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 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@vger.kernel.org # v6.12+
Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 mm/debug.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/debug.c b/mm/debug.c
index 8d2acf432385..b6bd9555ec7b 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -71,10 +71,10 @@ static void __dump_folio(struct folio *folio, struct page *page,
 		unsigned long pfn, unsigned long idx)
 {
 	struct address_space *mapping = folio_mapping(folio);
-	int mapcount = atomic_read(&page->_mapcount);
+	int mapcount = atomic_read(&page->_mapcount) + 1;
 	char *type = "";
 
-	mapcount = page_mapcount_is_type(mapcount) ? 0 : mapcount + 1;
+	mapcount = page_mapcount_is_type(mapcount) ? 0 : mapcount;
 	pr_warn("page: refcount:%d mapcount:%d mapping:%p index:%#lx pfn:%#lx\n",
 			folio_ref_count(folio), mapcount, mapping,
 			folio->index + idx, pfn);
-- 
2.48.1

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 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@vger.kernel.org # v6.12+
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>   mm/debug.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/debug.c b/mm/debug.c
> index 8d2acf432385..b6bd9555ec7b 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -71,10 +71,10 @@ static void __dump_folio(struct folio *folio, struct page *page,
>   		unsigned long pfn, unsigned long idx)
>   {
>   	struct address_space *mapping = folio_mapping(folio);
> -	int mapcount = atomic_read(&page->_mapcount);
> +	int mapcount = atomic_read(&page->_mapcount) + 1;
>   	char *type = "";
>   
> -	mapcount = page_mapcount_is_type(mapcount) ? 0 : mapcount + 1;
> +	mapcount = page_mapcount_is_type(mapcount) ? 0 : mapcount;
>   	pr_warn("page: refcount:%d mapcount:%d mapping:%p index:%#lx pfn:%#lx\n",
>   			folio_ref_count(folio), mapcount, mapping,
>   			folio->index + idx, pfn);

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


-- 
Cheers,

David / dhildenb