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

[Rafael J. Wysocki]

On Fri, Oct 4, 2024 at 3:25 PM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
>
> Hi Łukasz,
>
> On Fri, Oct 4, 2024 at 10:01 AM Lukasz Luba <lukasz.luba@xxxxxxx> wrote:
> >
> > Hi Rafael,
> >
> > On 10/3/24 13:25, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > >
> > > 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@xxxxxxxxxxxxxxx> # 6.8+
> > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > > ---
> > >
> > > 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).

Note that DEFINE_GUARD() is based on DEFINE_CLASS() and the guard()
macro is based on the CLASS() one, so it's basically the same
mechanism.