After fork() or sleep(), the process return to user space, `EFLAGS = IF`, but PIC doesn't work untill I reinit PIC. this bug maybe cause by `kern/irq.c` temporary fix in commit fc0e84caa1c3ae95998342f2b03125e2226d0dd6 e42e99b3f6e32a967af5acf015488549b63aa863 212905b84fb86a0511f48925f917c1511c319fc5