drbd: don't start a resync without access to up-to-date Data

In case both nodes are "inconsistent", invalidate would
have started a resync anyways, without a chance to ever
succeed, just filling the logs with warning messages.

Simply disallow that state change,
re-using the SS_NO_UP_TO_DATE_DISK return value.

This also changes the corresponding error string to
"Need access to UpToDate Data" -- I found the
"Refusing to be Primary without at least one UpToDate disk"
answer misleading in some situations anyways.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_main.c

@@ -684,6 +684,9 @@ static int is_valid_state(struct drbd_conf *mdev, union drbd_state ns)
 	else if (ns.conn > C_CONNECTED && ns.pdsk < D_INCONSISTENT)
 		rv = SS_NO_REMOTE_DISK;
 
+	else if (ns.conn > C_CONNECTED && ns.disk < D_UP_TO_DATE && ns.pdsk < D_UP_TO_DATE)
+		rv = SS_NO_UP_TO_DATE_DISK;
+
 	else if ((ns.conn == C_CONNECTED ||
 		  ns.conn == C_WF_BITMAP_S ||
 		  ns.conn == C_SYNC_SOURCE ||

drivers/block/drbd/drbd_strings.c

@@ -70,7 +70,7 @@ static const char *drbd_disk_s_names[] = {
 
 static const char *drbd_state_sw_errors[] = {
 	[-SS_TWO_PRIMARIES] = "Multiple primaries not allowed by config",
-	[-SS_NO_UP_TO_DATE_DISK] = "Refusing to be Primary without at least one UpToDate disk",
+	[-SS_NO_UP_TO_DATE_DISK] = "Need access to UpToDate data",
 	[-SS_NO_LOCAL_DISK] = "Can not resync without local disk",
 	[-SS_NO_REMOTE_DISK] = "Can not resync without remote disk",
 	[-SS_CONNECTED_OUTDATES] = "Refusing to be Outdated while Connected",