Commit 626ff4f8 authored by Yu Kuai's avatar Yu Kuai Committed by Jens Axboe
Browse files

blk-mq: convert to serialize updating nr_requests with update_nr_hwq_lock 



request_queue->nr_requests can be changed by:

a) switch elevator by updating nr_hw_queues
b) switch elevator by elevator sysfs attribute
c) configue queue sysfs attribute nr_requests

Current lock order is:

1) update_nr_hwq_lock, case a,b
2) freeze_queue
3) elevator_lock, case a,b,c

And update nr_requests is seriablized by elevator_lock() already,
however, in the case c, we'll have to allocate new sched_tags if
nr_requests grow, and do this with elevator_lock held and queue
freezed has the risk of deadlock.

Hence use update_nr_hwq_lock instead, make it possible to allocate
memory if tags grow, meanwhile also prevent nr_requests to be changed
concurrently.

Signed-off-by: default avatarYu Kuai <yukuai3@huawei.com>
Reviewed-by: default avatarNilay Shroff <nilay@linux.ibm.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent b46d4c44

block/blk-sysfs.c

+20 −5
Original line number Diff line number Diff line
@@ -68,13 +68,17 @@ queue_requests_store(struct gendisk *disk, const char *page, size_t count) 
	int ret, err;

	unsigned int memflags;

	struct request_queue *q = disk->queue;

	struct blk_mq_tag_set *set = q->tag_set;



	ret = queue_var_store(&nr, page, count);

	if (ret < 0)

		return ret;



	memflags = blk_mq_freeze_queue(q);

	mutex_lock(&q->elevator_lock);

	/*

	 * Serialize updating nr_requests with concurrent queue_requests_store()

	 * and switching elevator.

	 */

	down_write(&set->update_nr_hwq_lock);



	if (nr == q->nr_requests)

		goto unlock;
@@ -82,20 +86,31 @@ queue_requests_store(struct gendisk *disk, const char *page, size_t count) 
	if (nr < BLKDEV_MIN_RQ)

		nr = BLKDEV_MIN_RQ;



	if (nr <= q->tag_set->reserved_tags ||

	/*

	 * Switching elevator is protected by update_nr_hwq_lock:

	 *  - read lock is held from elevator sysfs attribute;

	 *  - write lock is held from updating nr_hw_queues;

	 * Hence it's safe to access q->elevator here with write lock held.

	 */

	if (nr <= set->reserved_tags ||

	    (q->elevator && nr > MAX_SCHED_RQ) ||

	    (!q->elevator && nr > q->tag_set->queue_depth)) {

	    (!q->elevator && nr > set->queue_depth)) {

		ret = -EINVAL;

		goto unlock;

	}



	memflags = blk_mq_freeze_queue(q);

	mutex_lock(&q->elevator_lock);



	err = blk_mq_update_nr_requests(disk->queue, nr);

	if (err)

		ret = err;



unlock:

	mutex_unlock(&q->elevator_lock);

	blk_mq_unfreeze_queue(q, memflags);



unlock:

	up_write(&set->update_nr_hwq_lock);

	return ret;

}