linux-kernel - Re: [PATCH v2] sched/rt: Rework for_each_process_thread() iterations in tg_has_rt

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Date:   Wed, 25 Apr 2018 21:49:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     Juri Lelli <juri.lelli@...il.com>, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched/rt: Rework for_each_process_thread() iterations
 in tg_has_rt_tasks()

On Fri, Apr 20, 2018 at 01:06:31PM +0300, Kirill Tkhai wrote:
> @@ -2406,12 +2407,15 @@ static inline int tg_has_rt_tasks(struct task_group *tg)
>  	if (task_group_is_autogroup(tg))
>  		return 0;
>  
> -	for_each_process_thread(g, p) {
> -		if (rt_task(p) && task_group(p) == tg)
> -			return 1;
> -	}
> +	css_task_iter_start(&tg->css, 0, &it);
> +	while ((task = css_task_iter_next(&it)))
> +		if (rt_task(task)) {
> +			ret = 1;
> +			break;
> +		}

Aside from the missing {} there, the patch looks OK I suppose.

The races found seems somewhat dodgy, but like you argue, they're not in
fact new :/


> +	css_task_iter_end(&it);
>  
> -	return 0;
> +	return ret;
>  }
>