Force kcopyd to be single-threaded. For now, snapshotting cannot handle
multiple kcopyd threads. When we determine the correct way to make snapshot
safe for a multithreaded kcopyd, this patch can be removed.

--- diff/drivers/md/kcopyd.c	2004-05-27 14:23:52.000000000 +0100
+++ source/drivers/md/kcopyd.c	2004-05-27 14:24:06.000000000 +0100
@@ -645,7 +645,7 @@
 	if (r)
 		return r;
 
-	_kcopyd_wq = create_workqueue("kcopyd");
+	_kcopyd_wq = create_singlethread_workqueue("kcopyd");
 	if (!_kcopyd_wq) {
 		jobs_exit();
 		return -ENOMEM;