11gR1 to 11gR2 Upgrade: cluvfy tool found some mandatory patches are not installed

The cluvfy tool found some mandatory patches are not installed.
These patches need to be installed before the upgrade can proceed.
The pre-upgrade checks failed, aborting the upgrade

The above error is mis-leading sometimes. Look under the log file at
$GRID_HOME/cfgtoollogs/crsconfig and re-run the cluvfy commands listed there manually by removing the "-_patch_only"

/bin/su oragrid -c ' /opt/app/oragrid/oracle/product/11.2.0.3/bin/cluvfy stage -pre crsinst -n myrac1,myrac2 -upgrade -src_crshome /opt/app/oracle/product/crs -dest_crshome /opt/app/oragrid/oracle/product/11.2.0.3 -dest_version 11.2.0.3.0 '

if the above comes back without issues then the problem is the environment variables ORA_CRS_HOME. If that is set at the session from where you are running rootupgrade.sh, then you will see the above error.

unset ORA_CRS_HOME and re-run the rootupgrade.sh and it should finish without errors.

Oracle Note 1498538.1 has more details about it as well.