diff -r c800f72f0a7d -r 7d95498e6a7b drivers/xen/blktap/control.c
--- a/drivers/xen/blktap/control.c	Wed Feb 03 11:35:24 2010 -0800
+++ b/drivers/xen/blktap/control.c	Wed Feb 03 11:55:32 2010 -0800
@@ -23,6 +23,7 @@
 	init_rwsem(&tap->tap_sem);
 	init_waitqueue_head(&tap->wq);
 	atomic_set(&tap->refcnt, 0);
+	sg_init_table(tap->sg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
 
 	tap->minor = minor;
 }