nfsd: Update callback sequnce id only CB_SEQUENCE success

When testing pnfs layout, nfsd got error NFS4ERR_SEQ_MISORDERED.
It is caused by nfs return NFS4ERR_DELAY before validate_seqid(),
don't update the sequnce id, but nfsd updates the sequnce id !!!

According to RFC5661 20.9.3,
" If CB_SEQUENCE returns an error, then the state of the slot
(sequence ID, cached reply) MUST NOT change. "

Signed-off-by: Kinglong Mee <[e-mail]>
Signed-off-by: J. Bruce Fields <[e-mail]>

fs/nfsd/nfs4callback.c

···
 	if (unlikely(status || cb->cb_status))
 		return status;
 
+	cb->cb_update_seq_nr = true;
 	return decode_cb_sequence4resok(xdr, cb);
 }
 
···
 	u32 minorversion = clp->cl_minorversion;
 
 	cb->cb_minorversion = minorversion;
+	cb->cb_update_seq_nr = false;
 	cb->cb_status = 0;
 	if (minorversion) {
 		if (!nfsd41_cb_get_slot(clp, task))
···
 		clp->cl_minorversion);
 
 	if (clp->cl_minorversion) {
-		/* No need for lock, access serialized in nfsd4_cb_prepare */
-		if (!task->tk_status)
+		/*
+		 * No need for lock, access serialized in nfsd4_cb_prepare
+		 *
+		 * RFC5661 20.9.3
+		 * If CB_SEQUENCE returns an error, then the state of the slot
+		 * (sequence ID, cached reply) MUST NOT change.
+		 */
+		if (cb->cb_update_seq_nr)
 			++clp->cl_cb_session->se_cb_seq_nr;
+
 		clear_bit(0, &clp->cl_cb_slot_busy);
 		rpc_wake_up_next(&clp->cl_cb_waitq);
 		dprintk("%s: freed slot, new seqid=%d\n", __func__,
···
 	cb->cb_ops = ops;
 	INIT_WORK(&cb->cb_work, nfsd4_run_cb_work);
 	cb->cb_status = 0;
+	cb->cb_update_seq_nr = false;
 	cb->cb_need_restart = false;
 }
 

fs/nfsd/state.h

···
 	struct nfsd4_callback_ops *cb_ops;
 	struct work_struct cb_work;
 	int cb_status;
+	bool cb_update_seq_nr;
 	bool cb_need_restart;
 };