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

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Message-ID: <20170830091409.y2d4puph3qn2jwxx@hirez.programming.kicks-ass.net>
Date:   Wed, 30 Aug 2017 11:14:09 +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 11:12:23AM +0200, Peter Zijlstra wrote:
> On Wed, Aug 30, 2017 at 06:01:59PM +0900, Byungchul Park wrote:
> > 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.
> 
> The only dependencies that are lost are those between the first work and
> the setup of the workqueue thread.
> 
> And there obviously _should_ not be any dependencies between those. A
> work should not depend on the setup of the thread.

Furthermore, the save/restore can't preserve those dependencies. The
moment a work exhausts xhlocks[] they are gone. So by assuming the first
work _will_ exhaust the history there is effectively nothing lost.