Messages in this thread | | | Date | Wed, 17 Jun 2009 14:00:04 +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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Eric Dumazet wrote: > Patrick McHardy a écrit : >> 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. >> > > Hmm... now we could have the reverse case : > > __nf_conntrack_confirm() could be "interrupted" by __nf_ct_refresh_acct() > > 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; > > << What happens if another packet is handled by __nf_ct_refresh_acct here >> > (seeing or not the IPS_CONFIRMED_BIT) >> > > add_timer(&ct->timeout); > > << or here ? >> > > > 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); > > Problem is timeout.expires is either a relative or absolute timeout, and changes happen > in __nf_conntrack_confirm() or __nf_ct_refresh_acct(). > > We must have a synchronization (an barriers), a single bit wont be enough.
Please have a look at the second patch I just sent. It relies on the RCU barriers to make sure all stores are visible before other CPUs can find the conntrack.
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