scsi: core: set result when the command cannot be dispatched

When SCSI blk-mq is enabled, there is a bug in handling errors in
scsi_queue_rq.  Specifically, the bug is not setting result field of
scsi_request correctly when the dispatch of the command has been
failed. Since the upper layer code including the sg_io ioctl expects to
receive any error status from result field of scsi_request, the error is
silently ignored and this could cause data corruptions for some
applications.

Fixes: d285203c ("scsi: add support for a blk-mq based I/O path.")
Cc: <stable@vger.kernel.org>
Signed-off-by: Jaesoo Lee <jalee@purestorage.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_lib.c

@@ -1706,8 +1706,12 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
 			ret = BLK_STS_DEV_RESOURCE;
 		break;
 	default:
+		if (unlikely(!scsi_device_online(sdev)))
+			scsi_req(req)->result = DID_NO_CONNECT << 16;
+		else
+			scsi_req(req)->result = DID_ERROR << 16;
 		/*
-		 * Make sure to release all allocated ressources when
+		 * Make sure to release all allocated resources when
 		 * we hit an error, as we will never see this command
 		 * again.
 		 */