cpufreq: intel_pstate: Fix object lifecycle issue in update_qos_request()

The cpufreq_cpu_put() call in update_qos_request() takes place too early
because the latter subsequently calls freq_qos_update_request() that
indirectly accesses the policy object in question through the QoS request
object passed to it.

Fortunately, update_qos_request() is called under intel_pstate_driver_lock,
so this issue does not matter for changing the intel_pstate operation
mode, but it theoretically can cause a crash to occur on CPU device hot
removal (which currently can only happen in virt, but it is formally
supported nevertheless).

Address this issue by modifying update_qos_request() to drop the
reference to the policy later.

Fixes: da5c504 ("cpufreq: intel_pstate: Implement QoS supported freq constraints")
Cc: 5.4+ <stable@vger.kernel.org> # 5.4+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Zihuan Zhang <zhangzihuan@kylinos.cn>
Link: https://patch.msgid.link/2255671.irdbgypaU6@rafael.j.wysocki

Author: rafaeljw

drivers/cpufreq/intel_pstate.c

@@ -1667,10 +1667,10 @@ static void update_qos_request(enum freq_qos_req_type type)
 			continue;
 
 		req = policy->driver_data;
-		cpufreq_cpu_put(policy);
-
-		if (!req)
+		if (!req) {
+			cpufreq_cpu_put(policy);
 			continue;
+		}
 
 		if (hwp_active)
 			intel_pstate_get_hwp_cap(cpu);
@@ -1686,6 +1686,8 @@ static void update_qos_request(enum freq_qos_req_type type)
 
 		if (freq_qos_update_request(req, freq) < 0)
 			pr_warn("Failed to update freq constraint: CPU%d\n", i);
+
+		cpufreq_cpu_put(policy);
 	}
 }