[PATCH 3.11 021/144] cpuset: fix a race condition in __cpuset_node_allowed_softwall()

[Luis Henriques]

3.11.10.7 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Li Zefan <lizefan at huawei.com>

commit 99afb0fd5f05aac467ffa85c36778fec4396209b upstream.

It's not safe to access task's cpuset after releasing task_lock().
Holding callback_mutex won't help.

Signed-off-by: Li Zefan <lizefan at huawei.com>
Signed-off-by: Tejun Heo <tj at kernel.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/cpuset.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 84773c7..26e7a5d 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2518,9 +2518,9 @@ int __cpuset_node_allowed_softwall(int node, gfp_t gfp_mask)
 
 	task_lock(current);
 	cs = nearest_hardwall_ancestor(task_cs(current));
+	allowed = node_isset(node, cs->mems_allowed);
 	task_unlock(current);
 
-	allowed = node_isset(node, cs->mems_allowed);
 	mutex_unlock(&callback_mutex);
 	return allowed;
 }
-- 
1.9.1