s390/dasd: prevent inconsistent LCU device data

Prevent _lcu_update from adding a device to a pavgroup if the LCU still
requires an update. The data is not reliable any longer and in parallel
devices might have been moved on the lists already.
This might lead to list corruptions or invalid PAV grouping.
Only add devices to a pavgroup if the LCU is up to date. Additional steps
are taken by the scheduled lcu update.

Fixes: 8e09f215 ("[S390] dasd: add hyper PAV support to DASD device driver, part 1")
Cc: stable@vger.kernel.org
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Jan Hoeppner <hoeppner@linux.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/s390/block/dasd_alias.c

@@ -511,6 +511,14 @@ static int _lcu_update(struct dasd_device *refdev, struct alias_lcu *lcu)
 		return rc;
 
 	spin_lock_irqsave(&lcu->lock, flags);
+	/*
+	 * there is another update needed skip the remaining handling
+	 * the data might already be outdated
+	 * but especially do not add the device to an LCU with pending
+	 * update
+	 */
+	if (lcu->flags & NEED_UAC_UPDATE)
+		goto out;
 	lcu->pav = NO_PAV;
 	for (i = 0; i < MAX_DEVICES_PER_LCU; ++i) {
 		switch (lcu->uac->unit[i].ua_type) {
@@ -529,6 +537,7 @@ static int _lcu_update(struct dasd_device *refdev, struct alias_lcu *lcu)
 				 alias_list) {
 		_add_device_to_lcu(lcu, device, refdev);
 	}
+out:
 	spin_unlock_irqrestore(&lcu->lock, flags);
 	return 0;
 }