rq-qos: use a mb for got_token

rq-qos: use a mb for got_token

Oleg noticed that our checking of data.got_token is unsafe in the
cleanup case, and should really use a memory barrier.  Use a wmb on the
write side, and a rmb() on the read side.  We don't need one in the main
loop since we're saved by set_current_state().

Reviewed-by: Oleg Nesterov <[email protected]>
Signed-off-by: Josef Bacik <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>