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

From: Ding Tianhong <[email-masked]>
Date: Thu, 9 Jan 2014 20:04:25 +0800

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()?

> -	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);
>  
>