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

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Message-Id: <200704222141.00680.rjw@sisk.pl>
Date:	Sun, 22 Apr 2007 21:40:59 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, ego@...ibm.com,
	Oleg Nesterov <oleg@...sign.ru>, linux-kernel@...r.kernel.org,
	vatsa@...ibm.com, paulmck@...ibm.com, pavel@....cz
Subject: [RFC][PATCH -mm 3/3] freezer: Fix problem with kthread_stop

From: Rafael J. Wysocki <rjw@...k.pl>

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().

Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---
 kernel/kthread.c |    9 +++++++++
 1 file changed, 9 insertions(+)

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
@@ -13,6 +13,7 @@
 #include <linux/file.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/freezer.h>
 #include <asm/semaphore.h>
 
 /*
@@ -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);
 
-
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