linux-kernel - Re: [PATCH 1/2] mm: Fix parameter passed to page_mapcount_is

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Message-ID: <b6478ad2-7169-42be-b9ba-e703fdbbd553@redhat.com>
Date: Fri, 21 Mar 2025 11:13:41 +0100
From: David Hildenbrand <david@...hat.com>
To: Gavin Shan <gshan@...hat.com>, linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
 willy@...radead.org, vbabka@...e.cz, osalvador@...e.de, gehao@...inos.cn,
 shan.gavin@...il.com
Subject: Re: [PATCH 1/2] mm: Fix parameter passed to page_mapcount_is_type()

On 21.03.25 06:31, Gavin Shan wrote:
> As the comments of page_mapcount_is_type() indicate, the parameter
> passed to the function should be one more than page->__mapcount.
> However, page->__mapcount (equivalent to page->page_type) is passed to
> the function by commit 4ffca5a96678 ("mm: support only one page_type per
> page") where page_type_has_type() is replaced by page_mapcount_is_type(),
> but the parameter isn't adjusted.
> 
> Fix the parameter passed to page_mapcount_is_type() to be (page->__mapcount
> + 1).
> 
> Fixes: 4ffca5a96678 ("mm: support only one page_type per page")
> Cc: stable@...r.kernel.org # v6.12+
> Signed-off-by: Gavin Shan <gshan@...hat.com>
> ---
>   include/linux/page-flags.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 36d283552f80..ad87b4cf1f9a 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -950,7 +950,7 @@ static inline bool page_mapcount_is_type(unsigned int mapcount)
>   
>   static inline bool page_has_type(const struct page *page)
>   {
> -	return page_mapcount_is_type(data_race(page->page_type));
> +	return page_mapcount_is_type(data_race(page->page_type) + 1);

Probably we should just call page_type_has_type() instead?

-- 
Cheers,

David / dhildenb