Merge branch 'tipc-link-starvation'

Jon Maloy says:

====================
tipc: improve interaction socket-link

We fix a very real starvation problem that may occur when a link
encounters send buffer congestion. At the same time we make the
interaction between the socket and link layer simpler and more
consistent.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/bcast.c

@@ -174,7 +174,7 @@ static void tipc_bcbase_xmit(struct net *net, struct sk_buff_head *xmitq)
  *                    and to identified node local sockets
  * @net: the applicable net namespace
  * @list: chain of buffers containing message
- * Consumes the buffer chain, except when returning -ELINKCONG
+ * Consumes the buffer chain.
  * Returns 0 if success, otherwise errno: -ELINKCONG,-EHOSTUNREACH,-EMSGSIZE
  */
 int tipc_bcast_xmit(struct net *net, struct sk_buff_head *list)
@@ -197,7 +197,7 @@ int tipc_bcast_xmit(struct net *net, struct sk_buff_head *list)
 	tipc_bcast_unlock(net);
 
 	/* Don't send to local node if adding to link failed */
-	if (unlikely(rc)) {
+	if (unlikely(rc && (rc != -ELINKCONG))) {
 		__skb_queue_purge(&rcvq);
 		return rc;
 	}
@@ -206,7 +206,7 @@ int tipc_bcast_xmit(struct net *net, struct sk_buff_head *list)
 	tipc_bcbase_xmit(net, &xmitq);
 	tipc_sk_mcast_rcv(net, &rcvq, &inputq);
 	__skb_queue_purge(list);
-	return 0;
+	return rc;
 }
 
 /* tipc_bcast_rcv - receive a broadcast packet, and deliver to rcv link

net/tipc/link.c

@@ -776,60 +776,47 @@ int tipc_link_timeout(struct tipc_link *l, struct sk_buff_head *xmitq)
 
 /**
  * link_schedule_user - schedule a message sender for wakeup after congestion
- * @link: congested link
- * @list: message that was attempted sent
+ * @l: congested link
+ * @hdr: header of message that is being sent
  * Create pseudo msg to send back to user when congestion abates
- * Does not consume buffer list
  */
-static int link_schedule_user(struct tipc_link *link, struct sk_buff_head *list)
+static int link_schedule_user(struct tipc_link *l, struct tipc_msg *hdr)
 {
-	struct tipc_msg *msg = buf_msg(skb_peek(list));
-	int imp = msg_importance(msg);
-	u32 oport = msg_origport(msg);
-	u32 addr = tipc_own_addr(link->net);
+	u32 dnode = tipc_own_addr(l->net);
+	u32 dport = msg_origport(hdr);
 	struct sk_buff *skb;
 
-	/* This really cannot happen...  */
-	if (unlikely(imp > TIPC_CRITICAL_IMPORTANCE)) {
-		pr_warn("%s<%s>, send queue full", link_rst_msg, link->name);
-		return -ENOBUFS;
-	}
-	/* Non-blocking sender: */
-	if (TIPC_SKB_CB(skb_peek(list))->wakeup_pending)
-		return -ELINKCONG;
-
 	/* Create and schedule wakeup pseudo message */
 	skb = tipc_msg_create(SOCK_WAKEUP, 0, INT_H_SIZE, 0,
-			      addr, addr, oport, 0, 0);
+			      dnode, l->addr, dport, 0, 0);
 	if (!skb)
 		return -ENOBUFS;
-	TIPC_SKB_CB(skb)->chain_sz = skb_queue_len(list);
-	TIPC_SKB_CB(skb)->chain_imp = imp;
-	skb_queue_tail(&link->wakeupq, skb);
-	link->stats.link_congs++;
+	msg_set_dest_droppable(buf_msg(skb), true);
+	TIPC_SKB_CB(skb)->chain_imp = msg_importance(hdr);
+	skb_queue_tail(&l->wakeupq, skb);
+	l->stats.link_congs++;
 	return -ELINKCONG;
 }
 
 /**
  * link_prepare_wakeup - prepare users for wakeup after congestion
- * @link: congested link
- * Move a number of waiting users, as permitted by available space in
- * the send queue, from link wait queue to node wait queue for wakeup
+ * @l: congested link
+ * Wake up a number of waiting users, as permitted by available space
+ * in the send queue
  */
 void link_prepare_wakeup(struct tipc_link *l)
 {
-	int pnd[TIPC_SYSTEM_IMPORTANCE + 1] = {0,};
-	int imp, lim;
 	struct sk_buff *skb, *tmp;
+	int imp, i = 0;
 
 	skb_queue_walk_safe(&l->wakeupq, skb, tmp) {
 		imp = TIPC_SKB_CB(skb)->chain_imp;
-		lim = l->backlog[imp].limit;
-		pnd[imp] += TIPC_SKB_CB(skb)->chain_sz;
-		if ((pnd[imp] + l->backlog[imp].len) >= lim)
-			break;
+		if (l->backlog[imp].len < l->backlog[imp].limit) {
 			skb_unlink(skb, &l->wakeupq);
 			skb_queue_tail(l->inputq, skb);
+		} else if (i++ > 10) {
+			break;
+		}
 	}
 }
 
@@ -869,8 +856,7 @@ void tipc_link_reset(struct tipc_link *l)
  * @list: chain of buffers containing message
  * @xmitq: returned list of packets to be sent by caller
  *
- * Consumes the buffer chain, except when returning -ELINKCONG,
- * since the caller then may want to make more send attempts.
+ * Consumes the buffer chain.
  * Returns 0 if success, or errno: -ELINKCONG, -EMSGSIZE or -ENOBUFS
  * Messages at TIPC_SYSTEM_IMPORTANCE are always accepted
  */
@@ -879,7 +865,7 @@ int tipc_link_xmit(struct tipc_link *l, struct sk_buff_head *list,
 {
 	struct tipc_msg *hdr = buf_msg(skb_peek(list));
 	unsigned int maxwin = l->window;
-	unsigned int i, imp = msg_importance(hdr);
+	int imp = msg_importance(hdr);
 	unsigned int mtu = l->mtu;
 	u16 ack = l->rcv_nxt - 1;
 	u16 seqno = l->snd_nxt;
@@ -888,19 +874,22 @@ int tipc_link_xmit(struct tipc_link *l, struct sk_buff_head *list,
 	struct sk_buff_head *backlogq = &l->backlogq;
 	struct sk_buff *skb, *_skb, *bskb;
 	int pkt_cnt = skb_queue_len(list);
+	int rc = 0;
 
-	/* Match msg importance against this and all higher backlog limits: */
-	if (!skb_queue_empty(backlogq)) {
-		for (i = imp; i <= TIPC_SYSTEM_IMPORTANCE; i++) {
-			if (unlikely(l->backlog[i].len >= l->backlog[i].limit))
-				return link_schedule_user(l, list);
-		}
-	}
 	if (unlikely(msg_size(hdr) > mtu)) {
 		skb_queue_purge(list);
 		return -EMSGSIZE;
 	}
 
+	/* Allow oversubscription of one data msg per source at congestion */
+	if (unlikely(l->backlog[imp].len >= l->backlog[imp].limit)) {
+		if (imp == TIPC_SYSTEM_IMPORTANCE) {
+			pr_warn("%s<%s>, link overflow", link_rst_msg, l->name);
+			return -ENOBUFS;
+		}
+		rc = link_schedule_user(l, hdr);
+	}
+
 	if (pkt_cnt > 1) {
 		l->stats.sent_fragmented++;
 		l->stats.sent_fragments += pkt_cnt;
@@ -946,7 +935,7 @@ int tipc_link_xmit(struct tipc_link *l, struct sk_buff_head *list,
 		skb_queue_splice_tail_init(list, backlogq);
 	}
 	l->snd_nxt = seqno;
-	return 0;
+	return rc;
 }
 
 void tipc_link_advance_backlog(struct tipc_link *l, struct sk_buff_head *xmitq)

net/tipc/msg.h

@@ -98,8 +98,6 @@ struct tipc_skb_cb {
 	u32 bytes_read;
 	struct sk_buff *tail;
 	bool validated;
-	bool wakeup_pending;
-	u16 chain_sz;
 	u16 chain_imp;
 	u16 ackers;
 };

net/tipc/name_table.c

@@ -608,7 +608,7 @@ u32 tipc_nametbl_translate(struct net *net, u32 type, u32 instance,
  * Returns non-zero if any off-node ports overlap
  */
 int tipc_nametbl_mc_translate(struct net *net, u32 type, u32 lower, u32 upper,
-			      u32 limit, struct tipc_plist *dports)
+			      u32 limit, struct list_head *dports)
 {
 	struct name_seq *seq;
 	struct sub_seq *sseq;
@@ -633,7 +633,7 @@ int tipc_nametbl_mc_translate(struct net *net, u32 type, u32 lower, u32 upper,
 		info = sseq->info;
 		list_for_each_entry(publ, &info->node_list, node_list) {
 			if (publ->scope <= limit)
-				tipc_plist_push(dports, publ->ref);
+				u32_push(dports, publ->ref);
 		}
 
 		if (info->cluster_list_size != info->node_list_size)
@@ -1022,40 +1022,84 @@ int tipc_nl_name_table_dump(struct sk_buff *skb, struct netlink_callback *cb)
 	return skb->len;
 }
 
-void tipc_plist_push(struct tipc_plist *pl, u32 port)
+struct u32_item {
+	struct list_head list;
+	u32 value;
+};
+
+bool u32_find(struct list_head *l, u32 value)
 {
-	struct tipc_plist *nl;
+	struct u32_item *item;
 
-	if (likely(!pl->port)) {
-		pl->port = port;
-		return;
+	list_for_each_entry(item, l, list) {
+		if (item->value == value)
+			return true;
 	}
-	if (pl->port == port)
-		return;
-	list_for_each_entry(nl, &pl->list, list) {
-		if (nl->port == port)
-			return;
+	return false;
+}
+
+bool u32_push(struct list_head *l, u32 value)
+{
+	struct u32_item *item;
+
+	list_for_each_entry(item, l, list) {
+		if (item->value == value)
+			return false;
 	}
-	nl = kmalloc(sizeof(*nl), GFP_ATOMIC);
-	if (nl) {
-		nl->port = port;
-		list_add(&nl->list, &pl->list);
+	item = kmalloc(sizeof(*item), GFP_ATOMIC);
+	if (unlikely(!item))
+		return false;
+
+	item->value = value;
+	list_add(&item->list, l);
+	return true;
+}
+
+u32 u32_pop(struct list_head *l)
+{
+	struct u32_item *item;
+	u32 value = 0;
+
+	if (list_empty(l))
+		return 0;
+	item = list_first_entry(l, typeof(*item), list);
+	value = item->value;
+	list_del(&item->list);
+	kfree(item);
+	return value;
+}
+
+bool u32_del(struct list_head *l, u32 value)
+{
+	struct u32_item *item, *tmp;
+
+	list_for_each_entry_safe(item, tmp, l, list) {
+		if (item->value != value)
+			continue;
+		list_del(&item->list);
+		kfree(item);
+		return true;
+	}
+	return false;
+}
+
+void u32_list_purge(struct list_head *l)
+{
+	struct u32_item *item, *tmp;
+
+	list_for_each_entry_safe(item, tmp, l, list) {
+		list_del(&item->list);
+		kfree(item);
 	}
 }
 
-u32 tipc_plist_pop(struct tipc_plist *pl)
+int u32_list_len(struct list_head *l)
 {
-	struct tipc_plist *nl;
-	u32 port = 0;
+	struct u32_item *item;
+	int i = 0;
 
-	if (likely(list_empty(&pl->list))) {
-		port = pl->port;
-		pl->port = 0;
-		return port;
+	list_for_each_entry(item, l, list) {
+		i++;
 	}
-	nl = list_first_entry(&pl->list, typeof(*nl), list);
-	port = nl->port;
-	list_del(&nl->list);
-	kfree(nl);
-	return port;
+	return i;
 }

net/tipc/name_table.h

@@ -99,7 +99,7 @@ int tipc_nl_name_table_dump(struct sk_buff *skb, struct netlink_callback *cb);
 
 u32 tipc_nametbl_translate(struct net *net, u32 type, u32 instance, u32 *node);
 int tipc_nametbl_mc_translate(struct net *net, u32 type, u32 lower, u32 upper,
-			      u32 limit, struct tipc_plist *dports);
+			      u32 limit, struct list_head *dports);
 struct publication *tipc_nametbl_publish(struct net *net, u32 type, u32 lower,
 					 u32 upper, u32 scope, u32 port_ref,
 					 u32 key);
@@ -116,18 +116,11 @@ void tipc_nametbl_unsubscribe(struct tipc_subscription *s);
 int tipc_nametbl_init(struct net *net);
 void tipc_nametbl_stop(struct net *net);
 
-struct tipc_plist {
-	struct list_head list;
-	u32 port;
-};
-
-static inline void tipc_plist_init(struct tipc_plist *pl)
-{
-	INIT_LIST_HEAD(&pl->list);
-	pl->port = 0;
-}
-
-void tipc_plist_push(struct tipc_plist *pl, u32 port);
-u32 tipc_plist_pop(struct tipc_plist *pl);
+bool u32_push(struct list_head *l, u32 value);
+u32 u32_pop(struct list_head *l);
+bool u32_find(struct list_head *l, u32 value);
+bool u32_del(struct list_head *l, u32 value);
+void u32_list_purge(struct list_head *l);
+int u32_list_len(struct list_head *l);
 
 #endif

net/tipc/node.c

@@ -1167,7 +1167,7 @@ static int __tipc_nl_add_node(struct tipc_nl_msg *msg, struct tipc_node *node)
  * @list: chain of buffers containing message
  * @dnode: address of destination node
  * @selector: a number used for deterministic link selection
- * Consumes the buffer chain, except when returning -ELINKCONG
+ * Consumes the buffer chain.
  * Returns 0 if success, otherwise: -ELINKCONG,-EHOSTUNREACH,-EMSGSIZE,-ENOBUF
  */
 int tipc_node_xmit(struct net *net, struct sk_buff_head *list,
@@ -1206,10 +1206,10 @@ int tipc_node_xmit(struct net *net, struct sk_buff_head *list,
 	spin_unlock_bh(&le->lock);
 	tipc_node_read_unlock(n);
 
-	if (likely(rc == 0))
-		tipc_bearer_xmit(net, bearer_id, &xmitq, &le->maddr);
-	else if (rc == -ENOBUFS)
+	if (unlikely(rc == -ENOBUFS))
 		tipc_node_link_down(n, bearer_id, false);
+	else
+		tipc_bearer_xmit(net, bearer_id, &xmitq, &le->maddr);
 
 	tipc_node_put(n);
 
@@ -1221,20 +1221,15 @@ int tipc_node_xmit(struct net *net, struct sk_buff_head *list,
  * messages, which will not be rejected
  * The only exception is datagram messages rerouted after secondary
  * lookup, which are rare and safe to dispose of anyway.
- * TODO: Return real return value, and let callers use
- * tipc_wait_for_sendpkt() where applicable
  */
 int tipc_node_xmit_skb(struct net *net, struct sk_buff *skb, u32 dnode,
 		       u32 selector)
 {
 	struct sk_buff_head head;
-	int rc;
 
 	skb_queue_head_init(&head);
 	__skb_queue_tail(&head, skb);
-	rc = tipc_node_xmit(net, &head, dnode, selector);
-	if (rc == -ELINKCONG)
-		kfree_skb(skb);
+	tipc_node_xmit(net, &head, dnode, selector);
 	return 0;
 }