memcg: disable hierarchy support if bound to the legacy cgroup hierarchy

If the memory cgroup controller is initially mounted in the scope of the
default cgroup hierarchy and then remounted to a legacy hierarchy, it will
still have hierarchy support enabled, which is incorrect.  We should
disable hierarchy support if bound to the legacy cgroup hierarchy.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9fe07692eaad..b34ef4a32a3b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5232,7 +5232,9 @@ static void mem_cgroup_bind(struct cgroup_subsys_state *root_css)
          * on for the root memcg is enough.
          */
         if (cgroup_on_dfl(root_css->cgroup))
-                mem_cgroup_from_css(root_css)->use_hierarchy = true;
+                root_mem_cgroup->use_hierarchy = true;
+        else
+                root_mem_cgroup->use_hierarchy = false;
 }
 
 static u64 memory_current_read(struct cgroup_subsys_state *css,