Date:   Fri, 3 Mar 2023 14:35:40 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Paolo Abeni <pabeni@redhat.com>
Cc:     Naresh Kamboju <naresh.kamboju@linaro.org>, 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>,
        Matthieu Baerts <matthieu.baerts@tessares.net>,
        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 01:41:00PM +0100, Paolo Abeni wrote:
> On Fri, 2023-03-03 at 12:44 +0100, Greg Kroah-Hartman wrote:
> > On Fri, Mar 03, 2023 at 12:39:07PM +0100, Paolo Abeni wrote:
> > > Additionally, some self-tests check for known bugs/regressions. Running
> > > them on older kernel will cause real trouble, and checking for bug
> > > presence in the running kernel would be problematic at best, I think.
> > 
> > No, not at all, why wouldn't you want to test for know bugs and
> > regressions and fail?  That's a great thing to do, and so you will know
> > to backport those bugfixes to those older kernels if you have to use
> > them.
> 
> I'm sorry, I likely was not clear at all. What I mean is that the self-
> test for a bug may trigger e.g. memory corruption on the bugged kernel
> (or more specifically to networking, the infamous, recurring
> "unregister_netdevice: waiting for ...") which in turn could cause
> random failures later.
> 
> If that specific case runs on older (unpatched) kernel will screw the
> overall tests results. The same could happen in less-detectable way for
> old bugs non explicitly checked by any test, but still triggered by the
> test-suite. As a consequence I expect that the results observed running
> newer self-tests on older kernel are unreliable. 

For the stable/LTS kernel trees, they should _never_ be unreliable,
otherwise that means we have missed a needed fix and so we need to
resolve that.

Which is why I always recommend running the latest selftests on all
older kernels, and have for a very long time now.

thanks,

greg k-h