Subject: Re: [PATCH] bonding: start slaves with link down for ARP monitor

From: Flavio Leitner <[email-masked]>
Date: Sat, 14 Apr 2012 01:53:19 -0300

On Thu, 12 Apr 2012 20:38:09 +0200
Michal Kubecek <[email-masked]> wrote:

> Initialize slave device link state as down if ARP monitor
> is active. Also shift initial value of its last_arp_tx so that
> it doesn't immediately cause fake detection of "up" state.
> 
> When ARP monitoring is used, initializing the slave device with
> up link state can cause ARP monitor to detect link failure
> before the device is really up (with igb driver, this can take
> more than two seconds).
> 
> Signed-off-by: Michal Kubecek <[email-masked]>
> ---
> 
> When MII monitoring is active for a bond, initial link state of slaves
> is set according to real link state of the corresponding device,
> otherwise it is always set to UP. This makes sense if no monitoring is
> active but with ARP monitoring, it can lead to situations like this:
> 
> [ 1280.431383] bonding: bond0: setting mode to active-backup (1).
> [ 1280.443305] bonding: bond0: adding ARP target 10.11.0.8.
> [ 1280.454079] bonding: bond0: setting arp_validate to all (3).
> [ 1280.465561] bonding: bond0: Setting ARP monitoring interval to 500.
> [ 1280.480366] ADDRCONF(NETDEV_UP): bond0: link is not ready
> [ 1280.491471] bonding: bond0: Adding slave eth1.
> [ 1280.584158] bonding: bond0: making interface eth1 the new active one.
> [ 1280.597274] bonding: bond0: first active interface up!
> [ 1280.607675] bonding: bond0: enslaving eth1 as an active interface with an up link.
> [ 1280.623567] ADDRCONF(NETDEV_CHANGE): bond0: link becomes ready
> [ 1280.635511] bonding: bond0: Adding slave eth2.
> [ 1280.726423] bonding: bond0: enslaving eth2 as a backup interface with an up link.
> [ 1281.976030] bonding: bond0: link status definitely down for interface eth1, disabling it
> [ 1281.992350] bonding: bond0: making interface eth2 the new active one.
> [ 1282.639276] igb: eth1 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX
> [ 1283.002282] bonding: bond0: link status definitely down for interface eth2, disabling it
> [ 1283.018713] bonding: bond0: now running without any active interface !
> [ 1283.529415] bonding: bond0: link status definitely up for interface eth1.
> [ 1283.543075] bonding: bond0: making interface eth1 the new active one.
> [ 1283.556614] bonding: bond0: first active interface up!
> 
> Here eth1 is enslaved with link state UP but before the device is really
> UP, ARP monitor detects it is actually down (it takes more than two
> seconds and arp_interval was set to 500). This causes a spurious failure
> in logs and in statistics.
> 
> I propose to initialize slaves with DOWN link state if ARP monitor is
> active so that the ARP monitor can switch it to UP when appropriate.
> This also requires adjusting the initial value of last_arp_rx as setting
> it to current jiffies would pretend a packet arrived when slave was
> initialized, leading to DOWN -> UP -> DOWN -> UP sequence.
> 
> ---
>  drivers/net/bonding/bond_main.c |   36 ++++++++++++++++++++++--------------
>  1 files changed, 22 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 62d2409..c1eda74 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -1727,6 +1727,9 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
>  	read_lock(&bond->lock);
>  
>  	new_slave->last_arp_rx = jiffies;
> +	if (bond->params.arp_interval)
> +		new_slave->last_arp_rx -=
> +			(msecs_to_jiffies(bond->params.arp_interval) + 1);

I don't see the point of checking bond->params.arp_interval.
Why not simply:

- 	new_slave->last_arp_rx = jiffies;
+	/* put it behind to avoid fake initial link up detection */
+	new_slave->last_arp_rx = jiffies -
+		 (msecs_to_jiffies(bond->params.arp_interval) + 1);

Other than that, works here.

fbl