netdev - Re: [PATCH net 14/14] netfilter: ipset: fix performance regression in swap operation

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Message-ID: <54f00e7c-8628-1705-8600-e9ad3a0dc677@netfilter.org>
Date: Wed, 17 Jan 2024 17:23:25 +0100 (CET)
From: Jozsef Kadlecsik <kadlec@...filter.org>
To: Eric Dumazet <edumazet@...gle.com>
cc: Pablo Neira Ayuso <pablo@...filter.org>, netfilter-devel@...r.kernel.org, 
    davem@...emloft.net, netdev@...r.kernel.org, kuba@...nel.org, 
    pabeni@...hat.com, fw@...len.de
Subject: Re: [PATCH net 14/14] netfilter: ipset: fix performance regression
 in swap operation

Hi,

On Wed, 17 Jan 2024, Eric Dumazet wrote:

> On Wed, Jan 17, 2024 at 5:00 PM Pablo Neira Ayuso <pablo@...filter.org> wrote:
> >
> > From: Jozsef Kadlecsik <kadlec@...filter.org>
> >
> > The patch "netfilter: ipset: fix race condition between swap/destroy
> > and kernel side add/del/test", commit 28628fa9 fixes a race condition.
> > But the synchronize_rcu() added to the swap function unnecessarily slows
> > it down: it can safely be moved to destroy and use call_rcu() instead.
> > Thus we can get back the same performance and preventing the race condition
> > at the same time.
> 
> ...
> 
> >
> > @@ -2357,6 +2369,9 @@ ip_set_net_exit(struct net *net)
> >
> >         inst->is_deleted = true; /* flag for ip_set_nfnl_put */
> >
> > +       /* Wait for call_rcu() in destroy */
> > +       rcu_barrier();
> > +
> >         nfnl_lock(NFNL_SUBSYS_IPSET);
> >         for (i = 0; i < inst->ip_set_max; i++) {
> >                 set = ip_set(inst, i);
> > --
> > 2.30.2
> >
> 
> If I am reading this right, time for netns dismantles will increase,
> even for netns not using ipset
> 
> If there is no other option, please convert "struct pernet_operations
> ip_set_net_ops".exit to an exit_batch() handler,
> to at least have a factorized  rcu_barrier();

You are right, the call to rcu_barrier() can safely be moved to 
ip_set_fini(). I'm going to prepare a new version of the patch.

Thanks for catching it.

Best regards,
Jozsef
-- 
E-mail  : kadlec@...ckhole.kfki.hu, kadlecsik.jozsef@...ner.hu
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Address : Wigner Research Centre for Physics
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