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

Rafael J. Wysocki
2010-11-30T22:28:21Z

On Tuesday, November 30, 2010, Alan Stern wrote:
> 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.

I'll do that in a separate 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.

I already have fixed it.

The name is unfortunate indeed, perhaps it's better to call that function
pm_new_wakeup_events() or something like this.

Thanks,
Rafael