linux-kernel - Re: [RFC][PATCH] tracing: Warn and notify if tracepoints are not loaded due to module taint

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Date:	Wed, 26 Feb 2014 11:15:42 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH] tracing: Warn and notify if tracepoints are not
 loaded due to module taint

On Wed, 26 Feb 2014 12:48:12 +0000 (UTC)
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> > How about instead of a WARN, you use a normal KERN_ERR printk(). There's
> > no point to the entire WARN state dump, that's needlessly verbose.
> > 
> > When you have a normal error print you can have as many as are required
> > and put the mod name back in.
> 
> The good old printk KERN_ERR is a very good idea. I agree that WARN() is
> too verbose for our needs here.

Actually, it's not so bad for the WARN() after my last patch to only
allocate (or even process tracepoints) if mod->num_tracepionts is
greater than zero. I didn't realize you were wasting memory for all
modules that were loaded.

My fear with the KERN_ERR is that it wont be noticeable enough. Where
as a stack dump is something that will catch people's attention.

And as Rusty has said, if you are loading a module that is forced, or
something strange, it is broken. The failure of loading the tracepoints
of a module is a bug if the module happens to have tracepoints.

After the MOD_SIG fix, any failure should be a big banner bug. Either
they are using a forced module with tracepoints that should not be
loaded. Or they have tracepoints is a non-GPL module (which is also a
big no-no).

-- Steve
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