2 files changed, 10 insertions, 2 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 53e81a61be57..74e8b8e4cd7f 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -281,6 +281,9 @@ enum {
          *   and take masks of ancestors with non-empty cpus/mems, instead of
          *   being moved to an ancestor.
          *
+         * - cpuset: a task can be moved into an empty cpuset, and again it
+         *   takes masks of ancestors.
+         *
          * - memcg: use_hierarchy is on by default and the cgroup file for
          *   the flag is not created.
          *
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 3473dd2580d1..3b3fdfdd4d78 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -479,7 +479,7 @@ static int validate_change(const struct cpuset *cur, const struct cpuset *trial)
          */
         ret = -ENOSPC;
         if ((cgroup_task_count(cur->css.cgroup) || cur->attach_in_progress) &&
-            (cpumask_empty(trial->cpus_allowed) ||
+            (cpumask_empty(trial->cpus_allowed) &&
              nodes_empty(trial->mems_allowed)))
                 goto out;
 
@@ -1466,8 +1466,13 @@ static int cpuset_can_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
 
         mutex_lock(&cpuset_mutex);
 
+        /*
+         * We allow to move tasks into an empty cpuset if sane_behavior
+         * flag is set.
+         */
         ret = -ENOSPC;
-        if (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
+        if (!cgroup_sane_behavior(cgrp) &&
+            (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed)))
                 goto out_unlock;
 
         cgroup_taskset_for_each(task, cgrp, tset) {