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

[Alan Stern]

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

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