tipc: convert node lock to rwlock

According to the node FSM a node in state SELF_UP_PEER_UP cannot
change state inside a lock context, except when a TUNNEL_PROTOCOL
(SYNCH or FAILOVER) packet arrives. However, the node's individual
links may still change state.

Since each link now is protected by its own spinlock, we finally have
the conditions in place to convert the node spinlock to an rwlock_t.
If the node state and arriving packet type are rigth, we can let the
link directly receive the packet under protection of its own spinlock
and the node lock in read mode. In all other cases we use the node
lock in write mode. This enables full concurrent execution between
parallel links during steady-state traffic situations, i.e., 99+ %
of the time.

This commit implements this change.
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

@@ -1547,7 +1547,7 @@ static struct tipc_node *tipc_link_find_owner(struct net *net,
 	*bearer_id = 0;
 	rcu_read_lock();
 	list_for_each_entry_rcu(n_ptr, &tn->node_list, list) {
-		tipc_node_lock(n_ptr);
+		tipc_node_read_lock(n_ptr);
 		for (i = 0; i < MAX_BEARERS; i++) {
 			l_ptr = n_ptr->links[i].link;
 			if (l_ptr && !strcmp(l_ptr->name, link_name)) {
@@ -1556,7 +1556,7 @@ static struct tipc_node *tipc_link_find_owner(struct net *net,
 				break;
 			}
 		}
-		tipc_node_unlock(n_ptr);
+		tipc_node_read_unlock(n_ptr);
 		if (found_node)
 			break;
 	}
@@ -1658,7 +1658,7 @@ int tipc_nl_link_set(struct sk_buff *skb, struct genl_info *info)
 	if (!node)
 		return -EINVAL;
 
-	tipc_node_lock(node);
+	tipc_node_read_lock(node);
 
 	link = node->links[bearer_id].link;
 	if (!link) {
@@ -1699,7 +1699,7 @@ int tipc_nl_link_set(struct sk_buff *skb, struct genl_info *info)
 	}
 
 out:
-	tipc_node_unlock(node);
+	tipc_node_read_unlock(node);
 
 	return res;
 }
@@ -1898,10 +1898,10 @@ int tipc_nl_link_dump(struct sk_buff *skb, struct netlink_callback *cb)
 
 		list_for_each_entry_continue_rcu(node, &tn->node_list,
 						 list) {
-			tipc_node_lock(node);
+			tipc_node_read_lock(node);
 			err = __tipc_nl_add_node_links(net, &msg, node,
 						       &prev_link);
-			tipc_node_unlock(node);
+			tipc_node_read_unlock(node);
 			if (err)
 				goto out;
 
@@ -1913,10 +1913,10 @@ int tipc_nl_link_dump(struct sk_buff *skb, struct netlink_callback *cb)
 			goto out;
 
 		list_for_each_entry_rcu(node, &tn->node_list, list) {
-			tipc_node_lock(node);
+			tipc_node_read_lock(node);
 			err = __tipc_nl_add_node_links(net, &msg, node,
 						       &prev_link);
-			tipc_node_unlock(node);
+			tipc_node_read_unlock(node);
 			if (err)
 				goto out;
 
@@ -1967,16 +1967,16 @@ int tipc_nl_link_get(struct sk_buff *skb, struct genl_info *info)
 		if (!node)
 			return -EINVAL;
 
-		tipc_node_lock(node);
+		tipc_node_read_lock(node);
 		link = node->links[bearer_id].link;
 		if (!link) {
-			tipc_node_unlock(node);
+			tipc_node_read_unlock(node);
 			nlmsg_free(msg.skb);
 			return -EINVAL;
 		}
 
 		err = __tipc_nl_add_link(net, &msg, link, 0);
-		tipc_node_unlock(node);
+		tipc_node_read_unlock(node);
 		if (err) {
 			nlmsg_free(msg.skb);
 			return err;
@@ -2021,18 +2021,18 @@ int tipc_nl_link_reset_stats(struct sk_buff *skb, struct genl_info *info)
 	node = tipc_link_find_owner(net, link_name, &bearer_id);
 	if (!node)
 		return -EINVAL;
+
 	le = &node->links[bearer_id];
-	tipc_node_lock(node);
+	tipc_node_read_lock(node);
 	spin_lock_bh(&le->lock);
 	link = le->link;
 	if (!link) {
-		tipc_node_unlock(node);
+		spin_unlock_bh(&le->lock);
+		tipc_node_read_unlock(node);
 		return -EINVAL;
 	}
-
 	link_reset_statistics(link);
 	spin_unlock_bh(&le->lock);
-	tipc_node_unlock(node);
-
+	tipc_node_read_unlock(node);
 	return 0;
 }

net/tipc/node.h

@@ -109,7 +109,7 @@ struct tipc_bclink_entry {
 struct tipc_node {
 	u32 addr;
 	struct kref kref;
-	spinlock_t lock;
+	rwlock_t lock;
 	struct net *net;
 	struct hlist_node hash;
 	int active_links[2];
@@ -145,7 +145,8 @@ void tipc_node_detach_link(struct tipc_node *n_ptr, struct tipc_link *l_ptr);
 bool tipc_node_is_up(struct tipc_node *n);
 int tipc_node_get_linkname(struct net *net, u32 bearer_id, u32 node,
 			   char *linkname, size_t len);
-void tipc_node_unlock(struct tipc_node *node);
+void tipc_node_read_lock(struct tipc_node *n);
+void tipc_node_read_unlock(struct tipc_node *node);
 int tipc_node_xmit(struct net *net, struct sk_buff_head *list, u32 dnode,
 		   int selector);
 int tipc_node_xmit_skb(struct net *net, struct sk_buff *skb, u32 dest,
@@ -157,11 +158,6 @@ int tipc_node_add_conn(struct net *net, u32 dnode, u32 port, u32 peer_port);
 void tipc_node_remove_conn(struct net *net, u32 dnode, u32 port);
 int tipc_nl_node_dump(struct sk_buff *skb, struct netlink_callback *cb);
 
-static inline void tipc_node_lock(struct tipc_node *node)
-{
-	spin_lock_bh(&node->lock);
-}
-
 static inline struct tipc_link *node_active_link(struct tipc_node *n, int sel)
 {
 	int bearer_id = n->active_links[sel & 1];