virtio-net: set queues after driver_ok

Commit 25266128 ("virtio-net: fix race between set queues and
probe") tries to fix the race between set queues and probe by calling
_virtnet_set_queues() before DRIVER_OK is set. This violates virtio
spec. Fixing this by setting queues after virtio_device_ready().

Note that rtnl needs to be held for userspace requests to change the
number of queues. So we are serialized in this way.

Fixes: 25266128 ("virtio-net: fix race between set queues and probe")
Reported-by: Dragos Tatulea <dtatulea@nvidia.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -4219,8 +4219,6 @@ static int virtnet_probe(struct virtio_device *vdev)
 	if (vi->has_rss || vi->has_rss_hash_report)
 		virtnet_init_default_rss(vi);
 
-	_virtnet_set_queues(vi, vi->curr_queue_pairs);
-
 	/* serialize netdev register + virtio_device_ready() with ndo_open() */
 	rtnl_lock();
 
@@ -4233,6 +4231,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 
 	virtio_device_ready(vdev);
 
+	_virtnet_set_queues(vi, vi->curr_queue_pairs);
+
 	/* a random MAC address has been assigned, notify the device.
 	 * We don't fail probe if VIRTIO_NET_F_CTRL_MAC_ADDR is not there
 	 * because many devices work fine without getting MAC explicitly