netdev - Re: [PATCH next v5 2/6] bonding: implement bond_poll

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Date:	Wed, 18 Feb 2015 17:30:53 -0800
From:	Mahesh Bandewar <maheshb@...gle.com>
To:	Nikolay Aleksandrov <nikolay@...hat.com>
Cc:	Jay Vosburgh <j.vosburgh@...il.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	Veaceslav Falico <vfalico@...il.com>,
	David Miller <davem@...emloft.net>,
	Maciej Zenczykowski <maze@...gle.com>,
	netdev <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH next v5 2/6] bonding: implement bond_poll_controller()

On Wed, Feb 18, 2015 at 5:19 PM, Mahesh Bandewar <maheshb@...gle.com> wrote:
> On Wed, Feb 18, 2015 at 4:10 PM, Nikolay Aleksandrov <nikolay@...hat.com> wrote:
>> On 02/18/2015 11:31 PM, Mahesh Bandewar wrote:
>>> This patches implements the poll_controller support for all
>>> bonding driver. If the slaves have poll_controller net_op defined,
>>> this implementation calls them. This is mode agnostic implementation
>>> and iterates through all slaves (based on mode) and calls respective
>>> handler.
>>>
>>> Signed-off-by: Mahesh Bandewar <maheshb@...gle.com>
>>> ---
>>> v1:
>>>    Initial version
>>> v2:
>>>    Eliminate bool variable.
>>> v3:
>>>    Rebase
>>> v4:
>>>    Removed 3AD port_operational check
>>> v5:
>>>    Added rtnl protection for bond_for_each_slave()
>>>
>>>  drivers/net/bonding/bond_main.c | 33 +++++++++++++++++++++++++++++++++
>>>  1 file changed, 33 insertions(+)
>>>
>>
>> Hi Mahesh,
>> I should've explained more in my review, you cannot sleep in
>> bond_poll_controller() so you cannot acquire rtnl like that. I was thinking
>> more about using rcu and switching to the _rcu version of
>> bond_for_each_slave instead.
>>
> That makes sense. The path that triggered this netpoll() could have
> been holding the rtnl  itself and this would be a problem. I think
> using the _rcu variant of the slave iterator is a good idea, my bad!
>
... however we cannot use the _rcu variant either since there is the
netpoll mutex (ni->dev_lock)!
The fact that we are here itself means that something bad had happened
and trying to take additional lock(s) would complicate the situation
further.


>> Cheers,
>>  Nik
>>
>>> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>>> index b979c265fc51..63e6c0dbe7b3 100644
>>> --- a/drivers/net/bonding/bond_main.c
>>> +++ b/drivers/net/bonding/bond_main.c
>>> @@ -928,6 +928,39 @@ static inline void slave_disable_netpoll(struct slave *slave)
>>>
>>>  static void bond_poll_controller(struct net_device *bond_dev)
>>>  {
>>> +     struct bonding *bond = netdev_priv(bond_dev);
>>> +     struct slave *slave = NULL;
>>> +     struct list_head *iter;
>>> +     struct ad_info ad_info;
>>> +     struct netpoll_info *ni;
>>> +     const struct net_device_ops *ops;
>>> +
>>> +     if (BOND_MODE(bond) == BOND_MODE_8023AD)
>>> +             if (bond_3ad_get_active_agg_info(bond, &ad_info))
>>> +                     return;
>>> +
>>> +     rtnl_lock();
>>> +     bond_for_each_slave(bond, slave, iter) {
>>> +             ops = slave->dev->netdev_ops;
>>> +             if (!bond_slave_is_up(slave) || !ops->ndo_poll_controller)
>>> +                     continue;
>>> +
>>> +             if (BOND_MODE(bond) == BOND_MODE_8023AD) {
>>> +                     struct aggregator *agg =
>>> +                         SLAVE_AD_INFO(slave)->port.aggregator;
>>> +
>>> +                     if (agg &&
>>> +                         agg->aggregator_identifier != ad_info.aggregator_id)
>>> +                             continue;
>>> +             }
>>> +
>>> +             ni = rcu_dereference_bh(slave->dev->npinfo);
>>> +             if (down_trylock(&ni->dev_lock))
>>> +                     continue;
>>> +             ops->ndo_poll_controller(slave->dev);
>>> +             up(&ni->dev_lock);
>>> +     }
>>> +     rtnl_unlock();
>>>  }
>>>
>>>  static void bond_netpoll_cleanup(struct net_device *bond_dev)
>>>
>>
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