An Air Canada Boeing 777-300, registration C-FIUW performing flight AC-849 from London Heathrow,EN (UK) to Toronto,ON (Canada) with 253 people on board, had just passed the top of climb out of London when the flight crew declared PAN PAN following a report of smoke in a lavatory. Cabin crew identified a passenger's laptop as source of the smoke, the laptop was put into an according bag and cooled with water, the smoke ceased. After the source of the smoke was confirmed the flight crew cancelled PAN and continued the flight to Toronto for a safe landing.

https://flightaware.com/live/flight/ACA849/history/20191203/1510Z/EGLL/CYYZ