linux-kernel - Re: [PATCH] kprobes: disable preempt for module_text

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Message-ID: <20081104142824.GA24326@in.ibm.com>
Date:	Tue, 4 Nov 2008 19:58:24 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>, mhiramat@...hat.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kprobes: disable preempt for module_text_address()

On Tue, Nov 04, 2008 at 01:56:21PM +0800, Lai Jiangshan wrote:
> 
> __register_kprobe() may be preempted after module_text_address()
> but before try_module_get(), and in this interval the module may be
> unloaded and try_module_get(probed_mod) will access to invalid address.
> this patch uses preempt_disable() to protect it.

Looking at other users of try_module_get, I don't see this as a usage
model being followed elsewhere. Also, in case such a preemption does
happen, module_is_live() will fail and we should still be ok.

I don't see a reason for this patch unless there is a clear failure case
(register_kprobe failing 'cos of a module unload is perfectly ok).

Ananth
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