Date:   Fri, 3 Mar 2023 11:26:42 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Matthieu Baerts <matthieu.baerts@tessares.net>
Cc:     Naresh Kamboju <naresh.kamboju@linaro.org>,
        Paolo Abeni <pabeni@redhat.com>, stable@vger.kernel.org,
        patches@lists.linux.dev, linux-kernel@vger.kernel.org,
        torvalds@linux-foundation.org, akpm@linux-foundation.org,
        linux@roeck-us.net, shuah@kernel.org, patches@kernelci.org,
        lkft-triage@lists.linaro.org, pavel@denx.de, jonathanh@nvidia.com,
        f.fainelli@gmail.com, sudipm.mukherjee@gmail.com,
        srw@sladewatkins.net, rwarsow@gmx.de, mptcp@lists.linux.dev,
        Florian Westphal <fw@strlen.de>,
        Mat Martineau <mathew.j.martineau@linux.intel.com>,
        Anders Roxell <anders.roxell@linaro.org>
Subject: Re: [PATCH 6.1 00/42] 6.1.15-rc1 review
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On Fri, Mar 03, 2023 at 10:47:33AM +0100, Matthieu Baerts wrote:
> Hi Greg, Naresh, Paolo,
> 
> Thank you for the new version and for having reported the issue and running MPTCP selftests!
> 
> 3 Mar 2023 10:23:06 Greg Kroah-Hartman <gregkh@linuxfoundation.org>:
> 
> > On Fri, Mar 03, 2023 at 02:34:05PM +0530, Naresh Kamboju wrote:
> >> On Fri, 3 Mar 2023 at 13:34, Paolo Abeni <pabeni@redhat.com> wrote:
> >>>
> >>> Hello,
> >>>
> >>> On Fri, 2023-03-03 at 01:32 +0530, Naresh Kamboju wrote:
> >>>> On Thu, 2 Mar 2023 at 16:30, Naresh Kamboju <naresh.kamboju@linaro.org> wrote:
> >>>>>
> >>>>> On Thu, 2 Mar 2023 at 16:00, Greg Kroah-Hartman
> >>>>> <gregkh@linuxfoundation.org> wrote:
> >>>>>> …
> >>>>>
> >>>>> ....
> >>>>>
> >>>>>> …
> >>>>>
> >>>>> Me either.
> >>>>> That is the reason I have shared "Assertion" above.
> >>>>>
> >>>>>> …
> >>>>>
> >>>>> We are running our bisection scripts.
> >>>>
> >>>> We have tested with 6.1.14 kselftests source again and it passes.
> >>>> Now that we have upgraded to 6.2.1 kselftests source, we find that
> >>>> there is this problem reported. so, not a kernel regression.
> >>>
> >>> I read the above as you are running self-tests from 6.2.1 on top of an
> >>> older (6.1) kernel. Is that correct?
> >>
> >> correct.
> >>
> >>> If so failures are expected;
> >
> > Shouldn't the test be able to know that "new features" are not present
> > and properly skip the test for when that happens?  Otherwise this feels
> > like a problem going forward as no one will know if this feature can be
> > used or not (assuming it is a new feature and not just a functional
> > change.)
> 
> All MPTCP selftests are designed to run on the same kernel version
> they are attached to. This allows us to do more checks knowing they
> are not supposed to fail on newer kernel versions and not being
> skipped if there is an error when trying to use the new feature. If
> there are fixes, we make sure the stable team is Cc'ed. If there are
> API changes, it would be visible because we would need to adapt
> existing selftests.

"Features" are not usually limited to specific kernel versions (think
about the mess that "enterprise" kernels create by backports).  And if
they are, running a userspace test should be able to detect if the
feature is present or not by the error returned to it, right?  If not,
then the feature is mis-designed.

> That's how we thought we should design MPTCP selftests. Maybe we need to change this design?

Yes, please "skip" tests for features that are just not present, do not
fail them.

> Is it a common practice to run selftests' latest version on older kernels?

Yes.

thanks,

greg k-h