1 files changed, 31 insertions, 7 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a9318963d5d5..2bc3fbe93154 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4763,6 +4763,33 @@ static void mem_cgroup_reparent_charges(struct mem_cgroup *memcg)
 }
 
 /*
+ * 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;
         }