Ingo,
    here 's a patch for 2.6.14-rc4-rt1 that fixes two things:

1) Deregister futex returns -EBUSY instead of -EINVAL if a thread tries 
to deregister a pthread_mutex that another thread has locked.

2)  Make the fast path robust.  If a pthread_mutex is only locked in 
user space we need to clear the owner when
the thread dies.  This makes both the 'rt_mutex is locked in the kernel' 
and the 'pthread_mutex is only locked in user space'
paths robust.

David