[PATCH 4/5] s390/dasd: Fix read inconsistency for ESE DASD devices

[Stefan Haberland <sth@linux.ibm.com>]

From: Jan Höppner <hoeppner@linux.ibm.com>

Read requests that return with NRF error are partially completed in
dasd_eckd_ese_read(). The function keeps track of the amount of
processed bytes and the driver will eventually return this information
back to the block layer for further processing via __dasd_cleanup_cqr()
when the request is in the final stage of processing (from the driver's
perspective).

For this, blk_update_request() is used which requires the number of
bytes to complete the request. As per documentation the nr_bytes
parameter is described as follows:
   "number of bytes to complete for @req".

This was mistakenly interpreted as "number of bytes _left_ for @req"
leading to new requests with incorrect data length. The consequence are
inconsistent and completely wrong read requests as data from random
memory areas are read back.

Fix this by correctly specifying the amount of bytes that should be used
to complete the request.

Fixes: 5e6bdd37c552 ("s390/dasd: fix data corruption for thin provisioned devices")
Cc: stable@vger.kernel.org # 5.3+
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
---
 drivers/s390/block/dasd.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/s390/block/dasd.c b/drivers/s390/block/dasd.c
index d62a4c673962..ba6d78789660 100644
--- a/drivers/s390/block/dasd.c
+++ b/drivers/s390/block/dasd.c
@@ -2778,8 +2778,7 @@ static void __dasd_cleanup_cqr(struct dasd_ccw_req *cqr)
 		 * complete a request partially.
 		 */
 		if (proc_bytes) {
-			blk_update_request(req, BLK_STS_OK,
-					   blk_rq_bytes(req) - proc_bytes);
+			blk_update_request(req, BLK_STS_OK, proc_bytes);
 			blk_mq_requeue_request(req, true);
 		} else if (likely(!blk_should_fake_timeout(req->q))) {
 			blk_mq_complete_request(req);
-- 
2.32.0