Datapatch CDB / PDB hits prereq checks failed

Symptom:

     When we patch PSU on CDB / PDB , we need to ./datapatch -verbose under Opatch

     It reports
      Error: prereq checks failed!
  patch 21555660: The database must be in upgrade mode

Reason:

     Patch 21555660 (Database PSU 12.1.0.2.5, Oracle JavaVM Component ) is not in place of CDB/PDBs. It needs outages to upgrade this OJVM to pass thorough.

     Check both CDB and PDBs for that as the component applies to each PDBs

    sql: select comp_name, version from  dba_registry where comp_name like   '%JAVA Virtual Machin%' and status = 'VALID';

Solution:

If it is CDB$ROOT
  alter system set cluster_database=false scope=spfile;
  startup upgrade
  rerun datapatch
  alter system set cluster_database=true scope=spfile;
  startup

If it is PDB$SEED or other PDB
    alter pluggable database <PDB>  open upgrade;
    rerun datapatch
    alter pluggable database <PDB>  close immediate;
    alter pluggable database <PDB> open;