From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EB984309F0E for ; Fri, 24 Oct 2025 09:28:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761298119; cv=none; b=e+Dab1c3Gbykc1vYN2Q4o0wFb6pyEc4w00A67NNqZDMNNPorqEdkijyIwcJFOKonI4dPS4rJYwhLWAVCIhNfOEfwT/RFDRbcLAqoeFzrBy86WTzIEj9hdO4hej7Rr5+Wah3yygkNG4QUSTMSnp/9qIbrm0GeDuWlDKerRwn5wUY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761298119; c=relaxed/simple; bh=k7xngE3GO/Y4YrPPxiGXifV1ruEinc/ketHeBWH7bzA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=mSvZjjUkK9vHxKs3s2g3OhFovtQlFDAEisrhKsQYkhxj2AgaaJE+or1nr+wm9SbP/X6eOowgtNA/289pd1TR9pvl55dJPCU9JuHooAlz3XEahv7LDDMAK+ZzNeJrrdbitPBF/dzrfrx5M9U+nveSMlmgljjoQ9JXpk5tGcy5fbE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=HPJiCYOF; arc=none smtp.client-ip=95.215.58.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="HPJiCYOF" Message-ID: <49a186cf-c248-45ff-a61c-a6de1a3a98b7@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1761298114; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=WEjiKaJQmXfdvCFlzkFqU/zz27ee+mxZNS3z1hWWko4=; b=HPJiCYOFHl7B44O3yhgS2sA0eZwd/Z/eqa//JdqqG9CBe4DhWJCsZN3Hi+9ELs/9pGVrKA 4b2T2eJPJnglMw/NBxx2mJgE+xOQyExKN9BUC4RD7mN7sqOQxBKCIc0OoB0IVr91qLdgWz 0AY1awteljfV/UOiMJi7eDfClZqmOmQ= Date: Fri, 24 Oct 2025 17:27:42 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v2] slab: Fix obj_ext is mistakenly considered NULL due to race condition To: Harry Yoo Cc: Vlastimil Babka , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Suren Baghdasaryan , Shakeel Butt , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hao Ge References: <20251023143313.1327968-1-hao.ge@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Hao Ge In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT Hi Harry On 2025/10/24 16:54, Harry Yoo wrote: > On Thu, Oct 23, 2025 at 10:33:13PM +0800, Hao Ge wrote: >> 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. > Massaging this a little bit: > > "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 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() > You mean "when the process that failed to allocate the vector loses the > cmpxchg()"? Yes, I apologize for not being clear enough in my description here. >> 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 > nit: > ^ missing > period > (.) here > > With the comments resolved, > Reviewed-by: Harry Yoo A period is indeed missing here. Hi Vlastimil Thank you for adding V2 to your tree. Now, should I resubmit V3, or can you assist with making these modifications in your tree? > >> + * 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