memcg: fix kmemcg registration for late caches

The designed workflow for the caches in kmemcg is: register it with
memcg_register_cache() if kmemcg is already available or later on when a
new kmemcg appears at memcg_update_cache_sizes() which will handle all
caches in the system.  The caches created at boot time will be handled
by the later, and the memcg-caches as well as any system caches that are
registered later on by the former.

There is a bug, however, in memcg_register_cache: we correctly set up
the array size, but do not mark the cache as a root cache.

This means that allocations for any cache appearing late in the game
will see memcg->memcg_params->is_root_cache == false, and in particular,
trigger VM_BUG_ON(!cachep->memcg_params->is_root_cache) in
__memcg_kmem_cache_get.

The obvious fix is to include the missing assignment.

Signed-off-by: Glauber Costa <glommer@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
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 09255ec8159c..fbb60b103e64 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3030,7 +3030,9 @@ int memcg_register_cache(struct mem_cgroup *memcg, struct kmem_cache *s,
         if (memcg) {
                 s->memcg_params->memcg = memcg;
                 s->memcg_params->root_cache = root_cache;
-        }
+        } else
+                s->memcg_params->is_root_cache = true;
+
         return 0;
 }