memcg, tcp_kmem: check for cg_proto in sock_update_memcg

sk_prot->proto_cgroup is allowed to return NULL but sock_update_memcg
doesn't check for NULL.  The function relies on the mem_cgroup_is_root
check because we shouldn't get NULL otherwise because mem_cgroup_from_task
will always return !NULL.

All other callers are checking for NULL and we can safely replace
mem_cgroup_is_root() check by cg_proto != NULL which will be more
straightforward (proto_cgroup returns NULL for the root memcg already).

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

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 191d8aa..3033e6c 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -315,8 +315,7 @@ void sock_update_memcg(struct sock *sk)
                rcu_read_lock();
                memcg = mem_cgroup_from_task(current);
                cg_proto = sk->sk_prot->proto_cgroup(memcg);
-               if (!mem_cgroup_is_root(memcg) &&
-                   memcg_proto_active(cg_proto) &&
+               if (cg_proto && memcg_proto_active(cg_proto) &&
                    css_tryget_online(&memcg->css)) {
                        sk->sk_cgrp = cg_proto;
                }