s->table wasn't being set in the snapshot contructor
--- diff/drivers/md/dm-snapshot.c	2003-06-17 10:05:34.000000000 +0100
+++ source/drivers/md/dm-snapshot.c	2003-06-17 10:05:39.000000000 +0100
@@ -488,6 +488,7 @@
 	s->valid = 1;
 	s->last_percent = 0;
 	init_rwsem(&s->lock);
+	s->table = ti->table;
 
 	/* Allocate hash table for COW data */
 	if (init_hash_tables(s)) {