Subject: Re: [RFT 3/4] Use mod_timer_noact to remove nf_conntrack_lock

From: Eric Dumazet <[email-masked]>
Date: Wed, 18 Feb 2009 15:01:19 +0100

Stephen Hemminger a écrit :
> Now that we are using mod_timer_noact() for timer updates there's no need to
> hold the global lock during the timer update since the actual timeout update
> is now protected by the timer locking.
> 
> Signed-off-by: Martin Josefsson <[email-masked]>
> 
> ---
>  net/netfilter/nf_conntrack_core.c |    9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> --- a/net/netfilter/nf_conntrack_core.c	2009-02-17 10:55:33.370882059 -0800
> +++ b/net/netfilter/nf_conntrack_core.c	2009-02-17 13:48:25.080060712 -0800
> @@ -793,13 +793,12 @@ void __nf_ct_refresh_acct(struct nf_conn
>  	NF_CT_ASSERT(ct->timeout.data == (unsigned long)ct);
>  	NF_CT_ASSERT(skb);
>  
> -	spin_lock_bh(&nf_conntrack_lock);
> -
>  	/* Only update if this is not a fixed timeout */
>  	if (test_bit(IPS_FIXED_TIMEOUT_BIT, &ct->status))
>  		goto acct;
>  
> -	/* If not in hash table, timer will not be active yet */
> +	/* If not in hash table, timer will not be active yet,
> +	   we are the only one able to see it. */
>  	if (!nf_ct_is_confirmed(ct)) {
>  		ct->timeout.expires = extra_jiffies;
>  		event = IPCT_REFRESH;
> @@ -821,16 +820,16 @@ acct:
>  	if (do_acct) {
>  		struct nf_conn_counter *acct;
>  
> +		spin_lock_bh(&nf_conntrack_lock);
>  		acct = nf_conn_acct_find(ct);
>  		if (acct) {
>  			acct[CTINFO2DIR(ctinfo)].packets++;
>  			acct[CTINFO2DIR(ctinfo)].bytes +=
>  				skb->len - skb_network_offset(skb);
>  		}
> +		spin_unlock_bh(&nf_conntrack_lock);
>  	}
>  
> -	spin_unlock_bh(&nf_conntrack_lock);
> -
>  	/* must be unlocked when calling event cache */
>  	if (event)
>  		nf_conntrack_event_cache(event, ct);
> 

Unfortunatly, this patch changes nothing, as most of the time, do_acct is true.

We also need to fine lock the accounting part as well.

	spin_lock_bh(&ct->some_lock);
	acct = nf_conn_acct_find(ct);
	if (acct) {
		acct[CTINFO2DIR(ctinfo)].packets++;
		acct[CTINFO2DIR(ctinfo)].bytes +=
			skb->len - skb_network_offset(skb);
	}
	spin_unlock_bh(&ct->some_lock);