Subject: Re: [PATCH net-next v4 1/6] bonding: simplify and use RCU protection for 3ad xmit path

From: Ding Tianhong <[email-masked]>
Date: Mon, 09 Sep 2013 22:53:20 +0800

于 2013/9/9 17:57, Veaceslav Falico 写道:
> On Mon, Sep 09, 2013 at 04:58:29PM +0800, Ding Tianhong wrote:
>> On 2013/9/8 14:05, Ding Tianhong wrote:
>>
>> Hi Veaceslav and Nik:
>>
>> please take a moment to reveiw the function just modify for 
>> bond_XXX_rcu,
>> and give me some advice. thanks for the help again.:)
>>
>> +#define bond_first_slave_rcu(bond) \
>> + list_first_or_null_rcu(&(bond)->slave_list, struct slave, list);
>> +#define bond_last_slave_rcu(bond) \
>> + ({struct list_head *__slave_list = &(bond)->slave_list; \
>> + struct list_head __rcu *__prev = \
>> + (*((struct list_head __rcu **)(&(__slave_list)->prev)));\
>> + likely(__slave_list != __prev) ? \
>> + container_of(__prev, struct slave, list) : NULL;})
>
> Please take a look at Nikolay's reply to my RCU email -
> http://www.spinics.net/lists/netdev/msg249805.html . And mine also, to 
> his
> email. In short - RCU doesn't guarantee ->prev, so better take the 
> approach
> of eliminating bond_last/prev_slave completely.
>
yes, I see the message, the list_del_rcu will make the slave->list 
->prev = LIST_POISON2,
the bond->slave_list will not be set to the messae, the prev will point 
a slave->list or itself,
so I think it will be ok here, please correct me if I miss something.

Best Regards
Ding

>> +
>> #define bond_is_first_slave(bond, pos) ((pos)->list.prev == 
>> &(bond)->slave_list)
>> #define bond_is_last_slave(bond, pos) ((pos)->list.next == 
>> &(bond)->slave_list)
>>
>> @@ -93,6 +117,29 @@
>> (bond_is_first_slave(bond, pos) ? bond_last_slave(bond) : \
>> bond_to_slave((pos)->list.prev))
>>
>> +/* Since bond_first/last_slave_rcu can return NULL, these can return 
>> NULL too */
>> +#define bond_next_slave_rcu(bond, pos) \
>> + ({struct list_head *__slave_list = &(bond)->slave_list; \
>> + struct list_head __rcu *__next = list_next_rcu(__slave_list); \
>> + struct list_head *__pos_list = &(pos)->list; \
>> + struct list_head __rcu *__pos_next = list_next_rcu(__pos_list); \
>> + likely(__pos_next != __slave_list) ? \
>> + container_of(__pos_next, struct slave, list) : \
>> + container_of(__next, struct slave, list); \
>> + })
>
> Nice, but can be shortened - we know that pos won't go away.

OK, clean it soon.

>
>> +
>> +#define bond_prev_slave_rcu(bond, pos) \
>> + ({struct list_head *__slave_list = &(bond)->slave_list; \
>> + struct list_head __rcu *__prev = \
>> + (*((struct list_head __rcu **)(&(__slave_list)->prev)));\
>> + struct list_head *__pos_list = &(pos)->list; \
>> + struct list_head __rcu *__pos_prev = (__pos_list->prev 
>> !=LIST_POISON2) ? \
yes, the pos->list will be set to LIST_POISON2 by list_del_rcu, so I add 
a check for it, But
take the approach of eliminating bond_last/prev_slave completely is a 
wise decision, I agree.

>> + (*((struct list_head __rcu **)(&(__pos_list)->prev))) : NULL; \
>> + likely(__pos_prev != __slave_list) ? \
>> + ((__pos_prev) ? list_entry_rcu(__pos_prev, struct slave, list) : 
>> NULL;) : \
>> + (list_entry_rcu(__prev, struct slave, list)); \
>> + })
>
> Same remark as above about prev.
>
>> +
>>
>>
>> -#define bond_for_each_slave_from(bond, pos, cnt, start) \
>> - for (cnt = 0, pos = start; pos && cnt < (bond)->slave_cnt; \
>> - cnt++, pos = bond_next_slave(bond, pos))
>> -
>> +#define bond_for_each_slave_from(bond, pos, start) \
>> + for (pos = start; pos; (pos = bond_next_slave(bond, pos)) != start ? \
>> + (pos) : (pos = NULL))
>> +
>> +#define bond_for_each_slave_from_rcu(bond, pos, start) \
yes, it is a little tedious. I think it could be more easier and shorter.

>> + for ({struct list_head *__start = &(start)->list; \
>> + struct list_head *__slave_list = &(bond)->slave_list; \
>> + pos = list_entry_rcu(__start, struct slave, list);}; \
>> + pos; \
the only way to get out of the loop is that pos is NULL.
>> + {struct list_head __rcu *__next = list_next_rcu(pos->next); \
>> + __next != __slave_list ? \
>> + __next : __next = list_next_rcu(__next->next); \
first, check whether the pos->next is the last one in the slave_list, if 
it does, get the
first slave of the bond->slave_list.
>>
>> + __next != __start ? \
>> + pos = list_entry_rcu(__next, struct slave, list) : \
>> + pos = NULL; \
second, check whether the pos is reach the start, if not, continue, 
otherwise, the pos
will be set to NULL, so break the loop.
>> + })
>
> Jeez, I don't even want to review it. It's too complex and too hard to
> maintain, even if it works. Can you please make something 
> shorter/easier to
> understand?
>

Best Regards.
Ding

>> +
>>
>> Best regards
>> Ding
>>
>>
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>>
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