linux-kernel - Re: [PATCH 05/12] sched: Move sched_class::prio

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Message-ID: <717a0743-6d8f-4e35-8f2f-70a158b31147@arm.com>
Date: Tue, 13 Jan 2026 11:45:43 +0100
From: Pierre Gondois <pierre.gondois@....com>
To: K Prateek Nayak <kprateek.nayak@....com>,
 Peter Zijlstra <peterz@...radead.org>, tj@...nel.org
Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, juri.lelli@...hat.com,
 vincent.guittot@...aro.org, dietmar.eggemann@....com, rostedt@...dmis.org,
 bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.com,
 longman@...hat.com, hannes@...xchg.org, mkoutny@...e.com,
 void@...ifault.com, arighi@...dia.com, changwoo@...lia.com,
 cgroups@...r.kernel.org, sched-ext@...ts.linux.dev, liuwenfang@...or.com,
 tglx@...utronix.de, Christian Loehle <christian.loehle@....com>
Subject: Re: [PATCH 05/12] sched: Move sched_class::prio_changed() into the
 change pattern

Hello Prateek,

On 1/13/26 05:12, K Prateek Nayak wrote:
> Hello Pierre,
>
> On 1/13/2026 2:14 AM, Pierre Gondois wrote:
>> Hello Peter,
>>
>> It seems this patch:
>> 6455ad5346c9 ("sched: Move sched_class::prio_changed() into the change pattern")
>> is triggering the following warning:
>> rq_pin_lock()
>> \-WARN_ON_ONCE(rq->balance_callback && rq->balance_callback != &balance_push_callback);
> Can you check if the following solution helps your case too:
> https://lore.kernel.org/all/20260106104113.GX3707891@noisy.programming.kicks-ass.net/
>
I can still see the issue.
It seems the task deadline is also updated in:
sched_change_end()
\-enqueue_task_dl()
   \-enqueue_dl_entity()
     \-setup_new_dl_entity()
       \-replenish_dl_new_period()
if the task's period finished.

So in sched_change_end(), the task priority (i.e. p->dl.deadline) is 
updated.
This results in having an old_deadline earlier than the new p->dl.deadline.
Thus the rq->balance_callback:

prio_changed_dl() {
...
if (dl_time_before(old_deadline, p->dl.deadline))
   deadline_queue_pull_task(rq);
...
}