Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765391AbZFQMAV (ORCPT ); Wed, 17 Jun 2009 08:00:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759544AbZFQMAG (ORCPT ); Wed, 17 Jun 2009 08:00:06 -0400 Received: from stinky.trash.net ([213.144.137.162]:65105 "EHLO stinky.trash.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757071AbZFQMAF (ORCPT ); Wed, 17 Jun 2009 08:00:05 -0400 Message-ID: <4A38DAC4.2050902@trash.net> Date: Wed, 17 Jun 2009 14:00:04 +0200 From: Patrick McHardy User-Agent: Mozilla-Thunderbird 2.0.0.19 (X11/20090103) MIME-Version: 1.0 To: Eric Dumazet CC: Ingo Molnar , David Miller , Thomas Gleixner , torvalds@linux-foundation.org, akpm@linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [bug] __nf_ct_refresh_acct(): WARNING: at lib/list_debug.c:30 __list_add+0x7d/0xad() 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> <4A38D9BE.3020403@gmail.com> In-Reply-To: <4A38D9BE.3020403@gmail.com> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2105 Lines: 55 Eric Dumazet wrote: > Patrick McHardy a ?crit : >> 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/