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]) by smtp.lore.kernel.org (Postfix) with ESMTP id 272EBC4345F for ; Wed, 24 Apr 2024 19:50:18 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6CD278D002B; Wed, 24 Apr 2024 15:50:18 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 67D328D0028; Wed, 24 Apr 2024 15:50:18 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4F5908D002B; Wed, 24 Apr 2024 15:50:18 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 30B2C8D0028 for ; Wed, 24 Apr 2024 15:50:18 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id BC22181073 for ; Wed, 24 Apr 2024 19:50:17 +0000 (UTC) X-FDA: 82045466874.16.0FE94EA Received: from out-189.mta1.migadu.com (out-189.mta1.migadu.com [95.215.58.189]) by imf09.hostedemail.com (Postfix) with ESMTP id CB09F140009 for ; Wed, 24 Apr 2024 19:50:15 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b="Ul/oMFKP"; spf=pass (imf09.hostedemail.com: domain of shakeel.butt@linux.dev designates 95.215.58.189 as permitted sender) smtp.mailfrom=shakeel.butt@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1713988216; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Hk4Hjf7MO1vgoycrQr13hwP52DhwjBNF8O6idPkuyDo=; b=Zm1Ikf6vaF85AraTwRTuwbgCf63pGLX3uqopEQ3ujsbKy/bcC2LFUiKfZHKDLYqi+krz8m LmBgILYUNwUKijMf5OAcCkzEE3V5GXegXM17a7z65lMfSsmeYr+yHUPEDIsbHui6MhC67r n1P+I+AQJE2PYTZ9yFw3FuvZBsuiXgY= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1713988216; a=rsa-sha256; cv=none; b=XJMgePlJds0agUw/3ijvJ4xMdj+pz/89XWld0zVi1sv2xJOfd9ruRnrKbMCmTR1Rx5NGci 4aBmdZSQRfDk1XGyzDRsonDEePT4lvecMiydPJj74KueueJ1ozocGAQIYHKal2iAVihSR0 xc0TwC/A+xP4IUHPFxTaAOrDhFuKK0U= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b="Ul/oMFKP"; spf=pass (imf09.hostedemail.com: domain of shakeel.butt@linux.dev designates 95.215.58.189 as permitted sender) smtp.mailfrom=shakeel.butt@linux.dev; dmarc=pass (policy=none) header.from=linux.dev Date: Wed, 24 Apr 2024 12:50:07 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1713988213; 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: in-reply-to:in-reply-to:references:references; bh=Hk4Hjf7MO1vgoycrQr13hwP52DhwjBNF8O6idPkuyDo=; b=Ul/oMFKP3dKHsGVy/pJ1kPeMNR7LtzOTJ2czKmpnMyMG72gr6xDzmIAzTSaYAyofYcQXAX Bo1J72cDI101j1Z57LZ9MfLIN5KasMGqH9Ueaav5Ib+QH6C9DYq4GHiMcd9Kf4csLE6Fja NU9Kyf9zCpqkm3UrQtUYh90eO8Yq0Cc= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Shakeel Butt To: Breno Leitao Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Andrew Morton , leit@meta.com, "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" , "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" , open list Subject: Re: [PATCH] memcg: Fix data-race KCSAN bug in rstats Message-ID: References: <20240424125940.2410718-1-leitao@debian.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240424125940.2410718-1-leitao@debian.org> X-Migadu-Flow: FLOW_OUT X-Stat-Signature: pm6myxqsg6715n3m6nwkqneg8frttuwk X-Rspamd-Queue-Id: CB09F140009 X-Rspamd-Server: rspam06 X-Rspam-User: X-HE-Tag: 1713988215-457772 X-HE-Meta: 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 qEGc8No2 ZW+weRHh4EH082hVMFwxGyFePY2wH4Ehg783XIiFpJSmPgjs3V84ofTBt3Irg1vq+TO4cBAMaGe83Wra+3TNuGpH430WMHQUDUlLEuZmhI8YxfzICnAW78snsNPDE8oq63YpduONwl3kYSMAgt8chodSFHC308zSewVLsCLAboFQHK72FsW7tmSeiv9TTy7w9l76Qc1gImj9BPFY= 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: On Wed, Apr 24, 2024 at 05:59:39AM -0700, Breno Leitao wrote: > A data-race issue in memcg rstat occurs when two distinct code paths > access the same 4-byte region concurrently. KCSAN detection triggers the > following BUG as a result. > > BUG: KCSAN: data-race in __count_memcg_events / mem_cgroup_css_rstat_flush > > write to 0xffffe8ffff98e300 of 4 bytes by task 5274 on cpu 17: > mem_cgroup_css_rstat_flush (mm/memcontrol.c:5850) > cgroup_rstat_flush_locked (kernel/cgroup/rstat.c:243 (discriminator 7)) > cgroup_rstat_flush (./include/linux/spinlock.h:401 kernel/cgroup/rstat.c:278) > mem_cgroup_flush_stats.part.0 (mm/memcontrol.c:767) > memory_numa_stat_show (mm/memcontrol.c:6911) > > > read to 0xffffe8ffff98e300 of 4 bytes by task 410848 on cpu 27: > __count_memcg_events (mm/memcontrol.c:725 mm/memcontrol.c:962) > count_memcg_event_mm.part.0 (./include/linux/memcontrol.h:1097 ./include/linux/memcontrol.h:1120) > handle_mm_fault (mm/memory.c:5483 mm/memory.c:5622) > > > value changed: 0x00000029 -> 0x00000000 > > The race occurs because two code paths access the same "stats_updates" > location. Although "stats_updates" is a per-CPU variable, it is remotely > accessed by another CPU at > cgroup_rstat_flush_locked()->mem_cgroup_css_rstat_flush(), leading to > the data race mentioned. > > Considering that memcg_rstat_updated() is in the hot code path, adding > a lock to protect it may not be desirable, especially since this > variable pertains solely to statistics. > > Therefore, annotating accesses to stats_updates with READ/WRITE_ONCE() > can prevent KCSAN splats and potential partial reads/writes. > > Suggested-by: Shakeel Butt > Signed-off-by: Breno Leitao Acked-by: Shakeel Butt