linux-kernel - Re: [PATCH v3 21/33] tracing: Add support for 'synthetic' events

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Date:   Wed, 4 Oct 2017 14:08:16 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Tom Zanussi <tom.zanussi@...ux.intel.com>
Cc:     tglx@...utronix.de, mhiramat@...nel.org, namhyung@...nel.org,
        vedang.patel@...el.com, bigeasy@...utronix.de,
        joel.opensrc@...il.com, joelaf@...gle.com,
        mathieu.desnoyers@...icios.com, baohong.liu@...el.com,
        rajvi.jingar@...el.com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org
Subject: Re: [PATCH v3 21/33] tracing: Add support for 'synthetic' events

On Fri, 22 Sep 2017 15:00:01 -0500
Tom Zanussi <tom.zanussi@...ux.intel.com> wrote:



> +/* This function releases synth_event_mutex */
> +static int unregister_synth_event(struct synth_event *event)
> +{
> +	struct trace_event_call *call = &event->call;
> +	int ret;
> +
> +	mutex_unlock(&synth_event_mutex);
> +	ret = trace_remove_event_call(call);
> +	mutex_lock(&synth_event_mutex);
> +
> +	return ret;
> +}
> +
> +static int remove_synth_event(struct synth_event *event)
> +{
> +	int ret = unregister_synth_event(event);
> +
> +	if (!ret)
> +		list_del(&event->list);
> +
> +	return ret;
> +}
> +


> +/* This function releases synth_event_mutex */
> +static int release_all_synth_events(void)
> +{
> +	struct synth_event *event, *e;
> +	int ret = 0;
> +
> +	mutex_lock(&synth_event_mutex);
> +
> +	list_for_each_entry(event, &synth_event_list, list) {
> +		if (event->ref) {
> +			ret = -EBUSY;
> +			goto out;
> +		}
> +	}
> +
> +	list_for_each_entry_safe(event, e, &synth_event_list, list) {

remove_synth_event() releases synth_event_mutex, which is racy, as more
than one instance can do the deletion.

Perhaps we should remove all the events off the synth_event_list under
the lock, release the lock, and then remove the trace events attached
to them?

-- Steve


> +		ret = remove_synth_event(event);
> +		if (!ret)
> +			free_synth_event(event);
> +	}
> + out:
> +	mutex_unlock(&synth_event_mutex);
> +
> +	return ret;
> +}
> +
> +