xenbus: rebind irq on restore

When restoring, rebind the existing xenbus irq to the new xenbus event
channel.  (It turns out in practice that this is always the same, and
is never updated on restore.  That's a bug, but Xeno-linux has been
like this for a long time, so it can't really be fixed.)
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

drivers/xen/xenbus/xenbus_comms.c

@@ -203,7 +203,6 @@ int xb_read(void *data, unsigned len)
 int xb_init_comms(void)
 {
 	struct xenstore_domain_interface *intf = xen_store_interface;
-	int err;
 
 	if (intf->req_prod != intf->req_cons)
 		printk(KERN_ERR "XENBUS request ring is not quiescent "
@@ -216,11 +215,12 @@ int xb_init_comms(void)
 		intf->rsp_cons = intf->rsp_prod;
 	}
 
-	if (xenbus_irq)
-		unbind_from_irqhandler(xenbus_irq, &xb_waitq);
-
-	err = bind_evtchn_to_irqhandler(
-		xen_store_evtchn, wake_waiting,
+	if (xenbus_irq) {
+		/* Already have an irq; assume we're resuming */
+		rebind_evtchn_irq(xen_store_evtchn, xenbus_irq);
+	} else {
+		int err;
+		err = bind_evtchn_to_irqhandler(xen_store_evtchn, wake_waiting,
 						0, "xenbus", &xb_waitq);
 		if (err <= 0) {
 			printk(KERN_ERR "XENBUS request irq failed %i\n", err);
@@ -228,6 +228,7 @@ int xb_init_comms(void)
 		}
 
 		xenbus_irq = err;
+	}
 
 	return 0;
 }