From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 2/5] nfnetlink_queue: Use rcu_barrier() on module
 unload.
Date: Tue, 9 Jun 2009 22:38:16 -0700
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Cc: "David S. Miller" <davem@davemloft.net>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	urs.thuermann@volkswagen.de, oliver.hartkopp@volkswagen.de,
	wg@grandegger.com, vladislav.yasevich@hp.com, sri@us.ibm.com,
	linux-sctp@vger.kernel.org, Trond.Myklebust@netapp.com,
	linux-nfs@vger.kernel.org, netfilter-devel@vger.kernel.org
To: Jesper Dangaard Brouer <hawk@comx.dk>
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On Mon, 08 Jun 2009 15:11:33 +0200 Jesper Dangaard Brouer <hawk@comx.dk> wrote:

> This module uses rcu_call() thus it should use rcu_barrier() on module unload.
> 
> Also fixed a trivial typo 'nfetlink' -> 'nfnetlink' in comment.
> 
> Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>
> ---
> 
>  net/netfilter/nfnetlink_queue.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c
> index 8c86011..71daa09 100644
> --- a/net/netfilter/nfnetlink_queue.c
> +++ b/net/netfilter/nfnetlink_queue.c
> @@ -1,6 +1,6 @@
>  /*
>   * This is a module which is used for queueing packets and communicating with
> - * userspace via nfetlink.
> + * userspace via nfnetlink.
>   *
>   * (C) 2005 by Harald Welte <laforge@netfilter.org>
>   * (C) 2007 by Patrick McHardy <kaber@trash.net>
> @@ -932,6 +932,8 @@ static void __exit nfnetlink_queue_fini(void)
>  #endif
>  	nfnetlink_subsys_unregister(&nfqnl_subsys);
>  	netlink_unregister_notifier(&nfqnl_rtnl_notifier);
> +
> +	rcu_barrier(); /* Wait for completion of call_rcu()'s */
>  }
>  
>  MODULE_DESCRIPTION("netfilter packet queue handler");

Possibly you've fixed the bug which the module_put(THIS_MODULE) in
instance_destroy_rcu() is addressing.

Do we still need to take a ref against the module for each instance
once the above fix is in place?

<goes git mining>

Nope, the THIS_MODULE games have been there since day one, and I can't
work out why they're there.  net/netfilter/nfnetlink_log.c has them
too.