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Date: Tue, 22 Aug 2017 17:51:00 +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
Message-ID: <20170822085100.GH20323@X58A-UD3R>
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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?

> The 'fake' lock connects the lock chain inside the work to the
> lock-chain at flush_work() and thus detects these. That's perfectly
> fine.
> 
> It just seems to confuse the completions stuff... Let me go read Dave's
> email and see if I can come up with something.