s390/dasd: Use correct lock while counting channel queue length

The lock around counting the channel queue length in the BIODASDINFO
ioctl was incorrectly changed to the dasd_block->queue_lock with commit
583d653 ("dasd: remove dead code"). This can lead to endless list
iterations and a subsequent crash.

The queue_lock is supposed to be used only for queue lists belonging to
dasd_block. For dasd_device related queue lists the ccwdev lock must be
used.

Fix the mentioned issues by correctly using the ccwdev lock instead of
the queue lock.

Fixes: 583d653 ("dasd: remove dead code")
Cc: [email protected] # v5.0+
Signed-off-by: Jan Höppner <[email protected]>
Reviewed-by: Stefan Haberland <[email protected]>
Signed-off-by: Stefan Haberland <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: hoeppnerj

drivers/s390/block/dasd_ioctl.c

@@ -552,10 +552,10 @@ static int __dasd_ioctl_information(struct dasd_block *block,
 
 	memcpy(dasd_info->type, base->discipline->name, 4);
 
-	spin_lock_irqsave(&block->queue_lock, flags);
+	spin_lock_irqsave(get_ccwdev_lock(base->cdev), flags);
 	list_for_each(l, &base->ccw_queue)
 		dasd_info->chanq_len++;
-	spin_unlock_irqrestore(&block->queue_lock, flags);
+	spin_unlock_irqrestore(get_ccwdev_lock(base->cdev), flags);
 	return 0;
 }