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

Alan Stern
2008-01-05T20:08:48Z

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:

> +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.

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().

Alan Stern