drm/radeon: take the mode_config mutex when dealing with hpds (v2)

commit 39fa10f7 upstream.

Since we are messing with state in the worker.

v2: drop the changes in the mst worker
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/gpu/drm/radeon/radeon_irq_kms.c

@@ -79,10 +79,12 @@ static void radeon_hotplug_work_func(struct work_struct *work)
 	struct drm_mode_config *mode_config = &dev->mode_config;
 	struct drm_connector *connector;
 
+	mutex_lock(&mode_config->mutex);
 	if (mode_config->num_connector) {
 		list_for_each_entry(connector, &mode_config->connector_list, head)
 			radeon_connector_hotplug(connector);
 	}
+	mutex_unlock(&mode_config->mutex);
 	/* Just fire off a uevent and let userspace tell us what to do */
 	drm_helper_hpd_irq_event(dev);
 }