NFSv4: Ensure nfs_callback_down() calls svc_destroy()

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index fcd97406..2c042f8 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -73,6 +73,7 @@
 		svc_process(serv, rqstp);
 	}
 
+	svc_exit_thread(rqstp);
 	nfs_callback_info.pid = 0;
 	complete(&nfs_callback_info.stopped);
 	unlock_kernel();