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Subject: Re: INFO: possible circular locking dependency at
 cleanup_workqueue_thread
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>, Zdenek Kabelac <zdenek.kabelac@gmail.com>,
       "Rafael J. Wysocki" <rjw@sisk.pl>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Date: Wed, 20 May 2009 16:12:15 +0200
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On Wed, 2009-05-20 at 15:55 +0200, Oleg Nesterov wrote:
> On 05/20, Peter Zijlstra wrote:
> >
> > On Wed, 2009-05-20 at 15:18 +0200, Oleg Nesterov wrote:
> > > On 05/20, Peter Zijlstra wrote:
> > > >
> > > > Breaking the setup_lock -> cpu_add_remove_lock dependency seems
> > > > sufficient.
> > >
> > > Hmm. What do you mean? Afaics setup_lock -> cpu_add_remove_lock
> > > is not a problem?
> >
> > >From what I could see that is the only dependency that makes
> > cpu_add_remove_lock nest under "events" workqueue 'lock', which is what
> > is generating the deadlock.
> 
> But cpu_add_remove_lock does not participate in this deadlock, see
> http://marc.info/?l=linux-kernel&m=124274977707363 ?
> 
> Perhaps you mean something else, could you spell in that case?

Ah, right, I knew I should have payed more attention when reading the
thread. Yes breaking that chain around dpm_list_mutex would also work,
and solve this other deadlock too.