a glutton for punishment, work, etc.

a ˌglutton for ˈpunishment, ˈwork, etc.

(informal) a person who seems to like doing unpleasant or difficult things: You’re going to drive all the way to London and back in a day? You’re a glutton for punishment, aren’t you?She’s a glutton for work. She stays late every evening.
A glutton is a person who is too fond of food. In this idiom, it refers to a person who seems to be very fond of the thing mentioned.
See also: glutton