Messages in this thread | | | Date | Wed, 4 Mar 2015 05:46:54 +0100 | From | Ingo Molnar <> | Subject | Re: [tip:perf/core] Revert "perf: Remove the extra validity check on nr_pages" |
| |
* Liang, Kan <kan.liang@intel.com> wrote:
> > * 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? > > 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!
Thanks,
Ingo
| |