From: Johannes Weiner <hannes@cmpxchg.org>
To: Jiayuan Chen <jiayuan.chen@linux.dev>
Cc: linux-mm@kvack.org, stable@vger.kernel.org,
syzbot+ced4d9a8cadb5ef3adae@syzkaller.appspotmail.com,
Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Shakeel Butt <shakeel.butt@linux.dev>,
Muchun Song <muchun.song@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
Yosry Ahmed <yosry@kernel.org>, Chris Li <chrisl@kernel.org>,
Jens Axboe <axboe@kernel.dk>, Jan Kara <jack@suse.cz>,
Tejun Heo <tj@kernel.org>,
cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/memcontrol: fix data-race on reading jiffies_64
Date: Thu, 27 Aug 2026 10:59:17 -0400 [thread overview]
Message-ID: <20260827145917.GB3004@cmpxchg.org> (raw)
In-Reply-To: <20260827025457.116191-1-jiayuan.chen@linux.dev>
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: <stable@vger.kernel.org>
> 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 <jiayuan.chen@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
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()
prev parent reply other threads:[~2026-08-27 14:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-27 2:54 [PATCH] mm/memcontrol: fix data-race on reading jiffies_64 Jiayuan Chen
2026-08-27 3:08 ` Muchun Song
2026-08-27 14:16 ` Michal Hocko
2026-08-27 14:59 ` Johannes Weiner [this message]
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