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

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Date:	Mon, 03 Mar 2008 22:53:34 +0800
From:	Yi Yang <yi.y.yang@...el.com>
To:	Dmitry Adamushko <dmitry.adamushko@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG 2.6.25-rc3] scheduler/hotplug: some processes are
	dealocked when cpu is set to offline

On Mon, 2008-03-03 at 13:02 +0100, Dmitry Adamushko wrote:
> On 03/03/2008, Ingo Molnar <mingo@...e.hu> wrote:
> >
> >  * Dmitry Adamushko <dmitry.adamushko@...il.com> wrote:
> >
> >  >                 per_cpu(watchdog_task, hotcpu) = NULL;
> >  > +               mlseep(1);
> >
> >
> > that wont build very well ...
> 
> yeah, I forgot to mention that it's not even compile-tested :-/
> I re-created it from scratch instead of looking for the original one.
> 
> please, this one (again, not compile-tested)
> 
> --- softlockup-prev-2.c 2008-03-03 12:38:36.000000000 +0100
> +++ softlockup.c        2008-03-03 13:00:20.000000000 +0100
> @@ -294,6 +294,7 @@ cpu_callback(struct notifier_block *nfb,
>         case CPU_DEAD_FROZEN:
>                 p = per_cpu(watchdog_task, hotcpu);
>                 per_cpu(watchdog_task, hotcpu) = NULL;
> +               msleep(1);
>                 kthread_stop(p);
>                 break;
>  #endif /* CONFIG_HOTPLUG_CPU */

I don't think it can fix this issue, it only gives one chance to
scheduler, i think there are another potential and very serious issues
inside of scheduler or locking or what else we don't know.

Maybe migration is a doubtful point as Gautham mentioned.
> 

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