Subject: Re: [bug] __nf_ct_refresh_acct(): WARNING: at lib/list_debug.c:30 __list_add+0x7d/0xad()

From: Patrick McHardy <[email-masked]>
Date: Wed, 17 Jun 2009 13:38:37 +0200

Eric Dumazet wrote:
> IPS_CONFIRMED_BIT is set under nf_conntrack_lock (in __nf_conntrack_confirm()),
> we probably want to add a synchronisation under ct->lock as well,
> or __nf_ct_refresh_acct() could set ct->timeout.expires to extra_jiffies,
> while a different cpu could confirm the conntrack.

Before the conntrack is confirmed, it is exclusively handled by a
single CPU. I agree that we need to make sure the IPS_CONFIRMED_BIT
is visible before we add the conntrack to the hash table since the
lookup is lockless, but simply moving the set_bit before the hash
insertion should be fine I think.

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 5f72b94..22755fa 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -425,6 +425,7 @@ __nf_conntrack_confirm(struct sk_buff *skb)
 	/* Remove from unconfirmed list */
 	hlist_nulls_del_rcu(&ct->tuplehash[IP_CT_DIR_ORIGINAL].hnnode);
 
+	set_bit(IPS_CONFIRMED_BIT, &ct->status);
 	__nf_conntrack_hash_insert(ct, hash, repl_hash);
 	/* Timer relative to confirmation time, not original
 	   setting time, otherwise we'd get timer wrap in
@@ -432,7 +433,6 @@ __nf_conntrack_confirm(struct sk_buff *skb)
 	ct->timeout.expires += jiffies;
 	add_timer(&ct->timeout);
 	atomic_inc(&ct->ct_general.use);
-	set_bit(IPS_CONFIRMED_BIT, &ct->status);
 	NF_CT_STAT_INC(net, insert);
 	spin_unlock_bh(&nf_conntrack_lock);
 	help = nfct_help(ct);