linux-kernel - Re: [PATCH v6 7/7] tracing: Add a probe that attaches to trace events

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Date:   Thu, 19 Aug 2021 00:03:42 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Tzvetomir Stoyanov" <tz.stoyanov@...il.com>,
        Tom Zanussi <zanussi@...nel.org>,
        linux-trace-devel@...r.kernel.org
Subject: Re: [PATCH v6 7/7] tracing: Add a probe that attaches to trace
 events

On Thu, 19 Aug 2021 12:56:52 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> > static bool find_event_probe(const char *group, const char *event)
> > {
> > 	struct dyn_event *ev;
> > 	struct trace_eprobe *ep;
> > 
> > 	for_each_dyn_event(ev) {
> > 		if (ev->ops != &eprobe_dyn_event_ops)
> > 			continue;
> > 		
> > 		ep = to_trace_eprobe(ev);
> > 		if (strcmp(ep->tp.event->class.system, group) == 0 &&
> > 		    strcmp(ep->tp.event->call.name, event) == 0)
> > 			return true;
> > 	}
> > 	return false;
> > }  
> 
> Yeah, but I think this should be done with event_mutex, shouldn't it?

Probably. I noticed that it was updated under the dyn_event_ops_mutex,
and thought that was enough protection. But I now see the lockdep
assert on the event_mutex in the other functions.

Is there ever a case where this list is updated without
dyn_event_ops_mutex held?

-- Steve