[PATCH 4/5] ppc64: make soft_enabled irqs preempt safe

[Paul Mackerras]

Hugh Dickins writes:

> local_irq_restore be careful to access hard_enabled and lppaca before
> setting soft_enabled, which may well permit preemption.  Use local_paca

The reason for testing hard_enabled *after* setting soft_enabled is to
avoid a race.  If we load hard_enabled first, as your patch does, then
an interrupt could come in between that load and the store that sets
soft_enabled, and we would miss that and not hard-enable as we should.

I'm not sure what the solution is.  I suppose we could disable
preemption, although I'd rather something lighter-weight if possible.

Paul.