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>

1 files changed, 10 insertions, 3 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 21c272d517bc..d2186ecb36f7 100644
--- 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;