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SubjectRe: [RFC PATCH 13/19] cpufreq: fix locking of policy->rwsem in cpufreq_offline_prepare
On 11-01-16, 17:35, Juri Lelli wrote:
> There are paths in cpufreq_offline_prepare where policy is used, but its
> rwsem is not held.
>
> Fix it.
>
> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> Signed-off-by: Juri Lelli <juri.lelli@arm.com>
> ---
> drivers/cpufreq/cpufreq.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)

I know the locking in general in cpufreq core is poor. We recently
fixed lots of issues in governors ..

> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 2c7cc6c73..91158b0 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1332,13 +1332,13 @@ static void cpufreq_offline_prepare(unsigned int cpu)
> return;
> }
>
> + down_write(&policy->rwsem);
> if (has_target()) {
> int ret = __cpufreq_governor(policy, CPUFREQ_GOV_STOP);
> if (ret)
> pr_err("%s: Failed to stop governor\n", __func__);
> }
>
> - down_write(&policy->rwsem);
> cpumask_clear_cpu(cpu, policy->cpus);
>
> if (policy_is_inactive(policy)) {
> @@ -1356,12 +1356,16 @@ static void cpufreq_offline_prepare(unsigned int cpu)
> /* Start governor again for active policy */
> if (!policy_is_inactive(policy)) {

Why shouldn't this be under the lock?

> if (has_target()) {
> - int ret = __cpufreq_governor(policy, CPUFREQ_GOV_START);
> + int ret;
> +
> + down_write(&policy->rwsem);
> + ret = __cpufreq_governor(policy, CPUFREQ_GOV_START);
> if (!ret)
> ret = __cpufreq_governor(policy, CPUFREQ_GOV_LIMITS);
>
> if (ret)
> pr_err("%s: Failed to start governor\n", __func__);
> + up_write(&policy->rwsem);
> }
> } else if (cpufreq_driver->stop_cpu) {
> cpufreq_driver->stop_cpu(policy);

And this ?

--
viresh

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