linux-kernel - Re: perf/ftrace lockup on 3.12-rc6 with trigger code

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Message-ID: <20131026084836.GC14237@gmail.com>
Date:	Sat, 26 Oct 2013 10:48:36 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Dave Jones <davej@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: perf/ftrace lockup on 3.12-rc6 with trigger code


* Vince Weaver <vincent.weaver@...ne.edu> wrote:

> I don't know if there are any better ways to try to debug things 
> than the printk route.  Though that has its own problems as the 
> printk's themselves start showing up in the ftrace traces.

One additional brute-force method is earlyprintk=...,keep and 
marking the (handful of) earlyprintk functions (and snprintf) 
notrace, plus turning off printk itself completely.

That gives a completely instrumentation-free and locking-free 
console output function of last resort :-/

Thanks,

	Ingo
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