netdev - Re: [PATCH net-next v4 05/17] net: sched: traverse chains in block with tcf_get_next

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Date:   Fri, 15 Feb 2019 14:21:05 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Vlad Buslov <vladbu@...lanox.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>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH net-next v4 05/17] net: sched: traverse chains in block
 with tcf_get_next_chain()

(Sorry for joining this late.)

On Mon, Feb 11, 2019 at 12:56 AM Vlad Buslov <vladbu@...lanox.com> wrote:
> @@ -2432,7 +2474,11 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb)
>         index_start = cb->args[0];
>         index = 0;
>
> -       list_for_each_entry(chain, &block->chain_list, list) {
> +       for (chain = __tcf_get_next_chain(block, NULL);
> +            chain;
> +            chain_prev = chain,
> +                    chain = __tcf_get_next_chain(block, chain),
> +                    tcf_chain_put(chain_prev)) {

Why do you want to take the block->lock in each iteration
of the loop rather than taking once for the whole loop?