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Date:   Tue, 8 Jan 2019 23:37:46 +0100
From:   Florian Westphal <fw@strlen.de>
To:     Anatol Pomozov <anatol.pomozov@gmail.com>
Cc:     fw@strlen.de, Dmitry Vyukov <dvyukov@google.com>,
        paulmck@linux.ibm.com, LKML <linux-kernel@vger.kernel.org>
Subject: Re: seqcount usage in xt_replace_table()
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Anatol Pomozov <anatol.pomozov@gmail.com> wrote:
> Or maybe xt_replace_table() can be enhanced? When I hear that
> something waits until an event happens on all CPUs I think about
> wait_event() function. Would it be better for xt_replace_table() to
> introduce an atomic counter that is decremented by CPUs, and the main
> CPU waits until the counter gets zero?

That would mean placing an additional atomic op into the
iptables evaluation path (ipt_do_table and friends).

Only alternative I see that might work is synchronize_rcu (the
_do_table functions are called with rcu read lock held).

I guess current scheme is cheaper though.