From: Tejun Heo <tj@kernel.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: cgroups@vger.kernel.org, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Zefan Li <lizefan.x@bytedance.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 1/2] cgroup: Use irqsave in cgroup_rstat_flush_locked().
Date: Tue, 1 Mar 2022 20:38:51 -1000 [thread overview]
Message-ID: <Yh8Q+wjgk6dkDphR@slm.duckdns.org> (raw)
In-Reply-To: <20220301122143.1521823-2-bigeasy@linutronix.de>
Hello,
On Tue, Mar 01, 2022 at 01:21:42PM +0100, Sebastian Andrzej Siewior wrote:
> All callers of cgroup_rstat_flush_locked() acquire cgroup_rstat_lock
> either with spin_lock_irq() or spin_lock_irqsave().
> cgroup_rstat_flush_locked() itself acquires cgroup_rstat_cpu_lock which
> is a raw_spin_lock. This lock is also acquired in cgroup_rstat_updated()
> in IRQ context and therefore requires _irqsave() locking suffix in
> cgroup_rstat_flush_locked().
> Since there is no difference between spin_lock_t and raw_spin_lock_t
> on !RT lockdep does not complain here. On RT lockdep complains because
> the interrupts were not disabled here and a deadlock is possible.
>
> Acquire the raw_spin_lock_t with disabled interrupts.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Can you please add a comment explaining why irqsave is being used? As it
stands, it just looks spurious.
Thanks.
--
tejun
next prev parent reply other threads:[~2022-03-02 6:38 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <[PATCH 0/2] Correct locking assumption on PREEMPT_RT>
[not found] ` <20220301122143.1521823-1-bigeasy@linutronix.de>
2022-03-01 12:21 ` Sebastian Andrzej Siewior
2022-03-02 6:38 ` Tejun Heo [this message]
2022-03-02 14:46 ` [PATCH] cgroup: Add a comment to cgroup_rstat_flush_locked() Sebastian Andrzej Siewior
2022-03-02 15:47 ` Tejun Heo
2022-03-01 12:21 ` [PATCH 2/2] mm: workingset: Replace IRQ-off check with a lockdep assert Sebastian Andrzej Siewior
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