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

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Date:   Sat, 20 May 2017 17:16:45 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Jiri Pirko <jiri@...nulli.us>
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

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.