netdev - Re: [PATCH] inet_diag: make config INET

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Message-ID: <50601E6C.3070106@cn.fujitsu.com>
Date:	Mon, 24 Sep 2012 16:48:44 +0800
From:	Gao feng <gaofeng@...fujitsu.com>
To:	Jan Engelhardt <jengelh@...i.de>
CC:	Stephen Hemminger <stephen.hemminger@...tta.com>,
	netdev@...r.kernel.org, davem@...emloft.net, kuznet@....inr.ac.ru
Subject: Re: [PATCH] inet_diag: make config INET_DIAG bool

于 2012年09月23日 21:40, Jan Engelhardt 写道:
> On Sunday 2012-09-23 06:36, Stephen Hemminger wrote:
> 
>>> when inet_diag being compiled as module, inet_diag_handler_dump
>>> set netlink_dump_control.dump to inet_diag_dump,so if module
>>> inet_diag is unloaded,netlink will still try to call this function
>>> in netlink_dump. this will cause kernel panic.
>>
>> Another way to handle this to just get rid of inet_diag_exit
>> so that module can be loaded but not unloaded.
> 
> Why don't we unset netlink_dump_control.dump on exit?


Though I like this idea,but it may cause dead lock.
netlink_dimp [mutex_lock(netlink_sock->cb_mutex) here]
   |->inet_diag_dump
	|->__inet_diag_dump
	    |->inet_diag_lock_handler [may try to load tcp_diag here,
					so we need module_mutex lock]

And on module exit,we already get module_mutex lock,
if we unset netlink_sock->cb,we need to get mutex lock of netlink_sock->cb_mutex.

I think this will cause dead lock.

I don't know if I should change this patch as Stephen said,because I don't know
witch one is better.

Any comments?
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