[PATCH 3.19 055/123] cpuset: fix a warning when clearing configured masks in old hierarchy

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

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

From: Zefan Li <redacted>

commit 79063bffc81f82689bd90e16da1b49408f3bf095 upstream.

When we clear cpuset.cpus, cpuset.effective_cpus won't be cleared:

  # mount -t cgroup -o cpuset xxx /mnt
  # mkdir /mnt/tmp
  # echo 0 > /mnt/tmp/cpuset.cpus
  # echo > /mnt/tmp/cpuset.cpus
  # cat cpuset.cpus

  # cat cpuset.effective_cpus
  0-15

And a kernel warning in update_cpumasks_hier() is triggered:

 ------------[ cut here ]------------
 WARNING: CPU: 0 PID: 4028 at kernel/cpuset.c:894 update_cpumasks_hier+0x471/0x650()

Signed-off-by: Zefan Li <redacted>
Signed-off-by: Tejun Heo <tj@kernel.org>
Tested-by: Serge Hallyn <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/cpuset.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c

@@ -873,7 +873,7 @@ static void update_cpumasks_hier(struct
 		 * If it becomes empty, inherit the effective mask of the
 		 * parent, which is guaranteed to have some CPUs.
 		 */
-		if (cpumask_empty(new_cpus))
+		if (cgroup_on_dfl(cp->css.cgroup) && cpumask_empty(new_cpus))
 			cpumask_copy(new_cpus, parent->effective_cpus);
 
 		/* Skip the whole subtree if the cpumask remains the same. */

@@ -1129,7 +1129,7 @@ static void update_nodemasks_hier(struct
 		 * If it becomes empty, inherit the effective mask of the
 		 * parent, which is guaranteed to have some MEMs.
 		 */
-		if (nodes_empty(*new_mems))
+		if (cgroup_on_dfl(cp->css.cgroup) && nodes_empty(*new_mems))
 			*new_mems = parent->effective_mems;
 
 		/* Skip the whole subtree if the nodemask remains the same. */