Re: [PATCH 1/8] PM: Add suspend block api.

Alan Stern
2010-05-06T19:40:48Z

On Thu, 6 May 2010, Rafael J. Wysocki wrote:

> > Here's a completely new issue. When using opportunistic suspends on an
> > SMP system, it could happen that the system gets a wakeup event and
> > this routine starts running again before the event's IRQ handler has
> > finished (or has enabled a suspend blocker). The system would
> > re-suspend too soon.
>
> This routine will be run from a freezable workqueue.

But how do you know that processes won't get unfrozen until all the
pending IRQs have been handled? Imagine something like this:

CPU 0 CPU 1
----- -----
Wake up non-boot CPUs
Resume devices Invoke the IRQ handler

[ CPU 0 should wait here for the handler to finish,
but it doesn't ]

Defrost threads Handler running...
Workqueue routine runs
Start another suspend
Handler enables a suspend blocker,
but it's too late

Alan Stern