cpuset: fix a race condition in __cpuset_node_allowed_softwall()

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@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 57eb98d..1e2c5f0 100644 (file)
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2366,9 +2366,9 @@ 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;
 }