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

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Date:	Wed, 17 Jun 2009 17:29:11 +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 :
> Patrick McHardy wrote:
>> Eric Dumazet wrote:
>>> Patrick McHardy a écrit :
>>>> No, before it is confirmed, its only visible to the CPU handling
>>>> the initial packet of a connection. Confirmation is the step that
>>>> makes it visible to other CPUs.
>>>
>>> Thanks Patrick, I missed this, and your patch seems fine now :)
>>
>> Thanks for your help, I'll send it to Dave later today.
> 
> I'm having some trouble figuring out the exact events that would
> lead to the timer base corruption. Ingo, could you please test
> this patch to make sure it also fixes the problem?
> 
> 

;)

Event can be described as following :

CPU1					CPU2

/* __nf_conntrack_confirm() */
__nf_conntrack_hash_insert(ct, hash, repl_hash);
// now 'ct' is visible by other cpus
					// search conntrack and find ct
// timeout.expires becomes absolute here
ct->timeout.expires += jiffies;
add_timer(&ct->timeout);

					/* __nf_ct_refresh_acct() */
					if (!nf_ct_is_confirmed(ct)) {
					// we *believe* timeout.expires 
					// is not yet in use by timer code
					// and is still a relative quantity.
					// We want to 'update' it but we should not !
						ct->timeout.expires = extra_jiffies;  << CORRUPTION >>
					} else {
// too late :(
set_bit(IPS_CONFIRMED_BIT, &ct->status);



This is how I understood the problem, but I may be wrong ?

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