Subject: Re: [PATCH v2 net-next 3/3] bonding: fix __get_active_agg() RCU logic

From: Veaceslav Falico <[email-masked]>
Date: Thu, 9 Jan 2014 13:13:28 +0100

On Thu, Jan 09, 2014 at 08:04:25PM +0800, Ding Tianhong wrote:
>On 2014/1/9 19:20, Veaceslav Falico wrote:
>> Currently, the implementation is meaningless - once again, we take the
>> slave structure and use it after we've exited RCU critical section.
>>
>> Fix this by removing the rcu_read_lock() from __get_active_agg(), and
>> ensuring that all its callers are holding either RCU or RTNL lock.
>>
>> Fixes: be79bd048 ("bonding: add RCU for bond_3ad_state_machine_handler()")
>> CC: [email-masked]
>> CC: Jay Vosburgh <[email-masked]>
>> CC: Andy Gospodarek <[email-masked]>
>> Signed-off-by: Veaceslav Falico <[email-masked]>
>> ---
>>
>> Notes:
>>     v1 -> v2:
>>     Don't use RCU primitives as we can hold RTNL.
>>
>>  drivers/net/bonding/bond_3ad.c | 12 +++++-------
>>  1 file changed, 5 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
>> index d2782c8..845545b 100644
>> --- a/drivers/net/bonding/bond_3ad.c
>> +++ b/drivers/net/bonding/bond_3ad.c
>> @@ -674,6 +674,8 @@ static u32 __get_agg_bandwidth(struct aggregator *aggregator)
>>  /**
>>   * __get_active_agg - get the current active aggregator
>>   * @aggregator: the aggregator we're looking at
>> + *
>> + * Caller must hold either RCU or RTNL lock.
>>   */
>>  static struct aggregator *__get_active_agg(struct aggregator *aggregator)
>>  {
>> @@ -681,13 +683,9 @@ static struct aggregator *__get_active_agg(struct aggregator *aggregator)
>>  	struct list_head *iter;
>>  	struct slave *slave;
>>
>> -	rcu_read_lock();
>> -	bond_for_each_slave_rcu(bond, slave, iter)
>> -		if (SLAVE_AD_INFO(slave).aggregator.is_active) {
>> -			rcu_read_unlock();
>> +	bond_for_each_slave(bond, slave, iter)
>> +		if (SLAVE_AD_INFO(slave).aggregator.is_active)
>>  			return &(SLAVE_AD_INFO(slave).aggregator);
>> -		}
>
>Is the bond_for_each_slave safe in rcu_read_lock()?

Yeah, good catch, responded in the second patch.

Thanks for the review!

>
>
>> -	rcu_read_unlock();
>>
>>  	return NULL;
>>  }
>> @@ -1495,11 +1493,11 @@ static void ad_agg_selection_logic(struct aggregator *agg)
>>  	struct slave *slave;
>>  	struct port *port;
>>
>> +	rcu_read_lock();
>>  	origin = agg;
>>  	active = __get_active_agg(agg);
>>  	best = (active && agg_device_up(active)) ? active : NULL;
>>
>> -	rcu_read_lock();
>>  	bond_for_each_slave_rcu(bond, slave, iter) {
>>  		agg = &(SLAVE_AD_INFO(slave).aggregator);
>>
>>
>
>