Re: [PATCH 01/18] tracing: Add function based events

[Steven Rostedt]

On Mon, 5 Feb 2018 10:00:50 -0500
Steven Rostedt <rost...@goodmis.org> wrote:

> On Mon, 5 Feb 2018 09:24:23 +0100
> Jiri Olsa <jo...@redhat.com> wrote:
> 
> 
> > should this be done under 'func_event_mutex' ?  
> 
> Probably.

I think we only need to add the list.

> 
> > 
> > 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