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

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Message-ID: <20170822051438.GD20323@X58A-UD3R>
Date:   Tue, 22 Aug 2017 14:14:38 +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 Mon, Aug 21, 2017 at 05:46:00PM +0200, Peter Zijlstra wrote:
> Now given the above observance rule and the fact that the below report
> is from the complete, the thing that happened appears to be:
> 
> 
> 	lockdep_map_acquire(&work->lockdep_map)
> 	down_write(&A)
> 
> 			down_write(&A)
> 			wait_for_completion(&C)
> 
> 					lockdep_map_acquire(&work_lockdep_map);
> 					complete(&C)
> 
> Which lockdep then puked over because both sides saw the same work
> class.
> 
> Byungchul; should we not exclude the work class itself, it appears to me
> the workqueue code is explicitly parallel, or am I confused again?

Do you mean the lockdep_map_acquire(&work->lockdep_map) used manuallly?

That was introduced by Johannes:

commit 4e6045f134784f4b158b3c0f7a282b04bd816887
"workqueue: debug flushing deadlocks with lockdep"

I am not sure but, for that purpose, IMHO, we can use a
lockdep_map_acquire_read() instead, in process_one_work(), can't we?