| Message ID | 20220512204143.3961150-1-minchan@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v5] mm: fix is_pinnable_page against on cma page | expand |
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,
On Thu, May 12, 2022 at 01:51:47PM -0700, John Hubbard wrote: > 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> Just caught after clicked the button with my fat finger :( Thanks, John! Andrew, Could you pick this up? From 90ad049d48f5c36075f17ac996dfe3c33127aeb6 Mon Sep 17 00:00:00 2001 From: Minchan Kim <minchan@kernel.org> Date: Mon, 2 May 2022 10:03:48 -0700 Subject: [PATCH v5] mm: fix is_pinnable_page against on cma page 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: David Hildenbrand <david@redhat.com> Reviewed-by: John Hubbard <jhubbard@nvidia.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 | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 6acca5cecbc5..b23c6f1b90b5 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1625,8 +1625,21 @@ 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. + */ + int __mt = get_pageblock_migratetype(page); + 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)
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. + */ + 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)
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(-)