Commit a3996d11 authored by Nilay Shroff's avatar Nilay Shroff Committed by Jens Axboe
Browse files

block: protect debugfs attrs using elevator_lock instead of sysfs_lock 



Currently, the block debugfs attributes (tags, tags_bitmap, sched_tags,
and sched_tags_bitmap) are protected using q->sysfs_lock. However, these
attributes are updated in multiple scenarios:
- During driver probe method
- During an elevator switch/update
- During an nr_hw_queues update
- When writing to the sysfs attribute nr_requests

All these update paths (except driver probe method, which doesn't
require any protection) are already protected using q->elevator_lock. To
ensure consistency and proper synchronization, replace q->sysfs_lock
with q->elevator_lock for protecting these debugfs attributes.

Signed-off-by: default avatarNilay Shroff <nilay@linux.ibm.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250313115235.3707600-2-nilay@linux.ibm.com


[axboe: some commit message rewording/fixes]
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 75618ac6

block/blk-mq-debugfs.c

+8 −8
Original line number Diff line number Diff line
@@ -400,12 +400,12 @@ static int hctx_tags_show(void *data, struct seq_file *m) 
	struct request_queue *q = hctx->queue;

	int res;



	res = mutex_lock_interruptible(&q->sysfs_lock);

	res = mutex_lock_interruptible(&q->elevator_lock);

	if (res)

		goto out;

	if (hctx->tags)

		blk_mq_debugfs_tags_show(m, hctx->tags);

	mutex_unlock(&q->sysfs_lock);

	mutex_unlock(&q->elevator_lock);



out:

	return res;
@@ -417,12 +417,12 @@ static int hctx_tags_bitmap_show(void *data, struct seq_file *m) 
	struct request_queue *q = hctx->queue;

	int res;



	res = mutex_lock_interruptible(&q->sysfs_lock);

	res = mutex_lock_interruptible(&q->elevator_lock);

	if (res)

		goto out;

	if (hctx->tags)

		sbitmap_bitmap_show(&hctx->tags->bitmap_tags.sb, m);

	mutex_unlock(&q->sysfs_lock);

	mutex_unlock(&q->elevator_lock);



out:

	return res;
@@ -434,12 +434,12 @@ static int hctx_sched_tags_show(void *data, struct seq_file *m) 
	struct request_queue *q = hctx->queue;

	int res;



	res = mutex_lock_interruptible(&q->sysfs_lock);

	res = mutex_lock_interruptible(&q->elevator_lock);

	if (res)

		goto out;

	if (hctx->sched_tags)

		blk_mq_debugfs_tags_show(m, hctx->sched_tags);

	mutex_unlock(&q->sysfs_lock);

	mutex_unlock(&q->elevator_lock);



out:

	return res;
@@ -451,12 +451,12 @@ static int hctx_sched_tags_bitmap_show(void *data, struct seq_file *m) 
	struct request_queue *q = hctx->queue;

	int res;



	res = mutex_lock_interruptible(&q->sysfs_lock);

	res = mutex_lock_interruptible(&q->elevator_lock);

	if (res)

		goto out;

	if (hctx->sched_tags)

		sbitmap_bitmap_show(&hctx->sched_tags->bitmap_tags.sb, m);

	mutex_unlock(&q->sysfs_lock);

	mutex_unlock(&q->elevator_lock);



out:

	return res;

include/linux/blkdev.h

+3 −3
Original line number Diff line number Diff line
@@ -566,9 +566,9 @@ struct request_queue { 
	 * nr_requests and wbt latency, this lock also protects the sysfs attrs

	 * nr_requests and wbt_lat_usec. Additionally the nr_hw_queues update

	 * may modify hctx tags, reserved-tags and cpumask, so this lock also

	 * helps protect the hctx attrs. To ensure proper locking order during

	 * an elevator or nr_hw_queue update, first freeze the queue, then

	 * acquire ->elevator_lock.

	 * helps protect the hctx sysfs/debugfs attrs. To ensure proper locking

	 * order during an elevator or nr_hw_queue update, first freeze the

	 * queue, then acquire ->elevator_lock.

	 */

	struct mutex		elevator_lock;