linux-kernel - [PATCH v2 0/2] Fix parameter passed to page_mapcount_is

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Message-ID: <20250321120222.1456770-1-gshan@redhat.com>
Date: Fri, 21 Mar 2025 22:02:20 +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 0/2] Fix parameter passed to page_mapcount_is_type()

Found by code inspection. There are two places where the parameter
passed to page_mapcount_is_type() is (page->_mapcount), which is
incorrect since it should be one more than the value, as explained in
the comments to page_mapcount_is_type(): (a) page_has_type() in
page-flags.h (b) __dump_folio() in mm/debug.c

PATCH[1] fixes the parameter for (a)
PATCH[2] fixes the parameter for (b)

Note that the issue doesn't cause any visible impacts due to the
safety gap introduced by PGTY_mapcount_underflow limit. So the
tag 'Cc: stable@...r.kernel.org' isn't needed.

Changelog
=========
v2:
  * Improved commit log                                (Vlastimi/David)
  * Use page_type_has_type() in page_has_type()        (David)

Gavin Shan (2):
  mm: Fix parameter passed to page_mapcount_is_type()
  mm/debug: Fix parameter passed to page_mapcount_is_type()

 include/linux/page-flags.h | 2 +-
 mm/debug.c                 | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

-- 
2.48.1