Warnock, who joined Rovers from Liverpool in January 2007, has expressed his delight at committing his immediate future to the Premier League side.
He told the club's official website: "It is fantastic, I think the club offering me a new deal is reward for what I've been doing and obviously I've been doing something right.
"It is a massive thing to be offered a new contract and when you see how the club is progressing and how things are going then you want to be part of that, and things are going well so I can't really argue."
Olsson is just 19 and is delighted with the deal that comes after making his second league appearance in the win over Derby on the weekend.
"I'm very happy to have signed a new deal, it is what I've been working hard for, to get a contract with the first team," Olsson said.
"I've been doing well, I've been working hard, I came here two years ago and now I'm delighted to get that first-team contract.
"I've been in the squad a lot of times and on the bench too in some games, so my aim for next season is to be more involved and play more first-team games.
"I'm learning all the time in training and I'm delighted that the manager has shown this faith in me."