On Thu, Mar 04, 2021 at 08:41:45PM +0100, Eric Dumazet wrote:
> On Thu, Mar 4, 2021 at 8:06 PM Jakub Kicinski <k...@kernel.org> wrote:
> >
> > On Thu, 4 Mar 2021 13:51:15 +0100 Eric Dumazet wrote:
> > > I think we are over thinking this really (especially if the fix needs
> > > a change in core networking or drivers)
> > >
> > > We can reuse TSQ logic to have a chance to recover when the clone is
> > > eventually freed.
> > > This will be more generic, not only for the SYN+data of FastOpen.
> > >
> > > Can you please test the following patch ?
> >
> > #7 - Eric comes up with something much better :)
> >
> >
> > But so far doesn't seem to quite do it, I'm looking but maybe you'll
> > know right away (FWIW testing a v5.6 backport but I don't think TSQ
> > changed?):
> >
> > On __tcp_retransmit_skb kretprobe:
> >
> > ==> Hit TFO case ret:-16 ca_state:0 skb:ffff888fdb4bac00!
> >
> > First hit:
> > __tcp_retransmit_skb+1
> > tcp_rcv_state_process+2488
> > tcp_v6_do_rcv+405
> > tcp_v6_rcv+2984
> > ip6_protocol_deliver_rcu+180
> > ip6_input_finish+17
> >
> > Successful hit:
> > __tcp_retransmit_skb+1
> > tcp_retransmit_skb+18
> > tcp_retransmit_timer+716
> > tcp_write_timer_handler+136
> > tcp_write_timer+141
> > call_timer_fn+43
> >
> > skb:ffff888fdb4bac00 --- delay:51642us bytes_acked:1
>
>
> Humm maybe one of the conditions used in tcp_tsq_write() does not hold...
>
> if (tp->lost_out > tp->retrans_out &&
> tp->snd_cwnd > tcp_packets_in_flight(tp)) {
> tcp_mstamp_refresh(tp);
> tcp_xmit_retransmit_queue(sk);
> }
>
> Maybe FastOpen case is 'special' and tp->lost_out is wrong.
Something like this? (completely untested)
--
Jonathan
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 69a545db80d2..92bc9b0f4955 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5995,8 +5995,10 @@ static bool tcp_rcv_fastopen_synack(struct sock *sk,
struct sk_buff *synack,
else
tp->fastopen_client_fail = TFO_DATA_NOT_ACKED;
skb_rbtree_walk_from(data) {
+ tcp_mark_skb_lost(sk, data);
if (__tcp_retransmit_skb(sk, data, 1))
break;
+ tp->retrans_out += tcp_skb_pcount(data);
}
tcp_rearm_rto(sk);
NET_INC_STATS(sock_net(sk),
