2007 Mazda 6 diesel wagon the DFT was done in November 2016 I stalled it 2 and started it up 30 mins up the road and started up with white smoke and then it started to over rev itself and i turned it off and started it up again 5 mins later it had a knocking sound from the motor what could it be?

 

Death

 

I think it's the head gasket.

 

Could be a leaking injector.