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Date:   Thu, 28 Sep 2023 22:09:46 +0200
From:   Florian Westphal <fw@strlen.de>
To:     Jozsef Kadlecsik <kadlec@netfilter.org>
Cc:     Pablo Neira Ayuso <pablo@netfilter.org>,
        Florian Westphal <fw@strlen.de>, Phil Sutter <phil@nwl.cc>,
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Subject: Re: [nf PATCH v2 8/8] netfilter: nf_tables: Add locking for
 NFT_MSG_GETSETELEM_RESET requests
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Jozsef Kadlecsik <kadlec@netfilter.org> wrote:
> On Thu, 28 Sep 2023, Pablo Neira Ayuso wrote:
> > One concern might be deadlock due to reordering, but I don't see how
> > that can happen.
> 
> The same problem exists ipset: when a set is listed/saved (dumped), 
> concurrent destroy/rename/swap for the same set must be excluded. As 
> neither spinlock nor mutex helps, a reference counter is used: the start 
> of the dump increases it and by checking it all concurrent events can 
> safely be rejected by returning EBUSY.

Thanks for sharing!

I assume that means that a dumper that starts a dump, and then
goes to sleep before closing the socket/finishing the dump can
block further ipset updates, is that correct?

(I assume so, I don't see a solution that doesn't trade one problem
 for another).