[PATCH V2 17/20] block: move debugfs/sysfs register out of freezing queue

[Ming Lei <ming.lei@xxxxxxxxxx>]

Move debugfs/sysfs register out of freezing queue in
__blk_mq_update_nr_hw_queues(), so that the following lockdep dependency
can be killed:

	#2 (&q->q_usage_counter(io)#16){++++}-{0:0}:
	#1 (fs_reclaim){+.+.}-{0:0}:
	#0 (&sb->s_type->i_mutex_key#3){+.+.}-{4:4}: //debugfs

And registering/un-registering debugfs/sysfs does not require queue to be
frozen.

Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
 block/blk-mq.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9a361a173a8e..8d08127e40be 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4946,15 +4946,15 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
 	if (set->nr_maps == 1 && nr_hw_queues == set->nr_hw_queues)
 		return;
 
-	memflags = memalloc_noio_save();
-	list_for_each_entry(q, &set->tag_list, tag_set_list)
-		blk_mq_freeze_queue_nomemsave(q);
-
 	list_for_each_entry(q, &set->tag_list, tag_set_list) {
 		blk_mq_debugfs_unregister_hctxs(q);
 		blk_mq_sysfs_unregister_hctxs(q);
 	}
 
+	memflags = memalloc_noio_save();
+	list_for_each_entry(q, &set->tag_list, tag_set_list)
+		blk_mq_freeze_queue_nomemsave(q);
+
 	if (blk_mq_realloc_tag_set_tags(set, nr_hw_queues) < 0)
 		goto reregister;
 
@@ -4977,12 +4977,6 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
 		blk_mq_map_swqueue(q);
 	}
 
-reregister:
-	list_for_each_entry(q, &set->tag_list, tag_set_list) {
-		blk_mq_sysfs_register_hctxs(q);
-		blk_mq_debugfs_register_hctxs(q);
-	}
-
 	list_for_each_entry(q, &set->tag_list, tag_set_list) {
 		/*
 		 * nr_hw_queues is changed and elevator data depends on
@@ -5006,6 +5000,12 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
 	}
 	memalloc_noio_restore(memflags);
 
+reregister:
+	list_for_each_entry(q, &set->tag_list, tag_set_list) {
+		blk_mq_sysfs_register_hctxs(q);
+		blk_mq_debugfs_register_hctxs(q);
+	}
+
 	/* Free the excess tags when nr_hw_queues shrink. */
 	for (i = set->nr_hw_queues; i < prev_nr_hw_queues; i++)
 		__blk_mq_free_map_and_rqs(set, i);
-- 
2.47.0