From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DB0ACC61DD3 for ; Thu, 3 Sep 2026 14:41:35 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A67B86B0088; Thu, 3 Sep 2026 10:41:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A3FD36B008A; Thu, 3 Sep 2026 10:41:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 956686B008C; Thu, 3 Sep 2026 10:41:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 6D4206B0088 for ; Thu, 3 Sep 2026 10:41:34 -0400 (EDT) Received: from smtpin09.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 042BD1402B1 for ; Thu, 3 Sep 2026 14:41:33 +0000 (UTC) X-FDA: 85172714508.09.FA4BDBB Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf12.hostedemail.com (Postfix) with ESMTP id 39E6940004 for ; Thu, 3 Sep 2026 14:41:32 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=SAVaVQQF; spf=pass (imf12.hostedemail.com: domain of vbabka@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=vbabka@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1788446492; b=3gd57D4nJzlux77CU3kNWbFX1F7A43huayeROl5Ge9QID36AEhDFdeUvim51He7FV2DkHg WK6ROOoOwIRHgzgIr+g+7r9XRRgvXnlo02Tx2j2NOphroBH04fF6+bSHvJMeusE6bD1Wlr dXCESNwlYT60hCXq1nFFRY3OcFJRAzQ= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=SAVaVQQF; spf=pass (imf12.hostedemail.com: domain of vbabka@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=vbabka@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1788446492; h=from:from:sender: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:dkim-signature; bh=PzZhIe3Q+No1BnEVYJ2mpKzW0HoiA7Ne257cS+OSDa8=; b=nNaUAmd5rT6hiu6Yh9IomlnwDUaB58SBQcad66C9N9RvXAoYREjALXSiX8dn2fW1OllrNJ +tKGCDhs/csmheuOvHkxaThy4K0bi4mf+A0gVh4dJSluxpPSDphT8K6gMTNItKISi/KO0r fUGYVGpk+g/9/CpFqE0m1lIUk9wVaKs= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id B77A160546; Thu, 3 Sep 2026 14:41:31 +0000 (UTC) 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 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; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20260903-slab-fix-aba-v3-1-b44cb6badd54@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 39E6940004 X-Stat-Signature: s85gqjs5un8ui4ggnhj49xdqbip1do5w X-HE-Tag: 1788446492-421026 X-HE-Meta: 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 r3cXtSsi EMSaqtzKwVDg1LHpY1BPfFpRcPiuXAnULxxA/yCWjA27bxEZHwoQhkMKs1eojX437qUmojN3HwqZLJVU92Dzjx6dZLsenC0508bBI0gWbXKabXFnETA70Ux81I4W3nyTaeQ3z1qdvirtP4qnHe69jGsTk5TY/GR1syTLfjsjrr9QR5S+TqaCggaLXW+j4LcLJ3bwtu8N/yw9oy54qqqtRIukQpNWEHLPOg2xonmOJT2+EexNktGbzmJeGj9jMPEoDTrLSLPFsOaTLTJ/D7QBfE8+RbdDOpJR1+/q2XhwH/H2AcDzQd9Twq2PcJXB5XPrZtmP5LGiztZsraNov7s+PyBo2mdvNHDIRjTDR Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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!