hv_netvsc: Fix unwanted wakeup after tx_disable

After queue stopped, the wakeup mechanism may wake it up again
when ring buffer usage is lower than a threshold. This may cause
send path panic on NULL pointer when we stopped all tx queues in
netvsc_detach and start removing the netvsc device.

This patch fix it by adding a tx_disable flag to prevent unwanted
queue wakeup.

Fixes: 7b2ee50c ("hv_netvsc: common detach logic")
Reported-by: Mohammed Gamal <mgamal@redhat.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/hyperv_net.h

@@ -987,6 +987,7 @@ struct netvsc_device {
 
 	wait_queue_head_t wait_drain;
 	bool destroy;
+	bool tx_disable; /* if true, do not wake up queue again */
 
 	/* Receive buffer allocated by us but manages by NetVSP */
 	void *recv_buf;

drivers/net/hyperv/netvsc.c

@@ -110,6 +110,7 @@ static struct netvsc_device *alloc_net_device(void)
 
 	init_waitqueue_head(&net_device->wait_drain);
 	net_device->destroy = false;
+	net_device->tx_disable = false;
 
 	net_device->max_pkt = RNDIS_MAX_PKT_DEFAULT;
 	net_device->pkt_align = RNDIS_PKT_ALIGN_DEFAULT;
@@ -719,7 +720,7 @@ static void netvsc_send_tx_complete(struct net_device *ndev,
 	} else {
 		struct netdev_queue *txq = netdev_get_tx_queue(ndev, q_idx);
 
-		if (netif_tx_queue_stopped(txq) &&
+		if (netif_tx_queue_stopped(txq) && !net_device->tx_disable &&
 		    (hv_get_avail_to_write_percent(&channel->outbound) >
 		     RING_AVAIL_PERCENT_HIWATER || queue_sends < 1)) {
 			netif_tx_wake_queue(txq);
@@ -874,7 +875,8 @@ static inline int netvsc_send_pkt(
 	} else if (ret == -EAGAIN) {
 		netif_tx_stop_queue(txq);
 		ndev_ctx->eth_stats.stop_queue++;
-		if (atomic_read(&nvchan->queue_sends) < 1) {
+		if (atomic_read(&nvchan->queue_sends) < 1 &&
+		    !net_device->tx_disable) {
 			netif_tx_wake_queue(txq);
 			ndev_ctx->eth_stats.wake_queue++;
 			ret = -ENOSPC;

drivers/net/hyperv/netvsc_drv.c

@@ -109,6 +109,15 @@ static void netvsc_set_rx_mode(struct net_device *net)
 	rcu_read_unlock();
 }
 
+static void netvsc_tx_enable(struct netvsc_device *nvscdev,
+			     struct net_device *ndev)
+{
+	nvscdev->tx_disable = false;
+	virt_wmb(); /* ensure queue wake up mechanism is on */
+
+	netif_tx_wake_all_queues(ndev);
+}
+
 static int netvsc_open(struct net_device *net)
 {
 	struct net_device_context *ndev_ctx = netdev_priv(net);
@@ -129,7 +138,7 @@ static int netvsc_open(struct net_device *net)
 	rdev = nvdev->extension;
 	if (!rdev->link_state) {
 		netif_carrier_on(net);
-		netif_tx_wake_all_queues(net);
+		netvsc_tx_enable(nvdev, net);
 	}
 
 	if (vf_netdev) {
@@ -184,6 +193,17 @@ static int netvsc_wait_until_empty(struct netvsc_device *nvdev)
 	}
 }
 
+static void netvsc_tx_disable(struct netvsc_device *nvscdev,
+			      struct net_device *ndev)
+{
+	if (nvscdev) {
+		nvscdev->tx_disable = true;
+		virt_wmb(); /* ensure txq will not wake up after stop */
+	}
+
+	netif_tx_disable(ndev);
+}
+
 static int netvsc_close(struct net_device *net)
 {
 	struct net_device_context *net_device_ctx = netdev_priv(net);
@@ -192,7 +212,7 @@ static int netvsc_close(struct net_device *net)
 	struct netvsc_device *nvdev = rtnl_dereference(net_device_ctx->nvdev);
 	int ret;
 
-	netif_tx_disable(net);
+	netvsc_tx_disable(nvdev, net);
 
 	/* No need to close rndis filter if it is removed already */
 	if (!nvdev)
@@ -920,7 +940,7 @@ static int netvsc_detach(struct net_device *ndev,
 
 	/* If device was up (receiving) then shutdown */
 	if (netif_running(ndev)) {
-		netif_tx_disable(ndev);
+		netvsc_tx_disable(nvdev, ndev);
 
 		ret = rndis_filter_close(nvdev);
 		if (ret) {
@@ -1908,7 +1928,7 @@ static void netvsc_link_change(struct work_struct *w)
 		if (rdev->link_state) {
 			rdev->link_state = false;
 			netif_carrier_on(net);
-			netif_tx_wake_all_queues(net);
+			netvsc_tx_enable(net_device, net);
 		} else {
 			notify = true;
 		}
@@ -1918,7 +1938,7 @@ static void netvsc_link_change(struct work_struct *w)
 		if (!rdev->link_state) {
 			rdev->link_state = true;
 			netif_carrier_off(net);
-			netif_tx_stop_all_queues(net);
+			netvsc_tx_disable(net_device, net);
 		}
 		kfree(event);
 		break;
@@ -1927,7 +1947,7 @@ static void netvsc_link_change(struct work_struct *w)
 		if (!rdev->link_state) {
 			rdev->link_state = true;
 			netif_carrier_off(net);
-			netif_tx_stop_all_queues(net);
+			netvsc_tx_disable(net_device, net);
 			event->event = RNDIS_STATUS_MEDIA_CONNECT;
 			spin_lock_irqsave(&ndev_ctx->lock, flags);
 			list_add(&event->list, &ndev_ctx->reconfig_events);