[PATCH 5.4.y] s390/dasd: Use correct lock while counting channel queue length

["Jan Höppner" <hoeppner@linux.ibm.com>]

The lock around counting the channel queue length in the BIODASDINFO
ioctl was incorrectly changed to the dasd_block->queue_lock with commit
583d6535cb9d ("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: 583d6535cb9d ("dasd: remove dead code")
Cc: stable@vger.kernel.org # v5.0+
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://lore.kernel.org/r/20230609153750.1258763-2-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(cherry picked from commit ccc45cb4e7271c74dbb27776ae8f73d84557f5c6)
---
 drivers/s390/block/dasd_ioctl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/block/dasd_ioctl.c b/drivers/s390/block/dasd_ioctl.c
index 9a5f3add325f..c995dae5cc6f 100644
--- a/drivers/s390/block/dasd_ioctl.c
+++ b/drivers/s390/block/dasd_ioctl.c
@@ -516,10 +516,10 @@ 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);
 
 	rc = 0;
 	if (copy_to_user(argp, dasd_info,
-- 
2.39.2