tipc: fix failover problem

We see the following scenario:
1) Link endpoint B on node 1 discovers that its peer endpoint is gone.
   Since there is a second working link, failover procedure is started.
2) Link endpoint A on node 1 sends a FAILOVER message to peer endpoint
   A on node 2. The node item 1->2 goes to state FAILINGOVER.
3) Linke endpoint A/2 receives the failover, and is supposed to take
   down its parallell link endpoint B/2, while producing a FAILOVER
   message to send back to A/1.
4) However, B/2 has already been deleted, so no FAILOVER message can
   created.
5) Node 1->2 remains in state FAILINGOVER forever, refusing to receive
   any messages that can bring B/1 up again. We are left with a non-
   redundant link between node 1 and 2.

We fix this with letting endpoint A/2 build a dummy FAILOVER message
to send to back to A/1, so that the situation can be resolved.

Signed-off-by: LUU Duc Canh <canh.d.luu@dektech.com.au>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 0 deletions

diff --git a/net/tipc/node.c b/net/tipc/node.c
index 68014f1b6976..b0ee25f1f2e6 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -111,6 +111,7 @@ struct tipc_node {
         int action_flags;
         struct list_head list;
         int state;
+        bool failover_sent;
         u16 sync_point;
         int link_cnt;
         u16 working_links;
@@ -680,6 +681,7 @@ static void __tipc_node_link_up(struct tipc_node *n, int bearer_id,
                 *slot0 = bearer_id;
                 *slot1 = bearer_id;
                 tipc_node_fsm_evt(n, SELF_ESTABL_CONTACT_EVT);
+                n->failover_sent = false;
                 n->action_flags |= TIPC_NOTIFY_NODE_UP;
                 tipc_link_set_active(nl, true);
                 tipc_bcast_add_peer(n->net, nl, xmitq);
@@ -1615,6 +1617,15 @@ static bool tipc_node_check_state(struct tipc_node *n, struct sk_buff *skb,
                         tipc_skb_queue_splice_tail_init(tipc_link_inputq(pl),
                                                         tipc_link_inputq(l));
                 }
+                /* If parallel link was already down, and this happened before
+                 * the tunnel link came up, FAILOVER was never sent. Ensure that
+                 * FAILOVER is sent to get peer out of NODE_FAILINGOVER state.
+                 */
+                if (n->state != NODE_FAILINGOVER && !n->failover_sent) {
+                        tipc_link_create_dummy_tnl_msg(l, xmitq);
+                        n->failover_sent = true;
+                }
+
                 /* If pkts arrive out of order, use lowest calculated syncpt */
                 if (less(syncpt, n->sync_point))
                         n->sync_point = syncpt;