linux-kernel - [PATCH 5/5] memcg, tcp_kmem: check for cg_proto in sock_update

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Date:	Wed, 15 Jul 2015 13:14:45 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>
Cc:	Vladimir Davydov <vdavydov@...allels.com>,
	Tejun Heo <tj@...nel.org>, <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>
Subject: [PATCH 5/5] memcg, tcp_kmem: check for cg_proto in sock_update_memcg

From: Michal Hocko <mhocko@...e.cz>

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).

Reviewed-by: Vladimir Davydov <vdavydov@...allels.com>
Signed-off-by: Michal Hocko <mhocko@...e.cz>
---
 mm/memcontrol.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5d4fba8cbdd0..cf9fb1f41831 100644
--- 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;
 		}
-- 
2.1.4

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