1 files changed, 7 insertions, 1 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 850009a7101e..2b8ba3aebf6e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3377,9 +3377,15 @@ static void setup_zone_migrate_reserve(struct zone *zone)
         unsigned long block_migratetype;
         int reserve;
 
-        /* Get the start pfn, end pfn and the number of blocks to reserve */
+        /*
+         * Get the start pfn, end pfn and the number of blocks to reserve
+         * We have to be careful to be aligned to pageblock_nr_pages to
+         * make sure that we always check pfn_valid for the first page in
+         * the block.
+         */
         start_pfn = zone->zone_start_pfn;
         end_pfn = start_pfn + zone->spanned_pages;
+        start_pfn = roundup(start_pfn, pageblock_nr_pages);
         reserve = roundup(min_wmark_pages(zone), pageblock_nr_pages) >>
                                                         pageblock_order;