func (tr *authTransport) RoundTrip(orig *http.Request) (*http.Response, error) {
  ...
  tr.mu.Lock()
  tr.modReq[orig] = req  //PROTECTED
  tr.mu.Unlock()
  ...
  resp, err := tr.RoundTripper.RoundTrip(req)
  if err != nil {
     delete(tr.modReq, orig)  //NOT PROTECTED
     return nil, err
  }
   if len(resp.Header["X-Docker-Token"]) > 0 {
     tr.token = resp.Header["X-Docker-Token"]
  }
  resp.Body = &ioutils.OnEOFReader{
     Rc: resp.Body,
     Fn: func() {
        tr.mu.Lock()
        delete(tr.modReq, orig)  //PROTECTED
        tr.mu.Unlock()
     },
  }
  return resp, nil
}

// CancelRequest cancels an in-flight request by closing its connection.
func (tr *authTransport) CancelRequest(req *http.Request) {
  type canceler interface {
     CancelRequest(*http.Request)
  }
  if cr, ok := tr.RoundTripper.(canceler); ok {
     tr.mu.Lock()
     modReq := tr.modReq[req]  //PROTECTED
     delete(tr.modReq, req)  //PROTECTED
     tr.mu.Unlock()
     cr.CancelRequest(modReq)
  }
}