Re: [RFC][PATCH] PM: Make PM core handle device registrations concurrent with suspend/hibernation

[Alan Stern <stern@rowland.harvard.edu>]

On Thu, 6 Mar 2008, Rafael J. Wysocki wrote:

> On Thursday, 6 of March 2008, Alan Stern wrote:
> > On Thu, 6 Mar 2008, Rafael J. Wysocki wrote:
> > 
> > > > I thought of one more thing you might want to add: device_pm_add() 
> > > > doesn't handle the case where dev->parent is NULL.
> > > 
> > > I'm not sure what you mean.
> > > 
> > > If dev->parent is NULL, we get into the "successful" branch where the device is
> > > added to dpm_active.  Do you think we should add any extra handling of this
> > > case?
> > 
> > If a device is registered after dpm_suspend() has returned, the
> > device won't be suspended properly before the system goes to sleep.  
> > 
> > If the device has a parent then you're okay, because the parent must
> > already be suspended and so device_pm_add() will fail.  But if the
> > device doesn't have a parent then device_pm_add() will succeed, which
> > you don't want.
> 
> Well, can it happen in practice?  If it can, then what way can it happen?

Yes, it can happen in practice when a new module is loaded.  In some 
ways, modules' init routines are like probe methods.

Maybe it can happen some other ways too, but I don't know of any.

> It seems to me that we're discussing purely academic stuff here.  If it turns
> out to be of any practical relevance, it will be trivial to add the handling of
> it in the future.

To be safe, I think we should make system sleep mutually exclusive with 
module loading.

Alan Stern