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mm/debug: 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 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 for page_mapcount_is_type() to be (page->__mapcount +
1). Note that the issue doesn't cause any visible impacts due to the
safety gap introduced by PGTY_mapcount_underflow limit.

[akpm@linux-foundation.org: simplify __dump_folio(), per David]
Link: https://lkml.kernel.org/r/20250321120222.1456770-3-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>

authored by

Gavin Shan and committed by
Andrew Morton 79049bb4 979f3ef0

+4 -2
+4 -2
mm/debug.c
··· 71 71 unsigned long pfn, unsigned long idx) 72 72 { 73 73 struct address_space *mapping = folio_mapping(folio); 74 - int mapcount = atomic_read(&page->_mapcount); 74 + int mapcount = atomic_read(&page->_mapcount) + 1; 75 75 char *type = ""; 76 76 77 - mapcount = page_mapcount_is_type(mapcount) ? 0 : mapcount + 1; 77 + if (page_mapcount_is_type(mapcount)) 78 + mapcount = 0; 79 + 78 80 pr_warn("page: refcount:%d mapcount:%d mapping:%p index:%#lx pfn:%#lx\n", 79 81 folio_ref_count(folio), mapcount, mapping, 80 82 folio->index + idx, pfn);