memcg: free spare array to avoid memory leak

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 <handai.szj@taobao.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 31ab9c3f0178d3f7193d5e2b6e6935926cf1d48d..b659260c56ad5591c4debdae6b865a057fb01b7c 100644 (file)
--- 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 */