On 3/21/25 06:31, Gavin Shan wrote: > Found by code inspection. There are two places where the parameter > passed to page_mapcount_is_type() is (page->__mapcount), which is > correct 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 IIUC you are right. Luckily thanks to the the PGTY_mapcount_underflow limit, this off-by-one error doesn't currently cause visible issues i.e. misclassifications legitimate mapcount as page type and vice versa, right? We'd have to have a mapcount underflown severely right to the limit to make that off-by-one error cross it? I wonder if a more future-proof solution would be to redefine page_mapcount_is_type() instead to not subtract. But I'll leave that to willy. > PATCH[1] fixes the parameter for (a) > PATCH[2] fixes the parameter for (b) > > 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(-) >
