> Author: rscheff
> Date: Thu May 21 19:46:11 2020
> New Revision: 361342
> URL: https://svnweb.freebsd.org/changeset/base/361342
>
> Log:
Partial merge of r360477:
> MFC r360477: Correctly set up the initial TCP congestion window in all cases
>
> by not including the SYN bit sequence space in cwnd related calculations.
> Snd_und is adjusted explicitly in all cases, outside the cwnd update,
> instead.
>
> This fixes an off-by-one conformance issue with regular TCP sessions
> not using Appropriate Byte Counting (RFC3465), sending one more
> packet during the initial window than expected.
There should of been a note here:
This does NOT contain the merge of the change to bbrv1 since at this
time that code does not exist in stable/12, and there is no plan to
merge that code to stable/12.
>
> PR: 235256
> Reviewed by: tuexen (mentor), rgrimes (mentor, blanket)
> Approved by: tuexen (mentor), rgrimes (mentor, blanket)
> MFC after: 3 weeks
> Sponsored by: NetApp, Inc.
> Differential Revision: https://reviews.freebsd.org/D19000
>
> Modified:
> stable/12/sys/netinet/tcp_input.c
> stable/12/sys/netinet/tcp_stacks/rack.c
> Directory Properties:
> stable/12/ (props changed)
>
> Modified: stable/12/sys/netinet/tcp_input.c
> ==============================================================================
> --- stable/12/sys/netinet/tcp_input.c Thu May 21 19:45:14 2020
> (r361341)
> +++ stable/12/sys/netinet/tcp_input.c Thu May 21 19:46:11 2020
> (r361342)
> @@ -1519,7 +1519,7 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru
> struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos)
> {
> int thflags, acked, ourfinisacked, needoutput = 0, sack_changed;
> - int rstreason, todrop, win;
> + int rstreason, todrop, win, incforsyn = 0;
> uint32_t tiwin;
> uint16_t nsegs;
> char *s;
> @@ -2432,12 +2432,6 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru
> if (IS_FASTOPEN(tp->t_flags) && tp->t_tfo_pending) {
> tcp_fastopen_decrement_counter(tp->t_tfo_pending);
> tp->t_tfo_pending = NULL;
> -
> - /*
> - * Account for the ACK of our SYN prior to
> - * regular ACK processing below.
> - */
> - tp->snd_una++;
> }
> if (tp->t_flags & TF_NEEDFIN) {
> tcp_state_change(tp, TCPS_FIN_WAIT_1);
> @@ -2458,6 +2452,13 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru
> tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
> }
> /*
> + * Account for the ACK of our SYN prior to
> + * regular ACK processing below, except for
> + * simultaneous SYN, which is handled later.
> + */
> + if (SEQ_GT(th->th_ack, tp->snd_una) && !(tp->t_flags &
> TF_NEEDSYN))
> + incforsyn = 1;
> + /*
> * If segment contains data or ACK, will call tcp_reass()
> * later; if not, do so now to pass queued data to user.
> */
> @@ -2751,6 +2752,15 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru
> process_ACK:
> INP_WLOCK_ASSERT(tp->t_inpcb);
>
> + /*
> + * Adjust for the SYN bit in sequence space,
> + * but don't account for it in cwnd calculations.
> + * This is for the SYN_RECEIVED, non-simultaneous
> + * SYN case. SYN_SENT and simultaneous SYN are
> + * treated elsewhere.
> + */
> + if (incforsyn)
> + tp->snd_una++;
> acked = BYTES_THIS_ACK(tp, th);
> KASSERT(acked >= 0, ("%s: acked unexepectedly negative "
> "(tp->snd_una=%u, th->th_ack=%u, tp=%p, m=%p)", __func__,
>
> Modified: stable/12/sys/netinet/tcp_stacks/rack.c
> ==============================================================================
> --- stable/12/sys/netinet/tcp_stacks/rack.c Thu May 21 19:45:14 2020
> (r361341)
> +++ stable/12/sys/netinet/tcp_stacks/rack.c Thu May 21 19:46:11 2020
> (r361342)
> @@ -5580,12 +5580,6 @@ rack_do_syn_recv(struct mbuf *m, struct tcphdr *th, st
> if (IS_FASTOPEN(tp->t_flags) && tp->t_tfo_pending) {
> tcp_fastopen_decrement_counter(tp->t_tfo_pending);
> tp->t_tfo_pending = NULL;
> -
> - /*
> - * Account for the ACK of our SYN prior to
> - * regular ACK processing below.
> - */
> - tp->snd_una++;
> }
> if (tp->t_flags & TF_NEEDFIN) {
> tcp_state_change(tp, TCPS_FIN_WAIT_1);
> @@ -5603,6 +5597,13 @@ rack_do_syn_recv(struct mbuf *m, struct tcphdr *th, st
> if (!IS_FASTOPEN(tp->t_flags))
> cc_conn_init(tp);
> }
> + /*
> + * Account for the ACK of our SYN prior to
> + * regular ACK processing below, except for
> + * simultaneous SYN, which is handled later.
> + */
> + if (SEQ_GT(th->th_ack, tp->snd_una) && !(tp->t_flags & TF_NEEDSYN))
> + tp->snd_una++;
> /*
> * If segment contains data or ACK, will call tcp_reass() later; if
> * not, do so now to pass queued data to user.
>
--
Rod Grimes rgri...@freebsd.org
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