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From: Tejun Heo <>
Cc:, Rik van Riel <>
Subject: Re: [PATCH cgroup/for-5.14-fixes] cgroup: rstat: fix A-A deadlock on 32bit around u64_stats_sync
Date: Tue, 27 Jul 2021 13:13:21 -1000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Tue, Jul 27, 2021 at 01:04:49PM -1000, Tejun Heo wrote:
> 0fa294fb1985 ("cgroup: Replace cgroup_rstat_mutex with a spinlock") added
> cgroup_rstat_flush_irqsafe() allowing flushing to happen from the irq
> context. However, rstat paths use u64_stats_sync to synchronize access to
> 64bit stat counters on 32bit machines. u64_stats_sync is implemented using
> seq_lock and trying to read from an irq context can lead to A-A deadlock if
> the irq happens to interrupt the stat update.
> Fix it by using the irqsafe variants - u64_stats_update_begin_irqsave() and
> u64_stats_update_end_irqrestore() - in the update paths. Note that none of
> this matters on 64bit machines. All these are just for 32bit SMP setups.
> Signed-off-by: Tejun Heo <>
> Reported-by: Rik van Riel <>

Applying this to cgroup/for-5.14-fixes with stable tag added.



      reply	other threads:[~2021-07-27 23:13 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-27 23:04 Tejun Heo
2021-07-27 23:13 ` Tejun Heo [this message]

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