diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a9318963d5d5f1a13b30328973049a071b404513..2bc3fbe931549bd728034b4c014531119c97e1e3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4762,6 +4762,33 @@ static void mem_cgroup_reparent_charges(struct mem_cgroup *memcg)
 	} while (usage > 0);
 }
 
+/*
+ * This mainly exists for tests during the setting of set of use_hierarchy.
+ * Since this is the very setting we are changing, the current hierarchy value
+ * is meaningless
+ */
+static inline bool __memcg_has_children(struct mem_cgroup *memcg)
+{
+	struct cgroup *pos;
+
+	/* bounce at first found */
+	cgroup_for_each_child(pos, memcg->css.cgroup)
+		return true;
+	return false;
+}
+
+/*
+ * Must be called with cgroup_lock held, unless the cgroup is guaranteed to be
+ * already dead (in mem_cgroup_force_empty(), for instance).  This is different
+ * from mem_cgroup_count_children(), in the sense that we don't really care how
+ * many children we have; we only need to know if we have any.  It also counts
+ * any memcg without hierarchy as infertile.
+ */
+static inline bool memcg_has_children(struct mem_cgroup *memcg)
+{
+	return memcg->use_hierarchy && __memcg_has_children(memcg);
+}
+
 /*
  * Reclaims as many pages from the given memcg as possible and moves
  * the rest to the parent.
@@ -4847,7 +4874,7 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
 	 */
 	if ((!parent_memcg || !parent_memcg->use_hierarchy) &&
 				(val == 1 || val == 0)) {
-		if (list_empty(&cont->children))
+		if (!__memcg_has_children(memcg))
 			memcg->use_hierarchy = val;
 		else
 			retval = -EBUSY;
@@ -4964,8 +4991,7 @@ static int memcg_update_kmem_limit(struct cgroup *cont, u64 val)
 	cgroup_lock();
 	mutex_lock(&set_limit_mutex);
 	if (!memcg->kmem_account_flags && val != RESOURCE_MAX) {
-		if (cgroup_task_count(cont) || (memcg->use_hierarchy &&
-						!list_empty(&cont->children))) {
+		if (cgroup_task_count(cont) || memcg_has_children(memcg)) {
 			ret = -EBUSY;
 			goto out;
 		}
@@ -5373,8 +5399,7 @@ static int mem_cgroup_swappiness_write(struct cgroup *cgrp, struct cftype *cft,
 	cgroup_lock();
 
 	/* If under hierarchy, only empty-root can set this value */
-	if ((parent->use_hierarchy) ||
-	    (memcg->use_hierarchy && !list_empty(&cgrp->children))) {
+	if ((parent->use_hierarchy) || memcg_has_children(memcg)) {
 		cgroup_unlock();
 		return -EINVAL;
 	}
@@ -5709,8 +5734,7 @@ static int mem_cgroup_oom_control_write(struct cgroup *cgrp,
 
 	cgroup_lock();
 	/* oom-kill-disable is a flag for subhierarchy. */
-	if ((parent->use_hierarchy) ||
-	    (memcg->use_hierarchy && !list_empty(&cgrp->children))) {
+	if ((parent->use_hierarchy) || memcg_has_children(memcg)) {
 		cgroup_unlock();
 		return -EINVAL;
 	}