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From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: ego@in.ibm.com
Subject: Re: [RFC][PATCH -mm 3/3] freezer: Fix problem with kthread_stop
Date: Mon, 23 Apr 2007 23:30:24 +0200
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Cc: Oleg Nesterov <oleg@tv-sign.ru>, Andrew Morton <akpm@linux-foundation.org>,
       Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
       vatsa@in.ibm.com, paulmck@us.ibm.com, pavel@ucw.cz
References: <20070419120131.GB13435@in.ibm.com> <20070423204637.GA441@tv-sign.ru> <20070423211616.GA27214@in.ibm.com>
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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