tcp: consider using standard rtx logic in tcp_rcv_fastopen_synack()

Jakub reported Data included in a Fastopen SYN that had to be
retransmit would have to wait for an RTO if TX completions are slow,
even with prior fix.

This is because tcp_rcv_fastopen_synack() does not use standard
rtx logic, meaning TSQ handler exits early in tcp_tsq_write()
because tp->lost_out == tp->retrans_out

Lets make tcp_rcv_fastopen_synack() use standard rtx logic,
by using tcp_mark_skb_lost() on the skb thats needs to be
sent again.

Not this raised a warning in tcp_fastretrans_alert() during my tests
since we consider the data not being aknowledged
by the receiver does not mean packet was lost on the network.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Jakub Kicinski <kuba@kernel.org>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 69a545db80d2ead47ffcf2f3819a6d066e95f35d..4cf4dd532d1c65bba417a66ba6b7783491b6380a 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2914,7 +2914,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
        /* D. Check state exit conditions. State can be terminated
         *    when high_seq is ACKed. */
        if (icsk->icsk_ca_state == TCP_CA_Open) {
-               WARN_ON(tp->retrans_out != 0);
+               WARN_ON(tp->retrans_out != 0 && !tp->syn_data);
                tp->retrans_stamp = 0;
        } else if (!before(tp->snd_una, tp->high_seq)) {
                switch (icsk->icsk_ca_state) {
@@ -5994,11 +5994,9 @@ static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
                        tp->fastopen_client_fail = TFO_SYN_RETRANSMITTED;
                else
                        tp->fastopen_client_fail = TFO_DATA_NOT_ACKED;
-               skb_rbtree_walk_from(data) {
-                       if (__tcp_retransmit_skb(sk, data, 1))
-                               break;
-               }
-               tcp_rearm_rto(sk);
+               skb_rbtree_walk_from(data)
+                        tcp_mark_skb_lost(sk, data);
+               tcp_xmit_retransmit_queue(sk);
                NET_INC_STATS(sock_net(sk),
                                LINUX_MIB_TCPFASTOPENACTIVEFAIL);
                return true;