linux-kernel - Re: [PATCH v1 4/7] powercap/dtpm: Destroy hierarchy function

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Date:   Wed, 16 Feb 2022 17:31:52 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     rjw@...ysocki.net, heiko@...ech.de, lukasz.luba@....com,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Daniel Lezcano <daniel.lezcano@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v1 4/7] powercap/dtpm: Destroy hierarchy function

On Sun, 30 Jan 2022 at 22:02, Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>
> The hierarchy creation function exits but without a destroy hierarchy
> function. Due to that, the modules creating the hierarchy can not be
> unloaded properly because they don't have an exit callback.
>
> Provide the dtpm_destroy_hierarchy() function to remove the previously
> created hierarchy.
>
> The function relies on all the release mechanisms implemented by the
> underlying powercap framework.
>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
>  drivers/powercap/dtpm.c | 43 +++++++++++++++++++++++++++++++++++++++++
>  include/linux/dtpm.h    |  3 +++
>  2 files changed, 46 insertions(+)
>
> diff --git a/drivers/powercap/dtpm.c b/drivers/powercap/dtpm.c
> index 7bddd25a6767..d9d74f981118 100644
> --- a/drivers/powercap/dtpm.c
> +++ b/drivers/powercap/dtpm.c
> @@ -617,3 +617,46 @@ int dtpm_create_hierarchy(struct of_device_id *dtpm_match_table)
>         return ret;
>  }
>  EXPORT_SYMBOL_GPL(dtpm_create_hierarchy);
> +
> +static void __dtpm_destroy_hierarchy(struct dtpm *dtpm)
> +{
> +       struct dtpm *child, *aux;
> +
> +       list_for_each_entry_safe(child, aux, &dtpm->children, sibling)
> +               __dtpm_destroy_hierarchy(child);
> +
> +       /*
> +        * At this point, we know all children were removed from the
> +        * recursive call before
> +        */
> +       dtpm_unregister(dtpm);
> +}
> +
> +void dtpm_destroy_hierarchy(void)
> +{
> +       int i;
> +
> +       mutex_lock(&dtpm_lock);
> +
> +       if (!pct)

As I kind of indicated in one of the earlier replies, it looks like
dtpm_lock is being used to protect the global "pct". What else?

Rather than doing it like this, couldn't you instead let
dtpm_create_hiearchy() return a handle/cookie for a "dtpm hierarchy".
This handle then needs to be passed to dtpm_destroy_hierarchy().

In this way, the "pct" doesn't need to be protected and you wouldn't
need the global "pct" at all. Although, maybe there would be other
problems with this?

> +               goto out_unlock;
> +
> +       __dtpm_destroy_hierarchy(root);
> +
> +
> +       for (i = 0; i < ARRAY_SIZE(dtpm_subsys); i++) {
> +
> +               if (!dtpm_subsys[i]->exit)
> +                       continue;
> +
> +               dtpm_subsys[i]->exit();
> +       }
> +
> +       powercap_unregister_control_type(pct);
> +
> +       pct = NULL;
> +
> +out_unlock:
> +       mutex_unlock(&dtpm_lock);
> +}
> +EXPORT_SYMBOL_GPL(dtpm_destroy_hierarchy);
> diff --git a/include/linux/dtpm.h b/include/linux/dtpm.h
> index f7a25c70dd4c..a4a13514b730 100644
> --- a/include/linux/dtpm.h
> +++ b/include/linux/dtpm.h
> @@ -37,6 +37,7 @@ struct device_node;
>  struct dtpm_subsys_ops {
>         const char *name;
>         int (*init)(void);
> +       void (*exit)(void);
>         int (*setup)(struct dtpm *, struct device_node *);
>  };
>
> @@ -67,4 +68,6 @@ void dtpm_unregister(struct dtpm *dtpm);
>  int dtpm_register(const char *name, struct dtpm *dtpm, struct dtpm *parent);
>
>  int dtpm_create_hierarchy(struct of_device_id *dtpm_match_table);
> +
> +void dtpm_destroy_hierarchy(void);
>  #endif

Kind regards
Uffe