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From: Masami Hiramatsu <>
To: Andrew Morton <>
Subject: Re: [PATCH] kprobes: bugfix: try_module_get even if calling_mod is NULL
Date: Fri, 07 Nov 2008 11:28:02 +0900	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Andrew Morton wrote:
> I do not understand this description "Get probed module even if the
> caller is in the kernel core code".
> What bug is being fixed here?  What is the kernel behaviour before and
> after the patch?

When someone called register_*probe() from kernel-core code(not from
module) and that probes a kernel module, users can remove the probed
module because kprobe doesn't increment reference counter of the module.
(on the other hand, if the kernel-module calls register_*probe,
kprobe increments refcount of the probed module.)

Currently, we have no register_*probe() calling from kernel-core(except
smoke-test, but the smoke-test doesn't probe module), so there is no
real bugs. But the logic is wrong(or not fair) and it can causes a
problem when someone might want to probe module from kernel.

After this patch is applied, even if someone put register_*probe() call
in the kernel-core code, it increments the reference counter of the
probed module, and it prevents user to remove the module until stopping
probing it.

> Was the bug present in 2.6.27, 2.6.26 etc?  Or was it a post-2.6.28
> regression?

Hmm, it might be an enhancement, because currently the kernel doesn't
have real bugs.

Thank you,

Masami Hiramatsu

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


  reply	other threads:[~2008-11-07  2:30 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-11-04  5:56 [PATCH] kprobes: disable preempt for module_text_address() Lai Jiangshan
2008-11-04 14:28 ` Ananth N Mavinakayanahalli
2008-11-05  0:53   ` Lai Jiangshan
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 [this message]
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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