linux-kernel - Re: [PATCH 1/2] mmiotrace: fix buffer overrun detection

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Message-ID: <20081124221849.33c91bcf@daedalus.pq.iki.fi>
Date:	Mon, 24 Nov 2008 22:18:49 +0200
From:	Pekka Paalanen <pq@....fi>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel <linux-kernel@...r.kernel.org>, fweisbec@...il.com
Subject: Re: [PATCH 1/2] mmiotrace: fix buffer overrun detection

On Sun, 23 Nov 2008 20:34:13 +0100
Ingo Molnar <mingo@...e.hu> wrote:

> Sure - applied them to tip/tracing/urgent:
> 
>   fb91ee6: tracing, doc: update mmiotrace documentation
>   7ee1768: x86, mmiotrace: fix buffer overrun detection
> 
> Does this make mmiotrace fully functional in .28 ?

Oh right, the busylooping bug when echoing into trace_marker,
I already forgot about that, since I couldn't reproduce it.
I guess there's nothing to do, until someone finds a way to
reproduce it.

I could speculate about buffer wrap-around issues or such, but
that requires some serious code reviewing. Btw. C-c'ing didn't
interrupt the shell while spinning. The spinning ended when I
switched the tracer or disabled it, IIRC.

(This is related to 2.6.28-rc6.)

On Sun, 23 Nov 2008, Pekka Paalanen wrote:

> There's also another issue, but I am not sure how to reproduce it.
> The symptom is, that
> echo whatever > /debug/tracing/trace_marker
> gets stuck in a loop, bash eats 100% CPU: 10% user, 90% system.
> I got that twice today, like this: after a fresh boot echoing 64, 200,
> 70 to trace_entries, switching between nop and mmiotrace tracers,
> echoing 0 or 1 to tracing_enabled, and running the testmmiotrace
> module. At some point the user marker got stuck.
> 
> But then I tried to do that a third time by repeating some usage
> patterns I thought might trigger it, but it didn't happen.


-- 
Pekka Paalanen
http://www.iki.fi/pq/
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