thermal: core: Delay exposing sysfs interface

There's a race between initializing the governor and userspace accessing
the sysfs interface. From time to time the Intel graphics CI shows this
signature:

	<1>[] #PF: error_code(0x0000) - not-present page
	<6>[] PGD 0 P4D 0
	<4>[] Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI
	<4>[] CPU: 3 UID: 0 PID: 562 Comm: thermald Not tainted 6.14.0-rc4-CI_DRM_16208-g7e37396f86d8+ #1
	<4>[] Hardware name: Intel Corporation Twin Lake Client Platform/AlderLake-N LP5 RVP, BIOS TWLNFWI1.R00.5222.A01.2405290634 05/29/2024
	<4>[] RIP: 0010:policy_show+0x1a/0x40

thermald tries to read the policy file between the sysfs files being
created and the governor set by thermal_set_governor(), which causes the
NULL pointer dereference.

Similarly to the hwmon interface, delay exposing the sysfs files to when
the governor is already set.

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13655
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
---
The race window is not that big. I could reproduce it and confirm
the fix by doing this:

1) Add a udelay() in thermal_zone_device_register_with_trips
2) A busy loop cat'ing the file

	$ while [ 1 ]; do
		cat /sys/devices/virtual/thermal/thermal_zone0/policy > /dev/null 2>&1
	  done
3) rebind processor_thermal_device_pci
---
 drivers/thermal/thermal_core.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)


---
base-commit: 8aed61b8334e00f4fe5de9f2df1cd183dc328a9d
change-id: 20250307-thermal-sysfs-race-808f6f8376f4

Best regards,

On Sat, Mar 8, 2025 at 2:02 AM Lucas De Marchi <lucas.demarchi@intel.com> wrote:
>
> There's a race between initializing the governor and userspace accessing
> the sysfs interface. From time to time the Intel graphics CI shows this
> signature:
>
>         <1>[] #PF: error_code(0x0000) - not-present page
>         <6>[] PGD 0 P4D 0
>         <4>[] Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI
>         <4>[] CPU: 3 UID: 0 PID: 562 Comm: thermald Not tainted 6.14.0-rc4-CI_DRM_16208-g7e37396f86d8+ #1
>         <4>[] Hardware name: Intel Corporation Twin Lake Client Platform/AlderLake-N LP5 RVP, BIOS TWLNFWI1.R00.5222.A01.2405290634 05/29/2024
>         <4>[] RIP: 0010:policy_show+0x1a/0x40
>
> thermald tries to read the policy file between the sysfs files being
> created and the governor set by thermal_set_governor(), which causes the
> NULL pointer dereference.
>
> Similarly to the hwmon interface, delay exposing the sysfs files to when
> the governor is already set.
>
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13655
> Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
> ---
> The race window is not that big. I could reproduce it and confirm
> the fix by doing this:
>
> 1) Add a udelay() in thermal_zone_device_register_with_trips
> 2) A busy loop cat'ing the file
>
>         $ while [ 1 ]; do
>                 cat /sys/devices/virtual/thermal/thermal_zone0/policy > /dev/null 2>&1
>           done
> 3) rebind processor_thermal_device_pci
> ---
>  drivers/thermal/thermal_core.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> index 2328ac0d8561b..f96ca27109288 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -1589,26 +1589,26 @@ thermal_zone_device_register_with_trips(const char *type,
>
>         tz->state = TZ_STATE_FLAG_INIT;
>
> +       result = dev_set_name(&tz->device, "thermal_zone%d", tz->id);
> +       if (result)
> +               goto remove_id;
> +
> +       thermal_zone_device_init(tz);
> +
> +       result = thermal_zone_init_governor(tz);
> +       if (result)
> +               goto remove_id;
> +
>         /* sys I/F */
>         /* Add nodes that are always present via .groups */
>         result = thermal_zone_create_device_groups(tz);
>         if (result)
>                 goto remove_id;
>
> -       result = dev_set_name(&tz->device, "thermal_zone%d", tz->id);
> -       if (result) {
> -               thermal_zone_destroy_device_groups(tz);
> -               goto remove_id;
> -       }
> -       thermal_zone_device_init(tz);
>         result = device_register(&tz->device);
>         if (result)
>                 goto release_device;
>
> -       result = thermal_zone_init_governor(tz);
> -       if (result)
> -               goto unregister;
> -
>         if (!tz->tzp || !tz->tzp->no_hwmon) {
>                 result = thermal_add_hwmon_sysfs(tz);
>                 if (result)
>
> ---

Applied as 6.15 material, thanks!