linux-kernel - Re: [question] NR

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Date:	Wed, 24 Nov 2010 14:56:06 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Paul Mundt <lethal@...ux-sh.org>
cc:	Haojian Zhuang <haojian.zhuang@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [question] NR_IRQS in genirq

On Wed, 24 Nov 2010, Paul Mundt wrote:

> On Wed, Nov 24, 2010 at 03:28:37PM +0800, Haojian Zhuang wrote:
> > Hi all,
> > 
> > I'm using the latest kernel 2.6.37-rc1. Now I met some issues on genirq.
> > 
> > 1. While SPARSE IRQ is enabled, nr_irqs may be larger than NR_IRQS.
> > But the allocated_irqs bitmap (kernel/irq/irqdesc.c) is restricted in
> > NR_IRQS. Is it an issue?
> > 
> > 2. irqs_resend bitmap of kernel/irq/resend.c is also restricted in
> > NR_IRQS. Is it an issue, too?
> > 
> Perhaps something like:
> 
> diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
> index 9988d03..11bd76c 100644
> --- a/kernel/irq/irqdesc.c
> +++ b/kernel/irq/irqdesc.c
> @@ -215,6 +215,11 @@ int __init early_irq_init(void)
>  	initcnt = arch_probe_nr_irqs();
>  	printk(KERN_INFO "NR_IRQS:%d nr_irqs:%d %d\n", NR_IRQS, nr_irqs, initcnt);
>  
> +	if (unlikely(nr_irqs > NR_IRQS)) {
> +		WARN(1, "Probed more than NR_IRQS, chomping.\n");
> +		nr_irqs = NR_IRQS;
> +	}

Yep, we need that sanity check, but the WARN() is overkill as we
already know the call chain :)

Thanks,

	tglx
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