cgroup: fix idr leak for the first cgroup root

The valid cgroup hierarchy ID range includes 0, so we can't filter for
positive numbers when freeing it, or it'll leak the first ID. No big
deal, just disruptive when reading the code.

The ID is freed during error handling and when the reference count
hits zero, so the double-free test is not necessary; remove it.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 86cb5c6e89320f28e17691c6d69e58c9dfde81fb..36fc0ff506c349d53f4f495aacdceef4702de470 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1158,18 +1158,12 @@ static void cgroup_exit_root_id(struct cgroup_root *root)
 {
        lockdep_assert_held(&cgroup_mutex);
 
-       if (root->hierarchy_id) {
-               idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
-               root->hierarchy_id = 0;
-       }
+       idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
 }
 
 static void cgroup_free_root(struct cgroup_root *root)
 {
        if (root) {
-               /* hierarchy ID should already have been released */
-               WARN_ON_ONCE(root->hierarchy_id);
-
                idr_destroy(&root->cgroup_idr);
                kfree(root);
        }