drm/core: Fix old_fb handling in pan_display_atomic.

Don't touch plane->old_fb/fb without having the right locks held.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1447237751-9663-6-git-send-email-maarten.lankhorst@ubuntu.com

drivers/gpu/drm/drm_fb_helper.c

@@ -1227,7 +1227,9 @@ static int pan_display_atomic(struct fb_var_screeninfo *var,
 	struct drm_fb_helper *fb_helper = info->par;
 	struct drm_device *dev = fb_helper->dev;
 	struct drm_atomic_state *state;
+	struct drm_plane *plane;
 	int i, ret;
+	unsigned plane_mask;
 
 	state = drm_atomic_state_alloc(dev);
 	if (!state)
@@ -1235,19 +1237,22 @@ static int pan_display_atomic(struct fb_var_screeninfo *var,
 
 	state->acquire_ctx = dev->mode_config.acquire_ctx;
 retry:
+	plane_mask = 0;
 	for(i = 0; i < fb_helper->crtc_count; i++) {
 		struct drm_mode_set *mode_set;
 
 		mode_set = &fb_helper->crtc_info[i].mode_set;
 
-		mode_set->crtc->primary->old_fb = mode_set->crtc->primary->fb;
-
 		mode_set->x = var->xoffset;
 		mode_set->y = var->yoffset;
 
 		ret = __drm_atomic_helper_set_config(mode_set, state);
 		if (ret != 0)
 			goto fail;
+
+		plane = mode_set->crtc->primary;
+		plane_mask |= drm_plane_index(plane);
+		plane->old_fb = plane->fb;
 	}
 
 	ret = drm_atomic_commit(state);
@@ -1259,26 +1264,7 @@ static int pan_display_atomic(struct fb_var_screeninfo *var,
 
 
 fail:
-	for(i = 0; i < fb_helper->crtc_count; i++) {
-		struct drm_mode_set *mode_set;
-		struct drm_plane *plane;
-
-		mode_set = &fb_helper->crtc_info[i].mode_set;
-		plane = mode_set->crtc->primary;
-
-		if (ret == 0) {
-			struct drm_framebuffer *new_fb = plane->state->fb;
-
-			if (new_fb)
-				drm_framebuffer_reference(new_fb);
-			plane->fb = new_fb;
-			plane->crtc = plane->state->crtc;
-
-			if (plane->old_fb)
-				drm_framebuffer_unreference(plane->old_fb);
-		}
-		plane->old_fb = NULL;
-	}
+	drm_atomic_clean_old_fb(dev, plane_mask, ret);
 
 	if (ret == -EDEADLK)
 		goto backoff;