Re: [PATCH] PM: Prevent dpm_prepare() from returning errors unnecessarily

Alan Stern
2010-11-30T15:13:45Z

On Mon, 29 Nov 2010, Rafael J. Wysocki wrote:

> > Oh, I see. This is a tricky issue. Every driver for a device that can
> > have wakeup-enabled children needs to worry about the race between
> > suspending the device and receiving a wakeup request from a child.
> > For example, in drivers/usb/core/hcd-pci.c, the suspend_common()
> > routine goes out of its way to return -EBUSY if device_may_wakeup() is
> > true and the controller's root hub has a pending wakeup request.
> >
> > How should drivers handle this in general? Should we make an effort to
> > convert them to use the wakeup framework so they they can let the PM
> > core take care of these races?
>
> I think so.
>
> We also need to put a pm_check_wakeup_events() check into dpm_suspend() IMO,
> so that we abort the suspending of devices as soon as a wakeup event is
> reported.

You might as well add that into this patch.

> > Do we have to consider similar races during runtime suspend?
>
> Ideally, yes, but I'm not sure if that's generally possible. IMO, it won't be
> a big deal if a parent device is suspended and immediately resumed occasionally
> due to a pending wakeup signal from one of its children. It may be a problem
> if that happens too often, though.

Okay.

> Does it mean you're fine with the patch?

Provided you repair the error that Lei Ming pointed out. That's the
problem with functions that return Boolean values -- you have to name
them very carefully. Ideally the name should be a predicate or a
question.

Alan Stern