linux-kernel - Re: perf per-symbol histogram causes memory corruption

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Date:	Thu, 25 Feb 2010 12:11:48 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	David Miller <davem@...emloft.net>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:	a.p.zijlstra@...llo.nl, paulus@...ba.org,
	linux-kernel@...r.kernel.org,
	Frédéric Weisbecker 
	<fweisbec@...il.com>
Subject: Re: perf per-symbol histogram causes memory corruption


(Added Arnaldo to the Cc: - he's maintaining the symbol lookup bits of perf.)

* David Miller <davem@...emloft.net> wrote:

> When builtin-annotate.c processes sample events via
> process_sample_event() it uses 'sample_filter'
> 
> sample_filter() sizes the histogram object for a symbol based upon the
> size, calculated as "sym->end - sym->start", to determine the number
> of IP sample slots to allocate.
> 
> The problem is, the sym->end value is not stable at this point.
> 
> For example, dso__load_sym() first loads all of the symbols, then it
> makes another pass over the symbols by calling symbols__fixup_end()
> which will adjust the sym->end values of various symbols.
> 
> At this point, the histogram IP sample array allocated by
> sample_filter() can become too small, and hits recorded can thus
> access past the end of the array corrupting memory.
> 
> I get this very reliably on sparc64, and it took me a few days to root
> cause this. :-)
> 
> I don't see an immediate way to fix this, any ideas?
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