On Sun, 8 May 2011, Rafael J. Wysocki wrote:

> From: Rafael J. Wysocki <rjw@sisk.pl>
> 
> Make generic power domains support system-wide power transitions
> (system suspend and hibernation).  Add suspend, resume, freeze and
> thaw callbacks to be associated with struct generic_power_domain
> objects and make pm_genpd_init() use them as appropriate.

...

> Index: linux-2.6/drivers/base/power/domain.c
> ===================================================================
> --- linux-2.6.orig/drivers/base/power/domain.c
> +++ linux-2.6/drivers/base/power/domain.c
> @@ -273,6 +273,280 @@ static int pm_genpd_runtime_resume(struc
> 
>  #endif /* CONFIG_PM_RUNTIME */
> 
> +#ifdef CONFIG_PM_SLEEP
> +
> +/**
> + * pm_genpd_powered_down - Check if power has been removed from a power domain.
> + * @genpd: Power domain to check.
> + */
> +static bool pm_genpd_powered_down(struct generic_power_domain *genpd)
> +{
> +	bool ret;
> +
> +	mutex_lock(&genpd->lock);
> +	ret = genpd->power_is_off;
> +	mutex_unlock(&genpd->lock);
> +
> +	return ret;
> +}

What is the purpose of the mutex?  On the face of it, there's nothing 
to prevent another thread from changing the domain's power state in 
between the mutex_unlock() call and the return statement.

Alan Stern