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") page_type_has_type() is replaced by page_mapcount_is_type(),
but the parameter isn't adjusted.

Fix it by replacing page_mapcount_is_type() with page_type_has_type()
in page_has_type(). Note that the issue doesn't cause any visible impacts
due to the safety gap introduced by PGTY_mapcount_underflow limit.

Fixes: 4ffca5a96678 ("mm: support only one page_type per page")
Signed-off-by: Gavin Shan <gshan@redhat.com>
Acked-by: David Hildenbrand <david@redhat.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..e1a9f84bd5ab 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_type_has_type(data_race(page->page_type));
 }
 
 #define FOLIO_TYPE_OPS(lname, fname)					\
-- 
2.48.1

On 3/21/25 13:02, 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") page_type_has_type() is replaced by page_mapcount_is_type(),
> but the parameter isn't adjusted.
> 
> Fix it by replacing page_mapcount_is_type() with page_type_has_type()
> in page_has_type(). Note that the issue doesn't cause any visible impacts
> due to the safety gap introduced by PGTY_mapcount_underflow limit.
> 
> Fixes: 4ffca5a96678 ("mm: support only one page_type per page")
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> Acked-by: David Hildenbrand <david@redhat.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  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..e1a9f84bd5ab 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_type_has_type(data_race(page->page_type));
>  }
>  
>  #define FOLIO_TYPE_OPS(lname, fname)					\