linux-kernel - [PATCH v2 1/2] mm: Fix parameter passed to page_mapcount_is

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Message-ID: <20250321120222.1456770-2-gshan@redhat.com>
Date: Fri, 21 Mar 2025 22:02:21 +1000
From: Gavin Shan <gshan@...hat.com>
To: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org,
	willy@...radead.org,
	david@...hat.com,
	vbabka@...e.cz,
	linmiaohe@...wei.com,
	gehao@...inos.cn,
	shan.gavin@...il.com
Subject: [PATCH v2 1/2] mm: Fix parameter passed to page_mapcount_is_type()

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