linux-kernel - [PATCH 5/7] Freezer: Fix kthread_create vs freezer theoretical race

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Message-Id: <200705110041.17783.rjw@sisk.pl>
Date:	Fri, 11 May 2007 00:41:16 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Gautham R Shenoy <ego@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...sign.ru>, Pavel Machek <pavel@....cz>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 5/7] Freezer: Fix kthread_create vs freezer theoretical race

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

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.

[akpm@...ux-foundation.org: s/BUG_ON/WARN_ON+recover]

Signed-off-by: Oleg Nesterov <oleg@...sign.ru>
Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---
 kernel/kthread.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

Index: linux-2.6/kernel/kthread.c
===================================================================
--- linux-2.6.orig/kernel/kthread.c	2007-05-10 21:44:23.000000000 +0200
+++ linux-2.6/kernel/kthread.c	2007-05-10 21:44:43.000000000 +0200
@@ -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();
 
@@ -162,7 +162,10 @@ EXPORT_SYMBOL(kthread_create);
  */
 void kthread_bind(struct task_struct *k, unsigned int cpu)
 {
-	BUG_ON(k->state != TASK_INTERRUPTIBLE);
+	if (k->state != TASK_UNINTERRUPTIBLE) {
+		WARN_ON(1);
+		return;
+	}
 	/* Must have done schedule() in kthread() before we set_task_cpu */
 	wait_task_inactive(k);
 	set_task_cpu(k, cpu);

-
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