netdev - Re: [PATCH 02/17] netfilter: nat: remove module reference counting from NAT protocols

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Message-ID: <1321860997.17419.7.camel@edumazet-laptop>
Date:	Mon, 21 Nov 2011 08:36:37 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	kaber@...sh.net
Cc:	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	ulrich.weber@...hos.com
Subject: Re: [PATCH 02/17] netfilter: nat: remove module reference counting
 from NAT protocols

Le lundi 21 novembre 2011 à 06:45 +0100, kaber@...sh.net a écrit :
> From: Patrick McHardy <kaber@...sh.net>
> 
> The only remaining user of NAT protocol module reference counting is NAT
> ctnetlink support. Since this is a fairly short sequence of code, convert
> over to use RCU and remove module reference counting.
> 
> Signed-off-by: Patrick McHardy <kaber@...sh.net>

> @@ -612,16 +592,18 @@ static int nfnetlink_parse_nat_proto(struct nlattr *attr,
>  	if (err < 0)
>  		return err;
>  
> -	npt = nf_nat_proto_find_get(nf_ct_protonum(ct));
> +	rcu_read_lock();
> +	npt = __nf_nat_proto_find(nf_ct_protonum(ct));
>  	if (npt->nlattr_to_range)
>  		err = npt->nlattr_to_range(tb, range);
> -	nf_nat_proto_put(npt);
> +	rcu_read_unlock();
>  	return err;
>  }

Seems good, but you should explain in changelog why its safe.

(Using rcu also means special action must be taken in the write side,
here the module removal)

>  
>  static const struct nla_policy nat_nla_policy[CTA_NAT_MAX+1] = {
>  	[CTA_NAT_MINIP]		= { .type = NLA_U32 },
>  	[CTA_NAT_MAXIP]		= { .type = NLA_U32 },
> +	[CTA_NAT_PROTO]		= { .type = NLA_NESTED },
>  };

I just dont understand this part :-(



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