On Tue, Feb 9, 2016 at 4:46 AM, Viresh Kumar viresh.kumar@linaro.org wrote:
This isn't followed properly by all parts of the core code, some follow it, whereas others don't.
"The cpufreq core code is not consistent with respect to invoking __cpufreq_governor() under policy->rwsem."
Enforcing it will also enable us to remove cpufreq_governor_lock, that is used today because we can't guarantee that __cpufreq_governor() isn't executed in parallel.
"Changing all code to always hold policy->rwsem around __cpufreq_governor() invocations will allow us to ..."
We should also ensure that the lock is held across state changes to the governors.
For example, while adding a CPU to the policy on cpu-online path, we need to stop the governor, change policy->cpus, start the governor and then refresh its limits. The complete sequence must be guaranteed to execute without any concurrent races. And that can be achieved using policy->rwsem around these use cases.
Also note that cpufreq_driver->stop_cpu() and ->exit() can get called while policy->rwsem is held. That shouldn't have any side effects though.
The last paragraph is unclear.
Is it supposed to mean that the change will cause cpufreq_driver->stop_cpu() and ->exit() to be called under policy->rwsem sometimes?
Thanks, Rafael