4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eduardo Otubo <ot...@redhat.com>


[ Upstream commit 5b5971df3bc2775107ddad164018a8a8db633b81 ]

v2:
 * Replace busy wait with wait_event()/wake_up_all()
 * Cannot garantee that at the time xennet_remove is called, the
   xen_netback state will not be XenbusStateClosed, so added a
   condition for that
 * There's a small chance for the xen_netback state is
   XenbusStateUnknown by the time the xen_netfront switches to Closed,
   so added a condition for that.

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 <ot...@redhat.com>
Acked-by: Juergen Gross <jgr...@suse.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 drivers/net/xen-netfront.c |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -86,6 +86,8 @@ struct netfront_cb {
 /* IRQ name is queue name with "-tx" or "-rx" appended */
 #define IRQ_NAME_SIZE (QUEUE_NAME_SIZE + 3)
 
+static DECLARE_WAIT_QUEUE_HEAD(module_unload_q);
+
 struct netfront_stats {
        u64                     packets;
        u64                     bytes;
@@ -2037,10 +2039,12 @@ static void netback_changed(struct xenbu
                break;
 
        case XenbusStateClosed:
+               wake_up_all(&module_unload_q);
                if (dev->state == XenbusStateClosed)
                        break;
                /* Missed the backend's CLOSING state -- fallthrough */
        case XenbusStateClosing:
+               wake_up_all(&module_unload_q);
                xenbus_frontend_closed(dev);
                break;
        }
@@ -2146,6 +2150,20 @@ static int xennet_remove(struct xenbus_d
 
        dev_dbg(&dev->dev, "%s\n", dev->nodename);
 
+       if (xenbus_read_driver_state(dev->otherend) != XenbusStateClosed) {
+               xenbus_switch_state(dev, XenbusStateClosing);
+               wait_event(module_unload_q,
+                          xenbus_read_driver_state(dev->otherend) ==
+                          XenbusStateClosing);
+
+               xenbus_switch_state(dev, XenbusStateClosed);
+               wait_event(module_unload_q,
+                          xenbus_read_driver_state(dev->otherend) ==
+                          XenbusStateClosed ||
+                          xenbus_read_driver_state(dev->otherend) ==
+                          XenbusStateUnknown);
+       }
+
        xennet_disconnect_backend(info);
 
        unregister_netdev(info->netdev);


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