From: Jakub Kicinski <kuba@kernel.org>
To: "Ricardo B. Marlière (SUSE)" <ricardo@marliere.net>
Cc: "David S. Miller" <davem@davemloft.net>,
"Eric Dumazet" <edumazet@google.com>,
"Paolo Abeni" <pabeni@redhat.com>,
"Simon Horman" <horms@kernel.org>,
"Shuah Khan" <shuah@kernel.org>,
"David Ahern" <dsahern@kernel.org>,
"Toke Høiland-Jørgensen" <toke@redhat.com>,
netdev@vger.kernel.org, linux-kselftest@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net v2] selftests/net: Fix icmp.sh race between ping and tcpdump startup
Date: Fri, 11 Sep 2026 17:40:45 -0700 [thread overview]
Message-ID: <20260911174045.76579e91@kernel.org> (raw)
In-Reply-To: <20260911-selftests-net-icmp_race-v2-1-c7458dec9d0b@marliere.net>
On Fri, 11 Sep 2026 15:41:33 -0300 Ricardo B. Marlière (SUSE) wrote:
> icmp.sh backgrounds ping and then starts tcpdump, with no synchronization
> between the two. If tcpdump is not capturing yet by the time the ICMP
> unreachable replies come back, the test fails even though the kernel
> behaved correctly:
>
> FAIL - got ICMP response from , should be 192.0.0.8
>
> The empty address is misleading: it means the capture matched nothing
> before its 10s timeout, not that the reply had a wrong source address.
> NS1's Icmp InDestUnreachs counter still increments across such a failure,
> so the replies were generated and did reach NS1. Ping sends several probes
> over its 3s deadline, so losing every one of them takes a multi-second
> stall in tcpdump startup, which does happen on loaded CI hosts [1].
>
> Fix it by starting tcpdump first and waiting for its "listening" banner
> via slowwait() before sending traffic. Run ping synchronously, then kill
> and reap tcpdump if it did not already exit on -c 1.
It used to pass in NIPA CI and now it fails:
https://netdev-ctrl.bots.linux.dev/logs/vmksft/net-dbg/results/819341/86-icmp-sh/stdout
> Fixes: 7e9838b7915e ("selftests/net: Add icmp.sh for testing ICMP dummy address responses")
Please don't add Fixes tags to selftest improvements.
> Link: https://openqa.opensuse.org/tests/5907626/logfile?filename=icmp_sh.tap.txt#line-2 [1]
> Signed-off-by: Ricardo B. Marlière (SUSE) <ricardo@marliere.net>
next prev parent reply other threads:[~2026-09-12 0:40 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-11 18:41 Ricardo B. Marlière (SUSE)
2026-09-12 0:40 ` Jakub Kicinski [this message]
2026-09-12 17:41 ` Ricardo B. Marlière (SUSE)
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