What was found
DURING CLIMBOUT OF DFW COCKPIT CREW SMELLED SMOKE. SUBSEQUENTLY HAD AN LAVATORY SMOKE EAD ALERT. SMOKE PERSISTED FOR 3-4 MIN, THEN WENT OUT. F/A'S REPORT DENSE SMOKE ESCAPE FROM CREW REST MODULE WHEN DOOR WAS OPENED AFTER LANDING. RETURNED TO DFW. REPLACED FWD CABIN TRIM AIR VALVE. PERFORMED AIR CONDITION PACK AND DISTRIBUTION DUCT CLEANING PER M/M. RAN ENGINES, OPERATIONAL CHECK NORMAL. DURING PACK AND DISTRIBUTION DUCT CLEAN FOUND NR 3 TURBINE BYPASS VALVE INOP. REPLACED SAME.