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

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Message-ID: <aRXyxWeh81-aTHaC@google.com>
Date: Thu, 13 Nov 2025 15:01:25 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.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 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.

--
Carlos Llamas