linux-kernel - Re: [PATCH v3 1/3] lockdep: Make LOCKDEP_CROSSRELEASE configs all part of PROVE

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Message-ID: <20170822085100.GH20323@X58A-UD3R>
Date:   Tue, 22 Aug 2017 17:51:00 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org,
        kernel-team@....com, Arnaldo Carvalho de Melo <acme@...nel.org>,
        Dave Chinner <david@...morbit.com>, Tejun Heo <tj@...nel.org>,
        johannes@...solutions.net
Subject: Re: [PATCH v3 1/3] lockdep: Make LOCKDEP_CROSSRELEASE configs all
 part of PROVE_LOCKING

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.