Subject: Re: [PATCH 1/1] bonding: Use notifiers for slave link state detection

From: zhuyj <[email-masked]>
Date: Tue, 26 Jan 2016 14:26:53 +0800

On 01/26/2016 02:00 PM, Jay Vosburgh wrote:
> zhuyj <[email-masked]> wrote:
>
>> On 01/26/2016 08:43 AM, Jay Vosburgh wrote:
>>> <[email-masked]> wrote:
>>>
>>>> From: Zhu Yanjun <[email-masked]>
>>>>
>>>> Bonding will utilize notifier callbacks to detect slave
>>>> link state changes. It is intended to be used with miimon
>>>> set to zero, and does not support the updelay or downdelay
>>>> options to bonding.
>>>>
>>>> Because of link flap from the slave interface, if the notifier
>>>> is NETDEV_UP while the actual link state is down, it is not
>>>> necessary to continue.
>>>>
>>>> Signed-off-by: Jay Vosburgh <[email-masked]>
>>> 	I haven't signed off on this patch.
>>>
>>> 	I've just started some testing, but as before immediately get an
>>> RCU warning; it looks to be coming from bond_miimon_inspect_slave();
>>>
>>> [  316.473050] bond1: Enslaving eth1 as a backup interface with an up link
>>> [  316.473059]
>>> [  316.473806] ===============================
>>> [  316.475630] [ INFO: suspicious RCU usage. ]
>>> [  316.477519] 4.4.0+ #38 Not tainted
>>> [  316.479094] -------------------------------
>>> [  316.480765] drivers/net/bonding/bond_main.c:2024 suspicious rcu_dereference_check() usage!
>>>
>>> 	This is presumably because the "case NETDEV_DOWN" call to
>>> bond_miimon_inspect_slave does not hold RCU.  It does hold RTNL, though,
>>> which should be safe for this usage (RTNL mutexes changes to the active
>>> slave).  The appended patch on top of the original makes the warning go
>>> away.
>>>
>>> 	I'm still testing the patch and have no comment about its
>>> functionality as yet.
>>>
>>> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>>> index 9f67948..e3faee9 100644
>>> --- a/drivers/net/bonding/bond_main.c
>>> +++ b/drivers/net/bonding/bond_main.c
>>> @@ -2014,14 +2014,14 @@ static int bond_slave_info_query(struct net_device *bond_dev, struct ifslave *in
>>>      /*-------------------------------- Monitoring
>>> -------------------------------*/
>>>    -/* called with rcu_read_lock() */
>>> +/* called with rcu_read_lock() or RTNL */
>>>    static int bond_miimon_inspect_slave(struct bonding *bond, struct slave *slave,
>>>    				     unsigned long event)
>>>    {
>>>    	int link_state;
>>>    	bool ignore_updelay;
>>>    -	ignore_updelay = !rcu_dereference(bond->curr_active_slave);
>>> +	ignore_updelay = !rcu_dereference_rtnl(bond->curr_active_slave);
>> Thanks a lot.
>> Because kernel v4.4 needs this kind of patch, I backport this patch from
>> net-next to kernel v4.4.
>>
>> If it is not appropriate, I will revert this patch.
> 	I don't understand what you mean here.
>
> 	I've tested the patch (with my above modification), and while I
> seem to be hitting an unrelated bug in the ARP monitor, I believe this
> patch will misbehave when the ARP monitor is running.
>
> 	For example, if arp_interval=1000 and miimon=0, the link state
> notifier callback will change a slave to up should a notifier event take
> place.  So, hypothetically, if a slave is "down" according to the ARP
> monitor (but actually carrier up), and then experience a carrier down
> then up transition, the slave would be set to "up" even though the ARP
> monitor believes it to be down.
>
> 	I'm not able to induce the speedy link flap events, so I'm not
> sure about this portion of the patch:
>
> +	/* Because of link flap from the slave interface, it is possilbe that
> +	 * the notifiler is NETDEV_UP while the actual link state is down. If
> +	 * so, it is not necessary to contiune.
> +	 */
> +	switch (event) {
> +	case NETDEV_UP:
> +		if (!link_state)
> +			return 0;
> +		break;
> +
> +	case NETDEV_DOWN:
> +		if (link_state)
> +			return 0;
> +		break;
> +	}
> +
>
> 	Unless I misunderstood, Emil's comments elsewhere suggest that
> the current ixgbe driver won't cause those, though.
This patch will avoid useless configuration because of link flap.

Hi, Emil

Does the current ixgbe driver not cause link flap?

Thanks a lot.
Zhu Yanjun

>
> 	-J
>
> ---
> 	-Jay Vosburgh, [email-masked]
>