Stanse found a locking problem in vhost_set_vring:
several returns from VHOST_SET_VRING_KICK, VHOST_SET_VRING_CALL,
VHOST_SET_VRING_ERR with the vq->mutex held.
Fix these up.
Reported-by: NJiri Slaby <jirislaby@gmail.com>
Acked-by: NLaurent Chavey <chavey@google.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>