[CPUFREQ] Fix stale cpufreq_cpu_governor pointer

Dave,

Attached is an update of my patch against the cpufreq fixes branch.

Before applying the patch I compiled and booted the tree to see if the panic
was still there -- to my surprise it was not.  This is because of the conversion
of cpufreq_cpu_governor to a char[].

While the panic is kaput, the problem of stale data continues and my patch is
still valid.  It is possible to end up with the wrong governor after hotplug
events because CPUFREQ_DEFAULT_GOVERNOR is statically linked to a default,
while the cpu siblings may have had a different governor assigned by a user.

ie) the patch is still needed in order to keep the governors assigned
properly when hotplugging devices
Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Dave Jones <davej@redhat.com>

drivers/cpufreq/cpufreq.c

@@ -951,10 +951,13 @@ err_out_kobj_put:
 static int cpufreq_add_dev(struct sys_device *sys_dev)
 {
 	unsigned int cpu = sys_dev->id;
-	int ret = 0;
+	int ret = 0, found = 0;
 	struct cpufreq_policy *policy;
 	unsigned long flags;
 	unsigned int j;
+#ifdef CONFIG_HOTPLUG_CPU
+	int sibling;
+#endif
 
 	if (cpu_is_offline(cpu))
 		return 0;
@@ -1001,7 +1004,19 @@ static int cpufreq_add_dev(struct sys_device *sys_dev)
 	INIT_WORK(&policy->update, handle_update);
 
 	/* Set governor before ->init, so that driver could check it */
-	policy->governor = CPUFREQ_DEFAULT_GOVERNOR;
+#ifdef CONFIG_HOTPLUG_CPU
+	for_each_online_cpu(sibling) {
+		struct cpufreq_policy *cp = per_cpu(cpufreq_cpu_data, sibling);
+		if (cp && cp->governor &&
+		    (cpumask_test_cpu(cpu, cp->related_cpus))) {
+			policy->governor = cp->governor;
+			found = 1;
+			break;
+		}
+	}
+#endif
+	if (!found)
+		policy->governor = CPUFREQ_DEFAULT_GOVERNOR;
 	/* call driver. From then on the cpufreq must be able
 	 * to accept all calls to ->verify and ->setpolicy for this CPU
 	 */
@@ -1610,9 +1625,22 @@ EXPORT_SYMBOL_GPL(cpufreq_register_governor);
 
 void cpufreq_unregister_governor(struct cpufreq_governor *governor)
 {
+#ifdef CONFIG_HOTPLUG_CPU
+	int cpu;
+#endif
+
 	if (!governor)
 		return;
 
+#ifdef CONFIG_HOTPLUG_CPU
+	for_each_present_cpu(cpu) {
+		if (cpu_online(cpu))
+			continue;
+		if (!strcmp(per_cpu(cpufreq_cpu_governor, cpu), governor->name))
+			strcpy(per_cpu(cpufreq_cpu_governor, cpu), "\0");
+	}
+#endif
+
 	mutex_lock(&cpufreq_governor_mutex);
 	list_del(&governor->governor_list);
 	mutex_unlock(&cpufreq_governor_mutex);