netdev - Re: [PATCH net-next v6 06/11] net: sched: add 'delete' function to action ops

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Message-ID: <vbfh8k2bltt.fsf@reg-r-vrt-018-180.mtr.labs.mlnx>
Date:   Fri, 10 Aug 2018 12:41:18 +0300
From:   Vlad Buslov <vladbu@...lanox.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yevgeny Kliteynik <kliteyn@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>
Subject: Re: [PATCH net-next v6 06/11] net: sched: add 'delete' function to action ops


On Thu 09 Aug 2018 at 19:38, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Thu, Jul 5, 2018 at 7:24 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>>
>> Extend action ops with 'delete' function. Each action type to implements
>> its own delete function that doesn't depend on rtnl lock.
>>
>> Implement delete function that is required to delete actions without
>> holding rtnl lock. Use action API function that atomically deletes action
>> only if it is still in action idr. This implementation prevents concurrent
>> threads from deleting same action twice.
>
> I fail to understand why you introduce ops->delete(), it seems all
> you want is getting the tn->idrinfo, but you already have tc_action
> before calling ops->delete(), and tc_action has ->idrinfo...
>
> Each type of action does the same too, that is, just calling
> tcf_idr_delete_index()...

I agree with your assessment. Should have implemented it by just calling
tcf_idr_delete_index() directly.

>
> This changelog sucks again, it claims for skipping rtnl lock,
> but you can skip rtnl lock by just calling tcf_idr_delete_index()
> directly too, it is not the reason for adding ops->delete().

My intention was to implement some generic and parallel-safe API that
could be used to implement delete for all actions. It turns out that, as
you noted, just calling tcf_idr_delete_index() is enough because any
special per-action delete code is already implemented by ops->cleanup().