From: Hao Ge Date: Thu, 23 Oct 2025 14:33:13 +0000 (+0800) Subject: slab: Fix obj_ext mistakenly considered NULL due to race condition X-Git-Tag: v6.18-rc3~22^2 X-Git-Url: https://gentwo.org/gitweb/?a=commitdiff_plain;h=7f434e1d9a17ca5f567c9796c9c105a65c18db9a;p=linux%2F.git slab: Fix obj_ext mistakenly considered NULL due to race condition If two competing threads enter alloc_slab_obj_exts(), and the one that allocates the vector wins the cmpxchg(), the other thread that failed allocation mistakenly assumes that slab->obj_exts is still empty due to its own allocation failure. This will then trigger warnings with CONFIG_MEM_ALLOC_PROFILING_DEBUG checks in the subsequent free path. Therefore, let's check the result of cmpxchg() to see if marking the allocation as failed was successful. If it wasn't, check whether the winning side has succeeded its allocation (it might have been also marking it as failed) and if yes, return success. Suggested-by: Harry Yoo Fixes: f7381b911640 ("slab: mark slab->obj_exts allocation failures unconditionally") Cc: Signed-off-by: Hao Ge Link: https://patch.msgid.link/20251023143313.1327968-1-hao.ge@linux.dev Reviewed-by: Suren Baghdasaryan Reviewed-by: Harry Yoo Signed-off-by: Vlastimil Babka --- diff --git a/mm/slub.c b/mm/slub.c index 87a1d2f9de0d..d4367f25b20d 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2052,9 +2052,9 @@ static inline void mark_objexts_empty(struct slabobj_ext *obj_exts) } } -static inline void mark_failed_objexts_alloc(struct slab *slab) +static inline bool mark_failed_objexts_alloc(struct slab *slab) { - cmpxchg(&slab->obj_exts, 0, OBJEXTS_ALLOC_FAIL); + return cmpxchg(&slab->obj_exts, 0, OBJEXTS_ALLOC_FAIL) == 0; } static inline void handle_failed_objexts_alloc(unsigned long obj_exts, @@ -2076,7 +2076,7 @@ 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_failed_objexts_alloc(struct slab *slab) {} +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) {} @@ -2124,8 +2124,14 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, slab_nid(slab)); } if (!vec) { - /* Mark vectors which failed to allocate */ - mark_failed_objexts_alloc(slab); + /* + * Try to mark vectors which failed to allocate. + * If this operation fails, there may be a racing process + * that has already completed the allocation. + */ + if (!mark_failed_objexts_alloc(slab) && + slab_obj_exts(slab)) + return 0; return -ENOMEM; }