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

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Date:   Tue, 6 Feb 2018 22:09:17 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        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>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        linux-rt-users@...r.kernel.org, linux-trace-users@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Clark Williams <williams@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [PATCH 01/18] tracing: Add function based events

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

> On Mon, 5 Feb 2018 09:24:23 +0100
> Jiri Olsa <jolsa@...hat.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