Commit 3c17a346 authored by Yu Kuai's avatar Yu Kuai Committed by Jens Axboe
Browse files

blk-rq-qos: fix possible debugfs_mutex deadlock 



Currently rq-qos debugfs entries are created from rq_qos_add(), while
rq_qos_add() can be called while queue is still frozen. This can
deadlock because creating new entries can trigger fs reclaim.

Fix this problem by delaying creating rq-qos debugfs entries after queue
is unfrozen.

- For wbt, 1) it can be initialized by default, fix it by calling new
  helper after wbt_init() from wbt_init_enable_default(); 2) it can be
  initialized by sysfs, fix it by calling new helper after queue is
  unfrozen from wbt_set_lat().
- For iocost and iolatency, they can only be initialized by blkcg
  configuration, however, they don't have debugfs entries for now, hence
  they are not handled yet.

Signed-off-by: default avatarYu Kuai <yukuai@fnnas.com>
Reviewed-by: default avatarNilay Shroff <nilay@linux.ibm.com>
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Reviewed-by: default avatarHannes Reinecke <hare@suse.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 3f0bea9f

block/blk-rq-qos.c

+0 −7
Original line number Diff line number Diff line
@@ -347,13 +347,6 @@ int rq_qos_add(struct rq_qos *rqos, struct gendisk *disk, enum rq_qos_id id, 
	blk_queue_flag_set(QUEUE_FLAG_QOS_ENABLED, q);



	blk_mq_unfreeze_queue(q, memflags);



	if (rqos->ops->debugfs_attrs) {

		mutex_lock(&q->debugfs_mutex);

		blk_mq_debugfs_register_rqos(rqos);

		mutex_unlock(&q->debugfs_mutex);

	}



	return 0;

ebusy:

	blk_mq_unfreeze_queue(q, memflags);

block/blk-wbt.c

+12 −1
Original line number Diff line number Diff line
@@ -774,6 +774,7 @@ EXPORT_SYMBOL_GPL(wbt_enable_default); 


void wbt_init_enable_default(struct gendisk *disk)

{

	struct request_queue *q = disk->queue;

	struct rq_wb *rwb;



	if (!__wbt_enable_default(disk))
@@ -783,8 +784,14 @@ void wbt_init_enable_default(struct gendisk *disk) 
	if (WARN_ON_ONCE(!rwb))

		return;



	if (WARN_ON_ONCE(wbt_init(disk, rwb)))

	if (WARN_ON_ONCE(wbt_init(disk, rwb))) {

		wbt_free(rwb);

		return;

	}



	mutex_lock(&q->debugfs_mutex);

	blk_mq_debugfs_register_rq_qos(q);

	mutex_unlock(&q->debugfs_mutex);

}



static u64 wbt_default_latency_nsec(struct request_queue *q)
@@ -1008,5 +1015,9 @@ int wbt_set_lat(struct gendisk *disk, s64 val) 
	blk_mq_unquiesce_queue(q);

out:

	blk_mq_unfreeze_queue(q, memflags);

	mutex_lock(&q->debugfs_mutex);

	blk_mq_debugfs_register_rq_qos(q);

	mutex_unlock(&q->debugfs_mutex);



	return ret;

}