To make the kernel preemptive in the real-time enhanced Linux, there are two approaches. The Linux kernel itself is modified to be preemptive. The first is to insert preemption points into the kernel. In the traditional Linux, critical regions are guarded from other process access by prohibiting process preemption during a system call execution. To insert preemption points into the kernel, we need to divide the critical regions and prepare the preempted process restarting mechanism.