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

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Message-ID: <20250715063314.43a993f9@kernel.org>
Date: Tue, 15 Jul 2025 06:33:14 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Paolo Abeni <pabeni@...hat.com>, Neal Cardwell <ncardwell@...gle.com>
Cc: Matthieu Baerts <matttbe@...nel.org>, Eric Dumazet
 <edumazet@...gle.com>, Simon Horman <horms@...nel.org>, Kuniyuki Iwashima
 <kuniyu@...gle.com>, 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, 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 "`