Messages in this thread Patch in this message | | | Date | Wed, 17 Jun 2009 13:51:45 +0200 | From | Patrick McHardy <> | Subject | Re: [bug] __nf_ct_refresh_acct(): WARNING: at lib/list_debug.c:30 __list_add+0x7d/0xad() |
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Patrick McHardy wrote: > 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. >
A slightly changed version which moves hash insertion to the end and adds a comment about ordering. This make sure the timer is actually running before the conntrack can be found be other CPUs.
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index 5f72b94..e2cc707 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -425,7 +425,6 @@ __nf_conntrack_confirm(struct sk_buff *skb) /* Remove from unconfirmed list */ hlist_nulls_del_rcu(&ct->tuplehash[IP_CT_DIR_ORIGINAL].hnnode); - __nf_conntrack_hash_insert(ct, hash, repl_hash); /* Timer relative to confirmation time, not original setting time, otherwise we'd get timer wrap in weird delay cases. */ @@ -433,8 +432,15 @@ __nf_conntrack_confirm(struct sk_buff *skb) add_timer(&ct->timeout); atomic_inc(&ct->ct_general.use); set_bit(IPS_CONFIRMED_BIT, &ct->status); + + /* Since the lookup is lockless, hash insertion must be after starting the + * timer and setting the CONFIRMED bit. The RCU barriers guarantee that no + * other CPU can find the conntrack before the above stores are visible. + */ + __nf_conntrack_hash_insert(ct, hash, repl_hash); NF_CT_STAT_INC(net, insert); spin_unlock_bh(&nf_conntrack_lock); + help = nfct_help(ct); if (help && help->helper) nf_conntrack_event_cache(IPCT_HELPER, ct); | |