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Date: Wed, 20 May 2009 15:09:20 +0800
Message-ID: <d82e647a0905200009pc894d4yed0f81c83443a0ee@mail.gmail.com>
Subject: Re: INFO: possible circular locking dependency at 
	cleanup_workqueue_thread
From: Ming Lei <tom.leiming@gmail.com>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@elte.hu>,
       Zdenek Kabelac <zdenek.kabelac@gmail.com>,
       "Rafael J. Wysocki" <rjw@sisk.pl>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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2009/5/20 Johannes Berg <johannes@sipsolutions.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.

-- 
Lei Ming