netdev - Re: [PATCH net-next v2] net: sched: change tcf_del

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Message-ID: <vbfefdzm74n.fsf@reg-r-vrt-018-180.mtr.labs.mlnx>
Date:   Wed, 12 Sep 2018 11:50:48 +0300
From:   Vlad Buslov <vladbu@...lanox.com>
To:     Cong Wang <xiyou.wangcong@...il.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>
Subject: Re: [PATCH net-next v2] net: sched: change tcf_del_walker() to take idrinfo->lock


On Fri 07 Sep 2018 at 19:12, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Fri, Sep 7, 2018 at 6:52 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>>
>> Action API was changed to work with actions and action_idr in concurrency
>> safe manner, however tcf_del_walker() still uses actions without taking a
>> reference or idrinfo->lock first, and deletes them directly, disregarding
>> possible concurrent delete.
>>
>> Add tc_action_wq workqueue to action API. Implement
>> tcf_idr_release_unsafe() that assumes external synchronization by caller
>> and delays blocking action cleanup part to tc_action_wq workqueue. Extend
>> tcf_action_cleanup() with 'async' argument to indicate that function should
>> free action asynchronously.
>
> Where exactly is blocking in tcf_action_cleanup()?
>
> From your code, it looks like free_tcf(), but from my observation,
> the only blocking function inside is tcf_action_goto_chain_fini()
> which calls __tcf_chain_put(). But, __tcf_chain_put() is blocking
> _ONLY_ when tc_chain_notify() is called, for tc action it is never
> called.
>
> So, what else is blocking?

__tcf_chain_put() calls tc_chain_tmplt_del(), which calls
ops->tmplt_destroy(). This last function uses hw offload API, which is
blocking.