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

[Jakub Kicinski <kuba@kernel.org>]

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 "`