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

From: Steven Rostedt <rostedt@goodmis.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Tzvetomir Stoyanov" <tz.stoyanov@gmail.com>,
	Tom Zanussi <zanussi@kernel.org>,
	linux-trace-devel@vger.kernel.org
Subject: Re: [PATCH v6 7/7] tracing: Add a probe that attaches to trace events
Date: Thu, 19 Aug 2021 00:03:42 -0400	[thread overview]
Message-ID: <20210819000342.615e68c7@oasis.local.home> (raw)
In-Reply-To: <20210819125652.bb6b980cf0ef04e0158bc564@kernel.org>

On Thu, 19 Aug 2021 12:56:52 +0900
Masami Hiramatsu <mhiramat@kernel.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