[BUGFIX][PATCH] fix node hotplug zonelist build

[KAMEZAWA Hiroyuki]

At memory hotplug, we reflesh zonelists when we online a page in a new zone.
It means that 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 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@xxxxxxxxxxxxxx>
---
 mm/memory_hotplug.c |    6 ++++++
 1 file changed, 6 insertions(+)

Index: linux-3.0-rc1/mm/memory_hotplug.c
===================================================================
--- linux-3.0-rc1.orig/mm/memory_hotplug.c
+++ linux-3.0-rc1/mm/memory_hotplug.c
@@ -494,6 +494,12 @@ static pg_data_t __ref *hotadd_new_pgdat
 	/* 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;
 }
 

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