memcg: root_cgroup cannot reach mem_cgroup_move_parent
The root cgroup cannot be destroyed so we never hit it down the
mem_cgroup_pre_destroy path and mem_cgroup_force_empty_write shouldn't
even try to do anything if called for the root.
This means that mem_cgroup_move_parent doesn't have to bother with the
root cgroup and it can assume it can always move charges upwards.
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Glauber Costa <glommer@parallels.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 07d92b8..916132a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2715,9 +2715,7 @@
unsigned long uninitialized_var(flags);
int ret;
- /* Is ROOT ? */
- if (mem_cgroup_is_root(child))
- return -EINVAL;
+ VM_BUG_ON(mem_cgroup_is_root(child));
ret = -EBUSY;
if (!get_page_unless_zero(page))
@@ -3823,6 +3821,8 @@
struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
int ret;
+ if (mem_cgroup_is_root(memcg))
+ return -EINVAL;
css_get(&memcg->css);
ret = mem_cgroup_force_empty(memcg);
css_put(&memcg->css);