From: Jason Baron <jbaron@akamai.com>
To: Andrew Morton <akpm@linux-foundation.org>,
Christoph Hellwig <hch@lst.de>
Cc: Ingo Molnar <mingo@redhat.com>,
eter Zijlstra <peterz@infradead.org>,
Al Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: waitqueue lockdep annotation
Date: Thu, 30 Nov 2017 16:38:02 -0500 [thread overview]
Message-ID: <dd769c95-3eea-93a4-9da4-cb0024461a9b@akamai.com> (raw)
In-Reply-To: <20171130125050.1faba3f06fc572846f792f17@linux-foundation.org>
On 11/30/2017 03:50 PM, Andrew Morton wrote:
> On Thu, 30 Nov 2017 06:20:35 -0800 Christoph Hellwig <hch@lst.de> wrote:
>
>> Hi all,
>>
>> this series adds a strategic lockdep_assert_held to __wake_up_common
>> to ensure callers really do hold the wait_queue_head lock when calling
>> the unlocked wake_up variants. It turns out epoll did not do this
>> for a fairly common path (hit all the time by systemd during bootup),
>> so the second patch fixed this instance as well.
>
> What are the runtime effects of the epoll bug?
>
I don't think there is a bug here. The 'wake_up_locked()' calls in epoll
are being protected by the ep->lock, not the wait_queue_head lock. So
arguably the 'annotation' is wrong, but I don't think there is a bug
beyond that.
Thanks,
-Jason
next prev parent reply other threads:[~2017-11-30 21:38 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-30 14:20 waitqueue lockdep annotation Christoph Hellwig
2017-11-30 14:20 ` [PATCH 1/2] sched/wait: assert the wait_queue_head lock is held in __wake_up_common Christoph Hellwig
2017-11-30 14:20 ` [PATCH 2/2] epoll: use proper wake_up variant in ep_poll_callback Christoph Hellwig
2017-11-30 20:50 ` waitqueue lockdep annotation Andrew Morton
2017-11-30 21:38 ` Jason Baron [this message]
2017-11-30 22:11 ` Christoph Hellwig
2017-11-30 22:18 ` Jason Baron
2017-12-01 17:11 ` Christoph Hellwig
2017-12-01 19:00 ` Jason Baron
2017-12-01 22:02 ` Christoph Hellwig
2017-12-01 22:34 ` Jason Baron
2017-12-01 23:03 ` Christoph Hellwig
2017-12-05 15:24 ` Jason Baron
2017-12-05 15:36 ` Davidlohr Bueso
2017-12-06 23:51 ` Christoph Hellwig
2017-12-06 23:52 Christoph Hellwig
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