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Thu, 27 Aug 2026 07:59:19 -0700 (PDT) Received: from localhost ([2605:8600:200:1a83:fe59:7385:2855:8588]) by smtp.gmail.com with ESMTPSA id 00721157ae682-85b5bc34efasm11365667b3.7.2026.08.27.07.59.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Aug 2026 07:59:18 -0700 (PDT) Date: Thu, 27 Aug 2026 10:59:17 -0400 From: Johannes Weiner To: Jiayuan Chen Cc: linux-mm@kvack.org, stable@vger.kernel.org, syzbot+ced4d9a8cadb5ef3adae@syzkaller.appspotmail.com, Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Yosry Ahmed , Chris Li , Jens Axboe , Jan Kara , Tejun Heo , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/memcontrol: fix data-race on reading jiffies_64 Message-ID: <20260827145917.GB3004@cmpxchg.org> References: <20260827025457.116191-1-jiayuan.chen@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260827025457.116191-1-jiayuan.chen@linux.dev> X-Stat-Signature: ywynahisw4ybnbzyy6tsm8wmhkkg7433 X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 1AAD540005 X-Rspam-User: X-HE-Tag: 1787842759-924804 X-HE-Meta: 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 nUEKxcu5 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 27, 2026 at 10:54:56AM +0800, Jiayuan Chen wrote: > KCSAN reported a data-race between tick_do_update_jiffies64() updating > jiffies_64 and mem_cgroup_flush_stats_ratelimited() reading it directly. > > Unlike jiffies, jiffies_64 is not volatile, so raw reads are plain > accesses and can even be torn on 32-bit. Use get_jiffies_64() instead, > and fix the same pattern in mem_cgroup_flush_foreign(). > > Cc: > Fixes: 508bed884767 ("mm: memcg: change flush_next_time to flush_last_time") > Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing") > Reported-by: syzbot+ced4d9a8cadb5ef3adae@syzkaller.appspotmail.com > Signed-off-by: Jiayuan Chen Acked-by: Johannes Weiner Minor nit: > @@ -785,7 +785,7 @@ void mem_cgroup_flush_stats(struct mem_cgroup *memcg) > void mem_cgroup_flush_stats_ratelimited(struct mem_cgroup *memcg) > { > /* Only flush if the periodic flusher is one full cycle late */ > - if (time_after64(jiffies_64, READ_ONCE(flush_last_time) + 2*FLUSH_TIME)) > + if (time_after64(get_jiffies_64(), READ_ONCE(flush_last_time) + 2 * FLUSH_TIME)) > mem_cgroup_flush_stats(memcg); time_is_after_jiffies64()