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

From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Andrew Morton <akpm@osdl.org>
Cc: Pavel Machek <pavel@ucw.cz>, LKML <linux-kernel@vger.kernel.org>,
	Oleg Nesterov <oleg@tv-sign.ru>,
	Aneesh Kumar <aneesh.kumar@gmail.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@in.ibm.com>,
	Gautham R Shenoy <ego@in.ibm.com>
Subject: [PATCH -mm 1/7] Freezer: Read PF_BORROWED_MM in a nonracy way
Date: Thu, 1 Mar 2007 16:06:46 +0100	[thread overview]
Message-ID: <200703011606.47776.rjw@sisk.pl> (raw)
In-Reply-To: <200703011605.46692.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-2.6.20-mm2/kernel/power/process.c
===================================================================

--- linux-2.6.20-mm2.orig/kernel/power/process.c	2007-02-25 14:02:55.000000000 +0100
+++ linux-2.6.20-mm2/kernel/power/process.c	2007-02-25 14:03:51.000000000 +0100
@@ -8,6 +8,7 @@
 
 #undef DEBUG
 
+#include <linux/sched.h>
 #include <linux/smp_lock.h>
 #include <linux/interrupt.h>
 #include <linux/suspend.h>
@@ -87,7 +88,12 @@ 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)

