tipc: fix hanging clients using poll with EPOLLOUT flag

commit 517d7c79 ("tipc: fix hanging poll() for stream sockets")
introduced a regression for clients using non-blocking sockets.
After the commit, we send EPOLLOUT event to the client even in
TIPC_CONNECTING state. This causes the subsequent send() to fail
with ENOTCONN, as the socket is still not in TIPC_ESTABLISHED state.

In this commit, we:
- improve the fix for hanging poll() by replacing sk_data_ready()
  with sk_state_change() to wake up all clients.
- revert the faulty updates introduced by commit 517d7c79
  ("tipc: fix hanging poll() for stream sockets").

Fixes: 517d7c79 ("tipc: fix hanging poll() for stream sockets")
Signed-off-by: Parthasarathy Bhuvaragan <parthasarathy.bhuvaragan@gmail.com>
Acked-by: Jon Maloy <jon.maloy@ericsson.se>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/socket.c

@@ -736,11 +736,11 @@ static __poll_t tipc_poll(struct file *file, struct socket *sock,
 
 	switch (sk->sk_state) {
 	case TIPC_ESTABLISHED:
-	case TIPC_CONNECTING:
 		if (!tsk->cong_link_cnt && !tsk_conn_cong(tsk))
 			revents |= EPOLLOUT;
 		/* fall through */
 	case TIPC_LISTEN:
+	case TIPC_CONNECTING:
 		if (!skb_queue_empty(&sk->sk_receive_queue))
 			revents |= EPOLLIN | EPOLLRDNORM;
 		break;
@@ -2043,7 +2043,7 @@ static bool tipc_sk_filter_connect(struct tipc_sock *tsk, struct sk_buff *skb)
 			if (msg_data_sz(hdr))
 				return true;
 			/* Empty ACK-, - wake up sleeping connect() and drop */
-			sk->sk_data_ready(sk);
+			sk->sk_state_change(sk);
 			msg_set_dest_droppable(hdr, 1);
 			return false;
 		}