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

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Message-ID: <20260108020450.44953-1-lianux.mm@gmail.com>
Date: Thu,  8 Jan 2026 10:04:50 +0800
From: wang lian <lianux.mm@...il.com>
To: kevin.brodsky@....com
Cc: akpm@...ux-foundation.org,
	broonie@...nel.org,
	david@...nel.org,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	linux-mm@...ck.org,
	lorenzo.stoakes@...cle.com,
	ryan.roberts@....com,
	shuah@...nel.org,
	wang lian <lianux.mm@...il.com>
Subject: Re: [PATCH v2 4/8] selftests/mm: fix usage of FORCE_READ() in cow tests

> 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.
> 
> Convert all the remaining FORCE_READ() to fault in the mapped page,
> as was originally intended. This allows the huge_zeropage tests to
> run again (3 tests in total).
> 
> Fixes: 5bbc2b785e63 ("selftests/mm: fix FORCE_READ to read input value correctly")
> Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>

Hi Kevin,

Thanks for the fix.

This was indeed an oversight on my part. When we previously discussed this
refactoring with Ziyan and Lorenzo (and the community) regarding commit
3f6bfd4789a0 ("selftests/mm: reuse FORCE_READ to replace "asm volatile
("" : "+r" (XXX));""), the intention was to switch FORCE_READ to take a
value. I clearly missed updating these specific call sites in cow.c
during that transition.

Sorry for the trouble and the skipped tests. The changes look correct to
me.

Reviewed-by: wang lian <lianux.mm@...il.com>

--
Best Regards,
wang lian