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McKenney" , John Hubbard , John Dias , Minchan Kim , David Hildenbrand Subject: [PATCH v5] mm: fix is_pinnable_page against on cma page Date: Thu, 12 May 2022 13:41:43 -0700 Message-Id: <20220512204143.3961150-1-minchan@kernel.org> X-Mailer: git-send-email 2.36.0.550.gb090851708-goog MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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" Cc: John Hubbard Cc: David Hildenbrand Signed-off-by: Minchan Kim --- * 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. + */ + 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) -- 2.36.0.550.gb090851708-goog