On Mon, 5 Feb 2018 10:00:50 -0500
Steven Rostedt [off-list ref] wrote:

On Mon, 5 Feb 2018 09:24:23 +0100
Jiri Olsa [off-list ref] wrote:

quoted

should this be done under 'func_event_mutex' ?  

Probably.

I think we only need to add the list.

quoted

I tried and crashed the system by running 2 scripts with:

  echo 'ip_rcv(u64 skb, u64 dev)' > /sys/kernel/debug/tracing/function_events
  echo 'SyS_openat(int dfd, string buf, x32 flags, x32 mode)' >> /sys/kernel/debug/tracing/function_events
  echo 'SyS_open(x8[32] buf, x32 flags, x32 mode)' >> /sys/kernel/debug/tracing/function_events
 

There's no reason that we can't have more than one function  event
attached to the same function. I'm adding this:

diff --git a/kernel/trace/trace_event_ftrace.c b/kernel/trace/trace_event_ftrace.c
index b145639eac45..928168fc2025 100644
--- a/kernel/trace/trace_event_ftrace.c
+++ b/kernel/trace/trace_event_ftrace.c

@@ -1275,12 +1275,6 @@ static int create_function_event(int argc, char **argv)
 	if (state != FUNC_STATE_END)
 		goto fail;
 
-	ret = -EALREADY;
-	list_for_each_entry(fe, &func_events, list) {
-		if (strcmp(fe->func, func_event->func) == 0)
-			goto fail;
-	}
-
 	ret = ftrace_set_filter(&func_event->ops, func_event->func,
 				strlen(func_event->func), 0);
 	if (ret < 0)

@@ -1290,7 +1284,9 @@ static int create_function_event(int argc, char **argv)
 	if (ret < 0)
 		goto fail;
 
+	mutex_lock(&func_event_mutex);
 	list_add_tail(&func_event->list, &func_events);
+	mutex_unlock(&func_event_mutex);
 	return 0;
  fail:
 	free_func_event(func_event);

-- Steve