Enable the new code that checks that an exception isn't already being copied.
--- diff/drivers/md/dm-snapshot.c	2003-12-29 10:13:48.000000000 +0000
+++ source/drivers/md/dm-snapshot.c	2003-12-29 10:14:26.000000000 +0000
@@ -1051,18 +1051,13 @@
 			if (first)
 				queue_bio(&pe->origin_bios, bio);
 
-#if 0
 			if (!pe->started) {
 				pe->started = 1;
 				up_write(&pe->snap->lock);
 				start_copy(pe);
 			} else
 				up_write(&pe->snap->lock);
-#else
-			pe->started = 1;
-			up_write(&pe->snap->lock);
-			start_copy(pe);
-#endif
+
 			first = 0;
 			pe = list_entry(pe->siblings.next,
 					struct pending_exception, siblings);