linux-kernel - Re: [tracing, hang] dumping events gets stuck in synchronise

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Message-ID: <1282050158.3268.1303.camel@gandalf.stny.rr.com>
Date:	Tue, 17 Aug 2010 09:02:38 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org
Subject: Re: [tracing, hang] dumping events gets stuck in synchronise_sched

On Tue, 2010-08-17 at 21:52 +1000, Dave Chinner wrote:
> On Tue, Aug 17, 2010 at 04:37:44PM +0800, Lai Jiangshan wrote:
> > On 08/17/2010 03:37 PM, Dave Chinner wrote:
> > > Tracing folks,
> > > 
> > > I've got a machine stuck with a cpu spinning in a tight loop (the
> > > new writeback/sync livelock avoidance code is, well, livelocking),
> > > and I was trying to find out what triggered by using the writeback
> > > trace events. Unfortunately, I can't dump the trace events because
> > > it gets stuck here:
> > 
> > > 
> > > Given that the trace events are there mainly for debugging, this
> > > seems like a bit of an oversight - hanging a CPU in a tight loop is
> > > not an uncommon event during code development....
> > > 
> > 
> > You can try 'cat trace_pipe', if I did not miss you meaning.
> 
> I'll try it, but I'm really after the static event list which is why
> I'm using the trace file rather than trace_pipe. I want the history,
> not new events as they happen. 

When the systems locks up, I assume you want to see why? The trace_pipe
should show that without locking the system.

You could also try downloading trace-cmd and running the tracer with
that. That will save all traces to a file while running the trace.

-- Steve


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