On Wed, 2015-07-08 at 11:23 +0530, Viresh Kumar wrote:
> When all CPUs of a policy are hot-unplugged, we EXIT the governor but
> don't mark policy->governor as NULL. This was done in order to keep last
> used governor's information intact in sysfs, while the CPUs are offline.
>
> We also missed marking policy->governor as NULL while restoring the
> policy. Because of that, we call __cpufreq_governor(CPUFREQ_GOV_LIMITS)
> for an uninitialized policy. Which eventually returns -EBUSY.
>
> Fix this by setting policy->governor to NULL while restoring the policy.
>
> Reported-by: Pi-Cheng Chen <pi-cheng.c...@linaro.org>
> Reported-by: "Jon Medhurst (Tixy)" <t...@linaro.org>
> Fixes: 18bf3a124ef8 ("cpufreq: Mark policy->governor = NULL for inactive
> policies")
> Signed-off-by: Viresh Kumar <viresh.ku...@linaro.org>
> ---
Tested-by: Jon Medhurst <t...@linaro.org>
Thanks for that.
I believe this also fixes the other issue I mentioned (nullptr deref in
in arm_big_little driver). To test that, after applying this patch, I
modified the code to force __cpufreq_governor to still return an error
when a cpu is hotpluged back in. Now the arm_big_little driver doesn't
get called when I manually poke scaling_setspeed, presumably because
policy->governor==NULL prevents that from reaching the driver?
> For 4.2-rc
>
> drivers/cpufreq/cpufreq.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index b612411655f9..2c22e3902e72 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1132,6 +1132,7 @@ static struct cpufreq_policy
> *cpufreq_policy_restore(unsigned int cpu)
>
> down_write(&policy->rwsem);
> policy->cpu = cpu;
> + policy->governor = NULL;
> up_write(&policy->rwsem);
> }
>
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