Re: [PATCH 2/3] thermal: core: fix: Initialize the max_state variable to 0

Eduardo Valentin
2014-10-02T22:27:04Z

Hello Lukasz,

On Wed, Sep 24, 2014 at 10:27:11AM +0200, Lukasz Majewski wrote:
> Pointer to the uninitialized max_state variable is passed to get the
> maximal cooling state.
> For CPU cooling device (cpu_cooling.c) the cpufreq_get_max_state() is
> called, which even when error occurs will return the max_state variable
> unchanged.
> Since error for ->get_max_state() is not checked, the automatically

Good that you added a fix in your series for this.

> allocated value of max_state is used for (upper > max_state) comparison.
> For any possible max_state value it is very unlikely that it will be less
> than upper.
> As a consequence, the cooling device is bind even without the backed
> cpufreq table initialized.
>
> This initialization will prevent from accidental binding trip points to
> cpu freq cooling frequencies when cpufreq driver itself is not yet fully
> initialized.

Although I agree with the fix, as long as we also include a check for
the .get_max_state return value, I believe the problem you are
describing is about initialization sequence.

In general, I believe we need a better
sequencing between thermal and cpufreq subsystems. One way out is to
include a check for cpufreq driver in the thermal driver, and return
-EPROBE_DEFER when cpufreq is not ready.

>
> Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
> ---
> drivers/thermal/thermal_core.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> index 454884a..747618a 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -927,7 +927,7 @@ int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
> struct thermal_instance *pos;
> struct thermal_zone_device *pos1;
> struct thermal_cooling_device *pos2;
> - unsigned long max_state;
> + unsigned long max_state = 0;
> int result;
>
> if (trip >= tz->trips || (trip < 0 && trip != THERMAL_TRIPS_NONE))
> --
> 2.0.0.rc2
>