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 14:33:50 +0200 Message-ID: <4A38E2AE.3030106@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> <4A38D9BE.3020403@gmail.com> <4A38DAC4.2050902@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]:46433 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752989AbZFQMeK (ORCPT ); Wed, 17 Jun 2009 08:34:10 -0400 In-Reply-To: <4A38DAC4.2050902@trash.net> Sender: netdev-owner@vger.kernel.org List-ID: Patrick McHardy a =E9crit : > Eric Dumazet wrote: >> Patrick McHardy a =E9crit : >>> 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. >>> >> >> >> 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. >=20 > 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. >=20 Sorry, I dont understand how your second patch corrects the problem. This (unconfirmed) conntrack is visible by another cpu. This other cpu can call __nf_ct_refresh_acct() while this cpu runs in __nf_conntrack_confirm() @@ -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); =20 - __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); <<<< another cpu could here change timeout.expires (thinking its still = relative) >>>> atomic_inc(&ct->ct_general.use); set_bit(IPS_CONFIRMED_BIT, &ct->status); + + /* Since the lookup is lockless, hash insertion must be after startin= g the + * timer and setting the CONFIRMED bit. The RCU barriers guarantee th= at no + * other CPU can find the conntrack before the above stores are visib= le. + */ + __nf_conntrack_hash_insert(ct, hash, repl_hash); NF_CT_STAT_INC(net, insert); spin_unlock_bh(&nf_conntrack_lock); help =3D nfct_help(ct); if (help && help->helper) nf_conntrack_event_cache(IPCT_HELPER, ct);