Re: [PATCH v4 7/7] selftests: prctl: introduce tests for disabling THPs except for madvise

[Mark Brown <broonie@kernel.org>]

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On Thu, Aug 14, 2025 at 11:49:15AM +0100, Lorenzo Stoakes wrote:
> On Thu, Aug 14, 2025 at 11:32:55AM +0200, David Hildenbrand wrote:
> > On 13.08.25 20:52, Lorenzo Stoakes wrote:

> > > I can't see anything in the kernel to #ifdef it out so I suppose you mean
> > > running these tests on an older kernel?

...

> > > But this is an unsupported way of running self-tests, they are tied to the
> > > kernel version in which they reside, and test that specific version.

> > > Unless I'm missing something here?

> > I remember we allow for a bit of flexibility when it is simple to handle.

> > Is that documented somewhere?

> Not sure if it's documented, but it'd make testing extremely egregious if
> you had to consider all of the possible kernels and interactions and etc.

> I think it's 'if it happens to work then fine' but otherwise it is expected
> that the tests match the kernel.

> It's also very neat that with a revision you get a set of (hopefully)
> working tests for that revision :)

Some people do try to run the selftests with older kernels, they're
trying to get better coverage for the stables.  For a lot of areas the
skipping falls out natually since there's some optionality (so even with
the same kernel version you might not have the feature in the running
kernel) or it's a new API which has a discovery mechanism in the ABI
anyway.  OTOH some areas have been actively hostile to the idea of
running on older kernels so there are things that do break when you try.
TBH so long as the tests don't crash the system or something people are
probably just going to ignore any tests that have never passed.

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