Linux Kernel文档中的以下句子是什么意思？

Question

In the Linux kernel source code, the file Documentation/scheduler/sched-arch.txt contains the following lines.

Your cpu_idle routines need to obey the following rules:

Preempt should now disabled over idle routines. Should only be enabled to call schedule() then disabled again.

I am relatively new to the Linux kernel world, so I can think of three possible interpretations for the first line for implementors of a cpu_idle routine.

1. We should assume that preemption is disabled.
2. We should verify that preemption is disabled
3. We should ensure that preemption is disabled.

Does anyone with more kernel experience know the correct interpretation?

Answer 1

Yikes. If you're adding support for a new platform, please update that comment while you're at it.

I haven't done Linux kernel development in a long time, but as far as I can tell, it should say "Preemption is disabled [by the kernel] while running your cpu_idle routine. You should enable it only to call schedule(), and then disable it again immediately."

For example, in the PPC idle.c, the while loop ends with:

preempt_enable_no_resched();
schedule();
preempt_disable();

and doesn't touch preemption otherwise.