User session hung

One of our user is running a session that usually runs fairly quick and at the most 20 minutes. But these two days, the session just hung. I am able to identify the session and kill it. But I am not sure how I should go about investigate for the root cause.

The top command showed high usage of CPU. AWR report does show some I/O and row lock contention. But the lock contention is for another table which has nothing to do with the session that hangs. What would cause the unnecessary I/O bottleneck? Also, usually insert and updates would cause the db writer to be busy and generate logs, correct? At that time we had about 4 log switch in 30 minutes.