linux-kernel - Re: [PATCH?] Livelock in pick_next_task_fair() / idle

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Date:	Fri, 3 Jul 2015 18:39:28 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	Rabin Vincent <rabin.vincent@...s.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>,
	Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH?] Livelock in pick_next_task_fair() / idle_balance()

On Thu, Jul 02, 2015 at 07:25:11AM +0800, Yuyang Du wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 40a7fcb..f7cc1ef 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5898,6 +5898,10 @@ static int detach_tasks(struct lb_env *env)
>  		return 0;
>  
>  	while (!list_empty(tasks)) {
> +
> +		if (env->idle == CPU_NEWLY_IDLE && env->src_rq->nr_running <= 1)

Should we make that ->idle != CPU_NOT_IDLE ?

> +			break;
> +
>  		p = list_first_entry(tasks, struct task_struct, se.group_node);
>  
>  		env->loop++;
--
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