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:	Fri, 7 Mar 2008 05:54:51 +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 03/06, Gautham R Shenoy wrote:
>
> On Tue, Mar 04, 2008 at 06:01:07PM +0300, Oleg Nesterov wrote:
> > +static void check_running_task(struct task_struct *t, unsigned long now)
> > +{
> > +	if (!sysctl_hung_task_timeout_secs)
> > +		return;
> > +
> 
> This function gets called only when t->xxx == 0,
> so the if below doesn't mean much, does it? :)
> 
> > +	if (time_before(now, t->xxx + HZ * sysctl_hung_task_timeout_secs)
> > +		return;
> .......
>
> > @@ -192,15 +214,17 @@ static void check_hung_uninterruptible_t
> >  	if ((tainted & TAINT_DIE) || did_panic)
> >  		return;
> > 
> > -	read_lock(&tasklist_lock);
> > +	rcu_read_lock();
> >  	do_each_thread(g, t) {
> >  		if (!--max_count)
> >  			goto unlock;
> >  		if (t->state & TASK_UNINTERRUPTIBLE)
> >  			check_hung_task(t, now);
> > +		if (!t->xxx)
> > +			check_running_task(t, jiff);

Of course, the check above should be

		if (1t->xxx)
			check_running_task(t, jiff);

Thanks!

>From another message,
>
> 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 assume you fixed the patch before using it ;)

Just to be sure, there were no "bad ->cpu..." messages, yes?

Oleg.

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