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From: Ingo Molnar <mingo@kernel.org>
To: hpa@zytor.com, ak@linux.intel.com, acme@redhat.com,
	kan.liang@intel.com, a.p.zijlstra@chello.nl,
	linux-kernel@vger.kernel.org, xiakaixu@huawei.com,
	tglx@linutronix.de
Cc: linux-tip-commits@vger.kernel.org
Subject: Re: [tip:perf/core] Revert "perf: Remove the extra validity check on nr_pages"
Date: Tue, 3 Mar 2015 09:44:08 +0100	[thread overview]
Message-ID: <20150303084407.GA1448@gmail.com> (raw)
In-Reply-To: <tip-2ed11312eb19506c027e7cac039994ad42a9cb2c@git.kernel.org>


* tip-bot for Kan Liang <tipbot@zytor.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

  reply	other threads:[~2015-03-03  8:44 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-02  7:14 [PATCH 1/1] " kan.liang
2015-03-02 21:03 ` Arnaldo Carvalho de Melo
2015-03-03  6:26 ` [tip:perf/core] " tip-bot for Kan Liang
2015-03-03  8:44   ` Ingo Molnar [this message]
2015-03-03 20:04     ` Liang, Kan
2015-03-04  4:46       ` Ingo Molnar
2015-03-04 14:06         ` Liang, Kan
2015-03-04 20:28           ` Ingo Molnar

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