s390/dasd: fix hanging DASD driver unbind

In case of an unbind of the DASD device driver the function
dasd_generic_remove() is called which shuts down the device.
Among others this functions removes the int_handler from the cdev.
During shutdown the device cancels all outstanding IO requests and waits
for completion of the clear request.
Unfortunately the clear interrupt will never be received when there is no
interrupt handler connected.

Fix by moving the int_handler removal after the call to the state machine
where no request or interrupt is outstanding.

Cc: stable@vger.kernel.org
Signed-off-by: NStefan Haberland <sth@linux.ibm.com>
Tested-by: NBjoern Walk <bwalk@linux.ibm.com>
Reviewed-by: NJan Hoeppner <hoeppner@linux.ibm.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/s390/block/dasd.c

@@ -3487,8 +3487,6 @@ void dasd_generic_remove(struct ccw_device *cdev)
 	struct dasd_device *device;
 	struct dasd_block *block;
 
-	cdev->handler = NULL;
-
 	device = dasd_device_from_cdev(cdev);
 	if (IS_ERR(device)) {
 		dasd_remove_sysfs_files(cdev);
@@ -3507,6 +3505,7 @@ void dasd_generic_remove(struct ccw_device *cdev)
 	 * no quite down yet.
 	 */
 	dasd_set_target_state(device, DASD_STATE_NEW);
+	cdev->handler = NULL;
 	/* dasd_delete_device destroys the device reference. */
 	block = device->block;
 	dasd_delete_device(device);