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Message-ID: <4A38D9BE.3020403@gmail.com>
Date: Wed, 17 Jun 2009 13:55:42 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: Patrick McHardy <kaber@...sh.net>
CC: Ingo Molnar <mingo@...e.hu>, David Miller <davem@...emloft.net>,
Thomas Gleixner <tglx@...utronix.de>,
torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [bug] __nf_ct_refresh_acct(): WARNING: at lib/list_debug.c:30
__list_add+0x7d/0xad()
Patrick McHardy a écrit :
> 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.
>
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.
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