linux-kernel - Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation

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Date:   Thu, 31 Aug 2017 17:15:01 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, tj@...nel.org, boqun.feng@...il.com,
        david@...morbit.com, johannes@...solutions.net, oleg@...hat.com,
        linux-kernel@...r.kernel.org, kernel-team@....com
Subject: Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation

On Thu, Aug 31, 2017 at 10:04:42AM +0200, Peter Zijlstra wrote:
> On Wed, Aug 30, 2017 at 08:25:46PM +0900, Byungchul Park wrote:
> 
> > For example - I'm giving you the same example repeatedly:
> > 
> > context X                 context Y
> > ---------                 ---------
> >                           wait_for_completion(C)
> > acquire(A)
> > process_one_work()
> >    acquire(B)
> >    work->fn()
> >       complete(C)
> > 
> > Please check C->A and C->B.
> 
> Is there a caller of procesS_one_work() that holds a lock?

It's not important. Ok, check the following, instead:

context X                 context Y
---------                 ---------
                          wait_for_completion(C)
acquire(A)
release(A)
process_one_work()
   acquire(B)
   release(B)
   work->fn()
      complete(C)

We don't need to lose C->A and C->B dependencies unnecessarily.