>
>
> * tip-bot for Kan Liang <[email protected]> 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?
nr_pages == 0 is valid, we cannot return -EINVAL. Because
vma_size = vma->vm_end - vma->vm_start;
nr_pages = (vma_size / PAGE_SIZE) - 1;
So here we only want to check is_power_of_2
when the pages > 1 (or nr_pages > 0).
Thanks,
Kan
>
> Thanks,
>
> Ingo
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