Commit 9dc7a882 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

block: move hctx debugfs/sysfs registering out of freezing queue 



Move hctx 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 hctx debugfs/sysfs does not require queue to
be frozen:

- hctx sysfs attributes show() are drained when removing kobject, and
  there isn't store() implementation for hctx sysfs attributes

- debugfs entry read() is drained too when removing debugfs directory,
  and there isn't write() implementation for hctx debugfs too

- so it is safe to register/unregister hctx sysfs/debugfs without
  freezing queue because the cod paths changes nothing, and we just
  need to keep hctx live

Reviewed-by: default avatarHannes Reinecke <hare@suse.de>
Reviewed-by: default avatarNilay Shroff <nilay@linux.ibm.com>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250505141805.2751237-23-ming.lei@redhat.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 559dc111

block/blk-mq.c

+7 −8
Original line number Diff line number Diff line
@@ -5005,14 +5005,14 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, 
		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);

	}



	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;
@@ -5035,16 +5035,15 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, 
		blk_mq_map_swqueue(q);

	}



	/* elv_update_nr_hw_queues() unfreeze queue for us */

	list_for_each_entry(q, &set->tag_list, tag_set_list)

		elv_update_nr_hw_queues(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);

	}



	/* elv_update_nr_hw_queues() unfreeze queue for us */

	list_for_each_entry(q, &set->tag_list, tag_set_list)

		elv_update_nr_hw_queues(q);



	memalloc_noio_restore(memflags);



	/* Free the excess tags when nr_hw_queues shrink. */