[PATCH] Fix copying of pgdat array on each node for ia64 memory hotplug

I found a bug in memory hot-add code for ia64.

IA64's code has copies of pgdat's array on each node to reduce memory
access over crossing node.  This array is used by NODE_DATA() macro.  When
new node is hot-added, this pgdat's array should be updated and copied on
new node too.

However, I used for_each_online_node() in scatter_node_data() to copy
it. This meant its array is not copied on new node.
Because initialization of structures for new node was halfway,
so online_node_map couldn't be set at this time.

To copy arrays on new node, I changed it to check value of pgdat_list[]
which is source array of copies.  I tested this patch with my Memory Hotadd
emulation on Tiger4.  This patch is for 2.6.17-git20.
Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/ia64/mm/discontig.c

@@ -313,9 +313,19 @@ static void __meminit scatter_node_data(void)
 	pg_data_t **dst;
 	int node;
 
-	for_each_online_node(node) {
-		dst = LOCAL_DATA_ADDR(pgdat_list[node])->pg_data_ptrs;
-		memcpy(dst, pgdat_list, sizeof(pgdat_list));
+	/*
+	 * for_each_online_node() can't be used at here.
+	 * node_online_map is not set for hot-added nodes at this time,
+	 * because we are halfway through initialization of the new node's
+	 * structures.  If for_each_online_node() is used, a new node's
+	 * pg_data_ptrs will be not initialized. Insted of using it,
+	 * pgdat_list[] is checked.
+	 */
+	for_each_node(node) {
+		if (pgdat_list[node]) {
+			dst = LOCAL_DATA_ADDR(pgdat_list[node])->pg_data_ptrs;
+			memcpy(dst, pgdat_list, sizeof(pgdat_list));
+		}
 	}
 }