From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [bug] __nf_ct_refresh_acct(): WARNING: at lib/list_debug.c:30 __list_add+0x7d/0xad() Date: Wed, 17 Jun 2009 13:55:42 +0200 Message-ID: <4A38D9BE.3020403@gmail.com> References: <20090615.050449.144947903.davem@davemloft.net> <20090616091538.GA4184@elte.hu> <20090616.034752.226811527.davem@davemloft.net> <20090616105304.GA3579@elte.hu> <20090616122415.GA16630@elte.hu> <20090617092152.GA17449@elte.hu> <4A38C2F3.3000009@gmail.com> <4A38D5BD.2040502@trash.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Ingo Molnar , David Miller , Thomas Gleixner , torvalds@linux-foundation.org, akpm@linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Patrick McHardy Return-path: Received: from gw1.cosmosbay.com ([212.99.114.194]:39105 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763385AbZFQL42 (ORCPT ); Wed, 17 Jun 2009 07:56:28 -0400 In-Reply-To: <4A38D5BD.2040502@trash.net> Sender: netdev-owner@vger.kernel.org List-ID: Patrick McHardy a =E9crit : > 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_jif= fies, >> while a different cpu could confirm the conntrack. >=20 > 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. >=20 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); =20 + 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 +=3D jiffies; << What happens if another packet is handled by __nf_ct_refresh_acct he= re >> (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 =3D nfct_help(ct); Problem is timeout.expires is either a relative or absolute timeout, an= d changes happen in __nf_conntrack_confirm() or __nf_ct_refresh_acct(). We must have a synchronization (an barriers), a single bit wont be enou= gh.