linux-kernel - Re: tracing ring_buffer

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Message-ID: <20120524225703.GA31149@redhat.com>
Date:	Thu, 24 May 2012 18:57:03 -0400
From:	Dave Jones <davej@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: tracing ring_buffer_resize oops.

On Thu, May 24, 2012 at 06:49:41PM -0400, Steven Rostedt wrote:
 > On Thu, 2012-05-24 at 16:05 -0400, Dave Jones wrote:
 > > On Thu, May 24, 2012 at 03:24:55PM -0400, Steven Rostedt wrote:
 > >  > On Thu, 2012-05-24 at 15:11 -0400, Dave Jones wrote:
 > >  > 
 > >  > >  > Also, how reproducible is it? When it triggered for me, it was constant.
 > >  > >  > Every boot and test failed. But after I did the make mrproper, I have
 > >  > >  > not been able to trigger it again. This is why I put it down as a bad
 > >  > >  > build.
 > >  > > 
 > >  > > happens every time for me so far.
 > >  > 
 > >  > Did you also do a make mrproper and try again?
 > > 
 > > ok, that's nasty.  Works fine after a make clean.
 > > 
 > 
 > Hmm, I did two make mrproper builds and they both failed. So this isn't
 > a build issue. Must just be some nasty race. I'm still leaning that this
 > has to do with the breakpoint function tracing updates.
 > 
 > Looking deeper into it.
 > 
 > -- Steve

Possibly unrelated, but I found that it only worked once per boot. Is that expected ?

echo irqsoff > current_tracer
echo latency-format > trace_options
echo 0 > tracing_max_latency
echo 1 > tracing_on
blah
echo 0 > tracing_on
cat trace

showed me a trace as I expected

repeating the same commands then got me an empty trace.

what gives ?

	Dave

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