linux-kernel - Re: [PATCH v2] sched/fair: Fix insertion in rq->leaf_cfs_rq

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Date:   Wed, 30 Jan 2019 15:01:44 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com, tj@...nel.org,
        sargun@...gun.me
Subject: Re: [PATCH v2] sched/fair: Fix insertion in rq->leaf_cfs_rq_list

On Wed, Jan 30, 2019 at 03:01:04PM +0100, Peter Zijlstra wrote:
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -282,13 +282,15 @@ static inline struct cfs_rq *group_cfs_r
>  	return grp->my_q;
>  }
>  
> -static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
> +static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
>  {
>  	struct rq *rq = rq_of(cfs_rq);
>  	int cpu = cpu_of(rq);
>  
>  	if (cfs_rq->on_list)
> -		return;
> +		return rq->tmp_alone_branch == &rq->leaf_cfs_rq_list;

And I'm almost certain that can be: return true, but got my brain in a
twist.

> +
> +	cfs_rq->on_list = 1;
>  
>  	/*
>  	 * Ensure we either appear before our parent (if already