[added to the 3.18 stable tree] cpuset: fix a warning when clearing configured masks in old hierarchy

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From: Zefan Li <lizefan@xxxxxxxxxx>

This patch has been added to the 3.18 stable tree. If you have any
objections, please let us know.

===============

[ Upstream commit 79063bffc81f82689bd90e16da1b49408f3bf095 ]

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()

Cc: <stable@xxxxxxxxxxxxxxx> # 3.17+
Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Tested-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
---
 kernel/cpuset.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 7e59b7b..d492162 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -863,7 +863,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct cpumask *new_cpus)
 		 * 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. */
@@ -1119,7 +1119,7 @@ static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
 		 * 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. */
-- 
2.1.0

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