tracing: Fix very unlikely race of registering two stat tracers (dfb6cd1e) · Commits · 戴 / test

Looking through old emails in my INBOX, I came across a patch from Luis Henriques that attempted to fix a race of two stat tracers registering the same stat trace (extremely unlikely, as this is done in the kernel, and probably doesn't even exist). The submitted patch wasn't quite right as it needed to deal with clean up a bit better (if two stat tracers were the same, it would have the same files). But to make the code cleaner, all we needed to do is to keep the all_stat_sessions_mutex held for most of the registering function. Link: http://lkml.kernel.org/r/1410299375-20068-1-git-send-email-luis.henriques@canonical.com Fixes: ("tracing/ftrace: separate events tracing and stats tracing engine") Reported-by:

Luis Henriques <luis.henriques@canonical.com> Signed-off-by:

Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_stat.c

+9 −10

Original line number	Diff line number	Diff line
		@@ -304,7 +304,7 @@ static int init_stat_file(struct stat_session *session)
		int register_stat_tracer(struct tracer_stat *trace)
		{
		struct stat_session session, node;
		int ret;
		int ret = -EINVAL;

		if (!trace)
		return -EINVAL;
		@@ -315,17 +315,15 @@ int register_stat_tracer(struct tracer_stat *trace)
		/* Already registered? */
		mutex_lock(&all_stat_sessions_mutex);
		list_for_each_entry(node, &all_stat_sessions, session_list) {
		if (node->ts == trace) {
		mutex_unlock(&all_stat_sessions_mutex);
		return -EINVAL;
		}
		if (node->ts == trace)
		goto out;
		}
		mutex_unlock(&all_stat_sessions_mutex);

		ret = -ENOMEM;
		/* Init the session */
		session = kzalloc(sizeof(*session), GFP_KERNEL);
		if (!session)
		return -ENOMEM;
		goto out;

		session->ts = trace;
		INIT_LIST_HEAD(&session->session_list);
		@@ -334,15 +332,16 @@ int register_stat_tracer(struct tracer_stat *trace)
		ret = init_stat_file(session);
		if (ret) {
		destroy_session(session);
		return ret;
		goto out;
		}

		ret = 0;
		/* Register */
		mutex_lock(&all_stat_sessions_mutex);
		list_add_tail(&session->session_list, &all_stat_sessions);
		out:
		mutex_unlock(&all_stat_sessions_mutex);

		return 0;
		return ret;
		}

		void unregister_stat_tracer(struct tracer_stat *trace)

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