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

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Date:   Thu, 24 Aug 2017 15:11:53 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Oleg Nesterov <oleg@...hat.com>, 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 Wed, Aug 23, 2017 at 07:47:14PM +0200, Peter Zijlstra wrote:
> Those are fine and are indeed the flush_work() vs work inversion.
> 
> The two straight forward annotations are:
> 
> flush_work(work)	process_one_work(wq, work)
>   A(work)		  A(work)
>   R(work)		  work->func(work);
> 			  R(work)
> 
> Which catches:
> 
> Task-1:			work:
> 
>   mutex_lock(&A);	mutex_lock(&A);
>   flush_work(work);

I'm not sure but, with LOCKDEP_COMPLETE enabled, this issue would
automatically be covered w/o additional A(work)/R(work). Right?

A(work)/R(work) seem to be used for preventing wait_for_completion()
in flush_work() from waiting for the completion forever because of the
work using mutex_lock(&A). Am I understanding correctly?

If yes, we can use just LOCKDEP_COMPLETE for that purpose.

> And the analogous:
> 
> flush_workqueue(wq)	process_one_work(wq, work)
>   A(wq)			  A(wq)
>   R(wq)			  work->func(work);
>				  (wq)