netdev - Re: [PATCH] netfilter: use per-cpu spinlock rather than RCU (v3)

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Date:	Thu, 16 Apr 2009 14:24:06 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Patrick McHardy <kaber@...sh.net>
cc:	Eric Dumazet <dada1@...mosbay.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Jeff Chua <jeff.chua.linux@...il.com>,
	paulmck@...ux.vnet.ibm.com, David Miller <davem@...emloft.net>,
	paulus@...ba.org, mingo@...e.hu, torvalds@...ux-foundation.org,
	laijs@...fujitsu.com, r000n@...0n.net,
	linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
	netdev@...r.kernel.org, benh@...nel.crashing.org
Subject: Re: [PATCH] netfilter: use per-cpu spinlock rather than RCU (v3)


On Thursday 2009-04-16 14:12, Patrick McHardy wrote:
> Jan Engelhardt wrote:
>> On Wednesday 2009-04-15 23:07, Eric Dumazet wrote:
>>> Stephen Hemminger a écrit :
>>>> Looks like there is some recursive path into ip_tables that makes the
>>>> per-cpu spinlock break.  I get lockup's with KVM networking.
>>>>
>>>> Suggestions?
>>> Well, it seems original patch was not so bad after all
>>>
>>> http://lists.netfilter.org/pipermail/netfilter-devel/2006-January/023175.html
>>>
>>> So change per-cpu spinlocks to per-cpu rwlocks 
>>> and use read_lock() in ipt_do_table() to allow recursion...
>>>
>> iptables cannot quite recurse into itself due to the comefrom stuff.
>
> Actually it can by using the REJECT target:

Yes, but it has to return an absolute verdict (which REJECT does),
so it's not really a recursion, it's more like a goto without return.
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