linux-kernel - Re: [PATCH] tracing: Fix race where eprobes can be called before the event

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Message-ID: <20221123160246.348c11b4@gandalf.local.home>
Date:   Wed, 23 Nov 2022 16:02:46 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
        Rafael Mendonca <rafaelmendsr@...il.com>,
        Tzvetomir Stoyanov <tz.stoyanov@...il.com>,
        Tom Zanussi <zanussi@...nel.org>
Subject: Re: [PATCH] tracing: Fix race where eprobes can be called before
 the event

On Fri, 18 Nov 2022 21:18:09 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> This looks good to me.
> 
> Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> BTW, would other trigger callbacks also need to add similar checks?

I just checked, and yes, I think that histograms (the only other trigger
that has EVENT_CMD_FL_NEEDS_REC set) has the same issue, and requires:

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 087c19548049..1c82478e8dff 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5143,6 +5143,9 @@ static void event_hist_trigger(struct event_trigger_data *data,
 	void *key = NULL;
 	unsigned int i;
 
+	if (unlikely(!rbe))
+		return;
+
 	memset(compound_key, 0, hist_data->key_size);
 
 	for_each_hist_key_field(i, hist_data) {


I'll add that next.

-- Steve