linux-kernel - Re: [PATCHv2] perf: Fix vmalloc ring buffer free function

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Message-ID: <1363019193.14933.14.camel@laptop>
Date:	Mon, 11 Mar 2013 17:26:33 +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: [PATCHv2] perf: Fix vmalloc ring buffer free function

On Mon, 2013-03-11 at 12:21 +0100, Jiri Olsa wrote:
> >  pg_nr     = offset >> page_shift;
> >  pg_offset = offset & (1 << page_shift) - 1;
> > 
> > You just wrecked that.
> > 
> > >     handle->page &= rb->nr_pages - 1;
> 
> here's ^^^ where the handle->page becomes 0 due to (rb->nr_pages == 0)

then that'll be &= -1, which is a nop, no?

Also, you wrecked it for anything that uses some intermediate page
order (we currently don't).

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