I've been debugging some problems with interrupts and vt switch on
i9xx, I suppose suspend/resume might be affected as well..

The X DRI code reference counts the lock nesting, so two locks requires
two unlocks, this is needed to make sure we can lock for LeaveVT, on top
of the wakeup handler lock and not lose the lock,

However on VT switch the driver calls the i830DRILock which doesn't actually
call DRILock as it checks the LockHeld variable.

I'm not sure what the correct fix is, I've made my tree call DRILock and
DRIUnlock directly on LeaveVT and EnterVT respectively.... and it seems to fix
the problem for me..