On 23-11-17, 01:29, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
>
> It is possible to remove a cpufreq governor module after
> cpufreq_parse_governor() has returned success in
> store_scaling_governor() and before cpufreq_set_policy()
> acquires a reference to it, because the governor list is
> not protected during that period and nothing prevents the
> governor from being unregistered then. The pointer to the
> governor structure coming from cpufreq_parse_governor() may
> become stale as a result of that.
>
> Prevent that from happening by acquiring an extra reference
> to the governor module temporarily in cpufreq_parse_governor(),
> under cpufreq_governor_mutex, and dropping it in
> store_scaling_governor(), when cpufreq_set_policy() returns.
>
> Note that the second cpufreq_parse_governor() call site is fine,
> because it only cares about the policy member of new_policy.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
> ---
> drivers/cpufreq/cpufreq.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> Index: linux-pm/drivers/cpufreq/cpufreq.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/cpufreq.c
> +++ linux-pm/drivers/cpufreq/cpufreq.c
> @@ -607,11 +607,13 @@ static int cpufreq_parse_governor(char *
> if (cpufreq_driver->setpolicy) {
> if (!strncasecmp(str_governor, "performance",
> CPUFREQ_NAME_LEN)) {
> policy->policy = CPUFREQ_POLICY_PERFORMANCE;
> + policy->governor = NULL;
> return 0;
> }
>
> if (!strncasecmp(str_governor, "powersave", CPUFREQ_NAME_LEN)) {
> policy->policy = CPUFREQ_POLICY_POWERSAVE;
> + policy->governor = NULL;
Why are the above two changes required? policy->governor should always be NULL
for setpolicy drivers anyway.
--
viresh
