linux-kernel - Re: [PATCH v2 1/2] thermal: core: Reference count the zone in thermal_zone_get_by

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Message-ID: <b2d949a2-2586-44ec-b0e7-0879fd3ac7cf@arm.com>
Date: Fri, 4 Oct 2024 09:02:30 +0100
From: Lukasz Luba <lukasz.luba@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux PM <linux-pm@...r.kernel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, Zhang Rui <rui.zhang@...el.com>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v2 1/2] thermal: core: Reference count the zone in
 thermal_zone_get_by_id()

Hi Rafael,

On 10/3/24 13:25, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> There are places in the thermal netlink code where nothing prevents
> the thermal zone object from going away while being accessed after it
> has been returned by thermal_zone_get_by_id().
> 
> To address this, make thermal_zone_get_by_id() get a reference on the
> thermal zone device object to be returned with the help of get_device(),
> under thermal_list_lock, and adjust all of its callers to this change
> with the help of the cleanup.h infrastructure.
> 
> Fixes: 1ce50e7d408e ("thermal: core: genetlink support for events/cmd/sampling")
> Cc: 6.8+ <stable@...r.kernel.org> # 6.8+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> v1 -> v2: Use the cleanup.h infrastructure to reduce the amount of code changes.
> 
> ---
>   drivers/thermal/thermal_core.c    |    1 +
>   drivers/thermal/thermal_core.h    |    3 +++
>   drivers/thermal/thermal_netlink.c |    9 +++------
>   3 files changed, 7 insertions(+), 6 deletions(-)
> 
> Index: linux-pm/drivers/thermal/thermal_core.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_core.c
> +++ linux-pm/drivers/thermal/thermal_core.c
> @@ -728,6 +728,7 @@ struct thermal_zone_device *thermal_zone
>   	mutex_lock(&thermal_list_lock);
>   	list_for_each_entry(tz, &thermal_tz_list, node) {
>   		if (tz->id == id) {
> +			get_device(&tz->device);
>   			match = tz;
>   			break;
>   		}
> Index: linux-pm/drivers/thermal/thermal_core.h
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_core.h
> +++ linux-pm/drivers/thermal/thermal_core.h
> @@ -194,6 +194,9 @@ int for_each_thermal_governor(int (*cb)(
>   
>   struct thermal_zone_device *thermal_zone_get_by_id(int id);
>   
> +DEFINE_CLASS(thermal_zone_get_by_id, struct thermal_zone_device *,
> +	     if (_T) put_device(&_T->device), thermal_zone_get_by_id(id), int id)
> +
>   static inline bool cdev_is_power_actor(struct thermal_cooling_device *cdev)
>   {
>   	return cdev->ops->get_requested_power && cdev->ops->state2power &&
> Index: linux-pm/drivers/thermal/thermal_netlink.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_netlink.c
> +++ linux-pm/drivers/thermal/thermal_netlink.c
> @@ -443,7 +443,6 @@ static int thermal_genl_cmd_tz_get_trip(
>   {
>   	struct sk_buff *msg = p->msg;
>   	const struct thermal_trip_desc *td;
> -	struct thermal_zone_device *tz;
>   	struct nlattr *start_trip;
>   	int id;
>   
> @@ -452,7 +451,7 @@ static int thermal_genl_cmd_tz_get_trip(
>   
>   	id = nla_get_u32(p->attrs[THERMAL_GENL_ATTR_TZ_ID]);
>   
> -	tz = thermal_zone_get_by_id(id);
> +	CLASS(thermal_zone_get_by_id, tz)(id);
>   	if (!tz)
>   		return -EINVAL;
>   
> @@ -488,7 +487,6 @@ out_cancel_nest:
>   static int thermal_genl_cmd_tz_get_temp(struct param *p)
>   {
>   	struct sk_buff *msg = p->msg;
> -	struct thermal_zone_device *tz;
>   	int temp, ret, id;
>   
>   	if (!p->attrs[THERMAL_GENL_ATTR_TZ_ID])
> @@ -496,7 +494,7 @@ static int thermal_genl_cmd_tz_get_temp(
>   
>   	id = nla_get_u32(p->attrs[THERMAL_GENL_ATTR_TZ_ID]);
>   
> -	tz = thermal_zone_get_by_id(id);
> +	CLASS(thermal_zone_get_by_id, tz)(id);
>   	if (!tz)
>   		return -EINVAL;
>   
> @@ -514,7 +512,6 @@ static int thermal_genl_cmd_tz_get_temp(
>   static int thermal_genl_cmd_tz_get_gov(struct param *p)
>   {
>   	struct sk_buff *msg = p->msg;
> -	struct thermal_zone_device *tz;
>   	int id, ret = 0;
>   
>   	if (!p->attrs[THERMAL_GENL_ATTR_TZ_ID])
> @@ -522,7 +519,7 @@ static int thermal_genl_cmd_tz_get_gov(s
>   
>   	id = nla_get_u32(p->attrs[THERMAL_GENL_ATTR_TZ_ID]);
>   
> -	tz = thermal_zone_get_by_id(id);
> +	CLASS(thermal_zone_get_by_id, tz)(id);
>   	if (!tz)
>   		return -EINVAL;
>   
> 
> 
> 

I wasn't aware of that helpers in cleanup.h.

Could you help me to understand when this this
'if (_T) put_device((&_T->device)' will be called?

Regards,
Lukasz