netdev - Re: [PATCH net-2.6 v2] pkt_sched: gen

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Date:	Wed, 9 Jun 2010 11:33:29 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Changli Gao <xiaosuo@...il.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Stephen Hemminger <shemminger@...tta.com>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH net-2.6 v2] pkt_sched: gen_estimator: add a new lock

On Wed, Jun 09, 2010 at 11:39:10AM +0200, Eric Dumazet wrote:
...
> Here is v2 of patch, adding protection in gen_estimator_active() as
> well.
> 
> [PATCH net-2.6 v2] pkt_sched: gen_estimator: add a new lock
> 
> gen_kill_estimator() / gen_new_estimator() is not always called with
> RTNL held.
> 
> net/netfilter/xt_RATEEST.c is one user of these API that do not hold
> RTNL, so random corruptions can occur between "tc" and "iptables".
> 
> Add a new fine grained lock instead of trying to use RTNL in netfilter.

Btw, maybe it's a different case, but RTNL happens in netfilter already
(nf_conntrack_helper.c, nf_conntrack_proto.c).

It would be nice to mention Changli's argument that
gen_replace_estimator isn't atomic operation after this change.

> @@ -312,8 +315,14 @@ EXPORT_SYMBOL(gen_replace_estimator);
>  bool gen_estimator_active(const struct gnet_stats_basic_packed *bstats,
>  			  const struct gnet_stats_rate_est *rate_est)
>  {
> +	bool res;
> +
>  	ASSERT_RTNL();

This line should go away as well.

I'm OK with this patch unless there is an alternative xt_RATEEST RTNL
fix available.

Jarek P.
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