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

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Date:	Tue, 12 Mar 2013 13:38:39 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCHv3] perf: Fix vmalloc ring buffer free function

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.

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