From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 B30E62C6B7 for ; Mon, 6 May 2024 00:58:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714957107; cv=none; b=SjQKVOPS8Mw+FE2I9Pcav3HVy7nF0Ehp2wY8zATGMdj7fhjNtI+DsbfF9HATw2YPhVuiwY20/8obumhnilRD1XlhOon/WH+IZSD0I4xyrrRtacy7cJz63Gi5hJHkLTAypq10QVGRBh53rNoP5uZafWLaIarjHcJjqyaiJYcXdCc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714957107; c=relaxed/simple; bh=Iyz+Zjuffk1jMulLiY+ohGFSW/vgQ4CNmmkQMmilrNc=; h=Date:To:From:Subject:Message-Id; b=Rxwdg9sUfXLCaSu5wbFog8hBV56Nh5Nzqt7mpmzEF9X8f9Lm41TC2K9GyHwR5LCcFX3rWJs0Hc/+rK1pdTGAkZU/aDe0KZYTTuaUz5cIEP2RZMrI84eqgrq2pHcZCJ2Al4kxQkZ0RFkNDUJLo3KxmORQ/MfndZ1OpjcBY2NnYNo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=mBgM17fL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="mBgM17fL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 87A79C113CC; Mon, 6 May 2024 00:58:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1714957107; bh=Iyz+Zjuffk1jMulLiY+ohGFSW/vgQ4CNmmkQMmilrNc=; h=Date:To:From:Subject:From; b=mBgM17fLF0J8EfzSEAX+/BAq1c8wcjol11kmMDD9UurSOwgAiJY2HvvbpdklS4Wpr H/WFeLFIpFG4n9nWSO/sdgxpCr7xIt6od+P+r258gvqQXVd+kaPyTAi9p4l3ndIcHk w3VoV+m46JrzGaoRAGhc2jJlpzZVL5SS6fZLrL3c= Date: Sun, 05 May 2024 17:58:27 -0700 To: mm-commits@vger.kernel.org,yosryahmed@google.com,songmuchun@bytedance.com,shakeel.butt@linux.dev,roman.gushchin@linux.dev,mhocko@suse.com,hannes@cmpxchg.org,leitao@debian.org,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-stable] memcg-fix-data-race-kcsan-bug-in-rstats.patch removed from -mm tree Message-Id: <20240506005827.87A79C113CC@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: memcg: fix data-race KCSAN bug in rstats has been removed from the -mm tree. Its filename was memcg-fix-data-race-kcsan-bug-in-rstats.patch This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Breno Leitao Subject: memcg: fix data-race KCSAN bug in rstats Date: Wed, 24 Apr 2024 05:59:39 -0700 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. Link: https://lkml.kernel.org/r/20240424125940.2410718-1-leitao@debian.org Fixes: 9cee7e8ef3e3 ("mm: memcg: optimize parent iteration in memcg_rstat_updated()") Signed-off-by: Breno Leitao Suggested-by: Shakeel Butt Acked-by: Johannes Weiner Acked-by: Shakeel Butt Reviewed-by: Yosry Ahmed Cc: Michal Hocko Cc: Roman Gushchin Cc: Muchun Song Signed-off-by: Andrew Morton --- mm/memcontrol.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) --- a/mm/memcontrol.c~memcg-fix-data-race-kcsan-bug-in-rstats +++ a/mm/memcontrol.c @@ -715,6 +715,7 @@ static inline void memcg_rstat_updated(s { struct memcg_vmstats_percpu *statc; int cpu = smp_processor_id(); + unsigned int stats_updates; if (!val) return; @@ -722,8 +723,9 @@ static inline void memcg_rstat_updated(s cgroup_rstat_updated(memcg->css.cgroup, cpu); statc = this_cpu_ptr(memcg->vmstats_percpu); for (; statc; statc = statc->parent) { - statc->stats_updates += abs(val); - if (statc->stats_updates < MEMCG_CHARGE_BATCH) + stats_updates = READ_ONCE(statc->stats_updates) + abs(val); + WRITE_ONCE(statc->stats_updates, stats_updates); + if (stats_updates < MEMCG_CHARGE_BATCH) continue; /* @@ -731,9 +733,9 @@ static inline void memcg_rstat_updated(s * redundant. Avoid the overhead of the atomic update. */ if (!memcg_vmstats_needs_flush(statc->vmstats)) - atomic64_add(statc->stats_updates, + atomic64_add(stats_updates, &statc->vmstats->stats_updates); - statc->stats_updates = 0; + WRITE_ONCE(statc->stats_updates, 0); } } @@ -5887,7 +5889,7 @@ static void mem_cgroup_css_rstat_flush(s } } } - statc->stats_updates = 0; + WRITE_ONCE(statc->stats_updates, 0); /* We are in a per-cpu loop here, only do the atomic write once */ if (atomic64_read(&memcg->vmstats->stats_updates)) atomic64_set(&memcg->vmstats->stats_updates, 0); _ Patches currently in -mm which might be from leitao@debian.org are