On Thu, 28 Mar 2019 17:48:45 +0000
Haiyang Zhang [off-list ref] wrote:

+static inline void netvsc_tx_enable(struct netvsc_device *nvscdev,
+				    struct net_device *ndev)
+{
+	nvscdev->tx_disable = false;
+	mb(); /* ensure queue wake up mechanism is on */
+
+	netif_tx_wake_all_queues(ndev);
+}

You don't need a full mb(). virt_wmb() should be sufficient.

Could I suggest an alternative approach.
You don't need to introduce a local tx_disable flag, the only place where a wakeup
could cause problems is after a send_completion was processed during detach state.

Instead, just avoid wakeup in that place.

--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c

@@ -720,6 +720,7 @@ static void netvsc_send_tx_complete(struct net_device *ndev,
                struct netdev_queue *txq = netdev_get_tx_queue(ndev, q_idx);
 
                if (netif_tx_queue_stopped(txq) &&
+                   netif_device_present(ndev) &&
                    (hv_get_avail_to_write_percent(&channel->outbound) >
                     RING_AVAIL_PERCENT_HIWATER || queue_sends < 1)) {
                        netif_tx_wake_queue(txq);