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

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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: Hannes Reinecke <hare@suse.de>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250505141805.2751237-23-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2025-05-05 22:18:00 +08:00 committed by Jens Axboe
parent 559dc11143
commit 9dc7a882ce
1 changed files with 7 additions and 8 deletions
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15
block/blk-mq.c
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@ -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. */