netdev - Re: [PATCH v5 2/2] sock: Move the socket inuse to namespace.

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Date:   Fri, 8 Dec 2017 13:28:22 +0800
From:   Tonghao Zhang <xiangxia.m.yue@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH v5 2/2] sock: Move the socket inuse to namespace.

On Fri, Dec 8, 2017 at 1:20 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Thu, 2017-12-07 at 08:45 -0800, Tonghao Zhang wrote:
>> In some case, we want to know how many sockets are in use in
>> different _net_ namespaces. It's a key resource metric.
>>
>
> ...
>
>> +static void sock_inuse_add(struct net *net, int val)
>> +{
>> +     if (net->core.prot_inuse)
>> +             this_cpu_add(*net->core.sock_inuse, val);
>> +}
>
> This is very confusing.
>
> Why testing net->core.prot_inuse for NULL is needed at all ?
>
> Why not testing net->core.sock_inuse instead ?
>
Hi Eric and Cong, oh it's a typo. it's net->core.sock_inuse there. Why
we should check the net->core.sock_inuse
Now show you the code:

cleanup_net will call all of the network namespace exit methods,
rcu_barrier, and then remove the _net_ namespace.

cleanup_net:
    list_for_each_entry_reverse(ops, &pernet_list, list)
         ops_exit_list(ops, &net_exit_list);

    rcu_barrier(); /* for netlink sock, the ‘deferred_put_nlk_sk’ will
be called. But sock_inuse has been released. */


    /* Finally it is safe to free my network namespace structure */
    list_for_each_entry_safe(net, tmp, &net_exit_list, exit_list) {}



Release the netlink sock created in kernel(not hold the _net_ namespace):

netlink_release
       call_rcu(&nlk->rcu, deferred_put_nlk_sk);

deferred_put_nlk_sk
       sk_free(sk);


I may add a comment for sock_inuse_add in v6.