drm/i915: delay master/sarea deref for legacy ioctls

... past the check for DRIVER_MODESET. Avoids races with userspace
opening a master and our sarea setup.

Cc: Signed-off-by: Stéphane Marchesin <marcheu@chromium.org>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_dma.c

@@ -626,9 +626,8 @@ static int i915_batchbuffer(struct drm_device *dev, void *data,
 			    struct drm_file *file_priv)
 {
 	drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
-	struct drm_i915_master_private *master_priv = dev->primary->master->driver_priv;
-	drm_i915_sarea_t *sarea_priv = (drm_i915_sarea_t *)
-	    master_priv->sarea_priv;
+	struct drm_i915_master_private *master_priv;
+	drm_i915_sarea_t *sarea_priv;
 	drm_i915_batchbuffer_t *batch = data;
 	int ret;
 	struct drm_clip_rect *cliprects = NULL;
@@ -636,6 +635,9 @@ static int i915_batchbuffer(struct drm_device *dev, void *data,
 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		return -ENODEV;
 
+	master_priv = dev->primary->master->driver_priv;
+	sarea_priv = (drm_i915_sarea_t *) master_priv->sarea_priv;
+
 	if (!dev_priv->dri1.allow_batchbuffer) {
 		DRM_ERROR("Batchbuffer ioctl disabled\n");
 		return -EINVAL;
@@ -682,9 +684,8 @@ static int i915_cmdbuffer(struct drm_device *dev, void *data,
 			  struct drm_file *file_priv)
 {
 	drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
-	struct drm_i915_master_private *master_priv = dev->primary->master->driver_priv;
-	drm_i915_sarea_t *sarea_priv = (drm_i915_sarea_t *)
-	    master_priv->sarea_priv;
+	struct drm_i915_master_private *master_priv;
+	drm_i915_sarea_t *sarea_priv;
 	drm_i915_cmdbuffer_t *cmdbuf = data;
 	struct drm_clip_rect *cliprects = NULL;
 	void *batch_data;
@@ -696,6 +697,9 @@ static int i915_cmdbuffer(struct drm_device *dev, void *data,
 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		return -ENODEV;
 
+	master_priv = dev->primary->master->driver_priv;
+	sarea_priv = (drm_i915_sarea_t *) master_priv->sarea_priv;
+
 	RING_LOCK_TEST_WITH_RETURN(dev, file_priv);
 
 	if (cmdbuf->num_cliprects < 0)