Re: [tip:perf/core] Revert "perf: Remove the extra validity check on nr_pages"

[Ingo Molnar <mingo@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