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

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Message-ID: <49F12DEA.6070404@redhat.com>
Date:	Thu, 23 Apr 2009 23:11:38 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Tim Abbott <tabbott@....EDU>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Anders Kaseorg <andersk@....EDU>, 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>,
	Jeffrey B Arnold <jbarnold@....EDU>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Subject: Re: [PATCH 1/5] ftrace: use module notifier for function tracer

Tim Abbott wrote:
> The reason that we want to export text_mutex is that it can be useful for 
> the Ksplice core (still kernel/ksplice.c) to be built as a module.  This 
> is desirable when a different version of the kernel/ksplice.c code is 
> needed in order to apply a particular update (e.g. because there was a bug 
> in Ksplice).

Ah, OK. Certainly, Ksplice can't patch itself. It might be a good reason for
exporting text_mutex.


> I agree that great care should be taken when writing code that patches the 
> kernel's text.  However, I don't think failing to export text_mutex to GPL 
> modules helps ensure that.  In particular, not exporting text_mutex 
> doesn't prevent modules from patching the kernel text.  It just prevents 
> any modules that do so from grabbing the appropriate lock.

What I'm concerned about exporting locking staffs is that may cause
a dead lock. However, we've already exported module_mutex.
I don't think that exporting text_mutex is more considerable than that. :-)

Thank you,

-- 
Masami Hiramatsu

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

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

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