linux-kernel - Re: waitqueue lockdep annotation

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Date:   Fri, 1 Dec 2017 18:11:02 +0100
From:   Christoph Hellwig <hch@....de>
To:     Jason Baron <jbaron@...mai.com>
Cc:     Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter 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, Nov 30, 2017 at 05:18:07PM -0500, Jason Baron wrote:
> Yes, but for those cases it uses the ep->poll_wait waitqueue not the
> ep->wq, which is guarded by the ep->wq->lock.

True.  So it looks like we have one waitqueue in the system that is
special in providing its own synchronization for waitqueues while
entirely ignoring the waitqueue code documentation that states that
waitqueues are internally synchronized.

We could drop the lockdep annotation, updated the documentation and
not add any validation of the assumptions, or just make epoll fit the
scheme used by everyone else.  So either we can drop these patches, or
I need to fix up more of the epoll code.