Messages in this thread | | | From | Zi Yan <> | Subject | Re: [PATCH v1 01/18] mm: allow for detecting underflows with page_mapcount() again | Date | Tue, 09 Apr 2024 16:06:15 -0400 |
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On 9 Apr 2024, at 15:22, David Hildenbrand wrote:
> Commit 53277bcf126d ("mm: support page_mapcount() on page_has_type() > pages") made it impossible to detect mapcount underflows by treating > any negative raw mapcount value as a mapcount of 0. > > We perform such underflow checks in zap_present_folio_ptes() and > zap_huge_pmd(), which would currently no longer trigger. > > Let's check against PAGE_MAPCOUNT_RESERVE instead by using > page_type_has_type(), like page_has_type() would, so we can still catch > some underflows. > > Fixes: 53277bcf126d ("mm: support page_mapcount() on page_has_type() pages") > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > include/linux/mm.h | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index ef34cf54c14f..0fb8a40f82dd 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1229,11 +1229,10 @@ static inline void page_mapcount_reset(struct page *page) > */ > static inline int page_mapcount(struct page *page) > { > - int mapcount = atomic_read(&page->_mapcount) + 1; > + int mapcount = atomic_read(&page->_mapcount); > > /* Handle page_has_type() pages */ > - if (mapcount < 0) > - mapcount = 0; > + mapcount = page_type_has_type(mapcount) ? 0 : mapcount + 1; > if (unlikely(PageCompound(page))) > mapcount += folio_entire_mapcount(page_folio(page));
LGTM. This could be picked up separately. Reviewed-by: Zi Yan <ziy@nvidia.com>
-- Best Regards, Yan, Zi [unhandled content-type:application/pgp-signature] | |