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 <[email protected]> Signed-off-by: KAMEZAWA Hiroyuki <[email protected]> Acked-by: Mel Gorman <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
iegor · Jan 23, 2012 · 656a070 · 656a070
1 parent 687875f
commit 656a070
Showing 1 changed file with 10 additions and 3 deletions.
diff --git 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;