netdev - Re: [PATCH net-next v4 17/17] net: sched: unlock rules update API

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Message-ID: <CAM_iQpW4Tn4qVynrRK6NK13UtHJ4QfS-Z2mcjMk46qL_QJBg+A@mail.gmail.com>
Date:   Mon, 18 Feb 2019 10:56:08 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH net-next v4 17/17] net: sched: unlock rules update API

On Mon, Feb 11, 2019 at 12:56 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>
> Register netlink protocol handlers for message types RTM_NEWTFILTER,
> RTM_DELTFILTER, RTM_GETTFILTER as unlocked. Set rtnl_held variable that
> tracks rtnl mutex state to be false by default.
>
> Introduce tcf_proto_is_unlocked() helper that is used to check
> tcf_proto_ops->flag to determine if ops can be called without taking rtnl
> lock. Manually lookup Qdisc, class and block in rule update handlers.
> Verify that both Qdisc ops and proto ops are unlocked before using any of
> their callbacks, and obtain rtnl lock otherwise.

So if you end goal is to completely get rid of RTNL from tc filter and
action control path, why this change is needed?

I was expecting you to break down the RTNL lock down to each
block/filter chain, which should be done in this patchset. So again,
why do we still need RTNL for some cases?

Please state the reasoning in your changelog, rather than just
describing what your code does.

Thanks.