linux-kernel - Re: [PATCH v2 4/8] selftests/mm: fix usage of FORCE

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Message-ID: <4d3361e4-90e8-409f-bde5-b09de53137b1@arm.com>
Date: Mon, 19 Jan 2026 14:24:03 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>, linux-mm@...ck.org,
 linux-kselftest@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Mark Brown
 <broonie@...nel.org>, Ryan Roberts <ryan.roberts@....com>,
 Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH v2 4/8] selftests/mm: fix usage of FORCE_READ() in cow
 tests

On 19/01/2026 11:50, David Hildenbrand (Red Hat) wrote:
> On 1/7/26 17:48, Kevin Brodsky wrote:
>> Commit 5bbc2b785e63 ("selftests/mm: fix FORCE_READ to read input
>> value correctly") modified FORCE_READ() to take a value instead of a
>> pointer. It also changed most of the call sites accordingly, but
>> missed many of them in cow.c. In those cases, we ended up with the
>> pointer itself being read, not the memory it points to.
>>
>> No failure occurred as a result, so it looks like the tests work
>> just fine without faulting in. However, the huge_zeropage tests
>> explicitly check that pages are populated, so those became skipped.
>
> Right, that's nasty! Thanks!
>
> For all cases, we could probably just fail if the memory is not
> populated after FORCE_READ().
>
> Would you have time to prepare a patch for that?

Sure, I guess we could even have a helper that performs a FORCE_READ()
and then returns the result of pagemap_is_populated().

- Kevin