linux-kernel - [PATCH 4/5] blkcg: blkcg_activate_policy() should initialize ancestors first

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Date:   Thu, 13 Jun 2019 15:30:40 -0700
From:   Tejun Heo <tj@...nel.org>
To:     axboe@...nel.dk, jbacik@...com
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        kernel-team@...com, dennis@...nel.org, jack@...e.cz,
        Tejun Heo <tj@...nel.org>
Subject: [PATCH 4/5] 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@...nel.org>
---
 block/blk-cgroup.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

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 @@ int blkcg_activate_policy(struct request_queue *q,
 
 	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])
-- 
2.17.1