netvsc: uses RCU instead of removal flag

It is cleaner to use RCU protected pointer (nvdev_ctx->nvdev)
to indicate device is in removed state, rather than having a separate
boolean flag. By using the pointer the context can be checked
by static checkers and dynamic lockdep.
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/hyperv_net.h

@@ -708,9 +708,6 @@ struct net_device_context {
 	u32 speed;
 	struct netvsc_ethtool_stats eth_stats;
 
-	/* the device is going away */
-	bool start_remove;
-
 	/* State to manage the associated VF interface. */
 	struct net_device __rcu *vf_netdev;
 

drivers/net/hyperv/netvsc.c

@@ -605,7 +605,6 @@ static void netvsc_send_tx_complete(struct netvsc_device *net_device,
 {
 	struct sk_buff *skb = (struct sk_buff *)(unsigned long)desc->trans_id;
 	struct net_device *ndev = hv_get_drvdata(device);
-	struct net_device_context *net_device_ctx = netdev_priv(ndev);
 	struct vmbus_channel *channel = device->channel;
 	u16 q_idx = 0;
 	int queue_sends;
@@ -639,7 +638,6 @@ static void netvsc_send_tx_complete(struct netvsc_device *net_device,
 		wake_up(&net_device->wait_drain);
 
 	if (netif_tx_queue_stopped(netdev_get_tx_queue(ndev, q_idx)) &&
-	    !net_device_ctx->start_remove &&
 	    (hv_ringbuf_avail_percent(&channel->outbound) > RING_AVAIL_PERCENT_HIWATER ||
 	     queue_sends < 1))
 		netif_tx_wake_queue(netdev_get_tx_queue(ndev, q_idx));
@@ -1326,8 +1324,6 @@ int netvsc_device_add(struct hv_device *device,
 	/* Writing nvdev pointer unlocks netvsc_send(), make sure chn_table is
 	 * populated.
 	 */
-	wmb();
-
 	rcu_assign_pointer(net_device_ctx->nvdev, net_device);
 
 	/* Connect with the NetVsp */

drivers/net/hyperv/netvsc_drv.c

@@ -760,7 +760,7 @@ static int netvsc_set_channels(struct net_device *net,
 	if (count > net->num_tx_queues || count > net->num_rx_queues)
 		return -EINVAL;
 
-	if (net_device_ctx->start_remove || !nvdev || nvdev->destroy)
+	if (!nvdev || nvdev->destroy)
 		return -ENODEV;
 
 	if (nvdev->nvsp_version < NVSP_PROTOCOL_VERSION_5)
@@ -776,7 +776,6 @@ static int netvsc_set_channels(struct net_device *net,
 			return ret;
 	}
 
-	net_device_ctx->start_remove = true;
 	rndis_filter_device_remove(dev, nvdev);
 
 	ret = netvsc_set_queues(net, dev, count);
@@ -785,8 +784,6 @@ static int netvsc_set_channels(struct net_device *net,
 	else
 		netvsc_set_queues(net, dev, nvdev->num_chn);
 
-	net_device_ctx->start_remove = false;
-
 	if (was_running)
 		ret = netvsc_open(net);
 
@@ -860,7 +857,7 @@ static int netvsc_change_mtu(struct net_device *ndev, int mtu)
 	bool was_running;
 	int ret;
 
-	if (ndevctx->start_remove || !nvdev || nvdev->destroy)
+	if (!nvdev || nvdev->destroy)
 		return -ENODEV;
 
 	was_running = netif_running(ndev);
@@ -875,7 +872,6 @@ static int netvsc_change_mtu(struct net_device *ndev, int mtu)
 	device_info.num_chn = nvdev->num_chn;
 	device_info.max_num_vrss_chns = nvdev->num_chn;
 
-	ndevctx->start_remove = true;
 	rndis_filter_device_remove(hdev, nvdev);
 
 	/* 'nvdev' has been freed in rndis_filter_device_remove() ->
@@ -888,8 +884,6 @@ static int netvsc_change_mtu(struct net_device *ndev, int mtu)
 
 	rndis_filter_device_add(hdev, &device_info);
 
-	ndevctx->start_remove = false;
-
 	if (was_running)
 		ret = netvsc_open(ndev);
 
@@ -1245,10 +1239,10 @@ static void netvsc_link_change(struct work_struct *w)
 	unsigned long flags, next_reconfig, delay;
 
 	rtnl_lock();
-	if (ndev_ctx->start_remove)
+	net_device = rtnl_dereference(ndev_ctx->nvdev);
+	if (!net_device)
 		goto out_unlock;
 
-	net_device = rtnl_dereference(ndev_ctx->nvdev);
 	rdev = net_device->extension;
 
 	next_reconfig = ndev_ctx->last_reconfig + LINKCHANGE_INT;
@@ -1509,8 +1503,6 @@ static int netvsc_probe(struct hv_device *dev,
 
 	hv_set_drvdata(dev, net);
 
-	net_device_ctx->start_remove = false;
-
 	INIT_DELAYED_WORK(&net_device_ctx->dwork, netvsc_link_change);
 	INIT_WORK(&net_device_ctx->work, do_set_multicast);
 
@@ -1579,26 +1571,20 @@ static int netvsc_remove(struct hv_device *dev)
 
 	ndev_ctx = netdev_priv(net);
 
-	/* Avoid racing with netvsc_change_mtu()/netvsc_set_channels()
-	 * removing the device.
-	 */
-	rtnl_lock();
-	ndev_ctx->start_remove = true;
-	rtnl_unlock();
+	netif_device_detach(net);
 
 	cancel_delayed_work_sync(&ndev_ctx->dwork);
 	cancel_work_sync(&ndev_ctx->work);
 
-	/* Stop outbound asap */
-	netif_tx_disable(net);
-
-	unregister_netdev(net);
-
 	/*
 	 * Call to the vsc driver to let it know that the device is being
-	 * removed
+	 * removed. Also blocks mtu and channel changes.
 	 */
+	rtnl_lock();
 	rndis_filter_device_remove(dev, ndev_ctx->nvdev);
+	rtnl_unlock();
+
+	unregister_netdev(net);
 
 	hv_set_drvdata(dev, NULL);