linux-kernel - [PATCH 5/8] sh: Fix possible race on task->mm

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Message-ID: <20120207065038.GE1496@oksana.dev.rtsoft.ru>
Date:	Tue, 7 Feb 2012 10:50:38 +0400
From:	Anton Vorontsov <anton.vorontsov@...aro.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Russell King <linux@....linux.org.uk>,
	Mike Frysinger <vapier@...too.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Richard Weinberger <richard@....at>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 5/8] sh: Fix possible race on task->mm

Checking for task->mm is dangerous as ->mm might disappear (exit_mm()
assigns NULL under task_lock(), so tasklist lock is not enough).

We can't use get_task_mm()/mmput() pair as mmput() might sleep,
so let's take the task lock while we care about its mm.

Signed-off-by: Anton Vorontsov <anton.vorontsov@...aro.org>
---
 arch/sh/kernel/smp.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/arch/sh/kernel/smp.c b/arch/sh/kernel/smp.c
index 3147a9a..11d29dc 100644
--- a/arch/sh/kernel/smp.c
+++ b/arch/sh/kernel/smp.c
@@ -154,9 +154,12 @@ int __cpu_disable(void)
 	local_flush_tlb_all();
 
 	read_lock(&tasklist_lock);
-	for_each_process(p)
+	for_each_process(p) {
+		task_lock(p);
 		if (p->mm)
 			cpumask_clear_cpu(cpu, mm_cpumask(p->mm));
+		task_unlock(p);
+	}
 	read_unlock(&tasklist_lock);
 
 	return 0;
-- 
1.7.7.6

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