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From: Lai Jiangshan <>
Cc: Andrew Morton <>,
	David Miller <>,,
	Linux Kernel Mailing List <>
Subject: Re: [PATCH] kprobes: disable preempt for module_text_address()
Date: Wed, 05 Nov 2008 08:53:41 +0800	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Ananth N Mavinakayanahalli wrote:
> 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.

when preemption happen, and mod is freed, module_is_live() will access to
invalid address. So it's NOT OK.

Other users of try_module_get() are correct. most are like this:

void func(XXX, XXXX)

Because we have had a reference to the module before calling try_module_get().
this means the module is still in the kernel when try_module_get() called.
so we do not need any protection for using try_module_get().
<in other word, caller of func() has made sure the module will not be unloaded>

In this function __register_kprobe(), probed_mod is the return value of
module_text_address(), probed_mod will go in any time before try_module_get().

> 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

  reply	other threads:[~2008-11-05  0:56 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-11-04  5:56 Lai Jiangshan
2008-11-04 14:28 ` Ananth N Mavinakayanahalli
2008-11-05  0:53   ` Lai Jiangshan [this message]
2008-11-05  1:27 ` Masami Hiramatsu
2008-11-05  1:47   ` Lai Jiangshan
2008-11-05 19:30     ` Hiroshi Shimamoto
2008-11-05 21:40     ` Masami Hiramatsu
2008-11-05 22:46       ` Hiroshi Shimamoto
2008-11-05 23:07         ` Masami Hiramatsu
2008-11-06  0:06           ` [PATCH] kprobes: bugfix: try_module_get even if calling_mod is NULL Masami Hiramatsu
2008-11-07  1:00             ` Andrew Morton
2008-11-07  2:28               ` Masami Hiramatsu
2008-11-07  2:54                 ` Andrew Morton
2008-11-07  4:46                   ` Ananth N Mavinakayanahalli
2008-11-06  1:06       ` [PATCH] kprobes: disable preempt for module_text_address() Lai Jiangshan
2008-11-06 15:37         ` [PATCH] kprobes: disable preempt for module_text_address() and kernel_text_address() Masami Hiramatsu
2008-11-07  0:32           ` Lai Jiangshan

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