Commit 78c27134 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

block: move wbt_enable_default() out of queue freezing from sched ->exit() 



scheduler's ->exit() is called with queue frozen and elevator lock is held, and
wbt_enable_default() can't be called with queue frozen, otherwise the
following lockdep warning is triggered:

	#6 (&q->rq_qos_mutex){+.+.}-{4:4}:
	#5 (&eq->sysfs_lock){+.+.}-{4:4}:
	#4 (&q->elevator_lock){+.+.}-{4:4}:
	#3 (&q->q_usage_counter(io)#3){++++}-{0:0}:
	#2 (fs_reclaim){+.+.}-{0:0}:
	#1 (&sb->s_type->i_mutex_key#3){+.+.}-{4:4}:
	#0 (&q->debugfs_mutex){+.+.}-{4:4}:

Fix the issue by moving wbt_enable_default() out of bfq's exit(), and
call it from elevator_change_done().

Meantime add disk->rqos_state_mutex for covering wbt state change, which
matches the purpose more than ->elevator_lock.

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/20250505141805.2751237-26-ming.lei@redhat.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 7ed7fa56

block/bfq-iosched.c

+1 −1
Original line number Diff line number Diff line
@@ -7211,7 +7211,7 @@ static void bfq_exit_queue(struct elevator_queue *e) 


	blk_stat_disable_accounting(bfqd->queue);

	blk_queue_flag_clear(QUEUE_FLAG_DISABLE_WBT_DEF, bfqd->queue);

	wbt_enable_default(bfqd->queue->disk);

	set_bit(ELEVATOR_FLAG_ENABLE_WBT_ON_EXIT, &e->flags);



	kfree(bfqd);

}

block/blk-sysfs.c

+4 −6
Original line number Diff line number Diff line
@@ -560,7 +560,7 @@ static ssize_t queue_wb_lat_show(struct gendisk *disk, char *page) 
	ssize_t ret;

	struct request_queue *q = disk->queue;



	mutex_lock(&q->elevator_lock);

	mutex_lock(&disk->rqos_state_mutex);

	if (!wbt_rq_qos(q)) {

		ret = -EINVAL;

		goto out;
@@ -573,7 +573,7 @@ static ssize_t queue_wb_lat_show(struct gendisk *disk, char *page) 


	ret = sysfs_emit(page, "%llu\n", div_u64(wbt_get_min_lat(q), 1000));

out:

	mutex_unlock(&q->elevator_lock);

	mutex_unlock(&disk->rqos_state_mutex);

	return ret;

}
@@ -593,7 +593,6 @@ static ssize_t queue_wb_lat_store(struct gendisk *disk, const char *page, 
		return -EINVAL;



	memflags = blk_mq_freeze_queue(q);

	mutex_lock(&q->elevator_lock);



	rqos = wbt_rq_qos(q);

	if (!rqos) {
@@ -618,11 +617,12 @@ static ssize_t queue_wb_lat_store(struct gendisk *disk, const char *page, 
	 */

	blk_mq_quiesce_queue(q);



	mutex_lock(&disk->rqos_state_mutex);

	wbt_set_min_lat(q, val);

	mutex_unlock(&disk->rqos_state_mutex);



	blk_mq_unquiesce_queue(q);

out:

	mutex_unlock(&q->elevator_lock);

	blk_mq_unfreeze_queue(q, memflags);



	return ret;
@@ -871,9 +871,7 @@ int blk_register_queue(struct gendisk *disk) 


	if (queue_is_mq(q))

		elevator_set_default(q);

	mutex_lock(&q->elevator_lock);

	wbt_enable_default(disk);

	mutex_unlock(&q->elevator_lock);



	blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q);

block/blk-wbt.c

+6 −0
Original line number Diff line number Diff line
@@ -704,6 +704,8 @@ void wbt_enable_default(struct gendisk *disk) 
	struct rq_qos *rqos;

	bool enable = IS_ENABLED(CONFIG_BLK_WBT_MQ);



	mutex_lock(&disk->rqos_state_mutex);



	if (blk_queue_disable_wbt(q))

		enable = false;
@@ -712,8 +714,10 @@ void wbt_enable_default(struct gendisk *disk) 
	if (rqos) {

		if (enable && RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT)

			RQWB(rqos)->enable_state = WBT_STATE_ON_DEFAULT;

		mutex_unlock(&disk->rqos_state_mutex);

		return;

	}

	mutex_unlock(&disk->rqos_state_mutex);



	/* Queue not registered? Maybe shutting down... */

	if (!blk_queue_registered(q))
@@ -773,11 +777,13 @@ void wbt_disable_default(struct gendisk *disk) 
	struct rq_wb *rwb;

	if (!rqos)

		return;

	mutex_lock(&disk->rqos_state_mutex);

	rwb = RQWB(rqos);

	if (rwb->enable_state == WBT_STATE_ON_DEFAULT) {

		blk_stat_deactivate(rwb->cb);

		rwb->enable_state = WBT_STATE_OFF_DEFAULT;

	}

	mutex_unlock(&disk->rqos_state_mutex);

}

EXPORT_SYMBOL_GPL(wbt_disable_default);

block/elevator.c

+5 −0
Original line number Diff line number Diff line
@@ -637,8 +637,13 @@ static int elevator_change_done(struct request_queue *q, 
	int ret = 0;



	if (ctx->old) {

		bool enable_wbt = test_bit(ELEVATOR_FLAG_ENABLE_WBT_ON_EXIT,

				&ctx->old->flags);



		elv_unregister_queue(q, ctx->old);

		kobject_put(&ctx->old->kobj);

		if (enable_wbt)

			wbt_enable_default(q->disk);

	}

	if (ctx->new) {

		ret = elv_register_queue(q, ctx->new, !ctx->no_uevent);

block/elevator.h

+1 −0
Original line number Diff line number Diff line
@@ -122,6 +122,7 @@ struct elevator_queue 


#define ELEVATOR_FLAG_REGISTERED	0

#define ELEVATOR_FLAG_DYING		1

#define ELEVATOR_FLAG_ENABLE_WBT_ON_EXIT	2



/*

 * block elevator interface