Messages in this thread | | | Date | Thu, 12 May 2022 13:51:47 -0700 | Subject | Re: [PATCH v5] mm: fix is_pinnable_page against on cma page | From | John Hubbard <> |
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On 5/12/22 13:41, Minchan Kim wrote: > Pages on CMA area could have MIGRATE_ISOLATE as well as MIGRATE_CMA > so current is_pinnable_page could miss CMA pages which has MIGRATE_ > ISOLATE. It ends up pinning CMA pages as longterm at pin_user_pages > APIs so CMA allocation keep failed until the pin is released. > > CPU 0 CPU 1 - Task B > > cma_alloc > alloc_contig_range > pin_user_pages_fast(FOLL_LONGTERM) > change pageblock as MIGRATE_ISOLATE > internal_get_user_pages_fast > lockless_pages_from_mm > gup_pte_range > try_grab_folio > is_pinnable_page > return true; > So, pinned the page successfully. > page migration failure with pinned page > .. > .. After 30 sec > unpin_user_page(page) > > CMA allocation succeeded after 30 sec. > > The CMA allocation path protects the migration type change race > using zone->lock but what GUP path need to know is just whether the > page is on CMA area or not rather than exact migration type. > Thus, we don't need zone->lock but just checks migration type in > either of (MIGRATE_ISOLATE and MIGRATE_CMA). > > Adding the MIGRATE_ISOLATE check in is_pinnable_page could cause > rejecting of pinning pages on MIGRATE_ISOLATE pageblocks even > though it's neither CMA nor movable zone if the page is temporarily > unmovable. However, such a migration failure by unexpected temporal > refcount holding is general issue, not only come from MIGRATE_ISOLATE > and the MIGRATE_ISOLATE is also transient state like other temporal > elevated refcount problem. > > Cc: "Paul E . McKenney" <paulmck@kernel.org> > Cc: John Hubbard <jhubbard@nvidia.com> > Cc: David Hildenbrand <david@redhat.com> > Signed-off-by: Minchan Kim <minchan@kernel.org> > --- > * from v4 - https://lore.kernel.org/all/20220510211743.95831-1-minchan@kernel.org/ > * clarification why we need READ_ONCE - Paul > * Adding a comment about READ_ONCE - John > > * from v3 - https://lore.kernel.org/all/20220509153430.4125710-1-minchan@kernel.org/ > * Fix typo and adding more description - akpm > > * from v2 - https://lore.kernel.org/all/20220505064429.2818496-1-minchan@kernel.org/ > * Use __READ_ONCE instead of volatile - akpm > > * from v1 - https://lore.kernel.org/all/20220502173558.2510641-1-minchan@kernel.org/ > * fix build warning - lkp > * fix refetching issue of migration type > * add side effect on !ZONE_MOVABLE and !MIGRATE_CMA in description - david > > include/linux/mm.h | 16 ++++++++++++++-- > 1 file changed, 14 insertions(+), 2 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 6acca5cecbc5..2d7a5d87decd 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1625,8 +1625,20 @@ static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma, > #ifdef CONFIG_MIGRATION > static inline bool is_pinnable_page(struct page *page) > { > - return !(is_zone_movable_page(page) || is_migrate_cma_page(page)) || > - is_zero_pfn(page_to_pfn(page)); > +#ifdef CONFIG_CMA > + /* > + * Defend against future compiler LTO features, or code refactoring > + * that inlines the above function, by forcing a single read. Because, > + * this routine races with set_pageblock_migratetype(), and we want to > + * avoid reading zero, when actually one or the other flags was set. > + */
The most interesting line got dropped in this version. :)
This is missing:
int __mt = get_pageblock_migratetype(page);
Assuming that that is restored, please feel free to add:
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
thanks, -- John Hubbard NVIDIA
> + int mt = __READ_ONCE(__mt); > + > + if (mt & (MIGRATE_CMA | MIGRATE_ISOLATE)) > + return false; > +#endif > + > + return !(is_zone_movable_page(page) || is_zero_pfn(page_to_pfn(page))); > } > #else > static inline bool is_pinnable_page(struct page *page)
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