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

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Message-ID: <8834c825579a054d51be3d60405c0b204fa5c24b.camel@redhat.com>
Date: Thu, 18 Jan 2024 12:08:02 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Eric Dumazet <edumazet@...gle.com>, 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, fw@...len.de
Subject: Re: [PATCH net 14/14] netfilter: ipset: fix performance regression
 in swap operation

On Wed, 2024-01-17 at 17:28 +0100, Eric Dumazet wrote:
> 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.

Given the timing, if we merge this series as is, it could go very soon
into Linus' tree. I think it would be better to avoid introducing known
regressions there. 

Any strong opinions vs holding this series until the problems are
fixed? Likely a new PR will be required.

Thanks,

Paolo