linux-kernel - [RFC][PATCH 14/14] function_graph: Allow for more than one callback to be registered

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Date:   Wed, 21 Nov 2018 20:27:22 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Andy Lutomirski <luto@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: [RFC][PATCH 14/14] function_graph: Allow for more than one callback to be registered

From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>

Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/fgraph.c | 50 +++++++++++++++++++++++--------------------
 1 file changed, 27 insertions(+), 23 deletions(-)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 6e5efe1663b9..8a99eaa46b43 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -753,24 +753,27 @@ int register_ftrace_graph(struct fgraph_ops *gops)
 	register_pm_notifier(&ftrace_suspend_notifier);
 
 	ftrace_graph_active++;
-	ret = start_graph_tracing();
-	if (ret) {
-		ftrace_graph_active--;
-		goto out;
-	}
+	if (ftrace_graph_active == 1) {
+		ret = start_graph_tracing();
+		if (ret) {
+			ftrace_graph_active--;
+			goto out;
+		}
 
-	ftrace_graph_return = gops->retfunc;
-	/*
-	 * Update the indirect function to the entryfunc, and the
-	 * function that gets called to the entry_test first. Then
-	 * call the update fgraph entry function to determine if
-	 * the entryfunc should be called directly or not.
-	 */
-	__ftrace_graph_entry = gops->entryfunc;
-	ftrace_graph_entry = ftrace_graph_entry_test;
-	update_function_graph_func();
+		ftrace_graph_return = gops->retfunc;
 
-	ret = ftrace_startup(&graph_ops, FTRACE_START_FUNC_RET);
+		/*
+		 * Update the indirect function to the entryfunc, and the
+		 * function that gets called to the entry_test first. Then
+		 * call the update fgraph entry function to determine if
+		 * the entryfunc should be called directly or not.
+		 */
+		__ftrace_graph_entry = gops->entryfunc;
+		ftrace_graph_entry = ftrace_graph_entry_test;
+		update_function_graph_func();
+
+		ret = ftrace_startup(&graph_ops, FTRACE_START_FUNC_RET);
+	}
 out:
 	mutex_unlock(&ftrace_lock);
 	return ret;
@@ -800,13 +803,14 @@ void unregister_ftrace_graph(struct fgraph_ops *gops)
 	}
 
 	ftrace_graph_active--;
-	ftrace_graph_return = (trace_func_graph_ret_t)ftrace_stub;
-	ftrace_graph_entry = ftrace_graph_entry_stub;
-	__ftrace_graph_entry = ftrace_graph_entry_stub;
-	ftrace_shutdown(&graph_ops, FTRACE_STOP_FUNC_RET);
-	unregister_pm_notifier(&ftrace_suspend_notifier);
-	unregister_trace_sched_switch(ftrace_graph_probe_sched_switch, NULL);
-
+	if (ftrace_graph_active == 0) {
+		ftrace_graph_return = (trace_func_graph_ret_t)ftrace_stub;
+		ftrace_graph_entry = ftrace_graph_entry_stub;
+		__ftrace_graph_entry = ftrace_graph_entry_stub;
+		ftrace_shutdown(&graph_ops, FTRACE_STOP_FUNC_RET);
+		unregister_pm_notifier(&ftrace_suspend_notifier);
+		unregister_trace_sched_switch(ftrace_graph_probe_sched_switch, NULL);
+	}
  out:
 	mutex_unlock(&ftrace_lock);
 }
-- 
2.19.1