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 15:45:04 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Willem de Bruijn <willemb@...gle.com>,
        Andrei Gherzan <andrei.gherzan@...onical.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        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, 2023-01-31 at 08:33 -0500, Willem de Bruijn wrote:
> 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

Agreed. Additionally you could use constant, sub-second delay (say 0.1)
to keep the runtime delta relatively low.

Cheers,

Paolo