linux-kernel - Re: [PATCH 3/5] sched/deadline: Fix wrong cpudl_find() in check_preempt_equal

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Date:	Tue, 27 Jan 2015 13:48:15 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Xunlei Pang <pang.xunlei@...aro.org>
Cc:	linux-kernel@...r.kernel.org, Juri Lelli <juri.lelli@...il.com>
Subject: Re: [PATCH 3/5] sched/deadline: Fix wrong cpudl_find() in
 check_preempt_equal_dl()

On Mon, Jan 19, 2015 at 04:49:38AM +0000, Xunlei Pang wrote:
> +++ b/kernel/sched/deadline.c
> @@ -943,14 +943,23 @@ out:
>  	return cpu;
>  }
>  
> +static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
> +
>  static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
>  {
> +	struct cpumask *later_mask =
> +			this_cpu_cpumask_var_ptr(local_cpu_mask_dl);
> +
> +	/* Make sure the mask is initialized first */
> +	if (unlikely(!later_mask))
> +		return;
> +
>  	/*
>  	 * Current can't be migrated, useless to reschedule,
>  	 * let's hope p can move out.
>  	 */
>  	if (rq->curr->nr_cpus_allowed == 1 ||
> -	    cpudl_find(&rq->rd->cpudl, rq->curr, NULL) == -1)
> +	    cpudl_find(&rq->rd->cpudl, rq->curr, later_mask) == -1)
>  		return;
>  
>  	/*

But but, should you not put something in that mask before you use it?
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