[PATCH] mm-memcontrol-convert-reclaim-iterator-to-simple-css-refcounting-fix

[Michal Hocko]

Make sure that the cached reference is always released.

Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
---
 mm/memcontrol.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bdcd0416a017..42842a47b4c1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1160,9 +1160,17 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
 	}
 
 	if (reclaim) {
-		if (cmpxchg(&iter->position, pos, memcg) == pos && memcg)
-			css_get(&memcg->css);
+		if (cmpxchg(&iter->position, pos, memcg) == pos) {
+			if (memcg)
+				css_get(&memcg->css);
+			if (pos)
+				css_put(&pos->css);
+		}
 
+		/*
+		 * pairs with css_tryget when dereferencing iter->position
+		 * above.
+		 */
 		if (pos)
 			css_put(&pos->css);
 
-- 
2.1.1

-- 
Michal Hocko
SUSE Labs
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