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Message-ID: <20231207181342.525181-1-edumazet@google.com>
Date: Thu, 7 Dec 2023 18:13:42 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>
Cc: David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org, eric.dumazet@...il.com,
Eric Dumazet <edumazet@...gle.com>, Neal Cardwell <ncardwell@...gle.com>,
David Morley <morleyd@...gle.com>
Subject: [PATCH net] tcp: fix tcp_disordered_ack() vs usec TS resolution
After commit 939463016b7a ("tcp: change data receiver flowlabel after one dup")
we noticed an increase of TCPACKSkippedPAWS events.
Neal Cardwell tracked the issue to tcp_disordered_ack() assumption
about remote peer TS clock.
RFC 1323 & 7323 are suggesting the following:
"timestamp clock frequency in the range 1 ms to 1 sec per tick
between 1ms and 1sec."
This has to be adjusted for 1 MHz clock frequency.
This hints at reorders of SACK packets on send side,
this might deserve a future patch.
(skb->ooo_okay is always set for pure ACK packets)
Fixes: 614e8316aa4c ("tcp: add support for usec resolution in TCP TS values")
Co-developed-by: Neal Cardwell <ncardwell@...gle.com>
Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: David Morley <morleyd@...gle.com>
---
net/ipv4/tcp_input.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 90de838a274519110ce0ac84552c4caedb826eb7..701cb87043f28079286044208128c2d687908991 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4368,6 +4368,23 @@ EXPORT_SYMBOL(tcp_do_parse_auth_options);
* up to bandwidth of 18Gigabit/sec. 8) ]
*/
+/* Estimates max number of increments of remote peer TSval in
+ * a replay window (based on our current RTO estimation).
+ */
+static u32 tcp_tsval_replay(const struct sock *sk)
+{
+ /* If we use usec TS resolution,
+ * then expect the remote peer to use the same resolution.
+ */
+ if (tcp_sk(sk)->tcp_usec_ts)
+ return inet_csk(sk)->icsk_rto * (USEC_PER_SEC / HZ);
+
+ /* RFC 7323 recommends a TSval clock between 1ms and 1sec.
+ * We know that some OS (including old linux) can use 1200 Hz.
+ */
+ return inet_csk(sk)->icsk_rto * 1200 / HZ;
+}
+
static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
{
const struct tcp_sock *tp = tcp_sk(sk);
@@ -4375,7 +4392,7 @@ static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
u32 seq = TCP_SKB_CB(skb)->seq;
u32 ack = TCP_SKB_CB(skb)->ack_seq;
- return (/* 1. Pure ACK with correct sequence number. */
+ return /* 1. Pure ACK with correct sequence number. */
(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
/* 2. ... and duplicate ACK. */
@@ -4385,7 +4402,8 @@ static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
/* 4. ... and sits in replay window. */
- (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
+ (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <=
+ tcp_tsval_replay(sk);
}
static inline bool tcp_paws_discard(const struct sock *sk,
--
2.43.0.472.g3155946c3a-goog
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