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 13:46:13 -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 17:24:47 +0000 (UTC)
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> ----- Original Message -----
> > 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>
> > Sent: Wednesday, February 26, 2014 11:15:42 AM
> > 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).
> 
> Agreed that after the skip for modules containing 0 tracepoints, it gets
> much more specific. I like that.
> 
> So then a WARN_ON() that prints the specific module name involved would
> be the way to go ?


OK, I have a series of patches to fix a lot of these problems that I
will be posting soon. I'm fine with either a WARN() here (with module
name) or just a pr_err(). Which of theses do others think is the proper
answer?

Peter, Rusty, Andrew?

-- Steve
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