linux-kernel - Re: [PATCH 02/10] perf, trace: Use per-tracepoint-per-cpu hlist to track events

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Date:	Fri, 21 May 2010 10:04:03 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/10] perf, trace: Use per-tracepoint-per-cpu hlist to
 track events

On Fri, 2010-05-21 at 11:02 +0200, Peter Zijlstra wrote:
> plain text document attachment (perf-trace-per-cpu-fold.patch)
> Avoid the swevent hash-table by using per-tracepoint hlists.
> 
> Also, avoid conditionals on the fast path by ordering with probe unregister
> so that we should never get on the callback path without the data being there.
> 

> -void perf_trace_disable(int event_id)
> +void perf_trace_destroy(struct perf_event *p_event)
>  {
> -	struct ftrace_event_call *event;
> +	struct ftrace_event_call *tp_event = p_event->tp_event;
> +	int i;
>  
> -	mutex_lock(&event_mutex);
> -	list_for_each_entry(event, &ftrace_events, list) {
> -		if (event->id == event_id) {
> -			perf_trace_event_disable(event);
> -			module_put(event->mod);
> -			break;
> +	if (--tp_event->perf_refcount > 0)
> +		return;
> +

You remove the event_mutex and then update the tp_event->perf_refcount
without any protection.

That tp_event->perf_refcount is global to the event not to the perf
event.

-- Steve

> +	tp_event->perf_event_disable(tp_event);
> +
> +	free_percpu(tp_event->perf_events);
> +	tp_event->perf_events = NULL;
> +
> +	if (!--total_ref_count) {
> +		for (i = 0; i < 4; i++) {
> +			free_percpu(perf_trace_buf[i]);
> +			perf_trace_buf[i] = NULL;
>  		}
>  	}
> -	mutex_unlock(&event_mutex);
>  }
>  


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