[S390] permanent subchannel busy conditions may cause I/O stall

In special conditions where a subchannel rejects the HALT I/O-
instruction with a busy indication (cc 2), I/O may stall.
I/O request termination logic retries HALT I/O indefinitely
because it expects HALT I/O to alter the subchannel status which
is not true when cc 2 is returned.
In case of a busy indication, try CLEAR I/O instruction immediately.
Signed-off-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/cio/device_fsm.c

@@ -152,6 +152,7 @@ ccw_device_cancel_halt_clear(struct ccw_device *cdev)
 		if (cdev->private->iretry) {
 			cdev->private->iretry--;
 			ret = cio_halt(sch);
+			if (ret != -EBUSY)
 				return (ret == 0) ? -EBUSY : ret;
 		}
 		/* halt io unsuccessful. */