vdpa_sim_net: complete the initialization before register the device

Initialization must be completed before calling _vdpa_register_device()
since it can connect the device to the vDPA bus, so requests can arrive
after that call.

So for example vdpasim_net_work(), which uses the net->*_stats variables,
can be scheduled before they are initialized.

Let's move _vdpa_register_device() to the end of vdpasim_net_dev_add()
and add a comment to avoid future issues.

Fixes: 0899774c ("vdpa_sim_net: vendor satistics")
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20230329160321.187176-1-sgarzare@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/vdpa/vdpa_sim/vdpa_sim_net.c

@@ -466,16 +466,21 @@ static int vdpasim_net_dev_add(struct vdpa_mgmt_dev *mdev, const char *name,
 
 	vdpasim_net_setup_config(simdev, config);
 
-	ret = _vdpa_register_device(&simdev->vdpa, VDPASIM_NET_VQ_NUM);
-	if (ret)
-		goto reg_err;
-
 	net = sim_to_net(simdev);
 
 	u64_stats_init(&net->tx_stats.syncp);
 	u64_stats_init(&net->rx_stats.syncp);
 	u64_stats_init(&net->cq_stats.syncp);
 
+	/*
+	 * Initialization must be completed before this call, since it can
+	 * connect the device to the vDPA bus, so requests can arrive after
+	 * this call.
+	 */
+	ret = _vdpa_register_device(&simdev->vdpa, VDPASIM_NET_VQ_NUM);
+	if (ret)
+		goto reg_err;
+
 	return 0;
 
 reg_err: