[PATCH] xen-netfront: remove warning when unloading module

[Eduardo Otubo <otubo@redhat.com>]

When unloading module xen_netfront from guest, dmesg would output
warning messages like below:

  [  105.236836] xen:grant_table: WARNING: g.e. 0x903 still in use!
  [  105.236839] deferring g.e. 0x903 (pfn 0x35805)

This problem relies on netfront and netback being out of sync. By the time
netfront revokes the g.e.'s netback didn't have enough time to free all of
them, hence displaying the warnings on dmesg.

The trick here is to make netfront to wait until netback frees all the g.e.'s
and only then continue to cleanup for the module removal, and this is done by
manipulating both device states.

Signed-off-by: Eduardo Otubo <otubo@redhat.com>
---
 drivers/net/xen-netfront.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 8b8689c6d887..b948e2a1ce40 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -2130,6 +2130,17 @@ static int xennet_remove(struct xenbus_device *dev)
 
 	dev_dbg(&dev->dev, "%s\n", dev->nodename);
 
+	xenbus_switch_state(dev, XenbusStateClosing);
+	while (xenbus_read_driver_state(dev->otherend) != XenbusStateClosing){
+		cpu_relax();
+		schedule();
+	}
+	xenbus_switch_state(dev, XenbusStateClosed);
+	while (dev->xenbus_state != XenbusStateClosed){
+		cpu_relax();
+		schedule();
+	}
+
 	xennet_disconnect_backend(info);
 
 	unregister_netdev(info->netdev);
-- 
2.13.6