From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vijay Subramanian Subject: [PATCH net-next 1/1] tcp: Prevent needless syn-ack rexmt during TWHS Date: Thu, 25 Oct 2012 17:45:56 -0700 Message-ID: <1351212356-11964-1-git-send-email-subramanian.vijay@gmail.com> Cc: davem@davemloft.net, Venkat Venkatsubra , Elliot Hughes , Vijay Subramanian , Eric Dumazet To: netdev@vger.kernel.org Return-path: Received: from mail-pb0-f46.google.com ([209.85.160.46]:62775 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755375Ab2JZA21 (ORCPT ); Thu, 25 Oct 2012 20:28:27 -0400 Received: by mail-pb0-f46.google.com with SMTP id rr4so2385603pbb.19 for ; Thu, 25 Oct 2012 17:28:26 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: If server socket is slow to accept() connections, request_socks can represent connections for which the three-way handshake is already done. From client's point of view, the connection is in ESTABLISHED state but on server side, socket is not in accept_queue or ESTABLISHED state. When the syn-ack timer expires, because of the order in which tests are performed, server can retransmit the synack repeatedly. Following patch prevents the server from retransmitting the synack needlessly (and prevents client from replying with ack). This reduces traffic when server is slow to accept() connections. If the server socket has received the third ack during connection establishment, this is remembered in inet_rsk(req)->acked. The request_sock will expire in around 30 seconds and will be dropped if it does not move into accept_queue. With help from Eric Dumazet. Reported-by: Elliot Hughes Cc: Eric Dumazet Signed-off-by: Vijay Subramanian --- Ignoring "WARNING: line over 80 characters" in the interest of readability. Eric, What about your earlier patch that modified sk_acceptq_is_full()? net/ipv4/inet_connection_sock.c | 5 ++--- 1 files changed, 2 insertions(+), 3 deletions(-) diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c index d34ce29..4e8e52e 100644 --- a/net/ipv4/inet_connection_sock.c +++ b/net/ipv4/inet_connection_sock.c @@ -598,9 +598,8 @@ void inet_csk_reqsk_queue_prune(struct sock *parent, &expire, &resend); req->rsk_ops->syn_ack_timeout(parent, req); if (!expire && - (!resend || - !req->rsk_ops->rtx_syn_ack(parent, req, NULL) || - inet_rsk(req)->acked)) { + (!resend || inet_rsk(req)->acked || + !req->rsk_ops->rtx_syn_ack(parent, req, NULL))) { unsigned long timeo; if (req->retrans++ == 0) -- 1.7.0.4