linux-kernel - Re: [PATCH] selftests/mm: fix division-by-zero in uffd-unit-tests

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Message-ID: <b4291d0d-b913-4e61-9f9d-fbebd1eb4720@lucifer.local>
Date: Thu, 13 Nov 2025 15:03:06 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Carlos Llamas <cmllamas@...gle.com>
Cc: "David Hildenbrand (Red Hat)" <david@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Xu <peterx@...hat.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Shuah Khan <shuah@...nel.org>, Ujwal Kundur <ujwal.kundur@...il.com>,
        Brendan Jackman <jackmanb@...gle.com>, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        "open list:MEMORY MANAGEMENT - USERFAULTFD" <linux-mm@...ck.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH] selftests/mm: fix division-by-zero in uffd-unit-tests

On Thu, Nov 13, 2025 at 03:01:25PM +0000, Carlos Llamas wrote:
> On Thu, Nov 13, 2025 at 09:54:37AM +0000, Lorenzo Stoakes wrote:
> > On Thu, Nov 13, 2025 at 10:06:42AM +0100, David Hildenbrand (Red Hat) wrote:
> > > On 13.11.25 04:46, Carlos Llamas wrote:
> > > > Commit 4dfd4bba8578 ("selftests/mm/uffd: refactor non-composite global
> > > > vars into struct") moved some of the operations previously implemented
> > > > in uffd_setup_environment() earlier in the main test loop.
> > > >
> > > > The calculation of nr_pages, which involves a division by page_size, now
> > > > occurs before checking that default_huge_page_size() returns a non-zero
> > > > This leads to a division-by-zero error on systems with !CONFIG_HUGETLB.
> > > >
> > > > Fix this by relocating the non-zero page_size check before the nr_pages
> > > > calculation, as it was originally implemented.
> > > >
> > > > Cc: stable@...r.kernel.org
> > >
> > > Do we CC stable on unit tests? From my recollection, no.
> >
> > Yeah please let's not.
>
> Oops, I keep getting confused about this Cc stable thing. Please let me
> know if a v2 dropping the tag is needed.

No need, Andrew should spot the objection and drop the tag :)

>
> --
> Carlos Llamas

Cheers, Lorenzo