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

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Date:	Tue, 24 Apr 2007 02:46:16 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	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 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(). 

> 
> Even if I am wrong, I think we should not use task_lock() for the freezing
> related code, except in freezer.[ch]
> 
> Note also that without CONFIG_FREEZER freezer_should_exempt() == 0, so we
> will do unneeded task_lock/task_unlock.
> 
> Oleg.
> 

Thanks and Regards
gautham.
-- 
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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