IMO Henry's diagram is perfect - so far as it goes What he misses is that you pass through A in a recovery from a preceding dive. Yes you are wings level at this point but you do need about 2 g at the same time. As BOAC says you are doing a (low g) twisted loop. Indeed it is the twisted bit that allows you to loop at such a low g without running out of airspeed.
Re accidents during barrel rolls at airshows when I was a CAA display authorisation examiner I used to fail anybody doing a barrel roll along the display line unless they started it rolling TOWARDS the crowd. This is because the roll only goes wrong in the second half and if you start it towards the crowd then during the nasty second half you will be pulling and travelling away from the crowd as you woosh into the deck.