* Liang, Kan <kan.li...@intel.com> wrote:
> > * Liang, Kan <kan.li...@intel.com> wrote:
> >
> > > > * tip-bot for Kan Liang <tip...@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))
> > > > return -EINVAL;
> > > >
> > > > 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).
> >
> > I don't think you answered my first question, on which my later
> > comments rely:
> >
> > > > Hm, what does is_power_of_2(0) return? It should return 0, because 0
> > is
> > > > not a power of 2!
>
> Yes, is_power_of_2(0) returns 0.
Oh, indeed, and I clearly cannot read code: your original argument and
the revert is correct, sorry about the confusion!
Thanks,
Ingo
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