linux-kernel - Re: [PATCH v9 tip 6/9] samples: bpf: simple non-portable kprobe filter example

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Message-ID: <55104BF8.8000606@plumgrid.com>
Date:	Mon, 23 Mar 2015 10:23:04 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"David S. Miller" <davem@...emloft.net>,
	Daniel Borkmann <daniel@...earbox.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-api@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 tip 6/9] samples: bpf: simple non-portable kprobe filter
 example

On 3/23/15 12:29 AM, Ingo Molnar wrote:
>
>> **                                                      **
>> ** This means that this is a DEBUG kernel and it is     **
>> ** unsafe for production use.                           **
>
> But I think printing that it's unsafe for production use is over the
> top: it's up to the admin whether it's safe or unsafe, just like
> inserting a kprobe can be safe or unsafe.
>
> Informing that something happened is enough.

Well that is Steven's banner and I agree that it's a bit extreme.
I think it's done on purpose to scary people away from using
trace_printk() for anything other than debug.
It applies to both native trace_printk() for kernel debugging and
for bpf_trace_printk() for debugging of bpf programs.
I don't have a strong opinion about native case, but for bpf I do want
this banner to be scary. Otherwise it's too easy to start using
bpf_trace_printk() to pass event notifications to user space.
bpf_trace_printk and trace_pipe parsing shouldn't be used as a way
to communicate between programs and user space.
At the end, in actual production use, bpf programs won't be using it
and no banner will be seen.
Anyway, I don't think I can change this banner in this patch set.
If we decide to relax it, it should be done via Steven's tree.
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