linux-kernel - Re: waitqueue lockdep annotation

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Message-Id: <20171130125050.1faba3f06fc572846f792f17@linux-foundation.org>
Date:   Thu, 30 Nov 2017 12:50:50 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Ingo Molnar <mingo@...hat.com>,
        eter Zijlstra <peterz@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: waitqueue lockdep annotation

On Thu, 30 Nov 2017 06:20:35 -0800 Christoph Hellwig <hch@....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?