netdev - Re: [PATCH net-next 1/5] bonding: convert to list API and replace bond's custom list

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Date:	Wed, 31 Jul 2013 21:00:35 +0200
From:	Nikolay Aleksandrov <nikolay@...hat.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
CC:	netdev@...r.kernel.org, andy@...yhouse.net, davem@...emloft.net,
	fubar@...ibm.com
Subject: Re: [PATCH net-next 1/5] bonding: convert to list API and replace
 bond's custom list

On 07/31/2013 08:56 PM, Stephen Hemminger wrote:
> On Wed, 31 Jul 2013 20:44:49 +0200
> Nikolay Aleksandrov <nikolay@...hat.com> wrote:
> 
>> On 07/31/2013 08:37 PM, Stephen Hemminger wrote:
>>> On Wed, 31 Jul 2013 17:12:29 +0200
>>> Nikolay Aleksandrov <nikolay@...hat.com> wrote:
>>>
>>>> diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
>>>> index 390061d..80e288c 100644
>>>> --- a/drivers/net/bonding/bond_3ad.c
>>>> +++ b/drivers/net/bonding/bond_3ad.c
>>>> @@ -143,10 +143,13 @@ static inline struct bonding *__get_bond_by_port(struct port *port)
>>>>   */
>>>>  static inline struct port *__get_first_port(struct bonding *bond)
>>>>  {
>>>> +	struct slave *first_slave;
>>>> +
>>>>  	if (bond->slave_cnt == 0)
>>>>  		return NULL;
>>>> +	first_slave = bond_first_slave(bond);
>>>
>>> As Jay said, it would be be better to have bond_first_slave return
>>> NULL (if no slaves), and eliminate slave_cnt. It would also fix
>>> a race here between slave_cnt and all slave's being removed.
>>>
>> Hi Stephen,
>> First off - thank you for the review.
>>
>> What do you mean by eliminate slave_cnt ?
>> We need it for various calculations throughout the bonding.
>> There's no race here because read_lock(&bond->lock) is held every time this
>> is called and slave_cnt can change only under write_lock of the same lock,
>> the 3ad code is not yet converted to RCU.
>>
>> Nik
> 
> I would hope the goal would be to eliminate all read_lock's and allow
> it to be totally RCU based.
> 
> You could then reduce slave_cnt to being only accessed by under a spin_lock
> when doing management actions.
> 
Yes, that is the end goal. And my end-implementation does just that -
removes curr_slave_lock completely and makes bond->lock a spinlock. But for
now we need it for the parts that aren't converted, as I said in the
beginning I'm doing the conversion gradually and there will be a special
series that takes care of 3ad mode as there are many potential problems for
RCU there because of its current design.
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