Re: [PATCH V5 08/14] PM / Domains: Add function to remove a pm-domain

[Ulf Hansson <ulf.hansson-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On 28 January 2016 at 17:33, Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> wrote:
> The genpd framework allows users to add power-domains via the
> pm_genpd_init() function, however, there is no corresponding function
> to remove a power-domain. For most devices this may be fine as the power
> domains are never removed, however, for devices that wish to populate
> the power-domains from within a driver, having the ability to remove a
> power domain if the probing of the device fails or the driver is unloaded
> is necessary. Therefore, add a function to remove a power-domain. Please
> note that the power domain can only be removed if there are no devices
> using the power-domain and it is not linked to another domain.
>
> Signed-off-by: Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
> ---
>  drivers/base/power/domain.c | 26 ++++++++++++++++++++++++++
>  include/linux/pm_domain.h   |  5 +++++
>  2 files changed, 31 insertions(+)
>
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index 45e3641b427d..b4120121bcac 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -1529,6 +1529,32 @@ void pm_genpd_init(struct generic_pm_domain *genpd,
>  }
>  EXPORT_SYMBOL_GPL(pm_genpd_init);
>
> +/**
> + * pm_genpd_remove - Remove a generic I/O PM domain object.
> + * @genpd: PM domain object to remove.
> + */
> +int pm_genpd_remove(struct generic_pm_domain *genpd)
> +{
> +       if (IS_ERR_OR_NULL(genpd))
> +               return -EINVAL;
> +
> +       mutex_lock(&genpd->lock);

pm_genpd_summary_show() first locks the gpd_list_lock, then the genpd lock.

Please preserve that order here as well, to prevent potential deadlocks.

> +
> +       if (!list_empty(&genpd->master_links)
> +           || !list_empty(&genpd->slave_links) || genpd->device_count) {
> +               mutex_unlock(&genpd->lock);
> +               return -EBUSY;
> +       }
> +
> +       mutex_lock_nested(&gpd_list_lock, SINGLE_DEPTH_NESTING);

Why the nesting, can this really cause lockdep warnings?

> +       list_del(&genpd->gpd_list_node);
> +       mutex_unlock(&gpd_list_lock);
> +       mutex_unlock(&genpd->lock);

Before returning, you need to make sure there isn't a scheduled work
for powering off the genpd.
That might happen for example happen via genpd_poweroff_unused().

Otherwise, the caller of pm_genpd_remove() might free the memory while
the genpd struct is still in use...

I assume a cancel_delayed_work_sync() should do the trick here.

> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(pm_genpd_remove);
> +
>  #ifdef CONFIG_PM_GENERIC_DOMAINS_OF
>  /*
>   * Device Tree based PM domain providers.
> diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
> index db21d3995f7e..0d661998fa74 100644
> --- a/include/linux/pm_domain.h
> +++ b/include/linux/pm_domain.h
> @@ -123,6 +123,7 @@ extern int pm_genpd_remove_subdomain(struct generic_pm_domain *genpd,
>                                      struct generic_pm_domain *target);
>  extern void pm_genpd_init(struct generic_pm_domain *genpd,
>                           struct dev_power_governor *gov, bool is_off);
> +extern int pm_genpd_remove(struct generic_pm_domain *genpd);
>
>  extern struct dev_power_governor simple_qos_governor;
>  extern struct dev_power_governor pm_domain_always_on_gov;
> @@ -161,6 +162,10 @@ static inline void pm_genpd_init(struct generic_pm_domain *genpd,
>                                  struct dev_power_governor *gov, bool is_off)
>  {
>  }
> +static inline int pm_genpd_remove(struct generic_pm_domain *genpd)
> +{
> +       return -ENOTSUPP;
> +}
>  #endif
>
>  static inline int pm_genpd_add_device(struct generic_pm_domain *genpd,
> --
> 2.1.4
>

Kind regards
Uffe