ORA-01092 & ORA-39701 during Startup upgrade

SQL> startup upgrade
ORACLE instance started.

Total System Global Area 4.0486E+10 bytes
Fixed Size                  2261968 bytes
Variable Size            6845107248 bytes
Database Buffers         3.3554E+10 bytes
Redo Buffers               84606976 bytes
Database mounted.
ORA-01092: ORACLE instance terminated. Disconnection forced
ORA-39701: database must be mounted EXCLUSIVE for UPGRADE or DOWNGRADE
Process ID: 122696
Session ID: 267 Serial number: 3

Issue : The parameter cluster_database was set to true. We need to change it to false to start the RAC database in upgrade database

SQL> startup
ORACLE instance started.

Total System Global Area 4.0486E+10 bytes
Fixed Size                  2261968 bytes
Variable Size            6845107248 bytes
Database Buffers         3.3554E+10 bytes
Redo Buffers               84606976 bytes
Database mounted.
Database opened.
SQL> alter system set cluster_database=false scope=spfile sid='*';

System altered.

SQL> show parameter cluster

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
cluster_database                     boolean     TRUE
cluster_database_instances           integer     2
cluster_interconnects                string

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.

SQL> startup upgrade 
ORACLE instance started.

Total System Global Area 4.0486E+10 bytes
Fixed Size                  2261968 bytes
Variable Size            6845107248 bytes
Database Buffers         3.3554E+10 bytes
Redo Buffers               84606976 bytes
Database mounted.
Database opened.