[PATCH 1/7] Freezer: Read PF_BORROWED_MM in a nonracy way

["Rafael J. Wysocki" <rjw@sisk.pl>]

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

The reading of PF_BORROWED_MM in is_user_space() without task_lock() is racy. 
Fix it.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
---
 kernel/power/process.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

Index: linux-2.6/kernel/power/process.c
===================================================================
--- linux-2.6.orig/kernel/power/process.c	2007-05-10 21:44:23.000000000 +0200
+++ linux-2.6/kernel/power/process.c	2007-05-10 21:44:28.000000000 +0200
@@ -8,6 +8,7 @@
 
 #undef DEBUG
 
+#include <linux/sched.h>
 #include <linux/interrupt.h>
 #include <linux/suspend.h>
 #include <linux/module.h>
@@ -88,7 +89,12 @@ static void cancel_freezing(struct task_
 
 static inline int is_user_space(struct task_struct *p)
 {
-	return p->mm && !(p->flags & PF_BORROWED_MM);
+	int ret;
+
+	task_lock(p);
+	ret = p->mm && !(p->flags & PF_BORROWED_MM);
+	task_unlock(p);
+	return ret;
 }
 
 static unsigned int try_to_freeze_tasks(int freeze_user_space)