driver core: numa: fix BUILD_BUG_ON for node_read_distance

node_read_distance() has a BUILD_BUG_ON() to prevent buffer overruns when
the number of nodes printed will exceed the buffer length.

Each node only needs four chars: three for distance (maximum distance is
255) and one for a seperating space or a trailing newline.
Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/node.c

@@ -165,8 +165,11 @@ static ssize_t node_read_distance(struct sys_device * dev,
 	int len = 0;
 	int i;
 
-	/* buf currently PAGE_SIZE, need ~4 chars per node */
-	BUILD_BUG_ON(MAX_NUMNODES*4 > PAGE_SIZE/2);
+	/*
+	 * buf is currently PAGE_SIZE in length and each node needs 4 chars
+	 * at the most (distance + space or newline).
+	 */
+	BUILD_BUG_ON(MAX_NUMNODES * 4 > PAGE_SIZE);
 
 	for_each_online_node(i)
 		len += sprintf(buf + len, "%s%d", i ? " " : "", node_distance(nid, i));