linux-kernel - Re: [PATCH] netfilter: use per-cpu recursive spinlock (v6)

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Message-ID: <49E763DB.1000706@trash.net>
Date:	Thu, 16 Apr 2009 18:59:07 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Eric Dumazet <dada1@...mosbay.com>, paulmck@...ux.vnet.ibm.com,
	Stephen Hemminger <shemminger@...tta.com>,
	David Miller <davem@...emloft.net>, jeff.chua.linux@...il.com,
	paulus@...ba.org, mingo@...e.hu, laijs@...fujitsu.com,
	jengelh@...ozas.de, 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 recursive spinlock  (v6)

Linus Torvalds wrote:
> Guys, this whole discussion has just been filled with crazy crap. Can 
> somebody even explain why we care so deeply about some counters for 
> something that we just _deleted_ and that have random values anyway?
> 
> I can see the counters being interesting while a firewall is active, but I 
> sure don't see what's so wonderfully interesting after-the-fact about a 
> counter on something that NO LONGER EXISTS that it has to be somehow 
> "exactly right".

They're copied to userspace after replacing the ruleset, associated with
the rules that are still active after the change and then added to the
current counters in a second operation. The end result is that the
counters are accurate for rules not changed.

> Show of hands, here: tell me a single use that really _requires_ those 
> exact counters of a netfilter rule that got deleted and is no longer 
> active?

People use netfilter for accounting quite a lot. Having dynamic updates
is also not uncommon, so this might actually matter.


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