vfio: ccw: fix error return in vfio_ccw_sch_event

If the device has not been registered, or there is work pending,
we should reschedule a sch_event call again.
Signed-off-by: NDong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Message-Id: <20180502072559.50691-1-bjsdjshi@linux.vnet.ibm.com>
Reviewed-by: NCornelia Huck <cohuck@redhat.com>
Signed-off-by: NCornelia Huck <cohuck@redhat.com>

drivers/s390/cio/vfio_ccw_drv.c

@@ -177,6 +177,7 @@ static int vfio_ccw_sch_event(struct subchannel *sch, int process)
 {
 	struct vfio_ccw_private *private = dev_get_drvdata(&sch->dev);
 	unsigned long flags;
+	int rc = -EAGAIN;
 
 	spin_lock_irqsave(sch->lock, flags);
 	if (!device_is_registered(&sch->dev))
@@ -187,6 +188,7 @@ static int vfio_ccw_sch_event(struct subchannel *sch, int process)
 
 	if (cio_update_schib(sch)) {
 		vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_NOT_OPER);
+		rc = 0;
 		goto out_unlock;
 	}
 
@@ -195,11 +197,12 @@ static int vfio_ccw_sch_event(struct subchannel *sch, int process)
 		private->state = private->mdev ? VFIO_CCW_STATE_IDLE :
 				 VFIO_CCW_STATE_STANDBY;
 	}
+	rc = 0;
 
 out_unlock:
 	spin_unlock_irqrestore(sch->lock, flags);
 
-	return 0;
+	return rc;
 }
 
 static struct css_device_id vfio_ccw_sch_ids[] = {