linux-kernel - Re: [RFC PATCH 5/6 v4] perf: Fix race in callchains

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Message-ID: <20100817045331.GE24726@drongo>
Date:	Tue, 17 Aug 2010 14:53:31 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	Will Deacon <will.deacon@....com>,
	Paul Mundt <lethal@...ux-sh.org>,
	David Miller <davem@...emloft.net>,
	Borislav Petkov <bp@...64.org>
Subject: Re: [RFC PATCH 5/6 v4] perf: Fix race in callchains

On Tue, Aug 17, 2010 at 03:34:06AM +0200, Frederic Weisbecker wrote:

> Now that software events don't have interrupt disabled anymore in
> the event path, callchains can nest on any context. So seperating
> nmi and others contexts in two buffers has become racy.
> 
> Fix this by providing one buffer per nesting level. Given the size
> of the callchain entries (2040 bytes * 4), we now need to allocate
> them dynamically.
> 
> v2: Fixed put_callchain_entry call after recursion.
>     Fix the type of the recursion, it must be an array.
> 
> v3: Use a manual pr cpu allocation (temporary solution until NMIs
>     can safely access vmalloc'ed memory).

It would be nice to make these allocations node-local.

Also, I see that we're allocating 4 buffers per cpu on powerpc when we
strictly only need 3, but I don't suppose that really matters.

Paul.
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