drm/gma500: Lock struct_mutex around cursor updates

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=64361
Cc: <stable@vger.kernel.org>
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>

drivers/gpu/drm/gma500/gma_display.c

@@ -349,6 +349,7 @@ int gma_crtc_cursor_set(struct drm_crtc *crtc,
 	/* If we didn't get a handle then turn the cursor off */
 	if (!handle) {
 		temp = CURSOR_MODE_DISABLE;
+		mutex_lock(&dev->struct_mutex);
 
 		if (gma_power_begin(dev, false)) {
 			REG_WRITE(control, temp);
@@ -365,6 +366,7 @@ int gma_crtc_cursor_set(struct drm_crtc *crtc,
 			gma_crtc->cursor_obj = NULL;
 		}
 
+		mutex_unlock(&dev->struct_mutex);
 		return 0;
 	}
 
@@ -374,9 +376,12 @@ int gma_crtc_cursor_set(struct drm_crtc *crtc,
 		return -EINVAL;
 	}
 
+	mutex_lock(&dev->struct_mutex);
 	obj = drm_gem_object_lookup(dev, file_priv, handle);
-	if (!obj)
-		return -ENOENT;
+	if (!obj) {
+		ret = -ENOENT;
+		goto unlock;
+	}
 
 	if (obj->size < width * height * 4) {
 		dev_dbg(dev->dev, "Buffer is too small\n");
@@ -440,10 +445,13 @@ int gma_crtc_cursor_set(struct drm_crtc *crtc,
 	}
 
 	gma_crtc->cursor_obj = obj;
+unlock:
+	mutex_unlock(&dev->struct_mutex);
 	return ret;
 
 unref_cursor:
 	drm_gem_object_unreference(obj);
+	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }