Re: [RFC] sched,livepatch: call klp_try_switch_task in __cond_resched

[Song Liu]

> On May 9, 2022, at 12:04 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> On Sat, May 07, 2022 at 10:46:28AM -0700, Song Liu wrote:
>> Busy kernel threads may block the transition of livepatch. Call
>> klp_try_switch_task from __cond_resched to make the transition easier.
> 
> What will a PREEMPT=y kernel do? How is it not a problem there, and if
> it is, this will not help that.
> 
> That is; I don't think this can be right.

I guess on PREEMPT=y kernel, we can simply preempt the long running 
kernel thread and check the transition? 

In this case (PREEMPT=n), we see a long running kernel thread could not
finish the transition. It calls cond_resched() and gets rescheduled 
(moves among different cores). However, it never finishes the transition,
because live patch doesn’t get a chance to check the stack. 

Does this answer the question?

Thanks,
Song