linux-kernel - Re: [PATCH] selftest: mm: Test if hugepage does not get leaked during __bio_release

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Date: Fri, 24 May 2024 12:13:04 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: David Hildenbrand <david@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>
Cc: Donet Tom <donettom@...ux.ibm.com>, Shuah Khan <shuah@...nel.org>, Matthew Wilcox <willy@...radead.org>, Tony Battersby <tonyb@...ernetics.com>, linux-mm@...ck.org, linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org, Mike Rapoport <rppt@...nel.org>, Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH] selftest: mm: Test if hugepage does not get leaked during __bio_release_pages()

David Hildenbrand <david@...hat.com> writes:

dropping stable@...r.kernel.org

> On 24.05.24 04:57, Andrew Morton wrote:
>> On Thu, 23 May 2024 22:40:25 +0200 David Hildenbrand <david@...hat.com> wrote:
>> 
>>>> You have stable@...r.kernel.org in the mail headers, so I assume you're
>>>> proposing this for backporting.  When doing this, please include
>>>>
>>>> Cc: <stable@...r.kernel.org>
>>>>
>>>> in the changelog footers and also include a Fixes: target.  I'm
>>>> assuming the suitable Fixes: target for this patch is 38b43539d64b?
>>>
>>> This adds a new selfest to make sure what was fixed (and backported to
>>> stable) remains fixed.
>> 
>> Sure.  But we should provide -stable maintainers guidance for "how far
>> back to go".  There isn't much point in backporting this into kernels
>> where it's known to fail!
>
> I'm probably missing something important.
>
> 1) It's a test that does not fall into the common stable kernels 
> categories (see Documentation/process/stable-kernel-rules.rst).
>
> 2) If it fails in a kernel *it achieved its goal* of highlighting that 
> something serious is broken.
>
>> 
>> I'm still thinking that we want this in kernels which have 38b43539d64b?
>
> To hide that the other kernels are seriously broken and miss that fix?
>
> Really (1) this shouldn't be backported. I'm not even sure it should be 
> a selftest (sounds more like a reproducer that we usually attach to 
> commits, but that's too late). And if people care about backporting it, 
> (2) you really want this test to succeed everywhere. Especially also to 
> find kernels *without* 38b43539d64b


Sorry about the noise and cc'd to stable. I believe we don't need to
backport this test. The idea of adding a selftests was "also" to catch any
future bugs like this. 

I am unaware of any functional test suite where we could add such tests
like how filesystems have fstests. Hence the ideas was to add this in
selftests. 

So this begs the question which I also asked few people at LSFMM,
Does mm has any mmfvt (mm functional verification tests)? Should we have
something like this? Was it tried in past?

(Sorry, mmtests name is already taken - "MMTests is a configurable test suite that runs performance tests against arbitrary workloads.")

-ritesh

>
> -- 
> Cheers,
>
> David / dhildenb