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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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