netdev - Re: [PATCH net] netfilter: unlock xt_table earlier in __do

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Message-ID: <20180216110245.GB31046@breakpoint.cc>
Date:   Fri, 16 Feb 2018 12:02:45 +0100
From:   Florian Westphal <fw@...len.de>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>,
        netfilter-devel@...r.kernel.org, davem@...emloft.net,
        pablo@...filter.org, fw@...len.de
Subject: Re: [PATCH net] netfilter: unlock xt_table earlier in __do_replace

Xin Long <lucien.xin@...il.com> wrote:
> Now it's doing cleanup_entry for oldinfo under the xt_table lock,
> but it's not really necessary. After the replacement job is done
> in xt_replace_table, oldinfo is not used elsewhere any more, and
> it can be freed without xt_table lock safely.

Right.

> The important thing is that rtnl_lock is called in some xt_target
> destroy, which means rtnl_lock, a big lock is used in xt_table
> lock, a smaller one. It usually could be the reason why a dead
> lock may happen.

In which cases do we aquire the xt table mutex from places that hold
rtnl mutex?

> Besides, all xt_target/match checkentry is called out of xt_table
> lock. It's better also to move all cleanup_entry calling out of
> xt_table lock, just as do_replace_finish does for ebtables.

Agree but I don't see how this patch fixes a bug so I would prefer if
this could simmer in nf-next first.