linux-kernel - Re: [PATCH] irq: clear kstat

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Message-Id: <20090206140005.44b4bb50.akpm@linux-foundation.org>
Date:	Fri, 6 Feb 2009 14:00:05 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] irq: clear kstat_irqs

On Fri, 06 Feb 2009 13:50:47 -0800
Yinghai Lu <yinghai@...nel.org> wrote:

> +void clear_kstat_irqs(struct irq_desc *desc)
> +{
> +	unsigned long bytes;

size_t would be more formally correct.

> +	char *ptr;
> +
> +	ptr = (char *)desc->kstat_irqs;
> +	/* Compute how many bytes we need to clear */
> +	bytes = nr_cpu_ids * sizeof(unsigned int);

This is fragile.  For example, if someone changes ->kstat_irqs to long
then this code will secretly and subtly break.

If it used sizeof(*(desc->kstat_irqs)) then everything would magically
continue to work.

> +	memset(ptr, 0, bytes);
> +}

The whole function could be written as

	memset(desc->kstat_irqs, 0, nr_cpu_ids * sizeof(*(desc->kstat_irqs)));

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