Subject: Re: [PATCH net-next 5/6] bonding: restructure and simplify bond_for_each_slave_next()

From: Ding Tianhong <[email-masked]>
Date: Wed, 4 Sep 2013 14:23:51 +0800

On 2013/9/3 18:22, Nikolay Aleksandrov wrote:
> On 08/30/2013 12:05 PM, Ding Tianhong wrote:
>> remove the wordy int and add bond_for_each_slave_next_rcu() for future use.
>>
>> Signed-off-by: Ding Tianhong <[email-masked]>
>> Cc: Nikolay Aleksandrov <[email-masked]>
>> ---
>>  drivers/net/bonding/bond_alb.c  |  3 +--
>>  drivers/net/bonding/bond_main.c |  6 ++----
>>  drivers/net/bonding/bonding.h   | 19 +++++++++++++++----
>>  3 files changed, 18 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
>> index 3a5db7b..d266c56 100644
>> --- a/drivers/net/bonding/bond_alb.c
>> +++ b/drivers/net/bonding/bond_alb.c
>> @@ -383,7 +383,6 @@ static struct slave *rlb_next_rx_slave(struct bonding *bond)
>>  {
>>  	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
>>  	struct slave *rx_slave, *slave, *start_at;
>> -	int i = 0;
>>  
>>  	if (bond_info->next_rx_slave)
>>  		start_at = bond_info->next_rx_slave;
>> @@ -392,7 +391,7 @@ static struct slave *rlb_next_rx_slave(struct bonding *bond)
>>  
>>  	rx_slave = NULL;
>>  
>> -	bond_for_each_slave_from(bond, slave, i, start_at) {
>> +	bond_for_each_slave_from(bond, slave, start_at) {
>>  		if (SLAVE_IS_OK(slave)) {
>>  			if (!rx_slave) {
>>  				rx_slave = slave;
>> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>> index 4264a76..8c9902a 100644
>> --- a/drivers/net/bonding/bond_main.c
>> +++ b/drivers/net/bonding/bond_main.c
>> @@ -904,7 +904,6 @@ static struct slave *bond_find_best_slave(struct bonding *bond)
>>  	struct slave *new_active, *old_active;
>>  	struct slave *bestslave = NULL;
>>  	int mintime = bond->params.updelay;
>> -	int i;
>>  
>>  	new_active = bond->curr_active_slave;
>>  
>> @@ -923,7 +922,7 @@ static struct slave *bond_find_best_slave(struct bonding *bond)
>>  	/* remember where to stop iterating over the slaves */
>>  	old_active = new_active;
>>  
>> -	bond_for_each_slave_from(bond, new_active, i, old_active) {
>> +	bond_for_each_slave_from(bond, new_active, old_active) {
>>  		if (new_active->link == BOND_LINK_UP) {
>>  			return new_active;
>>  		} else if (new_active->link == BOND_LINK_BACK &&
>> @@ -2891,7 +2890,6 @@ do_failover:
>>  static void bond_ab_arp_probe(struct bonding *bond)
>>  {
>>  	struct slave *slave, *next_slave;
>> -	int i;
>>  
>>  	read_lock(&bond->curr_slave_lock);
>>  
>> @@ -2923,7 +2921,7 @@ static void bond_ab_arp_probe(struct bonding *bond)
>>  
>>  	/* search for next candidate */
>>  	next_slave = bond_next_slave(bond, bond->current_arp_slave);
>> -	bond_for_each_slave_from(bond, slave, i, next_slave) {
>> +	bond_for_each_slave_from(bond, slave, next_slave) {
>>  		if (IS_UP(slave->dev)) {
>>  			slave->link = BOND_LINK_BACK;
>>  			bond_set_slave_active_flags(slave);
>> diff --git a/drivers/net/bonding/bonding.h b/drivers/net/bonding/bonding.h
>> index 9898493..a3ab47f 100644
>> --- a/drivers/net/bonding/bonding.h
>> +++ b/drivers/net/bonding/bonding.h
>> @@ -119,14 +119,25 @@
>>   * bond_for_each_slave_from - iterate the slaves list from a starting point
>>   * @bond:	the bond holding this list.
>>   * @pos:	current slave.
>> - * @cnt:	counter for max number of moves
>>   * @start:	starting point.
>>   *
>>   * Caller must hold bond->lock
>>   */
>> -#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 (int cnt = 0, pos = start; pos && cnt < (bond)->slave_cnt; \
>> +	    cnt++, pos = bond_next_slave(bond, pos))
>> +
> Please read below the argument against using the nested cnt definition.
> 
>> +/**
>> + * bond_for_each_slave_from_rcu - iterate the slaves list from a starting point
>> + * @bond:	the bond holding this list.
>> + * @pos:	current slave.
>> + * @start:	starting point.
>> + *
>> + * Caller must hold rcu_read_lock
>> + */
>> +#define bond_for_each_slave_from_rcu(bond, pos, start) \
>> +	for (int cnt = 0, pos = start; pos && cnt < (bond)->slave_cnt; \
>> +	    cnt++, pos = bond_next_slave_rcu(bond, pos))
>>  
> I don't think you can rely on slave_cnt in RCU, you may go overboard and pass
> twice over the same slave if a slave gets removed, or the opposite. Also this
> definition of cnt is troublesome because the name is quite common, I don't know
> if it's accepted, but it if it is at least change the name to something like
> __cnt or anything that is less likely to be defined.
> The cnt argument goes for bond_for_each_slave_from as well.
> 

yes, more details need to think about, I modify the function to this:

#define bond_for_each_slave_from(bond, pos, start) \
        for (pos = start; (pos == bond_next_slave(bond, start) ? \
                    &pos->list != &bond->slave_list : \
                    &pos->list != &start->list); \
                    pos = bond_next_slave(bond, pos))

I think it is fine here, or I miss something, please tell me, thanks. :)

>>  /**
>>   * bond_for_each_slave - iterate over all slaves
>>
> 
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