linux-kernel - Re: INFO: possible circular locking dependency at cleanup_workqueue

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Date:	Wed, 20 May 2009 09:12:49 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Zdenek Kabelac <zdenek.kabelac@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: INFO: possible circular locking dependency at 
 cleanup_workqueue_thread

On Wed, 2009-05-20 at 15:09 +0800, Ming Lei wrote:
> 2009/5/20 Johannes Berg <johannes@...solutions.net>:
> > On Wed, 2009-05-20 at 11:36 +0800, Ming Lei wrote:
> >
> >> > Anyway, you can have a deadlock like this:
> >> >
> >> > CPU 3                   CPU 2                           CPU 1
> >> >                                                        suspend/hibernate
> >> >                        something:
> >> >                        rtnl_lock()                     device_pm_lock()
> >> >                                                        -> mutex_lock(&dpm_list_mtx)
> >> >
> >> >                        mutex_lock(&dpm_list_mtx)
> >>
> >> Would you give a explaination why mutex_lock(&dpm_list_mtx) runs in CPU2
> >> and depends on rtnl_lock?
> >
> > Why not? Something is registering a hotplugged netdev.
> 
> I see. I just feel a bit curious how lockdep may build the dependency
> of dpm_list_mtx on rtnl_lock,  and it  is certainly related with
> lockdep internal.

No, it's just the way drivers/base/power/ works -- it acquires the lock
when you register a new struct device.

johannes

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