netdev - Re: [RFT 3/3] iptables: lock free counters

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Date:	Mon, 09 Feb 2009 16:58:16 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Stephen Hemminger <shemminger@...tta.com>
CC:	David Miller <davem@...emloft.net>,
	Rick Jones <rick.jones2@...com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Eric Dumazet <dada1@...mosbay.com>, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org
Subject: Re: [RFT 3/3] iptables: lock free counters

Stephen Hemminger wrote:

> --- a/net/ipv4/netfilter/ip_tables.c	2009-01-29 11:09:20.720069979 -0800
> +++ b/net/ipv4/netfilter/ip_tables.c	2009-01-29 11:10:49.827070289 -0800
> @@ -347,9 +347,9 @@ ipt_do_table(struct sk_buff *skb,
>  	mtpar.family  = tgpar.family = NFPROTO_IPV4;
>  	tgpar.hooknum = hook;
>  
> -	read_lock_bh(&table->lock);
> +	rcu_read_lock_bh();
>  	IP_NF_ASSERT(table->valid_hooks & (1 << hook));
> -	private = table->private;
> +	private = rcu_dereference(table->private);
>  	table_base = (void *)private->entries[smp_processor_id()];
>  	e = get_entry(table_base, private->hook_entry[hook]);

I think this doesn't actually need the _bh rcu_read_lock() variant
since updates are never done in softirq context.

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