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

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Message-ID: <805065c4-b396-43e7-8a9f-f934ec616b31@redhat.com>
Date: Fri, 21 Mar 2025 12:28:08 +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 12:26, Gavin Shan wrote:
> On 3/21/25 8:13 PM, David Hildenbrand wrote:
>> 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?
>>
> 
> Yes, page_type_has_type() is better. It will be used in v2.


Feel free to add my

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb