[S390] dasd: prevent panic with unresumed devices

If a device is not resumed correctly the system crashes when this
device is set offline. This may happen if it gets disconnected
during suspend.
Check if the device is already removed from alias handling and skip
these steps to prevent the kernel panic.

Signed-off-by: Stefan Haberland <stefan.haberland@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/block/dasd_alias.c

@@ -319,6 +319,9 @@ void dasd_alias_disconnect_device_from_lcu(struct dasd_device *device)
 
 	private = (struct dasd_eckd_private *) device->private;
 	lcu = private->lcu;
+	/* nothing to do if already disconnected */
+	if (!lcu)
+		return;
 	device->discipline->get_uid(device, &uid);
 	spin_lock_irqsave(&lcu->lock, flags);
 	list_del_init(&device->alias_list);
@@ -680,6 +683,9 @@ int dasd_alias_remove_device(struct dasd_device *device)
 
 	private = (struct dasd_eckd_private *) device->private;
 	lcu = private->lcu;
+	/* nothing to do if already removed */
+	if (!lcu)
+		return 0;
 	spin_lock_irqsave(&lcu->lock, flags);
 	_remove_device_from_lcu(lcu, device);
 	spin_unlock_irqrestore(&lcu->lock, flags);