Re: [PATCH 08/10] cpufreq: Fix broken usage of governor->owner's refcount

Rafael J. Wysocki
2013-08-03T11:58:07Z

On Saturday, August 03, 2013 05:19:26 PM Viresh Kumar wrote:
> Governor's owner refcount usage was broken. We should increment refcount only
> when CPUFREQ_GOV_POLICY_INIT event has come and should decrement only if
> CPUFREQ_GOV_POLICY_EXIT has come.
>
> Lets fix it.

OK, and what happens if we don't fix it?

Rafael

> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> drivers/cpufreq/cpufreq.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index e9b969f..74d4969 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1707,8 +1707,9 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
> }
> }
>
> - if (!try_module_get(policy->governor->owner))
> - return -EINVAL;
> + if (event == CPUFREQ_GOV_POLICY_INIT)
> + if (!try_module_get(policy->governor->owner))
> + return -EINVAL;
>
> pr_debug("__cpufreq_governor for CPU %u, event %u\n",
> policy->cpu, event);
> @@ -1717,6 +1718,8 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
> if ((!policy->governor_enabled && (event == CPUFREQ_GOV_STOP)) ||
> (policy->governor_enabled && (event == CPUFREQ_GOV_START))) {
> mutex_unlock(&cpufreq_governor_lock);
> + if (event == CPUFREQ_GOV_POLICY_INIT)
> + module_put(policy->governor->owner);
> return -EBUSY;
> }
>
> @@ -1744,11 +1747,8 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
> mutex_unlock(&cpufreq_governor_lock);
> }
>
> - /* we keep one module reference alive for
> - each CPU governed by this CPU */
> - if ((event != CPUFREQ_GOV_START) || ret)
> - module_put(policy->governor->owner);
> - if ((event == CPUFREQ_GOV_STOP) && !ret)
> + if (((event == CPUFREQ_GOV_POLICY_INIT) && ret) ||
> + ((event == CPUFREQ_GOV_POLICY_EXIT) && !ret))
> module_put(policy->governor->owner);
>
> return ret;
>
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.