linux-kernel - Re: [input layer, lockdep warning] Re: [PATCH] cpuset: Rework sched domains and CPU hotplug handling (take 4)

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Message-ID: <20080820090454.ZZRA012@mailhub.coreip.homeip.net>
Date:	Wed, 20 Aug 2008 09:08:06 -0400
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Paul Jackson <pj@....com>, linux-kernel@...r.kernel.org,
	menage@...gle.com, a.p.zijlstra@...llo.nl, vegard.nossum@...il.com,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Max Krasnyansky <maxk@...lcomm.com>
Subject: Re: [input layer, lockdep warning] Re: [PATCH] cpuset: Rework
	sched domains and CPU hotplug handling (take 4)

On Wed, Aug 20, 2008 at 08:44:37AM +0200, Ingo Molnar wrote:
> 
> Dmitry,
> 
> this lockdep warning triggered again in -tip testing:
> 
> > > [   59.750200] =======================================================
> > > [   59.750200] [ INFO: possible circular locking dependency detected ]
> > > [   59.750200] 2.6.27-rc3-tip-00076-g75f9a29-dirty #1
> > > [   59.750200] -------------------------------------------------------
> > > [   59.750200] Xorg/6623 is trying to acquire lock:
> > > [   59.750200]  (cpu_add_remove_lock){--..}, at: [<c0147dae>] cpu_maps_update_begin+0x14/0x16
> > > [   59.750200] 
> > > [   59.750200] but task is already holding lock:
> > > [   59.750200]  (polldev_mutex){--..}, at: [<c07eb66f>] input_close_polled_device+0x22/0x47
> > > [   59.750200] 
> > > [   59.750200] which lock already depends on the new lock.
> 
> See the bootlog below. Upstream base of the tree below is 
> 1fca254274823876. The first warnings came with b635acec48.
> 

Ingo,

I am not quite sure why lockdep complains. From the input POV
everything is pretty simple - we use polldev_mutex to start ipolldevd
workqueue on demand, when first user appears, and also to destroy
workqueue after last iser is gone.

Is it reporoducible for you? Is it only with your tree or mainline as
well?

-- 
Dmitry
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