PM: QoS: Invalidate frequency QoS requests after removal

Switching cpufreq drivers (or switching operation modes of the
intel_pstate driver from "active" to "passive" and vice versa)
does not work on some x86 systems with ACPI after commit
3000ce3 ("cpufreq: Use per-policy frequency QoS"), because
the ACPI _PPC and thermal code uses the same frequency QoS request
object for a given CPU every time a cpufreq driver is registered
and freq_qos_remove_request() does not invalidate the request after
removing it from its QoS list, so freq_qos_add_request() complains
and fails when that request is passed to it again.

Fix the issue by modifying freq_qos_remove_request() to clear the qos
and type fields of the frequency request pointed to by its argument
after removing it from its QoS list so as to invalidate it.

Fixes: 3000ce3 ("cpufreq: Use per-policy frequency QoS")
Reported-and-tested-by: Doug Smythies <dsmythies@telus.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

kernel/power/qos.c

@@ -814,14 +814,20 @@ EXPORT_SYMBOL_GPL(freq_qos_update_request);
  */
 int freq_qos_remove_request(struct freq_qos_request *req)
 {
+	int ret;
+
 	if (!req)
 		return -EINVAL;
 
 	if (WARN(!freq_qos_request_active(req),
 		 "%s() called for unknown object\n", __func__))
 		return -EINVAL;
 
-	return freq_qos_apply(req, PM_QOS_REMOVE_REQ, PM_QOS_DEFAULT_VALUE);
+	ret = freq_qos_apply(req, PM_QOS_REMOVE_REQ, PM_QOS_DEFAULT_VALUE);
+	req->qos = NULL;
+	req->type = 0;
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(freq_qos_remove_request);