Drivers: hv: vss: Introduce timeout for communication with userspace

In contrast with KVP there is no timeout when communicating with
userspace VSS daemon. In case it gets stuck performing freeze/thaw
operation no message will be sent to the host so it will take very
long (around 10 minutes) before backup fails. Introduce 10 second
timeout using schedule_delayed_work().
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/hv_snapshot.c

@@ -28,7 +28,7 @@
 #define VSS_MINOR  0
 #define VSS_VERSION    (VSS_MAJOR << 16 | VSS_MINOR)
 
-
+#define VSS_USERSPACE_TIMEOUT (msecs_to_jiffies(10 * 1000))
 
 /*
  * Global state maintained for transaction that is being processed.
@@ -55,12 +55,24 @@ static const char vss_name[] = "vss_kernel_module";
 static __u8 *recv_buffer;
 
 static void vss_send_op(struct work_struct *dummy);
+static void vss_timeout_func(struct work_struct *dummy);
+
+static DECLARE_DELAYED_WORK(vss_timeout_work, vss_timeout_func);
 static DECLARE_WORK(vss_send_op_work, vss_send_op);
 
 /*
  * Callback when data is received from user mode.
  */
 
+static void vss_timeout_func(struct work_struct *dummy)
+{
+	/*
+	 * Timeout waiting for userspace component to reply happened.
+	 */
+	pr_warn("VSS: timeout waiting for daemon to reply\n");
+	vss_respond_to_host(HV_E_FAIL);
+}
+
 static void
 vss_cn_callback(struct cn_msg *msg, struct netlink_skb_parms *nsp)
 {
@@ -76,7 +88,8 @@ vss_cn_callback(struct cn_msg *msg, struct netlink_skb_parms *nsp)
 		return;
 
 	}
-	vss_respond_to_host(vss_msg->error);
+	if (cancel_delayed_work_sync(&vss_timeout_work))
+		vss_respond_to_host(vss_msg->error);
 }
 
 
@@ -223,6 +236,8 @@ void hv_vss_onchannelcallback(void *context)
 			case VSS_OP_FREEZE:
 			case VSS_OP_THAW:
 				schedule_work(&vss_send_op_work);
+				schedule_delayed_work(&vss_timeout_work,
+						      VSS_USERSPACE_TIMEOUT);
 				return;
 
 			case VSS_OP_HOT_BACKUP:
@@ -277,5 +292,6 @@ hv_vss_init(struct hv_util_service *srv)
 void hv_vss_deinit(void)
 {
 	cn_del_callback(&vss_id);
+	cancel_delayed_work_sync(&vss_timeout_work);
 	cancel_work_sync(&vss_send_op_work);
 }