According to IAAF competition rules art 163:
Lane Infringement(a) in all races run in lanes, each athlete shall keep within his allocated lane from start to finish. this shall also apply to any portion of a race run in lanes.
(b) in all races (or any part of races) not run in lanes, an athlete running on a bend, on the outer half of the track as per Rule 162.10, or on any curved part of the diversion from the track for the steeplechase water jump, shall not step or run on or inside the kerb or line marking the applicable border (the inside of the track, the outer half of the track, or any curved part of the diversion from the track for the steeplechase water jump).An athlete shall not be disqualified if he (a) is pushed or forced by another person to step or run outside his lane or on or inside the kerb or line marking the applicable border
So the runner who goes out of his lane will be disqualified, while the impeded runner will not be...