Hi,

With Nick's help I've figured this one out. There are two problems:

The first is an issue with the UP scheduler locking scheme. That's fixed by
ditching it completely and always using the MP scheme. I have checked that
in on the yamt-idlelwp branch. I think that should be enough to make arm
work when not under load.

The second is an issue with priority inheritance. When releasing a lock that
has waiters, turnstile_wakeup restores inherited priority but it gets the
locking wrong. There's a fix for that on the vmlocking branch - I'll merge
it to yamt-idlelwp (or even HEAD??) tomorrow since I expect that the branch
will be merged soon.

Cheers,
Andrew