linux-kernel - Re: [PATCH v2 1/1] ftrace: do not update max buffer with no users

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Date:	Thu, 13 Nov 2008 09:40:40 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Pekka Paalanen <pq@....fi>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH v2 1/1] ftrace: do not update max buffer with no users


* Steven Rostedt <rostedt@...dmis.org> wrote:

> Impact: only use max latency buffer when a user is configured
> 
> Pekka reported a bug with the resizing of the buffers when only the 
> MMIO tracer was configured. The issue was, to save memory, the max 
> latency trace buffer was only initialized if a tracer that uses it 
> is configured in.
> 
> What happened was that the max latency buffer was never initialized 
> when only the MMIO tracer was configurued. The MMIO tracer does not 
> use the max tracer, which kept it from being initialized. But the 
> resize code still tried to resize the max latency buffers, but 
> because they were never allocated, the resize code was passed a NULL 
> pointer.
> 
> This patch checks if the max tracer is NULL before resizing it. It 
> also hides the modification functions of the max tracer behind the 
> TRACER_MAX_TRACE config.
> 
> Reported-by: Pekka Paalanen <pq@....fi>
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> ---
>  kernel/trace/trace.c |  171 ++++++++++++++++++++++++++------------------------
>  1 files changed, 88 insertions(+), 83 deletions(-)

This is _way_ too much churn for .28, we need a much simpler solution.

	Ingo
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