git: 440f4ba18e3a - main - tcp: fix duplicate retransmissions when RTO happens during SACK loss recovery
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Date: Fri, 11 Oct 2024 11:56:44 UTC
The branch main has been updated by rscheff:
URL: https://cgit.FreeBSD.org/src/commit/?id=440f4ba18e3ab7be912858bbcb96a419fcf14809
commit 440f4ba18e3ab7be912858bbcb96a419fcf14809
Author: Richard Scheffenegger <rscheff@FreeBSD.org>
AuthorDate: 2024-10-10 10:50:22 +0000
Commit: Richard Scheffenegger <rscheff@FreeBSD.org>
CommitDate: 2024-10-10 11:02:47 +0000
tcp: fix duplicate retransmissions when RTO happens during SACK loss recovery
When snd_nxt doesn't track snd_max, partial SACK ACKs may elicit
unexpected duplicate retransmissions. This is usually masked by
LRO not necessarily ACKing every individual segment, and prior
to RFC6675 SACK loss recovery, harder to trigger even when an
RTO happens while SACK loss recovery is ongoing.
Address this by improving the logic when to start a SACK loss recovery
and how to deal with a RTO, as well as improvements to the adjusted
congestion window during transmission selection.
Reviewed By: tuexen, cc, #transport
Sponsored by: NetApp, Inc.
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D43355
---
sys/netinet/tcp_input.c | 18 ++++++++++--------
sys/netinet/tcp_output.c | 25 ++++++++++++++++---------
sys/netinet/tcp_sack.c | 22 ++++++++++++++--------
sys/netinet/tcp_var.h | 2 +-
4 files changed, 41 insertions(+), 26 deletions(-)
diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
index b64a71837ab4..5d14664f3fc0 100644
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -444,10 +444,7 @@ cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
case CC_RTO:
tp->t_dupacks = 0;
tp->t_bytes_acked = 0;
- if ((tp->t_rxtshift > 1) ||
- !((tp->t_flags & TF_SACK_PERMIT) &&
- (!TAILQ_EMPTY(&tp->snd_holes))))
- EXIT_RECOVERY(tp->t_flags);
+ EXIT_RECOVERY(tp->t_flags);
if (tp->t_flags2 & TF2_ECN_PERMIT)
tp->t_flags2 |= TF2_ECN_SND_CWR;
break;
@@ -2747,7 +2744,6 @@ enter_recovery:
}
if (tcp_is_sack_recovery(tp, &to)) {
TCPSTAT_INC(tcps_sack_recovery_episode);
- tp->snd_recover = tp->snd_nxt;
tp->snd_cwnd = maxseg;
(void) tcp_output(tp);
if (SEQ_GT(th->th_ack, tp->snd_una)) {
@@ -2790,8 +2786,12 @@ enter_recovery:
__func__));
if (tp->t_dupacks == 1)
tp->snd_limited = 0;
- tp->snd_cwnd =
- (tp->snd_nxt - tp->snd_una) +
+ if ((tp->snd_nxt == tp->snd_max) &&
+ (tp->t_rxtshift == 0))
+ tp->snd_cwnd =
+ SEQ_SUB(tp->snd_nxt,
+ tp->snd_una);
+ tp->snd_cwnd +=
(tp->t_dupacks - tp->snd_limited) *
maxseg;
/*
@@ -2840,7 +2840,9 @@ enter_recovery:
* counted as dupacks here.
*/
if (tcp_is_sack_recovery(tp, &to) &&
- (sack_changed != SACK_NOCHANGE)) {
+ (((tp->t_rxtshift == 0) && (sack_changed != SACK_NOCHANGE)) ||
+ ((tp->t_rxtshift > 0) && (sack_changed == SACK_NEWLOSS))) &&
+ (tp->snd_nxt == tp->snd_max)) {
tp->t_dupacks++;
/* limit overhead by setting maxseg last */
if (!IN_FASTRECOVERY(tp->t_flags) &&
diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
index 78ecfe5289b6..a048abf5f97a 100644
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -259,6 +259,7 @@ tcp_default_output(struct tcpcb *tp)
}
}
again:
+ sendwin = 0;
/*
* If we've recently taken a timeout, snd_max will be greater than
* snd_nxt. There may be SACK information that allows us to avoid
@@ -266,12 +267,12 @@ again:
*/
if ((tp->t_flags & TF_SACK_PERMIT) &&
SEQ_LT(tp->snd_nxt, tp->snd_max))
- tcp_sack_adjust(tp);
+ sendwin = tcp_sack_adjust(tp);
sendalot = 0;
tso = 0;
mtu = 0;
off = tp->snd_nxt - tp->snd_una;
- sendwin = min(tp->snd_wnd, tp->snd_cwnd);
+ sendwin = min(tp->snd_wnd, tp->snd_cwnd + sendwin);
flags = tcp_outflags[tp->t_state];
/*
@@ -288,7 +289,8 @@ again:
sack_bytes_rxmt = 0;
len = 0;
p = NULL;
- if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
+ if ((tp->t_flags & TF_SACK_PERMIT) &&
+ (IN_FASTRECOVERY(tp->t_flags) || SEQ_LT(tp->snd_nxt, tp->snd_max)) &&
(p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
uint32_t cwin;
@@ -387,7 +389,7 @@ after_sack_rexmit:
* in which case len is already set.
*/
if (sack_rxmit == 0) {
- if (sack_bytes_rxmt == 0) {
+ if ((sack_bytes_rxmt == 0) || SEQ_LT(tp->snd_nxt, tp->snd_max)) {
len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
off);
} else {
@@ -1636,11 +1638,16 @@ timer:
tp->snd_max = tp->snd_nxt + xlen;
}
if ((error == 0) &&
- (TCPS_HAVEESTABLISHED(tp->t_state) &&
- (tp->t_flags & TF_SACK_PERMIT) &&
- tp->rcv_numsacks > 0)) {
- /* Clean up any DSACK's sent */
- tcp_clean_dsack_blocks(tp);
+ (tp->rcv_numsacks > 0) &&
+ TCPS_HAVEESTABLISHED(tp->t_state) &&
+ (tp->t_flags & TF_SACK_PERMIT)) {
+ /* Clean up any DSACK's sent */
+ tcp_clean_dsack_blocks(tp);
+ }
+ if ((error == 0) &&
+ sack_rxmit &&
+ SEQ_LT(tp->snd_nxt, SEQ_MIN(p->rxmit, p->end))) {
+ tp->snd_nxt = SEQ_MIN(p->rxmit, p->end);
}
if (error) {
/*
diff --git a/sys/netinet/tcp_sack.c b/sys/netinet/tcp_sack.c
index 53a181703fe9..09e172ad4601 100644
--- a/sys/netinet/tcp_sack.c
+++ b/sys/netinet/tcp_sack.c
@@ -1006,7 +1006,7 @@ tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th, u_int *maxsegp)
highdata--;
highdata = SEQ_MIN(highdata, tp->snd_recover);
if (SEQ_LT(th->th_ack, highdata)) {
- tp->snd_fack = th->th_ack;
+ tp->snd_fack = SEQ_MAX(th->th_ack, tp->snd_fack);
if ((temp = tcp_sackhole_insert(tp, SEQ_MAX(th->th_ack,
highdata - maxseg), highdata, NULL)) != NULL) {
tp->sackhint.hole_bytes +=
@@ -1076,41 +1076,47 @@ tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
* After a timeout, the SACK list may be rebuilt. This SACK information
* should be used to avoid retransmitting SACKed data. This function
* traverses the SACK list to see if snd_nxt should be moved forward.
+ * In addition, cwnd will be inflated by the sacked bytes traversed when
+ * moving snd_nxt forward. This prevents a traffic burst after the final
+ * full ACK, and also keeps ACKs coming back.
*/
-void
+int
tcp_sack_adjust(struct tcpcb *tp)
{
+ int sacked = 0;
struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
INP_WLOCK_ASSERT(tptoinpcb(tp));
if (cur == NULL) {
/* No holes */
- return;
+ return (0);
}
if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack)) {
/* We're already beyond any SACKed blocks */
- return;
+ return (tp->sackhint.sacked_bytes);
}
- /*-
+ /*
* Two cases for which we want to advance snd_nxt:
* i) snd_nxt lies between end of one hole and beginning of another
* ii) snd_nxt lies between end of last hole and snd_fack
*/
while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
if (SEQ_LT(tp->snd_nxt, cur->end)) {
- return;
+ return (sacked);
}
+ sacked += p->start - cur->end;
if (SEQ_GEQ(tp->snd_nxt, p->start)) {
cur = p;
} else {
tp->snd_nxt = p->start;
- return;
+ return (sacked);
}
}
if (SEQ_LT(tp->snd_nxt, cur->end)) {
- return;
+ return (sacked);
}
tp->snd_nxt = tp->snd_fack;
+ return (tp->sackhint.sacked_bytes);
}
/*
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
index 8ff015b90f89..3fd6edccf365 100644
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -1508,7 +1508,7 @@ void tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_laststart,
tcp_seq rcv_lastend);
void tcp_clean_dsack_blocks(struct tcpcb *tp);
void tcp_clean_sackreport(struct tcpcb *tp);
-void tcp_sack_adjust(struct tcpcb *tp);
+int tcp_sack_adjust(struct tcpcb *tp);
struct sackhole *tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt);
void tcp_do_prr_ack(struct tcpcb *, struct tcphdr *, struct tcpopt *,
sackstatus_t, u_int *);