Re: [SPAM]Re: [Bug] Race condition between CPU hotplug off flow and __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: [SPAM]Re: [Bug] Race condition between CPU hotplug off flow and __sched_setscheduler()
Date: Mon, 23 May 2022 15:12:54 +0800	[thread overview]
Message-ID: <52eea711b8ce3151ff73bfb0289cc9da0e8c4a10.camel@mediatek.com> (raw)
In-Reply-To: <20220519134706.GH2578@worktop.programming.kicks-ass.net>

On Thu, 2022-05-19 at 15:47 +0200, Peter Zijlstra wrote:
> On Thu, May 19, 2022 at 08:53:15PM +0800, Jing-Ting Wu wrote:
> > Hi all
> > 
> > 
> > There is a race condition between CPU hotplug off flow and
> > __sched_setscheduler(), which will cause hang-up in CPU hotplug off
> > flow.
> 
> How easy can you reproduce; does the below hack make it better?

The issue can be reproduced in about 48 hours when hotplug up/down
frequently.

Thanks for your suggestion.
I think the hack patch could stay the rq->balance_callback when rq-
>callback = &balance_push_callback.
We can add hack patch to the stability test.

> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 95bac3b094b3..f18ee22b29bc 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4763,20 +4763,30 @@ struct callback_head balance_push_callback =
> {
>  	.func = (void (*)(struct callback_head *))balance_push,
>  };
>  
> -static inline struct callback_head *splice_balance_callbacks(struct
> rq *rq)
> +static inline struct callback_head *
> +__splice_balance_callbacks(struct rq *rq, bool foo)
>  {
>  	struct callback_head *head = rq->balance_callback;
>  
>  	lockdep_assert_rq_held(rq);
> -	if (head)
> -		rq->balance_callback = NULL;
> +	if (head) {
> +		if (foo && head == &balance_push_callback)
> +			head = NULL;
> +		else
> +			rq->balance_callback = NULL;
> +	}
>  
>  	return head;
>  }
>  
> +static inline struct callback_head *splice_balance_callbacks(struct
> rq *rq)
> +{
> +	return __splice_balance_callbacks(rq, true);
> +}
> +
>  static void __balance_callbacks(struct rq *rq)
>  {
> -	do_balance_callbacks(rq, splice_balance_callbacks(rq));
> +	do_balance_callbacks(rq, __splice_balance_callbacks(rq,
> false));
>  }
>  
>  static inline void balance_callbacks(struct rq *rq, struct
> callback_head *head)
> 

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