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

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Message-ID: <20210819001005.712e542a@oasis.local.home>
Date:   Thu, 19 Aug 2021 00:10:05 -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 00:03:42 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> 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.

Anyway, here's the new version:

static bool find_event_probe(const char *group, const char *event)
{
	struct trace_eprobe *ep;
	struct dyn_event *ev;
	bool ret = false;

	/*
	 * Must grab the event_mutex to prevent the list from being modified
	 * by other probes. But the event_probe being only created via the
	 * dynamic_events file, is only added under the dyn_event_ops_mutex,
	 * which is currently held. There is no race between this check and
	 * adding the new probe.
	 */
	mutex_lock(&event_mutex);
	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) {
			ret = true;
			break;
		}
	}
	mutex_lock(&event_mutex);

	return ret;
}


-- Steve