Re: selftests: net: RIP: 0010:lookup_reuseport

From: Naresh Kamboju
Date: Sat May 27 2023 - 14:02:43 EST

Hi Arnd,

On Sat, 27 May 2023 at 15:03, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Sat, May 27, 2023, at 05:49, Kuniyuki Iwashima wrote:
> > From: Jakub Kicinski <kuba@xxxxxxxxxx>
> > 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: 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