I have been looking into the articles on the web, but unfortunately I cannot find the clear answer. I guess one of them is the correct decoder_input_ids (label should be decoder_input_ids[1:] ?):
1) <s>...</s><pad>...<pad>
2) </s><s>...</s><pad>...<pad>
3) <pad><pad>...</s><s>...</s>

Thanks in advance.
+) I am going to fine-tune this model for free form QA.