linux-kernel - Re: [tip:perf/core] Revert "perf: Remove the extra validity check on nr

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Date:	Tue, 3 Mar 2015 09:44:08 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	hpa@...or.com, ak@...ux.intel.com, acme@...hat.com,
	kan.liang@...el.com, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org, xiakaixu@...wei.com,
	tglx@...utronix.de
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] Revert "perf: Remove the extra validity check on
 nr_pages"


* tip-bot for Kan Liang <tipbot@...or.com> wrote:

> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4446,7 +4446,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
>  	 * If we have rb pages ensure they're a power-of-two number, so we
>  	 * can do bitmasks instead of modulo.
>  	 */
> -	if (!is_power_of_2(nr_pages))
> +	if (nr_pages != 0 && !is_power_of_2(nr_pages))
>  		return -EINVAL;

Hm, what does is_power_of_2(0) return? It should return 0, because 0 
is not a power of 2!

and if it's fixed to return 0, then the check should properly be 
something like:

	if (!nr_pages || !is_power_of_2(nr_pages))

or so?

Thanks,

	Ingo
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