Linux Kernel 在任何時刻都處於三種狀況之一

        Linux Kernel 在任何時刻都處於三種狀況之一:

        1。In user space, executing user code in a process
        2。In kernel-space , in process context, executing on behalf of a specific process
        3。In kernel-space , in interrupt context, no associated with a process, handling an interrupt

        就算是在系統idle 時，kernel is executing an idle process in process context. 
        (from Linux.Kernel.Development.3rd.Edition -Robert Love)