--- st_cb_syncobj.c.orig	2016-10-14 10:52:02.867414704 +0900
+++ st_cb_syncobj.c	2016-10-15 12:36:42.093520250 +0900
@@ -36,20 +36,24 @@
 #include "pipe/p_screen.h"
 #include "st_context.h"
 #include "st_cb_syncobj.h"
+#include <pthread.h>
 
 struct st_sync_object {
    struct gl_sync_object b;
-
    struct pipe_fence_handle *fence;
+   mtx_t mtx;
 };
 
 
 static struct gl_sync_object * st_new_sync_object(struct gl_context *ctx,
                                                   GLenum type)
 {
-   if (type == GL_SYNC_FENCE)
-      return (struct gl_sync_object*)CALLOC_STRUCT(st_sync_object);
-   else
+   if (type == GL_SYNC_FENCE) {
+      struct st_sync_object * so = 
+         (struct st_sync_object*)CALLOC_STRUCT(st_sync_object);
+      mtx_init(&so->mtx, mtx_plain);
+      return (struct gl_sync_object *)so;
+   } else
       return NULL;
 }
 
@@ -61,6 +65,7 @@
 
    screen->fence_reference(screen, &so->fence, NULL);
    free(so->b.Label);
+   mtx_destroy(&so->mtx);
    free(so);
 }
 
@@ -82,15 +87,18 @@
    struct st_sync_object *so = (struct st_sync_object*)obj;
 
    /* If the fence doesn't exist, assume it's signalled. */
+   mtx_lock(&so->mtx);
    if (!so->fence) {
       so->b.StatusFlag = GL_TRUE;
-      return;
+      goto unlock_and_return;
    }
 
    if (screen->fence_finish(screen, so->fence, 0)) {
       screen->fence_reference(screen, &so->fence, NULL);
       so->b.StatusFlag = GL_TRUE;
    }
+ unlock_and_return:
+   mtx_unlock(&so->mtx);
 }
 
 static void st_client_wait_sync(struct gl_context *ctx,
@@ -100,20 +108,22 @@
    struct pipe_screen *screen = st_context(ctx)->pipe->screen;
    struct st_sync_object *so = (struct st_sync_object*)obj;
 
+   mtx_lock(&so->mtx);
    /* If the fence doesn't exist, assume it's signalled. */
    if (!so->fence) {
       so->b.StatusFlag = GL_TRUE;
-      return;
+      goto unlock_and_return;
    }
 
    /* 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)) {
+   if (screen->fence_finish(screen, so->fence, timeout)) {
       screen->fence_reference(screen, &so->fence, NULL);
       so->b.StatusFlag = GL_TRUE;
    }
+ unlock_and_return:
+   mtx_unlock(&so->mtx);
 }
 
 static void st_server_wait_sync(struct gl_context *ctx,