From e6c022a4fa2d2d9ca9d0a7ac3b05ad988f39fc30 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sat, 27 Oct 2012 23:16:46 +0000 Subject: tcp: better retrans tracking for defer-accept For passive TCP connections using TCP_DEFER_ACCEPT facility, we incorrectly increment req->retrans each time timeout triggers while no SYNACK is sent. SYNACK are not sent for TCP_DEFER_ACCEPT that were established (for which we received the ACK from client). Only the last SYNACK is sent so that we can receive again an ACK from client, to move the req into accept queue. We plan to change this later to avoid the useless retransmit (and potential problem as this SYNACK could be lost) TCP_INFO later gives wrong information to user, claiming imaginary retransmits. Decouple req->retrans field into two independent fields : num_retrans : number of retransmit num_timeout : number of timeouts num_timeout is the counter that is incremented at each timeout, regardless of actual SYNACK being sent or not, and used to compute the exponential timeout. Introduce inet_rtx_syn_ack() helper to increment num_retrans only if ->rtx_syn_ack() succeeded. Use inet_rtx_syn_ack() from tcp_check_req() to increment num_retrans when we re-send a SYNACK in answer to a (retransmitted) SYN. Prior to this patch, we were not counting these retransmits. Change tcp_v[46]_rtx_synack() to increment TCP_MIB_RETRANSSEGS only if a synack packet was successfully queued. Reported-by: Yuchung Cheng Signed-off-by: Eric Dumazet Cc: Julian Anastasov Cc: Vijay Subramanian Cc: Elliott Hughes Cc: Neal Cardwell Signed-off-by: David S. Miller --- net/ipv4/tcp_minisocks.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'net/ipv4/tcp_minisocks.c') diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c index 27536ba16c9..0404b3f4c95 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -552,7 +552,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, * it can be estimated (approximately) * from another data. */ - tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<retrans); + tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<num_timeout); paws_reject = tcp_paws_reject(&tmp_opt, th->rst); } } @@ -581,7 +581,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, * Note that even if there is new data in the SYN packet * they will be thrown away too. */ - req->rsk_ops->rtx_syn_ack(sk, req, NULL); + inet_rtx_syn_ack(sk, req); return NULL; } @@ -695,7 +695,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, /* Got ACK for our SYNACK, so update baseline for SYNACK RTT sample. */ if (tmp_opt.saw_tstamp && tmp_opt.rcv_tsecr) tcp_rsk(req)->snt_synack = tmp_opt.rcv_tsecr; - else if (req->retrans) /* don't take RTT sample if retrans && ~TS */ + else if (req->num_retrans) /* don't take RTT sample if retrans && ~TS */ tcp_rsk(req)->snt_synack = 0; /* For Fast Open no more processing is needed (sk is the @@ -705,7 +705,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, return sk; /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ - if (req->retrans < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept && + if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept && TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { inet_rsk(req)->acked = 1; NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); -- cgit v1.2.3-18-g5258