Re: INFO: possible circular locking dependency at cleanup_workqueue_thread

[Johannes Berg]

On Wed, 2009-05-20 at 15:09 +0800, Ming Lei wrote:
> 2009/5/20 Johannes Berg <johannes@xxxxxxxxxxxxxxxx>:
> > 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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