Avoid removing watch across suspend/suspend_cancel cycle

diff -r b358ebf1c416 drivers/xen/netfront/accel.c
--- a/drivers/xen/netfront/accel.c
+++ b/drivers/xen/netfront/accel.c
@@ -50,6 +50,8 @@ static int netfront_load_accelerator(str
 static int netfront_load_accelerator(struct netfront_info *np, 
 				     struct xenbus_device *dev, 
 				     const char *frontend);
+
+static void netfront_accelerator_remove_watch(struct netfront_info *np);
 
 /*
  * List of all netfront accelerator plugin modules available.  Each
@@ -164,8 +166,11 @@ void netfront_accelerator_add_watch(stru
 {
 	int err;
 	
-	/* Check we're not trying to overwrite an existing watch */
-	BUG_ON(np->accel_vif_state.accel_watch.node != NULL);
+	/* 
+	 * If old watch exists, e.g. from before suspend/resume,
+	 * remove it now 
+	 */
+	netfront_accelerator_remove_watch(np);
 
 	/* Get a watch on the accelerator plugin */
 	err = xenbus_watch_path2(np->xbdev, np->xbdev->otherend, 
@@ -180,6 +185,19 @@ void netfront_accelerator_add_watch(stru
 }
 
 
+static void 
+netfront_accelerator_purge_watch(struct netfront_accel_vif_state *vif_state)
+{
+	flush_workqueue(accel_watch_workqueue);
+
+	/* Clean up any state left from watch */
+	if (vif_state->accel_frontend != NULL) {
+		kfree(vif_state->accel_frontend);
+		vif_state->accel_frontend = NULL;
+	}
+}
+
+
 static
 void netfront_accelerator_remove_watch(struct netfront_info *np)
 {
@@ -191,13 +209,7 @@ void netfront_accelerator_remove_watch(s
 		kfree(vif_state->accel_watch.node);
 		vif_state->accel_watch.node = NULL;
 
-		flush_workqueue(accel_watch_workqueue);
-
-		/* Clean up any state left from watch */
-		if (vif_state->accel_frontend != NULL) {
-			kfree(vif_state->accel_frontend);
-			vif_state->accel_frontend = NULL;
-		}
+		netfront_accelerator_purge_watch(vif_state);
 	}	
 }
 
@@ -670,8 +682,6 @@ int netfront_accelerator_suspend(struct 
 {
 	int rc = 0;
 	
-	netfront_accelerator_remove_watch(np);
-
 	mutex_lock(&accelerator_mutex);
 
  	/* Check that we've got a device that was accelerated */
@@ -692,13 +702,16 @@ int netfront_accelerator_suspend_cancel(
 int netfront_accelerator_suspend_cancel(struct netfront_info *np,
  					struct xenbus_device *dev)
 {
+	netfront_accelerator_purge_watch(&np->accel_vif_state);
+
 	/* 
-	 * Setting the watch will cause it to fire and probe the
-	 * accelerator, so no need to call accelerator_probe_new_vif()
-	 * directly here
+	 * Gratuitously fire the watch handler to reinstate the
+	 * configured accelerator
 	 */
 	if (dev->state == XenbusStateConnected)
-		netfront_accelerator_add_watch(np);
+		queue_work(accel_watch_workqueue, 
+			   &np->accel_vif_state.accel_work);
+
 	return 0;
 }