netdev - Re: [PATCH v4 net-next 01/12] bonding: remove bond->lock from bond_arp

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Date:	Tue, 18 Feb 2014 07:12:22 +0100
From:	Veaceslav Falico <vfalico@...hat.com>
To:	Ding Tianhong <dingtianhong@...wei.com>
Cc:	netdev@...r.kernel.org, Jay Vosburgh <fubar@...ibm.com>,
	Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [PATCH v4 net-next 01/12] bonding: remove bond->lock from
 bond_arp_rcv

On Tue, Feb 18, 2014 at 12:02:41PM +0800, Ding Tianhong wrote:
>On 2014/2/17 22:41, Veaceslav Falico wrote:
>> We're always called with rcu_read_lock() held (bond_arp_rcv() is only
>> called from bond_handle_frame(), which is rx_handler and always called
>> under rcu from __netif_receive_skb_core() ).
>>
>> The slave active/passive and/or bonding params can change in-flight, however
>> we don't really care about that - we only modify the last time packet was
>> received, which is harmless.
>>
>> CC: Jay Vosburgh <fubar@...ibm.com>
>> CC: Andy Gospodarek <andy@...yhouse.net>
>> Signed-off-by: Veaceslav Falico <vfalico@...hat.com>
>> ---
>>  drivers/net/bonding/bond_main.c | 3 ---
>>  1 file changed, 3 deletions(-)
>>
>> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>> index 3bce855..3c50bec 100644
>> --- a/drivers/net/bonding/bond_main.c
>> +++ b/drivers/net/bonding/bond_main.c
>> @@ -2260,8 +2260,6 @@ int bond_arp_rcv(const struct sk_buff *skb, struct bonding *bond,
>>  	if (skb->protocol != __cpu_to_be16(ETH_P_ARP))
>>  		return RX_HANDLER_ANOTHER;
>>
>> -	read_lock(&bond->lock);
>> -
>>  	if (!slave_do_arp_validate(bond, slave))
>>  		goto out_unlock;
>>
>> @@ -2318,7 +2316,6 @@ int bond_arp_rcv(const struct sk_buff *skb, struct bonding *bond,
>>  		bond_validate_arp(bond, slave, tip, sip);
>>
>>  out_unlock:
>> -	read_unlock(&bond->lock);
>>  	if (arp != (struct arphdr *)skb->data)
>>  		kfree(arp);
>>  	return RX_HANDLER_ANOTHER;
>>
>
>I think it is not enough, you should add rcu_dereference for bond->curr_active_slave, it may be changed during
>the recv processing.

bond->lock has absolutely nothing to du with bond->curr_active_slave .

>
>Regards
>Ding
>
>
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