[PATCH v2] virtio_net: avoid using netif_tx_disable() for serializing tx routine

[Ake Koomsin <ake@igel.co.jp>]

Commit 713a98d90c5e ("virtio-net: serialize tx routine during reset")
introduces netif_tx_disable() after netif_device_detach() in order to
avoid use-after-free of tx queues. However, there are two issues.

1) Its operation is redundant with netif_device_detach() if the interface
   is running.
2) In case of the interface is not running before suspending and
   resuming, the tx does not get resumed by netif_device_attach().
   This results in losing network connectivity.

It is better to use netif_tx_lock()/netif_tx_unlock() instead for
serializing tx routine during reset. This also preserves the symmetry
of netif_device_detach() and netif_device_attach().

Fixes commit 713a98d90c5e ("virtio-net: serialize tx routine during reset")
Signed-off-by: Ake Koomsin <ake@igel.co.jp>
---
 drivers/net/virtio_net.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 3f5aa59c37b7..41ccf9c994a4 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2267,8 +2267,9 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
 	/* Make sure no work handler is accessing the device */
 	flush_work(&vi->config_work);
 
+	netif_tx_lock(vi->dev);
 	netif_device_detach(vi->dev);
-	netif_tx_disable(vi->dev);
+	netif_tx_unlock(vi->dev);
 	cancel_delayed_work_sync(&vi->refill);
 
 	if (netif_running(vi->dev)) {
@@ -2304,7 +2305,9 @@ static int virtnet_restore_up(struct virtio_device *vdev)
 		}
 	}
 
+	netif_tx_lock(vi->dev);
 	netif_device_attach(vi->dev);
+	netif_tx_unlock(vi->dev);
 	return err;
 }
 
-- 
2.19.1