mm/memory_hotplug.c: fix building of node hotplug zonelist

During memory hotplug we refresh zonelists when we online a page in a new
zone.  It means that the node's zonelist is not initialized until pages
are onlined.  So for example, "nid" passed by MEM_GOING_ONLINE notifier
will point to NODE_DATA(nid) which has no zone fallback list.  Moreover,
if we hot-add cpu-only nodes, alloc_pages() will do no fallback.

This patch makes a zonelist when a new pgdata is available.

Note: in production, at fujitsu, memory should be onlined before cpu
      and our server didn't have any memory-less nodes and had no problems.

      But recent changes in MEM_GOING_ONLINE+page_cgroup
      will access not initialized zonelist of node.
      Anyway, there are memory-less node and we need some care.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 9f646374e32f..02159c755136 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -494,6 +494,12 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
         /* init node's zones as empty zones, we don't have any present pages.*/
         free_area_init_node(nid, zones_size, start_pfn, zholes_size);
 
+        /*
+         * The node we allocated has no zone fallback lists. For avoiding
+         * to access not-initialized zonelist, build here.
+         */
+        build_all_zonelists(NULL);
+
         return pgdat;
 }