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

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Message-ID: <CANn89i+jS11sC6cXXFA+_ZVr9Oy6Hn1e3_5P_d4kSR2fWtisBA@mail.gmail.com>
Date: Wed, 17 Jan 2024 17:08:11 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Pablo Neira Ayuso <pablo@...filter.org>
Cc: 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 5:00 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();