Commit 3efe7571 authored by Nilay Shroff's avatar Nilay Shroff Committed by Jens Axboe
Browse files

block: protect nr_requests update using q->elevator_lock 



The sysfs attribute nr_requests could be simultaneously updated from
elevator switch/update or nr_hw_queue update code path. The update to
nr_requests for each of those code paths runs holding q->elevator_lock.
So we should protect access to sysfs attribute nr_requests using q->
elevator_lock instead of q->sysfs_lock.

Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarHannes Reinecke <hare@suse.de>
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarNilay Shroff <nilay@linux.ibm.com>
Link: https://lore.kernel.org/r/20250304102551.2533767-6-nilay@linux.ibm.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 1bf70d08

block/blk-sysfs.c

+5 −5
Original line number Diff line number Diff line
@@ -55,9 +55,9 @@ static ssize_t queue_requests_show(struct gendisk *disk, char *page) 
{

	ssize_t ret;



	mutex_lock(&disk->queue->sysfs_lock);

	mutex_lock(&disk->queue->elevator_lock);

	ret = queue_var_show(disk->queue->nr_requests, page);

	mutex_unlock(&disk->queue->sysfs_lock);

	mutex_unlock(&disk->queue->elevator_lock);

	return ret;

}
@@ -76,16 +76,16 @@ queue_requests_store(struct gendisk *disk, const char *page, size_t count) 
	if (ret < 0)

		return ret;



	mutex_lock(&q->sysfs_lock);

	memflags = blk_mq_freeze_queue(q);

	mutex_lock(&q->elevator_lock);

	if (nr < BLKDEV_MIN_RQ)

		nr = BLKDEV_MIN_RQ;



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

	if (err)

		ret = err;

	mutex_unlock(&q->elevator_lock);

	blk_mq_unfreeze_queue(q, memflags);

	mutex_unlock(&q->sysfs_lock);

	return ret;

}
@@ -692,7 +692,6 @@ static struct attribute *blk_mq_queue_attrs[] = { 
	/*

	 * Attributes which are protected with q->sysfs_lock.

	 */

	&queue_requests_entry.attr,

#ifdef CONFIG_BLK_WBT

	&queue_wb_lat_entry.attr,

#endif
@@ -701,6 +700,7 @@ static struct attribute *blk_mq_queue_attrs[] = { 
	 * q->sysfs_lock.

	 */

	&elv_iosched_entry.attr,

	&queue_requests_entry.attr,



	/*

	 * Attributes which don't require locking.

include/linux/blkdev.h

+6 −4
Original line number Diff line number Diff line
@@ -561,10 +561,12 @@ struct request_queue { 
	struct list_head	flush_list;



	/*

	 * Protects against I/O scheduler switching, specifically when

	 * updating q->elevator. To ensure proper locking order during

	 * an elevator update, first freeze the queue, then acquire

	 * ->elevator_lock.

	 * Protects against I/O scheduler switching, particularly when

	 * updating q->elevator. Since the elevator update code path may

	 * also modify q->nr_requests, this lock also protects the sysfs

	 * attribute nr_requests.

	 * To ensure proper locking order during an elevator update, first

	 * freeze the queue, then acquire ->elevator_lock.

	 */

	struct mutex		elevator_lock;