Commit 01b91bf1 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

block: don't grab elevator lock during queue initialization 

->elevator_lock depends on queue freeze lock, see block/blk-sysfs.c.

queue freeze lock depends on fs_reclaim.

So don't grab elevator lock during queue initialization which needs to
call kmalloc(GFP_KERNEL), and we can cut the dependency between
->elevator_lock and fs_reclaim, then the lockdep warning can be killed.

This way is safe because elevator setting isn't ready to run during
queue initialization.

There isn't such issue in __blk_mq_update_nr_hw_queues() because
memalloc_noio_save() is called before acquiring elevator lock.

Fixes the following lockdep warning:

https://lore.kernel.org/linux-block/67e6b425.050a0220.2f068f.007b.GAE@google.com/



Reported-by: default avatar <syzbot+4c7e0f9b94ad65811efb@syzkaller.appspotmail.com>
Cc: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250403105402.1334206-1-ming.lei@redhat.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent fb585552

block/blk-mq.c

+17 −7
Original line number Diff line number Diff line
@@ -4464,14 +4464,12 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx( 
	return NULL;

}



static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,

static void __blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,

				     struct request_queue *q)

{

	struct blk_mq_hw_ctx *hctx;

	unsigned long i, j;



	/* protect against switching io scheduler  */

	mutex_lock(&q->elevator_lock);

	for (i = 0; i < set->nr_hw_queues; i++) {

		int old_node;

		int node = blk_mq_get_hctx_node(set, i);
@@ -4504,7 +4502,19 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, 


	xa_for_each_start(&q->hctx_table, j, hctx, j)

		blk_mq_exit_hctx(q, set, hctx, j);

}



static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,

				   struct request_queue *q, bool lock)

{

	if (lock) {

		/* protect against switching io scheduler  */

		mutex_lock(&q->elevator_lock);

		__blk_mq_realloc_hw_ctxs(set, q);

		mutex_unlock(&q->elevator_lock);

	} else {

		__blk_mq_realloc_hw_ctxs(set, q);

	}



	/* unregister cpuhp callbacks for exited hctxs */

	blk_mq_remove_hw_queues_cpuhp(q);
@@ -4536,7 +4546,7 @@ int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set, 


	xa_init(&q->hctx_table);



	blk_mq_realloc_hw_ctxs(set, q);

	blk_mq_realloc_hw_ctxs(set, q, false);

	if (!q->nr_hw_queues)

		goto err_hctxs;
@@ -5032,7 +5042,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, 
fallback:

	blk_mq_update_queue_map(set);

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

		blk_mq_realloc_hw_ctxs(set, q);

		blk_mq_realloc_hw_ctxs(set, q, true);



		if (q->nr_hw_queues != set->nr_hw_queues) {

			int i = prev_nr_hw_queues;