drm/i915: Avoid tainting i915_gem_park() with wakeref.lock

While we need to flush the wakeref before parking, we do not need to
perform the i915_gem_park() itself underneath the wakeref lock, merely
the struct_mutex. If we rearrange the locks, we can avoid the unnecessary
tainting.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190614220616.24932-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_pm.c

@@ -48,23 +48,22 @@ static void idle_work_handler(struct work_struct *work)
 {
 	struct drm_i915_private *i915 =
 		container_of(work, typeof(*i915), gem.idle_work);
-	bool restart = true;
+	bool park;
 
-	cancel_delayed_work(&i915->gem.retire_work);
+	cancel_delayed_work_sync(&i915->gem.retire_work);
 	mutex_lock(&i915->drm.struct_mutex);
 
 	intel_wakeref_lock(&i915->gt.wakeref);
-	if (!intel_wakeref_active(&i915->gt.wakeref) && !work_pending(work)) {
-		i915_gem_park(i915);
-		restart = false;
-	}
+	park = !intel_wakeref_active(&i915->gt.wakeref) && !work_pending(work);
 	intel_wakeref_unlock(&i915->gt.wakeref);
-
-	mutex_unlock(&i915->drm.struct_mutex);
-	if (restart)
+	if (park)
+		i915_gem_park(i915);
+	else
 		queue_delayed_work(i915->wq,
 				   &i915->gem.retire_work,
 				   round_jiffies_up_relative(HZ));
+
+	mutex_unlock(&i915->drm.struct_mutex);
 }
 
 static void retire_work_handler(struct work_struct *work)