linux-kernel - Re: [PATCH] selftests/mm: fix FORCE_READ to read input value correctly.

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Message-ID: <20250806020744.yj2f7z6ntdqnv2ff@master>
Date: Wed, 6 Aug 2025 02:07:44 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Zi Yan <ziy@...dia.com>
Cc: wang lian <lianux.mm@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	David Hildenbrand <david@...hat.com>,
	Wei Yang <richard.weiyang@...il.com>,
	Christian Brauner <brauner@...nel.org>,
	Jann Horn <jannh@...gle.com>, Kairui Song <ryncsn@...il.com>,
	Liam Howlett <liam.howlett@...cle.com>,
	Mark Brown <broonie@...nel.org>, SeongJae Park <sj@...nel.org>,
	Shuah Khan <shuah@...nel.org>, Vlastimil Babka <vbabka@...e.cz>,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH] selftests/mm: fix FORCE_READ to read input value
 correctly.

On Tue, Aug 05, 2025 at 01:51:40PM -0400, Zi Yan wrote:
>FORCE_READ() converts input value x to its pointer type then reads from
>address x. This is wrong. If x is a non-pointer, it would be caught it
>easily. But all FORCE_READ() callers are trying to read from a pointer and
>FORCE_READ() basically reads a pointer to a pointer instead of the original
>typed pointer. Almost no access violation was found, except the one from
>split_huge_page_test.
>
>Fix it by implementing a simplified READ_ONCE() instead.
>
>Fixes: 3f6bfd4789a0 ("selftests/mm: reuse FORCE_READ to replace "asm volatile("" : "+r" (XXX));"")
>Signed-off-by: Zi Yan <ziy@...dia.com>
>---

Reviewed-by: Wei Yang <richard.weiyang@...il.com>

-- 
Wei Yang
Help you, Help me