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

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Date:	Fri, 29 Apr 2011 12:20:01 -0400
From:	Jon Masters <jonathan@...masters.org>
To:	Jan Beulich <JBeulich@...ell.com>
Cc:	David Miller <davem@...emloft.net>,
	Jon Masters <jcm@...masters.org>,
	shemminger@...ux-foundation.org, bridge@...ts.linux-foundation.org,
	jeffm@...e.com, Michal Marek <mmarek@...e.cz>,
	netdev@...r.kernel.org
Subject: Re: [PATCH] bridge: Module use count must be updated as	 bridges
 are created/destroyed

On Fri, 2011-04-29 at 17:07 +0100, Jan Beulich wrote:
> >>> On 29.04.11 at 18:05, Jon Masters <jonathan@...masters.org> wrote:
> > On Fri, 2011-04-29 at 13:08 +0200, Michal Marek wrote:
> >> On 29.4.2011 11:09, Jan Beulich wrote:
> >> >>>> On 29.04.11 at 10:44, David Miller<davem@...emloft.net>  wrote:
> > 
> >> >> 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).
> > 
> > Thanks. So the specific feature you mention was added precisely because
> > some folks wanted to clean up ununsed modules by removing all of their
> > dependencies. Since I've not been on this thread until now, can you let
> > me know what precisely you need, and why? We can make the unloading of
> > unused modules configurable, but it sounds like you're saying even that
> > isn't good enough. What actually happens, what's the bug experience?
> 
> The problem observed was that unloading (via modprobe -r)
> ebtable_broute.ko, bridge.ko was also unloaded, causing all
> bridged networking to stop functioning on a machine.

Ah, right...ouch. That would be a "little" problem. Short of having an
exclusion list and all that nonsense, probably best to start with either
removing the unload logic or making it globally configurable. Thanks.

Jon.


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