linux-kernel - Re: [PATCH v3] selftests/mm: add process

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Message-ID: <e05e7e0d-02e3-435c-bb82-91200a868448@lucifer.local>
Date: Fri, 11 Jul 2025 09:49:14 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Mark Brown <broonie@...nel.org>
Cc: Zi Yan <ziy@...dia.com>, wang lian <lianux.mm@...il.com>,
        Liam.Howlett@...cle.com, akpm@...ux-foundation.org, brauner@...nel.org,
        david@...hat.com, gkwang@...x-info.com, jannh@...gle.com,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-mm@...ck.org, p1ucky0923@...il.com, ryncsn@...il.com,
        shuah@...nel.org, sj@...nel.org, vbabka@...e.cz,
        zijing.zhang@...ton.me
Subject: Re: [PATCH v3] selftests/mm: add process_madvise() tests

On Fri, Jul 11, 2025 at 09:34:38AM +0100, Mark Brown wrote:
> On Thu, Jul 10, 2025 at 12:28:13PM -0400, Zi Yan wrote:
> > On 10 Jul 2025, at 4:42, Mark Brown wrote:
> > > On Wed, Jul 09, 2025 at 10:46:07AM -0400, Zi Yan wrote:
>
> > >> Right. My /usr/include/sys does not have pidfd.h. IMHO selftests
> > >> should not rely on userspace headers, otherwise we cannot test
> > >> latest kernel changes.
>
> > > That's not realistic, we need to be able to use things like libc and for
> > > many areas you'd just end up copying or reimplmenenting the userspace
> > > libraries.  There's some concerns for sure, for example we used to have
>
> > Sure. For libraries like libc, it is unrealistic to not rely on it.
> > But for header files, are we expecting to install any kernel headers
> > to the running system to get selftests compiled? If we are testing
> > RC versions and header files might change before the actual release,
> > that would pollute the system header files, right?
>
> Right, for the kernel's headers there's two things - we use a
> combination of tools/include and 'make headers_install' which populates
> usr/include in the kernel tree (apparently mm rejects the latter but it
> is widely used in the selftests, especially for architecture specifics).
> These install locally and used before the system headers.
>
> > > OTOH in a case like this where we can just refer directly to a kernel
> > > header for some constants or structs then it does make sense to use the
> > > kernel headers, or in other cases where we're testing things that are
>
> > That is exactly my point above.
>
> What was said was a bit stronger though, and might lead people down a
> wheel reinvention path.

Let's PLEASE not rehash all this again...

This patch literally just needs PIDFD_SELF, I've provided a couple of ways
of doing that without introducing this requirement.

We already have a test that uses this with no problems ever reported on
which this patch was based.

Thanks.