On Tue, May 24, 2022 at 10:15:25AM -0700, 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@xxxxxxxxxx> >From a memory-ordering viewpoint: Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > Cc: David Hildenbrand <david@xxxxxxxxxx> > Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > --- > * from v5 - https://lore.kernel.org/all/20220512204143.3961150-1-minchan@xxxxxxxxxx/ > * Use READ_ONCE in __get_pfnblock_flags_mask - Jason > * adding a comment about READ_ONCE - John > > * from v4 - https://lore.kernel.org/all/20220510211743.95831-1-minchan@xxxxxxxxxx/ > * 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@xxxxxxxxxx/ > * Fix typo and adding more description - akpm > > * from v2 - https://lore.kernel.org/all/20220505064429.2818496-1-minchan@xxxxxxxxxx/ > * Use __READ_ONCE instead of volatile - akpm > > * from v1 - https://lore.kernel.org/all/20220502173558.2510641-1-minchan@xxxxxxxxxx/ > * 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 | 9 +++++++-- > mm/page_alloc.c | 8 ++++++-- > 2 files changed, 13 insertions(+), 4 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 6acca5cecbc5..ba13411b6dca 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1625,8 +1625,13 @@ 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 > + int mt = get_pageblock_migratetype(page); > + > + if (mt == MIGRATE_CMA || mt == 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) > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 7a2053621e27..348071e5d8d9 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -482,8 +482,12 @@ unsigned long __get_pfnblock_flags_mask(const struct page *page, > bitidx = pfn_to_bitidx(page, pfn); > word_bitidx = bitidx / BITS_PER_LONG; > bitidx &= (BITS_PER_LONG-1); > - > - word = bitmap[word_bitidx]; > + /* > + * This races, without locks, with set_pfnblock_flags_mask(). Ensure > + * a consistent read of the memory array, so that results, even though > + * racy, are not corrupted. > + */ > + word = READ_ONCE(bitmap[word_bitidx]); > return (word >> bitidx) & mask; > } > > -- > 2.36.1.124.g0e6072fb45-goog >
