3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sha Zhengju <redacted>

commit 8c7577637ca31385e92769a77e2ab5b428e8b99c upstream.

When the last event is unregistered, there is no need to keep the spare
array anymore.  So free it to avoid memory leak.

Signed-off-by: Sha Zhengju <redacted>
Acked-by: KAMEZAWA Hiroyuki <redacted>
Reviewed-by: Kirill A. Shutemov <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <redacted>
---
 mm/memcontrol.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 31ab9c3..b659260 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -4507,6 +4507,12 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
 swap_buffers:
 	/* Swap primary and spare array */
 	thresholds->spare = thresholds->primary;
+	/* If all events are unregistered, free the spare array */
+	if (!new) {
+		kfree(thresholds->spare);
+		thresholds->spare = NULL;
+	}
+
 	rcu_assign_pointer(thresholds->primary, new);
 
 	/* To be sure that nobody uses thresholds */