Re: [PATCHv3] perf: Fix vmalloc ring buffer free function

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Tue, 2013-03-12 at 11:53 +0100, Jiri Olsa wrote:
> > @@ -316,7 +316,7 @@ void rb_free(struct ring_buffer *rb)
> >  struct page *
> >  perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
> >  {
> > -     if (pgoff > (1UL << page_order(rb)))
> > +     if (pgoff > rb->nr_pages)
> >               return NULL;
> 
> here it's the '>' that masks that there's actually (rb->nr_pages + 1) pages
> 
> >  
> >       return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE);
> > @@ -336,7 +336,7 @@ static void rb_free_work(struct work_struct *work)
> >       int i, nr;
> >  
> >       rb = container_of(work, struct ring_buffer, work);
> > -     nr = 1 << page_order(rb);
> > +     nr = rb->nr_pages;
> >  
> >       base = rb->user_page;
> >       for (i = 0; i < nr + 1; i++)
> 
> and here's the user plus one

Right, we could make that either '< nr' and '<= nr' or '<= nr+1' and '<
nr+1'. No real preference either way, but you're right in that being
consistent here makes sense.