Are you sure it has crashed?
If you are using the cpuse package to upgrade, I've had this stay at 58% for nearly 4 hours.
ssh to the MDS and run:
find $MDSDIR/customers/ -name "migrate*log" -exec ls -la {} \;
tail the most recent log to see things happening. When it finishes and moves to a different CMA/domain it will create a new log file in a new customer directory.
alternatively run top to see which process is eating all the CPU and be patient
Once the installation shows as complete the MDS will take a long time to start too.