From 686739f6af5e8d5687ffebbf1193ff066aada6d9 Mon Sep 17 00:00:00 2001
From: Hugh Dickins <hughd@google.com>
Date: Thu, 14 Jan 2016 15:21:37 -0800
Subject: [PATCH] memcg: avoid vmpressure oops when memcg disabled

A CONFIG_MEMCG=y kernel booted with "cgroup_disable=memory" crashes on a
NULL memcg (but non-NULL root_mem_cgroup) when vmpressure kicks in.
Here's the patch I use to avoid that, but you might prefer a test on
mem_cgroup_disabled() somewhere.

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/vmpressure.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index 506f03e4be47..9a6c0704211c 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -260,7 +260,7 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
 		enum vmpressure_levels level;
 
 		/* For now, no users for root-level efficiency */
-		if (memcg == root_mem_cgroup)
+		if (!memcg || memcg == root_mem_cgroup)
 			return;
 
 		spin_lock(&vmpr->sr_lock);
-- 
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