NFSD: Retransmit callbacks after client reconnects

NFSv4.1 clients assume that if they disconnect, that will force the
server to resend pending callback operations once a fresh connection
has been established.

Turns out NFSD has not been resending after reconnect.

Fixes: 7ba6cad6 ("nfsd: New helper nfsd4_cb_sequence_done() for processing more cb errors")
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4callback.c

@@ -1178,12 +1178,21 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback
 		break;
 	case -ESERVERFAULT:
 		++session->se_cb_seq_nr;
-		fallthrough;
+		nfsd4_mark_cb_fault(cb->cb_clp, cb->cb_seq_status);
+		ret = false;
+		break;
 	case 1:
+		/*
+		 * cb_seq_status remains 1 if an RPC Reply was never
+		 * received. NFSD can't know if the client processed
+		 * the CB_SEQUENCE operation. Ask the client to send a
+		 * DESTROY_SESSION to recover.
+		 */
+		fallthrough;
 	case -NFS4ERR_BADSESSION:
 		nfsd4_mark_cb_fault(cb->cb_clp, cb->cb_seq_status);
 		ret = false;
-		break;
+		goto need_restart;
 	case -NFS4ERR_DELAY:
 		cb->cb_seq_status = 1;
 		if (!rpc_restart_call(task))