linux-kernel - Re: [PATCH v2 3/4] selftests: net: udpgso_bench: Fix racing bug between the rx/tx programs

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Date:   Tue, 31 Jan 2023 08:33:23 -0500
From:   Willem de Bruijn <willemb@...gle.com>
To:     Andrei Gherzan <andrei.gherzan@...onical.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Shuah Khan <shuah@...nel.org>,
        netdev@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] selftests: net: udpgso_bench: Fix racing bug
 between the rx/tx programs

On Tue, Jan 31, 2023 at 8:06 AM Andrei Gherzan
<andrei.gherzan@...onical.com> wrote:
>
> "udpgro_bench.sh" invokes udpgso_bench_rx/udpgso_bench_tx programs
> subsequently and while doing so, there is a chance that the rx one is not
> ready to accept socket connections. This racing bug could fail the test
> with at least one of the following:
>
> ./udpgso_bench_tx: connect: Connection refused
> ./udpgso_bench_tx: sendmsg: Connection refused
> ./udpgso_bench_tx: write: Connection refused
>
> This change addresses this by making udpgro_bench.sh wait for the rx
> program to be ready before firing off the tx one - with an exponential back
> off algorithm from 1s to 10s.
>
> Signed-off-by: Andrei Gherzan <andrei.gherzan@...onical.com>

please CC: reviewers of previous revisions on new revisions

also for upcoming patches: please clearly mark net or net-next.
> ---
>  tools/testing/selftests/net/udpgso_bench.sh | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/tools/testing/selftests/net/udpgso_bench.sh b/tools/testing/selftests/net/udpgso_bench.sh
> index dc932fd65363..20b5db8fcbde 100755
> --- a/tools/testing/selftests/net/udpgso_bench.sh
> +++ b/tools/testing/selftests/net/udpgso_bench.sh
> @@ -7,6 +7,7 @@ readonly GREEN='\033[0;92m'
>  readonly YELLOW='\033[0;33m'
>  readonly RED='\033[0;31m'
>  readonly NC='\033[0m' # No Color
> +readonly TESTPORT=8000 # Keep this in sync with udpgso_bench_rx/tx

then also pass explicit -p argument to the processes to keep all three
consistent

>
>  readonly KSFT_PASS=0
>  readonly KSFT_FAIL=1
> @@ -56,10 +57,27 @@ trap wake_children EXIT
>
>  run_one() {
>         local -r args=$@
> +       local -r init_delay_s=1
> +       local -r max_delay_s=10
> +       local delay_s=0
> +       local nr_socks=0
>
>         ./udpgso_bench_rx &
>         ./udpgso_bench_rx -t &
>
> +       # Wait for the above test program to get ready to receive connections.
> +       delay_s="${init_delay_s}"
> +       while [ "$delay_s" -lt "$max_delay_s" ]; do
> +               nr_socks="$(ss -lnHi | grep -c "\*:${TESTPORT}")"
> +               [ "$nr_socks" -eq 2 ] && break
> +               sleep "$delay_s"
> +               delay="$((delay*2))"

I don't think we need exponential back-off for something this simple

> +       done
> +       if [ "$nr_socks" -ne 2 ]; then
> +               echo "timed out while waiting for udpgso_bench_rx"
> +               exit 1
> +       fi
> +
>         ./udpgso_bench_tx ${args}
>  }
>
> --
> 2.34.1
>