linux-kernel - Re: [PATCH 2/2] tracing/events/lockdep: move tracepoints within recursive protection

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Message-ID: <alpine.DEB.2.00.0904161343110.20429@gandalf.stny.rr.com>
Date:	Thu, 16 Apr 2009 13:45:03 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 2/2] tracing/events/lockdep: move tracepoints within
 recursive protection


On Thu, 16 Apr 2009, Peter Zijlstra wrote:

> On Thu, 2009-04-16 at 12:15 -0400, Steven Rostedt wrote:
> > plain text document attachment
> > (0002-tracing-events-lockdep-move-tracepoints-within-recu.patch)
> > From: Steven Rostedt <srostedt@...hat.com>
> > 
> > With the current location of the tracepoints in lockdep, the system
> > can hard lockup in minutes when the tracepoints are enabled.
> > 
> > Moving the tracepoints outside inside the lockdep protection solves
> > the issue.
> 
> NAK

Can we at least add this as a workaround. Basically, the lockdep
tracepoints are broken as is. I do not plan on changing the logic of the 
events to prevent nesting. That's a feature I use. If we don't allow 
nesting, we must drop events, which is bad.

The other answer is simply to remove the trace points in lockdep, until 
they work again.

-- Steve


> 
> the idea is to eventually move lockdep on top of the tracepoints. The
> tracer should grow to be more robust and handle recursion itself.
> 
> Its likely a case of the tracer using a spinlock or mutex in the
> tracepoint code. When I did the tracepoints I converted one such to a
> raw_spinlock_t in the trace_print code.
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