mm: __count_immobile_pages(): make sure the node is online

page_zone() requires an online node otherwise we are accessing NULL
NODE_DATA.  This is not an issue at the moment because node_zones are
located at the structure beginning but this might change in the future
so better be careful about that.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 21c272d..d2186ec 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5413,15 +5413,22 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count)
 
 bool is_pageblock_removable_nolock(struct page *page)
 {
-       struct zone *zone = page_zone(page);
-       unsigned long pfn = page_to_pfn(page);
+       struct zone *zone;
+       unsigned long pfn;
 
        /*
         * We have to be careful here because we are iterating over memory
         * sections which are not zone aware so we might end up outside of
         * the zone but still within the section.
+        * We have to take care about the node as well. If the node is offline
+        * its NODE_DATA will be NULL - see page_zone.
         */
-       if (!zone || zone->zone_start_pfn > pfn ||
+       if (!node_online(page_to_nid(page)))
+               return false;
+
+       zone = page_zone(page);
+       pfn = page_to_pfn(page);
+       if (zone->zone_start_pfn > pfn ||
                        zone->zone_start_pfn + zone->spanned_pages <= pfn)
                return false;