Suzuki Gixxer @ 12 thousand kms, there is a white colour smoke at full rpm and irritating sound from engine?

The irritating sound and white smoke is mostly caused when the engine is near to the point of seizing. You should not ride the bike until a mechanic checks the level of engine oil or it is even suggested to get it towed to the service center than taking the risk. The engine oil level in the engine would have gone significantly low, which causes the parts to generate more friction and then the white smoke. You should get your engine checked and get is repaired under the warranty period as the problem would have been caused due to the mistake of the service center mechanics also.