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

[Ulf Hansson]

On Sun, 30 Jan 2022 at 22:02, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx> 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@xxxxxxxxxx>

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

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
>