block: release q->elevator_lock in ioc_qos_write

JIRA: https://issues.redhat.com/browse/RHEL-112997

commit 89ed5fa
Author: Nilay Shroff <nilay@linux.ibm.com>
Date:   Wed Mar 19 16:23:45 2025 +0530

    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 <oliver.sang@intel.com>
    Closes: https://lore.kernel.org/oe-lkp/202503171650.cc082b66-lkp@intel.com
    Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
    Reviewed-by: Ming Lei <ming.lei@redhat.com>
    Link: https://lore.kernel.org/r/20250319105518.468941-2-nilay@linux.ibm.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Author: Ming Lei

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);