Date: Sat, 26 Oct 2013 10:48:36 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Vince Weaver <vincent.weaver@maine.edu>
Cc: linux-kernel@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Dave Jones <davej@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: perf/ftrace lockup on 3.12-rc6 with trigger code
Message-ID: <20131026084836.GC14237@gmail.com>
References: <alpine.DEB.2.10.1310241324330.4352@vincent-weaver-1.um.maine.edu>
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 <1382695687.12254.4.camel@pippen.local.home>
 <alpine.DEB.2.10.1310250906110.22710@vincent-weaver-1.um.maine.edu>
 <alpine.DEB.2.10.1310251726001.31246@vincent-weaver-1.um.maine.edu>
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* Vince Weaver <vincent.weaver@maine.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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