From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 A33AD4BCADD; Thu, 3 Sep 2026 14:41:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788446499; cv=none; b=YwYRH57Mth6aNsGJGwbH6h1wGhXxSP9A+8XQGCMKPmjs/NtxdWSg/VQoN3W/efQFr+gkin5cMRw1UG4Yp7UtIzwf5rL27f/6pdh7+EhBxwk2Vlf9ySqjVbnROSvpuUk0xR7aWyS6Uj7KUHNIz7ZSAC+s0vGW/PkIm3vqbctn3mk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788446499; c=relaxed/simple; bh=JhSWgUei4yqB6bcmIX2IASGgLwifRDZi4LiL4Gz4t7A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rOR741K4kfFlXLmKOtN+22ms/bIoDsPB1UGegyUYOs/s49VQqv9RMBzSRYzYSp2pYu9jAp9LTGIvfvN+Xni1df8PMQw4RuUfNrWopOAaqzOrU5FYae5sX2ZovNmzpmHR+v/7++rq7tSctx5nJCLhZI63wwx1FCT0XCcYt7LaLQI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SAVaVQQF; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SAVaVQQF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 719031F00A3F; Thu, 3 Sep 2026 14:41:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788446491; bh=PzZhIe3Q+No1BnEVYJ2mpKzW0HoiA7Ne257cS+OSDa8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=SAVaVQQF/fHOzwY7FRKO1yuARuC1zSlYldW5+IxjWAFwUePBUqcLX/JB5IeQjOI2f PUM/67YWns4IE6A4DrxElDCRaF4lUN1GKWnv7L1j/gJ7pYhIG4dlpegCtERfVcvmjK dTeIOvnpKlNSwvXe33JhkGqrtws2WYOppJ4EfRKl8sUCBVn6VkPntgXSxTd3gfcJjR 2dd9AXURFF8zFI077UF6VHOWXgbj5hbxofd/JscHFruDbm8ZAzCksVQXQ37aTMaNXe TMiEfCu2LsJ0H3X1/YI+f3PoSuRFXRt7ASQys/gAGmjZGQr2HbYsDF2vRqSXnPx2ya +qsNg7LznMxRg== Message-ID: <77453798-713a-4d10-a738-30763e2eb084@kernel.org> Date: Thu, 3 Sep 2026 16:41:28 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/slab: take n->list_lock in __slab_try_return_freelist() to avoid race Content-Language: en-US To: "Harry Yoo (Meta)" , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hyunwoo Kim , stable@vger.kernel.org References: <20260903-slab-fix-aba-v3-1-b44cb6badd54@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/3/26 16:32, Harry Yoo (Meta) wrote: > Commit ba7425312607 ("mm, slab: add an optimistic > __slab_try_return_freelist()") incorrectly assumed that nobody has freed > an object to the slab as long as slab->freelist is NULL and cmpxchg > succeeds. > > However, as reported by Hyunwoo Kim [1], other CPUs might have freed > an object to the slab, insert the slab to the partial list, then > allocated an object from the slab, and be in the middle of removing > the slab from the list under n->list_lock. > > Since __refill_objects_node() puts the slab back on pc.slabs > outside n->list_lock, it might insert the slab into that list while > the slab is concurrently being removed from n->partial. > This led to a list corruption [1]: > > list_add corruption. next->prev should be prev > (ffff888100000248), but was dead000000000122. > (next=ffffea000416e410). > kernel BUG at lib/list_debug.c:29! > Oops: invalid opcode: 0000 [#1] SMP NOPTI > CPU: 1 UID: 65534 PID: 144 Comm: poc Not tainted > 7.2.0-16172-gcf72cbb39da8-dirty #1 PREEMPT(lazy) > RIP: 0010:__list_add_valid_or_report+0x80/0xd0 > ... > Call Trace: > alloc_from_new_slab+0x183/0x300 > ___slab_alloc+0x31c/0x890 > __kmalloc_noprof+0x3d4/0x800 > lsm_blob_alloc+0x2d/0x50 > security_msg_msg_alloc+0x26/0x90 > load_msg+0x1aa/0x210 > do_msgsnd+0x91/0x800 > do_syscall_64+0x109/0x5d0 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > ... > Kernel panic - not syncing: Fatal exception > > This is a classic ABA problem where cmpxchg succeeds but the state has > changed since __refill_objects_node() took the freelist from the slab. > > As Vlastimil Babka mentioned [2], it should be rare to return more than > one slab (due to the racy read of slab->counters in > get_partial_node_bulk()). Therefore, instead of introducing additional > complexity, acquire and release n->list_lock twice in the worst case. > > Return the slab directly to the partial list and hold n->list_lock > across the cmpxchg and add_partial(). This is similar to the initial > version of commit ba7425312607 [3]. This is enough to avoid the race as > the list manipulation is serialized by n->list_lock. While at it, > bring back unlikely() hint now that the condition is unlikely. > > Reported-by: Hyunwoo Kim > Closes: https://lore.kernel.org/linux-mm/apPa-cGLcyt90l-E@v4bel [1] > Link: https://lore.kernel.org/linux-mm/ae25c193-b95f-40c1-83b6-1c2546467e41@kernel.org [2] > Link: https://lore.kernel.org/all/20260421-b4-refill-optimistic-return-v1-1-24f0bfc1acff@kernel.org [3] > Fixes: ba7425312607 ("mm, slab: add an optimistic __slab_try_return_freelist()") > Cc: stable@vger.kernel.org > Signed-off-by: Harry Yoo (Meta) Added to mm/slab.git slab/for-next-fixes, thanks!