netdev - Re: [PATCH net-next] net: sched: change tcf_del_walker() to use concurrent-safe delete

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Date:   Mon, 03 Sep 2018 23:33:26 +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] net: sched: change tcf_del_walker() to use concurrent-safe delete


On Mon 03 Sep 2018 at 18:50, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Mon, Sep 3, 2018 at 12:06 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
>> reference to them first and deletes them directly, disregarding possible
>> concurrent delete.
>>
>> Change tcf_del_walker() to use tcf_idr_delete_index() that doesn't require
>> caller to hold reference to action and accepts action id as argument,
>> instead of direct action pointer.
>
> Hmm, why doesn't tcf_del_walker() just take idrinfo->lock? At least
> tcf_dump_walker() already does.

Because tcf_del_walker() calls __tcf_idr_release(), which take
idrinfo->lock itself (deadlock). It also calls sleeping functions like
tcf_action_goto_chain_fini(), so just implementing function that
releases action without taking idrinfo->lock is not enough.