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

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Message-ID: <20070423104024.GB5635@elf.ucw.cz>
Date:	Mon, 23 Apr 2007 12:40:24 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, ego@...ibm.com,
	Oleg Nesterov <oleg@...sign.ru>, linux-kernel@...r.kernel.org,
	vatsa@...ibm.com, paulmck@...ibm.com
Subject: Re: [RFC][PATCH -mm 3/3] freezer: Fix problem with kthread_stop

Hi!

> Fix the problem with kthread_stop() that causes the freezer to fail if a
> freezable thread is attempting to stop a frozen one and that may cause the
> freezer to fail if the thread being stopped is freezable and
> try_to_freeze_tasks() is running concurrently with kthread_stop().

Parse error.

> Index: linux-2.6.21-rc6-mm1/kernel/kthread.c
> ===================================================================
> --- linux-2.6.21-rc6-mm1.orig/kernel/kthread.c	2007-04-09 15:23:48.000000000 +0200
> +++ linux-2.6.21-rc6-mm1/kernel/kthread.c	2007-04-22 19:05:29.000000000 +0200
> @@ -232,6 +233,14 @@ int kthread_stop(struct task_struct *k)
>  
>  	/* Now set kthread_should_stop() to true, and wake it up. */
>  	kthread_stop_info.k = k;
> +	if (!freezer_should_exempt(current)) {
> +		/* 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);
> +	}
>  	wake_up_process(k);
>  	put_task_struct(k);
>  

Do we need to take some locks to access other process' flags? Or do
frozen_exempt() etc take enough locks, already?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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