according to tweets and the following Swiss news website ( http://www.20min.ch/ro/sports/tennis...erer--31327590
), a Chinese webposter with the pseudo "Blue cat" started on the 25th of september posting on a frequented Chinese sports website a sentence "let you know that I'm going to kill Roger Federer" with a photoshop of a beheaded Fed.
Then he kept on every day.
That's why the Chinese security have been alerted since then and they are inquiring and should prevent people to approach too near to Fed. His practise will be closed to the public.
Besides, Fed landed on a small airport rather than in Shanghai main airport.