[issue727] unloading sound driver panics box

[Matthew Dillon]

:I agree, however we definitely want to avoid the interrupt thread blockin=
:g when grabbing the lock, because this will stall all interrupt processin=
:g on this IRQ.  Spinlocks worked very well since the first import of the =
:updated sound code, so we should keep them for this release.  We can stil=
:l find something better after the release.
:
:cheers
:  simon

    Interrupt threads have a higher priority then anything else.  The
    moment the lock is released the thread will run.  We don't
    do priority inheritence so it isn't perfect, but we also do not
    do preemptive scheduling between non-interrupt threads when a thread
    is in the kernel so it doesn't matter (the non-interrupt thread holding
    a sound lock will not be switched away).

						-Matt