linux-kernel - Re: Lockup in tracepoint unregister in sched switch ftrace plugin

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Date:	Tue, 21 Oct 2008 09:18:12 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Lockup in tracepoint unregister in sched switch ftrace plugin

On Tue, Oct 21, 2008 at 12:14:03AM -0400, Steven Rostedt wrote:
> 
> 
> [ Paul, Thomas, wake up ]

I am awake, but fortunately for me, Ingo woke up before I did.  ;-)

(Sorry, couldn't resist...)

						Thanx, Paul

> On Mon, 20 Oct 2008, Steven Rostedt wrote:
> > 
> >   which calls unregister_trace_sched_switch define as macro to:
> > 
> > kernel/tracepoint.c: tracepoint_probe_unregister
> >    " "  : remove_tracepoint
> > kernel/rcupdate.c: rcu_barrier_sched
> >    " "  : _rcu_barrier
> > 
> > where it gets stuck at that "wait_for_completion".
> > 
> > I'm not sure if, because this is a scheduler trace point that we are 
> > hitting some kind of race that is preventing the wait_for_completion to 
> > finish, or what.
> 
> Note, I just booted this kernel with CONFIG_NOHZ=n and it booted fine.
> This looks like a bug somewhere in tracepoints/RCU/dynamic-ticks
> 
> -- Steve
> 
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