path: root/net/ipv4/tcp_input.c
diff options
authorYuchung Cheng <ycheng@google.com>2019-04-29 15:46:13 -0700
committerDavid S. Miller <davem@davemloft.net>2019-05-01 11:47:54 -0400
commitbc9f38c8328e10c22cb2016d6131ea36141c8d11 (patch)
tree29684a2a2f3136f74849beb292f60bb6235ae1c0 /net/ipv4/tcp_input.c
parentnetdevsim: fix fall-through annotation (diff)
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>
Diffstat (limited to '')
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)
if (unlikely(rexmit == 2)) {