segfault on Linux

gistfile1.txt

$ build/lev tools/checkit tests/test-fs.lua 
*lev core started: 3842
✔ fs_sync_test: 10/10 within 0.178 ms
Lua Stack Dump: fs_open before set_callback starting at 5
1:  'LICENSE.txt'
2:  'r'
3:  438
4:  <function 0x419d3958>
5:  <userdata 0x419d39d8>
Core exited with status 0, signal 11



static int fs_open(lua_State* L) {
  int mode;
  uv_fs_cb cb;
  uv_loop_t *loop = luv_get_loop(L);
  int arg_n = lua_gettop(L);

  fs_req_holder *holder = (fs_req_holder *)create_obj_init_ref(L,
      sizeof(fs_req_holder), "lev.fs");
  uv_fs_t *req = &holder->req;

  int arg_i = 1;
  const char *path = luaL_checkstring(L, arg_i++);
  int flags = fs_checkflags(L, arg_i++);
  if (arg_i <= arg_n && lua_isnumber(L, arg_i)) {
    mode = luaL_checkint(L, arg_i++);
  } else {
    mode = 0666;
  }
  if (arg_i <= arg_n) {
luv_lua_debug_stackdump(L, "fs_open before set_callback");
    set_callback(L, CALLBACK_NAME, arg_i++);
    lev_handle_ref(L, (LevRefStruct_t *)holder, -1);
luv_lua_debug_stackdump(L, "fs_open after set_callback");
    cb = on_fs_callback;
  } else {
    cb = NULL;
  }
  uv_fs_open(loop, req, path, flags, mode, cb);
  int ret_n = push_results(L, req);
  if (!LEV_IS_ASYNC_REQ(req)) {
    uv_fs_req_cleanup(req);
  }
  return ret_n;
}