netdev - Re: [PATCH net-next 0/8] tcp: receiver changes

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Message-ID: <CAAVpQUBt7SWEz0gtZD2NkjRvHj6qmYij=mcW0G3+Qxgg53zv4A@mail.gmail.com>
Date: Tue, 15 Jul 2025 07:48:18 -0700
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Paolo Abeni <pabeni@...hat.com>, Neal Cardwell <ncardwell@...gle.com>, 
	Matthieu Baerts <matttbe@...nel.org>, Eric Dumazet <edumazet@...gle.com>, 
	Simon Horman <horms@...nel.org>, Willem de Bruijn <willemb@...gle.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next 0/8] tcp: receiver changes

On Tue, Jul 15, 2025 at 6:33 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Tue, 15 Jul 2025 06:28:29 -0700 Jakub Kicinski wrote:
> > # (null):17: error handling packet: timing error: expected outbound packet at 0.074144 sec but happened at -1752585909.757339 sec; tolerance 0.004000 sec
> > # script packet:  0.074144 S. 0:0(0) ack 1 <mss 1460,nop,wscale 0>
> > # actual packet: -1752585909.757339 S.0 0:0(0) ack 1 <mss 1460,nop,wscale 0>
>
> This is definitely compiler related, I rebuilt with clang and the build
> error goes away. Now I get a more sane failure:
>
> # tcp_rcv_big_endseq.pkt:41: error handling packet: timing error: expected outbound packet at 1.230105 sec but happened at 1.190101 sec; tolerance 0.005046 sec
> # script packet:  1.230105 . 1:1(0) ack 54001 win 0
> # actual packet:  1.190101 . 1:1(0) ack 54001 win 0
>
> $ gcc --version
> gcc (GCC) 15.1.1 20250521 (Red Hat 15.1.1-2)
>
> I don't understand why the ack is supposed to be delayed, should we
> just do this? (I think Eric is OOO, FWIW)
>
> diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcv_big_endseq.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcv_big_endseq.pkt
> index 7e170b94fd36..3848b419e68c 100644
> --- a/tools/testing/selftests/net/packetdrill/tcp_rcv_big_endseq.pkt
> +++ b/tools/testing/selftests/net/packetdrill/tcp_rcv_big_endseq.pkt
> @@ -38,7 +38,7 @@
>
>  // If queue is empty, accept a packet even if its end_seq is above wup + rcv_wnd
>    +0 < P. 4001:54001(50000) ack 1 win 257
> -  +.040 > .  1:1(0) ack 54001 win 0
> +  +0 > .  1:1(0) ack 54001 win 0
>
>  // Check LINUX_MIB_BEYOND_WINDOW has been incremented 3 times.
>  +0 `nstat | grep TcpExtBeyondWindow | grep -q " 3 "`

I remember I didn't see this error just after the commit that added the test,
and now I see the failure after commit 1d2fbaad7cd8c ("tcp: stronger
sk_rcvbuf checks").

[root@...ora packetdrill]# uname -r
6.16.0-rc5-01431-g75dff0584cce
[root@...ora packetdrill]# ./ksft_runner.sh tcp_rcv_big_endseq.pkt
TAP version 13
1..2
ok 1 ipv4
ok 2 ipv6
# Totals: pass:2 fail:0 xfail:0 xpass:0 skip:0 error:0

[root@...ora packetdrill]# uname -r
6.16.0-rc5-01432-g1d2fbaad7cd8
[root@...ora packetdrill]# ./ksft_runner.sh tcp_rcv_big_endseq.pkt
TAP version 13
1..2
tcp_rcv_big_endseq.pkt:41: error handling packet: timing error:
expected outbound packet at 1.148682 sec but happened at 1.108681 sec;
tolerance 0.005005 sec
script packet:  1.148682 . 1:1(0) ack 54001 win 0
actual packet:  1.108681 . 1:1(0) ack 54001 win 0
not ok 1 ipv4
tcp_rcv_big_endseq.pkt:41: error handling packet: timing error:
expected outbound packet at 1.146130 sec but happened at 1.106130 sec;
tolerance 0.005005 sec
script packet:  1.146130 . 1:1(0) ack 54001 win 0
actual packet:  1.106130 . 1:1(0) ack 54001 win 0
not ok 2 ipv6
# Totals: pass:0 fail:2 xfail:0 xpass:0 skip:0 error:0


On 75dff0584cce, the test failed if I removed the delay.
I haven't checked where it comes from, but probably that's
why Eric added the delay ?

[root@...ora packetdrill]# ./ksft_runner.sh tcp_rcv_big_endseq.pkt
TAP version 13
1..2
tcp_rcv_big_endseq.pkt:41: error handling packet: timing error:
expected outbound packet at 1.105941 sec but happened at 1.146774 sec;
tolerance 0.004000 sec
script packet:  1.105941 . 1:1(0) ack 54001 win 0
actual packet:  1.146774 . 1:1(0) ack 54001 win 0
not ok 1 ipv4
tcp_rcv_big_endseq.pkt:41: error handling packet: timing error:
expected outbound packet at 1.106215 sec but happened at 1.146815 sec;
tolerance 0.004000 sec
script packet:  1.106215 . 1:1(0) ack 54001 win 0
actual packet:  1.146815 . 1:1(0) ack 54001 win 0

not ok 2 ipv6
# Totals: pass:0 fail:2 xfail:0 xpass:0 skip:0 error:0