Control logic synthesis of discrete-event systems is considered in this paper in the setting of controlled Petri nets. The problem is to find a control policy that restricts the behavior of a controlled Petri net so that a collection of forbidden state conditions is satisfied. S-decreases are introduced as a tool for the control synthesis. The S-decreases are weight vectors defined on the places of a net such that the weighted sum of tokens in the net never increases with any transition firing. On the basis of S-decreases, the authors propose an efficient method for the synthesis of the maximally permissive state feedback control policy for a class of controlled Petri nets whose uncontrolled subnets are forward and backward conflict-free nets. This method upgrades all integer linear programming-based methods for which the authors only require solving much simpler linear programming problems to determine maximally permissive controls.