intel_pstate: Use del_timer_sync in intel_pstate_cpu_stop

commit c2294a2f upstream.

Ensure that no timer callback is running since we are about to free
the timer structure.  We cannot guarantee that the call back is called
on the CPU where the timer is running.
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com>
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

drivers/cpufreq/intel_pstate.c

@@ -635,7 +635,7 @@ static int intel_pstate_cpu_exit(struct cpufreq_policy *policy)
 {
 	int cpu = policy->cpu;
 
-	del_timer(&all_cpu_data[cpu]->timer);
+	del_timer_sync(&all_cpu_data[cpu]->timer);
 	kfree(all_cpu_data[cpu]);
 	all_cpu_data[cpu] = NULL;
 	return 0;