netdev - Re: [bug] __nf_ct_refresh_acct(): WARNING: at lib/list_debug.c:30 __list

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Date:	Wed, 17 Jun 2009 13:51:45 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
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 wrote:
> 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.
> 

A slightly changed version which moves hash insertion to the end
and adds a comment about ordering. This make sure the timer is
actually running before the conntrack can be found be other CPUs.



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