linux-kernel - Re: [RFC][PATCH -mm 3/3] freezer: Fix problem with kthread

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Message-Id: <200704232330.25886.rjw@sisk.pl>
Date:	Mon, 23 Apr 2007 23:30:24 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	ego@...ibm.com
Cc:	Oleg Nesterov <oleg@...sign.ru>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	vatsa@...ibm.com, paulmck@...ibm.com, pavel@....cz
Subject: Re: [RFC][PATCH -mm 3/3] freezer: Fix problem with kthread_stop

On Monday, 23 April 2007 23:16, Gautham R Shenoy wrote:
> On Tue, Apr 24, 2007 at 12:46:37AM +0400, Oleg Nesterov wrote:
> > On 04/23, Rafael J. Wysocki wrote:
> > >
> > > On Monday, 23 April 2007 14:35, Gautham R Shenoy wrote:
> > > > > +	if (!freezer_should_exempt(current)) {
> > > > 		task_lock(k);
> > > > > +		/* We are freezable, so we must make sure that the thread being
> > > > > +		 * stopped is not frozen and will not be frozen until it dies
> > > > > +		 */
> > > > > +		freezer_exempt(k);
> > > > > +		if (frozen(k))
> > > > > +			clear_frozen_flag(k);
> > > > 		task_unlock(k);
> > > > > +	}
> > > 
> > > Yes, that's correct.  We need to take task_lock() to avoid the race with
> > > refrigerator().
> > 
> > Even if we use thaw_task() ?
> 
> I don't think so. As you correctly pointed out, thaw_task() is race free
> w.r.t the refrigerator(). 

Agreed.

Rafael
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