On 21.03.25 16:19, Vlastimil Babka wrote:
On 3/21/25 13:02, 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 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.
Fixes: 4ffca5a96678 ("mm: support only one page_type per page")
Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
---
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;
At this point it would be perhaps more obvious:
if (page_mapcount_is_type(mapcount))
mapcount = 0;
Agreed, maybe Andrew can fix that up.
--
Cheers,
David / dhildenb
