linux-kernel - Re: [PATCH 6/7] smp/hotplug: Differentiate the AP-work lockdep class between up and down

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Message-ID: <20170925091633.s3mtuk3f7is5lj2e@hirez.programming.kicks-ass.net>
Date:   Mon, 25 Sep 2017 11:16:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Byungchul Park <byungchul.park@....com>
Cc:     mingo@...nel.org, tglx@...utronix.de, linux-kernel@...r.kernel.org,
        rostedt@...dmis.org, bigeasy@...utronix.de, efault@....de,
        max.byungchul.park@...il.com, kernel-team@....com
Subject: Re: [PATCH 6/7] smp/hotplug: Differentiate the AP-work lockdep class
 between up and down

On Mon, Sep 25, 2017 at 05:54:59PM +0900, Byungchul Park wrote:
> On Wed, Sep 20, 2017 at 07:00:20PM +0200, Peter Zijlstra wrote:
> > With lockdep-crossrelease we get deadlock reports that span cpu-up and
> > cpu-down chains. Such deadlocks cannot possibly happen because cpu-up
> > and cpu-down are globally serialized.
> > 
> >   CPU0                  CPU1                    CPU2
> >   cpuhp_up_callbacks:   takedown_cpu:           cpuhp_thread_fun:
> > 
> >   cpuhp_state
> >                         irq_lock_sparse()
> >     irq_lock_sparse()
> >                         wait_for_completion()
> >                                                 cpuhp_state
> >                                                 complete()
> > 
> > Now that we have consistent AP state, we can trivially separate the
> > AP-work class between up and down using st->bringup.
> 
> Could you tell me what branch you worked the patches based on?
> This is similar to the problem of workqueue so I want to fix it on
> top of yours, as well.

I wrote the patches on top of tip/master. Thomas maintains these bits so
hopefully he'll eventually merge them in the right tip tree.