Re: [PATCH V2 2/8] PM / OPP: Don't use OPP structure outside of rcu protected section

Stephen Boyd
2016-10-24T22:52:42Z

On 10/20, Viresh Kumar wrote:
> The OPP structure must not be used out of the rcu protected section.
> Cache the values to be used in separate variables instead.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Was this found by visual inspection or through some static
checker? Just curious.

> @@ -633,6 +634,14 @@ int dev_pm_opp_set_rate(struct device *dev, unsigned long target_freq)
> return ret;
> }
>
> + if (IS_ERR(old_opp)) {
> + old_u_volt = 0;
> + } else {
> + old_u_volt = old_opp->u_volt;
> + old_u_volt_min = old_opp->u_volt_min;
> + old_u_volt_max = old_opp->u_volt_max;
> + }
> +
> u_volt = opp->u_volt;
> u_volt_min = opp->u_volt_min;
> u_volt_max = opp->u_volt_max;
> @@ -677,9 +686,10 @@ int dev_pm_opp_set_rate(struct device *dev, unsigned long target_freq)
> __func__, old_freq);
> restore_voltage:
> /* This shouldn't harm even if the voltages weren't updated earlier */
> - if (!IS_ERR(old_opp))
> - _set_opp_voltage(dev, reg, old_opp->u_volt,
> - old_opp->u_volt_min, old_opp->u_volt_max);
> + if (old_u_volt) {

What if old_u_volt == 0 is valid? We could have another variable
like 'valid' or something that we use to figure out if we should
set values instead. Then this isn't a potential pitfall.

> + _set_opp_voltage(dev, reg, old_u_volt, old_u_volt_min,
> + old_u_volt_max);
> + }
>
> return ret;
> }

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