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Date: Tue, 22 Aug 2017 18:33:37 +0900
From: Byungchul Park <byungchul.park@lge.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, kernel-team@lge.com,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Dave Chinner <david@fromorbit.com>, Tejun Heo <tj@kernel.org>,
        johannes@sipsolutions.net
Subject: Re: [PATCH v3 1/3] lockdep: Make LOCKDEP_CROSSRELEASE configs all
 part of PROVE_LOCKING
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On Tue, Aug 22, 2017 at 11:21:41AM +0200, Peter Zijlstra wrote:
> On Tue, Aug 22, 2017 at 05:51:00PM +0900, Byungchul Park wrote:
> > On Tue, Aug 22, 2017 at 09:52:38AM +0200, Peter Zijlstra wrote:
> > > That wouldn't work. That annotation is to help find deadlocks like:
> > > 
> > > 
> > > 	mutex_lock(&A)
> > > 				<work>
> > > 				mutex_lock(&A)
> > > 
> > > 	flush_work(&work)
> > > 
> > 
> > I meant:
> > 
> >  	mutex_lock(&A)
> >  				<work>
> >  				lockdep_map_acquire_read(&work)
> >  				mutex_lock(&A)
> > 
> >  	lockdep_map_acquire(&work)
> >  	flush_work(&work)
> > 
> > I mean it can still be detected with a read acquisition in work.
> > Am I wrong?
> 
> Think so, although there's something weird with read locks that I keep
> forgetting. But I'm not sure it'll actually solve the problem. But I can

I mean, read acquisitions are nothing but ones allowing read ones to be
re-acquired legally, IOW, we want to check entrance of flush_work() and
works, not between works. That's why I suggested to use read ones in work
in that case.