On Tue, Apr 12, 2016 at 05:37:54PM +0100, Ian Campbell wrote:

Perhaps the guest end is turning shutdown(foo) directly into a vsock
message without or-ing in the current state?

Yes, you are right:

  lock_sock(sk);
  sk->sk_shutdown |= mode;
  sk->sk_state_change(sk);
  release_sock(sk);

  if (sk->sk_type == SOCK_STREAM) {
      sock_reset_flag(sk, SOCK_DONE);
      vsock_send_shutdown(sk, mode);

Although sk_shutdown is ORed correctly, vsock_send_shutdown() is called with
just the shutdown() argument.