Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 4 Jun 2020 10:57:12 +0200
From:   Petr Mladek <pmladek@suse.com>
To:     Cheng Jian <cj.chengjian@huawei.com>
Cc:     linux-kernel@vger.kernel.org, live-patching@vger.kernel.org,
        chenwandun@huawei.com, xiexiuqi@huawei.com,
        bobo.shaobowang@huawei.com, huawei.libin@huawei.com,
        jeyu@kernel.org, jikos@kernel.org
Subject: Re: [PATCH] module: make module symbols visible after init
Message-ID: <20200604085712.GD22497@linux-b0ei>
References: <20200603141200.17745-1-cj.chengjian@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200603141200.17745-1-cj.chengjian@huawei.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed 2020-06-03 14:12:00, Cheng Jian wrote:
> When lookup the symbols of module by module_kallsyms_lookup_name(),
> the symbols address is visible only if the module's status isn't
> MODULE_STATE_UNFORMED, This is problematic.
> 
> When complete_formation is done, the state of the module is modified
> to MODULE_STATE_COMING, and the symbol of module is visible to the
> outside.
> 
> At this time, the init function of the module has not been called,
> so if the address of the function symbol has been found and called,
> it may cause some exceptions.

It is really handful that module symbols can be found already when
the module is MODULE_STATE_COMING state. It is used by livepatching,
ftrace, and maybe some other subsystems.

The problem is that nobody is allowed to use (call) module symbols
before mod->init() is called and the module is moved to
MODULE_STATE_LIVE.

By other words. Any code that calls module symbols before the module
is fully initialized is buggy. The caller should get fixed,
not the kallsyms side.

Have you seen such a problem in the real life, please?

Best Regards,
Petr