Re: [PATCH v2 1/2] thermal: core: Reference count the zone in thermal_zone_get_by_id()

[Lukasz Luba <lukasz.luba@arm.com>]

On 10/4/24 14:25, Rafael J. Wysocki wrote:
> Hi Łukasz,
> 
> On Fri, Oct 4, 2024 at 10:01 AM Lukasz Luba <lukasz.luba@arm.com> wrote:
>>
>> Hi Rafael,
>>
>> On 10/3/24 13:25, Rafael J. Wysocki wrote:
>>> From: Rafael J. Wysocki <rafael.j.wysocki@intel.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@vger.kernel.org> # 6.8+
>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.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?
> 
> When the pointer variable initialized via the CLASS() macro goes out
> of scope (that is, before freeing the memory occupied by the pointer
> itself).


OK, so do we still need the old code in
thermal_zone_device_unregister(), which calls
put_device(&tz->device) ?
Maybe that code can go away?