linux-kernel - [PATCH -mm 1/6] Freezer: Read PF_BORROWED

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Message-Id: <200702260802.49295.rjw@sisk.pl>
Date:	Mon, 26 Feb 2007 08:02:48 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Andrew Morton <akpm@...l.org>
Cc:	Pavel Machek <pavel@....cz>, LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...sign.ru>,
	Aneesh Kumar <aneesh.kumar@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>
Subject: [PATCH -mm 1/6] Freezer: Read PF_BORROWED_MM in a nonracy way

From: Rafael J. Wysocki <rjw@...k.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@...k.pl>
Acked-by: Pavel Machek <pavel@....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
+++ linux-2.6.20-mm2/kernel/power/process.c
@@ -8,6 +8,7 @@
 
 #undef DEBUG
 
+#include <linux/sched.h>
 #include <linux/smp_lock.h>
 #include <linux/interrupt.h>
 #include <linux/suspend.h>
@@ -92,7 +93,12 @@ 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)

-
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