cpuset: fix a warning when clearing configured masks in old hierarchy

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@vger.kernel.org> # 3.17+
Signed-off-by: Zefan Li <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Tested-by: Serge Hallyn <serge.hallyn@canonical.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 89d4ed08afba..407611ba371b 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -873,7 +873,7 @@ 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. */
@@ -1129,7 +1129,7 @@ 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. */