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Correctly set up the initial TCP congestion window in all cases,

Browse source 
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.

PR:		235256
Reviewed by:	tuexen (mentor), rgrimes (mentor)
Approved by:	tuexen (mentor), rgrimes (mentor)
MFC after:	3 weeks
Sponsored by:	NetApp, Inc.
Differential Revision:	https://reviews.freebsd.org/D19000
This commit is contained in:
Richard Scheffenegger 2020-04-29 21:48:52 +00:00
parent b155807e48
commit b2ade6b166
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=360477
3 changed files with 31 additions and 18 deletions
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24
sys/netinet/tcp_input.c
View file

@ -1470,7 +1470,7 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
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;
@ -2374,12 +2374,6 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
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);
@ -2399,6 +2393,13 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
cc_conn_init(tp);
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.
@ -2693,6 +2694,15 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
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__,

12
sys/netinet/tcp_stacks/bbr.c
View file

@ -9326,11 +9326,6 @@ bbr_do_syn_recv(struct mbuf *m, struct tcphdr *th, struct socket *so,
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++;
}
/*
* Make transitions: SYN-RECEIVED -> ESTABLISHED SYN-RECEIVED* ->
@ -9353,6 +9348,13 @@ bbr_do_syn_recv(struct mbuf *m, struct tcphdr *th, struct socket *so,
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.

13
sys/netinet/tcp_stacks/rack.c
View file

@ -6540,12 +6540,6 @@ rack_do_syn_recv(struct mbuf *m, struct tcphdr *th, struct socket *so,
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);
@ -6563,6 +6557,13 @@ rack_do_syn_recv(struct mbuf *m, struct tcphdr *th, struct socket *so,
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.