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

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Date:	Fri, 22 May 2009 12:46:06 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	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 Tue, 2009-05-19 at 20:51 +0200, Oleg Nesterov 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)
> > > >
> > > > linkwatch_work
> > > >  -> rtnl_lock()
> > > > 							disable_nonboot_cpus()
> > >
> > > let's suppose disable_nonboot_cpus() does not take cpu_add_remove_lock,
> > >
> > > > 							-> flush CPU 3 workqueue
> > >
> > > in this case the deadlock is still here?
> > >
> > > We can't flush because we hold the lock (dpm_list_mtx) which depends
> > > on another lock taken by work->func(), the "classical" bug with flush.
> > >
> > > No?
> >
> > Yeah, it looks like cpu_add_remove_lock doesn't make a difference...
> > It's just lockdep reporting a longer chain that also leads to a
> > deadlock.
> 
> So. we should not call cpu_down/disable_nonboot_cpus under device_pm_lock().
> 
> At first glance this was changed by
> 
> 	PM: Change hibernation code ordering
> 	4aecd6718939eb3c4145b248369b65f7483a8a02
> 
> 	PM: Change suspend code ordering
> 	900af0d973856d6feb6fc088c2d0d3fde57707d3
> 
> commits. Rafael, could you take a look?

I just arrived at the same conclusion, heh. I can't say I understand
these changes though, the part about calling the platform differently
may make sense, but calling why disable non-boot CPUs at a different
place?

johannes

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