From: Zi Yan Subject: mm: wrap __find_buddy_pfn() with a necessary buddy page validation Whenever the buddy of a page is found from __find_buddy_pfn(), page_is_buddy() should be used to check its validity. Add a helper function find_buddy_page_pfn() to find the buddy page and do the check together. Link: https://lkml.kernel.org/r/20220401230804.1658207-2-zi.yan@sent.com Link: https://lore.kernel.org/linux-mm/CAHk-=wji_AmYygZMTsPMdJ7XksMt7kOur8oDfDdniBRMjm4VkQ@mail.gmail.com/ Link: https://lkml.kernel.org/r/7236E7CA-B5F1-4C04-AB85-E86FA3E9A54B@nvidia.com Suggested-by: Linus Torvalds Signed-off-by: Zi Yan Acked-by: Vlastimil Babka Acked-by: David Hildenbrand Cc: Steven Rostedt (Google) Cc: Mel Gorman Cc: Mike Rapoport Cc: Oscar Salvador Signed-off-by: Andrew Morton --- mm/internal.h | 117 ++++++++++++++++++++++++++++++++---------- mm/page_alloc.c | 52 ++---------------- mm/page_isolation.c | 9 +-- 3 files changed, 101 insertions(+), 77 deletions(-) --- a/mm/internal.h~mm-wrap-__find_buddy_pfn-with-a-necessary-buddy-page-validation +++ a/mm/internal.h @@ -212,6 +212,67 @@ struct alloc_context { }; /* + * This function returns the order of a free page in the buddy system. In + * general, page_zone(page)->lock must be held by the caller to prevent the + * page from being allocated in parallel and returning garbage as the order. + * If a caller does not hold page_zone(page)->lock, it must guarantee that the + * page cannot be allocated or merged in parallel. Alternatively, it must + * handle invalid values gracefully, and use buddy_order_unsafe() below. + */ +static inline unsigned int buddy_order(struct page *page) +{ + /* PageBuddy() must be checked by the caller */ + return page_private(page); +} + +/* + * Like buddy_order(), but for callers who cannot afford to hold the zone lock. + * PageBuddy() should be checked first by the caller to minimize race window, + * and invalid values must be handled gracefully. + * + * READ_ONCE is used so that if the caller assigns the result into a local + * variable and e.g. tests it for valid range before using, the compiler cannot + * decide to remove the variable and inline the page_private(page) multiple + * times, potentially observing different values in the tests and the actual + * use of the result. + */ +#define buddy_order_unsafe(page) READ_ONCE(page_private(page)) + +/* + * This function checks whether a page is free && is the buddy + * we can coalesce a page and its buddy if + * (a) the buddy is not in a hole (check before calling!) && + * (b) the buddy is in the buddy system && + * (c) a page and its buddy have the same order && + * (d) a page and its buddy are in the same zone. + * + * For recording whether a page is in the buddy system, we set PageBuddy. + * Setting, clearing, and testing PageBuddy is serialized by zone->lock. + * + * For recording page's order, we use page_private(page). + */ +static inline bool page_is_buddy(struct page *page, struct page *buddy, + unsigned int order) +{ + if (!page_is_guard(buddy) && !PageBuddy(buddy)) + return false; + + if (buddy_order(buddy) != order) + return false; + + /* + * zone check is done late to avoid uselessly calculating + * zone/node ids for pages that could never merge. + */ + if (page_zone_id(page) != page_zone_id(buddy)) + return false; + + VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy); + + return true; +} + +/* * Locate the struct page for both the matching buddy in our * pair (buddy1) and the combined O(n+1) page they form (page). * @@ -234,6 +295,35 @@ __find_buddy_pfn(unsigned long page_pfn, return page_pfn ^ (1 << order); } +/* + * Find the buddy of @page and validate it. + * @page: The input page + * @pfn: The pfn of the page, it saves a call to page_to_pfn() when the + * function is used in the performance-critical __free_one_page(). + * @order: The order of the page + * @buddy_pfn: The output pointer to the buddy pfn, it also saves a call to + * page_to_pfn(). + * + * The found buddy can be a non PageBuddy, out of @page's zone, or its order is + * not the same as @page. The validation is necessary before use it. + * + * Return: the found buddy page or NULL if not found. + */ +static inline struct page *find_buddy_page_pfn(struct page *page, + unsigned long pfn, unsigned int order, unsigned long *buddy_pfn) +{ + struct page *buddy; + unsigned long __buddy_pfn = __find_buddy_pfn(pfn, order); + + buddy = page + (__buddy_pfn - pfn); + if (buddy_pfn) + *buddy_pfn = __buddy_pfn; + + if (page_is_buddy(page, buddy, order)) + return buddy; + return NULL; +} + extern struct page *__pageblock_pfn_to_page(unsigned long start_pfn, unsigned long end_pfn, struct zone *zone); @@ -337,33 +427,6 @@ int find_suitable_fallback(struct free_a int migratetype, bool only_stealable, bool *can_steal); /* - * This function returns the order of a free page in the buddy system. In - * general, page_zone(page)->lock must be held by the caller to prevent the - * page from being allocated in parallel and returning garbage as the order. - * If a caller does not hold page_zone(page)->lock, it must guarantee that the - * page cannot be allocated or merged in parallel. Alternatively, it must - * handle invalid values gracefully, and use buddy_order_unsafe() below. - */ -static inline unsigned int buddy_order(struct page *page) -{ - /* PageBuddy() must be checked by the caller */ - return page_private(page); -} - -/* - * Like buddy_order(), but for callers who cannot afford to hold the zone lock. - * PageBuddy() should be checked first by the caller to minimize race window, - * and invalid values must be handled gracefully. - * - * READ_ONCE is used so that if the caller assigns the result into a local - * variable and e.g. tests it for valid range before using, the compiler cannot - * decide to remove the variable and inline the page_private(page) multiple - * times, potentially observing different values in the tests and the actual - * use of the result. - */ -#define buddy_order_unsafe(page) READ_ONCE(page_private(page)) - -/* * These three helpers classifies VMAs for virtual memory accounting. */ --- a/mm/page_alloc.c~mm-wrap-__find_buddy_pfn-with-a-necessary-buddy-page-validation +++ a/mm/page_alloc.c @@ -868,40 +868,6 @@ static inline void set_buddy_order(struc __SetPageBuddy(page); } -/* - * This function checks whether a page is free && is the buddy - * we can coalesce a page and its buddy if - * (a) the buddy is not in a hole (check before calling!) && - * (b) the buddy is in the buddy system && - * (c) a page and its buddy have the same order && - * (d) a page and its buddy are in the same zone. - * - * For recording whether a page is in the buddy system, we set PageBuddy. - * Setting, clearing, and testing PageBuddy is serialized by zone->lock. - * - * For recording page's order, we use page_private(page). - */ -static inline bool page_is_buddy(struct page *page, struct page *buddy, - unsigned int order) -{ - if (!page_is_guard(buddy) && !PageBuddy(buddy)) - return false; - - if (buddy_order(buddy) != order) - return false; - - /* - * zone check is done late to avoid uselessly calculating - * zone/node ids for pages that could never merge. - */ - if (page_zone_id(page) != page_zone_id(buddy)) - return false; - - VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy); - - return true; -} - #ifdef CONFIG_COMPACTION static inline struct capture_control *task_capc(struct zone *zone) { @@ -1010,18 +976,17 @@ static inline bool buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn, struct page *page, unsigned int order) { - struct page *higher_page, *higher_buddy; - unsigned long combined_pfn; + struct page *higher_page; + unsigned long higher_page_pfn; if (order >= MAX_ORDER - 2) return false; - combined_pfn = buddy_pfn & pfn; - higher_page = page + (combined_pfn - pfn); - buddy_pfn = __find_buddy_pfn(combined_pfn, order + 1); - higher_buddy = higher_page + (buddy_pfn - combined_pfn); + higher_page_pfn = buddy_pfn & pfn; + higher_page = page + (higher_page_pfn - pfn); - return page_is_buddy(higher_page, higher_buddy, order + 1); + return find_buddy_page_pfn(higher_page, higher_page_pfn, order + 1, + NULL) != NULL; } /* @@ -1075,10 +1040,9 @@ static inline void __free_one_page(struc migratetype); return; } - buddy_pfn = __find_buddy_pfn(pfn, order); - buddy = page + (buddy_pfn - pfn); - if (!page_is_buddy(page, buddy, order)) + buddy = find_buddy_page_pfn(page, pfn, order, &buddy_pfn); + if (!buddy) goto done_merging; if (unlikely(order >= pageblock_order)) { --- a/mm/page_isolation.c~mm-wrap-__find_buddy_pfn-with-a-necessary-buddy-page-validation +++ a/mm/page_isolation.c @@ -70,7 +70,6 @@ static void unset_migratetype_isolate(st unsigned long flags, nr_pages; bool isolated_page = false; unsigned int order; - unsigned long pfn, buddy_pfn; struct page *buddy; zone = page_zone(page); @@ -89,11 +88,9 @@ static void unset_migratetype_isolate(st if (PageBuddy(page)) { order = buddy_order(page); if (order >= pageblock_order && order < MAX_ORDER - 1) { - pfn = page_to_pfn(page); - buddy_pfn = __find_buddy_pfn(pfn, order); - buddy = page + (buddy_pfn - pfn); - - if (!is_migrate_isolate_page(buddy)) { + buddy = find_buddy_page_pfn(page, page_to_pfn(page), + order, NULL); + if (buddy && !is_migrate_isolate_page(buddy)) { isolated_page = !!__isolate_free_page(page, order); /* * Isolating a free page in an isolated pageblock _