Commit 0a47d2b4 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

block: don't acquire ->elevator_lock in blk_mq_map_swqueue and blk_mq_realloc_hw_ctxs 



Both blk_mq_map_swqueue() and blk_mq_realloc_hw_ctxs() are called before
the request queue is added to tagset list, so the two won't run concurrently
with blk_mq_update_nr_hw_queues().

When the two functions are only called from queue initialization or
blk_mq_update_nr_hw_queues(), elevator switch can't happen.

So remove ->elevator_lock uses from the two functions.

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>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250505141805.2751237-24-ming.lei@redhat.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 9dc7a882

block/blk-mq.c

+4 −15
Original line number Diff line number Diff line
@@ -4156,8 +4156,6 @@ static void blk_mq_map_swqueue(struct request_queue *q) 
	struct blk_mq_ctx *ctx;

	struct blk_mq_tag_set *set = q->tag_set;



	mutex_lock(&q->elevator_lock);



	queue_for_each_hw_ctx(q, hctx, i) {

		cpumask_clear(hctx->cpumask);

		hctx->nr_ctx = 0;
@@ -4262,8 +4260,6 @@ static void blk_mq_map_swqueue(struct request_queue *q) 
		hctx->next_cpu = blk_mq_first_mapped_cpu(hctx);

		hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;

	}



	mutex_unlock(&q->elevator_lock);

}



/*
@@ -4567,16 +4563,9 @@ 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, bool lock)

				   struct request_queue *q)

{

	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);
@@ -4608,7 +4597,7 @@ int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set, 


	xa_init(&q->hctx_table);



	blk_mq_realloc_hw_ctxs(set, q, false);

	blk_mq_realloc_hw_ctxs(set, q);

	if (!q->nr_hw_queues)

		goto err_hctxs;
@@ -5019,7 +5008,7 @@ 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, true);

		blk_mq_realloc_hw_ctxs(set, q);



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

			int i = prev_nr_hw_queues;