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From: Jason Baron <jbaron@akamai.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@redhat.com>,
	Peter 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: Fri, 1 Dec 2017 14:00:33 -0500	[thread overview]
Message-ID: <57869c0c-764c-ff99-93cd-8020f8ceea9e@akamai.com> (raw)
In-Reply-To: <20171201171102.GA20072@lst.de>



On 12/01/2017 12:11 PM, Christoph Hellwig wrote:
> 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.
> 

You could leave the annotation and do something like:
s/ep->lock/ep->wq->lock. And then that would remove the ep->lock saving
a bit of space.

Thanks,

-Jason

  reply	other threads:[~2017-12-01 19:01 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
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 [this message]
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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