diff options
Diffstat (limited to 'mm/internal.h')
| -rw-r--r-- | mm/internal.h | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/mm/internal.h b/mm/internal.h index 4c1d604c396c..86ae964a25b0 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -164,7 +164,8 @@ isolate_migratepages_range(struct compact_control *cc, * 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. + * page cannot be allocated or merged in parallel. Alternatively, it must + * handle invalid values gracefully, and use page_order_unsafe() below. */ static inline unsigned long page_order(struct page *page) { @@ -172,6 +173,19 @@ static inline unsigned long page_order(struct page *page) return page_private(page); } +/* + * Like page_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. + * + * ACCESS_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 page_order_unsafe(page) ACCESS_ONCE(page_private(page)) + static inline bool is_cow_mapping(vm_flags_t flags) { return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; |