linux-kernel - Re: [PATCH net-next 0/7] net/selftests: TCP-AO selftests updates

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Message-ID: <8c2835ed-9066-4adb-8f8b-f38416d97849@redhat.com>
Date: Tue, 30 Jul 2024 12:51:40 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: 0x7f454c46@...il.com, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Shuah Khan <shuah@...nel.org>
Cc: Mohammad Nassiri <mnassiri@...na.com>, netdev@...r.kernel.org,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 0/7] net/selftests: TCP-AO selftests updates

On 7/30/24 04:12, Dmitry Safonov wrote:
> First 4 patches are more-or-less cleanups/preparations.
> 
> Patch 5 was sent to me/contributed off-list by Mohammad, who wants 32-bit
> kernels to run TCP-AO.
> 
> Patch 6 is a workaround/fix for slow VMs. Albeit, I can't reproduce
> the issue, but I hope it will fix netdev flakes for connect-deny-*
> tests.
> 
> And the biggest change is adding TCP-AO tracepoints to selftests.
> I think it's a good addition by the following reasons:
> - The related tracepoints are now tested;
> - It allows tcp-ao selftests to raise expectations on the kernel
>    behavior - up from the syscalls exit statuses + net counters.
> - Provides tracepoints usage samples.
> 
> As tracepoints are not a stable ABI, any kernel changes done to them
> will be reflected to the selftests, which also will allow users
> to see how to change their code. It's quite better than parsing dmesg
> (what BGP was doing pre-tracepoints, ugh).
> 
> Somewhat arguably, the code parses trace_pipe, rather than uses
> libtraceevent (which any sane user should do). The reason behind that is
> the same as for rt-netlink macros instead of libmnl: I'm trying
> to minimize the library dependencies of the selftests. And the
> performance of formatting text in kernel and parsing it again in a test
> is not critical.
> 
> Current output sample:
>> ok 73 Trace events matched expectations: 13 tcp_hash_md5_required[2] tcp_hash_md5_unexpected[4] tcp_hash_ao_required[3] tcp_ao_key_not_found[4]
> 
> Previously, tracepoints selftests were part of kernel tcp tracepoints
> submission [1], but since then the code was quite changed:
> - Now generic tracing setup is in lib/ftrace.c, separate from
>    lib/ftrace-tcp.c which utilizes TCP trace points. This separation
>    allows future selftests to trace non-TCP events, i.e. to find out
>    an skb's drop reason, which was useful in the creation of TCP-CLOSE
>    stress-test (not in this patch set, but used in attempt to reproduce
>    the issue from [2]).
> - Another change is that in the previous submission the trace events
>    where used only to detect unexpected TCP-AO/TCP-MD5 events. In this
>    version the selftests will fail if an expected trace event didn't
>    appear.
>    Let's see how reliable this is on the netdev bot - it obviously passes
>    on my testing, but potentially may require a temporary XFAIL patch
>    if it misbehaves on a slow VM.

It looks like this is not well digested by the CI, e.g.:

https://netdev.bots.linux.dev/flakes.html?tn-needle=tcp-ao

https://netdev-3.bots.linux.dev/vmksft-tcp-ao-dbg/results/705502/8-restore-ipv4/stdout

BTW wearing for a moment Cato the censor's shoes, I note that patch 1 && 
2 commit messages are quite more informal and less informative than the 
average;)

Thanks,

Paolo