scsi: core: Clear driver private data when retrying request

After commit 1bad6c4a57ef ("scsi: zero per-cmd private driver data for each
MQ I/O"), the xen-scsifront/virtio_scsi/snic drivers all removed code that
explicitly zeroed driver-private command data.

In combination with commit 464a00c9e0ad ("scsi: core: Kill DRIVER_SENSE"),
after virtio_scsi performs a capacity expansion, the first request will
return a unit attention to indicate that the capacity has changed. And then
the original command is retried. As driver-private command data was not
cleared, the request would return UA again and eventually time out and fail.

Zero driver-private command data when a request is retried.

Fixes: f7de50da1479 ("scsi: xen-scsifront: Remove code that zeroes driver-private command data")
Fixes: c2bb87318baa ("scsi: virtio_scsi: Remove code that zeroes driver-private command data")
Fixes: c3006a926468 ("scsi: snic: Remove code that zeroes driver-private command data")
Signed-off-by: Ye Bin <[e-mail]>
Reviewed-by: Bart Van Assche <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/scsi_lib.c

···
 	if (in_flight)
 		__set_bit(SCMD_STATE_INFLIGHT, &cmd->state);
 
-	/*
-	 * Only clear the driver-private command data if the LLD does not supply
-	 * a function to initialize that data.
-	 */
-	if (!shost->hostt->init_cmd_priv)
-		memset(cmd + 1, 0, shost->hostt->cmd_size);
-
 	cmd->prot_op = SCSI_PROT_NORMAL;
 	if (blk_rq_bytes(req))
 		cmd->sc_data_direction = rq_dma_dir(req);
···
 	}
 	if (!scsi_host_queue_ready(q, shost, sdev, cmd))
 		goto out_dec_target_busy;
+
+	/*
+	 * Only clear the driver-private command data if the LLD does not supply
+	 * a function to initialize that data.
+	 */
+	if (shost->hostt->cmd_size && !shost->hostt->init_cmd_priv)
+		memset(cmd + 1, 0, shost->hostt->cmd_size);
 
 	if (!(req->rq_flags & RQF_DONTPREP)) {
 		ret = scsi_prepare_cmd(req);