A320 EXPERIENCES SMOKE IN THE CABIN SHORTLY AFTER LNDG. FLT CREW DECLARES PRECAUTIONARY EMER BUT NO EVAC.

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WE MADE A NORMAL LNDG IN ZZZ. THE INTL RELIEF OFFICER; MR X; MADE THE LNDG. ALL PROCS AND INDICATIONS WERE NORMAL. APPROX 30 SECONDS AFTER WE TAXIED OFF THE RWY; I NOTICED A WHITE SMOKE SLOWLY FILL THE COCKPIT. IT SMELLED ELECTRICAL IN NATURE AND WAS NOT VERY DENSE. THE CAPT TURNED BACK TO ME AND SAID; 'IS THAT SMOKE?' AND I SAID 'YES.' AT THAT TIME THE LEAD FLT ATTENDANT CALLED THE CABIN AND RPTED SMOKE. THE CAPT ASKED ME TO OPEN THE COCKPIT DOOR. I GOT UP OUT OF THE JUMPSEAT AND OPENED THE DOOR. AS I DID; WE DECLARED AN EMER AND REQUESTED THE FIRE TRUCKS. I COULD SEE TO THE AFT OF THE ACFT AND THERE WAS A THIN WHITE SMOKE THROUGHOUT THE INTERIOR. I ASKED THE FLT ATTENDANT AT L1 WHAT SHE WITNESSED. SHE SAID A PUFF OF WHITE SMOKE ENTERED THE CABIN AS WE TURNED OFF THE RWY. I THEN WENT TO THE AFT OF THE CABIN TO INVESTIGATE THE SOURCE AND SPEAK TO THE AFT FLT ATTENDANTS DIRECTLY. THEY CONCURRED WITH THE L1. I QUICKLY WENT BACK TO THE FLT DECK TO RPT TO THE CAPT. THE SMOKE WAS DISSIPATING. MY IMPRESSION AT THAT TIME WAS THAT THE SITUATION WAS NOT DIRE GIVEN THE DISSIPATION AND INDICATIONS FROM THE FLT DECK WERE NORMAL. I TOLD THE CAPT THAT THE SMOKE WAS DISSIPATING AND NO SOURCE WAS DETECTED. AT THE GATE THE FIREMEN ENTERED THE ACFT FIRST AND SAID 'LET'S GET THE PAX OFF SO WE CAN DO A WALK-THROUGH.' WE DEPLANED THE PAX CALMLY WITHOUT INJURY OR PANIC. THE FIREMEN WALKED THROUGH AND COULD ND NO HOT SPOTS OR SMOKE SOURCE. THEY DECLARED THEIR JOB DONE AND WE SECURED THE ACFT. WE GATHERED THE CREW TOGETHER AND DEBRIEFED. THE ACFT WAS RELEASED TO THE MECHS.