[PATCH v3 1/1] mm/slab: mark alloc tags empty for sheaves allocated with __GFP_NO_OBJ_EXT

[Suren Baghdasaryan <surenb@google.com>]

alloc_empty_sheaf() allocates sheaves from SLAB_KMALLOC caches using
__GFP_NO_OBJ_EXT to avoid recursion, however it does not mark their
allocation tags empty before freeing, which results in a warning when
CONFIG_MEM_ALLOC_PROFILING_DEBUG is set. Fix this by marking allocation
tags for such sheaves as empty.

Reported-by: David Wang <00107082@163.com>
Closes: https://lore.kernel.org/all/20260223155128.3849-1-00107082@163.com/
Analyzed-by: Harry Yoo <harry.yoo@oracle.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Tested-by: Harry Yoo <harry.yoo@oracle.com>
Tested-by: David Wang <00107082@163.com>
---
 include/linux/gfp_types.h |  2 ++
 mm/slab.h                 |  4 ++--
 mm/slub.c                 | 33 +++++++++++++++++++++++----------
 3 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h
index 814bb2892f99..6c75df30a281 100644
--- a/include/linux/gfp_types.h
+++ b/include/linux/gfp_types.h
@@ -139,6 +139,8 @@ enum {
  * %__GFP_ACCOUNT causes the allocation to be accounted to kmemcg.
  *
  * %__GFP_NO_OBJ_EXT causes slab allocation to have no object extension.
+ * mark_obj_codetag_empty() should be called upon freeing for objects allocated
+ * with this flag to indicate that their NULL tags are expected and normal.
  */
 #define __GFP_RECLAIMABLE ((__force gfp_t)___GFP_RECLAIMABLE)
 #define __GFP_WRITE	((__force gfp_t)___GFP_WRITE)
diff --git a/mm/slab.h b/mm/slab.h
index 71c7261bf822..f6ef862b60ef 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -290,14 +290,14 @@ static inline void *nearest_obj(struct kmem_cache *cache,
 
 /* Determine object index from a given position */
 static inline unsigned int __obj_to_index(const struct kmem_cache *cache,
-					  void *addr, void *obj)
+					  void *addr, const void *obj)
 {
 	return reciprocal_divide(kasan_reset_tag(obj) - addr,
 				 cache->reciprocal_size);
 }
 
 static inline unsigned int obj_to_index(const struct kmem_cache *cache,
-					const struct slab *slab, void *obj)
+					const struct slab *slab, const void *obj)
 {
 	if (is_kfence_address(obj))
 		return 0;
diff --git a/mm/slub.c b/mm/slub.c
index 862642c165ed..34c32749f091 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2041,18 +2041,18 @@ static inline void dec_slabs_node(struct kmem_cache *s, int node,
 
 #ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
 
-static inline void mark_objexts_empty(struct slabobj_ext *obj_exts)
+static inline void mark_obj_codetag_empty(const void *obj)
 {
-	struct slab *obj_exts_slab;
+	struct slab *obj_slab;
 	unsigned long slab_exts;
 
-	obj_exts_slab = virt_to_slab(obj_exts);
-	slab_exts = slab_obj_exts(obj_exts_slab);
+	obj_slab = virt_to_slab(obj);
+	slab_exts = slab_obj_exts(obj_slab);
 	if (slab_exts) {
 		get_slab_obj_exts(slab_exts);
-		unsigned int offs = obj_to_index(obj_exts_slab->slab_cache,
-						 obj_exts_slab, obj_exts);
-		struct slabobj_ext *ext = slab_obj_ext(obj_exts_slab,
+		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);
 
 		if (unlikely(is_codetag_empty(&ext->ref))) {
@@ -2090,7 +2090,7 @@ static inline void handle_failed_objexts_alloc(unsigned long obj_exts,
 
 #else /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */
 
-static inline void mark_objexts_empty(struct slabobj_ext *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) {}
@@ -2211,7 +2211,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
 		 * assign slabobj_exts in parallel. In this case the existing
 		 * objcg vector should be reused.
 		 */
-		mark_objexts_empty(vec);
+		mark_obj_codetag_empty(vec);
 		if (unlikely(!allow_spin))
 			kfree_nolock(vec);
 		else
@@ -2254,7 +2254,7 @@ static inline void free_slab_obj_exts(struct slab *slab, bool allow_spin)
 	 * NULL, therefore replace NULL with CODETAG_EMPTY to indicate that
 	 * the extension for obj_exts is expected to be NULL.
 	 */
-	mark_objexts_empty(obj_exts);
+	mark_obj_codetag_empty(obj_exts);
 	if (allow_spin)
 		kfree(obj_exts);
 	else
@@ -2312,6 +2312,10 @@ static void alloc_slab_obj_exts_early(struct kmem_cache *s, struct slab *slab)
 
 #else /* CONFIG_SLAB_OBJ_EXT */
 
+static inline void mark_obj_codetag_empty(const void *obj)
+{
+}
+
 static inline void init_slab_obj_exts(struct slab *slab)
 {
 }
@@ -2783,6 +2787,15 @@ static inline struct slab_sheaf *alloc_empty_sheaf(struct kmem_cache *s,
 
 static void free_empty_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf)
 {
+	/*
+	 * If the sheaf was created with __GFP_NO_OBJ_EXT flag then its
+	 * corresponding extension is NULL and alloc_tag_sub() will throw a
+	 * warning, therefore replace NULL with CODETAG_EMPTY to indicate
+	 * that the extension for this sheaf is expected to be NULL.
+	 */
+	if (s->flags & SLAB_KMALLOC)
+		mark_obj_codetag_empty(sheaf);
+
 	kfree(sheaf);
 
 	stat(s, SHEAF_FREE);

base-commit: 7dff99b354601dd01829e1511711846e04340a69
-- 
2.53.0.414.gf7e9f6c205-goog