[PATCH V3] cpufreq: Warn users while freeing active policy

[PATCH V3] cpufreq: Warn users while freeing active policy

[Viresh Kumar]

With the new design in place, the show() and store() callbacks check if
the policy is active or not before proceeding any further to avoid
potential races. And in order to guarantee that cpufreq_policy_free()
must be called after clearing the policy->cpus mask, i.e. by marking the
policy inactive.

In order to avoid introducing a bug around this later, print a warning
message if we end up freeing an active policy.

Also update cpufreq_online() a bit to make sure we clear the cpus mask
for each error case before calling cpufreq_policy_free().

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
V3: BUG_ON() -> pr_warn()

 drivers/cpufreq/cpufreq.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 73432360e6e9..954eef26685f 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1273,6 +1273,13 @@ static void cpufreq_policy_free(struct cpufreq_policy *policy)
 	unsigned long flags;
 	int cpu;
 
+	/*
+	 * The callers must ensure the policy is inactive by now, to avoid any
+	 * races with show()/store() callbacks.
+	 */
+	if (unlikely(!policy_is_inactive(policy)))
+		pr_warn("%s: Freeing active policy\n", __func__);
+
 	/* Remove policy from list */
 	write_lock_irqsave(&cpufreq_driver_lock, flags);
 	list_del(&policy->policy_list);
@@ -1527,8 +1534,6 @@ static int cpufreq_online(unsigned int cpu)
 	for_each_cpu(j, policy->real_cpus)
 		remove_cpu_dev_symlink(policy, j, get_cpu_device(j));
 
-	cpumask_clear(policy->cpus);
-
 out_offline_policy:
 	if (cpufreq_driver->offline)
 		cpufreq_driver->offline(policy);
@@ -1538,6 +1543,7 @@ static int cpufreq_online(unsigned int cpu)
 		cpufreq_driver->exit(policy);
 
 out_free_policy:
+	cpumask_clear(policy->cpus);
 	up_write(&policy->rwsem);
 
 	cpufreq_policy_free(policy);
-- 
2.31.1.272.g89b43f80a514

Re: [PATCH V3] cpufreq: Warn users while freeing active policy

[Rafael J. Wysocki]

On Thu, Jul 7, 2022 at 11:58 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> With the new design in place, the show() and store() callbacks check if
> the policy is active or not before proceeding any further to avoid
> potential races. And in order to guarantee that cpufreq_policy_free()
> must be called after clearing the policy->cpus mask, i.e. by marking the
> policy inactive.
>
> In order to avoid introducing a bug around this later, print a warning
> message if we end up freeing an active policy.
>
> Also update cpufreq_online() a bit to make sure we clear the cpus mask
> for each error case before calling cpufreq_policy_free().
>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> V3: BUG_ON() -> pr_warn()
>
>  drivers/cpufreq/cpufreq.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 73432360e6e9..954eef26685f 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1273,6 +1273,13 @@ static void cpufreq_policy_free(struct cpufreq_policy *policy)
>         unsigned long flags;
>         int cpu;
>
> +       /*
> +        * The callers must ensure the policy is inactive by now, to avoid any
> +        * races with show()/store() callbacks.
> +        */
> +       if (unlikely(!policy_is_inactive(policy)))
> +               pr_warn("%s: Freeing active policy\n", __func__);
> +
>         /* Remove policy from list */
>         write_lock_irqsave(&cpufreq_driver_lock, flags);
>         list_del(&policy->policy_list);
> @@ -1527,8 +1534,6 @@ static int cpufreq_online(unsigned int cpu)
>         for_each_cpu(j, policy->real_cpus)
>                 remove_cpu_dev_symlink(policy, j, get_cpu_device(j));
>
> -       cpumask_clear(policy->cpus);
> -
>  out_offline_policy:
>         if (cpufreq_driver->offline)
>                 cpufreq_driver->offline(policy);
> @@ -1538,6 +1543,7 @@ static int cpufreq_online(unsigned int cpu)
>                 cpufreq_driver->exit(policy);
>
>  out_free_policy:
> +       cpumask_clear(policy->cpus);
>         up_write(&policy->rwsem);
>
>         cpufreq_policy_free(policy);
> --

Applied as 5.20 material, thanks!