linux-kernel - Re: [PATCH 1/3] fix kthread_create() vs freezer theoretical race

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Message-ID: <m1d527ook1.fsf@ebiederm.dsl.xmission.com>
Date:	Fri, 13 Apr 2007 17:13:50 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Davide Libenzi <davidel@...ilserver.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Roland McGrath <roland@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] fix kthread_create() vs freezer theoretical race

Oleg Nesterov <oleg@...sign.ru> writes:

> kthread() sleeps in TASK_INTERRUPTIBLE state waiting for the first wakeup.
> In theory, this wakeup may come from freeze_process()->signal_wake_up(),
> so the task can disappear even before kthread_create() sets its ->comm.
>
> Change kthread() to use TASK_UNINTERRUPTIBLE.

Yep.  That makes sense.

Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

>
> Signed-off-by: Oleg Nesterov <oleg@...sign.ru>
>
> --- 2.6.21-rc5/kernel/kthread.c~0_FREEZER 2007-04-13 14:52:44.000000000 +0400
> +++ 2.6.21-rc5/kernel/kthread.c	2007-04-13 15:36:43.000000000 +0400
> @@ -70,7 +70,7 @@ static int kthread(void *_create)
>  	data = create->data;
>  
>  	/* OK, tell user we're spawned, wait for stop or wakeup */
> -	__set_current_state(TASK_INTERRUPTIBLE);
> +	__set_current_state(TASK_UNINTERRUPTIBLE);
>  	complete(&create->started);
>  	schedule();
>  
> @@ -174,7 +174,7 @@ EXPORT_SYMBOL(kthread_create);
>   */
>  void kthread_bind(struct task_struct *k, unsigned int cpu)
>  {
> -	BUG_ON(k->state != TASK_INTERRUPTIBLE);
> +	BUG_ON(k->state != TASK_UNINTERRUPTIBLE);
>  	/* Must have done schedule() in kthread() before we set_task_cpu */
>  	wait_task_inactive(k);
>  	set_task_cpu(k, cpu);
-
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