From: Hugh Dickins <hughd@google.com>
Date: Thu, 23 Jan 2014 23:53:32 +0000 (-0800)
Subject: mm/memcg: iteration skip memcgs not yet fully initialized
X-Git-Tag: v3.12.11~96
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=ab9682ffb14f69c7547f5f13cd8cf5f37a76747a;p=kernel%2Fkernel-generic.git

mm/memcg: iteration skip memcgs not yet fully initialized

commit d8ad30559715ce97afb7d1a93a12fd90e8fff312 upstream.

It is surprising that the mem_cgroup iterator can return memcgs which
have not yet been fully initialized.  By accident (or trial and error?)
this appears not to present an actual problem; but it may be better to
prevent such surprises, by skipping memcgs not yet online.

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e0e9792..b55eb75 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1081,10 +1081,8 @@ skip_node:
 	 * protected by css_get and the tree walk is rcu safe.
 	 */
 	if (next_css) {
-		struct mem_cgroup *mem = mem_cgroup_from_css(next_css);
-
-		if (css_tryget(&mem->css))
-			return mem;
+		if ((next_css->flags & CSS_ONLINE) && css_tryget(next_css))
+			return mem_cgroup_from_css(next_css);
 		else {
 			prev_css = next_css;
 			goto skip_node;