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

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Date:	Tue, 21 Oct 2008 00:14:03 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Lockup in tracepoint unregister in sched switch ftrace plugin



[ Paul, Thomas, wake up ]

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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