Re: [PATCH] sched_ext: Fix spurious WARN on stale ops_state in ops_dequeue()

[Samuele Mariotti <smariotti@disroot.org>]

Hi Tejun,

>Let's not do the WARN and exit. We shouldn't get this wrong and if we get
>this wrong, it's going to be obvious from lockup detectors. Can you please
>add a comment explaining the retry condition tho?
>
>Thanks.
>
>-- 
>tejun

Thanks for the feedback. If I understood correctly, you prefer no retry
limit, letting the lockup detectors catch any real bug. I also added
unlikely() since the stale case is by definition rare.

Here is the updated version:

/*
  * If SCX_TASK_IN_CUSTODY is not set, opss is stale: finish_dispatch()
  * has already claimed the task and cleared SCX_TASK_IN_CUSTODY. Retry
  * to get a fresh view of p->scx.ops_state.
  */
if (unlikely(!(READ_ONCE(p->scx.flags) & SCX_TASK_IN_CUSTODY))) {
     cpu_relax();
     goto retry;
}

Let me know if this looks good to you.

Thanks,
Samuele