netdev - Re: Are concurrent calls to tc action ipt safe?

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Message-ID: <alpine.LSU.2.01.1007191841500.19191@obet.zrqbmnf.qr>
Date:	Mon, 19 Jul 2010 18:44:33 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	"Gerd v. Egidy" <lists@...dy.de>
cc:	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: Are concurrent calls to tc action ipt safe?

On Monday 2010-07-19 16:23, Gerd v. Egidy wrote:
>AFAIK, current iptables has a short race condition when two rules within the 
>same table are changed at once.
>
>E.g. when two users simultaneously call something like this
>iptables -t filter -A INPUT -s 192.168.1.1 -j MARK --set-mark 1
>and
>iptables -t filter -A INPUT -s 192.168.1.2 -j MARK --set-mark 2
>one of these entries can get lost.

There are many serialization techniques possible to serialize iptables 
execution.

>tc filter add dev eth0 parent ffff: protocol ip prio 1 u32  \
>match ip src 192.168.1.1 \
>action ipt -j MARK --set-mark 1
>
>Since this call uses the xtables targets I'm currently not sure if the same 
>problem regarding concurrent changes exists or not. Can anyone tell me if 
>concurrent calls like this are safe?

This target invocation is not in any table, thus there is no race 
condition.

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