[v1,1/7] powercap/dtpm: Change locking scheme

The different functions are all called through the
dtpm_create_hierarchy() which handle the mutex. The different
functions are used in this context, consequently with the lock always
held.

Remove all locks taken in the function and add the lock in the
hierarchy creation function.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
---
 drivers/powercap/dtpm.c | 95 ++++++++++++-----------------------------
 1 file changed, 27 insertions(+), 68 deletions(-)

On Sun, 30 Jan 2022 at 22:02, Daniel Lezcano <daniel.lezcano@linaro.org> wrote:
>
> The different functions are all called through the
> dtpm_create_hierarchy() which handle the mutex. The different
> functions are used in this context, consequently with the lock always
> held.
>
> Remove all locks taken in the function and add the lock in the
> hierarchy creation function.

I have to admit that the locking scheme looks quite odd in dtpm.c.
It's not really clear to me what the global "dtpm_lock" is there to
protect in the first place (except the global "pct" variable).
Nevertheless, this looks like a step in the right direction.

>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

Kind regards
Uffe


> ---
>  drivers/powercap/dtpm.c | 95 ++++++++++++-----------------------------
>  1 file changed, 27 insertions(+), 68 deletions(-)
>
> diff --git a/drivers/powercap/dtpm.c b/drivers/powercap/dtpm.c
> index 414826a1509b..0b0121c37a1b 100644
> --- a/drivers/powercap/dtpm.c
> +++ b/drivers/powercap/dtpm.c
> @@ -51,9 +51,7 @@ static int get_max_power_range_uw(struct powercap_zone *pcz, u64 *max_power_uw)
>  {
>         struct dtpm *dtpm = to_dtpm(pcz);
>
> -       mutex_lock(&dtpm_lock);
>         *max_power_uw = dtpm->power_max - dtpm->power_min;
> -       mutex_unlock(&dtpm_lock);
>
>         return 0;
>  }
> @@ -83,14 +81,7 @@ static int __get_power_uw(struct dtpm *dtpm, u64 *power_uw)
>
>  static int get_power_uw(struct powercap_zone *pcz, u64 *power_uw)
>  {
> -       struct dtpm *dtpm = to_dtpm(pcz);
> -       int ret;
> -
> -       mutex_lock(&dtpm_lock);
> -       ret = __get_power_uw(dtpm, power_uw);
> -       mutex_unlock(&dtpm_lock);
> -
> -       return ret;
> +       return __get_power_uw(to_dtpm(pcz), power_uw);
>  }
>
>  static void __dtpm_rebalance_weight(struct dtpm *dtpm)
> @@ -133,7 +124,16 @@ static void __dtpm_add_power(struct dtpm *dtpm)
>         }
>  }
>
> -static int __dtpm_update_power(struct dtpm *dtpm)
> +/**
> + * dtpm_update_power - Update the power on the dtpm
> + * @dtpm: a pointer to a dtpm structure to update
> + *
> + * Function to update the power values of the dtpm node specified in
> + * parameter. These new values will be propagated to the tree.
> + *
> + * Return: zero on success, -EINVAL if the values are inconsistent
> + */
> +int dtpm_update_power(struct dtpm *dtpm)
>  {
>         int ret;
>
> @@ -155,26 +155,6 @@ static int __dtpm_update_power(struct dtpm *dtpm)
>         return ret;
>  }
>
> -/**
> - * dtpm_update_power - Update the power on the dtpm
> - * @dtpm: a pointer to a dtpm structure to update
> - *
> - * Function to update the power values of the dtpm node specified in
> - * parameter. These new values will be propagated to the tree.
> - *
> - * Return: zero on success, -EINVAL if the values are inconsistent
> - */
> -int dtpm_update_power(struct dtpm *dtpm)
> -{
> -       int ret;
> -
> -       mutex_lock(&dtpm_lock);
> -       ret = __dtpm_update_power(dtpm);
> -       mutex_unlock(&dtpm_lock);
> -
> -       return ret;
> -}
> -
>  /**
>   * dtpm_release_zone - Cleanup when the node is released
>   * @pcz: a pointer to a powercap_zone structure
> @@ -191,20 +171,14 @@ int dtpm_release_zone(struct powercap_zone *pcz)
>         struct dtpm *dtpm = to_dtpm(pcz);
>         struct dtpm *parent = dtpm->parent;
>
> -       mutex_lock(&dtpm_lock);
> -
> -       if (!list_empty(&dtpm->children)) {
> -               mutex_unlock(&dtpm_lock);
> +       if (!list_empty(&dtpm->children))
>                 return -EBUSY;
> -       }
>
>         if (parent)
>                 list_del(&dtpm->sibling);
>
>         __dtpm_sub_power(dtpm);
>
> -       mutex_unlock(&dtpm_lock);
> -
>         if (dtpm->ops)
>                 dtpm->ops->release(dtpm);
>
> @@ -216,23 +190,12 @@ int dtpm_release_zone(struct powercap_zone *pcz)
>         return 0;
>  }
>
> -static int __get_power_limit_uw(struct dtpm *dtpm, int cid, u64 *power_limit)
> -{
> -       *power_limit = dtpm->power_limit;
> -       return 0;
> -}
> -
>  static int get_power_limit_uw(struct powercap_zone *pcz,
>                               int cid, u64 *power_limit)
>  {
> -       struct dtpm *dtpm = to_dtpm(pcz);
> -       int ret;
> -
> -       mutex_lock(&dtpm_lock);
> -       ret = __get_power_limit_uw(dtpm, cid, power_limit);
> -       mutex_unlock(&dtpm_lock);
> -
> -       return ret;
> +       *power_limit = to_dtpm(pcz)->power_limit;
> +
> +       return 0;
>  }
>
>  /*
> @@ -292,7 +255,7 @@ static int __set_power_limit_uw(struct dtpm *dtpm, int cid, u64 power_limit)
>
>                         ret = __set_power_limit_uw(child, cid, power);
>                         if (!ret)
> -                               ret = __get_power_limit_uw(child, cid, &power);
> +                               ret = get_power_limit_uw(&child->zone, cid, &power);
>
>                         if (ret)
>                                 break;
> @@ -310,8 +273,6 @@ static int set_power_limit_uw(struct powercap_zone *pcz,
>         struct dtpm *dtpm = to_dtpm(pcz);
>         int ret;
>
> -       mutex_lock(&dtpm_lock);
> -
>         /*
>          * Don't allow values outside of the power range previously
>          * set when initializing the power numbers.
> @@ -323,8 +284,6 @@ static int set_power_limit_uw(struct powercap_zone *pcz,
>         pr_debug("%s: power limit: %llu uW, power max: %llu uW\n",
>                  dtpm->zone.name, dtpm->power_limit, dtpm->power_max);
>
> -       mutex_unlock(&dtpm_lock);
> -
>         return ret;
>  }
>
> @@ -335,11 +294,7 @@ static const char *get_constraint_name(struct powercap_zone *pcz, int cid)
>
>  static int get_max_power_uw(struct powercap_zone *pcz, int id, u64 *max_power)
>  {
> -       struct dtpm *dtpm = to_dtpm(pcz);
> -
> -       mutex_lock(&dtpm_lock);
> -       *max_power = dtpm->power_max;
> -       mutex_unlock(&dtpm_lock);
> +       *max_power = to_dtpm(pcz)->power_max;
>
>         return 0;
>  }
> @@ -442,8 +397,6 @@ int dtpm_register(const char *name, struct dtpm *dtpm, struct dtpm *parent)
>         if (IS_ERR(pcz))
>                 return PTR_ERR(pcz);
>
> -       mutex_lock(&dtpm_lock);
> -
>         if (parent) {
>                 list_add_tail(&dtpm->sibling, &parent->children);
>                 dtpm->parent = parent;
> @@ -459,8 +412,6 @@ int dtpm_register(const char *name, struct dtpm *dtpm, struct dtpm *parent)
>         pr_debug("Registered dtpm node '%s' / %llu-%llu uW, \n",
>                  dtpm->zone.name, dtpm->power_min, dtpm->power_max);
>
> -       mutex_unlock(&dtpm_lock);
> -
>         return 0;
>  }
>
> @@ -605,8 +556,12 @@ int dtpm_create_hierarchy(struct of_device_id *dtpm_match_table)
>         struct device_node *np;
>         int i, ret;
>
> -       if (pct)
> -               return -EBUSY;
> +       mutex_lock(&dtpm_lock);
> +
> +       if (pct) {
> +               ret = -EBUSY;
> +               goto out_unlock;
> +       }
>
>         pct = powercap_register_control_type(NULL, "dtpm", NULL);
>         if (IS_ERR(pct)) {
> @@ -648,12 +603,16 @@ int dtpm_create_hierarchy(struct of_device_id *dtpm_match_table)
>                                 dtpm_subsys[i]->name, ret);
>         }
>
> +       mutex_unlock(&dtpm_lock);
> +
>         return 0;
>
>  out_err:
>         powercap_unregister_control_type(pct);
>  out_pct:
>         pct = NULL;
> +out_unlock:
> +       mutex_unlock(&dtpm_lock);
>
>         return ret;
>  }
> --
> 2.25.1
>