netdev - Re: [patch net-next 2/2] net/sched: fix filter flushing

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Date:   Sun, 21 May 2017 07:54:16 +0200
From:   Jiri Pirko <jiri@...nulli.us>
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>,
        Eric Dumazet <edumazet@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Simon Horman <simon.horman@...ronome.com>, mlxsw@...lanox.com,
        Colin King <colin.king@...onical.com>
Subject: Re: [patch net-next 2/2] net/sched: fix filter flushing

Sun, May 21, 2017 at 02:16:45AM CEST, xiyou.wangcong@...il.com wrote:
>On Sat, May 20, 2017 at 6:01 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>> +static void tcf_chain_destroy(struct tcf_chain *chain)
>> +{
>> +       list_del(&chain->list);
>> +       tcf_chain_flush(chain);
>>         kfree(chain);
>>  }
>>
>> @@ -510,7 +517,7 @@ static int tc_ctl_tfilter(struct sk_buff *skb, struct nlmsghdr *n,
>>
>>         if (n->nlmsg_type == RTM_DELTFILTER && prio == 0) {
>>                 tfilter_notify_chain(net, skb, n, chain, RTM_DELTFILTER);
>> -               tcf_chain_destroy(chain);
>> +               tcf_chain_flush(chain);
>
>
>I wonder if we should return EBUSY and do nothing in case of busy?
>The chain is no longer visual to new actions after your list_del(), but
>the old one could still use and see it.

No. User request to flush the chain, that is what happens in the past
and that is what should happen now.
If there is still a reference, the chain_put will keep the empty chain.
If there is no longer a reference, chain_put will destroy the chain. All
good.