block: release q->elevator_lock in ioc_qos_write

The ioc_qos_write method acquires q->elevator_lock to protect
updates to blk-wbt parameters. Once these updates are complete,
the lock should be released before returning from ioc_qos_write.

However, in one code path, the release of q->elevator_lock was
mistakenly omitted, potentially leading to a lock leak. This commit
fixes the issue by ensuring that q->elevator_lock is properly
released in all return paths of ioc_qos_write.

Fixes: 245618f ("block: protect wbt_lat_usec using q->elevator_lock")
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-lkp/[email protected]
Signed-off-by: Nilay Shroff <[email protected]>
Reviewed-by: Ming Lei <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: shroffni

block/blk-iocost.c

@@ -3348,6 +3348,7 @@ static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
 		wbt_enable_default(disk);
 
 	blk_mq_unquiesce_queue(disk->queue);
+	mutex_unlock(&disk->queue->elevator_lock);
 	blk_mq_unfreeze_queue(disk->queue, memflags);
 
 	blkg_conf_exit(&ctx);