batman-adv: wait multiple periods before activating bla

For some reasons (bridge forward delay, network device setup order, etc)
the initial bridge loop avoidance announcement packets may be lost. This
may lead to problems in finding other backbone gws, and therfore create
loops in the startup time.

Fix this by extending the waiting periods to 3 (define can be changed)
before allowing broadcast traffic.

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Antonio Quartulli <ordex@autistici.org>

net/batman-adv/bridge_loop_avoidance.c

@@ -378,6 +378,7 @@ batadv_bla_get_backbone_gw(struct batadv_priv *bat_priv, uint8_t *orig,
 	entry->crc = BATADV_BLA_CRC_INIT;
 	entry->bat_priv = bat_priv;
 	atomic_set(&entry->request_sent, 0);
+	atomic_set(&entry->wait_periods, 0);
 	memcpy(entry->orig, orig, ETH_ALEN);
 
 	/* one for the hash, one for returning */
@@ -407,6 +408,7 @@ batadv_bla_get_backbone_gw(struct batadv_priv *bat_priv, uint8_t *orig,
 
 		/* this will be decreased in the worker thread */
 		atomic_inc(&entry->request_sent);
+		atomic_set(&entry->wait_periods, BATADV_BLA_WAIT_PERIODS);
 		atomic_inc(&bat_priv->bla.num_requests);
 	}
 
@@ -1148,12 +1150,17 @@ static void batadv_bla_periodic_work(struct work_struct *work)
 			 * problems when we are not yet known as backbone gw
 			 * in the backbone.
 			 *
-			 * We can reset this now and allow traffic again.
+			 * We can reset this now after we waited some periods
+			 * to give bridge forward delays and bla group forming
+			 * some grace time.
 			 */
 
 			if (atomic_read(&backbone_gw->request_sent) == 0)
 				continue;
 
+			if (!atomic_dec_and_test(&backbone_gw->wait_periods))
+				continue;
+
 			atomic_dec(&backbone_gw->bat_priv->bla.num_requests);
 			atomic_set(&backbone_gw->request_sent, 0);
 		}