diff options
| author | Yuchung Cheng <ycheng@google.com> | 2019-04-30 01:46:13 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2019-05-01 18:47:54 +0300 |
| commit | bc9f38c8328e10c22cb2016d6131ea36141c8d11 (patch) | |
| tree | 29684a2a2f3136f74849beb292f60bb6235ae1c0 | |
| parent | 6d1474a94ea2641f56c7893eb1e30558fd92f55d (diff) | |
| download | linux-bc9f38c8328e10c22cb2016d6131ea36141c8d11.tar.xz | |
tcp: avoid unconditional congestion window undo on SYN retransmit
Previously if an active TCP open has SYN timeout, it always undo the
cwnd upon receiving the SYNACK. This is because tcp_clean_rtx_queue
would reset tp->retrans_stamp when SYN is acked, which fools then
tcp_try_undo_loss and tcp_packet_delayed. Addressing this issue is
required to properly support undo for spurious SYN timeout.
Fixing this is tricky -- for active TCP open tp->retrans_stamp
records the time when the handshake starts, not the first
retransmission time as the name may suggest. The simplest fix is
for tcp_packet_delayed to ensure it is valid before comparing with
other timestamp.
One side effect of this change is active TCP Fast Open that incurred
SYN timeout. Upon receiving a SYN-ACK that only acknowledged
the SYN, it would immediately retransmit unacknowledged data in
tcp_ack() because the data is marked lost after SYN timeout. But
the retransmission would have an incorrect ack sequence number since
rcv_nxt has not been updated yet tcp_rcv_synsent_state_process(), the
retransmission needs to properly handed by tcp_rcv_fastopen_synack()
like before.
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
| -rw-r--r-- | net/ipv4/tcp_input.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 97671bff597a..e2cbfc3ffa3f 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2252,7 +2252,7 @@ static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp, */ static inline bool tcp_packet_delayed(const struct tcp_sock *tp) { - return !tp->retrans_stamp || + return tp->retrans_stamp && tcp_tsopt_ecr_before(tp, tp->retrans_stamp); } @@ -3521,7 +3521,7 @@ static void tcp_xmit_recovery(struct sock *sk, int rexmit) { struct tcp_sock *tp = tcp_sk(sk); - if (rexmit == REXMIT_NONE) + if (rexmit == REXMIT_NONE || sk->sk_state == TCP_SYN_SENT) return; if (unlikely(rexmit == 2)) { |