linux-kernel - Re: [PATCH] sched/deadline: Test for CPU's presence explicitly

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Date:	Mon, 17 Feb 2014 15:50:27 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org,
	konrad.wilk@...cle.com, juri.lelli@...il.com
Subject: Re: [PATCH] sched/deadline: Test for CPU's presence explicitly

On Mon, Feb 17, 2014 at 09:12:33AM -0500, Boris Ostrovsky wrote:
> A hot-removed CPU may have ID that is numerically larger than the number of
> existing CPUs in the system (e.g. we can unplug CPU 4 from a system that
> has CPUs 0, 1 and 4).
> 
> Thus the WARN_ONs should check whether the CPU in question is currently
> present, not whether its ID value is less than num_present_cpus().
> 
> Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>

Thanks!, please also always CC the author of the code in question.

> ---
>  kernel/sched/cpudeadline.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> index 045fc74..5b8838b 100644
> --- a/kernel/sched/cpudeadline.c
> +++ b/kernel/sched/cpudeadline.c
> @@ -70,7 +70,7 @@ static void cpudl_heapify(struct cpudl *cp, int idx)
>  
>  static void cpudl_change_key(struct cpudl *cp, int idx, u64 new_dl)
>  {
> -	WARN_ON(idx > num_present_cpus() || idx == IDX_INVALID);
> +	WARN_ON(!cpu_present(idx) || idx == IDX_INVALID);
>  
>  	if (dl_time_before(new_dl, cp->elements[idx].dl)) {
>  		cp->elements[idx].dl = new_dl;
> @@ -117,7 +117,7 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
>  	}
>  
>  out:
> -	WARN_ON(best_cpu > num_present_cpus() && best_cpu != -1);
> +	WARN_ON(!cpu_present(best_cpu) && best_cpu != -1);
>  
>  	return best_cpu;
>  }
> @@ -137,7 +137,7 @@ void cpudl_set(struct cpudl *cp, int cpu, u64 dl, int is_valid)
>  	int old_idx, new_cpu;
>  	unsigned long flags;
>  
> -	WARN_ON(cpu > num_present_cpus());
> +	WARN_ON(!cpu_present(cpu));
>  
>  	raw_spin_lock_irqsave(&cp->lock, flags);
>  	old_idx = cp->cpu_to_idx[cpu];
> -- 
> 1.8.1.4
> 
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