Re: [PATCH v2 1/1] mm/slab: mark alloc tags empty for sheafs allocated with __GFP_NO_OBJ_EXT

[Suren Baghdasaryan <surenb@google.com>]

On Tue, Feb 24, 2026 at 6:50 PM David Wang <00107082@163.com> wrote:
>
> At 2026-02-25 06:11:32, "Suren Baghdasaryan" <surenb@google.com> wrote:
> >alloc_empty_sheaf() allocates sheafs 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 allocations 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>
> >---
> > mm/slab.h |  4 ++--
> > mm/slub.c | 23 +++++++++++++++--------
> > 2 files changed, 17 insertions(+), 10 deletions(-)
> >
> >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..5c76e55eee7d 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_objexts_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_objexts_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) {}
> >@@ -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_objexts_empty(const void *obj)
> >+{
> >+}
> >+
> > static inline void init_slab_obj_exts(struct slab *slab)
> > {
> > }
> >@@ -2783,6 +2787,9 @@ 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 (s->flags & SLAB_KMALLOC)
> >+              mark_objexts_empty(sheaf);
> >+
> >       kfree(sheaf);
> >
> >       stat(s, SHEAF_FREE);
> >
> >base-commit: 7dff99b354601dd01829e1511711846e04340a69
> >--
> >2.53.0.414.gf7e9f6c205-goog
>
> Tested-by: David Wang <00107082@163.com>

Thanks!
>
>
> David