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

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Message-ID: <20070413130119.GA164@tv-sign.ru>
Date:	Fri, 13 Apr 2007 17:01:19 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Davide Libenzi <davidel@...ilserver.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	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: [PATCH 1/3] fix kthread_create() vs freezer theoretical race

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.

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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