From a3225d111334c4b7bfb754f942a39a65e989b6e1 Mon Sep 17 00:00:00 2001
From: Eduardo Otubo <otubo@redhat.com>
Date: Thu, 23 Nov 2017 15:18:35 +0100
Subject: [PATCH 05/11] xen-netfront: remove warning when unloading module
Patch-mainline: v4.15-rc2
Git-commit: 5b5971df3bc2775107ddad164018a8a8db633b81
References: git-fixes

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 <otubo@redhat.com>
Acked-by: Juergen Gross <jgross@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Denis Kirjanov <denis.kirjanov@suse.com>
---
 drivers/net/xen-netfront.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 155d26f5a4aa..d18f9700d735 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -91,6 +91,8 @@ 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;
@@ -2208,10 +2210,12 @@ static void netback_changed(struct xenbus_device *dev,
 		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;
 	}
@@ -2317,6 +2321,20 @@ static int xennet_remove(struct xenbus_device *dev)
 
 	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);
-- 
2.16.4