6.12-stable review patch. If anyone has any objections, please let me know.
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From: Hao Ge gehao@kylinos.cn
commit 7f434e1d9a17ca5f567c9796c9c105a65c18db9a upstream.
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 harry.yoo@oracle.com Fixes: f7381b911640 ("slab: mark slab->obj_exts allocation failures unconditionally") Cc: stable@vger.kernel.org Signed-off-by: Hao Ge gehao@kylinos.cn Link: https://patch.msgid.link/20251023143313.1327968-1-hao.ge@linux.dev Reviewed-by: Suren Baghdasaryan surenb@google.com Reviewed-by: Harry Yoo harry.yoo@oracle.com Signed-off-by: Vlastimil Babka vbabka@suse.cz Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/slub.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-)
--- a/mm/slub.c +++ b/mm/slub.c @@ -1941,9 +1941,9 @@ static inline void mark_objexts_empty(st } }
-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, @@ -1965,7 +1965,7 @@ static inline void handle_failed_objexts #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) {}
@@ -1998,8 +1998,14 @@ int alloc_slab_obj_exts(struct slab *sla vec = kcalloc_node(objects, sizeof(struct slabobj_ext), gfp, 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; }