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

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Date:	Tue, 24 Apr 2007 00:46:37 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ego@...ibm.com, 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 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() ?

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.

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