why kernel Tainted after softlockup

ITNOA

I am using Ubuntu 16.04.6 LTS and I am running my program that have one real time thread with 100% core usage, in this situation kernel says in syslog like below

kernel: watchdog: BUG: soft lockup - CPU#1 stuck for 22s! …kernel: print all modules …

And after I see soft lockup kernel says in syslog like below

kernel: CPU: 1 PID: 53590 Comm: … Tainted: G OEL … #1

And after see above message, my server is hang completely and I have to reboot it. whiles my server have many cores, and only one core is 100%.

My kernel version is 4.15.

I have four questions:

1. Why my server is hang and freeze completely?
2. How to resolve that to not happened again?
3. Why after soft lockup I see kernel tainted?
4. How to say kernel (watchdog) to this situation is not BUG and it is normal?