[PATCH v1 1/3] cpufreq: intel_pstate: Fix object lifecycle issue in update_qos_request()

["Rafael J. Wysocki" <rafael@kernel.org>]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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: da5c504c7aae ("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>
---
 drivers/cpufreq/intel_pstate.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1708,10 +1708,10 @@ static void update_qos_request(enum freq
 			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);
@@ -1727,6 +1727,8 @@ static void update_qos_request(enum freq
 
 		if (freq_qos_update_request(req, freq) < 0)
 			pr_warn("Failed to update freq constraint: CPU%d\n", i);
+
+		cpufreq_cpu_put(policy);
 	}
 }