[PATCH 5/6] tcp: fastopen: retransmit data when only the SYN of a synack-with-data is acked
From: Jeremy Harris <hidden>
Date: 2025-05-16 15:56:05
Also in:
netdev
Subsystem:
networking [general], networking [tcp], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
A corner-case for the 3rd-ack after a data-on-synack is for only the SYN to be acked. Handle this by, in ack processing, when in SYN_RECV state (the state is not yet updated to ESTABLISHED) marking the retransmit-queue sk_buff as having been lost. Signed-off-by: Jeremy Harris <redacted> --- net/ipv4/tcp_input.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 345a08baaf02..a53021edddd5 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c@@ -4069,6 +4069,18 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) &rexmit); } + /* On receiving a 3rd-ack, if we never sent a packet via + * the normal means (which counts them), yet there is data + * remaining for retransmit, it was data-on-synack not acked; + * mark the skb for retransmission. + */ + if (sk->sk_state == TCP_SYN_RECV && tp->segs_out == 0) { + struct sk_buff *skb = tcp_rtx_queue_head(sk); + + if (skb) + tcp_mark_skb_lost(sk, skb); + } + /* If needed, reset TLP/RTO timer when RACK doesn't set. */ if (flag & FLAG_SET_XMIT_TIMER) tcp_set_xmit_timer(sk);
--
2.49.0