linux-kernel - Re: [PATCH sched_ext/for-6.12-fixes] sched_ext: Call __balance_callbacks() from __scx_task_iter_rq

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Message-ID: <20241031233634.GU14555@noisy.programming.kicks-ass.net>
Date: Fri, 1 Nov 2024 00:36:34 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Tejun Heo <tj@...nel.org>
Cc: David Vernet <void@...ifault.com>, linux-kernel@...r.kernel.org,
	sched-ext@...a.com, kernel-team@...a.com,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH sched_ext/for-6.12-fixes] sched_ext: Call
 __balance_callbacks() from __scx_task_iter_rq_unlock()

On Wed, Oct 30, 2024 at 11:41:39AM -1000, Tejun Heo wrote:

> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -1315,6 +1315,8 @@ static void scx_task_iter_start(struct s
>  static void __scx_task_iter_rq_unlock(struct scx_task_iter *iter)
>  {
>  	if (iter->locked) {
> +		/* ->switched_from() may have scheduled balance callbacks */
> +		__balance_callbacks(iter->rq);
>  		task_rq_unlock(iter->rq, iter->locked, &iter->rf);
>  		iter->locked = NULL;
>  	}

I think you need to unpin/repin around it. The balance callbacks like to
drop rq->lock at times.