tipc: simplify link supervision checkpointing

We change the sequence number checkpointing that is performed
by the timer in order to discover if the peer is active. Currently,
we store a checkpoint of the next expected sequence number "rcv_nxt"
at each timer expiration, and compare it to the current expected
number at next timeout expiration. Instead, we now use the already
existing field "silent_intv_cnt" for this task. We step the counter
at each timeout expiration, and zero it at each valid received packet.
If no valid packet has been received from the peer after "abort_limit"
number of silent timer intervals, the link is declared faulty and reset.

We also remove the multiple instances of timer activation from inside
the FSM function "link_state_event()", and now do it at only one place;
at the end of the timer function itself.

Reviewed-by: Erik Hugne <erik.hugne@ericsson.com>
Reviewed-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/link.c

@@ -86,7 +86,7 @@ static const struct nla_policy tipc_nl_prop_policy[TIPC_NLA_PROP_MAX + 1] = {
  */
 #define  STARTING_EVT    856384768	/* link processing trigger */
 #define  TRAFFIC_MSG_EVT 560815u	/* rx'd ??? */
-#define  TIMEOUT_EVT     560817u	/* link timer expired */
+#define  SILENCE_EVT     560817u	/* timer dicovered silence from peer */
 
 /*
  * State value stored in 'failover_pkts'
@@ -106,6 +106,7 @@ static void tipc_link_sync_rcv(struct tipc_node *n, struct sk_buff *buf);
 static void tipc_link_input(struct tipc_link *l, struct sk_buff *skb);
 static bool tipc_data_input(struct tipc_link *l, struct sk_buff *skb);
 static bool tipc_link_failover_rcv(struct tipc_link *l, struct sk_buff **skb);
+static void link_set_timer(struct tipc_link *link, unsigned long time);
 /*
  *  Simple link routines
  */
@@ -197,11 +198,12 @@ static void link_timeout(unsigned long data)
 	}
 
 	/* do all other link processing performed on a periodic basis */
-	link_state_event(l_ptr, TIMEOUT_EVT);
-
+	if (l_ptr->silent_intv_cnt || tipc_bclink_acks_missing(l_ptr->owner))
+		link_state_event(l_ptr, SILENCE_EVT);
+	l_ptr->silent_intv_cnt++;
 	if (skb_queue_len(&l_ptr->backlogq))
 		tipc_link_push_packets(l_ptr);
-
+	link_set_timer(l_ptr, l_ptr->keepalive_intv);
 	tipc_node_unlock(l_ptr->owner);
 	tipc_link_put(l_ptr);
 }
@@ -261,7 +263,6 @@ struct tipc_link *tipc_link_create(struct tipc_node *n_ptr,
 		/* note: peer i/f name is updated by reset/activate message */
 	memcpy(&l_ptr->media_addr, media_addr, sizeof(*media_addr));
 	l_ptr->owner = n_ptr;
-	l_ptr->checkpoint = 1;
 	l_ptr->peer_session = INVALID_SESSION;
 	l_ptr->bearer_id = b_ptr->identity;
 	link_set_supervision_props(l_ptr, b_ptr->tolerance);
@@ -468,7 +469,6 @@ void tipc_link_reset(struct tipc_link *l_ptr)
 	tipc_link_purge_backlog(l_ptr);
 	l_ptr->reasm_buf = NULL;
 	l_ptr->rcv_unacked = 0;
-	l_ptr->checkpoint = 1;
 	l_ptr->snd_nxt = 1;
 	l_ptr->silent_intv_cnt = 0;
 	l_ptr->stale_count = 0;
@@ -481,6 +481,7 @@ static void link_activate(struct tipc_link *link)
 
 	link->rcv_nxt = 1;
 	link->stats.recv_info = 1;
+	link->silent_intv_cnt = 0;
 	tipc_node_link_up(node, link);
 	tipc_bearer_add_dest(node->net, link->bearer_id, link->addr);
 }
@@ -501,45 +502,33 @@ static void link_state_event(struct tipc_link *l_ptr, unsigned int event)
 	if (!(l_ptr->flags & LINK_STARTED) && (event != STARTING_EVT))
 		return;		/* Not yet. */
 
-	if (l_ptr->flags & LINK_FAILINGOVER) {
-		if (event == TIMEOUT_EVT)
-			link_set_timer(l_ptr, timer_intv);
+	if (l_ptr->flags & LINK_FAILINGOVER)
 		return;
-	}
 
 	switch (l_ptr->state) {
 	case WORKING_WORKING:
 		switch (event) {
 		case TRAFFIC_MSG_EVT:
 		case ACTIVATE_MSG:
+			l_ptr->silent_intv_cnt = 0;
 			break;
-		case TIMEOUT_EVT:
-			if (l_ptr->rcv_nxt != l_ptr->checkpoint) {
-				l_ptr->checkpoint = l_ptr->rcv_nxt;
-				if (tipc_bclink_acks_missing(l_ptr->owner)) {
+		case SILENCE_EVT:
+			if (!l_ptr->silent_intv_cnt) {
+				if (tipc_bclink_acks_missing(l_ptr->owner))
 					tipc_link_proto_xmit(l_ptr, STATE_MSG,
 							     0, 0, 0, 0);
-					l_ptr->silent_intv_cnt++;
-				}
-				link_set_timer(l_ptr, timer_intv);
 				break;
 			}
 			l_ptr->state = WORKING_UNKNOWN;
-			l_ptr->silent_intv_cnt = 0;
 			tipc_link_proto_xmit(l_ptr, STATE_MSG, 1, 0, 0, 0);
-			l_ptr->silent_intv_cnt++;
-			link_set_timer(l_ptr, timer_intv);
 			break;
 		case RESET_MSG:
 			pr_debug("%s<%s>, requested by peer\n",
 				 link_rst_msg, l_ptr->name);
 			tipc_link_reset(l_ptr);
 			l_ptr->state = RESET_RESET;
-			l_ptr->silent_intv_cnt = 0;
 			tipc_link_proto_xmit(l_ptr, ACTIVATE_MSG,
 					     0, 0, 0, 0);
-			l_ptr->silent_intv_cnt++;
-			link_set_timer(l_ptr, timer_intv);
 			break;
 		default:
 			pr_debug("%s%u in WW state\n", link_unk_evt, event);
@@ -551,46 +540,32 @@ static void link_state_event(struct tipc_link *l_ptr, unsigned int event)
 		case ACTIVATE_MSG:
 			l_ptr->state = WORKING_WORKING;
 			l_ptr->silent_intv_cnt = 0;
-			link_set_timer(l_ptr, timer_intv);
 			break;
 		case RESET_MSG:
 			pr_debug("%s<%s>, requested by peer while probing\n",
 				 link_rst_msg, l_ptr->name);
 			tipc_link_reset(l_ptr);
 			l_ptr->state = RESET_RESET;
-			l_ptr->silent_intv_cnt = 0;
 			tipc_link_proto_xmit(l_ptr, ACTIVATE_MSG,
 					     0, 0, 0, 0);
-			l_ptr->silent_intv_cnt++;
-			link_set_timer(l_ptr, timer_intv);
 			break;
-		case TIMEOUT_EVT:
-			if (l_ptr->rcv_nxt != l_ptr->checkpoint) {
+		case SILENCE_EVT:
+			if (!l_ptr->silent_intv_cnt) {
 				l_ptr->state = WORKING_WORKING;
-				l_ptr->silent_intv_cnt = 0;
-				l_ptr->checkpoint = l_ptr->rcv_nxt;
-				if (tipc_bclink_acks_missing(l_ptr->owner)) {
+				if (tipc_bclink_acks_missing(l_ptr->owner))
 					tipc_link_proto_xmit(l_ptr, STATE_MSG,
 							     0, 0, 0, 0);
-					l_ptr->silent_intv_cnt++;
-				}
-				link_set_timer(l_ptr, timer_intv);
 			} else if (l_ptr->silent_intv_cnt <
 				   l_ptr->abort_limit) {
 				tipc_link_proto_xmit(l_ptr, STATE_MSG,
 						     1, 0, 0, 0);
-				l_ptr->silent_intv_cnt++;
-				link_set_timer(l_ptr, timer_intv);
 			} else {	/* Link has failed */
 				pr_debug("%s<%s>, peer not responding\n",
 					 link_rst_msg, l_ptr->name);
 				tipc_link_reset(l_ptr);
 				l_ptr->state = RESET_UNKNOWN;
-				l_ptr->silent_intv_cnt = 0;
 				tipc_link_proto_xmit(l_ptr, RESET_MSG,
 						     0, 0, 0, 0);
-				l_ptr->silent_intv_cnt++;
-				link_set_timer(l_ptr, timer_intv);
 			}
 			break;
 		default:
@@ -606,31 +581,22 @@ static void link_state_event(struct tipc_link *l_ptr, unsigned int event)
 			if (other && link_working_unknown(other))
 				break;
 			l_ptr->state = WORKING_WORKING;
-			l_ptr->silent_intv_cnt = 0;
 			link_activate(l_ptr);
 			tipc_link_proto_xmit(l_ptr, STATE_MSG, 1, 0, 0, 0);
-			l_ptr->silent_intv_cnt++;
 			if (l_ptr->owner->working_links == 1)
 				tipc_link_sync_xmit(l_ptr);
-			link_set_timer(l_ptr, timer_intv);
 			break;
 		case RESET_MSG:
 			l_ptr->state = RESET_RESET;
-			l_ptr->silent_intv_cnt = 0;
 			tipc_link_proto_xmit(l_ptr, ACTIVATE_MSG,
 					     1, 0, 0, 0);
-			l_ptr->silent_intv_cnt++;
-			link_set_timer(l_ptr, timer_intv);
 			break;
 		case STARTING_EVT:
 			l_ptr->flags |= LINK_STARTED;
-			l_ptr->silent_intv_cnt++;
 			link_set_timer(l_ptr, timer_intv);
 			break;
-		case TIMEOUT_EVT:
+		case SILENCE_EVT:
 			tipc_link_proto_xmit(l_ptr, RESET_MSG, 0, 0, 0, 0);
-			l_ptr->silent_intv_cnt++;
-			link_set_timer(l_ptr, timer_intv);
 			break;
 		default:
 			pr_err("%s%u in RU state\n", link_unk_evt, event);
@@ -644,21 +610,16 @@ static void link_state_event(struct tipc_link *l_ptr, unsigned int event)
 			if (other && link_working_unknown(other))
 				break;
 			l_ptr->state = WORKING_WORKING;
-			l_ptr->silent_intv_cnt = 0;
 			link_activate(l_ptr);
 			tipc_link_proto_xmit(l_ptr, STATE_MSG, 1, 0, 0, 0);
-			l_ptr->silent_intv_cnt++;
 			if (l_ptr->owner->working_links == 1)
 				tipc_link_sync_xmit(l_ptr);
-			link_set_timer(l_ptr, timer_intv);
 			break;
 		case RESET_MSG:
 			break;
-		case TIMEOUT_EVT:
+		case SILENCE_EVT:
 			tipc_link_proto_xmit(l_ptr, ACTIVATE_MSG,
 					     0, 0, 0, 0);
-			l_ptr->silent_intv_cnt++;
-			link_set_timer(l_ptr, timer_intv);
 			break;
 		default:
 			pr_err("%s%u in RR state\n", link_unk_evt, event);
@@ -1126,6 +1087,8 @@ void tipc_rcv(struct net *net, struct sk_buff *skb, struct tipc_bearer *b_ptr)
 			skb = NULL;
 			goto unlock;
 		}
+		l_ptr->silent_intv_cnt = 0;
+
 		/* Synchronize with parallel link if applicable */
 		if (unlikely((l_ptr->flags & LINK_SYNCHING) && !msg_dup(msg))) {
 			if (!link_synch(l_ptr))
@@ -1295,8 +1258,8 @@ static void link_handle_out_of_seq_msg(struct tipc_link *l_ptr,
 		return;
 	}
 
-	/* Record OOS packet arrival (force mismatch on next timeout) */
-	l_ptr->checkpoint--;
+	/* Record OOS packet arrival */
+	l_ptr->silent_intv_cnt = 0;
 
 	/*
 	 * Discard packet if a duplicate; otherwise add it to deferred queue
@@ -1480,7 +1443,7 @@ static void tipc_link_proto_rcv(struct tipc_link *l_ptr,
 		}
 
 		/* Record reception; force mismatch at next timeout: */
-		l_ptr->checkpoint--;
+		l_ptr->silent_intv_cnt = 0;
 
 		link_state_event(l_ptr, TRAFFIC_MSG_EVT);
 		l_ptr->stats.recv_states++;

net/tipc/link.h

@@ -107,7 +107,6 @@ struct tipc_stats {
  * @owner: pointer to peer node
  * @refcnt: reference counter for permanent references (owner node & timer)
  * @flags: execution state flags for link endpoint instance
- * @checkpoint: reference point for triggering link continuity checking
  * @peer_session: link session # being used by peer end of link
  * @peer_bearer_id: bearer id used by link's peer endpoint
  * @bearer_id: local bearer id used by link
@@ -151,7 +150,6 @@ struct tipc_link {
 
 	/* Management and link supervision data */
 	unsigned int flags;
-	u16 checkpoint;
 	u32 peer_session;
 	u32 peer_bearer_id;
 	u32 bearer_id;