From: Eric Dumazet <eric.dumazet@gmail.com>
To: Patrick McHardy <kaber@trash.net>
Cc: Ingo Molnar <mingo@elte.hu>, David Miller <davem@davemloft.net>,
Thomas Gleixner <tglx@linutronix.de>,
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()
Date: Wed, 17 Jun 2009 14:33:50 +0200 [thread overview]
Message-ID: <4A38E2AE.3030106@gmail.com> (raw)
In-Reply-To: <4A38DAC4.2050902@trash.net>
Patrick McHardy a écrit :
> 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.
>>>
>>
>>
>> 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.
>
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);
- __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 starting the
+ * timer and setting the CONFIRMED bit. The RCU barriers guarantee that no
+ * other CPU can find the conntrack before the above stores are visible.
+ */
+ __nf_conntrack_hash_insert(ct, hash, repl_hash);
NF_CT_STAT_INC(net, insert);
spin_unlock_bh(&nf_conntrack_lock);
help = nfct_help(ct);
if (help && help->helper)
nf_conntrack_event_cache(IPCT_HELPER, ct);
next prev parent reply other threads:[~2009-06-17 12:34 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-06-15 12:04 [GIT]: Networking David Miller
2009-06-16 9:15 ` Ingo Molnar
2009-06-16 9:19 ` David Miller
2009-06-16 9:33 ` Ingo Molnar
2009-06-16 9:44 ` Ingo Molnar
2009-06-16 9:44 ` Alan Cox
2009-06-16 9:48 ` Ingo Molnar
2009-06-16 9:56 ` David Miller
2009-06-16 10:11 ` Ingo Molnar
2009-06-16 10:35 ` David Miller
2009-06-16 13:38 ` Eric Dumazet
2009-06-16 14:19 ` Eric Dumazet
2009-06-16 18:59 ` Linus Torvalds
2009-06-16 19:08 ` David Miller
2009-06-16 19:37 ` Eric Dumazet
2009-06-16 20:12 ` Eric Dumazet
2009-06-17 6:41 ` [PATCH] net: correct off-by-one write allocations reports Eric Dumazet
2009-06-17 11:31 ` [PATCH] atm: sk_wmem_alloc initial value is one Eric Dumazet
2009-06-18 2:06 ` David Miller
2009-06-18 2:05 ` [PATCH] net: correct off-by-one write allocations reports David Miller
2009-06-17 11:32 ` [GIT]: Networking David Miller
2009-06-16 9:21 ` David Miller
2009-06-16 9:26 ` Ingo Molnar
2009-06-16 10:47 ` David Miller
2009-06-16 10:53 ` Ingo Molnar
2009-06-16 12:24 ` Ingo Molnar
2009-06-16 12:39 ` David Miller
2009-06-17 9:21 ` [bug] __nf_ct_refresh_acct(): WARNING: at lib/list_debug.c:30 __list_add+0x7d/0xad() Ingo Molnar
2009-06-17 10:18 ` Eric Dumazet
2009-06-17 11:08 ` Ingo Molnar
2009-06-17 11:35 ` David Miller
2009-06-18 5:23 ` Ingo Molnar
2009-06-18 5:58 ` Eric Dumazet
2009-06-18 9:47 ` Patrick McHardy
2009-06-18 14:56 ` Patrick McHardy
2009-06-18 15:46 ` Eric Dumazet
2009-06-18 16:09 ` Patrick McHardy
2009-06-18 16:13 ` Pablo Neira Ayuso
2009-06-18 22:46 ` [PATCH] netfilter: conntrack: death_by_timeout() fix Eric Dumazet
2009-06-19 11:15 ` Patrick McHardy
2009-06-20 15:47 ` [bug] __nf_ct_refresh_acct(): WARNING: at lib/list_debug.c:30 __list_add+0x7d/0xad() Ingo Molnar
2009-06-20 15:56 ` Patrick McHardy
2009-06-17 11:38 ` Patrick McHardy
2009-06-17 11:51 ` Patrick McHardy
2009-06-17 11:55 ` Eric Dumazet
2009-06-17 12:00 ` Patrick McHardy
2009-06-17 12:33 ` Eric Dumazet [this message]
2009-06-17 12:36 ` Patrick McHardy
2009-06-17 13:27 ` Eric Dumazet
2009-06-17 13:29 ` Patrick McHardy
2009-06-17 14:23 ` Patrick McHardy
2009-06-17 15:29 ` Eric Dumazet
2009-06-17 15:34 ` Patrick McHardy
2009-06-18 23:18 ` [GIT]: Networking Tilman Schmidt
2009-06-19 3:36 ` David Miller
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