mm: fix parameter passed to page_mapcount_is_type()

Patch series "Fix parameter passed to page_mapcount_is_type()", v2.

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@vger.kernel.org' isn't needed.

This patch (of 2):

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.

Link: https://lkml.kernel.org/r/20250321120222.1456770-1-gshan@redhat.com
Link: https://lkml.kernel.org/r/20250321120222.1456770-2-gshan@redhat.com
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>
Cc: gehao <gehao@kylinos.cn>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index e6a21b62dcceefb714e787a12d4010977b21ade6..d3909cb1e5766cc88f816f4807ef5cc43f4181d8 100644 (file)
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -982,7 +982,7 @@ 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)                                   \