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

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Message-ID: <CAJZ5v0g494bUwLbFDF_WHwLSMbu1iTxiynNwDqKktv3-4049Sw@mail.gmail.com>
Date: Fri, 4 Oct 2024 15:25:19 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Lukasz Luba <lukasz.luba@....com>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>, 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 Łukasz,

On Fri, Oct 4, 2024 at 10:01 AM Lukasz Luba <lukasz.luba@....com> wrote:
>
> 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?

When the pointer variable initialized via the CLASS() macro goes out
of scope (that is, before freeing the memory occupied by the pointer
itself).