I created a post function which will copy parents summary and description to custom fields called parent summary and parent description on a subtask. It happens whenever a new subtask is created under the parent.
Now i have an ask that whenever summary or description is updated, it should update in both places, if updated in the parent, then update should reflect in subtask and vice versa.
How can i achieve this? any thoughts
No real solution there but to keep those fields in sync you might want to look at Custom Listeners using Scrip Runner (https://scriptrunner.adaptavist.com/latest/jira/listeners.html#_issue_event_bundles, well documented with examples).
You might want to catch an event in the parent (issue updated) and check if summary and/or description have changed, then update the child's fields accordingly.
Hope this will help!