The code is racy and the check with cpuidle_curr_driver should be
done under the lock.

I don't find a path in the different drivers where that could happen
because the arch specific drivers are written in such way it is not
possible to register a driver while it is unregistered, except maybe
in a very improbable case when "intel_idle" and "processor_idle" are
competing. One could unregister a driver, while the other one is
registering.
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: NPeter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>