As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MUSTY ODOR AFTER TL TO THRUST SET POSITION ON TAKEOFF ROLL. AT 500 FT HAD A LAVATORY SMOKE WARNING MESSAGE. FA REPORTED SMOKE IN CABIN, RETURNED FOR LANDING. FA REPORTED THE SMOKE ODOR DISAPATED BY THE TIME OF FINAL APPROACH. REMOVED AND REPLACED BOTH ENGINES.