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

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Date:   Wed, 30 Aug 2017 10:53:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Byungchul Park <byungchul.park@....com>
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 Wed, Aug 30, 2017 at 04:41:17PM +0900, Byungchul Park wrote:
> On Wed, Aug 30, 2017 at 11:09:53AM +0900, Byungchul Park wrote:

> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > > ---
> > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> > > index c0331891dec1..ab3c0dc8c7ed 100644
> > > --- a/kernel/workqueue.c
> > > +++ b/kernel/workqueue.c
> > > @@ -2107,14 +2107,14 @@ __acquires(&pool->lock)
> > >  	 * Which would create W1->C->W1 dependencies, even though there is no
> > >  	 * actual deadlock possible. There are two solutions, using a
> > >  	 * read-recursive acquire on the work(queue) 'locks', but this will then
> > > -	 * hit the lockdep limitation on recursive locks, or simly discard
> > > +	 * hit the lockdep limitation on recursive locks, or simply discard
> > >  	 * these locks.
> > >  	 *
> > >  	 * AFAICT there is no possible deadlock scenario between the
> > >  	 * flush_work() and complete() primitives (except for single-threaded
> > >  	 * workqueues), so hiding them isn't a problem.
> > >  	 */
> > > -	crossrelease_hist_start(XHLOCK_PROC, true);
> > > +	lockdep_invariant_state(true);
> > 
> > This is what I am always curious about. It would be ok if you agree with
> > removing this work-around after fixing acquire things in wq. But, you
> > keep to say this is essencial.
> > 
> > You should focus on what dependencies actually are, than saparating
> > contexts unnecessarily. Of course, we have to do it for each work, _BUT_
> > not between outside of work and each work since there might be
> > dependencies between them certainly.
> 
> You have never answered it. I'm curious about your answer. If you can't,
> I think you have to revert all your patches. All yours are wrong.

Because I don't understand what you're on about. And my patches actually
work.