Re: [PATCH] PM: Acquire device locks on suspend

Rafael J. Wysocki
2008-01-10T16:56:42Z

On Thursday, 10 of January 2008, Alan Stern wrote:
> On Thu, 10 Jan 2008, Rafael J. Wysocki wrote:
>
> > On Wednesday, 9 of January 2008, Alan Stern wrote:
> > > On Wed, 9 Jan 2008, Rafael J. Wysocki wrote:
> > >
> > > > > In dpm_resume() you shouldn't need to use dpm_list_mtx at all, because
> > > > > the list_move_tail() comes before the resume_device(). It's the same
> > > > > as in dpm_power_up().
> > > >
> > > > Still, device_pm_schedule_removal() can (in theory) be called concurrently
> > > > with dpm_resume() by another thread and this might corrupt the list without
> > > > the locking.
> > >
> > > Any thread doing that would be in violation of the restrictions you're
> > > going to add to the kerneldoc for destroy_suspended_device().
> > >
> > > However the overhead for the locking isn't critical. There won't be
> > > any contention (if everything is working right) and it isn't a hot path
> > > anyway. So you can leave the extra locking in if you want. But then
> > > you should put it in all the routines where the lists get manipulated,
> > > not just some of them. That is: device_power_down(), dpm_power_up(),
> > > and even unregister_dropped_devices().
> >
> > Except for those run on one CPU with interrupts disabled, I think.
>
> Not unregister_dropped_devices()!

Sure, it will need locking around the check in while().

> > > > > Also, the kerneldoc for destroy_suspended_device() should contain an
> > > > > extra paragraph warning that the routine should never be called except
> > > > > within the scope of a system sleep transition. In practice this means
> > > > > it has to be directly or indirectly invoked by a suspend or resume
> > > > > method.
> > > >
> > > > Or by a CPU hotplug notifier (that will be the majority of cases, IMO).
> > >
> > > In your patch the call is made in response to a CPU_UP_CANCELED_FROZEN
> > > notification. Isn't it true that this notification is issued only as
> > > part of a system sleep transition?
> >
> > Yes, it is.
>
> So it counts as being indirectly invoked by a resume method.

Rather, by the resume core. Technically, it's invoked by
enable_nonboot_cpus(), which is not a resume method literally.

Greetings,
Rafael