netdev - Re: [PATCH] bridge: Module use count must be updated as bridges are created/destroyed

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Message-ID: <4DBA9C23.2000408@suse.cz>
Date:	Fri, 29 Apr 2011 13:08:19 +0200
From:	Michal Marek <mmarek@...e.cz>
To:	Jan Beulich <JBeulich@...ell.com>
Cc:	David Miller <davem@...emloft.net>,
	shemminger@...ux-foundation.org, bridge@...ts.linux-foundation.org,
	jeffm@...e.com, netdev@...r.kernel.org,
	Jon Masters <jcm@...masters.org>
Subject: Re: [PATCH] bridge: Module use count must be updated as	 bridges
 are created/destroyed

On 29.4.2011 11:09, Jan Beulich wrote:
>>>> On 29.04.11 at 10:44, David Miller<davem@...emloft.net>  wrote:
>> From: "Jan Beulich"<JBeulich@...ell.com>
>> Date: Fri, 29 Apr 2011 09:31:27 +0100
>>
>>>>>> On 29.04.11 at 10:10, David Miller<davem@...emloft.net>  wrote:
>>>> From: "Jan Beulich"<JBeulich@...ell.com>
>>>> Date: Fri, 29 Apr 2011 08:41:10 +0100
>>>>
>>>>> You talk of rmmod on the very module, but the issue is about
>>>>> modprobe -r on a dependent module. I cannot believe you consider
>>>>> it correct that *implicit* unloading of bridge.ko should happen when
>>>>> bridges are configured.
>>>>
>>>> Which module in particular depends upon bridge and causes the
>>>> problem?
>>>
>>> The problem was observed (a long time ago) with ebtable_broute,
>>> and I cannot see how this would have changed meanwhile.
>>
>> Well your change makes it so that someone who actually _wants_ to
>> unload the bridge module, regardless of configuration, cannot do so.
>>
>> I think that's a worse problem than this ebtables thing.
>>
>> Nothing on the system should be hitting modules with unload requests
>> unless the user explicitly asked for that specific module to be
>> unloaded.  At least not by default.
>>
>> So the me the problem is perhaps that "modprobe -r" does this auto
>> dependency unloading thing by default.
>>
>> When we first fixed network device drivers so that they now properly
>> always run with no module refcount at all, people complained because
>> there were some distributions that ran some daemon that periodically
>> looked for "unreferenced" modules and "helped" the user by
>> automatically unloaded them.
>>
>> We killed that foolish daemon, and we can fix "modprobe -r" too.
>
> Michal - aren't you the modutils maintainer?

That would be Jon (CC added).

> What are your thoughts
> here? (The original report we got is
> https://bugzilla.novell.com/show_bug.cgi?id=267651.)

I think that defaulting to not removing dependencies would be a good 
idea. But do not expect that it will help with those artificial tests, 
they will just proceed a few steps further until they hit the module 
with broken unloading ;-).

Michal

>
>> Does "rmmod" have this behavior too?  If not, and it does the right
>> thing by only unloaded what the user asked for, then people should
>> use that.
>
> No, it doesn't. Other than modprobe, rmmod deals only with the
> module specified.
>
>> I really don't in any way want to block people from being able to
>> cleanly unload the bridge module, regardless of configuration, if
>> that's what they want so your patch as written is not going to be
>> considered for inclusion.
>
> I understood that meanwhile, yet fail to see an alternative solution
> (imo this auto-unloading is quite desirable in other cases).
>
> Jan
>

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