Re: [PATCH] sched: Fix balance_push() vs __sched_setscheduler() - Jing-Ting Wu

From: Jing-Ting Wu <jing-ting.wu@mediatek.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>,
	Valentin Schneider <vschneid@redhat.com>, <tglx@linutronix.de>,
	<wsd_upstream@mediatek.com>, <linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-mediatek@lists.infradead.org>,
	<Jonathan.JMChen@mediatek.com>,
	"chris.redpath@arm.com" <chris.redpath@arm.com>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Vincent Donnefort <vdonnefort@gmail.com>,
	"Ingo Molnar" <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	"Vincent Guittot" <vincent.guittot@linaro.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	"Christian Brauner" <brauner@kernel.org>
Subject: Re: [PATCH] sched: Fix balance_push() vs __sched_setscheduler()
Date: Wed, 8 Jun 2022 22:16:43 +0800	[thread overview]
Message-ID: <7e49e2b73aae471514f277d89bc925da269c89d6.camel@mediatek.com> (raw)
In-Reply-To: <Yp/Frp7BMp9E5dSp@hirez.programming.kicks-ass.net>

Hi Peter

On Tue, 2022-06-07 at 23:39 +0200, Peter Zijlstra wrote:
> On Tue, Jun 07, 2022 at 10:40:36PM +0200, Peter Zijlstra wrote:
> > On Fri, Jun 03, 2022 at 12:15:51AM +0800, Jing-Ting Wu wrote:
> > > The patch is helpful to the syndrome, passed stability test over
> > > 10
> > > days so far. (as-is: < 48 hours failed)
> > 
> > Excellent, let me go write a Changelog for it, or something.
> 
> How's this then?

I think the description is fine.
Thanks for your help.

[...]
>  
> -static inline struct callback_head *splice_balance_callbacks(struct
> rq *rq)
> +static inline struct callback_head *
> +__splice_balance_callbacks(struct rq *rq, bool split)
>  {
>  	struct callback_head *head = rq->balance_callback;
>  
> +	if (likely(!head))
> +		return NULL;
> +
>  	lockdep_assert_rq_held(rq);
> -	if (head)
> +	/*
> +	 * Must not take balance_push_callback off the list when
> +	 * splace_balance_callbac() and balance_callbacks() are not

Should we change splace_balance_callbac() to splice_balance_callbacks()
at here?

> +	 * in the same rq->lock section.
> +	 *
> +	 * In that case it would be possible for __schedule() to
> interleave
> +	 * and observe the list empty.
> +	 */
> +	if (split && head == &balance_push_callback)
> +		head = NULL;
> +	else
>  		rq->balance_callback = NULL;
>  
>  	return head;
>  }
>  
[...]

Best Regards,
Jing-Ting Wu

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