netdev - Re: [net-next PATCH 1/2] fib_trie: Fix warning on fib4_rules

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Message-ID: <CAHA+R7NeYYmbyAuzNMtWQ4_T1Wq-mO42PmWfQp18ecOzYtX7wA@mail.gmail.com>
Date:	Mon, 30 Mar 2015 11:54:37 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	Alexander Duyck <alexander.h.duyck@...hat.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Cong Wang <xiyou.wangcong@...il.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [net-next PATCH 1/2] fib_trie: Fix warning on fib4_rules_exit

On Fri, Mar 27, 2015 at 4:29 PM, Alexander Duyck
<alexander.h.duyck@...hat.com> wrote:
>
> On 03/27/2015 03:14 PM, Cong Wang wrote:
>>
>> On Fri, Mar 27, 2015 at 2:14 PM, Alexander Duyck
>> <alexander.h.duyck@...hat.com> wrote:
>>>
>>> The issue was that as a part of exiting the default rules were being
>>> deleted which resulted in the local trie being unmerged.  By moving the
>>> freeing of the FIB tables up we can avoid the unmerge since there is no
>>> local table left when we call the fib4_rules_exit function.
>>>
>> This literally means we no longer need to call ops->delete()
>> in netns unregister path.
>
>
> You are confusing table entries and rules.  The tables are cleared, the
> rules still have to be deleted.  This patch breaks the reference counting
> for fib_num_tclassid_users.

It doesn't matter much here, the whole net is being unregistered,
we are holding rtnl lock and existing readers don't mind to read an incorrect
fib_num_tclassid_users.

>
>>
>> diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
>> index 68ea695..27b6e04 100644
>> --- a/net/core/fib_rules.c
>> +++ b/net/core/fib_rules.c
>> @@ -153,8 +153,6 @@ static void fib_rules_cleanup_ops(struct fib_rules_ops
>> *ops)
>>
>>          list_for_each_entry_safe(rule, tmp, &ops->rules_list, list) {
>>                  list_del_rcu(&rule->list);
>> -               if (ops->delete)
>> -                       ops->delete(rule);
>>                  fib_rule_put(rule);
>>          }
>>   }
>> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
>> index e5b6b05..1481b23 100644
>> --- a/net/ipv4/fib_frontend.c
>> +++ b/net/ipv4/fib_frontend.c
>> @@ -1178,6 +1178,7 @@ static void ip_fib_net_exit(struct net *net)
>>
>>   #ifdef CONFIG_IP_MULTIPLE_TABLES
>>          fib4_rules_exit(net);
>> +       fib_flush_external(net); // <-------- Maybe not needed either.
>>   #endif
>>
>>          for (i = 0; i < FIB_TABLE_HASHSZ; i++) {
>
>
> Take a look at fib4_rule_delete.  There is more there than just unmerge and
> flush external.

I am not stupid, what otherwise do you think the above fib_flush_external()
comes from?

Read fib4_rule_delete(), everything it cleans up is per net, you can argue
ipv4.fib_num_tclassid_users is a refcount for rules, but still the whole net
is being unregistered.
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