--- st_cb_syncobj.c.orig	2016-10-14 10:52:02.867414704 +0900
+++ st_cb_syncobj.c	2016-10-15 09:44:30.238203506 +0900
@@ -80,17 +80,29 @@
 {
    struct pipe_screen *screen = st_context(ctx)->pipe->screen;
    struct st_sync_object *so = (struct st_sync_object*)obj;
+   struct pipe_fence_handle * fence = NULL;
+   boolean success;
 
+   mtx_lock(&ctx->Shared->Mutex);
+   screen->fence_reference(screen, &fence, so->fence);
+   mtx_unlock(&ctx->Shared->Mutex);
    /* If the fence doesn't exist, assume it's signalled. */
-   if (!so->fence) {
+   thrd_micro_random_sleep();
+   if (!fence) {
       so->b.StatusFlag = GL_TRUE;
-      return;
+      goto quit;
    }
-
-   if (screen->fence_finish(screen, so->fence, 0)) {
+   success = screen->fence_finish(screen, fence, 0);
+   thrd_micro_random_sleep();
+   if (success) {
+      mtx_lock(&ctx->Shared->Mutex);
       screen->fence_reference(screen, &so->fence, NULL);
+      mtx_unlock(&ctx->Shared->Mutex);
+      thrd_micro_random_sleep();
       so->b.StatusFlag = GL_TRUE;
    }
+ quit:
+   screen->fence_reference(screen, &fence, NULL);
 }
 
 static void st_client_wait_sync(struct gl_context *ctx,
@@ -99,21 +111,32 @@
 {
    struct pipe_screen *screen = st_context(ctx)->pipe->screen;
    struct st_sync_object *so = (struct st_sync_object*)obj;
+   struct pipe_fence_handle * fence = NULL;
+   boolean success;
 
+   mtx_lock(&ctx->Shared->Mutex);
+   screen->fence_reference(screen, &fence, so->fence);
+   mtx_unlock(&ctx->Shared->Mutex);
    /* If the fence doesn't exist, assume it's signalled. */
-   if (!so->fence) {
+   thrd_micro_random_sleep();
+   if (!fence) {
       so->b.StatusFlag = GL_TRUE;
-      return;
+      goto quit;
    }
-
+   thrd_micro_random_sleep();
    /* We don't care about GL_SYNC_FLUSH_COMMANDS_BIT, because flush is
     * already called when creating a fence. */
-
-   if (so->fence &&
-       screen->fence_finish(screen, so->fence, timeout)) {
+   success = screen->fence_finish(screen, fence, timeout);
+   thrd_micro_random_sleep();
+   if (success) {
+      mtx_lock(&ctx->Shared->Mutex);
       screen->fence_reference(screen, &so->fence, NULL);
+      mtx_unlock(&ctx->Shared->Mutex);
+      thrd_micro_random_sleep();
       so->b.StatusFlag = GL_TRUE;
    }
+ quit:
+   screen->fence_reference(screen, &fence, NULL);
 }
 
 static void st_server_wait_sync(struct gl_context *ctx,