linux-kernel - Re: selftests: net: udpgso_bench.sh: RIP: 0010:lookup

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Message-ID: <CA+G9fYtzjP_EOjDFZYwTMjv5f3AK2pA_E6mk_mU5FQcZgo_qXQ@mail.gmail.com>
Date:   Sat, 27 May 2023 23:32:23 +0530
From:   Naresh Kamboju <naresh.kamboju@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Kuniyuki Iwashima <kuniyu@...zon.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        Dan Carpenter <dan.carpenter@...aro.org>,
        "David S . Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, lkft-triage@...ts.linaro.org,
        Xin Long <lucien.xin@...il.com>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Netdev <netdev@...r.kernel.org>, stable@...r.kernel.org,
        willemdebruijn.kernel@...il.com
Subject: Re: selftests: net: udpgso_bench.sh: RIP: 0010:lookup_reuseport

Hi Arnd,

On Sat, 27 May 2023 at 15:03, Arnd Bergmann <arnd@...db.de> wrote:
>
> On Sat, May 27, 2023, at 05:49, Kuniyuki Iwashima wrote:
> > From: Jakub Kicinski <kuba@...nel.org>
> > Date: Fri, 26 May 2023 20:16:07 -0700
> >> On Wed, 24 May 2023 13:24:15 +0530 Naresh Kamboju wrote:
> >> > While running selftests: net: udpgso_bench.sh on qemu-x86_64 the following
> >> > kernel crash noticed on stable rc 6.3.4-rc2 kernel.
> >>
> >> Can you repro this or it's just a one-off?
> >>
> >> Adding some experts to CC.
> >
> > FWIW, I couldn't reproduce it on my x86_64 QEMU setup & 6.4.0-rc3
> > at least 5 times, so maybe one-off ?
>
> This looks like one of several spurious reports that lkft has produced
> recently, where an 'int3' trap instruction is executed in a function
> that is live-patched, but at a point where the int3 is not expected.
>
> Anders managed to get a reproducer for one of these on his manchine
> yesterday, and has narrowed it down to failing on qemu-7.2.2 but
> not failing on qemu-8.0.

This is an added advantage to tests on multiple qemu versions
and comparing the difference in test results.
Thanks, Anders.

>
> The current theory right now is that this is a qemu bug when
> dealing with self-modifying x86 code that has been fixed in
> qemu-8.0 already, and my suggestion would be to ignore all bugs
> found by lkft that involve an 'int3' trap, and instead change
> the lkft setup to use either qemu-8.0 or run the test systems
> in kvm (which would also be much faster and save resources).

 I will send out an update to ignore the 'int3' trap email reports.

>
> Someone still needs to get to the bottom of this bug to see
> if it's in qemu or in the kernel livepatching code, but I'm
> sure it has nothing to do with the ipv6 stack.

Thank you Arnd.

- Naresh

>       Arnd