A fix for a locking bug which is triggered when a client tries to lock with

    flag DMA_QUIESCENT (typically the X server), but gets interrupted by a
    signal. The locking IOCTL should then return an error, but if
    DMA_QUIESCENT succeeds it returns 0, and the client falsely thinks it
    has the lock. In addition The client waits for DMA_QUISCENT and
    possibly DMA_READY without having the lock.