rq_qos_exit() removes the current q->rq_qos, this action has to be
done after queue is frozen, otherwise the IO queue path may never
be waken up, then IO hang is caused.

So fixes this issue by moving rq_qos_exit() after queue is frozen.

Cc: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Ming Lei <redacted>
---
 block/blk-core.c  | 3 +++
 block/blk-sysfs.c | 2 --
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 3ed60723e242..0a5a6cf5add7 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c

@@ -785,6 +785,9 @@ void blk_cleanup_queue(struct request_queue *q)
         * prevent that q->request_fn() gets invoked after draining finished.
         */
        blk_freeze_queue(q);
+
+       rq_qos_exit(q);
+
        spin_lock_irq(lock);
        queue_flag_set(QUEUE_FLAG_DEAD, q);
        spin_unlock_irq(lock);

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 3772671cf2bc..d4f1280965b6 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c

@@ -994,8 +994,6 @@ void blk_unregister_queue(struct gendisk *disk)
        kobject_del(&q->kobj);
        blk_trace_remove_sysfs(disk_to_dev(disk));

-       rq_qos_exit(q);
-
        mutex_lock(&q->sysfs_lock);
        if (q->request_fn || (q->mq_ops && q->elevator))
                elv_unregister_queue(q);
--

2.9.5