[net-next 0/3] tipc: improve interaction socket-link

[net-next 0/3] tipc: improve interaction socket-link

[Jon Maloy]

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.

Jon Maloy (3):
  tipc: unify tipc_wait_for_sndpkt() and tipc_wait_for_sndmsg()
    functions
  tipc: modify struct tipc_plist to be more versatile
  tipc: reduce risk of user starvation during link congestion

 net/tipc/bcast.c      |   6 +-
 net/tipc/link.c       |  75 ++++-----
 net/tipc/msg.h        |   2 -
 net/tipc/name_table.c | 100 +++++++----
 net/tipc/name_table.h |  21 +--
 net/tipc/node.c       |  15 +-
 net/tipc/socket.c     | 449 ++++++++++++++++++++++----------------------------
 7 files changed, 319 insertions(+), 349 deletions(-)

-- 
2.7.4


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[net-next 1/3] tipc: unify tipc_wait_for_sndpkt() and tipc_wait_for_sndmsg() functions

[Jon Maloy]

The functions tipc_wait_for_sndpkt() and tipc_wait_for_sndmsg() are very
similar. The latter function is also called from two locations, and
there will be more in the coming commits, which will all need to test on
different conditions.

Instead of making yet another duplicates of the function, we now
introduce a new macro tipc_wait_for_cond() where the wakeup condition
can be stated as an argument to the call. This macro replaces all
current and future uses of the two functions, which can now be
eliminated.

Acked-by: Parthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
---
 net/tipc/socket.c | 108 +++++++++++++++++++++++++-----------------------------
 1 file changed, 49 insertions(+), 59 deletions(-)

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index 800caaa..f27462e 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -110,7 +110,6 @@ static void tipc_write_space(struct sock *sk);
 static void tipc_sock_destruct(struct sock *sk);
 static int tipc_release(struct socket *sock);
 static int tipc_accept(struct socket *sock, struct socket *new_sock, int flags);
-static int tipc_wait_for_sndmsg(struct socket *sock, long *timeo_p);
 static void tipc_sk_timeout(unsigned long data);
 static int tipc_sk_publish(struct tipc_sock *tsk, uint scope,
 			   struct tipc_name_seq const *seq);
@@ -334,6 +333,49 @@ static int tipc_set_sk_state(struct sock *sk, int state)
 	return res;
 }
 
+static int tipc_sk_sock_err(struct socket *sock, long *timeout)
+{
+	struct sock *sk = sock->sk;
+	int err = sock_error(sk);
+	int typ = sock->type;
+
+	if (err)
+		return err;
+	if (typ == SOCK_STREAM || typ == SOCK_SEQPACKET) {
+		if (sk->sk_state == TIPC_DISCONNECTING)
+			return -EPIPE;
+		else if (!tipc_sk_connected(sk))
+			return -ENOTCONN;
+	}
+	if (!*timeout)
+		return -EAGAIN;
+	if (signal_pending(current))
+		return sock_intr_errno(*timeout);
+
+	return 0;
+}
+
+#define tipc_wait_for_cond(sock_, timeout_, condition_)			\
+({								        \
+	int rc_ = 0;							\
+	int done_ = 0;							\
+									\
+	while (!(condition_) && !done_) {				\
+		struct sock *sk_ = sock->sk;				\
+		DEFINE_WAIT_FUNC(wait_, woken_wake_function);		\
+									\
+		rc_ = tipc_sk_sock_err(sock_, timeout_);		\
+		if (rc_)						\
+			break;						\
+		prepare_to_wait(sk_sleep(sk_), &wait_,			\
+				TASK_INTERRUPTIBLE);			\
+		done_ = sk_wait_event(sk_, timeout_,			\
+				      (condition_), &wait_);		\
+		remove_wait_queue(sk_sleep(sk_), &wait_);		\
+	}								\
+	rc_;								\
+})
+
 /**
  * tipc_sk_create - create a TIPC socket
  * @net: network namespace (must be default network)
@@ -721,7 +763,7 @@ static int tipc_sendmcast(struct  socket *sock, struct tipc_name_seq *seq,
 
 		if (rc == -ELINKCONG) {
 			tsk->link_cong = 1;
-			rc = tipc_wait_for_sndmsg(sock, &timeo);
+			rc = tipc_wait_for_cond(sock, &timeo, !tsk->link_cong);
 			if (!rc)
 				continue;
 		}
@@ -830,31 +872,6 @@ static void tipc_sk_proto_rcv(struct tipc_sock *tsk, struct sk_buff *skb,
 	kfree_skb(skb);
 }
 
-static int tipc_wait_for_sndmsg(struct socket *sock, long *timeo_p)
-{
-	DEFINE_WAIT_FUNC(wait, woken_wake_function);
-	struct sock *sk = sock->sk;
-	struct tipc_sock *tsk = tipc_sk(sk);
-	int done;
-
-	do {
-		int err = sock_error(sk);
-		if (err)
-			return err;
-		if (sk->sk_shutdown & SEND_SHUTDOWN)
-			return -EPIPE;
-		if (!*timeo_p)
-			return -EAGAIN;
-		if (signal_pending(current))
-			return sock_intr_errno(*timeo_p);
-
-		add_wait_queue(sk_sleep(sk), &wait);
-		done = sk_wait_event(sk, timeo_p, !tsk->link_cong, &wait);
-		remove_wait_queue(sk_sleep(sk), &wait);
-	} while (!done);
-	return 0;
-}
-
 /**
  * tipc_sendmsg - send message in connectionless manner
  * @sock: socket structure
@@ -970,7 +987,7 @@ static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dsz)
 		}
 		if (rc == -ELINKCONG) {
 			tsk->link_cong = 1;
-			rc = tipc_wait_for_sndmsg(sock, &timeo);
+			rc = tipc_wait_for_cond(sock, &timeo, !tsk->link_cong);
 			if (!rc)
 				continue;
 		}
@@ -985,36 +1002,6 @@ static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dsz)
 	return rc;
 }
 
-static int tipc_wait_for_sndpkt(struct socket *sock, long *timeo_p)
-{
-	DEFINE_WAIT_FUNC(wait, woken_wake_function);
-	struct sock *sk = sock->sk;
-	struct tipc_sock *tsk = tipc_sk(sk);
-	int done;
-
-	do {
-		int err = sock_error(sk);
-		if (err)
-			return err;
-		if (sk->sk_state == TIPC_DISCONNECTING)
-			return -EPIPE;
-		else if (!tipc_sk_connected(sk))
-			return -ENOTCONN;
-		if (!*timeo_p)
-			return -EAGAIN;
-		if (signal_pending(current))
-			return sock_intr_errno(*timeo_p);
-
-		add_wait_queue(sk_sleep(sk), &wait);
-		done = sk_wait_event(sk, timeo_p,
-				     (!tsk->link_cong &&
-				      !tsk_conn_cong(tsk)) ||
-				      !tipc_sk_connected(sk), &wait);
-		remove_wait_queue(sk_sleep(sk), &wait);
-	} while (!done);
-	return 0;
-}
-
 /**
  * tipc_send_stream - send stream-oriented data
  * @sock: socket structure
@@ -1109,7 +1096,10 @@ static int __tipc_send_stream(struct socket *sock, struct msghdr *m, size_t dsz)
 
 			tsk->link_cong = 1;
 		}
-		rc = tipc_wait_for_sndpkt(sock, &timeo);
+		rc = tipc_wait_for_cond(sock, &timeo,
+					(!tsk->link_cong &&
+					 !tsk_conn_cong(tsk) &&
+					 tipc_sk_connected(sk)));
 	} while (!rc);
 
 	__skb_queue_purge(&pktchain);
-- 
2.7.4


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[net-next 2/3] tipc: modify struct tipc_plist to be more versatile

[Jon Maloy]

During multicast reception we currently use a simple linked list with
push/pop semantics to store port numbers.

We now see a need for a more generic list for storing values of type
u32. We therefore make some modifications to this list, while replacing
the prefix 'tipc_plist_' with 'u32_'. We also add a couple of new
functions which will come to use in the next commits.

Acked-by: Parthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
---
 net/tipc/name_table.c | 100 ++++++++++++++++++++++++++++++++++++--------------
 net/tipc/name_table.h |  21 ++++-------
 net/tipc/socket.c     |   8 ++--
 3 files changed, 83 insertions(+), 46 deletions(-)

diff --git a/net/tipc/name_table.c b/net/tipc/name_table.c
index e190460..5a86df1 100644
--- a/net/tipc/name_table.c
+++ b/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;
+	}
+	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;
 	}
-	nl = kmalloc(sizeof(*nl), GFP_ATOMIC);
-	if (nl) {
-		nl->port = port;
-		list_add(&nl->list, &pl->list);
+	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;
 }
diff --git a/net/tipc/name_table.h b/net/tipc/name_table.h
index 1524a73..c89bb3f 100644
--- a/net/tipc/name_table.h
+++ b/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
diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index f27462e..fae6a55 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -788,7 +788,7 @@ void tipc_sk_mcast_rcv(struct net *net, struct sk_buff_head *arrvq,
 		       struct sk_buff_head *inputq)
 {
 	struct tipc_msg *msg;
-	struct tipc_plist dports;
+	struct list_head dports;
 	u32 portid;
 	u32 scope = TIPC_CLUSTER_SCOPE;
 	struct sk_buff_head tmpq;
@@ -796,7 +796,7 @@ void tipc_sk_mcast_rcv(struct net *net, struct sk_buff_head *arrvq,
 	struct sk_buff *skb, *_skb;
 
 	__skb_queue_head_init(&tmpq);
-	tipc_plist_init(&dports);
+	INIT_LIST_HEAD(&dports);
 
 	skb = tipc_skb_peek(arrvq, &inputq->lock);
 	for (; skb; skb = tipc_skb_peek(arrvq, &inputq->lock)) {
@@ -810,8 +810,8 @@ void tipc_sk_mcast_rcv(struct net *net, struct sk_buff_head *arrvq,
 		tipc_nametbl_mc_translate(net,
 					  msg_nametype(msg), msg_namelower(msg),
 					  msg_nameupper(msg), scope, &dports);
-		portid = tipc_plist_pop(&dports);
-		for (; portid; portid = tipc_plist_pop(&dports)) {
+		portid = u32_pop(&dports);
+		for (; portid; portid = u32_pop(&dports)) {
 			_skb = __pskb_copy(skb, hsz, GFP_ATOMIC);
 			if (_skb) {
 				msg_set_destport(buf_msg(_skb), portid);
-- 
2.7.4

[net-next 3/3] tipc: reduce risk of user starvation during link congestion

[Jon Maloy]

The socket code currently handles link congestion by either blocking
and trying to send again when the congestion has abated, or just
returning to the user with -EAGAIN and let him re-try later.

This mechanism is prone to starvation, because the wakeup algorithm is
non-atomic. During the time the link issues a wakeup signal, until the
socket wakes up and re-attempts sending, other senders may have come
in between and occupied the free buffer space in the link. This in turn
may lead to a socket having to make many send attempts before it is
successful. In extremely loaded systems we have observed latency times
of several seconds before a low-priority socket is able to send out a
message.

In this commit, we simplify this mechanism and reduce the risk of the
described scenario happening. When a message is attempted sent via a
congested link, we now let it be added to the link's backlog queue
anyway, thus permitting an oversubscription of one message per source
socket. We still create a wakeup item and return an error code, hence
instructing the sender to block or stop sending. Only when enough space
has been freed up in the link's backlog queue do we issue a wakeup event
that allows the sender to continue with the next message, if any.

The fact that a socket now can consider a message sent even when the
link returns a congestion code means that the sending socket code can
be simplified. Also, since this is a good opportunity to get rid of the
obsolete 'mtu change' condition in the three socket send functions, we
now choose to refactor those functions completely.

Signed-off-by: Parthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
---
 net/tipc/bcast.c  |   6 +-
 net/tipc/link.c   |  75 +++++-------
 net/tipc/msg.h    |   2 -
 net/tipc/node.c   |  15 +--
 net/tipc/socket.c | 347 ++++++++++++++++++++++++------------------------------
 5 files changed, 194 insertions(+), 251 deletions(-)

diff --git a/net/tipc/bcast.c b/net/tipc/bcast.c
index aa1babb..c35fad3 100644
--- a/net/tipc/bcast.c
+++ b/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
diff --git a/net/tipc/link.c b/net/tipc/link.c
index bda89bf..b758ca8 100644
--- a/net/tipc/link.c
+++ b/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)
+		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;
-		skb_unlink(skb, &l->wakeupq);
-		skb_queue_tail(l->inputq, skb);
+		}
 	}
 }
 
@@ -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)
diff --git a/net/tipc/msg.h b/net/tipc/msg.h
index 8d40861..850ae0e 100644
--- a/net/tipc/msg.h
+++ b/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;
 };
diff --git a/net/tipc/node.c b/net/tipc/node.c
index 9d2f4c2..2883f6a 100644
--- a/net/tipc/node.c
+++ b/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;
 }
 
diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index fae6a55..d2f3539 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -67,12 +67,14 @@ enum {
  * @max_pkt: maximum packet size "hint" used when building messages sent by port
  * @portid: unique port identity in TIPC socket hash table
  * @phdr: preformatted message header used when sending messages
+ * #cong_links: list of congested links
  * @publications: list of publications for port
+ * @blocking_link: address of the congested link we are currently sleeping on
  * @pub_count: total # of publications port has made during its lifetime
  * @probing_state:
  * @conn_timeout: the time we can wait for an unresponded setup request
  * @dupl_rcvcnt: number of bytes counted twice, in both backlog and rcv queue
- * @link_cong: non-zero if owner must sleep because of link congestion
+ * @cong_link_cnt: number of congested links
  * @sent_unacked: # messages sent by socket, and not yet acked by peer
  * @rcv_unacked: # messages read by user, but not yet acked back to peer
  * @peer: 'connected' peer for dgram/rdm
@@ -87,13 +89,13 @@ struct tipc_sock {
 	u32 max_pkt;
 	u32 portid;
 	struct tipc_msg phdr;
-	struct list_head sock_list;
+	struct list_head cong_links;
 	struct list_head publications;
 	u32 pub_count;
 	uint conn_timeout;
 	atomic_t dupl_rcvcnt;
 	bool probe_unacked;
-	bool link_cong;
+	u16 cong_link_cnt;
 	u16 snt_unacked;
 	u16 snd_win;
 	u16 peer_caps;
@@ -118,8 +120,7 @@ static int tipc_sk_withdraw(struct tipc_sock *tsk, uint scope,
 static struct tipc_sock *tipc_sk_lookup(struct net *net, u32 portid);
 static int tipc_sk_insert(struct tipc_sock *tsk);
 static void tipc_sk_remove(struct tipc_sock *tsk);
-static int __tipc_send_stream(struct socket *sock, struct msghdr *m,
-			      size_t dsz);
+static int __tipc_sendstream(struct socket *sock, struct msghdr *m, size_t dsz);
 static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dsz);
 
 static const struct proto_ops packet_ops;
@@ -424,6 +425,7 @@ static int tipc_sk_create(struct net *net, struct socket *sock,
 	tsk = tipc_sk(sk);
 	tsk->max_pkt = MAX_PKT_DEFAULT;
 	INIT_LIST_HEAD(&tsk->publications);
+	INIT_LIST_HEAD(&tsk->cong_links);
 	msg = &tsk->phdr;
 	tn = net_generic(sock_net(sk), tipc_net_id);
 	tipc_msg_init(tn->own_addr, msg, TIPC_LOW_IMPORTANCE, TIPC_NAMED_MSG,
@@ -474,9 +476,14 @@ static void __tipc_shutdown(struct socket *sock, int error)
 	struct sock *sk = sock->sk;
 	struct tipc_sock *tsk = tipc_sk(sk);
 	struct net *net = sock_net(sk);
+	long timeout = CONN_TIMEOUT_DEFAULT;
 	u32 dnode = tsk_peer_node(tsk);
 	struct sk_buff *skb;
 
+	/* Avoid that hi-prio shutdown msgs bypass msgs in link wakeup queue */
+	tipc_wait_for_cond(sock, &timeout, (!tsk->cong_link_cnt &&
+					    !tsk_conn_cong(tsk)));
+
 	/* Reject all unreceived messages, except on an active connection
 	 * (which disconnects locally & sends a 'FIN+' to peer).
 	 */
@@ -547,7 +554,8 @@ static int tipc_release(struct socket *sock)
 
 	/* Reject any messages that accumulated in backlog queue */
 	release_sock(sk);
-
+	u32_list_purge(&tsk->cong_links);
+	tsk->cong_link_cnt = 0;
 	call_rcu(&tsk->rcu, tipc_sk_callback);
 	sock->sk = NULL;
 
@@ -690,7 +698,7 @@ static unsigned int tipc_poll(struct file *file, struct socket *sock,
 
 	switch (sk->sk_state) {
 	case TIPC_ESTABLISHED:
-		if (!tsk->link_cong && !tsk_conn_cong(tsk))
+		if (!tsk->cong_link_cnt && !tsk_conn_cong(tsk))
 			mask |= POLLOUT;
 		/* fall thru' */
 	case TIPC_LISTEN:
@@ -699,7 +707,7 @@ static unsigned int tipc_poll(struct file *file, struct socket *sock,
 			mask |= (POLLIN | POLLRDNORM);
 		break;
 	case TIPC_OPEN:
-		if (!tsk->link_cong)
+		if (!tsk->cong_link_cnt)
 			mask |= POLLOUT;
 		if (tipc_sk_type_connectionless(sk) &&
 		    (!skb_queue_empty(&sk->sk_receive_queue)))
@@ -718,63 +726,48 @@ static unsigned int tipc_poll(struct file *file, struct socket *sock,
  * @sock: socket structure
  * @seq: destination address
  * @msg: message to send
- * @dsz: total length of message data
- * @timeo: timeout to wait for wakeup
+ * @dlen: length of data to send
+ * @timeout: timeout to wait for wakeup
  *
  * Called from function tipc_sendmsg(), which has done all sanity checks
  * Returns the number of bytes sent on success, or errno
  */
 static int tipc_sendmcast(struct  socket *sock, struct tipc_name_seq *seq,
-			  struct msghdr *msg, size_t dsz, long timeo)
+			  struct msghdr *msg, size_t dlen, long timeout)
 {
 	struct sock *sk = sock->sk;
 	struct tipc_sock *tsk = tipc_sk(sk);
+	struct tipc_msg *hdr = &tsk->phdr;
 	struct net *net = sock_net(sk);
-	struct tipc_msg *mhdr = &tsk->phdr;
-	struct sk_buff_head pktchain;
-	struct iov_iter save = msg->msg_iter;
-	uint mtu;
+	int mtu = tipc_bcast_get_mtu(net);
+	struct sk_buff_head pkts;
 	int rc;
 
-	if (!timeo && tsk->link_cong)
-		return -ELINKCONG;
-
-	msg_set_type(mhdr, TIPC_MCAST_MSG);
-	msg_set_lookup_scope(mhdr, TIPC_CLUSTER_SCOPE);
-	msg_set_destport(mhdr, 0);
-	msg_set_destnode(mhdr, 0);
-	msg_set_nametype(mhdr, seq->type);
-	msg_set_namelower(mhdr, seq->lower);
-	msg_set_nameupper(mhdr, seq->upper);
-	msg_set_hdr_sz(mhdr, MCAST_H_SIZE);
-
-	skb_queue_head_init(&pktchain);
+	rc = tipc_wait_for_cond(sock, &timeout, !tsk->cong_link_cnt);
+	if (unlikely(rc))
+		return rc;
 
-new_mtu:
-	mtu = tipc_bcast_get_mtu(net);
-	rc = tipc_msg_build(mhdr, msg, 0, dsz, mtu, &pktchain);
-	if (unlikely(rc < 0))
+	msg_set_type(hdr, TIPC_MCAST_MSG);
+	msg_set_lookup_scope(hdr, TIPC_CLUSTER_SCOPE);
+	msg_set_destport(hdr, 0);
+	msg_set_destnode(hdr, 0);
+	msg_set_nametype(hdr, seq->type);
+	msg_set_namelower(hdr, seq->lower);
+	msg_set_nameupper(hdr, seq->upper);
+	msg_set_hdr_sz(hdr, MCAST_H_SIZE);
+
+	skb_queue_head_init(&pkts);
+	rc = tipc_msg_build(hdr, msg, 0, dlen, mtu, &pkts);
+	if (unlikely(rc != dlen))
 		return rc;
 
-	do {
-		rc = tipc_bcast_xmit(net, &pktchain);
-		if (likely(!rc))
-			return dsz;
-
-		if (rc == -ELINKCONG) {
-			tsk->link_cong = 1;
-			rc = tipc_wait_for_cond(sock, &timeo, !tsk->link_cong);
-			if (!rc)
-				continue;
-		}
-		__skb_queue_purge(&pktchain);
-		if (rc == -EMSGSIZE) {
-			msg->msg_iter = save;
-			goto new_mtu;
-		}
-		break;
-	} while (1);
-	return rc;
+	rc = tipc_bcast_xmit(net, &pkts);
+	if (unlikely(rc == -ELINKCONG)) {
+		tsk->cong_link_cnt = 1;
+		rc = 0;
+	}
+
+	return rc ? rc : dlen;
 }
 
 /**
@@ -898,35 +891,38 @@ static int tipc_sendmsg(struct socket *sock,
 	return ret;
 }
 
-static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dsz)
+static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dlen)
 {
-	DECLARE_SOCKADDR(struct sockaddr_tipc *, dest, m->msg_name);
 	struct sock *sk = sock->sk;
-	struct tipc_sock *tsk = tipc_sk(sk);
 	struct net *net = sock_net(sk);
-	struct tipc_msg *mhdr = &tsk->phdr;
-	u32 dnode, dport;
-	struct sk_buff_head pktchain;
-	bool is_connectionless = tipc_sk_type_connectionless(sk);
-	struct sk_buff *skb;
+	struct tipc_sock *tsk = tipc_sk(sk);
+	DECLARE_SOCKADDR(struct sockaddr_tipc *, dest, m->msg_name);
+	long timeout = sock_sndtimeo(sk, m->msg_flags & MSG_DONTWAIT);
+	struct list_head *clinks = &tsk->cong_links;
+	bool syn = !tipc_sk_type_connectionless(sk);
+	struct tipc_msg *hdr = &tsk->phdr;
 	struct tipc_name_seq *seq;
-	struct iov_iter save;
-	u32 mtu;
-	long timeo;
-	int rc;
+	struct sk_buff_head pkts;
+	u32 type, inst, domain;
+	u32 dnode, dport;
+	int mtu, rc;
 
-	if (dsz > TIPC_MAX_USER_MSG_SIZE)
+	if (unlikely(dlen > TIPC_MAX_USER_MSG_SIZE))
 		return -EMSGSIZE;
+
 	if (unlikely(!dest)) {
-		if (is_connectionless && tsk->peer.family == AF_TIPC)
-			dest = &tsk->peer;
-		else
+		dest = &tsk->peer;
+		if (!syn || dest->family != AF_TIPC)
 			return -EDESTADDRREQ;
-	} else if (unlikely(m->msg_namelen < sizeof(*dest)) ||
-		   dest->family != AF_TIPC) {
-		return -EINVAL;
 	}
-	if (!is_connectionless) {
+
+	if (unlikely(m->msg_namelen < sizeof(*dest)))
+		return -EINVAL;
+
+	if (unlikely(dest->family != AF_TIPC))
+		return -EINVAL;
+
+	if (unlikely(syn)) {
 		if (sk->sk_state == TIPC_LISTEN)
 			return -EPIPE;
 		if (sk->sk_state != TIPC_OPEN)
@@ -938,72 +934,62 @@ static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dsz)
 			tsk->conn_instance = dest->addr.name.name.instance;
 		}
 	}
-	seq = &dest->addr.nameseq;
-	timeo = sock_sndtimeo(sk, m->msg_flags & MSG_DONTWAIT);
 
-	if (dest->addrtype == TIPC_ADDR_MCAST) {
-		return tipc_sendmcast(sock, seq, m, dsz, timeo);
-	} else if (dest->addrtype == TIPC_ADDR_NAME) {
-		u32 type = dest->addr.name.name.type;
-		u32 inst = dest->addr.name.name.instance;
-		u32 domain = dest->addr.name.domain;
+	seq = &dest->addr.nameseq;
+	if (dest->addrtype == TIPC_ADDR_MCAST)
+		return tipc_sendmcast(sock, seq, m, dlen, timeout);
 
+	if (dest->addrtype == TIPC_ADDR_NAME) {
+		type = dest->addr.name.name.type;
+		inst = dest->addr.name.name.instance;
+		domain = dest->addr.name.domain;
 		dnode = domain;
-		msg_set_type(mhdr, TIPC_NAMED_MSG);
-		msg_set_hdr_sz(mhdr, NAMED_H_SIZE);
-		msg_set_nametype(mhdr, type);
-		msg_set_nameinst(mhdr, inst);
-		msg_set_lookup_scope(mhdr, tipc_addr_scope(domain));
+		msg_set_type(hdr, TIPC_NAMED_MSG);
+		msg_set_hdr_sz(hdr, NAMED_H_SIZE);
+		msg_set_nametype(hdr, type);
+		msg_set_nameinst(hdr, inst);
+		msg_set_lookup_scope(hdr, tipc_addr_scope(domain));
 		dport = tipc_nametbl_translate(net, type, inst, &dnode);
-		msg_set_destnode(mhdr, dnode);
-		msg_set_destport(mhdr, dport);
+		msg_set_destnode(hdr, dnode);
+		msg_set_destport(hdr, dport);
 		if (unlikely(!dport && !dnode))
 			return -EHOSTUNREACH;
+
 	} else if (dest->addrtype == TIPC_ADDR_ID) {
 		dnode = dest->addr.id.node;
-		msg_set_type(mhdr, TIPC_DIRECT_MSG);
-		msg_set_lookup_scope(mhdr, 0);
-		msg_set_destnode(mhdr, dnode);
-		msg_set_destport(mhdr, dest->addr.id.ref);
-		msg_set_hdr_sz(mhdr, BASIC_H_SIZE);
+		msg_set_type(hdr, TIPC_DIRECT_MSG);
+		msg_set_lookup_scope(hdr, 0);
+		msg_set_destnode(hdr, dnode);
+		msg_set_destport(hdr, dest->addr.id.ref);
+		msg_set_hdr_sz(hdr, BASIC_H_SIZE);
 	}
 
-	skb_queue_head_init(&pktchain);
-	save = m->msg_iter;
-new_mtu:
+	/* Block or return if destination link is congested */
+	rc = tipc_wait_for_cond(sock, &timeout, !u32_find(clinks, dnode));
+	if (unlikely(rc))
+		return rc;
+
+	skb_queue_head_init(&pkts);
 	mtu = tipc_node_get_mtu(net, dnode, tsk->portid);
-	rc = tipc_msg_build(mhdr, m, 0, dsz, mtu, &pktchain);
-	if (rc < 0)
+	rc = tipc_msg_build(hdr, m, 0, dlen, mtu, &pkts);
+	if (unlikely(rc != dlen))
 		return rc;
 
-	do {
-		skb = skb_peek(&pktchain);
-		TIPC_SKB_CB(skb)->wakeup_pending = tsk->link_cong;
-		rc = tipc_node_xmit(net, &pktchain, dnode, tsk->portid);
-		if (likely(!rc)) {
-			if (!is_connectionless)
-				tipc_set_sk_state(sk, TIPC_CONNECTING);
-			return dsz;
-		}
-		if (rc == -ELINKCONG) {
-			tsk->link_cong = 1;
-			rc = tipc_wait_for_cond(sock, &timeo, !tsk->link_cong);
-			if (!rc)
-				continue;
-		}
-		__skb_queue_purge(&pktchain);
-		if (rc == -EMSGSIZE) {
-			m->msg_iter = save;
-			goto new_mtu;
-		}
-		break;
-	} while (1);
+	rc = tipc_node_xmit(net, &pkts, dnode, tsk->portid);
+	if (unlikely(rc == -ELINKCONG)) {
+		u32_push(clinks, dnode);
+		tsk->cong_link_cnt++;
+		rc = 0;
+	}
 
-	return rc;
+	if (unlikely(syn && !rc))
+		tipc_set_sk_state(sk, TIPC_CONNECTING);
+
+	return rc ? rc : dlen;
 }
 
 /**
- * tipc_send_stream - send stream-oriented data
+ * tipc_sendstream - send stream-oriented data
  * @sock: socket structure
  * @m: data to send
  * @dsz: total length of data to be transmitted
@@ -1013,97 +999,69 @@ static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dsz)
  * Returns the number of bytes sent on success (or partial success),
  * or errno if no data sent
  */
-static int tipc_send_stream(struct socket *sock, struct msghdr *m, size_t dsz)
+static int tipc_sendstream(struct socket *sock, struct msghdr *m, size_t dsz)
 {
 	struct sock *sk = sock->sk;
 	int ret;
 
 	lock_sock(sk);
-	ret = __tipc_send_stream(sock, m, dsz);
+	ret = __tipc_sendstream(sock, m, dsz);
 	release_sock(sk);
 
 	return ret;
 }
 
-static int __tipc_send_stream(struct socket *sock, struct msghdr *m, size_t dsz)
+static int __tipc_sendstream(struct socket *sock, struct msghdr *m, size_t dlen)
 {
 	struct sock *sk = sock->sk;
-	struct net *net = sock_net(sk);
-	struct tipc_sock *tsk = tipc_sk(sk);
-	struct tipc_msg *mhdr = &tsk->phdr;
-	struct sk_buff_head pktchain;
 	DECLARE_SOCKADDR(struct sockaddr_tipc *, dest, m->msg_name);
-	u32 portid = tsk->portid;
-	int rc = -EINVAL;
-	long timeo;
-	u32 dnode;
-	uint mtu, send, sent = 0;
-	struct iov_iter save;
-	int hlen = MIN_H_SIZE;
-
-	/* Handle implied connection establishment */
-	if (unlikely(dest)) {
-		rc = __tipc_sendmsg(sock, m, dsz);
-		hlen = msg_hdr_sz(mhdr);
-		if (dsz && (dsz == rc))
-			tsk->snt_unacked = tsk_inc(tsk, dsz + hlen);
-		return rc;
-	}
-	if (dsz > (uint)INT_MAX)
-		return -EMSGSIZE;
-
-	if (unlikely(!tipc_sk_connected(sk))) {
-		if (sk->sk_state == TIPC_DISCONNECTING)
-			return -EPIPE;
-		else
-			return -ENOTCONN;
-	}
+	long timeout = sock_sndtimeo(sk, m->msg_flags & MSG_DONTWAIT);
+	struct tipc_sock *tsk = tipc_sk(sk);
+	struct tipc_msg *hdr = &tsk->phdr;
+	struct net *net = sock_net(sk);
+	struct sk_buff_head pkts;
+	u32 dnode = tsk_peer_node(tsk);
+	int send, sent = 0;
+	int rc = 0;
 
-	timeo = sock_sndtimeo(sk, m->msg_flags & MSG_DONTWAIT);
-	if (!timeo && tsk->link_cong)
-		return -ELINKCONG;
+	skb_queue_head_init(&pkts);
 
-	dnode = tsk_peer_node(tsk);
-	skb_queue_head_init(&pktchain);
+	if (unlikely(dlen > INT_MAX))
+		return -EMSGSIZE;
 
-next:
-	save = m->msg_iter;
-	mtu = tsk->max_pkt;
-	send = min_t(uint, dsz - sent, TIPC_MAX_USER_MSG_SIZE);
-	rc = tipc_msg_build(mhdr, m, sent, send, mtu, &pktchain);
-	if (unlikely(rc < 0))
+	/* Handle implicit connection setup */
+	if (unlikely(dest)) {
+		rc = __tipc_sendmsg(sock, m, dlen);
+		if (dlen && (dlen == rc))
+			tsk->snt_unacked = tsk_inc(tsk, dlen + msg_hdr_sz(hdr));
 		return rc;
+	}
 
 	do {
-		if (likely(!tsk_conn_cong(tsk))) {
-			rc = tipc_node_xmit(net, &pktchain, dnode, portid);
-			if (likely(!rc)) {
-				tsk->snt_unacked += tsk_inc(tsk, send + hlen);
-				sent += send;
-				if (sent == dsz)
-					return dsz;
-				goto next;
-			}
-			if (rc == -EMSGSIZE) {
-				__skb_queue_purge(&pktchain);
-				tsk->max_pkt = tipc_node_get_mtu(net, dnode,
-								 portid);
-				m->msg_iter = save;
-				goto next;
-			}
-			if (rc != -ELINKCONG)
-				break;
-
-			tsk->link_cong = 1;
-		}
-		rc = tipc_wait_for_cond(sock, &timeo,
-					(!tsk->link_cong &&
+		rc = tipc_wait_for_cond(sock, &timeout,
+					(!tsk->cong_link_cnt &&
 					 !tsk_conn_cong(tsk) &&
 					 tipc_sk_connected(sk)));
-	} while (!rc);
+		if (unlikely(rc))
+			break;
+
+		send = min_t(size_t, dlen - sent, TIPC_MAX_USER_MSG_SIZE);
+		rc = tipc_msg_build(hdr, m, sent, send, tsk->max_pkt, &pkts);
+		if (unlikely(rc != send))
+			break;
+
+		rc = tipc_node_xmit(net, &pkts, dnode, tsk->portid);
+		if (unlikely(rc == -ELINKCONG)) {
+			tsk->cong_link_cnt = 1;
+			rc = 0;
+		}
+		if (likely(!rc)) {
+			tsk->snt_unacked += tsk_inc(tsk, send + MIN_H_SIZE);
+			sent += send;
+		}
+	} while (sent < dlen && !rc);
 
-	__skb_queue_purge(&pktchain);
-	return sent ? sent : rc;
+	return rc ? rc : sent;
 }
 
 /**
@@ -1121,7 +1079,7 @@ static int tipc_send_packet(struct socket *sock, struct msghdr *m, size_t dsz)
 	if (dsz > TIPC_MAX_USER_MSG_SIZE)
 		return -EMSGSIZE;
 
-	return tipc_send_stream(sock, m, dsz);
+	return tipc_sendstream(sock, m, dsz);
 }
 
 /* tipc_sk_finish_conn - complete the setup of a connection
@@ -1688,6 +1646,7 @@ static bool filter_rcv(struct sock *sk, struct sk_buff *skb,
 	unsigned int limit = rcvbuf_limit(sk, skb);
 	int err = TIPC_OK;
 	int usr = msg_user(hdr);
+	u32 onode;
 
 	if (unlikely(msg_user(hdr) == CONN_MANAGER)) {
 		tipc_sk_proto_rcv(tsk, skb, xmitq);
@@ -1695,8 +1654,10 @@ static bool filter_rcv(struct sock *sk, struct sk_buff *skb,
 	}
 
 	if (unlikely(usr == SOCK_WAKEUP)) {
+		onode = msg_orignode(hdr);
 		kfree_skb(skb);
-		tsk->link_cong = 0;
+		u32_del(&tsk->cong_links, onode);
+		tsk->cong_link_cnt--;
 		sk->sk_write_space(sk);
 		return false;
 	}
@@ -2104,7 +2065,7 @@ static int tipc_accept(struct socket *sock, struct socket *new_sock, int flags)
 		struct msghdr m = {NULL,};
 
 		tsk_advance_rx_queue(sk);
-		__tipc_send_stream(new_sock, &m, 0);
+		__tipc_sendstream(new_sock, &m, 0);
 	} else {
 		__skb_dequeue(&sk->sk_receive_queue);
 		__skb_queue_head(&new_sk->sk_receive_queue, buf);
@@ -2565,7 +2526,7 @@ static const struct proto_ops stream_ops = {
 	.shutdown	= tipc_shutdown,
 	.setsockopt	= tipc_setsockopt,
 	.getsockopt	= tipc_getsockopt,
-	.sendmsg	= tipc_send_stream,
+	.sendmsg	= tipc_sendstream,
 	.recvmsg	= tipc_recv_stream,
 	.mmap		= sock_no_mmap,
 	.sendpage	= sock_no_sendpage
-- 
2.7.4

Re: [net-next 0/3] tipc: improve interaction socket-link

[David Miller]

From: Jon Maloy <jon.maloy@ericsson.com>
Date: Tue,  3 Jan 2017 10:26:45 -0500

> 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.

This doesn't apply to net-next, also the Date in your emails is 10 days
in the past.  What's going on here?

RE: [net-next 0/3] tipc: improve interaction socket-link

[Jon Maloy]

> -----Original Message-----
> From: netdev-owner@vger.kernel.org [mailto:netdev-owner@vger.kernel.org]
> On Behalf Of David Miller
> Sent: Monday, 16 January, 2017 14:45
> To: Jon Maloy <jon.maloy@ericsson.com>
> Cc: netdev@vger.kernel.org; viro@zeniv.linux.org.uk; Parthasarathy Bhuvaragan
> <parthasarathy.bhuvaragan@ericsson.com>; Ying Xue
> <ying.xue@windriver.com>; maloy@donjonn.com; tipc-
> discussion@lists.sourceforge.net
> Subject: Re: [net-next 0/3] tipc: improve interaction socket-link
> 
> From: Jon Maloy <jon.maloy@ericsson.com>
> Date: Tue,  3 Jan 2017 10:26:45 -0500
> 
> > 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.
> 
> This doesn't apply to net-next, also the Date in your emails is 10 days
> in the past.  What's going on here?

I don't know. This series was sent in on Jan 3rd, and applied by you the same day. Maybe the mail server decided to send you a duplicate?

///jon

Re: [net-next 0/3] tipc: improve interaction socket-link

[David Miller]

From: Jon Maloy <jon.maloy@ericsson.com>
Date: Mon, 16 Jan 2017 20:35:08 +0000

> 
> 
>> -----Original Message-----
>> From: netdev-owner@vger.kernel.org [mailto:netdev-owner@vger.kernel.org]
>> On Behalf Of David Miller
>> Sent: Monday, 16 January, 2017 14:45
>> To: Jon Maloy <jon.maloy@ericsson.com>
>> Cc: netdev@vger.kernel.org; viro@zeniv.linux.org.uk; Parthasarathy Bhuvaragan
>> <parthasarathy.bhuvaragan@ericsson.com>; Ying Xue
>> <ying.xue@windriver.com>; maloy@donjonn.com; tipc-
>> discussion@lists.sourceforge.net
>> Subject: Re: [net-next 0/3] tipc: improve interaction socket-link
>> 
>> From: Jon Maloy <jon.maloy@ericsson.com>
>> Date: Tue,  3 Jan 2017 10:26:45 -0500
>> 
>> > 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.
>> 
>> This doesn't apply to net-next, also the Date in your emails is 10 days
>> in the past.  What's going on here?
> 
> I don't know. This series was sent in on Jan 3rd, and applied by you the same day. Maybe the mail server decided to send you a duplicate?

If you look in the headers, they have "Received-by: " fields with
January 13th in the date.  So something pushed them out again.

Really strange...

[net-next 0/3] tipc: improve interaction socket-link

[Jon Maloy]

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.

Jon Maloy (3):
  tipc: unify tipc_wait_for_sndpkt() and tipc_wait_for_sndmsg()
    functions
  tipc: modify struct tipc_plist to be more versatile
  tipc: reduce risk of user starvation during link congestion

 net/tipc/bcast.c      |   6 +-
 net/tipc/link.c       |  75 ++++-----
 net/tipc/msg.h        |   2 -
 net/tipc/name_table.c | 100 +++++++----
 net/tipc/name_table.h |  21 +--
 net/tipc/node.c       |  15 +-
 net/tipc/socket.c     | 449 ++++++++++++++++++++++----------------------------
 7 files changed, 319 insertions(+), 349 deletions(-)

-- 
2.7.4


------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most 
engaging tech sites, SlashDot.org! http://sdm.link/slashdot

[net-next 3/3] tipc: reduce risk of user starvation during link congestion

[Jon Maloy]

The socket code currently handles link congestion by either blocking
and trying to send again when the congestion has abated, or just
returning to the user with -EAGAIN and let him re-try later.

This mechanism is prone to starvation, because the wakeup algorithm is
non-atomic. During the time the link issues a wakeup signal, until the
socket wakes up and re-attempts sending, other senders may have come
in between and occupied the free buffer space in the link. This in turn
may lead to a socket having to make many send attempts before it is
successful. In extremely loaded systems we have observed latency times
of several seconds before a low-priority socket is able to send out a
message.

In this commit, we simplify this mechanism and reduce the risk of the
described scenario happening. When a message is attempted sent via a
congested link, we now let it be added to the link's backlog queue
anyway, thus permitting an oversubscription of one message per source
socket. We still create a wakeup item and return an error code, hence
instructing the sender to block or stop sending. Only when enough space
has been freed up in the link's backlog queue do we issue a wakeup event
that allows the sender to continue with the next message, if any.

The fact that a socket now can consider a message sent even when the
link returns a congestion code means that the sending socket code can
be simplified. Also, since this is a good opportunity to get rid of the
obsolete 'mtu change' condition in the three socket send functions, we
now choose to refactor those functions completely.

Signed-off-by: Parthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
---
 net/tipc/bcast.c  |   6 +-
 net/tipc/link.c   |  75 +++++-------
 net/tipc/msg.h    |   2 -
 net/tipc/node.c   |  15 +--
 net/tipc/socket.c | 347 ++++++++++++++++++++++++------------------------------
 5 files changed, 194 insertions(+), 251 deletions(-)

diff --git a/net/tipc/bcast.c b/net/tipc/bcast.c
index aa1babb..c35fad3 100644
--- a/net/tipc/bcast.c
+++ b/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
diff --git a/net/tipc/link.c b/net/tipc/link.c
index bda89bf..b758ca8 100644
--- a/net/tipc/link.c
+++ b/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)
+		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;
-		skb_unlink(skb, &l->wakeupq);
-		skb_queue_tail(l->inputq, skb);
+		}
 	}
 }
 
@@ -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)
diff --git a/net/tipc/msg.h b/net/tipc/msg.h
index 8d40861..850ae0e 100644
--- a/net/tipc/msg.h
+++ b/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;
 };
diff --git a/net/tipc/node.c b/net/tipc/node.c
index 9d2f4c2..2883f6a 100644
--- a/net/tipc/node.c
+++ b/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;
 }
 
diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index fae6a55..d2f3539 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -67,12 +67,14 @@ enum {
  * @max_pkt: maximum packet size "hint" used when building messages sent by port
  * @portid: unique port identity in TIPC socket hash table
  * @phdr: preformatted message header used when sending messages
+ * #cong_links: list of congested links
  * @publications: list of publications for port
+ * @blocking_link: address of the congested link we are currently sleeping on
  * @pub_count: total # of publications port has made during its lifetime
  * @probing_state:
  * @conn_timeout: the time we can wait for an unresponded setup request
  * @dupl_rcvcnt: number of bytes counted twice, in both backlog and rcv queue
- * @link_cong: non-zero if owner must sleep because of link congestion
+ * @cong_link_cnt: number of congested links
  * @sent_unacked: # messages sent by socket, and not yet acked by peer
  * @rcv_unacked: # messages read by user, but not yet acked back to peer
  * @peer: 'connected' peer for dgram/rdm
@@ -87,13 +89,13 @@ struct tipc_sock {
 	u32 max_pkt;
 	u32 portid;
 	struct tipc_msg phdr;
-	struct list_head sock_list;
+	struct list_head cong_links;
 	struct list_head publications;
 	u32 pub_count;
 	uint conn_timeout;
 	atomic_t dupl_rcvcnt;
 	bool probe_unacked;
-	bool link_cong;
+	u16 cong_link_cnt;
 	u16 snt_unacked;
 	u16 snd_win;
 	u16 peer_caps;
@@ -118,8 +120,7 @@ static int tipc_sk_withdraw(struct tipc_sock *tsk, uint scope,
 static struct tipc_sock *tipc_sk_lookup(struct net *net, u32 portid);
 static int tipc_sk_insert(struct tipc_sock *tsk);
 static void tipc_sk_remove(struct tipc_sock *tsk);
-static int __tipc_send_stream(struct socket *sock, struct msghdr *m,
-			      size_t dsz);
+static int __tipc_sendstream(struct socket *sock, struct msghdr *m, size_t dsz);
 static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dsz);
 
 static const struct proto_ops packet_ops;
@@ -424,6 +425,7 @@ static int tipc_sk_create(struct net *net, struct socket *sock,
 	tsk = tipc_sk(sk);
 	tsk->max_pkt = MAX_PKT_DEFAULT;
 	INIT_LIST_HEAD(&tsk->publications);
+	INIT_LIST_HEAD(&tsk->cong_links);
 	msg = &tsk->phdr;
 	tn = net_generic(sock_net(sk), tipc_net_id);
 	tipc_msg_init(tn->own_addr, msg, TIPC_LOW_IMPORTANCE, TIPC_NAMED_MSG,
@@ -474,9 +476,14 @@ static void __tipc_shutdown(struct socket *sock, int error)
 	struct sock *sk = sock->sk;
 	struct tipc_sock *tsk = tipc_sk(sk);
 	struct net *net = sock_net(sk);
+	long timeout = CONN_TIMEOUT_DEFAULT;
 	u32 dnode = tsk_peer_node(tsk);
 	struct sk_buff *skb;
 
+	/* Avoid that hi-prio shutdown msgs bypass msgs in link wakeup queue */
+	tipc_wait_for_cond(sock, &timeout, (!tsk->cong_link_cnt &&
+					    !tsk_conn_cong(tsk)));
+
 	/* Reject all unreceived messages, except on an active connection
 	 * (which disconnects locally & sends a 'FIN+' to peer).
 	 */
@@ -547,7 +554,8 @@ static int tipc_release(struct socket *sock)
 
 	/* Reject any messages that accumulated in backlog queue */
 	release_sock(sk);
-
+	u32_list_purge(&tsk->cong_links);
+	tsk->cong_link_cnt = 0;
 	call_rcu(&tsk->rcu, tipc_sk_callback);
 	sock->sk = NULL;
 
@@ -690,7 +698,7 @@ static unsigned int tipc_poll(struct file *file, struct socket *sock,
 
 	switch (sk->sk_state) {
 	case TIPC_ESTABLISHED:
-		if (!tsk->link_cong && !tsk_conn_cong(tsk))
+		if (!tsk->cong_link_cnt && !tsk_conn_cong(tsk))
 			mask |= POLLOUT;
 		/* fall thru' */
 	case TIPC_LISTEN:
@@ -699,7 +707,7 @@ static unsigned int tipc_poll(struct file *file, struct socket *sock,
 			mask |= (POLLIN | POLLRDNORM);
 		break;
 	case TIPC_OPEN:
-		if (!tsk->link_cong)
+		if (!tsk->cong_link_cnt)
 			mask |= POLLOUT;
 		if (tipc_sk_type_connectionless(sk) &&
 		    (!skb_queue_empty(&sk->sk_receive_queue)))
@@ -718,63 +726,48 @@ static unsigned int tipc_poll(struct file *file, struct socket *sock,
  * @sock: socket structure
  * @seq: destination address
  * @msg: message to send
- * @dsz: total length of message data
- * @timeo: timeout to wait for wakeup
+ * @dlen: length of data to send
+ * @timeout: timeout to wait for wakeup
  *
  * Called from function tipc_sendmsg(), which has done all sanity checks
  * Returns the number of bytes sent on success, or errno
  */
 static int tipc_sendmcast(struct  socket *sock, struct tipc_name_seq *seq,
-			  struct msghdr *msg, size_t dsz, long timeo)
+			  struct msghdr *msg, size_t dlen, long timeout)
 {
 	struct sock *sk = sock->sk;
 	struct tipc_sock *tsk = tipc_sk(sk);
+	struct tipc_msg *hdr = &tsk->phdr;
 	struct net *net = sock_net(sk);
-	struct tipc_msg *mhdr = &tsk->phdr;
-	struct sk_buff_head pktchain;
-	struct iov_iter save = msg->msg_iter;
-	uint mtu;
+	int mtu = tipc_bcast_get_mtu(net);
+	struct sk_buff_head pkts;
 	int rc;
 
-	if (!timeo && tsk->link_cong)
-		return -ELINKCONG;
-
-	msg_set_type(mhdr, TIPC_MCAST_MSG);
-	msg_set_lookup_scope(mhdr, TIPC_CLUSTER_SCOPE);
-	msg_set_destport(mhdr, 0);
-	msg_set_destnode(mhdr, 0);
-	msg_set_nametype(mhdr, seq->type);
-	msg_set_namelower(mhdr, seq->lower);
-	msg_set_nameupper(mhdr, seq->upper);
-	msg_set_hdr_sz(mhdr, MCAST_H_SIZE);
-
-	skb_queue_head_init(&pktchain);
+	rc = tipc_wait_for_cond(sock, &timeout, !tsk->cong_link_cnt);
+	if (unlikely(rc))
+		return rc;
 
-new_mtu:
-	mtu = tipc_bcast_get_mtu(net);
-	rc = tipc_msg_build(mhdr, msg, 0, dsz, mtu, &pktchain);
-	if (unlikely(rc < 0))
+	msg_set_type(hdr, TIPC_MCAST_MSG);
+	msg_set_lookup_scope(hdr, TIPC_CLUSTER_SCOPE);
+	msg_set_destport(hdr, 0);
+	msg_set_destnode(hdr, 0);
+	msg_set_nametype(hdr, seq->type);
+	msg_set_namelower(hdr, seq->lower);
+	msg_set_nameupper(hdr, seq->upper);
+	msg_set_hdr_sz(hdr, MCAST_H_SIZE);
+
+	skb_queue_head_init(&pkts);
+	rc = tipc_msg_build(hdr, msg, 0, dlen, mtu, &pkts);
+	if (unlikely(rc != dlen))
 		return rc;
 
-	do {
-		rc = tipc_bcast_xmit(net, &pktchain);
-		if (likely(!rc))
-			return dsz;
-
-		if (rc == -ELINKCONG) {
-			tsk->link_cong = 1;
-			rc = tipc_wait_for_cond(sock, &timeo, !tsk->link_cong);
-			if (!rc)
-				continue;
-		}
-		__skb_queue_purge(&pktchain);
-		if (rc == -EMSGSIZE) {
-			msg->msg_iter = save;
-			goto new_mtu;
-		}
-		break;
-	} while (1);
-	return rc;
+	rc = tipc_bcast_xmit(net, &pkts);
+	if (unlikely(rc == -ELINKCONG)) {
+		tsk->cong_link_cnt = 1;
+		rc = 0;
+	}
+
+	return rc ? rc : dlen;
 }
 
 /**
@@ -898,35 +891,38 @@ static int tipc_sendmsg(struct socket *sock,
 	return ret;
 }
 
-static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dsz)
+static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dlen)
 {
-	DECLARE_SOCKADDR(struct sockaddr_tipc *, dest, m->msg_name);
 	struct sock *sk = sock->sk;
-	struct tipc_sock *tsk = tipc_sk(sk);
 	struct net *net = sock_net(sk);
-	struct tipc_msg *mhdr = &tsk->phdr;
-	u32 dnode, dport;
-	struct sk_buff_head pktchain;
-	bool is_connectionless = tipc_sk_type_connectionless(sk);
-	struct sk_buff *skb;
+	struct tipc_sock *tsk = tipc_sk(sk);
+	DECLARE_SOCKADDR(struct sockaddr_tipc *, dest, m->msg_name);
+	long timeout = sock_sndtimeo(sk, m->msg_flags & MSG_DONTWAIT);
+	struct list_head *clinks = &tsk->cong_links;
+	bool syn = !tipc_sk_type_connectionless(sk);
+	struct tipc_msg *hdr = &tsk->phdr;
 	struct tipc_name_seq *seq;
-	struct iov_iter save;
-	u32 mtu;
-	long timeo;
-	int rc;
+	struct sk_buff_head pkts;
+	u32 type, inst, domain;
+	u32 dnode, dport;
+	int mtu, rc;
 
-	if (dsz > TIPC_MAX_USER_MSG_SIZE)
+	if (unlikely(dlen > TIPC_MAX_USER_MSG_SIZE))
 		return -EMSGSIZE;
+
 	if (unlikely(!dest)) {
-		if (is_connectionless && tsk->peer.family == AF_TIPC)
-			dest = &tsk->peer;
-		else
+		dest = &tsk->peer;
+		if (!syn || dest->family != AF_TIPC)
 			return -EDESTADDRREQ;
-	} else if (unlikely(m->msg_namelen < sizeof(*dest)) ||
-		   dest->family != AF_TIPC) {
-		return -EINVAL;
 	}
-	if (!is_connectionless) {
+
+	if (unlikely(m->msg_namelen < sizeof(*dest)))
+		return -EINVAL;
+
+	if (unlikely(dest->family != AF_TIPC))
+		return -EINVAL;
+
+	if (unlikely(syn)) {
 		if (sk->sk_state == TIPC_LISTEN)
 			return -EPIPE;
 		if (sk->sk_state != TIPC_OPEN)
@@ -938,72 +934,62 @@ static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dsz)
 			tsk->conn_instance = dest->addr.name.name.instance;
 		}
 	}
-	seq = &dest->addr.nameseq;
-	timeo = sock_sndtimeo(sk, m->msg_flags & MSG_DONTWAIT);
 
-	if (dest->addrtype == TIPC_ADDR_MCAST) {
-		return tipc_sendmcast(sock, seq, m, dsz, timeo);
-	} else if (dest->addrtype == TIPC_ADDR_NAME) {
-		u32 type = dest->addr.name.name.type;
-		u32 inst = dest->addr.name.name.instance;
-		u32 domain = dest->addr.name.domain;
+	seq = &dest->addr.nameseq;
+	if (dest->addrtype == TIPC_ADDR_MCAST)
+		return tipc_sendmcast(sock, seq, m, dlen, timeout);
 
+	if (dest->addrtype == TIPC_ADDR_NAME) {
+		type = dest->addr.name.name.type;
+		inst = dest->addr.name.name.instance;
+		domain = dest->addr.name.domain;
 		dnode = domain;
-		msg_set_type(mhdr, TIPC_NAMED_MSG);
-		msg_set_hdr_sz(mhdr, NAMED_H_SIZE);
-		msg_set_nametype(mhdr, type);
-		msg_set_nameinst(mhdr, inst);
-		msg_set_lookup_scope(mhdr, tipc_addr_scope(domain));
+		msg_set_type(hdr, TIPC_NAMED_MSG);
+		msg_set_hdr_sz(hdr, NAMED_H_SIZE);
+		msg_set_nametype(hdr, type);
+		msg_set_nameinst(hdr, inst);
+		msg_set_lookup_scope(hdr, tipc_addr_scope(domain));
 		dport = tipc_nametbl_translate(net, type, inst, &dnode);
-		msg_set_destnode(mhdr, dnode);
-		msg_set_destport(mhdr, dport);
+		msg_set_destnode(hdr, dnode);
+		msg_set_destport(hdr, dport);
 		if (unlikely(!dport && !dnode))
 			return -EHOSTUNREACH;
+
 	} else if (dest->addrtype == TIPC_ADDR_ID) {
 		dnode = dest->addr.id.node;
-		msg_set_type(mhdr, TIPC_DIRECT_MSG);
-		msg_set_lookup_scope(mhdr, 0);
-		msg_set_destnode(mhdr, dnode);
-		msg_set_destport(mhdr, dest->addr.id.ref);
-		msg_set_hdr_sz(mhdr, BASIC_H_SIZE);
+		msg_set_type(hdr, TIPC_DIRECT_MSG);
+		msg_set_lookup_scope(hdr, 0);
+		msg_set_destnode(hdr, dnode);
+		msg_set_destport(hdr, dest->addr.id.ref);
+		msg_set_hdr_sz(hdr, BASIC_H_SIZE);
 	}
 
-	skb_queue_head_init(&pktchain);
-	save = m->msg_iter;
-new_mtu:
+	/* Block or return if destination link is congested */
+	rc = tipc_wait_for_cond(sock, &timeout, !u32_find(clinks, dnode));
+	if (unlikely(rc))
+		return rc;
+
+	skb_queue_head_init(&pkts);
 	mtu = tipc_node_get_mtu(net, dnode, tsk->portid);
-	rc = tipc_msg_build(mhdr, m, 0, dsz, mtu, &pktchain);
-	if (rc < 0)
+	rc = tipc_msg_build(hdr, m, 0, dlen, mtu, &pkts);
+	if (unlikely(rc != dlen))
 		return rc;
 
-	do {
-		skb = skb_peek(&pktchain);
-		TIPC_SKB_CB(skb)->wakeup_pending = tsk->link_cong;
-		rc = tipc_node_xmit(net, &pktchain, dnode, tsk->portid);
-		if (likely(!rc)) {
-			if (!is_connectionless)
-				tipc_set_sk_state(sk, TIPC_CONNECTING);
-			return dsz;
-		}
-		if (rc == -ELINKCONG) {
-			tsk->link_cong = 1;
-			rc = tipc_wait_for_cond(sock, &timeo, !tsk->link_cong);
-			if (!rc)
-				continue;
-		}
-		__skb_queue_purge(&pktchain);
-		if (rc == -EMSGSIZE) {
-			m->msg_iter = save;
-			goto new_mtu;
-		}
-		break;
-	} while (1);
+	rc = tipc_node_xmit(net, &pkts, dnode, tsk->portid);
+	if (unlikely(rc == -ELINKCONG)) {
+		u32_push(clinks, dnode);
+		tsk->cong_link_cnt++;
+		rc = 0;
+	}
 
-	return rc;
+	if (unlikely(syn && !rc))
+		tipc_set_sk_state(sk, TIPC_CONNECTING);
+
+	return rc ? rc : dlen;
 }
 
 /**
- * tipc_send_stream - send stream-oriented data
+ * tipc_sendstream - send stream-oriented data
  * @sock: socket structure
  * @m: data to send
  * @dsz: total length of data to be transmitted
@@ -1013,97 +999,69 @@ static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dsz)
  * Returns the number of bytes sent on success (or partial success),
  * or errno if no data sent
  */
-static int tipc_send_stream(struct socket *sock, struct msghdr *m, size_t dsz)
+static int tipc_sendstream(struct socket *sock, struct msghdr *m, size_t dsz)
 {
 	struct sock *sk = sock->sk;
 	int ret;
 
 	lock_sock(sk);
-	ret = __tipc_send_stream(sock, m, dsz);
+	ret = __tipc_sendstream(sock, m, dsz);
 	release_sock(sk);
 
 	return ret;
 }
 
-static int __tipc_send_stream(struct socket *sock, struct msghdr *m, size_t dsz)
+static int __tipc_sendstream(struct socket *sock, struct msghdr *m, size_t dlen)
 {
 	struct sock *sk = sock->sk;
-	struct net *net = sock_net(sk);
-	struct tipc_sock *tsk = tipc_sk(sk);
-	struct tipc_msg *mhdr = &tsk->phdr;
-	struct sk_buff_head pktchain;
 	DECLARE_SOCKADDR(struct sockaddr_tipc *, dest, m->msg_name);
-	u32 portid = tsk->portid;
-	int rc = -EINVAL;
-	long timeo;
-	u32 dnode;
-	uint mtu, send, sent = 0;
-	struct iov_iter save;
-	int hlen = MIN_H_SIZE;
-
-	/* Handle implied connection establishment */
-	if (unlikely(dest)) {
-		rc = __tipc_sendmsg(sock, m, dsz);
-		hlen = msg_hdr_sz(mhdr);
-		if (dsz && (dsz == rc))
-			tsk->snt_unacked = tsk_inc(tsk, dsz + hlen);
-		return rc;
-	}
-	if (dsz > (uint)INT_MAX)
-		return -EMSGSIZE;
-
-	if (unlikely(!tipc_sk_connected(sk))) {
-		if (sk->sk_state == TIPC_DISCONNECTING)
-			return -EPIPE;
-		else
-			return -ENOTCONN;
-	}
+	long timeout = sock_sndtimeo(sk, m->msg_flags & MSG_DONTWAIT);
+	struct tipc_sock *tsk = tipc_sk(sk);
+	struct tipc_msg *hdr = &tsk->phdr;
+	struct net *net = sock_net(sk);
+	struct sk_buff_head pkts;
+	u32 dnode = tsk_peer_node(tsk);
+	int send, sent = 0;
+	int rc = 0;
 
-	timeo = sock_sndtimeo(sk, m->msg_flags & MSG_DONTWAIT);
-	if (!timeo && tsk->link_cong)
-		return -ELINKCONG;
+	skb_queue_head_init(&pkts);
 
-	dnode = tsk_peer_node(tsk);
-	skb_queue_head_init(&pktchain);
+	if (unlikely(dlen > INT_MAX))
+		return -EMSGSIZE;
 
-next:
-	save = m->msg_iter;
-	mtu = tsk->max_pkt;
-	send = min_t(uint, dsz - sent, TIPC_MAX_USER_MSG_SIZE);
-	rc = tipc_msg_build(mhdr, m, sent, send, mtu, &pktchain);
-	if (unlikely(rc < 0))
+	/* Handle implicit connection setup */
+	if (unlikely(dest)) {
+		rc = __tipc_sendmsg(sock, m, dlen);
+		if (dlen && (dlen == rc))
+			tsk->snt_unacked = tsk_inc(tsk, dlen + msg_hdr_sz(hdr));
 		return rc;
+	}
 
 	do {
-		if (likely(!tsk_conn_cong(tsk))) {
-			rc = tipc_node_xmit(net, &pktchain, dnode, portid);
-			if (likely(!rc)) {
-				tsk->snt_unacked += tsk_inc(tsk, send + hlen);
-				sent += send;
-				if (sent == dsz)
-					return dsz;
-				goto next;
-			}
-			if (rc == -EMSGSIZE) {
-				__skb_queue_purge(&pktchain);
-				tsk->max_pkt = tipc_node_get_mtu(net, dnode,
-								 portid);
-				m->msg_iter = save;
-				goto next;
-			}
-			if (rc != -ELINKCONG)
-				break;
-
-			tsk->link_cong = 1;
-		}
-		rc = tipc_wait_for_cond(sock, &timeo,
-					(!tsk->link_cong &&
+		rc = tipc_wait_for_cond(sock, &timeout,
+					(!tsk->cong_link_cnt &&
 					 !tsk_conn_cong(tsk) &&
 					 tipc_sk_connected(sk)));
-	} while (!rc);
+		if (unlikely(rc))
+			break;
+
+		send = min_t(size_t, dlen - sent, TIPC_MAX_USER_MSG_SIZE);
+		rc = tipc_msg_build(hdr, m, sent, send, tsk->max_pkt, &pkts);
+		if (unlikely(rc != send))
+			break;
+
+		rc = tipc_node_xmit(net, &pkts, dnode, tsk->portid);
+		if (unlikely(rc == -ELINKCONG)) {
+			tsk->cong_link_cnt = 1;
+			rc = 0;
+		}
+		if (likely(!rc)) {
+			tsk->snt_unacked += tsk_inc(tsk, send + MIN_H_SIZE);
+			sent += send;
+		}
+	} while (sent < dlen && !rc);
 
-	__skb_queue_purge(&pktchain);
-	return sent ? sent : rc;
+	return rc ? rc : sent;
 }
 
 /**
@@ -1121,7 +1079,7 @@ static int tipc_send_packet(struct socket *sock, struct msghdr *m, size_t dsz)
 	if (dsz > TIPC_MAX_USER_MSG_SIZE)
 		return -EMSGSIZE;
 
-	return tipc_send_stream(sock, m, dsz);
+	return tipc_sendstream(sock, m, dsz);
 }
 
 /* tipc_sk_finish_conn - complete the setup of a connection
@@ -1688,6 +1646,7 @@ static bool filter_rcv(struct sock *sk, struct sk_buff *skb,
 	unsigned int limit = rcvbuf_limit(sk, skb);
 	int err = TIPC_OK;
 	int usr = msg_user(hdr);
+	u32 onode;
 
 	if (unlikely(msg_user(hdr) == CONN_MANAGER)) {
 		tipc_sk_proto_rcv(tsk, skb, xmitq);
@@ -1695,8 +1654,10 @@ static bool filter_rcv(struct sock *sk, struct sk_buff *skb,
 	}
 
 	if (unlikely(usr == SOCK_WAKEUP)) {
+		onode = msg_orignode(hdr);
 		kfree_skb(skb);
-		tsk->link_cong = 0;
+		u32_del(&tsk->cong_links, onode);
+		tsk->cong_link_cnt--;
 		sk->sk_write_space(sk);
 		return false;
 	}
@@ -2104,7 +2065,7 @@ static int tipc_accept(struct socket *sock, struct socket *new_sock, int flags)
 		struct msghdr m = {NULL,};
 
 		tsk_advance_rx_queue(sk);
-		__tipc_send_stream(new_sock, &m, 0);
+		__tipc_sendstream(new_sock, &m, 0);
 	} else {
 		__skb_dequeue(&sk->sk_receive_queue);
 		__skb_queue_head(&new_sk->sk_receive_queue, buf);
@@ -2565,7 +2526,7 @@ static const struct proto_ops stream_ops = {
 	.shutdown	= tipc_shutdown,
 	.setsockopt	= tipc_setsockopt,
 	.getsockopt	= tipc_getsockopt,
-	.sendmsg	= tipc_send_stream,
+	.sendmsg	= tipc_sendstream,
 	.recvmsg	= tipc_recv_stream,
 	.mmap		= sock_no_mmap,
 	.sendpage	= sock_no_sendpage
-- 
2.7.4


------------------------------------------------------------------------------
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