linux-kernel - Re: [PATCH v8 03/10] tracing: Add 'traceon' and 'traceoff' event trigger commands

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Date:	Fri, 6 Sep 2013 08:42:38 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Tom Zanussi <tom.zanussi@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v8 03/10] tracing: Add 'traceon' and 'traceoff' event
 trigger commands

On Fri, 06 Sep 2013 21:37:58 +0900
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:

> (2013/09/06 5:46), Steven Rostedt wrote:
> > On Mon,  2 Sep 2013 22:52:19 -0500
> > Tom Zanussi <tom.zanussi@...ux.intel.com> wrote:
> >>  extern void destroy_preds(struct ftrace_event_call *call);
> >> diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
> >> index 85319cf..5388d55 100644
> >> --- a/kernel/trace/trace_events_trigger.c
> >> +++ b/kernel/trace/trace_events_trigger.c
> >> @@ -28,6 +28,13 @@
> >>  static LIST_HEAD(trigger_commands);
> >>  static DEFINE_MUTEX(trigger_cmd_mutex);
> >>  
> >> +static void
> >> +trigger_data_free(struct event_trigger_data *data)
> >> +{
> >> +	synchronize_sched(); /* make sure current triggers exit before free */
> > 
> > Again, I think this can and should be synchronize_rcu().
> > 
> 
> As in the previous patch, event triggers called under preempt disabled.

Yeah, my fault. I was thinking tracepoints used rcu_read_lock(). This
is fine.

> 
> > +void event_triggers_call(struct ftrace_event_file *file)
> > +{
> > +	struct event_trigger_data *data;
> > +
> > +	if (list_empty(&file->triggers))
> > +		return;
> > +
> > +	preempt_disable_notrace();
> > +	list_for_each_entry_rcu(data, &file->triggers, list)
> > +		data->ops->func(data);
> > +	preempt_enable_notrace();
> > +}
> 
> In this case, I think synchronize_sched() is correct. Of course,
> we need to discuss why it needs to disable preempt here. :)
> 

Yeah, that is confusing.

-- Steve

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