linux-kernel - Re: [PATCH 01/12] perf: Use tracepoint_synchronize_unregister() to flush any pending tracepoint call

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Date:	Mon, 2 Aug 2010 11:14:46 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Li Zefan <lizf@...fujitsu.com>
Subject: Re: [PATCH 01/12] perf: Use tracepoint_synchronize_unregister() to
	flush any pending tracepoint call

* Frederic Weisbecker (fweisbec@...il.com) wrote:
> We use synchronize_sched() to ensure a tracepoint won't be called
> while/after we release the perf buffers it references.
> 
> But the tracepoint API has its own API for that:
> tracepoint_synchronize_unregister(). Use it instead as it's
> self-explanatory and eases maintainance.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Thanks!

Mathieu

> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Li Zefan <lizf@...fujitsu.com>
> ---
>  kernel/trace/trace_event_perf.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> index 2375165..000e6e8 100644
> --- a/kernel/trace/trace_event_perf.c
> +++ b/kernel/trace/trace_event_perf.c
> @@ -131,10 +131,10 @@ void perf_trace_destroy(struct perf_event *p_event)
>  	tp_event->class->reg(tp_event, TRACE_REG_PERF_UNREGISTER);
>  
>  	/*
> -	 * Ensure our callback won't be called anymore. See
> -	 * tracepoint_probe_unregister() and __DO_TRACE().
> +	 * Ensure our callback won't be called anymore. The buffers
> +	 * will be freed after that.
>  	 */
> -	synchronize_sched();
> +	tracepoint_synchronize_unregister();
>  
>  	free_percpu(tp_event->perf_events);
>  	tp_event->perf_events = NULL;
> -- 
> 1.6.2.3
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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