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

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Date:   Wed, 30 Aug 2017 18:01:59 +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

> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Wednesday, August 30, 2017 5:54 PM
> To: Byungchul Park
> 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.

My point is that we inevitably lose valuable dependencies by yours. That's
why I've endlessly asked you 'do you have any reason you try those patches?'
a ton of times. And you have never answered it.