Subject: Re: [TEST] conntrack_reverse_clash.sh flakes

From: Florian Westphal <[email-masked]>
Date: Mon, 8 Dec 2025 15:48:18 +0100

Jakub Kicinski <[email-masked]> wrote:
> We have a new faster NIPA setup, and now on non-debug builds we see 
> a few (4 a week to be exact) flakes in conntrack_reverse_clash.sh
> 
> List of flakes from the last 100 runs:
> https://netdev.bots.linux.dev/contest.html?pass=0&test=conntrack-reverse-clash-sh
> 
> Example:
> 
> # selftests: net/netfilter: conntrack_reverse_clash.sh
> # Port number changed, wanted 56789 got 5950
> # ERROR: SNAT performed without any matching snat rule
> # kill: sending signal to 16051 failed: No such process
> not ok 1 selftests: net/netfilter: conntrack_reverse_clash.sh # exit=1
> 
> Looks like the test also occasionally flaked on the old setup ("remote"
> column with "metal" instead of "virt") which is now shut down:
> 
> # selftests: net/netfilter: conntrack_reverse_clash.sh
> # Port number changed, wanted 56789 got 54630
> # Port number changed, wanted 56790 got 25814
> # ERROR: SNAT performed without any matching snat rule
> not ok 1 selftests: net/netfilter: conntrack_reverse_clash.sh # exit=1
> 
> so this isn't new, just more likely now..
> 
> Could you TAL when you have spare cycles? (BTW the new setup is owned 
> by netdev foundation so I can give you access if that helps).

No need, I can reproduce this:
# selftests: conntrack_reverse_clash.sh
# Port number changed, wanted 56790 got 64562 from 127.0.0.12
# ERROR: SNAT performed without any matching snat rule
# udp      17 30 src=127.0.0.11 dst=127.0.0.12 sport=56789 dport=56790 [UNREPLIED] src=127.0.0.12 dst=127.0.0.11 sport=56790 dport=56789 mark=0 use=1
# conntrack v1.4.8 (conntrack-tools): 1 flow entries have been shown.
# cpu=0         found=0 invalid=0 insert=0 insert_failed=0 drop=0 early_drop=0 error=0 search_restart=0 clash_resolve=0 chaintoolong=0
...

Looks like an actual bug to me, will need some time to investigate this.
If its too annoying consider disabling this particular test for now.

Thanks for reporting.