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

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Message-Id: <1242723104.17164.5.camel@johannes.local>
Date:	Tue, 19 May 2009 10:51:44 +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 Mon, 2009-05-18 at 21:47 +0200, Oleg Nesterov wrote:

> > Maybe it shouldn't do that from the CPU_POST_DEAD
> > notifier?
> 
> Well, in any case we should understand why we have the problem, before
> changing the code. And CPU_POST_DEAD is not special, why should we treat
> it specially and skip lock_map_acquire(wq->lockdep_map) ?

I'm not familiar enough with the code -- but what are we really trying
to do in CPU_POST_DEAD? It seems to me that at that time things must
already be off the CPU, so ...? On the other hand that calls
flush_cpu_workqueue() so it seems it would actually wait for the work to
be executed on some other CPU, within the CPU_POST_DEAD notification?

johannes

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