Mark all references in this\n \t * vector as empty to avoid warnings later on.\n \t */\n-\tif (obj_exts == OBJEXTS_ALLOC_FAIL) {\n-\t\tunsigned int i;\n+\tif (obj_exts != OBJEXTS_ALLOC_FAIL)\n+\t\treturn;\n+\n+\tstride = slab_obj_ext_size(slab) / sizeof(*vec);\n+\n+\tfor (unsigned int i = 0; i \u003c slab-\u003eobjects; i++) {\n+\t\tunion codetag_ref *ref = slab_obj_ext_codetag_ref(slab, vec);\n \n-\t\tfor (i = 0; i \u003c objects; i++)\n-\t\t\tset_codetag_empty(\u0026vec[i].ref);\n+\t\tset_codetag_empty(ref);\n+\t\tvec += stride;\n \t}\n }\n \n@@ -2113,8 +2126,8 @@ static inline void handle_failed_objexts_alloc(unsigned long obj_exts,\n \n static inline void mark_obj_codetag_empty(const void *obj) {}\n static inline bool mark_failed_objexts_alloc(struct slab *slab) { return false; }\n-static inline void handle_failed_objexts_alloc(unsigned long obj_exts,\n-\t\t\tstruct slabobj_ext *vec, unsigned int objects) {}\n+static inline void handle_failed_objexts_alloc(struct slab *slab,\n+\t\tunsigned long obj_exts, struct slabobj_ext *vec) {}\n \n #endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */\n \n@@ -2127,12 +2140,11 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,\n \t\t\tgfp_t gfp, unsigned int alloc_flags)\n {\n \tconst bool allow_spin = alloc_flags_allow_spinning(alloc_flags);\n-\tunsigned int objects = objs_per_slab(s, slab);\n \tbool new_slab = alloc_flags \u0026 SLAB_ALLOC_NEW_SLAB;\n \tunsigned long new_exts;\n \tunsigned long old_exts;\n \tstruct slabobj_ext *vec;\n-\tsize_t sz = sizeof(struct slabobj_ext) * slab-\u003eobjects;\n+\tsize_t sz = slab_obj_ext_size(slab) * slab-\u003eobjects;\n \n \tgfp \u0026= ~OBJCGS_CLEAR_MASK;\n \t/*\n@@ -2183,7 +2195,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,\n #endif\n retry:\n \told_exts = READ_ONCE(slab-\u003eobj_exts);\n-\thandle_failed_objexts_alloc(old_exts, vec, objects);\n+\thandle_failed_objexts_alloc(slab, old_exts, vec);\n \n \tif (new_slab) {\n \t\t/*\n@@ -2250,9 +2262,6 @@ static void alloc_slab_obj_exts_early(struct kmem_cache *s, struct slab *slab)\n \tvoid *addr;\n \tunsigned long obj_exts;\n \n-\t/* Initialize stride early to avoid memory ordering issues */\n-\tslab_set_stride(slab, sizeof(struct slabobj_ext));\n-\n \tif (!need_slab_obj_exts(s))\n \t\treturn;\n \n@@ -2278,15 +2287,14 @@ static void alloc_slab_obj_exts_early(struct kmem_cache *s, struct slab *slab)\n \n \t\tget_slab_obj_exts(obj_exts);\n \t\tfor_each_object(addr, s, slab_address(slab), slab-\u003eobjects)\n-\t\t\tmemset(kasan_reset_tag(addr) + offset, 0,\n-\t\t\t       sizeof(struct slabobj_ext));\n+\t\t\tmemset(kasan_reset_tag(addr) + offset, 0, slab_obj_ext_size(slab));\n \t\tput_slab_obj_exts(obj_exts);\n \n #ifdef CONFIG_MEMCG\n \t\tobj_exts |= MEMCG_DATA_OBJEXTS;\n #endif\n \t\tslab-\u003eobj_exts = obj_exts;\n-\t\tslab_set_stride(slab, s-\u003esize);\n+\t\tslab_set_obj_exts_in_object(slab);\n \t}\n }\n \n@@ -2352,6 +2360,9 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,\n \tif (alloc_flags \u0026 SLAB_ALLOC_NO_RECURSE)\n \t\treturn;\n \n+\tif (is_kfence_address(object))\n+\t\treturn;\n+\n \tslab = virt_to_slab(object);\n \tobj_exts = prepare_slab_obj_exts_hook(s, slab, flags, alloc_flags, object);\n \t/*\n@@ -2360,11 +2371,15 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,\n \t * check should be added before alloc_tag_add().\n \t */\n \tif (obj_exts) {\n-\t\tunsigned int obj_idx = obj_to_index(s, slab, object);\n+\t\tunion codetag_ref *ref;\n \n \t\tget_slab_obj_exts(obj_exts);\n-\t\tobj_ext = slab_obj_ext(slab, obj_exts, obj_idx);\n-\t\talloc_tag_add(\u0026obj_ext-\u003eref, current-\u003ealloc_tag, s-\u003esize);\n+\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+\n \t\tput_slab_obj_exts(obj_exts);\n \t} else {\n \t\talloc_tag_set_inaccurate(current-\u003ealloc_tag);\n@@ -2384,7 +2399,6 @@ static noinline void\n __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,\n \t\t\t       int objects)\n {\n-\tint i;\n \tunsigned long obj_exts;\n \n \t/* slab-\u003eobj_exts might not be NULL if it was created for MEMCG accounting. */\n@@ -2396,10 +2410,14 @@ __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p\n \t\treturn;\n \n \tget_slab_obj_exts(obj_exts);\n-\tfor (i = 0; i \u003c objects; i++) {\n-\t\tunsigned int off = obj_to_index(s, slab, p[i]);\n+\tfor (int i = 0; i \u003c objects; i++) {\n+\t\tstruct slabobj_ext *ext;\n+\n+\t\tif (is_kfence_address(p[i]))\n+\t\t\tcontinue;\n \n-\t\talloc_tag_sub(\u0026slab_obj_ext(slab, obj_exts, off)-\u003eref, s-\u003esize);\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}\n \tput_slab_obj_exts(obj_exts);\n }\n@@ -2412,6 +2430,25 @@ alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,\n \t\t__alloc_tagging_slab_free_hook(s, slab, p, objects);\n }\n \n+/*\n+ * Make sure the static key used by slab_obj_ext_has_codetag() reflects the\n+ * value of !mem_alloc_profiling_permanently_disabled()\n+ *\n+ * Any later mem alloc profiling shutdown won't be reflected in the static key\n+ * because obj_exts with codetags might already exist.\n+ */\n+static void __init slab_obj_ext_has_codetag_init(void)\n+{\n+\tbool need_codetag = !mem_alloc_profiling_permanently_disabled();\n+\n+\tif (need_codetag != static_key_enabled(\u0026slab_obj_ext_has_codetag_key)) {\n+\t\tif (need_codetag)\n+\t\t\tstatic_branch_enable(\u0026slab_obj_ext_has_codetag_key);\n+\t\telse\n+\t\t\tstatic_branch_disable(\u0026slab_obj_ext_has_codetag_key);\n+\t}\n+}\n+\n #else /* CONFIG_MEM_ALLOC_PROFILING */\n \n static inline void\n@@ -2426,6 +2463,10 @@ alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,\n {\n }\n \n+static inline void slab_obj_ext_has_codetag_init(void)\n+{\n+}\n+\n #endif /* CONFIG_MEM_ALLOC_PROFILING */\n \n \n@@ -2471,6 +2512,9 @@ void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,\n \tif (likely(!obj_exts))\n \t\treturn;\n \n+\tif (!slab_needs_objcg(slab))\n+\t\treturn;\n+\n \tget_slab_obj_exts(obj_exts);\n \t__memcg_slab_free_hook(s, slab, p, objects, obj_exts);\n \tput_slab_obj_exts(obj_exts);\n@@ -2484,7 +2528,6 @@ bool memcg_slab_post_charge(void *p, gfp_t flags)\n \tstruct kmem_cache *s;\n \tstruct page *page;\n \tstruct slab *slab;\n-\tunsigned long off;\n \n \tpage = virt_to_page(p);\n \tif (PageLargeKmalloc(page)) {\n@@ -2517,16 +2560,15 @@ bool memcg_slab_post_charge(void *p, gfp_t flags)\n \t * of slab_obj_exts being allocated from the same slab and thus the slab\n \t * becoming effectively unfreeable.\n \t */\n-\tif (is_kmalloc_normal(s))\n+\tif (!cache_needs_objcg(s))\n \t\treturn true;\n \n \t/* Ignore already charged objects. */\n \tobj_exts = slab_obj_exts(slab);\n \tif (obj_exts) {\n \t\tget_slab_obj_exts(obj_exts);\n-\t\toff = obj_to_index(s, slab, p);\n-\t\tobj_ext = slab_obj_ext(slab, obj_exts, off);\n-\t\tif (unlikely(obj_ext-\u003eobjcg)) {\n+\t\tobj_ext = slab_obj_ext(s, slab, obj_exts, p);\n+\t\tif (unlikely(slab_obj_ext_objcg(obj_ext))) {\n \t\t\tput_slab_obj_exts(obj_exts);\n \t\t\treturn true;\n \t\t}\n@@ -3391,10 +3433,15 @@ static struct slab *allocate_slab(struct kmem_cache *s, gfp_t flags,\n \t\tstat(s, ORDER_FALLBACK);\n \t}\n \n+\t/* Initializes frozen, inuse, and any extra 64bit-only flags */\n+\tslab-\u003ecounters = 0;\n+\n \tslab-\u003eobjects = oo_objects(oo);\n-\tslab-\u003einuse = 0;\n-\tslab-\u003efrozen = 0;\n \n+#ifdef CONFIG_64BIT\n+\tif (cache_needs_objcg(s))\n+\t\tslab-\u003eobj_exts_needs_objcg = 1;\n+#endif\n \tslab-\u003eslab_cache = s;\n \n \tkasan_poison_slab(slab);\n@@ -6526,7 +6573,7 @@ static inline size_t slab_ksize(struct slab *slab)\n \t */\n \tif (s-\u003eflags \u0026 (SLAB_TYPESAFE_BY_RCU | SLAB_STORE_USER))\n \t\treturn s-\u003einuse;\n-\telse if (obj_exts_in_object(s, slab))\n+\telse if (obj_exts_in_object(slab))\n \t\treturn s-\u003einuse;\n \t/*\n \t * Else we can use all the padding etc for the allocation\n@@ -7929,7 +7976,7 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s)\n \taligned_size = ALIGN(size, s-\u003ealign);\n #if defined(CONFIG_SLAB_OBJ_EXT) \u0026\u0026 defined(CONFIG_64BIT)\n \tif (slab_args_unmergeable(args, s-\u003eflags) \u0026\u0026\n-\t\t\t(aligned_size - size \u003e= sizeof(struct slabobj_ext)))\n+\t\t\t(aligned_size - size \u003e= cache_obj_ext_size(s)))\n \t\ts-\u003eflags |= SLAB_OBJ_EXT_IN_OBJ;\n #endif\n \tsize = aligned_size;\n@@ -8539,6 +8586,8 @@ void __init kmem_cache_init(void)\n \t\tboot_kmem_cache_node;\n \tint node;\n \n+\tslab_obj_ext_has_codetag_init();\n+\n \tif (debug_guardpage_minorder())\n \t\tslub_max_order = 0;\n \n"
}

best-expensive

null

{
  "EnableConfigs": [
    "MEM_ALLOC_PROFILING",
    "MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT",
    "MEMCG",
    "KFENCE"
  ],
  "FocusSymbols": [
    "alloc_slab_obj_exts",
    "__memcg_slab_post_alloc_hook",
    "__memcg_slab_free_hook",
    "__kfence_free",
    "__kmem_cache_create_args"
  ],
  "Reasoning": "The patch modifies the memory layout and handling of `struct slabobj_ext` in the slab allocator, which is used for memory allocation profiling and memory cgroup accounting. It optimizes the storage of `objcg` and `codetag_ref` pointers. These changes affect core slab allocation and freeing paths, making them highly reachable and functional.",
  "WorthFuzzing": true
}

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

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

Return WorthFuzzing=false if the patch only contains:
- Modifications to Documentation/, Kconfig files, or code comments.
- Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints.
- Changes to numeric constants or macros that do not functionally alter execution flow.
- Code paths that are impossible to reach in virtualized environments like GCE or QEMU,
even when utilizing software-emulated hardware (e.g., usb gadget, mac80211_hwsim).

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

When returning WorthFuzzing=true, you MUST ALSO:
1. Extract any specific kernel functions that should be heavily fuzzed into FocusSymbols.
   Avoid listing generic hot-path functions to prevent skewed test distributions.
2. Identify any specific CONFIG_ options required to properly test this new/modified feature.
   Go and look into the Kconfig files and check for ifdefs around the code, do not make assumptions.
   Do not list too generic configs (we already have them enabled). Only list those that
   specifically cover the modified code. List them in the EnableConfigs output array,
   and DO NOT add a 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

For your convenience, here is the diff of the changes:
commit 4a13bfca2427deea41b60eaabb8f8ec9e668853f
Author: syz-cluster <triage@syzkaller.com>
Date:   Mon Jul 20 20:20:20 2026 +0000

    syz-cluster: applied patch under review

diff --git a/Documentation/mm/allocation-profiling.rst b/Documentation/mm/allocation-profiling.rst
index 5389d241176a8a..d02eb54ee8f2c6 100644
--- a/Documentation/mm/allocation-profiling.rst
+++ b/Documentation/mm/allocation-profiling.rst
@@ -112,3 +112,10 @@ To do so:
 
 - Then, use the following form for your allocations:
   alloc_hooks_tag(ht->your_saved_tag, kmalloc_noprof(...))
+
+Notes
+=====
+
+- When a slab object is allocated from KFENCE, its accounting is skipped.
+  KFENCE allocations are rare and limited to a small number, so this omission
+  is negligible.
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index e1f46a0016fcfd..93869cc35c25bc 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1440,19 +1440,6 @@ static inline void mem_cgroup_flush_workqueue(void) { }
 static inline int mem_cgroup_init(void) { return 0; }
 #endif /* CONFIG_MEMCG */
 
-/*
- * Extended information for slab objects stored as an array in page->memcg_data
- * if MEMCG_DATA_OBJEXTS is set.
- */
-struct slabobj_ext {
-#ifdef CONFIG_MEMCG
-	struct obj_cgroup *objcg;
-#endif
-#ifdef CONFIG_MEM_ALLOC_PROFILING
-	union codetag_ref ref;
-#endif
-} __aligned(8);
-
 static inline struct lruvec *parent_lruvec(struct lruvec *lruvec)
 {
 	struct mem_cgroup *memcg;
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 3a14df50766ab0..f9132902c5a6dd 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -45,6 +45,7 @@ enum _slab_flag_bits {
 #endif
 #ifdef CONFIG_MEMCG
 	_SLAB_ACCOUNT,
+	_SLAB_MAY_ACCOUNT,
 #endif
 #ifdef CONFIG_KASAN_GENERIC
 	_SLAB_KASAN,
@@ -204,8 +205,10 @@ enum _slab_flag_bits {
  */
 #ifdef CONFIG_MEMCG
 # define SLAB_ACCOUNT		__SLAB_FLAG_BIT(_SLAB_ACCOUNT)
+# define SLAB_MAY_ACCOUNT	__SLAB_FLAG_BIT(_SLAB_MAY_ACCOUNT)
 #else
 # define SLAB_ACCOUNT		__SLAB_FLAG_UNUSED
+# define SLAB_MAY_ACCOUNT	__SLAB_FLAG_UNUSED
 #endif
 
 #ifdef CONFIG_KASAN_GENERIC
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 6577bd76954eb4..897ecf2594fb64 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -640,6 +640,9 @@ static unsigned long kfence_init_pool(void)
 		struct slab *slab = page_slab(page);
 		slab->obj_exts = (unsigned long)&kfence_metadata_init[i / 2 - 1].obj_exts |
 				 MEMCG_DATA_OBJEXTS;
+#ifdef CONFIG_64BIT
+		slab->obj_exts_needs_objcg = 1;
+#endif
 #endif
 	}
 
@@ -1249,7 +1252,7 @@ void __kfence_free(void *addr)
 	struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);
 
 #ifdef CONFIG_MEMCG
-	KFENCE_WARN_ON(meta->obj_exts.objcg);
+	KFENCE_WARN_ON(slab_obj_ext_objcg(&meta->obj_exts));
 #endif
 	/*
 	 * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing
diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c
index de2d0f7d62b15e..9867c03ef0ae3d 100644
--- a/mm/kfence/kfence_test.c
+++ b/mm/kfence/kfence_test.c
@@ -295,7 +295,7 @@ static void *test_alloc(struct kunit *test, size_t size, gfp_t gfp, enum allocat
 			 * memcg accounting works correctly.
 			 */
 			KUNIT_EXPECT_EQ(test, obj_to_index(s, slab, alloc), 0U);
-			KUNIT_EXPECT_EQ(test, objs_per_slab(s, slab), 1);
+			KUNIT_EXPECT_EQ(test, ((unsigned int)slab->objects), 1);
 
 			if (policy == ALLOCATE_ANY)
 				return alloc;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6dc4888a90f3fd..aace85fb99f973 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2865,18 +2865,19 @@ struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p)
 	 */
 	unsigned long obj_exts;
 	struct slabobj_ext *obj_ext;
-	unsigned int off;
+	struct obj_cgroup *objcg;
 
 	obj_exts = slab_obj_exts(slab);
 	if (!obj_exts)
 		return NULL;
 
-	get_slab_obj_exts(obj_exts);
-	off = obj_to_index(slab->slab_cache, slab, p);
-	obj_ext = slab_obj_ext(slab, obj_exts, off);
-	if (obj_ext->objcg) {
-		struct obj_cgroup *objcg = obj_ext->objcg;
+	if (!slab_needs_objcg(slab))
+		return NULL;
 
+	get_slab_obj_exts(obj_exts);
+	obj_ext = slab_obj_ext(slab->slab_cache, slab, obj_exts, p);
+	objcg = slab_obj_ext_objcg(obj_ext);
+	if (objcg) {
 		put_slab_obj_exts(obj_exts);
 		return obj_cgroup_memcg(objcg);
 	}
@@ -3541,7 +3542,6 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
 	size_t obj_size = obj_full_size(s);
 	struct obj_cgroup *objcg;
 	struct slab *slab;
-	unsigned long off;
 	size_t i;
 
 	/*
@@ -3583,6 +3583,9 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
 
 		slab = virt_to_slab(p[i]);
 
+		if (IS_ENABLED(CONFIG_DEBUG_VM) && WARN_ON_ONCE(!slab_needs_objcg(slab)))
+			continue;
+
 		if (!slab_obj_exts(slab) &&
 		    alloc_slab_obj_exts(slab, s, flags, slab_alloc_flags)) {
 			continue;
@@ -3616,10 +3619,11 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
 
 		obj_exts = slab_obj_exts(slab);
 		get_slab_obj_exts(obj_exts);
-		off = obj_to_index(s, slab, p[i]);
-		obj_ext = slab_obj_ext(slab, obj_exts, off);
+		obj_ext = slab_obj_ext(s, slab, obj_exts, p[i]);
+
 		obj_cgroup_get(objcg);
-		obj_ext->objcg = objcg;
+		slab_obj_ext_set_objcg(obj_ext, objcg);
+
 		put_slab_obj_exts(obj_exts);
 	}
 
@@ -3635,15 +3639,13 @@ void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
 		struct obj_cgroup *objcg;
 		struct slabobj_ext *obj_ext;
 		struct obj_stock_pcp *stock;
-		unsigned int off;
 
-		off = obj_to_index(s, slab, p[i]);
-		obj_ext = slab_obj_ext(slab, obj_exts, off);
-		objcg = obj_ext->objcg;
+		obj_ext = slab_obj_ext(s, slab, obj_exts, p[i]);
+		objcg = slab_obj_ext_objcg(obj_ext);
 		if (!objcg)
 			continue;
 
-		obj_ext->objcg = NULL;
+		slab_obj_ext_set_objcg(obj_ext, NULL);
 
 		stock = trylock_stock();
 		__refill_obj_stock(objcg, stock, obj_size, true);
diff --git a/mm/slab.h b/mm/slab.h
index f5e336b6b6b04c..18c2a807f023ce 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -81,10 +81,11 @@ struct freelist_counters {
 #ifdef CONFIG_64BIT
 					/*
 					 * Some optimizations use free bits in 'counters' field
-					 * to save memory. In case ->stride field is not available,
-					 * such optimizations are disabled.
+					 * to save memory or CPU. If these free bits are not
+					 * available, such optimizations are disabled.
 					 */
-					unsigned int stride;
+					unsigned obj_exts_in_object:1;
+					unsigned obj_exts_needs_objcg:1;
 #endif
 				};
 			};
@@ -330,12 +331,6 @@ static inline unsigned int obj_to_index(const struct kmem_cache *cache,
 	return __obj_to_index(cache, slab_address(slab), obj);
 }
 
-static inline int objs_per_slab(const struct kmem_cache *cache,
-				const struct slab *slab)
-{
-	return slab->objects;
-}
-
 /*
  * State of the slab allocator.
  *
@@ -555,6 +550,93 @@ static inline bool need_kmalloc_no_objext(void)
 	return false;
 }
 
+/*
+ * Extended information for slab objects stored as a pointer to an array in
+ * slab->obj_exts (aliasing page->memcg_data) if MEMCG_DATA_OBJEXTS is set.
+ */
+struct slabobj_ext {
+	/*
+	 * All elements of the union should be pointer-sized to avoid memory
+	 * waste
+	 */
+	union {
+#ifdef CONFIG_MEMCG
+		struct obj_cgroup *_objcg;
+#endif
+#ifdef CONFIG_MEM_ALLOC_PROFILING
+		union codetag_ref _ctref;
+#endif
+	};
+} __aligned(8);
+
+#ifdef CONFIG_MEM_ALLOC_PROFILING
+DECLARE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
+			 slab_obj_ext_has_codetag_key);
+
+static inline bool slab_obj_ext_has_codetag(void)
+{
+	return static_branch_maybe(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
+				   &slab_obj_ext_has_codetag_key);
+}
+#else
+static inline bool slab_obj_ext_has_codetag(void)
+{
+	return false;
+}
+#endif
+
+#ifdef CONFIG_MEMCG
+static inline bool cache_needs_objcg(struct kmem_cache *cache)
+{
+	return (cache->flags & SLAB_MAY_ACCOUNT);
+}
+
+static inline bool slab_needs_objcg(struct slab *slab)
+{
+#ifdef CONFIG_64BIT
+	return slab->obj_exts_needs_objcg;
+#else
+	return cache_needs_objcg(slab->slab_cache);
+#endif
+}
+#else
+static inline bool cache_needs_objcg(struct kmem_cache *cache)
+{
+	return false;
+}
+
+static inline bool slab_needs_objcg(struct slab *slab)
+{
+	return false;
+}
+#endif
+
+static inline size_t cache_obj_ext_size(struct kmem_cache *s)
+{
+	size_t sz = 0;
+
+	if (cache_needs_objcg(s))
+		sz += 1;
+
+	if (slab_obj_ext_has_codetag())
+		sz += 1;
+
+	return sizeof(struct slabobj_ext) * sz;
+}
+
+static inline size_t slab_obj_ext_size(struct slab *slab)
+{
+	size_t sz = 0;
+
+	if (slab_needs_objcg(slab))
+		sz += 1;
+
+	if (slab_obj_ext_has_codetag())
+		sz += 1;
+
+	return sizeof(struct slabobj_ext) * sz;
+}
+
 #ifdef CONFIG_SLAB_OBJ_EXT
 
 /*
@@ -572,7 +654,7 @@ static inline bool need_kmalloc_no_objext(void)
  * obj_exts = slab_obj_exts(slab);
  * if (obj_exts) {
  *         get_slab_obj_exts(obj_exts);
- *         obj_ext = slab_obj_ext(slab, obj_exts, obj_to_index(s, slab, obj));
+ *         obj_ext = slab_obj_ext(s, slab, obj_exts, obj);
  *         // do something with obj_ext
  *         put_slab_obj_exts(obj_exts);
  * }
@@ -610,48 +692,82 @@ static inline void put_slab_obj_exts(unsigned long obj_exts)
 }
 
 #ifdef CONFIG_64BIT
-static inline void slab_set_stride(struct slab *slab, unsigned int stride)
-{
-	slab->stride = stride;
-}
-static inline unsigned int slab_get_stride(struct slab *slab)
+static inline bool obj_exts_in_object(struct slab *slab)
 {
-	return slab->stride;
+	/*
+	 * Note we cannot rely on the SLAB_OBJ_EXT_IN_OBJ flag here and need to
+	 * check the per-slab bit. A cache can have SLAB_OBJ_EXT_IN_OBJ set, but
+	 * allocations within_slab_leftover are preferred. And those may be
+	 * possible or not depending on the particular slab's size.
+	 */
+	return slab->obj_exts_in_object;
 }
 #else
-static inline void slab_set_stride(struct slab *slab, unsigned int stride)
+static inline bool obj_exts_in_object(struct slab *slab)
 {
-	VM_WARN_ON_ONCE(stride != sizeof(struct slabobj_ext));
-}
-static inline unsigned int slab_get_stride(struct slab *slab)
-{
-	return sizeof(struct slabobj_ext);
+	return false;
 }
 #endif
 
 /*
  * slab_obj_ext - get the pointer to the slab object extension metadata
  * associated with an object in a slab.
+ * @s: cache that the slab blongs to
  * @slab: a pointer to the slab struct
  * @obj_exts: a pointer to the object extension vector
- * @index: an index of the object
+ * @obj: a pointer to the object
  *
  * Returns a pointer to the object extension associated with the object.
  * Must be called within a section covered by get/put_slab_obj_exts().
  */
-static inline struct slabobj_ext *slab_obj_ext(struct slab *slab,
-					       unsigned long obj_exts,
-					       unsigned int index)
+static inline struct slabobj_ext *
+slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts,
+	     const void *obj)
 {
 	struct slabobj_ext *obj_ext;
+	unsigned int index;
+	unsigned int stride;
 
 	VM_WARN_ON_ONCE(obj_exts != slab_obj_exts(slab));
 
-	obj_ext = (struct slabobj_ext *)(obj_exts +
-					 slab_get_stride(slab) * index);
+	index = obj_to_index(s, slab, obj);
+
+	if (!obj_exts_in_object(slab))
+		stride = slab_obj_ext_size(slab);
+	else
+		stride = s->size;
+
+	obj_ext = (struct slabobj_ext *)(obj_exts + index * stride);
+
 	return kasan_reset_tag(obj_ext);
 }
 
+#ifdef CONFIG_MEMCG
+static inline struct obj_cgroup *slab_obj_ext_objcg(struct slabobj_ext *obj_ext)
+{
+	/* if objcg exists, it comes first, so we don't need to do anything */
+	return obj_ext->_objcg;
+}
+
+static inline void slab_obj_ext_set_objcg(struct slabobj_ext *obj_ext,
+					  struct obj_cgroup *objcg)
+{
+	/* if objcg exists, it comes first, so we don't need to do anything */
+	obj_ext->_objcg = objcg;
+}
+#endif
+
+#ifdef CONFIG_MEM_ALLOC_PROFILING
+static inline union codetag_ref *
+slab_obj_ext_codetag_ref(struct slab *slab, struct slabobj_ext *obj_ext)
+{
+	if (slab_needs_objcg(slab))
+		obj_ext += 1;
+
+	return &obj_ext->_ctref;
+}
+#endif
+
 int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
 			gfp_t gfp, unsigned int alloc_flags);
 
@@ -662,16 +778,17 @@ static inline unsigned long slab_obj_exts(struct slab *slab)
 	return 0;
 }
 
-static inline struct slabobj_ext *slab_obj_ext(struct slab *slab,
-					       unsigned long obj_exts,
-					       unsigned int index)
+static inline struct slabobj_ext *
+slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts,
+	     const void *obj)
 {
 	return NULL;
 }
 
-static inline void slab_set_stride(struct slab *slab, unsigned int stride) { }
-static inline unsigned int slab_get_stride(struct slab *slab) { return 0; }
-
+static inline bool obj_exts_in_object(struct slab *slab)
+{
+	return false;
+}
 
 #endif /* CONFIG_SLAB_OBJ_EXT */
 
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 03ecac12cd865f..4e983e2503387a 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -52,7 +52,7 @@ struct kmem_cache *kmem_cache;
 		SLAB_OBJ_EXT_IN_OBJ)
 
 #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \
-			 SLAB_CACHE_DMA32 | SLAB_ACCOUNT)
+			 SLAB_CACHE_DMA32 | SLAB_ACCOUNT | SLAB_MAY_ACCOUNT)
 
 /*
  * Merge control. If this is set then no merging of slab caches will occur.
@@ -359,6 +359,13 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
 		goto out_unlock;
 	}
 
+	/*
+	 * For now we assume any cache can be used with __GFP_ACCOUNT and thus
+	 * may need to store objcg pointers for objects
+	 */
+	if (!mem_cgroup_kmem_disabled())
+		flags |= SLAB_MAY_ACCOUNT;
+
 	/* Fail closed on bad usersize of useroffset values. */
 	if (!IS_ENABLED(CONFIG_HARDENED_USERCOPY) ||
 	    WARN_ON(!args->usersize && args->useroffset) ||
@@ -984,11 +991,19 @@ new_kmalloc_cache(int idx, enum kmalloc_cache_type type)
 #endif
 
 	/*
-	 * If CONFIG_MEMCG is enabled, disable cache merging for
-	 * KMALLOC_NORMAL caches.
+	 * If memcg_kmem is enabled and this is a KMALLOC_NORMAL cache and  not
+	 * aliased with any other type, make sure it's never merged with any other
+	 * cache.
+	 *
+	 * In other cases the kmalloc cache may end up being used for a
+	 * __GFP_ACCOUNT allocation so mark it as such
 	 */
-	if (IS_ENABLED(CONFIG_MEMCG) && (type == KMALLOC_NORMAL))
-		flags |= SLAB_NO_MERGE;
+	if (!mem_cgroup_kmem_disabled()) {
+		if (type == KMALLOC_NORMAL && KMALLOC_RECLAIM != KMALLOC_NORMAL)
+			flags |= SLAB_NO_MERGE;
+		else
+			flags |= SLAB_MAY_ACCOUNT;
+	}
 
 	if (minalign > ARCH_KMALLOC_MINALIGN) {
 		aligned_size = ALIGN(aligned_size, minalign);
diff --git a/mm/slub.c b/mm/slub.c
index 0337e60db5ace0..e6148b73b92f88 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -213,6 +213,11 @@ DEFINE_STATIC_KEY_FALSE(slub_debug_enabled);
 static DEFINE_STATIC_KEY_FALSE(strict_numa);
 #endif
 
+#ifdef CONFIG_MEM_ALLOC_PROFILING
+DEFINE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
+			slab_obj_ext_has_codetag_key);
+#endif
+
 /* Structure holding extra parameters for slab allocations */
 struct slab_alloc_context {
 	unsigned long caller_addr;
@@ -803,7 +808,7 @@ static inline bool need_slab_obj_exts(struct kmem_cache *s)
 
 static inline unsigned int obj_exts_size_in_slab(struct slab *slab)
 {
-	return sizeof(struct slabobj_ext) * slab->objects;
+	return slab_obj_ext_size(slab) * slab->objects;
 }
 
 static inline unsigned long obj_exts_offset_in_slab(struct kmem_cache *s,
@@ -870,18 +875,6 @@ static inline bool obj_exts_in_slab(struct kmem_cache *s, struct slab *slab)
 #endif
 
 #if defined(CONFIG_SLAB_OBJ_EXT) && defined(CONFIG_64BIT)
-static bool obj_exts_in_object(struct kmem_cache *s, struct slab *slab)
-{
-	/*
-	 * Note we cannot rely on the SLAB_OBJ_EXT_IN_OBJ flag here and need to
-	 * check the stride. A cache can have SLAB_OBJ_EXT_IN_OBJ set, but
-	 * allocations within_slab_leftover are preferred. And those may be
-	 * possible or not depending on the particular slab's size.
-	 */
-	return obj_exts_in_slab(s, slab) &&
-	       (slab_get_stride(slab) == s->size);
-}
-
 static unsigned int obj_exts_offset_in_object(struct kmem_cache *s)
 {
 	unsigned int offset = get_info_end(s);
@@ -896,16 +889,20 @@ static unsigned int obj_exts_offset_in_object(struct kmem_cache *s)
 
 	return offset;
 }
-#else
-static inline bool obj_exts_in_object(struct kmem_cache *s, struct slab *slab)
+
+static inline void slab_set_obj_exts_in_object(struct slab *slab)
 {
-	return false;
+	slab->obj_exts_in_object = 1;
 }
-
+#else
 static inline unsigned int obj_exts_offset_in_object(struct kmem_cache *s)
 {
 	return 0;
 }
+
+static inline void slab_set_obj_exts_in_object(struct slab *slab)
+{
+}
 #endif
 
 #ifdef CONFIG_SLUB_DEBUG
@@ -1206,8 +1203,8 @@ static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p)
 
 	off += kasan_metadata_size(s, false);
 
-	if (obj_exts_in_object(s, slab))
-		off += sizeof(struct slabobj_ext);
+	if (obj_exts_in_object(slab))
+		off += slab_obj_ext_size(slab);
 
 	if (off != size_from_object(s))
 		/* Beginning of the filler is the free pointer */
@@ -1411,8 +1408,8 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p)
 
 	off += kasan_metadata_size(s, false);
 
-	if (obj_exts_in_object(s, slab))
-		off += sizeof(struct slabobj_ext);
+	if (obj_exts_in_object(slab))
+		off += slab_obj_ext_size(slab);
 
 	if (size_from_object(s) == off)
 		return 1;
@@ -1439,7 +1436,7 @@ slab_pad_check(struct kmem_cache *s, struct slab *slab)
 	length = slab_size(slab);
 	end = start + length;
 
-	if (obj_exts_in_slab(s, slab) && !obj_exts_in_object(s, slab)) {
+	if (obj_exts_in_slab(s, slab) && !obj_exts_in_object(slab)) {
 		remainder = length;
 		remainder -= obj_exts_offset_in_slab(s, slab);
 		remainder -= obj_exts_size_in_slab(slab);
@@ -2070,20 +2067,26 @@ static inline void mark_obj_codetag_empty(const void *obj)
 	obj_slab = virt_to_slab(obj);
 	slab_exts = slab_obj_exts(obj_slab);
 	if (slab_exts) {
+		struct slabobj_ext *ext;
+		union codetag_ref *ref;
+
 		get_slab_obj_exts(slab_exts);
-		unsigned int offs = obj_to_index(obj_slab->slab_cache,
-						 obj_slab, obj);
-		struct slabobj_ext *ext = slab_obj_ext(obj_slab,
-						       slab_exts, offs);
+		ext = slab_obj_ext(obj_slab->slab_cache, obj_slab, slab_exts, obj);
+		ref = slab_obj_ext_codetag_ref(obj_slab, ext);
+
+		if (is_kfence_address(obj)) {
+			put_slab_obj_exts(slab_exts);
+			return;
+		}
 
-		if (unlikely(is_codetag_empty(&ext->ref))) {
+		if (unlikely(is_codetag_empty(ref))) {
 			put_slab_obj_exts(slab_exts);
 			return;
 		}
 
 		/* codetag should be NULL here */
-		WARN_ON(ext->ref.ct);
-		set_codetag_empty(&ext->ref);
+		WARN_ON(ref->ct);
+		set_codetag_empty(ref);
 		put_slab_obj_exts(slab_exts);
 	}
 }
@@ -2093,19 +2096,29 @@ static inline bool mark_failed_objexts_alloc(struct slab *slab)
 	return cmpxchg(&slab->obj_exts, 0, OBJEXTS_ALLOC_FAIL) == 0;
 }
 
-static inline void handle_failed_objexts_alloc(unsigned long obj_exts,
-			struct slabobj_ext *vec, unsigned int objects)
+static inline void handle_failed_objexts_alloc(struct slab *slab,
+		unsigned long obj_exts, struct slabobj_ext *vec)
 {
+	unsigned int stride;
+
+	if (!mem_alloc_profiling_enabled())
+		return;
+
 	/*
 	 * If vector previously failed to allocate then we have live
 	 * objects with no tag reference. Mark all references in this
 	 * vector as empty to avoid warnings later on.
 	 */
-	if (obj_exts == OBJEXTS_ALLOC_FAIL) {
-		unsigned int i;
+	if (obj_exts != OBJEXTS_ALLOC_FAIL)
+		return;
+
+	stride = slab_obj_ext_size(slab) / sizeof(*vec);
+
+	for (unsigned int i = 0; i < slab->objects; i++) {
+		union codetag_ref *ref = slab_obj_ext_codetag_ref(slab, vec);
 
-		for (i = 0; i < objects; i++)
-			set_codetag_empty(&vec[i].ref);
+		set_codetag_empty(ref);
+		vec += stride;
 	}
 }
 
@@ -2113,8 +2126,8 @@ static inline void handle_failed_objexts_alloc(unsigned long obj_exts,
 
 static inline void mark_obj_codetag_empty(const void *obj) {}
 static inline bool mark_failed_objexts_alloc(struct slab *slab) { return false; }
-static inline void handle_failed_objexts_alloc(unsigned long obj_exts,
-			struct slabobj_ext *vec, unsigned int objects) {}
+static inline void handle_failed_objexts_alloc(struct slab *slab,
+		unsigned long obj_exts, struct slabobj_ext *vec) {}
 
 #endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */
 
@@ -2127,12 +2140,11 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
 			gfp_t gfp, unsigned int alloc_flags)
 {
 	const bool allow_spin = alloc_flags_allow_spinning(alloc_flags);
-	unsigned int objects = objs_per_slab(s, slab);
 	bool new_slab = alloc_flags & SLAB_ALLOC_NEW_SLAB;
 	unsigned long new_exts;
 	unsigned long old_exts;
 	struct slabobj_ext *vec;
-	size_t sz = sizeof(struct slabobj_ext) * slab->objects;
+	size_t sz = slab_obj_ext_size(slab) * slab->objects;
 
 	gfp &= ~OBJCGS_CLEAR_MASK;
 	/*
@@ -2183,7 +2195,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
 #endif
 retry:
 	old_exts = READ_ONCE(slab->obj_exts);
-	handle_failed_objexts_alloc(old_exts, vec, objects);
+	handle_failed_objexts_alloc(slab, old_exts, vec);
 
 	if (new_slab) {
 		/*
@@ -2250,9 +2262,6 @@ static void alloc_slab_obj_exts_early(struct kmem_cache *s, struct slab *slab)
 	void *addr;
 	unsigned long obj_exts;
 
-	/* Initialize stride early to avoid memory ordering issues */
-	slab_set_stride(slab, sizeof(struct slabobj_ext));
-
 	if (!need_slab_obj_exts(s))
 		return;
 
@@ -2278,15 +2287,14 @@ static void alloc_slab_obj_exts_early(struct kmem_cache *s, struct slab *slab)
 
 		get_slab_obj_exts(obj_exts);
 		for_each_object(addr, s, slab_address(slab), slab->objects)
-			memset(kasan_reset_tag(addr) + offset, 0,
-			       sizeof(struct slabobj_ext));
+			memset(kasan_reset_tag(addr) + offset, 0, slab_obj_ext_size(slab));
 		put_slab_obj_exts(obj_exts);
 
 #ifdef CONFIG_MEMCG
 		obj_exts |= MEMCG_DATA_OBJEXTS;
 #endif
 		slab->obj_exts = obj_exts;
-		slab_set_stride(slab, s->size);
+		slab_set_obj_exts_in_object(slab);
 	}
 }
 
@@ -2352,6 +2360,9 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,
 	if (alloc_flags & SLAB_ALLOC_NO_RECURSE)
 		return;
 
+	if (is_kfence_address(object))
+		return;
+
 	slab = virt_to_slab(object);
 	obj_exts = prepare_slab_obj_exts_hook(s, slab, flags, alloc_flags, object);
 	/*
@@ -2360,11 +2371,15 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,
 	 * check should be added before alloc_tag_add().
 	 */
 	if (obj_exts) {
-		unsigned int obj_idx = obj_to_index(s, slab, object);
+		union codetag_ref *ref;
 
 		get_slab_obj_exts(obj_exts);
-		obj_ext = slab_obj_ext(slab, obj_exts, obj_idx);
-		alloc_tag_add(&obj_ext->ref, current->alloc_tag, s->size);
+
+		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);
+
 		put_slab_obj_exts(obj_exts);
 	} else {
 		alloc_tag_set_inaccurate(current->alloc_tag);
@@ -2384,7 +2399,6 @@ static noinline void
 __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,
 			       int objects)
 {
-	int i;
 	unsigned long obj_exts;
 
 	/* slab->obj_exts might not be NULL if it was created for MEMCG accounting. */
@@ -2396,10 +2410,14 @@ __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p
 		return;
 
 	get_slab_obj_exts(obj_exts);
-	for (i = 0; i < objects; i++) {
-		unsigned int off = obj_to_index(s, slab, p[i]);
+	for (int i = 0; i < objects; i++) {
+		struct slabobj_ext *ext;
+
+		if (is_kfence_address(p[i]))
+			continue;
 
-		alloc_tag_sub(&slab_obj_ext(slab, obj_exts, off)->ref, s->size);
+		ext = slab_obj_ext(s, slab, obj_exts, p[i]);
+		alloc_tag_sub(slab_obj_ext_codetag_ref(slab, ext), s->size);
 	}
 	put_slab_obj_exts(obj_exts);
 }
@@ -2412,6 +2430,25 @@ alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,
 		__alloc_tagging_slab_free_hook(s, slab, p, objects);
 }
 
+/*
+ * Make sure the static key used by slab_obj_ext_has_codetag() reflects the
+ * value of !mem_alloc_profiling_permanently_disabled()
+ *
+ * Any later mem alloc profiling shutdown won't be reflected in the static key
+ * because obj_exts with codetags might already exist.
+ */
+static void __init slab_obj_ext_has_codetag_init(void)
+{
+	bool need_codetag = !mem_alloc_profiling_permanently_disabled();
+
+	if (need_codetag != static_key_enabled(&slab_obj_ext_has_codetag_key)) {
+		if (need_codetag)
+			static_branch_enable(&slab_obj_ext_has_codetag_key);
+		else
+			static_branch_disable(&slab_obj_ext_has_codetag_key);
+	}
+}
+
 #else /* CONFIG_MEM_ALLOC_PROFILING */
 
 static inline void
@@ -2426,6 +2463,10 @@ alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,
 {
 }
 
+static inline void slab_obj_ext_has_codetag_init(void)
+{
+}
+
 #endif /* CONFIG_MEM_ALLOC_PROFILING */
 
 
@@ -2471,6 +2512,9 @@ void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,
 	if (likely(!obj_exts))
 		return;
 
+	if (!slab_needs_objcg(slab))
+		return;
+
 	get_slab_obj_exts(obj_exts);
 	__memcg_slab_free_hook(s, slab, p, objects, obj_exts);
 	put_slab_obj_exts(obj_exts);
@@ -2484,7 +2528,6 @@ bool memcg_slab_post_charge(void *p, gfp_t flags)
 	struct kmem_cache *s;
 	struct page *page;
 	struct slab *slab;
-	unsigned long off;
 
 	page = virt_to_page(p);
 	if (PageLargeKmalloc(page)) {
@@ -2517,16 +2560,15 @@ bool memcg_slab_post_charge(void *p, gfp_t flags)
 	 * of slab_obj_exts being allocated from the same slab and thus the slab
 	 * becoming effectively unfreeable.
 	 */
-	if (is_kmalloc_normal(s))
+	if (!cache_needs_objcg(s))
 		return true;
 
 	/* Ignore already charged objects. */
 	obj_exts = slab_obj_exts(slab);
 	if (obj_exts) {
 		get_slab_obj_exts(obj_exts);
-		off = obj_to_index(s, slab, p);
-		obj_ext = slab_obj_ext(slab, obj_exts, off);
-		if (unlikely(obj_ext->objcg)) {
+		obj_ext = slab_obj_ext(s, slab, obj_exts, p);
+		if (unlikely(slab_obj_ext_objcg(obj_ext))) {
 			put_slab_obj_exts(obj_exts);
 			return true;
 		}
@@ -3391,10 +3433,15 @@ static struct slab *allocate_slab(struct kmem_cache *s, gfp_t flags,
 		stat(s, ORDER_FALLBACK);
 	}
 
+	/* Initializes frozen, inuse, and any extra 64bit-only flags */
+	slab->counters = 0;
+
 	slab->objects = oo_objects(oo);
-	slab->inuse = 0;
-	slab->frozen = 0;
 
+#ifdef CONFIG_64BIT
+	if (cache_needs_objcg(s))
+		slab->obj_exts_needs_objcg = 1;
+#endif
 	slab->slab_cache = s;
 
 	kasan_poison_slab(slab);
@@ -6526,7 +6573,7 @@ static inline size_t slab_ksize(struct slab *slab)
 	 */
 	if (s->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_STORE_USER))
 		return s->inuse;
-	else if (obj_exts_in_object(s, slab))
+	else if (obj_exts_in_object(slab))
 		return s->inuse;
 	/*
 	 * Else we can use all the padding etc for the allocation
@@ -7929,7 +7976,7 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s)
 	aligned_size = ALIGN(size, s->align);
 #if defined(CONFIG_SLAB_OBJ_EXT) && defined(CONFIG_64BIT)
 	if (slab_args_unmergeable(args, s->flags) &&
-			(aligned_size - size >= sizeof(struct slabobj_ext)))
+			(aligned_size - size >= cache_obj_ext_size(s)))
 		s->flags |= SLAB_OBJ_EXT_IN_OBJ;
 #endif
 	size = aligned_size;
@@ -8539,6 +8586,8 @@ void __init kmem_cache_init(void)
 		boot_kmem_cache_node;
 	int node;
 
+	slab_obj_ext_has_codetag_init();
+
 	if (debug_guardpage_minorder())
 		slub_max_order = 0;
 

gemini-3.1-pro-preview

null

null

							input: 12904
							output: 34
							thoughts: 367
						

**Analyzing a Slab Object Extension Optimization Patch**

Okay, so I've got this patch here that's tweaking how `struct slabobj_ext` is handled, specifically concerning memory allocation profiling and memory cgroup accounting – interesting. It looks like the goal is to optimize the structure by using a union to store pointers to `objcg` and `codetag_ref`, or allocating space for them only when they're actually needed. This makes sense; it's a common strategy for reducing memory overhead in performance-critical areas like the slab allocator. The introduction of `SLAB_MAY_ACCOUNT` is a nice touch, too; it adds a bit more fine-grained control.

Functionally, I need to verify that the patch doesn't break anything. It definitely touches core slab allocator logic and memcg accounting, so any missteps here could have pretty wide-reaching consequences. And, yeah, given how heavily slab allocation is used throughout the kernel, it's definitely reachable code. Worth a fuzzing campaign to see if any unexpected behaviors arise.

Now, let’s pinpoint the specific areas to scrutinize. I've got a list of the modified functions: `alloc_slab_obj_exts`, `__alloc_tagging_slab_alloc_hook`, `__alloc_tagging_slab_free_hook`, `memcg_slab_post_charge`, `__memcg_slab_post_alloc_hook`, `__memcg_slab_free_hook`, `kfence_init_pool`, `__kfence_free`, `mem_cgroup_from_obj_slab`, `kmem_cache_create_args`, and `new_kmalloc_cache`. Alright, let's start by digging into `mm/slub.c` and specifically, that `alloc_slab_obj_exts` function.

{
  "Expression": "alloc_slab_obj_exts",
  "PathPrefix": "mm/slub.c"
}

{
  "Output": "mm/slub.c=2134=static inline void init_slab_obj_exts(struct slab *slab)\n--\nmm/slub.c-2138-\nmm/slub.c:2139:int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,\nmm/slub.c-2140-\t\t\tgfp_t gfp, unsigned int alloc_flags)\n--\nmm/slub.c=2228=static inline void free_slab_obj_exts(struct slab *slab, bool allow_spin)\n--\nmm/slub.c-2259- */\nmm/slub.c:2260:static void alloc_slab_obj_exts_early(struct kmem_cache *s, struct slab *slab)\nmm/slub.c-2261-{\n--\nmm/slub.c=2307=static inline void init_slab_obj_exts(struct slab *slab)\n--\nmm/slub.c-2310-\nmm/slub.c:2311:static int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,\nmm/slub.c-2312-\t\t\t       gfp_t gfp, unsigned int alloc_flags)\n--\nmm/slub.c=2317=static inline void free_slab_obj_exts(struct slab *slab, bool allow_spin)\n--\nmm/slub.c-2320-\nmm/slub.c:2321:static inline void alloc_slab_obj_exts_early(struct kmem_cache *s,\nmm/slub.c-2322-\t\t\t\t\t\t       struct slab *slab)\n--\nmm/slub.c=2331=prepare_slab_obj_exts_hook(struct kmem_cache *s, struct slab *slab,\n--\nmm/slub.c-2334-\tif (!slab_obj_exts(slab) \u0026\u0026\nmm/slub.c:2335:\t    alloc_slab_obj_exts(slab, s, flags, alloc_flags)) {\nmm/slub.c-2336-\t\tpr_warn_once(\"%s, %s: Failed to create slab extension vector!\\n\",\n--\nmm/slub.c=3372=static __always_inline void account_slab(struct slab *slab, int order,\n--\nmm/slub.c-3378-\t\t\t!slab_obj_exts(slab))\nmm/slub.c:3379:\t\talloc_slab_obj_exts(slab, s, gfp,\nmm/slub.c-3380-\t\t\t\t    alloc_flags | SLAB_ALLOC_NEW_SLAB);\n--\nmm/slub.c=3401=static struct slab *allocate_slab(struct kmem_cache *s, gfp_t flags,\n--\nmm/slub.c-3456-\t */\nmm/slub.c:3457:\talloc_slab_obj_exts_early(s, slab);\nmm/slub.c-3458-\taccount_slab(slab, oo_order(oo), s, flags, alloc_flags);\n"
}

gemini-3.1-pro-preview

null

null

							input: 14514
							output: 37
							thoughts: 38
						

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

**Investigating Slab Allocator Hooks in memcontrol.c**

Alright, the objective here is to understand the interplay between the memory control group (memcg) system and the slab allocator. Specifically, I need to pinpoint where memcg hooks into the slab allocation and freeing processes. That means digging into `mm/memcontrol.c`, since that's where the core memcg logic resides, as a starting point.

My primary targets are the `__memcg_slab_post_alloc_hook` and `__memcg_slab_free_hook` functions. The names themselves are a strong clue. `post_alloc` implies something that happens after a slab object is allocated. The `free_hook` is what runs after a slab is freed. These hooks are likely the entry points where memcg tracks memory usage tied to slabs, accounting for allocation and deallocation within different control groups. I'll need to see *how* these hooks are used and what context they operate within. It'll be essential to determine how the hooks are registered and called in the slab allocator's functions. I anticipate the details are embedded inside the allocator's source code, possibly in functions like `kmem_cache_alloc` or `kmem_cache_free`. I expect that finding and studying how these hooks are registered is key to understanding how these allocation changes are tracked.

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

{
  "Output": "mm/memcontrol.c=3529=static inline size_t obj_full_size(struct kmem_cache *s)\n--\nmm/memcontrol.c-3537-\nmm/memcontrol.c:3538:bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,\nmm/memcontrol.c-3539-\t\t\t\t  gfp_t flags, unsigned int slab_alloc_flags,\n"
}

gemini-3.1-pro-preview

null

null

							input: 15035
							output: 35
							thoughts: 24
						

Here's my thought process, summarized as you requested:

**Navigating Slab Allocation in the Memory Controller**

Okay, so we're looking at memory control, specifically how slabs are managed within a memcg context. The task at hand likely involves freeing some slab objects, and that means diving into the mechanics of `__memcg_slab_free_hook`. That function's name is a pretty good indicator that it's involved in, well, *hooking* into the slab freeing process, likely to perform accounting or enforcement related to memory cgroups. Let's start by cracking open `mm/memcontrol.c` and see what's actually happening inside that function. That file is the central place to be for this kind of investigation. It will be interesting to see how the memcg structure and associated bookkeeping are integrated into the standard slab freeing flow.

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

{
  "Output": "mm/memcontrol.c=3538=bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,\n--\nmm/memcontrol.c-3632-\nmm/memcontrol.c:3633:void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,\nmm/memcontrol.c-3634-\t\t\t    void **p, int objects, unsigned long obj_exts)\n"
}

gemini-3.1-pro-preview

null

null

							input: 15411
							output: 37
							thoughts: 40
						

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

**Diving into Slab Allocation Tagging**

Alright, time to get my hands dirty. I need to refresh my understanding of the slab allocator's tagging hooks. Let's head straight for the source code, specifically `mm/slub.c`. I'm immediately interested in the implementation of the `__alloc_tagging_slab_alloc_hook` and `__alloc_tagging_slab_free_hook` functions. I want to see how the allocation and deallocation hooks for memory tagging are actually implemented at the slab level. I'm especially keen to examine the interaction between these hooks and the underlying slab management. Are they integrated directly into the `kmem_cache` structures? Are they called inline, or are they managed via a different mechanism? I need to understand the precise sequence of events when memory tagging is involved in slab allocation and deallocation. I'm also curious about the potential performance implications. How much overhead do these hooks introduce? Are there any optimizations in place to minimize the performance hit? This is where the devil is in the details. I know `slub.c` is where I'll find those answers.

{
  "Expression": "__alloc_tagging_slab_alloc_hook",
  "PathPrefix": "mm/slub.c"
}

{
  "Output": "mm/slub.c=2346=static noinline void\nmm/slub.c:2347:__alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,\nmm/slub.c-2348-\t\t\t\tunsigned int alloc_flags)\n--\nmm/slub.c=2390=alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,\n--\nmm/slub.c-2393-\tif (mem_alloc_profiling_enabled())\nmm/slub.c:2394:\t\t__alloc_tagging_slab_alloc_hook(s, object, flags, alloc_flags);\nmm/slub.c-2395-}\n"
}

gemini-3.1-pro-preview

null

null

							input: 15958
							output: 37
							thoughts: 26
						

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

**Diving into Slab Allocation Tagging**

Alright, I need to investigate the tagging mechanisms within the slab allocator, specifically how freeing memory is handled. The quickest route is usually to jump directly into the source code, so my immediate thought is to check `mm/slub.c`. I'm going to look for the `__alloc_tagging_slab_free_hook` function. This hook likely plays a crucial role in the specific allocation/deallocation tagging that I'm interested in. Understanding its implementation is key to understanding the overall tagging strategy and likely sheds light on how allocation tracking and integrity checking are performed during slab freeing. I expect it's going to be a key function in handling tagged slabs.

{
  "Expression": "__alloc_tagging_slab_free_hook",
  "PathPrefix": "mm/slub.c"
}

{
  "Output": "mm/slub.c=2398=static noinline void\nmm/slub.c:2399:__alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,\nmm/slub.c-2400-\t\t\t       int objects)\n--\nmm/slub.c=2426=alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,\n--\nmm/slub.c-2429-\tif (mem_alloc_profiling_enabled())\nmm/slub.c:2430:\t\t__alloc_tagging_slab_free_hook(s, slab, p, objects);\nmm/slub.c-2431-}\n"
}

gemini-3.1-pro-preview

null

null

							input: 16394
							output: 34
							thoughts: 23
						

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

**Diving into Slab Accounting**

Alright, I need to investigate the slab accounting within the memory controller, specifically focusing on `memcg_slab_post_charge`. This is where the crucial work happens *after* a slab allocation has completed. I want to understand how memory control groups are updated after memory has been claimed from the slab allocator. Is it a good idea to check this file first? Yes, that is a reasonable starting point. Let's see how memory usage and limits are being adjusted. I want to see the details of the post-charge accounting.

no matches

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

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 16599
							output: 34
							thoughts: 22
						

Okay, here's the summary, expressed as though I'm the one thinking it:

**Digging into Memory Accounting within the Kernel**

Right, so I'm looking into the kernel's memory management, specifically how it handles accounting related to SLUB caches and control groups. I need to understand how memory charges are handled after an allocation. My initial hunt leads me to `mm/slub.c`. Now, where exactly does the post-charge logic reside? The function name, `memcg_slab_post_charge`, suggests this is precisely what I'm after. This is where the real work of tracking memory usage within control groups happens after a slab allocation or freeing. Time to dive into this function and see how it interacts with the broader memcg infrastructure.

{
  "Expression": "memcg_slab_post_charge",
  "PathPrefix": "mm/slub.c"
}

{
  "Output": "mm/slub.c=2523=static __fastpath_inline\nmm/slub.c:2524:bool memcg_slab_post_charge(void *p, gfp_t flags)\nmm/slub.c-2525-{\n--\nmm/slub.c=2591=static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,\n--\nmm/slub.c-2595-\nmm/slub.c:2596:static inline bool memcg_slab_post_charge(void *p, gfp_t flags)\nmm/slub.c-2597-{\n--\nmm/slub.c=5005=bool kmem_cache_charge(void *objp, gfp_t gfpflags)\n--\nmm/slub.c-5009-\nmm/slub.c:5010:\treturn memcg_slab_post_charge(objp, gfpflags);\nmm/slub.c-5011-}\n"
}

gemini-3.1-pro-preview

null

null

							input: 17093
							output: 34
							thoughts: 31
						

Here's my take on the thought process, as if it were my own:

**KFENCE Deep Dive: Initialization and Deallocation**

Okay, so I need to refresh my memory on KFENCE's core workings, specifically how it initializes its memory pool and the mechanisms it uses for freeing memory. The likely place to start looking for those functions is in the `mm/kfence/core.c` file. I'm going to track down the `kfence_init_pool` function, to understand how the pool itself is set up, and I will also need to review `__kfence_free` to get the rundown on how memory is actually relinquished by KFENCE. That should give me the core picture I need to analyze its behavior.

{
  "Expression": "kfence_init_pool",
  "PathPrefix": "mm/kfence/core.c"
}

{
  "Output": "mm/kfence/core.c=599=static void rcu_guarded_free(struct rcu_head *h)\n--\nmm/kfence/core.c-610- */\nmm/kfence/core.c:611:static unsigned long kfence_init_pool(void)\nmm/kfence/core.c-612-\t__context_unsafe(/* constructor */)\n--\nmm/kfence/core.c-616-\nmm/kfence/core.c:617:\tif (!arch_kfence_init_pool())\nmm/kfence/core.c-618-\t\treturn (unsigned long)__kfence_pool;\n--\nmm/kfence/core.c-719-\nmm/kfence/core.c:720:static bool __init kfence_init_pool_early(void)\nmm/kfence/core.c-721-{\n--\nmm/kfence/core.c-726-\nmm/kfence/core.c:727:\taddr = kfence_init_pool();\nmm/kfence/core.c-728-\n--\nmm/kfence/core.c=994=void __init kfence_init(void)\n--\nmm/kfence/core.c-1001-\nmm/kfence/core.c:1002:\tif (!kfence_init_pool_early()) {\nmm/kfence/core.c-1003-\t\tpr_err(\"%s failed\\n\", __func__);\n--\nmm/kfence/core.c=1010=static int kfence_init_late(void)\n--\nmm/kfence/core.c-1050-\tmemzero_explicit(kfence_metadata_init, KFENCE_METADATA_SIZE);\nmm/kfence/core.c:1051:\taddr = kfence_init_pool();\nmm/kfence/core.c-1052-\tif (!addr) {\n--\nmm/kfence/core.c=1090=void kfence_shutdown_cache(struct kmem_cache *s)\n--\nmm/kfence/core.c-1095-\nmm/kfence/core.c:1096:\t/* Pairs with release in kfence_init_pool(). */\nmm/kfence/core.c-1097-\tif (!smp_load_acquire(\u0026kfence_metadata))\n"
}

gemini-3.1-pro-preview

null

null

							input: 17928
							output: 33
							thoughts: 22
						

Here's my thought process, summarized as you requested:

**Digging into Kernel Memory Management**

Okay, so I need to understand how `__kfence_free` works. I know that's part of the KFENCE (Kernel Electric Fence) project, so the likely starting point is in the core KFENCE implementation. Specifically, I'll navigate to the `mm/kfence/` directory and find `core.c`. That should contain the definition for `__kfence_free`, and likely the surrounding context I need. Time to dive in and get a handle on the specifics of this memory deallocation path within KFENCE.

{
  "Expression": "__kfence_free",
  "PathPrefix": "mm/kfence/core.c"
}

{
  "Output": "mm/kfence/core.c=1239=void *kfence_object_start(const void *addr)\n--\nmm/kfence/core.c-1249-\nmm/kfence/core.c:1250:void __kfence_free(void *addr)\nmm/kfence/core.c-1251-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 18217
							output: 36
							thoughts: 25
						

Okay, here's my take on those thoughts, framed as a first-person expert summary:

**Digging into Memory Control with `mem_cgroup_from_obj_slab`**

Alright, so I'm thinking about memory cgroups and specifically how the kernel tracks memory usage from slab allocations. To understand this properly, the logical starting point for me is `mm/memcontrol.c`. I need to figure out how the kernel associates a slab object with its corresponding memory cgroup, and `mem_cgroup_from_obj_slab` is the obvious function to investigate. It seems likely that this function is central to the tracking process; I need to look closely to see exactly how it maps a slab object's allocation back to a specific cgroup. Is it using the slab's metadata? Or is there some other magic involved? I expect to find some critical pointers or lookups here. This function is likely a cornerstone for accurate accounting, so understanding its inner workings is going to be important. Let's see how it works!

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

{
  "Output": "mm/memcontrol.c=2858=static __always_inline\nmm/memcontrol.c:2859:struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p)\nmm/memcontrol.c-2860-{\n--\nmm/memcontrol.c=2898=struct mem_cgroup *mem_cgroup_from_virt(void *p)\n--\nmm/memcontrol.c-2906-\tif (slab)\nmm/memcontrol.c:2907:\t\treturn mem_cgroup_from_obj_slab(slab, p);\nmm/memcontrol.c-2908-\treturn folio_memcg_check(virt_to_folio(p));\n"
}

gemini-3.1-pro-preview

null

null

							input: 18694
							output: 36
							thoughts: 34
						

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

**Analyzing Memory Allocation in the Kernel**

Alright, I'm going to start by looking at `mm/slab_common.c`. I know this is where the core slab allocator functions reside. Specifically, I'm interested in how `__kmem_cache_create_args` and `new_kmalloc_cache` work. I'll need to understand their roles in initializing and managing these kmem caches because those are the foundation for efficient kernel memory allocation. Understanding how those caches are setup is key to identifying potential performance bottlenecks or subtle memory-related bugs. Let's see how they interact.

{
  "Expression": "__kmem_cache_create_args",
  "PathPrefix": "mm/slab_common.c"
}

{
  "Output": "mm/slab_common.c=267=__kmem_cache_alias(const char *name, unsigned int size, slab_flags_t flags,\n--\nmm/slab_common.c-291-/**\nmm/slab_common.c:292: * __kmem_cache_create_args - Create a kmem cache.\nmm/slab_common.c-293- * @name: A string which is used in /proc/slabinfo to identify this cache.\n--\nmm/slab_common.c-317- */\nmm/slab_common.c:318:struct kmem_cache *__kmem_cache_create_args(const char *name,\nmm/slab_common.c-319-\t\t\t\t\t    unsigned int object_size,\n--\nmm/slab_common.c-408-}\nmm/slab_common.c:409:EXPORT_SYMBOL(__kmem_cache_create_args);\nmm/slab_common.c-410-\n"
}

gemini-3.1-pro-preview

null

null

							input: 19173
							output: 33
							thoughts: 9
						

Okay, here's my attempt at summarizing the thought process, tailored for an expert audience, and written in the first person:

**Initial Assessment: Examining a `kmalloc` Cache**

Alright, I'm looking at a new `kmalloc_cache`, and immediately, my mind starts ticking. The implications are clear. I need to understand its purpose within the kernel's memory management. Is this for a specific driver, a core subsystem, or a more general use case? The name itself often offers clues, so I'll be dissecting that very carefully to identify its role. I need to be asking myself about the intended size class and its relation to slab caches in use elsewhere.

My immediate concerns are around efficiency and fragmentation. Is this cache appropriately sized for its expected workload? Has the design considered the potential for internal fragmentation based on the object size? Are there potential overlaps with existing caches, and could we consolidate to improve overall memory utilization? What is the impact on cache line utilization? Does the cache make use of NUMA nodes effectively? I need to think about that, too.

I'm also curious about the allocation and freeing patterns. Is this cache being heavily contended, or is it relatively static? Frequent allocations and deallocations can lead to performance bottlenecks, so I have to be thinking about how it is being used, its lock contention, and the impact on other kernel operations. Are there any contention issues? Are there mutexes or spinlocks in place? How are they configured?

Finally, what are the error-handling mechanisms in place? A `kmalloc` cache is a critical resource, and I'll want to see how it handles potential memory allocation failures, or even if the cache becomes corrupted. Does it have appropriate checks and balances to prevent cascading failures? Are there instrumentation hooks for debugging? The answers to these questions are essential. I want to see if this design is robust or fragile.

{
  "Expression": "new_kmalloc_cache",
  "PathPrefix": "mm/slab_common.c"
}

{
  "Output": "mm/slab_common.c=962=static void __init\nmm/slab_common.c:963:new_kmalloc_cache(int idx, enum kmalloc_cache_type type)\nmm/slab_common.c-964-{\n--\nmm/slab_common.c=1026=void __init create_kmalloc_caches(void)\n--\nmm/slab_common.c-1036-\t\tif (KMALLOC_MIN_SIZE \u003c= 32)\nmm/slab_common.c:1037:\t\t\tnew_kmalloc_cache(1, type);\nmm/slab_common.c-1038-\t\tif (KMALLOC_MIN_SIZE \u003c= 64)\nmm/slab_common.c:1039:\t\t\tnew_kmalloc_cache(2, type);\nmm/slab_common.c-1040-\n--\nmm/slab_common.c-1042-\t\tfor (i = KMALLOC_SHIFT_LOW; i \u003c= KMALLOC_SHIFT_HIGH; i++)\nmm/slab_common.c:1043:\t\t\tnew_kmalloc_cache(i, type);\nmm/slab_common.c-1044-\t}\n"
}

gemini-3.1-pro-preview

null

null

							input: 19918
							output: 34
							thoughts: 315
						

**Analyzing Slab Allocation Hooks**

Okay, so I'm looking at this patch and it's touching a whole bunch of core slab allocation hooks: `alloc_slab_obj_exts`, `alloc_slab_obj_exts_early`, and a few others I recognize, namely `__alloc_tagging_slab_alloc_hook`, `__alloc_tagging_slab_free_hook`, `memcg_slab_post_charge`, `__memcg_slab_post_alloc_hook`, `__memcg_slab_free_hook`, and `mem_cgroup_from_obj_slab`. Seems pretty central to how the slab allocator works. I need to make sure I understand how this impacts the system.

My immediate focus here needs to be on: `alloc_slab_obj_exts`, `__alloc_tagging_slab_alloc_hook`, `__alloc_tagging_slab_free_hook`, `memcg_slab_post_charge`, `__memcg_slab_post_alloc_hook`, `__memcg_slab_free_hook`, and `mem_cgroup_from_obj_slab`. Those are the critical functions.

Wait a second, there are some preprocessor conditionals I need to take into account. `__alloc_tagging_slab_alloc_hook` and `__alloc_tagging_slab_free_hook` are only present if `CONFIG_MEM_ALLOC_PROFILING` is enabled. Also, `__memcg_slab_post_alloc_hook` and `__memcg_slab_free_hook` are dependent on `CONFIG_MEMCG`. Gotta keep that in mind when I'm assessing the overall impact. To be sure, I should probably check `mm/slub.c` for `alloc_slab_obj_exts`. Just want to have the context fully in my head.

{
  "Expression": "alloc_slab_obj_exts",
  "PathPrefix": "mm/slub.c"
}

{
  "Output": "mm/slub.c=2134=static inline void init_slab_obj_exts(struct slab *slab)\n--\nmm/slub.c-2138-\nmm/slub.c:2139:int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,\nmm/slub.c-2140-\t\t\tgfp_t gfp, unsigned int alloc_flags)\n--\nmm/slub.c=2228=static inline void free_slab_obj_exts(struct slab *slab, bool allow_spin)\n--\nmm/slub.c-2259- */\nmm/slub.c:2260:static void alloc_slab_obj_exts_early(struct kmem_cache *s, struct slab *slab)\nmm/slub.c-2261-{\n--\nmm/slub.c=2307=static inline void init_slab_obj_exts(struct slab *slab)\n--\nmm/slub.c-2310-\nmm/slub.c:2311:static int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,\nmm/slub.c-2312-\t\t\t       gfp_t gfp, unsigned int alloc_flags)\n--\nmm/slub.c=2317=static inline void free_slab_obj_exts(struct slab *slab, bool allow_spin)\n--\nmm/slub.c-2320-\nmm/slub.c:2321:static inline void alloc_slab_obj_exts_early(struct kmem_cache *s,\nmm/slub.c-2322-\t\t\t\t\t\t       struct slab *slab)\n--\nmm/slub.c=2331=prepare_slab_obj_exts_hook(struct kmem_cache *s, struct slab *slab,\n--\nmm/slub.c-2334-\tif (!slab_obj_exts(slab) \u0026\u0026\nmm/slub.c:2335:\t    alloc_slab_obj_exts(slab, s, flags, alloc_flags)) {\nmm/slub.c-2336-\t\tpr_warn_once(\"%s, %s: Failed to create slab extension vector!\\n\",\n--\nmm/slub.c=3372=static __always_inline void account_slab(struct slab *slab, int order,\n--\nmm/slub.c-3378-\t\t\t!slab_obj_exts(slab))\nmm/slub.c:3379:\t\talloc_slab_obj_exts(slab, s, gfp,\nmm/slub.c-3380-\t\t\t\t    alloc_flags | SLAB_ALLOC_NEW_SLAB);\n--\nmm/slub.c=3401=static struct slab *allocate_slab(struct kmem_cache *s, gfp_t flags,\n--\nmm/slub.c-3456-\t */\nmm/slub.c:3457:\talloc_slab_obj_exts_early(s, slab);\nmm/slub.c-3458-\taccount_slab(slab, oo_order(oo), s, flags, alloc_flags);\n"
}

gemini-3.1-pro-preview

null

null

							input: 21490
							output: 34
							thoughts: 28
						

Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Checking Slab Object Extension Availability**

Alright, before I dive into any more detailed analysis, I need to make a quick sanity check. I'm going to quickly confirm that `alloc_slab_obj_exts` is actually defined in the current configuration. This essentially means I'm checking if the `CONFIG_SLAB_OBJ_EXT` feature is enabled. It's a fundamental prerequisite. Without this, the function won't be in the kernel's symbol table, and any attempt to use it would be futile, leading to undefined behavior or compile-time errors. So, before I go any further, I'll confirm that this is a valid part of the available toolset. This saves me time in the long run. I don't want to chase down a rabbit hole of debugging if the root cause is simply a disabled feature. This also helps ensure any assumptions I make down the line regarding this functionality are valid.

{
  "Expression": "CONFIG_SLAB_OBJ_EXT",
  "PathPrefix": "mm/slub.c"
}

{
  "Output": "mm/slub.c=766=static inline unsigned long get_orig_size(struct kmem_cache *s, void *object)\n--\nmm/slub.c-781-\nmm/slub.c:782:#ifdef CONFIG_SLAB_OBJ_EXT\nmm/slub.c-783-\n--\nmm/slub.c=870=static inline bool obj_exts_in_slab(struct kmem_cache *s, struct slab *slab)\n--\nmm/slub.c-876-\nmm/slub.c:877:#if defined(CONFIG_SLAB_OBJ_EXT) \u0026\u0026 defined(CONFIG_64BIT)\nmm/slub.c-878-static unsigned int obj_exts_offset_in_object(struct kmem_cache *s)\n--\nmm/slub.c=2042=static inline void dec_slabs_node(struct kmem_cache *s, int node,\n--\nmm/slub.c-2057-\nmm/slub.c:2058:#ifdef CONFIG_SLAB_OBJ_EXT\nmm/slub.c-2059-\n--\nmm/slub.c=2260=static void alloc_slab_obj_exts_early(struct kmem_cache *s, struct slab *slab)\n--\nmm/slub.c-2300-\nmm/slub.c:2301:#else /* CONFIG_SLAB_OBJ_EXT */\nmm/slub.c-2302-\n--\nmm/slub.c=2321=static inline void alloc_slab_obj_exts_early(struct kmem_cache *s,\n--\nmm/slub.c-2325-\nmm/slub.c:2326:#endif /* CONFIG_SLAB_OBJ_EXT */\nmm/slub.c-2327-\n--\nmm/slub.c=7862=static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s)\n--\nmm/slub.c-7976-\taligned_size = ALIGN(size, s-\u003ealign);\nmm/slub.c:7977:#if defined(CONFIG_SLAB_OBJ_EXT) \u0026\u0026 defined(CONFIG_64BIT)\nmm/slub.c-7978-\tif (slab_args_unmergeable(args, s-\u003eflags) \u0026\u0026\n"
}

gemini-3.1-pro-preview

null

null

							input: 22387
							output: 30
							thoughts: 94
						

**Examining the Dependencies for Slabobj_ext Optimization**

Okay, so this patch is clearly targeting optimization of `struct slabobj_ext`. The first thing that jumps out is that `CONFIG_SLAB_OBJ_EXT` is definitely required. No surprises there. But now I'm thinking about the implications. Since this structure is being optimized, I need to consider all the places it's used. Right, it's used by both `CONFIG_MEM_ALLOC_PROFILING` and `CONFIG_MEMCG`. Those are the two key consumers of this structure. Got it. Now, to be absolutely certain, it's time to go straight to the source. Let's pull up `mm/slab.h` and take a look at the definition of `struct slabobj_ext` to understand the exact memory layout that's being tweaked. That'll give me the full context.

{
  "Expression": "struct slabobj_ext",
  "PathPrefix": "mm/slab.h"
}

{
  "Output": "mm/slab.h=541=static inline bool need_kmalloc_no_objext(void)\n--\nmm/slab.h-556- */\nmm/slab.h:557:struct slabobj_ext {\nmm/slab.h-558-\t/*\n--\nmm/slab.h=614=static inline size_t cache_obj_ext_size(struct kmem_cache *s)\n--\nmm/slab.h-623-\nmm/slab.h:624:\treturn sizeof(struct slabobj_ext) * sz;\nmm/slab.h-625-}\n--\nmm/slab.h=627=static inline size_t slab_obj_ext_size(struct slab *slab)\n--\nmm/slab.h-636-\nmm/slab.h:637:\treturn sizeof(struct slabobj_ext) * sz;\nmm/slab.h-638-}\n--\nmm/slab.h=706=static inline bool obj_exts_in_object(struct slab *slab)\n--\nmm/slab.h-722- */\nmm/slab.h:723:static inline struct slabobj_ext *\nmm/slab.h-724-slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts,\n--\nmm/slab.h-726-{\nmm/slab.h:727:\tstruct slabobj_ext *obj_ext;\nmm/slab.h-728-\tunsigned int index;\n--\nmm/slab.h-739-\nmm/slab.h:740:\tobj_ext = (struct slabobj_ext *)(obj_exts + index * stride);\nmm/slab.h-741-\n--\nmm/slab.h-745-#ifdef CONFIG_MEMCG\nmm/slab.h:746:static inline struct obj_cgroup *slab_obj_ext_objcg(struct slabobj_ext *obj_ext)\nmm/slab.h-747-{\n--\nmm/slab.h-751-\nmm/slab.h:752:static inline void slab_obj_ext_set_objcg(struct slabobj_ext *obj_ext,\nmm/slab.h-753-\t\t\t\t\t  struct obj_cgroup *objcg)\n--\nmm/slab.h=761=static inline union codetag_ref *\nmm/slab.h:762:slab_obj_ext_codetag_ref(struct slab *slab, struct slabobj_ext *obj_ext)\nmm/slab.h-763-{\n--\nmm/slab.h=776=static inline unsigned long slab_obj_exts(struct slab *slab)\n--\nmm/slab.h-780-\nmm/slab.h:781:static inline struct slabobj_ext *\nmm/slab.h-782-slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts,\n"
}

gemini-3.1-pro-preview

null

null

							input: 23456
							output: 36
							thoughts: 156
						

**Analyzing Slab Allocation and Tagging Hooks**

Okay, let's break this down. My focus right now is on understanding the interaction between slab allocation, object extensions, and memory control groups. I see a constellation of symbols that seem central to this: `alloc_slab_obj_exts`, `alloc_slab_obj_exts_early`, `__alloc_tagging_slab_alloc_hook`, `__alloc_tagging_slab_free_hook`, `memcg_slab_post_charge`, `__memcg_slab_post_alloc_hook`, `__memcg_slab_free_hook`, and `mem_cgroup_from_obj_slab`. It's a bit of a dance, and I need to figure out the steps.

Wait a second, wasn't `alloc_slab_obj_exts_early` declared as `static inline` or `static void`? That's interesting, as this would make the behavior of the hook dependent on inlining/compile-time optimization. That implies it might be used to optimize something that's otherwise done later. Okay, let's take a closer look at this early stage function. I need to refresh my memory on what that actually does within `mm/slub.c`. I will dive into the code for a better understanding.

{
  "Expression": "alloc_slab_obj_exts_early",
  "PathPrefix": "mm/slub.c"
}

{
  "Output": "mm/slub.c=2228=static inline void free_slab_obj_exts(struct slab *slab, bool allow_spin)\n--\nmm/slub.c-2259- */\nmm/slub.c:2260:static void alloc_slab_obj_exts_early(struct kmem_cache *s, struct slab *slab)\nmm/slub.c-2261-{\n--\nmm/slub.c=2317=static inline void free_slab_obj_exts(struct slab *slab, bool allow_spin)\n--\nmm/slub.c-2320-\nmm/slub.c:2321:static inline void alloc_slab_obj_exts_early(struct kmem_cache *s,\nmm/slub.c-2322-\t\t\t\t\t\t       struct slab *slab)\n--\nmm/slub.c=3401=static struct slab *allocate_slab(struct kmem_cache *s, gfp_t flags,\n--\nmm/slub.c-3456-\t */\nmm/slub.c:3457:\talloc_slab_obj_exts_early(s, slab);\nmm/slub.c-3458-\taccount_slab(slab, oo_order(oo), s, flags, alloc_flags);\n"
}

gemini-3.1-pro-preview

null

null

							input: 24271
							output: 28
							thoughts: 263
						

**Analyzing Memory Allocation Optimization**

Okay, so this is static, not changing. My focus symbols here are all related to slab object extensions: `alloc_slab_obj_exts`, `alloc_slab_obj_exts_early`, and the various hooking functions (`__alloc_tagging_slab_alloc_hook`, `__alloc_tagging_slab_free_hook`, `__memcg_slab_post_alloc_hook`, `__memcg_slab_free_hook`), along with `memcg_slab_post_charge` and `mem_cgroup_from_obj_slab`. This immediately suggests we're dealing with memory allocation and, more specifically, how these extensions interact with memory control groups (memcgs) and/or memory profiling.

The question then becomes: are `CONFIG_MEM_ALLOC_PROFILING` and `CONFIG_MEMCG` prerequisites here? Yes, it seems the patch is optimizing the memory layout of `struct slabobj_ext` which is used when *either* `CONFIG_MEM_ALLOC_PROFILING` or `CONFIG_MEMCG` is set. So, for proper configuration, I'll need to include `MEM_ALLOC_PROFILING` and `MEMCG` in `EnableConfigs`.

Hold on, I recall `MEMCG` is frequently enabled by default. However, it wouldn't hurt to be explicit and list it. `MEM_ALLOC_PROFILING` is definitely a dedicated configuration option for memory allocation profiling, and one that is probably less often enabled by default. I should double-check the `Kconfig` file for `MEM_ALLOC_PROFILING` to be absolutely certain of the default behavior and any relevant dependencies.

{
  "Expression": "config MEM_ALLOC_PROFILING",
  "PathPrefix": ""
}

{
  "Output": "lib/Kconfig.debug=1047=config CODE_TAGGING\n--\nlib/Kconfig.debug-1050-\nlib/Kconfig.debug:1051:config MEM_ALLOC_PROFILING\nlib/Kconfig.debug-1052-\tbool \"Enable memory allocation profiling\"\n--\nlib/Kconfig.debug-1064-\nlib/Kconfig.debug:1065:config MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT\nlib/Kconfig.debug-1066-\tbool \"Enable memory allocation profiling by default\"\n--\nlib/Kconfig.debug-1069-\nlib/Kconfig.debug:1070:config MEM_ALLOC_PROFILING_DEBUG\nlib/Kconfig.debug-1071-\tbool \"Memory allocation profiler debugging\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 25141
							output: 27
							thoughts: 55
						

Okay, let's see, my thinking is:

**Memory Allocation Profiling and Control Group Integration**

Right, so to get a really good handle on this, I'm thinking we need to flip on `MEM_ALLOC_PROFILING` and its default-enabled counterpart `MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT`. That's going to give us a granular view into the memory allocation behavior, which is critical for optimization. We *need* that data.

And while we're at it, `MEMCG` has got to be in the mix. Control groups are indispensable for isolating and managing resource consumption, and memory is obviously a big part of that equation. We need to be able to effectively isolate the processes and understand their behavior.

Finally, just a quick sanity check: I'll also want to confirm that `SLAB_OBJ_EXT` is exposed as a configurable option to the end-users. Sometimes these "internal" flags are hidden and it is useful to know if we can control it.

{
  "Expression": "config SLAB_OBJ_EXT",
  "PathPrefix": ""
}

{
  "Output": "init/Kconfig=1033=config NUMA_BALANCING_DEFAULT_ENABLED\n--\ninit/Kconfig-1040-\ninit/Kconfig:1041:config SLAB_OBJ_EXT\ninit/Kconfig-1042-\tbool\n"
}

gemini-3.1-pro-preview

null

null

							input: 25520
							output: 27
							thoughts: 45
						

**Investigating the `SLAB_OBJ_EXT` Boolean**

Okay, so I'm looking at this `SLAB_OBJ_EXT` flag and it's flagged as a hidden boolean, which immediately piques my interest. My intuition tells me it's probably triggered by either `MEMCG` or `MEM_ALLOC_PROFILING`. Those two are the usual suspects for influencing low-level memory management behaviors. Let's dig in and figure out the exact selection criteria for this flag. Knowing what enables `SLAB_OBJ_EXT` is critical for understanding its purpose and impact on the system. Time to trace the dependencies.

{
  "Expression": "select SLAB_OBJ_EXT",
  "PathPrefix": ""
}

{
  "Output": "init/Kconfig=1073=config MEMCG\n--\ninit/Kconfig-1076-\tselect EVENTFD\ninit/Kconfig:1077:\tselect SLAB_OBJ_EXT\ninit/Kconfig-1078-\tselect VM_EVENT_COUNTERS\n--\nlib/Kconfig.debug=1051=config MEM_ALLOC_PROFILING\n--\nlib/Kconfig.debug-1058-\tselect PAGE_EXTENSION\nlib/Kconfig.debug:1059:\tselect SLAB_OBJ_EXT\nlib/Kconfig.debug-1060-\thelp\n"
}

gemini-3.1-pro-preview

null

null

							input: 25888
							output: 32
							thoughts: 241
						

**My Analysis of Memory Management Configuration**

Okay, so based on the kernel code, enabling both `MEMCG` and `MEM_ALLOC_PROFILING` automatically brings in `SLAB_OBJ_EXT`. Therefore, the `EnableConfigs` list definitely needs to include both `MEMCG` and `MEM_ALLOC_PROFILING`. That's straightforward.

Now, I need to pick a good focus symbol. I was initially thinking about `alloc_slab_obj_exts_early`, but I need to make sure this is the right choice, so let's dig a bit deeper. It's static, which is a concern, but syzkaller *might* be able to fuzz it if it isn't inlined, so it may still be viable. Thankfully, `alloc_slab_obj_exts` itself is exported, or at least it isn't static, which looks better. Excellent. Then I see that `__alloc_tagging_slab_alloc_hook` and `__alloc_tagging_slab_free_hook` are also non-static. Good signs for fuzzing targets! Further, `memcg_slab_post_charge`, `__memcg_slab_post_alloc_hook`, `__memcg_slab_free_hook`, and `mem_cgroup_from_obj_slab` are all non-static as well. These are all good candidates.

Next, I need to confirm if `alloc_slab_obj_exts` is indeed exported. I need to verify that.

no matches

{
  "Expression": "EXPORT_SYMBOL.*alloc_slab_obj_exts",
  "PathPrefix": ""
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 26506
							output: 34
							thoughts: 59
						

**Analyzing the SLUB Allocator**

Okay, so I don't need to worry about exporting this thing; it just needs to be non-static. The key here is to figure out where it's being used and how it interacts with the rest of the memory management system. Let me see... I recall `alloc_slab_obj_exts` being called from both `mm/slub.c` – that's the SLUB allocator itself, obviously – and also from `mm/memcontrol.c`. That's interesting, suggesting potential interaction with memory control groups. Now, let's take a look at `mm/slab.h`. That's where the relevant structures and function declarations should be. I need to understand the interfaces and dependencies.

{
  "Expression": "int alloc_slab_obj_exts",
  "PathPrefix": "mm/slab.h"
}

{
  "Output": "mm/slab.h=762=slab_obj_ext_codetag_ref(struct slab *slab, struct slabobj_ext *obj_ext)\n--\nmm/slab.h-770-\nmm/slab.h:771:int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,\nmm/slab.h-772-\t\t\tgfp_t gfp, unsigned int alloc_flags);\n"
}

gemini-3.1-pro-preview

null

null

							input: 26882
							output: 37
							thoughts: 220
						

**Analyzing KFENCE and SLUB Symbols**

Okay, so this is definitely not a static situation, good. I need to make sure I understand the scope here. Let's dig into the code and look at `kfence_init_pool` and `__kfence_free` specifically. Alright, `kfence_init_pool` is defined as static, that makes sense. But `__kfence_free`... that's non-static. Bingo! We can add `__kfence_free` to `FocusSymbols`, that's what we want.

Now, let's take a look at what else is in `FocusSymbols` currently. Let's see... `alloc_slab_obj_exts`, `__alloc_tagging_slab_alloc_hook`, `__alloc_tagging_slab_free_hook`, `memcg_slab_post_charge`, `__memcg_slab_post_alloc_hook`, `__memcg_slab_free_hook`, `mem_cgroup_from_obj_slab`, and now, `__kfence_free`.

Hold on a second... are those `__alloc_tagging_slab_alloc_hook` and `__alloc_tagging_slab_free_hook` functions also static? Yes, they are! I'm looking right at it in `mm/slub.c` now, and they are static noinline functions. I need to keep that in mind as I process this.

{
  "Expression": "__alloc_tagging_slab_alloc_hook",
  "PathPrefix": "mm/slub.c"
}

{
  "Output": "mm/slub.c=2346=static noinline void\nmm/slub.c:2347:__alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,\nmm/slub.c-2348-\t\t\t\tunsigned int alloc_flags)\n--\nmm/slub.c=2390=alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,\n--\nmm/slub.c-2393-\tif (mem_alloc_profiling_enabled())\nmm/slub.c:2394:\t\t__alloc_tagging_slab_alloc_hook(s, object, flags, alloc_flags);\nmm/slub.c-2395-}\n"
}

gemini-3.1-pro-preview

null

null

							input: 27672
							output: 37
							thoughts: 47
						

Okay, here's my take on those thoughts, framed as my own reasoning:

**Analyzing Potential Fuzzing Targets**

Alright, so the targets we're looking at are marked as `static noinline`. Fine, that's not a showstopper; Syzkaller can still potentially get at them. No problem there.

My next step is to drill down into the likely areas of interest. Specifically, I should check out the potential hooks: `__memcg_slab_post_alloc_hook` and `__memcg_slab_free_hook`. These are the functions I'm most interested in at this juncture.

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

{
  "Output": "mm/memcontrol.c=3529=static inline size_t obj_full_size(struct kmem_cache *s)\n--\nmm/memcontrol.c-3537-\nmm/memcontrol.c:3538:bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,\nmm/memcontrol.c-3539-\t\t\t\t  gfp_t flags, unsigned int slab_alloc_flags,\n"
}

gemini-3.1-pro-preview

null

null

							input: 28021
							output: 36
							thoughts: 23
						

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

**Analyzing Dynamic Memory Allocation**

My mind is immediately drawn to the inherent dynamism of the topic. The very nature of this memory allocation process suggests that it's *not* a static problem. It’s fluid, constantly changing, and that's the core challenge. The implications of this are significant and must be kept in mind.

To tackle this, a natural first step is to dive into the `mem_cgroup_from_obj_slab` function. Understanding how the memory cgroup interacts with object slabs is paramount here. This function likely provides a crucial entry point to dissecting the allocation/deallocation mechanics at a granular level. Delving into its logic will reveal key insights into how memory is being managed and potentially where inefficiencies or leaks might be lurking within the system. It's a fundamental piece to understanding the puzzle.

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

{
  "Output": "mm/memcontrol.c=2858=static __always_inline\nmm/memcontrol.c:2859:struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p)\nmm/memcontrol.c-2860-{\n--\nmm/memcontrol.c=2898=struct mem_cgroup *mem_cgroup_from_virt(void *p)\n--\nmm/memcontrol.c-2906-\tif (slab)\nmm/memcontrol.c:2907:\t\treturn mem_cgroup_from_obj_slab(slab, p);\nmm/memcontrol.c-2908-\treturn folio_memcg_check(virt_to_folio(p));\n"
}

gemini-3.1-pro-preview

null

null

							input: 28467
							output: 34
							thoughts: 37
						

Okay, here's my interpretation of those thoughts, presented as my own mental process, given my expertise:

**Exclusionary Reasoning in Fuzzing Context**

Alright, so the first thing I see is something marked as `static __always_inline`. That instantly throws up a red flag in the context of fuzzing, particularly with Syzkaller. Because it's inline, it's baked into other code during compilation and doesn't exist as a standalone function that Syzkaller can directly target. Attempting to do so would be futile. Therefore, my immediate reaction is, "We need to exclude this from fuzzing." It's a dead end as a fuzzing target, likely just inlined as part of a larger, more interesting function. No point wasting time on it.

Now, let's pivot. Since this function is off the table, I need to find its callers. Which means I need to explore what function that makes sense to study in the place of this function. Let's see... I'll check `memcg_slab_post_charge`. This seems like a reasonable next step, given the context. It likely represents a point where memory accounting, related to slab caches and memory control groups, is handled. And if this inlined function is part of some crucial accounting process, then the calling function is likely to be an important entry point or point of failure.

{
  "Expression": "memcg_slab_post_charge",
  "PathPrefix": "mm/slub.c"
}

{
  "Output": "mm/slub.c=2523=static __fastpath_inline\nmm/slub.c:2524:bool memcg_slab_post_charge(void *p, gfp_t flags)\nmm/slub.c-2525-{\n--\nmm/slub.c=2591=static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,\n--\nmm/slub.c-2595-\nmm/slub.c:2596:static inline bool memcg_slab_post_charge(void *p, gfp_t flags)\nmm/slub.c-2597-{\n--\nmm/slub.c=5005=bool kmem_cache_charge(void *objp, gfp_t gfpflags)\n--\nmm/slub.c-5009-\nmm/slub.c:5010:\treturn memcg_slab_post_charge(objp, gfpflags);\nmm/slub.c-5011-}\n"
}

gemini-3.1-pro-preview

null

null

							input: 29105
							output: 36
							thoughts: 29
						

Okay, here's my take on those thoughts, framed as my own reasoning:

**Filtering Kernel Code: A Quick Assessment**

Alright, let's see... First off, that `static __fastpath_inline` directive is a clear exclusion. No need to spend any time on that. It's essentially an internal, optimized helper function. Moving on...

Now, `__kmem_cache_create_args`... That's a little more interesting, isn't it? I need to quickly assess if it's relevant to the current task. I'll need to figure out what it actually *does* within the kernel memory management scheme and determine whether it's something that needs to be considered, or if it's something I can safely exclude based on the current context. More information is required to make a decision about this.

{
  "Expression": "__kmem_cache_create_args",
  "PathPrefix": "mm/slab_common.c"
}

{
  "Output": "mm/slab_common.c=267=__kmem_cache_alias(const char *name, unsigned int size, slab_flags_t flags,\n--\nmm/slab_common.c-291-/**\nmm/slab_common.c:292: * __kmem_cache_create_args - Create a kmem cache.\nmm/slab_common.c-293- * @name: A string which is used in /proc/slabinfo to identify this cache.\n--\nmm/slab_common.c-317- */\nmm/slab_common.c:318:struct kmem_cache *__kmem_cache_create_args(const char *name,\nmm/slab_common.c-319-\t\t\t\t\t    unsigned int object_size,\n--\nmm/slab_common.c-408-}\nmm/slab_common.c:409:EXPORT_SYMBOL(__kmem_cache_create_args);\nmm/slab_common.c-410-\n"
}

gemini-3.1-pro-preview

null

null

							input: 29602
							output: 33
							thoughts: 21
						

Okay, here's my summary, in the first person, as if these are my thoughts, keeping in mind I'm an expert in my field:

**Internal Code Review: Inclusion & Refinement**

Alright, the initial review indicates this code can be exported. Good, that's a positive start. We can include it in the broader project, which is what we need.

But hold on, before we give this the green light, I need to zoom in. The use of `new_kmalloc_cache` has me slightly concerned. Is this the right implementation? Am I going to be dealing with the complexity of a custom cache? Or is it okay because it's managed correctly elsewhere? The use case isn't clear from just this snippet. It could be fine. I'll need to dig deeper into its implementation and integration points. This needs a closer look before I sign off.

{
  "Expression": "new_kmalloc_cache",
  "PathPrefix": "mm/slab_common.c"
}

{
  "Output": "mm/slab_common.c=962=static void __init\nmm/slab_common.c:963:new_kmalloc_cache(int idx, enum kmalloc_cache_type type)\nmm/slab_common.c-964-{\n--\nmm/slab_common.c=1026=void __init create_kmalloc_caches(void)\n--\nmm/slab_common.c-1036-\t\tif (KMALLOC_MIN_SIZE \u003c= 32)\nmm/slab_common.c:1037:\t\t\tnew_kmalloc_cache(1, type);\nmm/slab_common.c-1038-\t\tif (KMALLOC_MIN_SIZE \u003c= 64)\nmm/slab_common.c:1039:\t\t\tnew_kmalloc_cache(2, type);\nmm/slab_common.c-1040-\n--\nmm/slab_common.c-1042-\t\tfor (i = KMALLOC_SHIFT_LOW; i \u003c= KMALLOC_SHIFT_HIGH; i++)\nmm/slab_common.c:1043:\t\t\tnew_kmalloc_cache(i, type);\nmm/slab_common.c-1044-\t}\n"
}

gemini-3.1-pro-preview

null

null

							input: 30152
							output: 33
							thoughts: 127
						

**My Analysis of the Symbol List**

Okay, so I've been given a list of symbols to focus on. First, I'm going to quickly eliminate that `static void __init` one; it's initialization code and not relevant to my core analysis. Now, the final list includes: `alloc_slab_obj_exts`, `__alloc_tagging_slab_alloc_hook`, `__alloc_tagging_slab_free_hook`, `__memcg_slab_post_alloc_hook`, `__memcg_slab_free_hook`, `__kfence_free`, and `__kmem_cache_create_args`. Now I need to take a closer look and decide if those are exported or non-static. The next step is to examine whether `__kfence_free` is exported or not, or if it is non-static.

{
  "Expression": "__kfence_free",
  "PathPrefix": "mm/kfence/core.c"
}

{
  "Output": "mm/kfence/core.c=1239=void *kfence_object_start(const void *addr)\n--\nmm/kfence/core.c-1249-\nmm/kfence/core.c:1250:void __kfence_free(void *addr)\nmm/kfence/core.c-1251-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 30600
							output: 35
							thoughts: 21
						

Okay, here's my take on those thoughts, tailored for an expert audience, and delivered as a first-person summary:

**Assessing the Dynamic Nature**

Right, so it's not static. That's the key takeaway here. The behavior or state we're examining isn't fixed; it's changing, evolving. We need to understand the dynamism. My immediate thought is to check `alloc_slab_obj_exts`. That seems like the logical next step. It's often where you'll find the mutable or transient components, perhaps the allocation extensions, which are crucial when dealing with an element of change within our architecture. That function is likely to hold the core of the state that's responsible for managing this lack of static behavior. Time to dig in there.

{
  "Expression": "int alloc_slab_obj_exts",
  "PathPrefix": "mm/slub.c"
}

{
  "Output": "mm/slub.c=2134=static inline void init_slab_obj_exts(struct slab *slab)\n--\nmm/slub.c-2138-\nmm/slub.c:2139:int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,\nmm/slub.c-2140-\t\t\tgfp_t gfp, unsigned int alloc_flags)\n--\nmm/slub.c=2307=static inline void init_slab_obj_exts(struct slab *slab)\n--\nmm/slub.c-2310-\nmm/slub.c:2311:static int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,\nmm/slub.c-2312-\t\t\t       gfp_t gfp, unsigned int alloc_flags)\n"
}

gemini-3.1-pro-preview

null

null

							input: 31055
							output: 37
							thoughts: 37
						

Okay, here's my interpretation of those thoughts, tailored for an expert audience, presented in the first person:

**Analyzing Dynamic Slab Object Extension**

Alright, so the core concept here is that the slab allocator's behavior isn't fixed, and it changes when `CONFIG_SLAB_OBJ_EXT` is enabled. That immediately piques my interest – a dynamic condition always demands a closer look. I'm assuming we're talking about object extensions within the slab allocator, probably related to metadata or per-object data.

My immediate next step is to examine the allocation hook. Specifically, I need to understand what's happening within `__alloc_tagging_slab_alloc_hook`. This hook likely provides crucial insights. It's probably the point where the dynamic behavior manifests itself. I'll need to see how the allocation process is modified. I want to see how these object extensions are integrated. I'll be looking for changes in data structures, memory management strategies, or potentially even allocation algorithms specific to this configuration. It could involve tagging objects for later retrieval or some other kind of instrumentation. I'll need to trace the execution flow to understand the impact on performance and memory usage, and whether or not it aligns with the design goals and anticipated performance characteristics. I want to understand how it handles memory fragmentation and alignment, especially since we're dealing with an "extended" object. Essentially, I need to determine *how* the slab allocator is dynamically adapting and what implications that has.

{
  "Expression": "__alloc_tagging_slab_alloc_hook",
  "PathPrefix": "mm/slub.c"
}

{
  "Output": "mm/slub.c=2346=static noinline void\nmm/slub.c:2347:__alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,\nmm/slub.c-2348-\t\t\t\tunsigned int alloc_flags)\n--\nmm/slub.c=2390=alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,\n--\nmm/slub.c-2393-\tif (mem_alloc_profiling_enabled())\nmm/slub.c:2394:\t\t__alloc_tagging_slab_alloc_hook(s, object, flags, alloc_flags);\nmm/slub.c-2395-}\n"
}

gemini-3.1-pro-preview

null

null

							input: 31653
							output: 37
							thoughts: 33
						

Okay, here's my interpretation of those thoughts, crafted with the understanding that I'm discussing this with a fellow expert:

**Investigating a Potential Fuzzing Target**

Alright, so the initial clue points towards a function declared as `static noinline void`. Interesting – that `noinline` is often a red flag for fuzzing opportunities. Syzkaller, given its capabilities, should be able to get a look at it.

Now, let's dig deeper and see what we can find with `__alloc_tagging_slab_free_hook`. Let's see what we can find here.

{
  "Expression": "__alloc_tagging_slab_free_hook",
  "PathPrefix": "mm/slub.c"
}

{
  "Output": "mm/slub.c=2398=static noinline void\nmm/slub.c:2399:__alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,\nmm/slub.c-2400-\t\t\t       int objects)\n--\nmm/slub.c=2426=alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,\n--\nmm/slub.c-2429-\tif (mem_alloc_profiling_enabled())\nmm/slub.c:2430:\t\t__alloc_tagging_slab_free_hook(s, slab, p, objects);\nmm/slub.c-2431-}\n"
}

gemini-3.1-pro-preview

null

null

							input: 32059
							output: 37
							thoughts: 33
						

Okay, here's my interpretation of those thoughts, tailored for an expert audience, presented in the first person:

**Analyzing a Potential Fuzz Target**

Alright, so the initial assessment is that this function, identified as a `static noinline void`, is a viable candidate for Syzkaller fuzzing. The `static noinline` attributes immediately catch my eye; they hint at potential isolation, and the absence of inlining can be particularly beneficial for fuzzing as it simplifies control flow analysis. The fact that Syzkaller is being considered suggests it's likely a relatively simple function with direct external input.

My next step, and frankly, my *immediate* thought, is to check the `__memcg_slab_post_alloc_hook`. This is standard operating procedure, especially in memory management contexts. Given the "post-alloc" designation, it's likely a callback invoked after a slab allocation has occurred. My mental gears are already turning – what inputs does this hook receive? What is it *supposed* to do with the newly allocated memory? Is there a subtle race condition in this callback, or a possibility of memory corruption due to incorrect initialization, or the lack of it, or a use-after-free scenario? These are the primary questions I have based on just the name of the function and the initial assessment. This is where I'll begin my deeper analysis.

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

{
  "Output": "mm/memcontrol.c=3529=static inline size_t obj_full_size(struct kmem_cache *s)\n--\nmm/memcontrol.c-3537-\nmm/memcontrol.c:3538:bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,\nmm/memcontrol.c-3539-\t\t\t\t  gfp_t flags, unsigned int slab_alloc_flags,\n"
}

gemini-3.1-pro-preview

null

null

							input: 32548
							output: 35
							thoughts: 22
						

Okay, here's my interpretation of those thoughts, tailored for an expert audience, presented in the first person:

**Navigating the Ephemeral: A Dynamic Memory Landscape**

Alright, so the situation isn't straightforward. It's *non-static*, which immediately demands a more nuanced approach. We can't rely on assumptions of stability here; we need to account for volatility. It's got the whiff of a race condition, or perhaps something more deeply rooted in a dynamic allocation/deallocation cycle.

My initial hunch is something slab-related is causing this. Let's start by looking at `__memcg_slab_free_hook`. That function often gives good visibility into the lifecycle of slab allocations, specifically from a memory control group perspective. It is the logical point to investigate the origin of the observed non-static behaviors. I can use this as a starting point to see what the problem is.

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

{
  "Output": "mm/memcontrol.c=3538=bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,\n--\nmm/memcontrol.c-3632-\nmm/memcontrol.c:3633:void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,\nmm/memcontrol.c-3634-\t\t\t    void **p, int objects, unsigned long obj_exts)\n"
}

gemini-3.1-pro-preview

null

null

							input: 32933
							output: 36
							thoughts: 22
						

Okay, here's my summarized thought process, keeping in mind my expert understanding:

**Analyzing Non-Static Behavior**

Alright, I'm observing something that isn't behaving statically. That's the key starting point. I need to understand what's dynamically influencing the system. Given that, let's dive into the likely area of memory allocation and management, as the non-static nature hints at something that changes over time. Let's see... a good starting point would be to inspect how the system is creating these memory caches. Let's start by looking at `__kmem_cache_create_args`. That function is probably instrumental in how dynamic memory is being handled. This function is likely what's going on dynamically.

{
  "Expression": "__kmem_cache_create_args",
  "PathPrefix": "mm/slab_common.c"
}

{
  "Output": "mm/slab_common.c=267=__kmem_cache_alias(const char *name, unsigned int size, slab_flags_t flags,\n--\nmm/slab_common.c-291-/**\nmm/slab_common.c:292: * __kmem_cache_create_args - Create a kmem cache.\nmm/slab_common.c-293- * @name: A string which is used in /proc/slabinfo to identify this cache.\n--\nmm/slab_common.c-317- */\nmm/slab_common.c:318:struct kmem_cache *__kmem_cache_create_args(const char *name,\nmm/slab_common.c-319-\t\t\t\t\t    unsigned int object_size,\n--\nmm/slab_common.c-408-}\nmm/slab_common.c:409:EXPORT_SYMBOL(__kmem_cache_create_args);\nmm/slab_common.c-410-\n"
}

gemini-3.1-pro-preview

null

null

							input: 33400
							output: 25
							thoughts: 201
						

**Analyzing Memory Allocation Instrumentation**

Okay, so this is about exported symbols related to memory allocation, specifically slab allocators and related hooks. I see a list of `FocusSymbols` that are key: `alloc_slab_obj_exts`, the `__alloc_tagging_slab_*` hooks for both allocation and freeing, and then those memcg and kfence hooks. Then, I see `__kmem_cache_create_args` listed as well, which is important for understanding how the caches are configured.

Now, the `EnableConfigs` are what really pique my interest. `MEM_ALLOC_PROFILING`, `MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT`, and `MEMCG` – those are the key knobs here. The default enable flag, `MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT`, is definitely something I want to check. Enabling a profiling feature by default is fantastic for fuzzing and general analysis. It simplifies testing, so it seems like a useful flag to have.

Ah, but hold on. The `MEM_ALLOC_PROFILING` config has a dependency on `CODE_TAGGING`. I'll have to investigate that further. That's crucial. I need to understand how these tags are being used, and if code tagging is dependent on something else.

{
  "Expression": "config CODE_TAGGING",
  "PathPrefix": ""
}

{
  "Output": "lib/Kconfig.debug=1029=config DEBUG_STACKOVERFLOW\n--\nlib/Kconfig.debug-1046-\nlib/Kconfig.debug:1047:config CODE_TAGGING\nlib/Kconfig.debug-1048-\tbool\n"
}

gemini-3.1-pro-preview

null

null

							input: 33987
							output: 23
							thoughts: 89
						

Here's my take on the situation:

**Refactoring the Memory Profiling and KFENCE Configuration**

Okay, so I'm looking at how these memory features are configured. It looks like the `CODE_TAGGING` option is implicitly tied to `MEM_ALLOC_PROFILING`. That simplifies things; if we enable `MEM_ALLOC_PROFILING`, `CODE_TAGGING` is taken care of. So, really, all we need to focus on are `MEM_ALLOC_PROFILING` and `MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT`. And of course, we need to consider `MEMCG`, which is a different concern, but relevant in the bigger picture.

Now, I'm thinking about `KFENCE`. This patch touches `mm/kfence/core.c`, which is the key indicator. So, naturally, we should enable `KFENCE` to keep everything consistent.

{
  "Expression": "config KFENCE",
  "PathPrefix": ""
}

{
  "Output": "lib/Kconfig.kfence=3=config HAVE_ARCH_KFENCE\n--\nlib/Kconfig.kfence-5-\nlib/Kconfig.kfence:6:menuconfig KFENCE\nlib/Kconfig.kfence-7-\tbool \"KFENCE: low-overhead sampling-based memory safety error detector\"\n--\nlib/Kconfig.kfence=26=if KFENCE\nlib/Kconfig.kfence-27-\nlib/Kconfig.kfence:28:config KFENCE_SAMPLE_INTERVAL\nlib/Kconfig.kfence-29-\tint \"Default sample interval in milliseconds\"\n--\nlib/Kconfig.kfence-38-\nlib/Kconfig.kfence:39:config KFENCE_NUM_OBJECTS\nlib/Kconfig.kfence-40-\tint \"Number of guarded objects available\"\n--\nlib/Kconfig.kfence-47-\nlib/Kconfig.kfence:48:config KFENCE_DEFERRABLE\nlib/Kconfig.kfence-49-\tbool \"Use a deferrable timer to trigger allocations\"\n--\nlib/Kconfig.kfence-59-\nlib/Kconfig.kfence:60:config KFENCE_STATIC_KEYS\nlib/Kconfig.kfence-61-\tbool \"Use static keys to set up allocations\" if EXPERT\n--\nlib/Kconfig.kfence-74-\nlib/Kconfig.kfence:75:config KFENCE_STRESS_TEST_FAULTS\nlib/Kconfig.kfence-76-\tint \"Stress testing of fault handling and error reporting\" if EXPERT\n--\nlib/Kconfig.kfence-85-\nlib/Kconfig.kfence:86:config KFENCE_KUNIT_TEST\nlib/Kconfig.kfence-87-\ttristate \"KFENCE integration test suite\" if !KUNIT_ALL_TESTS\n"
}

gemini-3.1-pro-preview

null

null

							input: 34754
							output: 191
							thoughts: 1746
						

**My Analysis of the Patch and Fuzzing Strategy**

Okay, so I've been reviewing this patch that seems to be optimizing how `struct slabobj_ext` is handled within the slab allocator, specifically regarding memory allocation profiling and memory cgroup accounting. Let's break down my thought process:

Firstly, this patch definitely seems functional. I've confirmed that the critical function `__kfence_free` has been modified, which is a good indicator that the core logic is being touched. I've also checked `kfence_init_pool` and `test_alloc` to confirm the patch's integration within the existing infrastructure. Therefore, this is definitely worth fuzzing.

Now, let's talk focus symbols for fuzzing. Given my expertise, I want to hone in on areas most directly impacted by these changes. My initial thought was to exclude hot-path functions to provide a more focused fuzzer experience.

Initially, I looked at a comprehensive list. I quickly rejected several because they were `static` or `static inline`. I'm going to include the following symbols: `alloc_slab_obj_exts`, `__kmem_cache_create_args`, and `__kfence_free`. These are good start.

I want to include `__memcg_slab_post_alloc_hook` and `__memcg_slab_free_hook` because they represent the core logic changes for memcg, even if they are somewhat hot. Also, `__memcg_slab_post_alloc_hook` is only called for a subset of allocations, which is acceptable.

So the final list of FocusSymbols will be:

*   `alloc_slab_obj_exts`
*   `__memcg_slab_post_alloc_hook`
*   `__memcg_slab_free_hook`
*   `__kfence_free`
*   `__kmem_cache_create_args`

This set covers modifications in object extension vector allocation, `kfence` free handling, and memcg accounting, which are all directly relevant to the patch's optimizations. This feels like a balanced and effective strategy for uncovering any potential issues. The enabling configurations include MEM_ALLOC_PROFILING, MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT, MEMCG, and KFENCE. These will ensure that relevant code paths are activated during fuzzing.

{
  "EnableConfigs": [
    "MEM_ALLOC_PROFILING",
    "MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT",
    "MEMCG",
    "KFENCE"
  ],
  "FocusSymbols": [
    "alloc_slab_obj_exts",
    "__memcg_slab_post_alloc_hook",
    "__memcg_slab_free_hook",
    "__kfence_free",
    "__kmem_cache_create_args"
  ],
  "Reasoning": "The patch modifies the memory layout and handling of `struct slabobj_ext` in the slab allocator, which is used for memory allocation profiling and memory cgroup accounting. It optimizes the storage of `objcg` and `codetag_ref` pointers. These changes affect core slab allocation and freeing paths, making them highly reachable and functional.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "MEM_ALLOC_PROFILING",
    "MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT",
    "MEMCG",
    "KFENCE"
  ],
  "FocusSymbols": [
    "alloc_slab_obj_exts",
    "__memcg_slab_post_alloc_hook",
    "__memcg_slab_free_hook",
    "__kfence_free",
    "__kmem_cache_create_args"
  ],
  "Reasoning": "The patch modifies the memory layout and handling of `struct slabobj_ext` in the slab allocator, which is used for memory allocation profiling and memory cgroup accounting. It optimizes the storage of `objcg` and `codetag_ref` pointers. These changes affect core slab allocation and freeing paths, making them highly reachable and functional.",
  "WorthFuzzing": true
}