Engine quit and oil in the exhaust pipe

Was a fine ride until I started smoking like crazy, then in 15 seconds the engine lugged then quit. There's also oil coming out of the pipe. I sure hope it's something simple. I see in posts that there's an oil check valve that some say can be the culprit. I've read the Lube system in the Haynes book but I can't find that valve. Also, would a crankcase breather be another possibility?