diff options
| -rw-r--r-- | mm/compaction.c | 5 | ||||
| -rw-r--r-- | mm/internal.h | 8 |
2 files changed, 9 insertions, 4 deletions
diff --git a/mm/compaction.c b/mm/compaction.c index e0ab02d70f13..b48c5259ea33 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -523,7 +523,10 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc, if (!isolation_suitable(cc, page)) goto next_pageblock; - /* Skip if free */ + /* + * Skip if free. page_order cannot be used without zone->lock + * as nothing prevents parallel allocations or buddy merging. + */ if (PageBuddy(page)) continue; diff --git a/mm/internal.h b/mm/internal.h index 7e145e8cd1e6..612c14f5e0f5 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -143,9 +143,11 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc, #endif /* - * function for dealing with page's order in buddy system. - * zone->lock is already acquired when we use these. - * So, we don't need atomic page->flags operations here. + * 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. */ static inline unsigned long page_order(struct page *page) { |