See below.
> -----Original Message-----
> From: Tung Nguyen <tung.q.ngu...@dektech.com.au>
> Sent: 14-Nov-19 03:28
> To: tipc-discussion@lists.sourceforge.net; Jon Maloy
> <jon.ma...@ericsson.com>; ma...@donjonn.com;
> ying....@windriver.com
> Subject: [tipc-discussion] [net v2 1/1] tipc: fix duplicate SYN messages
> under link congestion
>
> Scenario:
> 1. A client socket initiates a SYN message to a listening socket.
> 2. The send link is congested, the SYN message is put in the
> send link and a wakeup message is put in wakeup queue.
> 3. The congestion situation is abated, the wakeup message is
> pulled out of the wakeup queue. Function tipc_sk_push_backlog()
> is called to send out delayed messages by Nagle. However,
> the client socket is still in CONNECTING state. So, it sends
> the SYN message in the socket write queue to the listening socket
> again.
> 4. The listening socket receives the first SYN message and creates
> first server socket. The client socket receives ACK- and establishes
> a connection to the first server socket. The client socket closes
> its connection with the first server socket.
> 5. The listening socket receives the second SYN message and creates
> second server socket. The second server socket sends ACK- to the
> client socket, but it has been closed. It results in connection
> refuse error when reading from the server socket in user space.
>
> Solution: return from function tipc_sk_push_backlog() immediately
> if there is pending SYN message in the socket write queue.
>
> v2: use Jon's suggestion.
>
> Fixes: c0bceb97db9e ("tipc: add smart nagle feature")
> Signed-off-by: Tung Nguyen <tung.q.ngu...@dektech.com.au>
> ---
> net/tipc/socket.c | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/net/tipc/socket.c b/net/tipc/socket.c
> index 5d7859a..7a402ee 100644
> --- a/net/tipc/socket.c
> +++ b/net/tipc/socket.c
> @@ -540,12 +540,10 @@ static void __tipc_shutdown(struct socket *sock, int
> error)
> tipc_wait_for_cond(sock, &timeout, (!tsk->cong_link_cnt &&
> !tsk_conn_cong(tsk)));
>
> - /* Push out unsent messages or remove if pending SYN */
> - skb = skb_peek(&sk->sk_write_queue);
> - if (skb && !msg_is_syn(buf_msg(skb)))
> - tipc_sk_push_backlog(tsk);
> - else
> - __skb_queue_purge(&sk->sk_write_queue);
> + /* Push out delayed messages if in Nagle mode */
> + tipc_sk_push_backlog(tsk);
> + /* Remove pending SYN */
> + __skb_queue_purge(&sk->sk_write_queue);
>
> /* Reject all unreceived messages, except on an active connection
> * (which disconnects locally & sends a 'FIN+' to peer).
> @@ -1248,11 +1246,17 @@ static void tipc_sk_push_backlog(struct tipc_sock
> *tsk)
> struct sk_buff_head *txq = &tsk->sk.sk_write_queue;
> struct net *net = sock_net(&tsk->sk);
> u32 dnode = tsk_peer_node(tsk);
> + struct sk_buff *skb;
> int rc;
>
> if (skb_queue_empty(txq) || tsk->cong_link_cnt)
> return;
>
> + skb = skb_peek(txq);
Move this line to before the if() clause.Then test for if (!skb ||...) instead
of skb_queue_empty().
This way we should save a couple of instructions.
Acked-by:jon
> + /* Do not send SYN again after congestion */
> + if (msg_is_syn(buf_msg(skb)))
> + return;
> +
> tsk->snt_unacked += tsk->snd_backlog;
> tsk->snd_backlog = 0;
> tsk->expect_ack = true;
> --
> 2.1.4
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