linux-kernel - Re: [PATCH 6.1 00/42] 6.1.15-rc1 review

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Date:   Fri, 3 Mar 2023 14:35:40 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Naresh Kamboju <naresh.kamboju@...aro.org>, stable@...r.kernel.org,
        patches@...ts.linux.dev, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
        linux@...ck-us.net, shuah@...nel.org, patches@...nelci.org,
        lkft-triage@...ts.linaro.org, pavel@...x.de, jonathanh@...dia.com,
        f.fainelli@...il.com, sudipm.mukherjee@...il.com,
        srw@...dewatkins.net, rwarsow@....de, mptcp@...ts.linux.dev,
        Florian Westphal <fw@...len.de>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Matthieu Baerts <matthieu.baerts@...sares.net>,
        Anders Roxell <anders.roxell@...aro.org>
Subject: Re: [PATCH 6.1 00/42] 6.1.15-rc1 review

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