linux-kernel - Re: [PATCH 1/5] ftrace: use module notifier for function tracer

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Message-ID: <49EFA0DE.9070407@redhat.com>
Date:	Wed, 22 Apr 2009 18:57:34 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Tim Abbott <tabbott@....EDU>
CC:	Ingo Molnar <mingo@...e.hu>, Rusty Russell <rusty@...tcorp.com.au>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Anders Kaseorg <andersk@....EDU>,
	Jeffrey B Arnold <jbarnold@....EDU>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Subject: Re: [PATCH 1/5] ftrace: use module notifier for function tracer

Tim Abbott wrote:
> On Wed, 22 Apr 2009, Ingo Molnar wrote:
> 
>> I suspect ksplice could make use of text_mutex?
> 
> Yes, this is what I was imagining.  Thanks for pointing this out!  I plan 
> to make Ksplice use this for the next version of the Ksplice patch series.

Could you also add "use text_poke() on x86" to your plan? :-)

> However, since Ksplice can be built as a module, we'll want to 
> EXPORT_SYMBOL_GPL(text_mutex).  The comment above text_mutex's definition 
> suggests some people would prefer not to have modules patching the kernel 
> text, and so this point might be contentious.  I've found support for 
> building Ksplice as a module to be a useful feature in case one needs to 
> use multiple different versions of Ksplice on the same system (e.g. 
> because the version built in to the kernel doesn't support a particular 
> patch).

Hmm, I can't agree that we allow module to modify kernel text...
Is that possible to separate kernel-text swapping routine from Ksplice
module? In that case, we don't need to export text_mutex.

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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