linux-kernel - Re: [PATCH 0/2] Fix (improve) deadlock condition on module removal netfilter socket option removal

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Date:	Wed, 05 Sep 2007 14:19:23 -0400
From:	Jon Masters <jonathan@...masters.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Neil Horman <nhorman@...driver.com>,
	Patrick McHardy <kaber@...sh.net>, adam@...drasil.com,
	jcm@...masters.org, netfilter-devel@...ts.netfilter.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Fix (improve) deadlock condition on module removal
	netfilter socket option removal

On Thu, 2007-09-06 at 03:41 +1000, Rusty Russell wrote:
> On Wed, 2007-09-05 at 13:08 -0400, Neil Horman wrote:
> > On Thu, Sep 06, 2007 at 02:13:26AM +1000, Rusty Russell wrote:
> > > On Wed, 2007-09-05 at 17:22 +0200, Patrick McHardy wrote:
> > > > But I'm wondering, wouldn't module refcounting alone fix this problem?
> > > > If we make nf_sockopt() call try_module_get(ops->owner), remove_module()
> > > > on ip_tables.ko would simply fail because the refcount is above zero
> > > > (so it would fail at point 3 above). Am I missing something important?
> > > 
> > > Yes, that seems the correct solution to me, too.  ISTR that this code
> > > predates the current module code.
> > > 
> > > Rusty.
> > 
> > Thanks guys-
> > 	When I first started looking at this problem I would have agreed with
> > you, that module reference counting alone would fix the problem.  However,
> > delete_module can work in either a non-blocking or a blocking mode.  rmmod
> > passes O_NONBLOCK to delete module, and so is fine, but modprobe does not.

> 	You have this backwards: O_NONBLOCK is the default.  That seems to be
> what everyone wants, although I implemented 'rmmod -w' because it seemed
> like a good option.

:-)

Thanks for keeping me copied. I'll think about the in-kernel module
situation when I get some time over the weekend - but shout if there's
an external impact sooner! :-)

Jon.


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