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SubjectRe: [PATCH] PM: Acquire device locks on suspend
Date
On Saturday, 5 of January 2008, Alan Stern wrote:
> On Sat, 5 Jan 2008, Rafael J. Wysocki wrote:
>
> > Greg, Andrew,
> >
> > The appended patch is a replacement for
> > gregkh-driver-pm-acquire-device-locks-prior-to-suspending.patch that deadlocked
> > suspend and hibernation on some systems.
> >
> > Please consider for applying.
>
> This warning message:
>
> > @@ -905,6 +915,13 @@ void device_del(struct device * dev)
> > struct device * parent = dev->parent;
> > struct class_interface *class_intf;
> >
> > + if (pm_sleep_lock()) {
> > + dev_warn(dev, "Illegal %s during suspend\n", __FUNCTION__);
> > + dump_stack();
> > + } else {
>
> will unavoidably be triggered by this code:

Ah, my fault, sorry.

> > +void device_pm_destroy_suspended(struct device *dev)
> > +{
> > + pr_debug("PM: Removing suspended device %s:%s\n",
> > + dev->bus ? dev->bus->name : "No Bus",
> > + kobject_name(&dev->kobj));
> > + mutex_lock(&dpm_list_mtx);
> > + list_del_init(&dev->power.entry);
> > + mutex_unlock(&dpm_list_mtx);
> > + up(&dev->sem);
> > + device_unregister(dev);
> > +}
>
> since the call to device_del() will occur while the pm_sleep_rwsem is
> still locked for writing. That's why I suggested not unregistering
> these devices until after everything else has been resumed and the
> rwsem has been dropped.

Hmm, well. I'll go back to the previous version, then. Sorry for the mess.

> Another thing to watch out for: Just in case somebody ends up calling
> destroy_suspended_device(dev) from within dev's own resume method, you
> should interchange the resume_device() and the list_move_tail()
> calls in dpm_resume().

However, if we unregister them all at once after releasing pm_sleep_rwsem,
that shouldn't be necessary, right?

Rafael


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