virtio/vsock: WARN_ONCE() for invalid state of socket

This adds WARN_ONCE() and return from stream dequeue callback when
socket's queue is empty, but 'rx_bytes' still non-zero. This allows
the detection of potential bugs due to packet merging (see previous
patch).
Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/vmw_vsock/virtio_transport_common.c

@@ -363,6 +363,13 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 	u32 free_space;
 
 	spin_lock_bh(&vvs->rx_lock);
+
+	if (WARN_ONCE(skb_queue_empty(&vvs->rx_queue) && vvs->rx_bytes,
+		      "rx_queue is empty, but rx_bytes is non-zero\n")) {
+		spin_unlock_bh(&vvs->rx_lock);
+		return err;
+	}
+
 	while (total < len && !skb_queue_empty(&vvs->rx_queue)) {
 		skb = skb_peek(&vvs->rx_queue);