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: <20080305135314.GA84@tv-sign.ru>
Date:	Wed, 5 Mar 2008 16:53:14 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Gautham R Shenoy <ego@...ibm.com>
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 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?

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

Oleg.

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