tipc: merge link->exec_mode and link->state into one FSM

Until now, we have been handling link failover and synchronization
by using an additional link state variable, "exec_mode". This variable
is not independent of the link FSM state, something causing a risk of
inconsistencies, apart from the fact that it clutters the code.

The conditions are now in place to define a new link FSM that covers
all existing use cases, including failover and synchronization, and
eliminate the "exec_mode" field altogether. The FSM must also support
non-atomic resetting of links, which will be introduced later.

The new link FSM is shown below, with 7 states and 8 events.
Only events leading to state change are shown as edges.

+------------------------------------+
|RESET_EVT                           |
|                                    |
|                             +--------------+
|           +-----------------|   SYNCHING   |-----------------+
|           |FAILURE_EVT      +--------------+   PEER_RESET_EVT|
|           |                  A            |                  |
|           |                  |            |                  |
|           |                  |            |                  |
|           |                  |SYNCH_      |SYNCH_            |
|           |                  |BEGIN_EVT   |END_EVT           |
|           |                  |            |                  |
|           V                  |            V                  V
|    +-------------+          +--------------+          +------------+
|    |  RESETTING  |<---------|  ESTABLISHED |--------->| PEER_RESET |
|    +-------------+ FAILURE_ +--------------+ PEER_    +------------+
|           |        EVT        |    A         RESET_EVT       |
|           |                   |    |                         |
|           |                   |    |                         |
|           |    +--------------+    |                         |
|  RESET_EVT|    |RESET_EVT          |ESTABLISH_EVT            |
|           |    |                   |                         |
|           |    |                   |                         |
|           V    V                   |                         |
|    +-------------+          +--------------+        RESET_EVT|
+--->|    RESET    |--------->| ESTABLISHING |<----------------+
     +-------------+ PEER_    +--------------+
      |           A  RESET_EVT       |
      |           |                  |
      |           |                  |
      |FAILOVER_  |FAILOVER_         |FAILOVER_
      |BEGIN_EVT  |END_EVT           |BEGIN_EVT
      |           |                  |
      V           |                  |
     +-------------+                 |
     | FAILINGOVER |<----------------+
     +-------------+

These changes are fully backwards compatible.

Tested-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>

3 files changed, 226 insertions, 180 deletions

diff --git a/net/tipc/link.c b/net/tipc/link.c
index 9a3ccf910c49..9840b03348e1 100644
--- a/net/tipc/link.c
+++ b/net/tipc/link.c
@@ -50,7 +50,6 @@
  */
 static const char *link_co_err = "Link tunneling error, ";
 static const char *link_rst_msg = "Resetting link ";
-static const char *link_unk_evt = "Unknown link event ";
 
 static const struct nla_policy tipc_nl_link_policy[TIPC_NLA_LINK_MAX + 1] = {
 	[TIPC_NLA_LINK_UNSPEC]		= { .type = NLA_UNSPEC },
@@ -85,46 +84,23 @@ static const struct nla_policy tipc_nl_prop_policy[TIPC_NLA_PROP_MAX + 1] = {
  */
 #define WILDCARD_SESSION 0x10000
 
-/* State value stored in 'failover_pkts'
+/* Link FSM states:
  */
-#define FIRST_FAILOVER 0xffffu
-
-/* Link FSM states and events:
- */
-enum {
-	TIPC_LINK_WORKING,
-	TIPC_LINK_PROBING,
-	TIPC_LINK_RESETTING,
-	TIPC_LINK_ESTABLISHING
-};
-
 enum {
-	PEER_RESET_EVT    = RESET_MSG,
-	ACTIVATE_EVT      = ACTIVATE_MSG,
-	TRAFFIC_EVT,      /* Any other valid msg from peer */
-	SILENCE_EVT       /* Peer was silent during last timer interval*/
+	LINK_ESTABLISHED     = 0xe,
+	LINK_ESTABLISHING    = 0xe  << 4,
+	LINK_RESET           = 0x1  << 8,
+	LINK_RESETTING       = 0x2  << 12,
+	LINK_PEER_RESET      = 0xd  << 16,
+	LINK_FAILINGOVER     = 0xf  << 20,
+	LINK_SYNCHING        = 0xc  << 24
 };
 
 /* Link FSM state checking routines
  */
-static int link_working(struct tipc_link *l)
-{
-	return l->state == TIPC_LINK_WORKING;
-}
-
-static int link_probing(struct tipc_link *l)
-{
-	return l->state == TIPC_LINK_PROBING;
-}
-
-static int link_resetting(struct tipc_link *l)
+static int link_is_up(struct tipc_link *l)
 {
-	return l->state == TIPC_LINK_RESETTING;
-}
-
-static int link_establishing(struct tipc_link *l)
-{
-	return l->state == TIPC_LINK_ESTABLISHING;
+	return l->state & (LINK_ESTABLISHED | LINK_SYNCHING);
 }
 
 static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
@@ -141,11 +117,29 @@ static bool tipc_data_input(struct tipc_link *l, struct sk_buff *skb);
 /*
  *  Simple non-static link routines (i.e. referenced outside this file)
  */
-int tipc_link_is_up(struct tipc_link *l_ptr)
+bool tipc_link_is_up(struct tipc_link *l)
 {
-	if (!l_ptr)
-		return 0;
-	return link_working(l_ptr) || link_probing(l_ptr);
+	return link_is_up(l);
+}
+
+bool tipc_link_is_reset(struct tipc_link *l)
+{
+	return l->state & (LINK_RESET | LINK_FAILINGOVER | LINK_ESTABLISHING);
+}
+
+bool tipc_link_is_synching(struct tipc_link *l)
+{
+	return l->state == LINK_SYNCHING;
+}
+
+bool tipc_link_is_failingover(struct tipc_link *l)
+{
+	return l->state == LINK_FAILINGOVER;
+}
+
+bool tipc_link_is_blocked(struct tipc_link *l)
+{
+	return l->state & (LINK_RESETTING | LINK_PEER_RESET | LINK_FAILINGOVER);
 }
 
 int tipc_link_is_active(struct tipc_link *l)
@@ -210,7 +204,7 @@ struct tipc_link *tipc_link_create(struct tipc_node *n_ptr,
 	l_ptr->tolerance = b_ptr->tolerance;
 	l_ptr->snd_nxt = 1;
 	l_ptr->rcv_nxt = 1;
-	l_ptr->state = TIPC_LINK_RESETTING;
+	l_ptr->state = LINK_RESET;
 
 	l_ptr->pmsg = (struct tipc_msg *)&l_ptr->proto_msg;
 	msg = l_ptr->pmsg;
@@ -265,120 +259,159 @@ void tipc_link_build_bcast_sync_msg(struct tipc_link *l,
  * tipc_link_fsm_evt - link finite state machine
  * @l: pointer to link
  * @evt: state machine event to be processed
- * @xmitq: queue to prepend created protocol message, if any
  */
-static int tipc_link_fsm_evt(struct tipc_link *l, int evt,
-			     struct sk_buff_head *xmitq)
+int tipc_link_fsm_evt(struct tipc_link *l, int evt)
 {
 	int rc = 0;
-	struct tipc_link *pl;
-	enum {
-		LINK_RESET     = 1,
-		LINK_ACTIVATE  = (1 << 1),
-		SND_PROBE      = (1 << 2),
-		SND_STATE      = (1 << 3),
-		SND_RESET      = (1 << 4),
-		SND_ACTIVATE   = (1 << 5),
-		SND_BCAST_SYNC = (1 << 6)
-	} actions = 0;
-
-	if (l->exec_mode == TIPC_LINK_BLOCKED)
-		return rc;
 
 	switch (l->state) {
-	case TIPC_LINK_WORKING:
+	case LINK_RESETTING:
 		switch (evt) {
-		case TRAFFIC_EVT:
-		case ACTIVATE_EVT:
+		case LINK_PEER_RESET_EVT:
+			l->state = LINK_PEER_RESET;
 			break;
-		case SILENCE_EVT:
-			l->state = TIPC_LINK_PROBING;
-			actions |= SND_PROBE;
+		case LINK_RESET_EVT:
+			l->state = LINK_RESET;
+			break;
+		case LINK_FAILURE_EVT:
+		case LINK_FAILOVER_BEGIN_EVT:
+		case LINK_ESTABLISH_EVT:
+		case LINK_FAILOVER_END_EVT:
+		case LINK_SYNCH_BEGIN_EVT:
+		case LINK_SYNCH_END_EVT:
+		default:
+			goto illegal_evt;
+		}
+		break;
+	case LINK_RESET:
+		switch (evt) {
+		case LINK_PEER_RESET_EVT:
+			l->state = LINK_ESTABLISHING;
 			break;
-		case PEER_RESET_EVT:
-			actions |= LINK_RESET | SND_ACTIVATE;
+		case LINK_FAILOVER_BEGIN_EVT:
+			l->state = LINK_FAILINGOVER;
+		case LINK_FAILURE_EVT:
+		case LINK_RESET_EVT:
+		case LINK_ESTABLISH_EVT:
+		case LINK_FAILOVER_END_EVT:
 			break;
+		case LINK_SYNCH_BEGIN_EVT:
+		case LINK_SYNCH_END_EVT:
 		default:
-			pr_debug("%s%u WORKING\n", link_unk_evt, evt);
+			goto illegal_evt;
 		}
 		break;
-	case TIPC_LINK_PROBING:
+	case LINK_PEER_RESET:
 		switch (evt) {
-		case TRAFFIC_EVT:
-		case ACTIVATE_EVT:
-			l->state = TIPC_LINK_WORKING;
+		case LINK_RESET_EVT:
+			l->state = LINK_ESTABLISHING;
 			break;
-		case PEER_RESET_EVT:
-			actions |= LINK_RESET | SND_ACTIVATE;
+		case LINK_PEER_RESET_EVT:
+		case LINK_ESTABLISH_EVT:
+		case LINK_FAILURE_EVT:
 			break;
-		case SILENCE_EVT:
-			if (l->silent_intv_cnt <= l->abort_limit) {
-				actions |= SND_PROBE;
-				break;
-			}
-			actions |= LINK_RESET | SND_RESET;
+		case LINK_SYNCH_BEGIN_EVT:
+		case LINK_SYNCH_END_EVT:
+		case LINK_FAILOVER_BEGIN_EVT:
+		case LINK_FAILOVER_END_EVT:
+		default:
+			goto illegal_evt;
+		}
+		break;
+	case LINK_FAILINGOVER:
+		switch (evt) {
+		case LINK_FAILOVER_END_EVT:
+			l->state = LINK_RESET;
 			break;
+		case LINK_PEER_RESET_EVT:
+		case LINK_RESET_EVT:
+		case LINK_ESTABLISH_EVT:
+		case LINK_FAILURE_EVT:
+			break;
+		case LINK_FAILOVER_BEGIN_EVT:
+		case LINK_SYNCH_BEGIN_EVT:
+		case LINK_SYNCH_END_EVT:
 		default:
-			pr_err("%s%u PROBING\n", link_unk_evt, evt);
+			goto illegal_evt;
 		}
 		break;
-	case TIPC_LINK_RESETTING:
+	case LINK_ESTABLISHING:
 		switch (evt) {
-		case TRAFFIC_EVT:
+		case LINK_ESTABLISH_EVT:
+			l->state = LINK_ESTABLISHED;
+			rc |= TIPC_LINK_UP_EVT;
 			break;
-		case ACTIVATE_EVT:
-			pl = node_active_link(l->owner, 0);
-			if (pl && link_probing(pl))
-				break;
-			l->state = TIPC_LINK_WORKING;
-			actions |= LINK_ACTIVATE;
-			if (!l->owner->working_links)
-				actions |= SND_BCAST_SYNC;
+		case LINK_FAILOVER_BEGIN_EVT:
+			l->state = LINK_FAILINGOVER;
+			break;
+		case LINK_PEER_RESET_EVT:
+		case LINK_RESET_EVT:
+		case LINK_FAILURE_EVT:
+		case LINK_SYNCH_BEGIN_EVT:
+		case LINK_FAILOVER_END_EVT:
+			break;
+		case LINK_SYNCH_END_EVT:
+		default:
+			goto illegal_evt;
+		}
+		break;
+	case LINK_ESTABLISHED:
+		switch (evt) {
+		case LINK_PEER_RESET_EVT:
+			l->state = LINK_PEER_RESET;
+			rc |= TIPC_LINK_DOWN_EVT;
+			break;
+		case LINK_FAILURE_EVT:
+			l->state = LINK_RESETTING;
+			rc |= TIPC_LINK_DOWN_EVT;
 			break;
-		case PEER_RESET_EVT:
-			l->state = TIPC_LINK_ESTABLISHING;
-			actions |= SND_ACTIVATE;
+		case LINK_RESET_EVT:
+			l->state = LINK_RESET;
 			break;
-		case SILENCE_EVT:
-			actions |= SND_RESET;
+		case LINK_ESTABLISH_EVT:
 			break;
+		case LINK_SYNCH_BEGIN_EVT:
+			l->state = LINK_SYNCHING;
+			break;
+		case LINK_SYNCH_END_EVT:
+		case LINK_FAILOVER_BEGIN_EVT:
+		case LINK_FAILOVER_END_EVT:
 		default:
-			pr_err("%s%u in RESETTING\n", link_unk_evt, evt);
+			goto illegal_evt;
 		}
 		break;
-	case TIPC_LINK_ESTABLISHING:
+	case LINK_SYNCHING:
 		switch (evt) {
-		case TRAFFIC_EVT:
-		case ACTIVATE_EVT:
-			pl = node_active_link(l->owner, 0);
-			if (pl && link_probing(pl))
-				break;
-			l->state = TIPC_LINK_WORKING;
-			actions |= LINK_ACTIVATE;
-			if (!l->owner->working_links)
-				actions |= SND_BCAST_SYNC;
+		case LINK_PEER_RESET_EVT:
+			l->state = LINK_PEER_RESET;
+			rc |= TIPC_LINK_DOWN_EVT;
+			break;
+		case LINK_FAILURE_EVT:
+			l->state = LINK_RESETTING;
+			rc |= TIPC_LINK_DOWN_EVT;
 			break;
-		case PEER_RESET_EVT:
+		case LINK_RESET_EVT:
+			l->state = LINK_RESET;
 			break;
-		case SILENCE_EVT:
-			actions |= SND_ACTIVATE;
+		case LINK_ESTABLISH_EVT:
+		case LINK_SYNCH_BEGIN_EVT:
 			break;
+		case LINK_SYNCH_END_EVT:
+			l->state = LINK_ESTABLISHED;
+			break;
+		case LINK_FAILOVER_BEGIN_EVT:
+		case LINK_FAILOVER_END_EVT:
 		default:
-			pr_err("%s%u ESTABLISHING\n", link_unk_evt, evt);
+			goto illegal_evt;
 		}
 		break;
 	default:
-		pr_err("Unknown link state %u/%u\n", l->state, evt);
-	}
-
-	/* Perform actions as decided by FSM */
-	if (actions & LINK_RESET) {
-		l->exec_mode = TIPC_LINK_BLOCKED;
-		rc = TIPC_LINK_DOWN_EVT;
+		pr_err("Unknown FSM state %x in %s\n", l->state, l->name);
 	}
-	if (actions & LINK_ACTIVATE)
-		rc = TIPC_LINK_UP_EVT;
-
+	return rc;
+illegal_evt:
+	pr_err("Illegal FSM event %x in state %x on link %s\n",
+	       evt, l->state, l->name);
 	return rc;
 }
 
@@ -432,12 +465,11 @@ int tipc_link_timeout(struct tipc_link *l, struct sk_buff_head *xmitq)
 	bool xmit = false;
 	bool prb = false;
 
-	if (l->exec_mode == TIPC_LINK_BLOCKED)
-		return rc;
-
 	link_profile_stats(l);
 
-	if (l->state == TIPC_LINK_WORKING) {
+	switch (l->state) {
+	case LINK_ESTABLISHED:
+	case LINK_SYNCHING:
 		if (!l->silent_intv_cnt) {
 			if (tipc_bclink_acks_missing(l->owner))
 				xmit = true;
@@ -445,17 +477,26 @@ int tipc_link_timeout(struct tipc_link *l, struct sk_buff_head *xmitq)
 			xmit = true;
 			prb = true;
 		} else {
-			l->exec_mode = TIPC_LINK_BLOCKED;
-			rc |= TIPC_LINK_DOWN_EVT;
+			rc |= tipc_link_fsm_evt(l, LINK_FAILURE_EVT);
 		}
 		l->silent_intv_cnt++;
-	} else if (l->state == TIPC_LINK_RESETTING) {
+		break;
+	case LINK_RESET:
 		xmit = true;
 		mtyp = RESET_MSG;
-	} else if (l->state == TIPC_LINK_ESTABLISHING) {
+		break;
+	case LINK_ESTABLISHING:
 		xmit = true;
 		mtyp = ACTIVATE_MSG;
+		break;
+	case LINK_RESETTING:
+	case LINK_PEER_RESET:
+	case LINK_FAILINGOVER:
+		break;
+	default:
+		break;
 	}
+
 	if (xmit)
 		tipc_link_build_proto_msg(l, mtyp, prb, 0, 0, 0, xmitq);
 
@@ -559,7 +600,7 @@ void tipc_link_reset(struct tipc_link *l)
 {
 	struct tipc_node *owner = l->owner;
 
-	l->state = TIPC_LINK_RESETTING;
+	tipc_link_fsm_evt(l, LINK_RESET_EVT);
 
 	/* Link is down, accept any session */
 	l->peer_session = WILDCARD_SESSION;
@@ -902,8 +943,7 @@ static int tipc_link_retransm(struct tipc_link *l, int retransm,
 		l->stale_count = 1;
 	} else if (++l->stale_count > 100) {
 		link_retransmit_failure(l, skb);
-		l->exec_mode = TIPC_LINK_BLOCKED;
-		return TIPC_LINK_DOWN_EVT;
+		return tipc_link_fsm_evt(l, LINK_FAILURE_EVT);
 	}
 	skb_queue_walk(&l->transmq, skb) {
 		if (!retransm)
@@ -1002,25 +1042,23 @@ static int tipc_link_input(struct tipc_link *l, struct sk_buff *skb)
 		l->stats.recv_bundled += msg_msgcnt(hdr);
 		while (tipc_msg_extract(skb, &iskb, &pos))
 			tipc_data_input(l, iskb);
-		return rc;
+		return 0;
 	} else if (usr == MSG_FRAGMENTER) {
 		l->stats.recv_fragments++;
 		if (tipc_buf_append(reasm_skb, &skb)) {
 			l->stats.recv_fragmented++;
 			tipc_data_input(l, skb);
 		} else if (!*reasm_skb) {
-			l->exec_mode = TIPC_LINK_BLOCKED;
-			l->state = TIPC_LINK_RESETTING;
-			rc = TIPC_LINK_DOWN_EVT;
+			return tipc_link_fsm_evt(l, LINK_FAILURE_EVT);
 		}
-		return rc;
+		return 0;
 	} else if (usr == BCAST_PROTOCOL) {
 		tipc_link_sync_rcv(node, skb);
-		return rc;
+		return 0;
 	}
 drop:
 	kfree_skb(skb);
-	return rc;
+	return 0;
 }
 
 static bool tipc_link_release_pkts(struct tipc_link *l, u16 acked)
@@ -1068,9 +1106,9 @@ int tipc_link_rcv(struct tipc_link *l, struct sk_buff *skb,
 			continue;
 		}
 
-		if (unlikely(!link_working(l))) {
-			rc = tipc_link_fsm_evt(l, TRAFFIC_EVT, xmitq);
-			if (!link_working(l)) {
+		if (unlikely(!link_is_up(l))) {
+			rc = tipc_link_fsm_evt(l, LINK_ESTABLISH_EVT);
+			if (!link_is_up(l)) {
 				kfree_skb(__skb_dequeue(arrvq));
 				return rc;
 			}
@@ -1192,7 +1230,7 @@ static void tipc_link_build_proto_msg(struct tipc_link *l, int mtyp, bool probe,
 	int node_up = l->owner->bclink.recv_permitted;
 
 	/* Don't send protocol message during reset or link failover */
-	if (l->exec_mode == TIPC_LINK_BLOCKED)
+	if (tipc_link_is_blocked(l))
 		return;
 
 	msg_set_type(hdr, mtyp);
@@ -1302,7 +1340,6 @@ tnl:
 		tnl->drop_point = l->rcv_nxt;
 		tnl->failover_reasm_skb = l->reasm_buf;
 		l->reasm_buf = NULL;
-		l->exec_mode = TIPC_LINK_BLOCKED;
 	}
 }
 
@@ -1323,7 +1360,7 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
 	char *if_name;
 	int rc = 0;
 
-	if (l->exec_mode == TIPC_LINK_BLOCKED)
+	if (tipc_link_is_blocked(l))
 		goto exit;
 
 	if (link_own_addr(l) > msg_prevnode(hdr))
@@ -1337,6 +1374,7 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
 		    (l->peer_session != WILDCARD_SESSION))
 			break;
 		/* fall thru' */
+
 	case ACTIVATE_MSG:
 
 		/* Complete own link name with peer's interface name */
@@ -1355,13 +1393,20 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
 		if (in_range(peers_prio, l->priority + 1, TIPC_MAX_LINK_PRI))
 			l->priority = peers_prio;
 
+		if (msg_type(hdr) == RESET_MSG) {
+			rc |= tipc_link_fsm_evt(l, LINK_PEER_RESET_EVT);
+		} else if (!link_is_up(l)) {
+			tipc_link_fsm_evt(l, LINK_PEER_RESET_EVT);
+			rc |= tipc_link_fsm_evt(l, LINK_ESTABLISH_EVT);
+		}
 		l->peer_session = msg_session(hdr);
 		l->peer_bearer_id = msg_bearer_id(hdr);
-		rc = tipc_link_fsm_evt(l, msg_type(hdr), xmitq);
 		if (l->mtu > msg_max_pkt(hdr))
 			l->mtu = msg_max_pkt(hdr);
 		break;
+
 	case STATE_MSG:
+
 		/* Update own tolerance if peer indicates a non-zero value */
 		if (in_range(peers_tol, TIPC_MIN_LINK_TOL, TIPC_MAX_LINK_TOL))
 			l->tolerance = peers_tol;
@@ -1370,11 +1415,11 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
 		l->stats.recv_states++;
 		if (msg_probe(hdr))
 			l->stats.recv_probes++;
-		rc = tipc_link_fsm_evt(l, TRAFFIC_EVT, xmitq);
-		if (!tipc_link_is_up(l))
+		rc = tipc_link_fsm_evt(l, LINK_ESTABLISH_EVT);
+		if (!link_is_up(l))
 			break;
 
-		/* Has peer sent packets we haven't received yet ? */
+		/* Send NACK if peer has sent pkts we haven't received yet */
 		if (more(peers_snd_nxt, l->rcv_nxt))
 			rcvgap = peers_snd_nxt - l->rcv_nxt;
 		if (rcvgap || (msg_probe(hdr)))
@@ -1387,6 +1432,7 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
 			rc = tipc_link_retransm(l, nacked_gap, xmitq);
 			l->stats.recv_nacks++;
 		}
+
 		tipc_link_advance_backlog(l, xmitq);
 		if (unlikely(!skb_queue_empty(&l->wakeupq)))
 			link_prepare_wakeup(l);
@@ -1463,19 +1509,7 @@ static void link_print(struct tipc_link *l, const char *str)
 	u16 head = hskb ? msg_seqno(buf_msg(hskb)) : l->snd_nxt;
 	u16 tail = l->snd_nxt - 1;
 
-	pr_info("%s Link <%s>:", str, l->name);
-
-	if (link_probing(l))
-		pr_cont(":P\n");
-	else if (link_establishing(l))
-		pr_cont(":E\n");
-	else if (link_resetting(l))
-		pr_cont(":R\n");
-	else if (link_working(l))
-		pr_cont(":W\n");
-	else
-		pr_cont("\n");
-
+	pr_info("%s Link <%s> state %x\n", str, l->name, l->state);
 	pr_info("XMTQ: %u [%u-%u], BKLGQ: %u, SNDNX: %u, RCVNX: %u\n",
 		skb_queue_len(&l->transmq), head, tail,
 		skb_queue_len(&l->backlogq), l->snd_nxt, l->rcv_nxt);
diff --git a/net/tipc/link.h b/net/tipc/link.h
index b317c4df9079..39b8c4c5121e 100644
--- a/net/tipc/link.h
+++ b/net/tipc/link.h
@@ -49,13 +49,17 @@
  */
 #define INVALID_LINK_SEQ 0x10000
 
-
-/* Link endpoint receive states
+/* Link FSM events:
  */
 enum {
-	TIPC_LINK_OPEN,
-	TIPC_LINK_BLOCKED,
-	TIPC_LINK_TUNNEL
+	LINK_ESTABLISH_EVT       = 0xec1ab1e,
+	LINK_PEER_RESET_EVT      = 0x9eed0e,
+	LINK_FAILURE_EVT         = 0xfa110e,
+	LINK_RESET_EVT           = 0x10ca1d0e,
+	LINK_FAILOVER_BEGIN_EVT  = 0xfa110bee,
+	LINK_FAILOVER_END_EVT    = 0xfa110ede,
+	LINK_SYNCH_BEGIN_EVT     = 0xc1ccbee,
+	LINK_SYNCH_END_EVT       = 0xc1ccede
 };
 
 /* Events returned from link at packet reception or at timeout
@@ -120,7 +124,6 @@ struct tipc_stats {
  * @pmsg: convenience pointer to "proto_msg" field
  * @priority: current link priority
  * @net_plane: current link network plane ('A' through 'H')
- * @exec_mode: transmit/receive mode for link endpoint instance
  * @backlog_limit: backlog queue congestion thresholds (indexed by importance)
  * @exp_msg_count: # of tunnelled messages expected during link changeover
  * @reset_rcv_checkpt: seq # of last acknowledged message at time of link reset
@@ -155,7 +158,7 @@ struct tipc_link {
 	u32 tolerance;
 	unsigned long keepalive_intv;
 	u32 abort_limit;
-	int state;
+	u32 state;
 	u32 silent_intv_cnt;
 	struct {
 		unchar hdr[INT_H_SIZE];
@@ -166,7 +169,6 @@ struct tipc_link {
 	char net_plane;
 
 	/* Failover/synch */
-	u8 exec_mode;
 	u16 drop_point;
 	struct sk_buff *failover_reasm_skb;
 
@@ -214,8 +216,13 @@ void tipc_link_tnl_prepare(struct tipc_link *l, struct tipc_link *tnl,
 			   int mtyp, struct sk_buff_head *xmitq);
 void tipc_link_build_bcast_sync_msg(struct tipc_link *l,
 				    struct sk_buff_head *xmitq);
+int tipc_link_fsm_evt(struct tipc_link *l, int evt);
 void tipc_link_reset_fragments(struct tipc_link *l_ptr);
-int tipc_link_is_up(struct tipc_link *l_ptr);
+bool tipc_link_is_up(struct tipc_link *l);
+bool tipc_link_is_reset(struct tipc_link *l);
+bool tipc_link_is_synching(struct tipc_link *l);
+bool tipc_link_is_failingover(struct tipc_link *l);
+bool tipc_link_is_blocked(struct tipc_link *l);
 int tipc_link_is_active(struct tipc_link *l_ptr);
 void tipc_link_purge_queues(struct tipc_link *l_ptr);
 void tipc_link_purge_backlog(struct tipc_link *l);
diff --git a/net/tipc/node.c b/net/tipc/node.c
index 9e20acffb3d4..a3ceeda2a80a 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -334,7 +334,6 @@ static void tipc_node_link_up(struct tipc_node *n, int bearer_id,
 	if (!ol) {
 		*slot0 = bearer_id;
 		*slot1 = bearer_id;
-		nl->exec_mode = TIPC_LINK_OPEN;
 		tipc_link_build_bcast_sync_msg(nl, xmitq);
 		node_established_contact(n);
 		return;
@@ -368,7 +367,7 @@ static void tipc_node_link_down(struct tipc_node *n, int bearer_id)
 	struct sk_buff_head xmitq;
 
 	l = n->links[bearer_id].link;
-	if (!l || !tipc_link_is_up(l))
+	if (!l || tipc_link_is_reset(l))
 		return;
 
 	__skb_queue_head_init(&xmitq);
@@ -414,6 +413,7 @@ static void tipc_node_link_down(struct tipc_node *n, int bearer_id)
 	n->sync_point = tnl->rcv_nxt + (U16_MAX / 2 - 1);
 	tipc_link_tnl_prepare(l, tnl, FAILOVER_MSG, &xmitq);
 	tipc_link_reset(l);
+	tipc_link_fsm_evt(l, LINK_FAILOVER_BEGIN_EVT);
 	tipc_bearer_xmit(n->net, tnl->bearer_id, &xmitq, maddr);
 }
 
@@ -749,7 +749,7 @@ static void node_lost_contact(struct tipc_node *n_ptr)
 		struct tipc_link *l_ptr = n_ptr->links[i].link;
 		if (!l_ptr)
 			continue;
-		l_ptr->exec_mode = TIPC_LINK_OPEN;
+		tipc_link_fsm_evt(l_ptr, LINK_FAILOVER_END_EVT);
 		kfree_skb(l_ptr->failover_reasm_skb);
 		l_ptr->failover_reasm_skb = NULL;
 		tipc_link_reset_fragments(l_ptr);
@@ -989,7 +989,7 @@ int tipc_node_xmit_skb(struct net *net, struct sk_buff *skb, u32 dnode,
  * Returns true if state is ok, otherwise consumes buffer and returns false
  */
 static bool tipc_node_check_state(struct tipc_node *n, struct sk_buff *skb,
-				  int bearer_id)
+				  int bearer_id, struct sk_buff_head *xmitq)
 {
 	struct tipc_msg *hdr = buf_msg(skb);
 	int usr = msg_user(hdr);
@@ -1042,42 +1042,47 @@ static bool tipc_node_check_state(struct tipc_node *n, struct sk_buff *skb,
 	/* Initiate or update failover mode if applicable */
 	if ((usr == TUNNEL_PROTOCOL) && (mtyp == FAILOVER_MSG)) {
 		syncpt = oseqno + exp_pkts - 1;
-		if (pl && tipc_link_is_up(pl)) {
+		if (pl && tipc_link_is_up(pl))
 			tipc_node_link_down(n, pl->bearer_id);
-			pl->exec_mode = TIPC_LINK_BLOCKED;
-		}
+
 		/* If pkts arrive out of order, use lowest calculated syncpt */
 		if (less(syncpt, n->sync_point))
 			n->sync_point = syncpt;
 	}
 
 	/* Open parallel link when tunnel link reaches synch point */
-	if ((n->state == NODE_FAILINGOVER) && (more(rcv_nxt, n->sync_point))) {
+	if ((n->state == NODE_FAILINGOVER) && !tipc_link_is_failingover(l)) {
+		if (!more(rcv_nxt, n->sync_point))
+			return true;
 		tipc_node_fsm_evt(n, NODE_FAILOVER_END_EVT);
 		if (pl)
-			pl->exec_mode = TIPC_LINK_OPEN;
+			tipc_link_fsm_evt(pl, LINK_FAILOVER_END_EVT);
 		return true;
 	}
 
 	/* Initiate or update synch mode if applicable */
 	if ((usr == TUNNEL_PROTOCOL) && (mtyp == SYNCH_MSG)) {
 		syncpt = iseqno + exp_pkts - 1;
+		if (!tipc_link_is_up(l)) {
+			tipc_link_fsm_evt(l, LINK_ESTABLISH_EVT);
+			tipc_node_link_up(n, bearer_id, xmitq);
+		}
 		if (n->state == SELF_UP_PEER_UP) {
 			n->sync_point = syncpt;
+			tipc_link_fsm_evt(l, LINK_SYNCH_BEGIN_EVT);
 			tipc_node_fsm_evt(n, NODE_SYNCH_BEGIN_EVT);
 		}
-		l->exec_mode = TIPC_LINK_TUNNEL;
 		if (less(syncpt, n->sync_point))
 			n->sync_point = syncpt;
 	}
 
 	/* Open tunnel link when parallel link reaches synch point */
-	if ((n->state == NODE_SYNCHING) && (l->exec_mode == TIPC_LINK_TUNNEL)) {
+	if ((n->state == NODE_SYNCHING) && tipc_link_is_synching(l)) {
 		if (pl)
 			dlv_nxt = mod(pl->rcv_nxt - skb_queue_len(pl->inputq));
 		if (!pl || more(dlv_nxt, n->sync_point)) {
+			tipc_link_fsm_evt(l, LINK_SYNCH_END_EVT);
 			tipc_node_fsm_evt(n, NODE_SYNCH_END_EVT);
-			l->exec_mode = TIPC_LINK_OPEN;
 			return true;
 		}
 		if ((usr == TUNNEL_PROTOCOL) && (mtyp == SYNCH_MSG))
@@ -1143,7 +1148,7 @@ void tipc_rcv(struct net *net, struct sk_buff *skb, struct tipc_bearer *b)
 		tipc_bclink_acknowledge(n, msg_bcast_ack(hdr));
 
 	/* Check and if necessary update node state */
-	if (likely(tipc_node_check_state(n, skb, bearer_id))) {
+	if (likely(tipc_node_check_state(n, skb, bearer_id, &xmitq))) {
 		rc = tipc_link_rcv(le->link, skb, &xmitq);
 		skb = NULL;
 	}