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Date:   Tue, 26 Sep 2023 11:34:43 +0200
From:   Phil Sutter <phil@nwl.cc>
To:     Florian Westphal <fw@strlen.de>
Cc:     Pablo Neira Ayuso <pablo@netfilter.org>,
        netfilter-devel@vger.kernel.org
Subject: Re: [nf PATCH 2/5] netfilter: nf_tables: Add locking for
 NFT_MSG_GETRULE_RESET requests
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On Mon, Sep 25, 2023 at 09:53:17PM +0200, Florian Westphal wrote:
> Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > On Sat, Sep 23, 2023 at 06:18:13PM +0200, Florian Westphal wrote:
> > > callback_that_might_reset()
> > > {
> > > 	try_module_get ...
> > > 	rcu_read_unlock()
> > > 	mutex_lock(net->commit_mutex)
> > > 	  dumper();
> > > 	mutex_unlock(net->commit_mutex)
> > > 	rcu_read_lock();
> > > 	module_put()
> > > }
> > >
> > > should do the trick.
> > 
> > Idiom above LGTM, *except for net->commit_mutex*. Please do not use
> > ->commit_mutex: This will stall ruleset updates for no reason, netlink
> > dump would grab and release such mutex for each netlink_recvmsg() call
> > and netlink dump side will always retry because of NLM_F_EINTR.
> 
> It will stall updates, but for good reason: we are making changes to the
> expressions state.

This also disqualifies the use of Pablo's suggested reset_lock, right?

Cheers, Phil