I am aware that common answers to
"What's going on?"
are phrases like:
"Not much. How about you?"
"Nothing much, you?",
but sometimes people use it in a manner like "hi" and you know that there isn't enough time to respond to it with the two above phrases. For instance, when they're just passing by you without stopping. In such cases, can we respond with the same phrase?
Example: Do the examples below sound natural?
He: What's going on? You: What's going on?
He: What's up? You: What's up?
He: How's it going? You: How's it going?
And if not, how do you handle such situations yourself?