blkcg: blkcg_activate_policy() should initialize ancestors first

When blkcg_activate_policy() is creating blkg_policy_data for existing
blkgs, it did in the wrong order - descendants first.  Fix it.  None
of the existing controllers seem affected by this.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 2 insertions, 1 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 04d286934c5e..440797293235 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1390,7 +1390,8 @@ pd_prealloc:
 
         spin_lock_irq(&q->queue_lock);
 
-        list_for_each_entry(blkg, &q->blkg_list, q_node) {
+        /* blkg_list is pushed at the head, reverse walk to init parents first */
+        list_for_each_entry_reverse(blkg, &q->blkg_list, q_node) {
                 struct blkg_policy_data *pd;
 
                 if (blkg->pd[pol->plid])