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

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Date: Wed, 17 Jan 2024 17:28:54 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Jozsef Kadlecsik <kadlec@...filter.org>
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

On Wed, Jan 17, 2024 at 5:23 PM Jozsef Kadlecsik <kadlec@...filter.org> wrote:
>
> 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.

I do not want to hold the series, your fix can be built as another
patch on top of this one.

Thanks.