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Date: Fri, 29 Apr 2011 18:00:39 +0200
From: Tejun Heo <tj@kernel.org>
To: Thilo-Alexander Ginkel <thilo@ginkel.com>
Cc: Arnd Bergmann <arnd@arndb.de>, "Rafael J. Wysocki" <rjw@sisk.pl>,
        linux-kernel@vger.kernel.org, dm-devel@redhat.com
Subject: Re: Soft lockup during suspend since ~2.6.36 [bisected]
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Hello,

On Fri, Apr 29, 2011 at 01:56:46AM +0200, Thilo-Alexander Ginkel wrote:
> On Thu, Apr 28, 2011 at 12:30, Tejun Heo <tj@kernel.org> wrote:
> > Does your kernel have preemption enabled?
> 
> CONFIG_PREEMPT is not set
> 
> > If not, does the following patch fix the problem?
> 
> Yep, looks good so far (at least in my virtualized test environment):
> 2.6.39-rc4 with your patch applied survived 100 suspend/resume cycles
> w/o locking up.

Awesome, I'll forward the patch to mainline and -stable.

> Just out of curiosity: Was this a new issue in 2.6.39-rc4 ord could
> this fix be backported to 2.6.38?

This needs to be backported.  It's an issue which has been there from
the initial implementation of cmwq.  It needs non-preemptive kernel
and rescuer kicking in at a very bad timing, so not many people seem
to have been affected by this.  Your setup somehow triggers it
reliably.

Thank you.

-- 
tejun