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

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Message-ID: <1507146618.14461.21.camel@tzanussi-mobl.amr.corp.intel.com>
Date:   Wed, 04 Oct 2017 14:50:18 -0500
From:   Tom Zanussi <tom.zanussi@...ux.intel.com>
To:     Steven Rostedt <rostedt@...dmis.org>
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 Wed, 2017-10-04 at 14:08 -0400, Steven Rostedt wrote:
> 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?
> 

Yeah, I think that makes sense, will change..

Thanks,

Tom

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