The priority inversion is one of the problems which may prevent the guarantee of the hard deadline tasks executions. The Priority Ceiling Protocol(PCP) could be a solution to the priority inversion problem. However, the single blocking property of PCP is sometimes very restrictive. In this paper, we propose a new protocol called Ceiling Adjustment Scheme(CAS), which adjusts the ceilings of shared resources by using the slack blocking time of hard deadline tasks while meeting their deadlines. Our simulation study shows that CAS experiences significantly reduced number of blockings(priority inversions) compared to that of PCP, and hence it achieves faster response times and reduced miss rates of soft deadline tasks under overload situations.