tipc: add neighbor monitoring framework

TIPC based clusters are by default set up with full-mesh link
connectivity between all nodes. Those links are expected to provide
a short failure detection time, by default set to 1500 ms. Because
of this, the background load for neighbor monitoring in an N-node
cluster increases with a factor N on each node, while the overall
monitoring traffic through the network infrastructure increases at
a ~(N * (N - 1)) rate. Experience has shown that such clusters don't
scale well beyond ~100 nodes unless we significantly increase failure
discovery tolerance.

This commit introduces a framework and an algorithm that drastically
reduces this background load, while basically maintaining the original
failure detection times across the whole cluster. Using this algorithm,
background load will now grow at a rate of ~(2 * sqrt(N)) per node, and
at ~(2 * N * sqrt(N)) in traffic overhead. As an example, each node will
now have to actively monitor 38 neighbors in a 400-node cluster, instead
of as before 399.

This "Overlapping Ring Supervision Algorithm" is completely distributed
and employs no centralized or coordinated state. It goes as follows:

- Each node makes up a linearly ascending, circular list of all its N
  known neighbors, based on their TIPC node identity. This algorithm
  must be the same on all nodes.

- The node then selects the next M = sqrt(N) - 1 nodes downstream from
  itself in the list, and chooses to actively monitor those. This is
  called its "local monitoring domain".

- It creates a domain record describing the monitoring domain, and
  piggy-backs this in the data area of all neighbor monitoring messages
  (LINK_PROTOCOL/STATE) leaving that node. This means that all nodes in
  the cluster eventually (default within 400 ms) will learn about
  its monitoring domain.

- Whenever a node discovers a change in its local domain, e.g., a node
  has been added or has gone down, it creates and sends out a new
  version of its node record to inform all neighbors about the change.

- A node receiving a domain record from anybody outside its local domain
  matches this against its own list (which may not look the same), and
  chooses to not actively monitor those members of the received domain
  record that are also present in its own list. Instead, it relies on
  indications from the direct monitoring nodes if an indirectly
  monitored node has gone up or down. If a node is indicated lost, the
  receiving node temporarily activates its own direct monitoring towards
  that node in order to confirm, or not, that it is actually gone.

- Since each node is actively monitoring sqrt(N) downstream neighbors,
  each node is also actively monitored by the same number of upstream
  neighbors. This means that all non-direct monitoring nodes normally
  will receive sqrt(N) indications that a node is gone.

- A major drawback with ring monitoring is how it handles failures that
  cause massive network partitionings. If both a lost node and all its
  direct monitoring neighbors are inside the lost partition, the nodes in
  the remaining partition will never receive indications about the loss.
  To overcome this, each node also chooses to actively monitor some
  nodes outside its local domain. Those nodes are called remote domain
  "heads", and are selected in such a way that no node in the cluster
  will be more than two direct monitoring hops away. Because of this,
  each node, apart from monitoring the member of its local domain, will
  also typically monitor sqrt(N) remote head nodes.

- As an optimization, local list status, domain status and domain
  records are marked with a generation number. This saves senders from
  unnecessarily conveying  unaltered domain records, and receivers from
  performing unneeded re-adaptations of their node monitoring list, such
  as re-assigning domain heads.

- As a measure of caution we have added the possibility to disable the
  new algorithm through configuration. We do this by keeping a threshold
  value for the cluster size; a cluster that grows beyond this value
  will switch from full-mesh to ring monitoring, and vice versa when
  it shrinks below the value. This means that if the threshold is set to
  a value larger than any anticipated cluster size (default size is 32)
  the new algorithm is effectively disabled. A patch set for altering the
  threshold value and for listing the table contents will follow shortly.

- This change is fully backwards compatible.
Acked-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/Makefile

@@ -6,7 +6,7 @@ obj-$(CONFIG_TIPC) := tipc.o
 
 tipc-y	+= addr.o bcast.o bearer.o \
 	   core.o link.o discover.o msg.o  \
-	   name_distr.o  subscr.o name_table.o net.o  \
+	   name_distr.o  subscr.o monitor.o name_table.o net.o  \
 	   netlink.o netlink_compat.o node.o socket.o eth_media.o \
 	   server.o socket.o
 

net/tipc/addr.h

@@ -73,4 +73,5 @@ int tipc_addr_node_valid(u32 addr);
 int tipc_in_scope(u32 domain, u32 addr);
 int tipc_addr_scope(u32 domain);
 char *tipc_addr_string_fill(char *string, u32 addr);
+
 #endif

net/tipc/bearer.c

 /*
  * net/tipc/bearer.c: TIPC bearer code
  *
- * Copyright (c) 1996-2006, 2013-2014, Ericsson AB
+ * Copyright (c) 1996-2006, 2013-2016, Ericsson AB
  * Copyright (c) 2004-2006, 2010-2013, Wind River Systems
  * All rights reserved.
  *
@@ -39,6 +39,7 @@
 #include "bearer.h"
 #include "link.h"
 #include "discover.h"
+#include "monitor.h"
 #include "bcast.h"
 #include "netlink.h"
 
@@ -313,6 +314,10 @@ static int tipc_enable_bearer(struct net *net, const char *name,
 	rcu_assign_pointer(tn->bearer_list[bearer_id], b);
 	if (skb)
 		tipc_bearer_xmit_skb(net, bearer_id, skb, &b->bcast_addr);
+
+	if (tipc_mon_create(net, bearer_id))
+		return -ENOMEM;
+
 	pr_info("Enabled bearer <%s>, discovery domain %s, priority %u\n",
 		name,
 		tipc_addr_string_fill(addr_string, disc_domain), priority);
@@ -348,6 +353,7 @@ static void bearer_disable(struct net *net, struct tipc_bearer *b)
 		tipc_disc_delete(b->link_req);
 	RCU_INIT_POINTER(tn->bearer_list[bearer_id], NULL);
 	kfree_rcu(b, rcu);
+	tipc_mon_delete(net, bearer_id);
 }
 
 int tipc_enable_l2_media(struct net *net, struct tipc_bearer *b,

net/tipc/bearer.h

 /*
  * net/tipc/bearer.h: Include file for TIPC bearer code
  *
- * Copyright (c) 1996-2006, 2013-2014, Ericsson AB
+ * Copyright (c) 1996-2006, 2013-2016, Ericsson AB
  * Copyright (c) 2005, 2010-2011, Wind River Systems
  * All rights reserved.
  *

net/tipc/core.c

@@ -57,6 +57,7 @@ static int __net_init tipc_init_net(struct net *net)
 
 	tn->net_id = 4711;
 	tn->own_addr = 0;
+	tn->mon_threshold = TIPC_DEF_MON_THRESHOLD;
 	get_random_bytes(&tn->random, sizeof(int));
 	INIT_LIST_HEAD(&tn->node_list);
 	spin_lock_init(&tn->node_list_lock);

net/tipc/core.h

@@ -66,11 +66,13 @@ struct tipc_bc_base;
 struct tipc_link;
 struct tipc_name_table;
 struct tipc_server;
+struct tipc_monitor;
 
 #define TIPC_MOD_VER "2.0.0"
 
-#define NODE_HTABLE_SIZE   512
-#define MAX_BEARERS	   3
+#define NODE_HTABLE_SIZE       512
+#define MAX_BEARERS	         3
+#define TIPC_DEF_MON_THRESHOLD  32
 
 extern int tipc_net_id __read_mostly;
 extern int sysctl_tipc_rmem[3] __read_mostly;
@@ -88,6 +90,10 @@ struct tipc_net {
 	u32 num_nodes;
 	u32 num_links;
 
+	/* Neighbor monitoring list */
+	struct tipc_monitor *monitors[MAX_BEARERS];
+	int mon_threshold;
+
 	/* Bearer list */
 	struct tipc_bearer __rcu *bearer_list[MAX_BEARERS + 1];
 
@@ -126,6 +132,11 @@ static inline struct list_head *tipc_nodes(struct net *net)
 	return &tipc_net(net)->node_list;
 }
 
+static inline unsigned int tipc_hashfn(u32 addr)
+{
+	return addr & (NODE_HTABLE_SIZE - 1);
+}
+
 static inline u16 mod(u16 x)
 {
 	return x & 0xffffu;

net/tipc/link.c

@@ -42,6 +42,7 @@
 #include "name_distr.h"
 #include "discover.h"
 #include "netlink.h"
+#include "monitor.h"
 
 #include <linux/pkt_sched.h>
 
@@ -95,6 +96,7 @@ struct tipc_stats {
  * @pmsg: convenience pointer to "proto_msg" field
  * @priority: current link priority
  * @net_plane: current link network plane ('A' through 'H')
+ * @mon_state: cookie with information needed by link monitor
  * @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
@@ -138,6 +140,7 @@ struct tipc_link {
 	char if_name[TIPC_MAX_IF_NAME];
 	u32 priority;
 	char net_plane;
+	struct tipc_mon_state mon_state;
 	u16 rst_cnt;
 
 	/* Failover/synch */
@@ -708,18 +711,25 @@ int tipc_link_timeout(struct tipc_link *l, struct sk_buff_head *xmitq)
 	bool setup = false;
 	u16 bc_snt = l->bc_sndlink->snd_nxt - 1;
 	u16 bc_acked = l->bc_rcvlink->acked;
-
-	link_profile_stats(l);
+	struct tipc_mon_state *mstate = &l->mon_state;
 
 	switch (l->state) {
 	case LINK_ESTABLISHED:
 	case LINK_SYNCHING:
-		if (l->silent_intv_cnt > l->abort_limit)
-			return tipc_link_fsm_evt(l, LINK_FAILURE_EVT);
 		mtyp = STATE_MSG;
+		link_profile_stats(l);
+		tipc_mon_get_state(l->net, l->addr, mstate, l->bearer_id);
+		if (mstate->reset || (l->silent_intv_cnt > l->abort_limit))
+			return tipc_link_fsm_evt(l, LINK_FAILURE_EVT);
 		state = bc_acked != bc_snt;
-		probe = l->silent_intv_cnt;
-		l->silent_intv_cnt++;
+		state |= l->bc_rcvlink->rcv_unacked;
+		state |= l->rcv_unacked;
+		state |= !skb_queue_empty(&l->transmq);
+		state |= !skb_queue_empty(&l->deferdq);
+		probe = mstate->probing;
+		probe |= l->silent_intv_cnt;
+		if (probe || mstate->monitoring)
+			l->silent_intv_cnt++;
 		break;
 	case LINK_RESET:
 		setup = l->rst_cnt++ <= 4;
@@ -830,6 +840,7 @@ void tipc_link_reset(struct tipc_link *l)
 	l->stats.recv_info = 0;
 	l->stale_count = 0;
 	l->bc_peer_is_up = false;
+	memset(&l->mon_state, 0, sizeof(l->mon_state));
 	tipc_link_reset_stats(l);
 }
 
@@ -1238,6 +1249,9 @@ static void tipc_link_build_proto_msg(struct tipc_link *l, int mtyp, bool probe,
 	struct tipc_msg *hdr;
 	struct sk_buff_head *dfq = &l->deferdq;
 	bool node_up = link_is_up(l->bc_rcvlink);
+	struct tipc_mon_state *mstate = &l->mon_state;
+	int dlen = 0;
+	void *data;
 
 	/* Don't send protocol message during reset or link failover */
 	if (tipc_link_is_blocked(l))
@@ -1250,12 +1264,13 @@ static void tipc_link_build_proto_msg(struct tipc_link *l, int mtyp, bool probe,
 		rcvgap = buf_seqno(skb_peek(dfq)) - l->rcv_nxt;
 
 	skb = tipc_msg_create(LINK_PROTOCOL, mtyp, INT_H_SIZE,
-			      TIPC_MAX_IF_NAME, l->addr,
+			      tipc_max_domain_size, l->addr,
 			      tipc_own_addr(l->net), 0, 0, 0);
 	if (!skb)
 		return;
 
 	hdr = buf_msg(skb);
+	data = msg_data(hdr);
 	msg_set_session(hdr, l->session);
 	msg_set_bearer_id(hdr, l->bearer_id);
 	msg_set_net_plane(hdr, l->net_plane);
@@ -1271,14 +1286,18 @@ static void tipc_link_build_proto_msg(struct tipc_link *l, int mtyp, bool probe,
 
 	if (mtyp == STATE_MSG) {
 		msg_set_seq_gap(hdr, rcvgap);
-		msg_set_size(hdr, INT_H_SIZE);
 		msg_set_probe(hdr, probe);
+		tipc_mon_prep(l->net, data, &dlen, mstate, l->bearer_id);
+		msg_set_size(hdr, INT_H_SIZE + dlen);
+		skb_trim(skb, INT_H_SIZE + dlen);
 		l->stats.sent_states++;
 		l->rcv_unacked = 0;
 	} else {
 		/* RESET_MSG or ACTIVATE_MSG */
 		msg_set_max_pkt(hdr, l->advertised_mtu);
-		strcpy(msg_data(hdr), l->if_name);
+		strcpy(data, l->if_name);
+		msg_set_size(hdr, INT_H_SIZE + TIPC_MAX_IF_NAME);
+		skb_trim(skb, INT_H_SIZE + TIPC_MAX_IF_NAME);
 	}
 	if (probe)
 		l->stats.sent_probes++;
@@ -1371,7 +1390,9 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
 	u16 peers_tol = msg_link_tolerance(hdr);
 	u16 peers_prio = msg_linkprio(hdr);
 	u16 rcv_nxt = l->rcv_nxt;
+	u16 dlen = msg_data_sz(hdr);
 	int mtyp = msg_type(hdr);
+	void *data;
 	char *if_name;
 	int rc = 0;
 
@@ -1381,6 +1402,10 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
 	if (tipc_own_addr(l->net) > msg_prevnode(hdr))
 		l->net_plane = msg_net_plane(hdr);
 
+	skb_linearize(skb);
+	hdr = buf_msg(skb);
+	data = msg_data(hdr);
+
 	switch (mtyp) {
 	case RESET_MSG:
 
@@ -1391,8 +1416,6 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
 		/* fall thru' */
 
 	case ACTIVATE_MSG:
-		skb_linearize(skb);
-		hdr = buf_msg(skb);
 
 		/* Complete own link name with peer's interface name */
 		if_name =  strrchr(l->name, ':') + 1;
@@ -1400,7 +1423,7 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
 			break;
 		if (msg_data_sz(hdr) < TIPC_MAX_IF_NAME)
 			break;
-		strncpy(if_name, msg_data(hdr),	TIPC_MAX_IF_NAME);
+		strncpy(if_name, data, TIPC_MAX_IF_NAME);
 
 		/* Update own tolerance if peer indicates a non-zero value */
 		if (in_range(peers_tol, TIPC_MIN_LINK_TOL, TIPC_MAX_LINK_TOL))
@@ -1448,6 +1471,8 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
 				rc = TIPC_LINK_UP_EVT;
 			break;
 		}
+		tipc_mon_rcv(l->net, data, dlen, l->addr,
+			     &l->mon_state, l->bearer_id);
 
 		/* Send NACK if peer has sent pkts we haven't received yet */
 		if (more(peers_snd_nxt, rcv_nxt) && !tipc_link_is_synching(l))

net/tipc/monitor.c

+/*
+ * net/tipc/monitor.c
+ *
+ * Copyright (c) 2016, Ericsson AB
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the names of the copyright holders nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * Alternatively, this software may be distributed under the terms of the
+ * GNU General Public License ("GPL") version 2 as published by the Free
+ * Software Foundation.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "core.h"
+#include "addr.h"
+#include "monitor.h"
+
+#define MAX_MON_DOMAIN       64
+#define MON_TIMEOUT          120000
+#define MAX_PEER_DOWN_EVENTS 4
+
+/* struct tipc_mon_domain: domain record to be transferred between peers
+ * @len: actual size of domain record
+ * @gen: current generation of sender's domain
+ * @ack_gen: most recent generation of self's domain acked by peer
+ * @member_cnt: number of domain member nodes described in this record
+ * @up_map: bit map indicating which of the members the sender considers up
+ * @members: identity of the domain members
+ */
+struct tipc_mon_domain {
+	u16 len;
+	u16 gen;
+	u16 ack_gen;
+	u16 member_cnt;
+	u64 up_map;
+	u32 members[MAX_MON_DOMAIN];
+};
+
+/* struct tipc_peer: state of a peer node and its domain
+ * @addr: tipc node identity of peer
+ * @head_map: shows which other nodes currently consider peer 'up'
+ * @domain: most recent domain record from peer
+ * @hash: position in hashed lookup list
+ * @list: position in linked list, in circular ascending order by 'addr'
+ * @applied: number of reported domain members applied on this monitor list
+ * @is_up: peer is up as seen from this node
+ * @is_head: peer is assigned domain head as seen from this node
+ * @is_local: peer is in local domain and should be continuously monitored
+ * @down_cnt: - numbers of other peers which have reported this on lost
+ */
+struct tipc_peer {
+	u32 addr;
+	struct tipc_mon_domain *domain;
+	struct hlist_node hash;
+	struct list_head list;
+	u8 applied;
+	u8 down_cnt;
+	bool is_up;
+	bool is_head;
+	bool is_local;
+};
+
+struct tipc_monitor {
+	struct hlist_head peers[NODE_HTABLE_SIZE];
+	int peer_cnt;
+	struct tipc_peer *self;
+	rwlock_t lock;
+	struct tipc_mon_domain cache;
+	u16 list_gen;
+	u16 dom_gen;
+	struct net *net;
+	struct timer_list timer;
+	unsigned long timer_intv;
+};
+
+static struct tipc_monitor *tipc_monitor(struct net *net, int bearer_id)
+{
+	return tipc_net(net)->monitors[bearer_id];
+}
+
+const int tipc_max_domain_size = sizeof(struct tipc_mon_domain);
+
+/* dom_rec_len(): actual length of domain record for transport
+ */
+static int dom_rec_len(struct tipc_mon_domain *dom, u16 mcnt)
+{
+	return ((void *)&dom->members - (void *)dom) + (mcnt * sizeof(u32));
+}
+
+/* dom_size() : calculate size of own domain based on number of peers
+ */
+static int dom_size(int peers)
+{
+	int i = 0;
+
+	while ((i * i) < peers)
+		i++;
+	return i < MAX_MON_DOMAIN ? i : MAX_MON_DOMAIN;
+}
+
+static void map_set(u64 *up_map, int i, unsigned int v)
+{
+	*up_map &= ~(1 << i);
+	*up_map |= (v << i);
+}
+
+static int map_get(u64 up_map, int i)
+{
+	return (up_map & (1 << i)) >> i;
+}
+
+static struct tipc_peer *peer_prev(struct tipc_peer *peer)
+{
+	return list_last_entry(&peer->list, struct tipc_peer, list);
+}
+
+static struct tipc_peer *peer_nxt(struct tipc_peer *peer)
+{
+	return list_first_entry(&peer->list, struct tipc_peer, list);
+}
+
+static struct tipc_peer *peer_head(struct tipc_peer *peer)
+{
+	while (!peer->is_head)
+		peer = peer_prev(peer);
+	return peer;
+}
+
+static struct tipc_peer *get_peer(struct tipc_monitor *mon, u32 addr)
+{
+	struct tipc_peer *peer;
+	unsigned int thash = tipc_hashfn(addr);
+
+	hlist_for_each_entry(peer, &mon->peers[thash], hash) {
+		if (peer->addr == addr)
+			return peer;
+	}
+	return NULL;
+}
+
+static struct tipc_peer *get_self(struct net *net, int bearer_id)
+{
+	struct tipc_monitor *mon = tipc_monitor(net, bearer_id);
+
+	return mon->self;
+}
+
+static inline bool tipc_mon_is_active(struct net *net, struct tipc_monitor *mon)
+{
+	struct tipc_net *tn = tipc_net(net);
+
+	return mon->peer_cnt > tn->mon_threshold;
+}
+
+/* mon_identify_lost_members() : - identify amd mark potentially lost members
+ */
+static void mon_identify_lost_members(struct tipc_peer *peer,
+				      struct tipc_mon_domain *dom_bef,
+				      int applied_bef)
+{
+	struct tipc_peer *member = peer;
+	struct tipc_mon_domain *dom_aft = peer->domain;
+	int applied_aft = peer->applied;
+	int i;
+
+	for (i = 0; i < applied_bef; i++) {
+		member = peer_nxt(member);
+
+		/* Do nothing if self or peer already see member as down */
+		if (!member->is_up || !map_get(dom_bef->up_map, i))
+			continue;
+
+		/* Loss of local node must be detected by active probing */
+		if (member->is_local)
+			continue;
+
+		/* Start probing if member was removed from applied domain */
+		if (!applied_aft || (applied_aft < i)) {
+			member->down_cnt = 1;
+			continue;
+		}
+
+		/* Member loss is confirmed if it is still in applied domain */
+		if (!map_get(dom_aft->up_map, i))
+			member->down_cnt++;
+	}
+}
+
+/* mon_apply_domain() : match a peer's domain record against monitor list
+ */
+static void mon_apply_domain(struct tipc_monitor *mon,
+			     struct tipc_peer *peer)
+{
+	struct tipc_mon_domain *dom = peer->domain;
+	struct tipc_peer *member;
+	u32 addr;
+	int i;
+
+	if (!dom || !peer->is_up)
+		return;
+
+	/* Scan across domain members and match against monitor list */
+	peer->applied = 0;
+	member = peer_nxt(peer);
+	for (i = 0; i < dom->member_cnt; i++) {
+		addr = dom->members[i];
+		if (addr != member->addr)
+			return;
+		peer->applied++;
+		member = peer_nxt(member);
+	}
+}
+
+/* mon_update_local_domain() : update after peer addition/removal/up/down
+ */
+static void mon_update_local_domain(struct tipc_monitor *mon)
+{
+	struct tipc_peer *self = mon->self;
+	struct tipc_mon_domain *cache = &mon->cache;
+	struct tipc_mon_domain *dom = self->domain;
+	struct tipc_peer *peer = self;
+	u64 prev_up_map = dom->up_map;
+	u16 member_cnt, i;
+	bool diff;
+
+	/* Update local domain size based on current size of cluster */
+	member_cnt = dom_size(mon->peer_cnt) - 1;
+	self->applied = member_cnt;
+
+	/* Update native and cached outgoing local domain records */
+	dom->len = dom_rec_len(dom, member_cnt);
+	diff = dom->member_cnt != member_cnt;
+	dom->member_cnt = member_cnt;
+	for (i = 0; i < member_cnt; i++) {
+		peer = peer_nxt(peer);
+		diff |= dom->members[i] != peer->addr;
+		dom->members[i] = peer->addr;
+		map_set(&dom->up_map, i, peer->is_up);
+		cache->members[i] = htonl(peer->addr);
+	}
+	diff |= dom->up_map != prev_up_map;
+	if (!diff)
+		return;
+	dom->gen = ++mon->dom_gen;
+	cache->len = htons(dom->len);
+	cache->gen = htons(dom->gen);
+	cache->member_cnt = htons(member_cnt);
+	cache->up_map = cpu_to_be64(dom->up_map);
+	mon_apply_domain(mon, self);
+}
+
+/* mon_update_neighbors() : update preceding neighbors of added/removed peer
+ */
+static void mon_update_neighbors(struct tipc_monitor *mon,
+				 struct tipc_peer *peer)
+{
+	int dz, i;
+
+	dz = dom_size(mon->peer_cnt);
+	for (i = 0; i < dz; i++) {
+		mon_apply_domain(mon, peer);
+		peer = peer_prev(peer);
+	}
+}
+
+/* mon_assign_roles() : reassign peer roles after a network change
+ * The monitor list is consistent at this stage; i.e., each peer is monitoring
+ * a set of domain members as matched between domain record and the monitor list
+ */
+static void mon_assign_roles(struct tipc_monitor *mon, struct tipc_peer *head)
+{
+	struct tipc_peer *peer = peer_nxt(head);
+	struct tipc_peer *self = mon->self;
+	int i = 0;
+
+	for (; peer != self; peer = peer_nxt(peer)) {
+		peer->is_local = false;
+
+		/* Update domain member */
+		if (i++ < head->applied) {
+			peer->is_head = false;
+			if (head == self)
+				peer->is_local = true;
+			continue;
+		}
+		/* Assign next domain head */
+		if (!peer->is_up)
+			continue;
+		if (peer->is_head)
+			break;
+		head = peer;
+		head->is_head = true;
+		i = 0;
+	}
+	mon->list_gen++;
+}
+
+void tipc_mon_remove_peer(struct net *net, u32 addr, int bearer_id)
+{
+	struct tipc_monitor *mon = tipc_monitor(net, bearer_id);
+	struct tipc_peer *self = get_self(net, bearer_id);
+	struct tipc_peer *peer, *prev, *head;
+
+	write_lock_bh(&mon->lock);
+	peer = get_peer(mon, addr);
+	if (!peer)
+		goto exit;
+	prev = peer_prev(peer);
+	list_del(&peer->list);
+	hlist_del(&peer->hash);
+	kfree(peer->domain);
+	kfree(peer);
+	mon->peer_cnt--;
+	head = peer_head(prev);
+	if (head == self)
+		mon_update_local_domain(mon);
+	mon_update_neighbors(mon, prev);
+
+	/* Revert to full-mesh monitoring if we reach threshold */
+	if (!tipc_mon_is_active(net, mon)) {
+		list_for_each_entry(peer, &self->list, list) {
+			kfree(peer->domain);
+			peer->domain = NULL;
+			peer->applied = 0;
+		}
+	}
+	mon_assign_roles(mon, head);
+exit:
+	write_unlock_bh(&mon->lock);
+}
+
+static bool tipc_mon_add_peer(struct tipc_monitor *mon, u32 addr,
+			      struct tipc_peer **peer)
+{
+	struct tipc_peer *self = mon->self;
+	struct tipc_peer *cur, *prev, *p;
+
+	p = kzalloc(sizeof(*p), GFP_ATOMIC);
+	*peer = p;
+	if (!p)
+		return false;
+	p->addr = addr;
+
+	/* Add new peer to lookup list */
+	INIT_LIST_HEAD(&p->list);
+	hlist_add_head(&p->hash, &mon->peers[tipc_hashfn(addr)]);
+
+	/* Sort new peer into iterator list, in ascending circular order */
+	prev = self;
+	list_for_each_entry(cur, &self->list, list) {
+		if ((addr > prev->addr) && (addr < cur->addr))
+			break;
+		if (((addr < cur->addr) || (addr > prev->addr)) &&
+		    (prev->addr > cur->addr))
+			break;
+		prev = cur;
+	}
+	list_add_tail(&p->list, &cur->list);
+	mon->peer_cnt++;
+	mon_update_neighbors(mon, p);
+	return true;
+}
+
+void tipc_mon_peer_up(struct net *net, u32 addr, int bearer_id)
+{
+	struct tipc_monitor *mon = tipc_monitor(net, bearer_id);
+	struct tipc_peer *self = get_self(net, bearer_id);
+	struct tipc_peer *peer, *head;
+
+	write_lock_bh(&mon->lock);
+	peer = get_peer(mon, addr);
+	if (!peer && !tipc_mon_add_peer(mon, addr, &peer))
+		goto exit;
+	peer->is_up = true;
+	head = peer_head(peer);
+	if (head == self)
+		mon_update_local_domain(mon);
+	mon_assign_roles(mon, head);
+exit:
+	write_unlock_bh(&mon->lock);
+}
+
+void tipc_mon_peer_down(struct net *net, u32 addr, int bearer_id)
+{
+	struct tipc_monitor *mon = tipc_monitor(net, bearer_id);
+	struct tipc_peer *self = get_self(net, bearer_id);
+	struct tipc_peer *peer, *head;
+	struct tipc_mon_domain *dom;
+	int applied;
+
+	write_lock_bh(&mon->lock);
+	peer = get_peer(mon, addr);
+	if (!peer) {
+		pr_warn("Mon: unknown link %x/%u DOWN\n", addr, bearer_id);
+		goto exit;
+	}
+	applied = peer->applied;
+	peer->applied = 0;
+	dom = peer->domain;
+	peer->domain = NULL;
+	if (peer->is_head)
+		mon_identify_lost_members(peer, dom, applied);
+	kfree(dom);
+	peer->is_up = false;
+	peer->is_head = false;
+	peer->is_local = false;
+	peer->down_cnt = 0;
+	head = peer_head(peer);
+	if (head == self)
+		mon_update_local_domain(mon);
+	mon_assign_roles(mon, head);
+exit:
+	write_unlock_bh(&mon->lock);
+}
+
+/* tipc_mon_rcv - process monitor domain event message
+ */
+void tipc_mon_rcv(struct net *net, void *data, u16 dlen, u32 addr,
+		  struct tipc_mon_state *state, int bearer_id)
+{
+	struct tipc_monitor *mon = tipc_monitor(net, bearer_id);
+	struct tipc_mon_domain *arrv_dom = data;
+	struct tipc_mon_domain dom_bef;
+	struct tipc_mon_domain *dom;
+	struct tipc_peer *peer;
+	u16 new_member_cnt = ntohs(arrv_dom->member_cnt);
+	int new_dlen = dom_rec_len(arrv_dom, new_member_cnt);
+	u16 new_gen = ntohs(arrv_dom->gen);
+	u16 acked_gen = ntohs(arrv_dom->ack_gen);
+	bool probing = state->probing;
+	int i, applied_bef;
+
+	state->probing = false;
+	if (!dlen)
+		return;
+
+	/* Sanity check received domain record */
+	if ((dlen < new_dlen) || ntohs(arrv_dom->len) != new_dlen) {
+		pr_warn_ratelimited("Received illegal domain record\n");
+		return;
+	}
+
+	/* Synch generation numbers with peer if link just came up */
+	if (!state->synched) {
+		state->peer_gen = new_gen - 1;
+		state->acked_gen = acked_gen;
+		state->synched = true;
+	}
+
+	if (more(acked_gen, state->acked_gen))
+		state->acked_gen = acked_gen;
+
+	/* Drop duplicate unless we are waiting for a probe response */
+	if (!more(new_gen, state->peer_gen) && !probing)
+		return;
+
+	write_lock_bh(&mon->lock);
+	peer = get_peer(mon, addr);
+	if (!peer || !peer->is_up)
+		goto exit;
+
+	/* Peer is confirmed, stop any ongoing probing */
+	peer->down_cnt = 0;
+
+	/* Task is done for duplicate record */
+	if (!more(new_gen, state->peer_gen))
+		goto exit;
+
+	state->peer_gen = new_gen;
+
+	/* Cache current domain record for later use */
+	dom_bef.member_cnt = 0;
+	dom = peer->domain;
+	if (dom)
+		memcpy(&dom_bef, dom, dom->len);
+
+	/* Transform and store received domain record */
+	if (!dom || (dom->len < new_dlen)) {
+		kfree(dom);
+		dom = kmalloc(new_dlen, GFP_ATOMIC);
+		peer->domain = dom;
+		if (!dom)
+			goto exit;
+	}
+	dom->len = new_dlen;
+	dom->gen = new_gen;
+	dom->member_cnt = new_member_cnt;
+	dom->up_map = be64_to_cpu(arrv_dom->up_map);
+	for (i = 0; i < new_member_cnt; i++)
+		dom->members[i] = ntohl(arrv_dom->members[i]);
+
+	/* Update peers affected by this domain record */
+	applied_bef = peer->applied;
+	mon_apply_domain(mon, peer);
+	mon_identify_lost_members(peer, &dom_bef, applied_bef);
+	mon_assign_roles(mon, peer_head(peer));
+exit:
+	write_unlock_bh(&mon->lock);
+}
+
+void tipc_mon_prep(struct net *net, void *data, int *dlen,
+		   struct tipc_mon_state *state, int bearer_id)
+{
+	struct tipc_monitor *mon = tipc_monitor(net, bearer_id);
+	struct tipc_mon_domain *dom = data;
+	u16 gen = mon->dom_gen;
+	u16 len;
+
+	if (!tipc_mon_is_active(net, mon))
+		return;
+
+	/* Send only a dummy record with ack if peer has acked our last sent */
+	if (likely(state->acked_gen == gen)) {
+		len = dom_rec_len(dom, 0);
+		*dlen = len;
+		dom->len = htons(len);
+		dom->gen = htons(gen);
+		dom->ack_gen = htons(state->peer_gen);
+		dom->member_cnt = 0;
+		return;
+	}
+	/* Send the full record */
+	read_lock_bh(&mon->lock);
+	len = ntohs(mon->cache.len);
+	*dlen = len;
+	memcpy(data, &mon->cache, len);
+	read_unlock_bh(&mon->lock);
+	dom->ack_gen = htons(state->peer_gen);
+}
+
+void tipc_mon_get_state(struct net *net, u32 addr,
+			struct tipc_mon_state *state,
+			int bearer_id)
+{
+	struct tipc_monitor *mon = tipc_monitor(net, bearer_id);
+	struct tipc_peer *peer;
+
+	/* Used cached state if table has not changed */
+	if (!state->probing &&
+	    (state->list_gen == mon->list_gen) &&
+	    (state->acked_gen == mon->dom_gen))
+		return;
+
+	read_lock_bh(&mon->lock);
+	peer = get_peer(mon, addr);
+	if (peer) {
+		state->probing = state->acked_gen != mon->dom_gen;
+		state->probing |= peer->down_cnt;
+		state->reset |= peer->down_cnt >= MAX_PEER_DOWN_EVENTS;
+		state->monitoring = peer->is_local;
+		state->monitoring |= peer->is_head;
+		state->list_gen = mon->list_gen;
+	}
+	read_unlock_bh(&mon->lock);
+}
+
+static void mon_timeout(unsigned long m)
+{
+	struct tipc_monitor *mon = (void *)m;
+	struct tipc_peer *self;
+	int best_member_cnt = dom_size(mon->peer_cnt) - 1;
+
+	write_lock_bh(&mon->lock);
+	self = mon->self;
+	if (self && (best_member_cnt != self->applied)) {
+		mon_update_local_domain(mon);
+		mon_assign_roles(mon, self);
+	}
+	write_unlock_bh(&mon->lock);
+	mod_timer(&mon->timer, jiffies + mon->timer_intv);
+}
+
+int tipc_mon_create(struct net *net, int bearer_id)
+{
+	struct tipc_net *tn = tipc_net(net);
+	struct tipc_monitor *mon;
+	struct tipc_peer *self;
+	struct tipc_mon_domain *dom;
+
+	if (tn->monitors[bearer_id])
+		return 0;
+
+	mon = kzalloc(sizeof(*mon), GFP_ATOMIC);
+	self = kzalloc(sizeof(*self), GFP_ATOMIC);
+	dom = kzalloc(sizeof(*dom), GFP_ATOMIC);
+	if (!mon || !self || !dom) {
+		kfree(mon);
+		kfree(self);
+		kfree(dom);
+		return -ENOMEM;
+	}
+	tn->monitors[bearer_id] = mon;
+	rwlock_init(&mon->lock);
+	mon->net = net;
+	mon->peer_cnt = 1;
+	mon->self = self;
+	self->domain = dom;
+	self->addr = tipc_own_addr(net);
+	self->is_up = true;
+	self->is_head = true;
+	INIT_LIST_HEAD(&self->list);
+	setup_timer(&mon->timer, mon_timeout, (unsigned long)mon);
+	mon->timer_intv = msecs_to_jiffies(MON_TIMEOUT + (tn->random & 0xffff));
+	mod_timer(&mon->timer, jiffies + mon->timer_intv);
+	return 0;
+}
+
+void tipc_mon_delete(struct net *net, int bearer_id)
+{
+	struct tipc_net *tn = tipc_net(net);
+	struct tipc_monitor *mon = tipc_monitor(net, bearer_id);
+	struct tipc_peer *self = get_self(net, bearer_id);
+	struct tipc_peer *peer, *tmp;
+
+	write_lock_bh(&mon->lock);
+	tn->monitors[bearer_id] = NULL;
+	list_for_each_entry_safe(peer, tmp, &self->list, list) {
+		list_del(&peer->list);
+		hlist_del(&peer->hash);
+		kfree(peer->domain);
+		kfree(peer);
+	}
+	mon->self = NULL;
+	write_unlock_bh(&mon->lock);
+	del_timer_sync(&mon->timer);
+	kfree(self->domain);
+	kfree(self);
+	kfree(mon);
+}

net/tipc/monitor.h

+/*
+ * net/tipc/monitor.h
+ *
+ * Copyright (c) 2015, Ericsson AB
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the names of the copyright holders nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * Alternatively, this software may be distributed under the terms of the
+ * GNU General Public License ("GPL") version 2 as published by the Free
+ * Software Foundation.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _TIPC_MONITOR_H
+#define _TIPC_MONITOR_H
+
+/* struct tipc_mon_state: link instance's cache of monitor list and domain state
+ * @list_gen: current generation of this node's monitor list
+ * @gen: current generation of this node's local domain
+ * @peer_gen: most recent domain generation received from peer
+ * @acked_gen: most recent generation of self's domain acked by peer
+ * @monitoring: this peer endpoint should continuously monitored
+ * @probing: peer endpoint should be temporarily probed for potential loss
+ * @synched: domain record's generation has been synched with peer after reset
+ */
+struct tipc_mon_state {
+	u16 list_gen;
+	u16 peer_gen;
+	u16 acked_gen;
+	bool monitoring :1;
+	bool probing    :1;
+	bool reset      :1;
+	bool synched    :1;
+};
+
+int tipc_mon_create(struct net *net, int bearer_id);
+void tipc_mon_delete(struct net *net, int bearer_id);
+
+void tipc_mon_peer_up(struct net *net, u32 addr, int bearer_id);
+void tipc_mon_peer_down(struct net *net, u32 addr, int bearer_id);
+void tipc_mon_prep(struct net *net, void *data, int *dlen,
+		   struct tipc_mon_state *state, int bearer_id);
+void tipc_mon_rcv(struct net *net, void *data, u16 dlen, u32 addr,
+		  struct tipc_mon_state *state, int bearer_id);
+void tipc_mon_get_state(struct net *net, u32 addr,
+			struct tipc_mon_state *state,
+			int bearer_id);
+void tipc_mon_remove_peer(struct net *net, u32 addr, int bearer_id);
+
+extern const int tipc_max_domain_size;
+#endif

net/tipc/node.c

@@ -40,6 +40,7 @@
 #include "name_distr.h"
 #include "socket.h"
 #include "bcast.h"
+#include "monitor.h"
 #include "discover.h"
 #include "netlink.h"
 
@@ -205,17 +206,6 @@ u16 tipc_node_get_capabilities(struct net *net, u32 addr)
 	return caps;
 }
 
-/*
- * A trivial power-of-two bitmask technique is used for speed, since this
- * operation is done for every incoming TIPC packet. The number of hash table
- * entries has been chosen so that no hash chain exceeds 8 nodes and will
- * usually be much smaller (typically only a single node).
- */
-static unsigned int tipc_hashfn(u32 addr)
-{
-	return addr & (NODE_HTABLE_SIZE - 1);
-}
-
 static void tipc_node_kref_release(struct kref *kref)
 {
 	struct tipc_node *n = container_of(kref, struct tipc_node, kref);
@@ -279,6 +269,7 @@ static void tipc_node_write_unlock(struct tipc_node *n)
 	u32 addr = 0;
 	u32 flags = n->action_flags;
 	u32 link_id = 0;
+	u32 bearer_id;
 	struct list_head *publ_list;
 
 	if (likely(!flags)) {
@@ -288,6 +279,7 @@ static void tipc_node_write_unlock(struct tipc_node *n)
 
 	addr = n->addr;
 	link_id = n->link_id;
+	bearer_id = link_id & 0xffff;
 	publ_list = &n->publ_list;
 
 	n->action_flags &= ~(TIPC_NOTIFY_NODE_DOWN | TIPC_NOTIFY_NODE_UP |
@@ -301,13 +293,16 @@ static void tipc_node_write_unlock(struct tipc_node *n)
 	if (flags & TIPC_NOTIFY_NODE_UP)
 		tipc_named_node_up(net, addr);
 
-	if (flags & TIPC_NOTIFY_LINK_UP)
+	if (flags & TIPC_NOTIFY_LINK_UP) {
+		tipc_mon_peer_up(net, addr, bearer_id);
 		tipc_nametbl_publish(net, TIPC_LINK_STATE, addr, addr,
 				     TIPC_NODE_SCOPE, link_id, addr);
-
-	if (flags & TIPC_NOTIFY_LINK_DOWN)
+	}
+	if (flags & TIPC_NOTIFY_LINK_DOWN) {
+		tipc_mon_peer_down(net, addr, bearer_id);
 		tipc_nametbl_withdraw(net, TIPC_LINK_STATE, addr,
 				      link_id, addr);
+	}
 }
 
 struct tipc_node *tipc_node_create(struct net *net, u32 addr, u16 capabilities)
@@ -691,6 +686,7 @@ static void tipc_node_link_down(struct tipc_node *n, int bearer_id, bool delete)
 	struct tipc_link *l = le->link;
 	struct tipc_media_addr *maddr;
 	struct sk_buff_head xmitq;
+	int old_bearer_id = bearer_id;
 
 	if (!l)
 		return;
@@ -710,6 +706,8 @@ static void tipc_node_link_down(struct tipc_node *n, int bearer_id, bool delete)
 		tipc_link_fsm_evt(l, LINK_RESET_EVT);
 	}
 	tipc_node_write_unlock(n);
+	if (delete)
+		tipc_mon_remove_peer(n->net, n->addr, old_bearer_id);
 	tipc_bearer_xmit(n->net, bearer_id, &xmitq, maddr);
 	tipc_sk_rcv(n->net, &le->inputq);
 }