linux-kernel - Re: [BUG 2.6.25-rc3] scheduler/hotplug: some processes are dealocked when cpu is set to offline

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Message-ID: <20080306111525.GA23865@in.ibm.com>
Date:	Thu, 6 Mar 2008 16:45:25 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Yi Yang <yi.y.yang@...el.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [BUG 2.6.25-rc3] scheduler/hotplug: some processes are
	dealocked when cpu is set to offline

On Wed, Mar 05, 2008 at 04:53:14PM +0300, Oleg Nesterov wrote:
> On 03/05, Gautham R Shenoy wrote:
> >
> > On Tue, Mar 04, 2008 at 06:01:07PM +0300, Oleg Nesterov wrote:
> > > On 03/04, Gautham R Shenoy wrote:
> > > >
> > > > So at times, the callback thread is blocked on kthread_stop(k) in
> > > > softlockup.c, while other time, it was blocked in
> > > > cleanup_workqueue_threads() in workqueue.c. 
> > > 
> > > >From another message:
> > > >
> > > > However, it remains in R< state
> > > 
> > > What about cwq->thread? Was it TASK_RUNNING too?
> > 
> > No, it was in TASK_UNINTERRUPTIBLE state. The last thing it ever
> > executed was the wait_for_completion in flush_cpu_workqueue()
> 
> You misunderstood ;) The task doing _cpu_down() hang in flush_cpu_workqueue(),
> because cwq->thread doesn't want to die. But what was cwq->thread->state?
> 

Yup, sorry for that stupid reply.

> Could you try the patch? Yi constantly sees the tasks in R< state.
> I am starting to suspect some scheduling issue.

Me too. With your patch applied there were quite a few tasks in the
running state which didn't get the cpu for more than 120 seconds.

I could be a scheduler problem which CPU-Hotplug is able to catch more
easily. Will try a git bisect.


> 
> Oleg.

-- 
Thanks and Regards
gautham
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