linux-kernel - Re: [PATCH v1 1/3] thermal: core: Make thermal_zone_device_unregister() return after freeing the zone

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Date:   Mon, 11 Dec 2023 17:28:40 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Lukasz Luba <lukasz.luba@....com>
Subject: Re: [PATCH v1 1/3] thermal: core: Make
 thermal_zone_device_unregister() return after freeing the zone

On 08/12/2023 20:13, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Make thermal_zone_device_unregister() wait until all of the references
> to the given thermal zone object have been dropped and free it before
> returning.
> 
> This guarantees that when thermal_zone_device_unregister() returns,
> there is no leftover activity regarding the thermal zone in question
> which is required by some of its callers (for instance, modular driver
> code that wants to know when it is safe to let the module go away).
> 
> Subsequently, this will allow some confusing device_is_registered()
> checks to be dropped from the thermal sysfs and core code.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---

Definitively agree on the change

Acked-by: Daniel Lezcano <daniel.lezcano@...aro.org>

Would it make sense to use kref_get/put ?


>   drivers/thermal/thermal_core.c |    6 +++++-
>   include/linux/thermal.h        |    2 ++
>   2 files changed, 7 insertions(+), 1 deletion(-)
> 
> Index: linux-pm/drivers/thermal/thermal_core.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_core.c
> +++ linux-pm/drivers/thermal/thermal_core.c
> @@ -822,7 +822,7 @@ static void thermal_release(struct devic
>   		tz = to_thermal_zone(dev);
>   		thermal_zone_destroy_device_groups(tz);
>   		mutex_destroy(&tz->lock);
> -		kfree(tz);
> +		complete(&tz->removal);
>   	} else if (!strncmp(dev_name(dev), "cooling_device",
>   			    sizeof("cooling_device") - 1)) {
>   		cdev = to_cooling_device(dev);
> @@ -1315,6 +1315,7 @@ thermal_zone_device_register_with_trips(
>   	INIT_LIST_HEAD(&tz->thermal_instances);
>   	ida_init(&tz->ida);
>   	mutex_init(&tz->lock);
> +	init_completion(&tz->removal);
>   	id = ida_alloc(&thermal_tz_ida, GFP_KERNEL);
>   	if (id < 0) {
>   		result = id;
> @@ -1494,6 +1495,9 @@ void thermal_zone_device_unregister(stru
>   	put_device(&tz->device);
>   
>   	thermal_notify_tz_delete(tz_id);
> +
> +	wait_for_completion(&tz->removal);
> +	kfree(tz);
>   }
>   EXPORT_SYMBOL_GPL(thermal_zone_device_unregister);
>   
> Index: linux-pm/include/linux/thermal.h
> ===================================================================
> --- linux-pm.orig/include/linux/thermal.h
> +++ linux-pm/include/linux/thermal.h
> @@ -117,6 +117,7 @@ struct thermal_cooling_device {
>    * @id:		unique id number for each thermal zone
>    * @type:	the thermal zone device type
>    * @device:	&struct device for this thermal zone
> + * @removal:	removal completion
>    * @trip_temp_attrs:	attributes for trip points for sysfs: trip temperature
>    * @trip_type_attrs:	attributes for trip points for sysfs: trip type
>    * @trip_hyst_attrs:	attributes for trip points for sysfs: trip hysteresis
> @@ -156,6 +157,7 @@ struct thermal_zone_device {
>   	int id;
>   	char type[THERMAL_NAME_LENGTH];
>   	struct device device;
> +	struct completion removal;
>   	struct attribute_group trips_attribute_group;
>   	struct thermal_attr *trip_temp_attrs;
>   	struct thermal_attr *trip_type_attrs;
> 
> 
> 

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