[CentOS] system hangs

It seems system was in hung state . The message

> Feb 21 22:26:23 <server> kernel: INFO: task perl:20596 blocked for more
than 120 seconds.

Just indicates that process 20596 was stuck/hang in cpu for more than 120
seconds. To begin with the troubleshooting,
I would suggest you to check what this process does. Whether this required
any REMOTE storage/disk access.
Btw, the same perl process is going to D state/hang state first/always ?

If no remote storage/disk access is required for this perl application AND
In case you are running this application
as root user, try run this application as a normal user in which a resource
limitation is applicable via limits.conf.

If the process required a storage/NFS access, you may want to check the
disk/storage status at the time when application
moved to D state. I understand that you can't predict the issue time and
perform all the checks mentioned above.
afaik, to find the root cause of this problem, you may want to analyse core
dump collected at the time of the issue.

Cheers,
Dominic