Interrupt handler会复用当前被中断task的kernel stack，它并不是一个真正的task，也不拥有task_struct。因此一旦被调度出去，就无法再被调度回来继续执行。所以interrupt handler不允许被抢占。
参考资料：
Why can’t you sleep in an interrupt handler in the Linux kernel? Is this true of all OS kernels?；
Why kernel code/thread executing in interrupt context cannot sleep?;
Are there any difference between “kernel preemption” and “interrupt”?;
Why can not processes switch in atomic context?。