Date: Thu, 6 Nov 2008 18:54:56 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Masami Hiramatsu <mhiramat@redhat.com>
Cc: h-shimamoto@ct.jp.nec.com, ananth@in.ibm.com, laijs@cn.fujitsu.com,
       davem@davemloft.net, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kprobes: bugfix: try_module_get even if calling_mod is
 NULL
Message-Id: <20081106185456.0b1d00eb.akpm@linux-foundation.org>
In-Reply-To: <4913A7B2.9000609@redhat.com>
References: <490FE405.1000105@cn.fujitsu.com>
	<4910F697.2050203@redhat.com>
	<4910FB3D.4020805@cn.fujitsu.com>
	<491212C0.4030900@redhat.com>
	<4912222F.9040605@ct.jp.nec.com>
	<49122745.4090004@redhat.com>
	<49123521.6020608@redhat.com>
	<20081106170023.d5349c42.akpm@linux-foundation.org>
	<4913A7B2.9000609@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1897
Lines: 46

On Fri, 07 Nov 2008 11:28:02 +0900 Masami Hiramatsu <mhiramat@redhat.com> wrote:

> 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.
> 

OK, thanks, so I scheduled this for 2.6.29.

Also, I decided that
kprobes-disable-preempt-for-module_text_address-and-kernel_text_address.patch
is needed in 2.6.28.  Please let me know if that was incorrect.  Please
also let me know if you think that patch is needed in 2.6.27.x or
earlier.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/