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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1761230048; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=6+PDu1BKpeekQuNXNoUHSooGzAkk2JG8H4zonFnyfOo=; b=omPdSohLRvyzB0wgHZjOYuoN/Sn8Xiq4qDJvMpEU6zK2LjG1wybI/5t1+xPCS0Uge4TRN6 +Hiu659NVfrHAcTfx+amzmScXnMpSYNZIbbVW5FTgOc8AoUK42k2vD9LcouSEIAaigp+a0 uU8yjl8J5d+neUeFd0EBsbi2qzma0m0= From: Hao Ge To: Vlastimil Babka , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Suren Baghdasaryan Cc: Shakeel Butt , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hao Ge Subject: [PATCH v2] slab: Fix obj_ext is mistakenly considered NULL due to race condition Date: Thu, 23 Oct 2025 22:33:13 +0800 Message-Id: <20251023143313.1327968-1-hao.ge@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: ac39s3y6twkonquon59gyggnoon7sayk X-Rspamd-Queue-Id: 05C6A180015 X-Rspamd-Server: rspam06 X-Rspam-User: X-HE-Tag: 1761230050-168620 X-HE-Meta: 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 j338q4M7 xFzLsryn0K3S37MA= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Hao Ge If two competing threads enter alloc_slab_obj_exts(), if the process that allocates the vector wins cmpxchg(), and the other thread mistakenly assume slab->obj_ext is still empty due to its own allocation failure. This will then trigger warnings enforced by CONFIG_MEM_ALLOC_PROFILING_DEBUG checks in the subsequent free path. Therefore, let's add an additional check when the process that allocates the vector loses the cmpxchg() Suggested-by: Harry Yoo Signed-off-by: Hao Ge --- v2: Revise the solution according to Harry's suggestion. Add Suggested-by: Harry Yoo --- mm/slub.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index d4403341c9df..d7bfec6c0171 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; } -- 2.25.1