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Date: Mon, 22 Dec 2025 12:16:14 +0100
From: Florian Westphal <fw@strlen.de>
To: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: syzbot <syzbot+ff16b505ec9152e5f448@syzkaller.appspotmail.com>,
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	netfilter-devel@vger.kernel.org, pabeni@redhat.com, phil@nwl.cc,
	syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [netfilter?] possible deadlock in
 nf_tables_dumpreset_obj
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References: <6945f4b4.a70a0220.207337.0121.GAE@google.com>
 <aUh_3mVRV8OrGsVo@strlen.de>
 <aUkNtgPyic8_fBd5@chamomile>
 <aUkPz0extqKuB7Bl@chamomile>
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In-Reply-To: <aUkPz0extqKuB7Bl@chamomile>

Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > > CPU0: 'nft reset'.
> > > CPU1: 'ipset list' (anything in ipset doing a netlink dump op)
> > > CPU2: 'iptables-nft -A ... -m set ...'
> > > 
> > > ... can result in:
> > > 
> > > CPU0                    CPU1                            CPU2
> > > ----                    ----                            ----
> > > lock(nlk_cb_mutex-NETFILTER);
> > >                         lock(nfnl_subsys_ipset);
> > >                                                        lock(&nft_net->commit_mutex);
> > >                         lock(nlk_cb_mutex-NETFILTER);
> > >                                                        lock(nfnl_subsys_ipset);
> > > lock(&nft_net->commit_mutex);
> 
> Would it work to use a separated mutex for reset itself?

I think so, yes, its only job is to prevent concurrent reset actions,
the objects themselves are protected by rcu.

Parallel add/removal should be fine.