blk-mq: move blk_mq_update_nr_hw_queues synchronize_rcu call

This fixes the
4.9 backport commit f530afb9
which was
upstream commit f5bbbbe4.

The upstream commit added a call to synchronize_rcu to
_blk_mq_update_nr_hw_queues, just after freezing queues.

In the backport this landed (in blk_mq_update_nr_hw_queues instead),
just after unfreezeing queues.

This commit moves the call to its intended place.

Fixes: f530afb9 ("blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter")
Signed-off-by: Giuliano Procida <gprocida@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

block/blk-mq.c

@@ -2331,6 +2331,10 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)
 
 	list_for_each_entry(q, &set->tag_list, tag_set_list)
 		blk_mq_freeze_queue(q);
+	/*
+	 * Sync with blk_mq_queue_tag_busy_iter.
+	 */
+	synchronize_rcu();
 
 	set->nr_hw_queues = nr_hw_queues;
 	list_for_each_entry(q, &set->tag_list, tag_set_list) {
@@ -2346,10 +2350,6 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)
 
 	list_for_each_entry(q, &set->tag_list, tag_set_list)
 		blk_mq_unfreeze_queue(q);
-	/*
-	 * Sync with blk_mq_queue_tag_busy_iter.
-	 */
-	synchronize_rcu();
 }
 EXPORT_SYMBOL_GPL(blk_mq_update_nr_hw_queues);