drm/i915: Add i915_gem_request_unreference__unlocked

We were missing a convenience stub to aquire the right mutex whilst
dropping the request, so add it.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -2142,6 +2142,19 @@ i915_gem_request_unreference(struct drm_i915_gem_request *req)
 	kref_put(&req->ref, i915_gem_request_free);
 }
 
+static inline void
+i915_gem_request_unreference__unlocked(struct drm_i915_gem_request *req)
+{
+	if (req && !atomic_add_unless(&req->ref.refcount, -1, 1)) {
+		struct drm_device *dev = req->ring->dev;
+
+		mutex_lock(&dev->struct_mutex);
+		if (likely(atomic_dec_and_test(&req->ref.refcount)))
+			i915_gem_request_free(&req->ref);
+		mutex_unlock(&dev->struct_mutex);
+	}
+}
+
 static inline void i915_gem_request_assign(struct drm_i915_gem_request **pdst,
 					   struct drm_i915_gem_request *src)
 {

drivers/gpu/drm/i915/i915_gem.c

@@ -2866,9 +2866,7 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
 	ret = __i915_wait_request(req, reset_counter, true,
 				  args->timeout_ns > 0 ? &args->timeout_ns : NULL,
 				  file->driver_priv);
-	mutex_lock(&dev->struct_mutex);
-	i915_gem_request_unreference(req);
-	mutex_unlock(&dev->struct_mutex);
+	i915_gem_request_unreference__unlocked(req);
 	return ret;
 
 out:
@@ -4071,9 +4069,7 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
 	if (ret == 0)
 		queue_delayed_work(dev_priv->wq, &dev_priv->mm.retire_work, 0);
 
-	mutex_lock(&dev->struct_mutex);
-	i915_gem_request_unreference(target);
-	mutex_unlock(&dev->struct_mutex);
+	i915_gem_request_unreference__unlocked(target);
 
 	return ret;
 }