Re: [PATCH v2 10/10] sched/eevdf: Move to a single runqueue

[K Prateek Nayak]

Hello John,

On 5/14/2026 7:06 AM, John Stultz wrote:
> So looking at the callstack when I see the failure:
> proxy_find_task()
>   proxy_force_return()
>     proxy_resched_idle()  <- sets rq->donor to idle
>     attach_one_task()
>       wakeup_preempt()
>         wakeup_preempt_fair()

After this point, I would have expected we called idle class's
wakeup_preempt() since that is the donor context ...

>           update_protect_slice() <- called with the donor's se
>             calc_delta_fair()
>               __calc_delta() <- div by zero
> 
> Basically we end up in wakeup_preempt_fair() with rq->donor ==
> rq->idle because we earlier called proxy_resched_idle().

Could you check if following makes things better:

  (Only build tested)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3ae5f19c1b7e..77f4ebe8f5c7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6653,6 +6653,7 @@ static inline void proxy_set_task_cpu(struct task_struct *p, int cpu)
 static inline struct task_struct *proxy_resched_idle(struct rq *rq)
 {
 	put_prev_set_next_task(rq, rq->donor, rq->idle);
+	rq->next_class = &idle_sched_class;
 	rq_set_donor(rq, rq->idle);
 	set_tsk_need_resched(rq->idle);
 	return rq->idle;
---

I'm just getting started for the day so it'll be a while before I
actually get to test this on top of flat cgroup bits which I haven't yet
run with SCHED_PROXY_EXEC enabled.

-- 
Thanks and Regards,
Prateek