linux-kernel - Re: [PATCH] sched: Fix balance_push() vs __sched

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Message-ID: <7e49e2b73aae471514f277d89bc925da269c89d6.camel@mediatek.com>
Date:   Wed, 8 Jun 2022 22:16:43 +0800
From:   Jing-Ting Wu <jing-ting.wu@...iatek.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>, <tglx@...utronix.de>,
        <wsd_upstream@...iatek.com>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        <Jonathan.JMChen@...iatek.com>,
        "chris.redpath@....com" <chris.redpath@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Donnefort <vdonnefort@...il.com>,
        "Ingo Molnar" <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        "Vincent Guittot" <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        "Christian Brauner" <brauner@...nel.org>
Subject: Re: [PATCH] sched: Fix balance_push() vs __sched_setscheduler()

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