[PATCH] mm: __count_immobile_pages make sure the node is online

[Michal Hocko]

page_zone requires to have 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@xxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
 mm/page_alloc.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 485be89..c6fb8ea 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5607,14 +5607,21 @@ __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 (!node_online(page_to_nid(page)))
+		return false;
+
+	zone = page_zone(page);
+	pfn = page_to_pfn(page);
 	if (!zone || zone->zone_start_pfn > pfn ||
 			zone->zone_start_pfn + zone->spanned_pages <= pfn)
 		return false;
-- 
1.7.7.3

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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