linux-kernel - Re: waitqueue lockdep annotation

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Message-ID: <2fd9dc6b-9201-67db-b81e-a783daf0ce50@akamai.com>
Date:   Fri, 1 Dec 2017 17:34:50 -0500
From:   Jason Baron <jbaron@...mai.com>
To:     Christoph Hellwig <hch@....de>
Cc:     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 12/01/2017 05:02 PM, Christoph Hellwig wrote:
> On Fri, Dec 01, 2017 at 02:00:33PM -0500, Jason Baron wrote:
>> 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.
> 
> Looks like this isn't going to work due to ep_poll_safewake taking
> another waitqueue lock.  If we had a strict lock order it might work,
> but the mess in ep_call_nested makes me fear it doesn't.
> 

hmmm...I'm not sure how this suggestion would change the locking rules
from what we currently have. Right now, we use ep->lock, if we remove
that and use ep->wq->lock instead, there is just a 1-to-1 mapping there
that has not changed, since ep->wq->lock currently is completely not
being used.

Thanks,

-Jason