div64 would loop forever if a was > 2^63.
--- diff/drivers/md/dm-iostats.c	2002-12-17 16:57:32.000000000 +0000
+++ source/drivers/md/dm-iostats.c	2002-12-17 16:55:47.000000000 +0000
@@ -147,7 +147,7 @@
 	*n = 0;
 	while (a >= b) {
 		for (acc = b, prev = 0, i = 1;
-		     acc <= a;
+		     (acc <= a) && i;
 		     prev = acc, acc <<= 1, i <<= 1)
 			;