netdev - Re: [PATCH] bonding: fix arp_validate toggling in active-backup mode

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Date:   Mon, 13 May 2019 09:43:30 -0700
From:   Jay Vosburgh <jay.vosburgh@...onical.com>
To:     Jarod Wilson <jarod@...hat.com>
cc:     linux-kernel@...r.kernel.org, Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] bonding: fix arp_validate toggling in active-backup mode

Jarod Wilson <jarod@...hat.com> wrote:

>On 5/10/19 6:53 PM, Jay Vosburgh wrote:
>> Jarod Wilson <jarod@...hat.com> wrote:
>>
>>> There's currently a problem with toggling arp_validate on and off with an
>>> active-backup bond. At the moment, you can start up a bond, like so:
>>>
>>> modprobe bonding mode=1 arp_interval=100 arp_validate=0 arp_ip_targets=192.168.1.1
>>> ip link set bond0 down
>>> echo "ens4f0" > /sys/class/net/bond0/bonding/slaves
>>> echo "ens4f1" > /sys/class/net/bond0/bonding/slaves
>>> ip link set bond0 up
>>> ip addr add 192.168.1.2/24 dev bond0
>>>
>>> Pings to 192.168.1.1 work just fine. Now turn on arp_validate:
>>>
>>> echo 1 > /sys/class/net/bond0/bonding/arp_validate
>>>
>>> Pings to 192.168.1.1 continue to work just fine. Now when you go to turn
>>> arp_validate off again, the link falls flat on it's face:
>>>
>>> echo 0 > /sys/class/net/bond0/bonding/arp_validate
>>> dmesg
>>> ...
>>> [133191.911987] bond0: Setting arp_validate to none (0)
>>> [133194.257793] bond0: bond_should_notify_peers: slave ens4f0
>>> [133194.258031] bond0: link status definitely down for interface ens4f0, disabling it
>>> [133194.259000] bond0: making interface ens4f1 the new active one
>>> [133197.330130] bond0: link status definitely down for interface ens4f1, disabling it
>>> [133197.331191] bond0: now running without any active interface!
>>>
>>> The problem lies in bond_options.c, where passing in arp_validate=0
>>> results in bond->recv_probe getting set to NULL. This flies directly in
>>> the face of commit 3fe68df97c7f, which says we need to set recv_probe =
>>> bond_arp_recv, even if we're not using arp_validate. Said commit fixed
>>> this in bond_option_arp_interval_set, but missed that we can get to that
>>> same state in bond_option_arp_validate_set as well.
>>>
>>> One solution would be to universally set recv_probe = bond_arp_recv here
>>> as well, but I don't think bond_option_arp_validate_set has any business
>>> touching recv_probe at all, and that should be left to the arp_interval
>>> code, so we can just make things much tidier here.
>>>
>>> Fixes: 3fe68df97c7f ("bonding: always set recv_probe to bond_arp_rcv in arp monitor")
>>
>> 	Is the above Fixes: tag correct?  3fe68df97c7f is not the source
>> of the erroneous logic being removed, which was introduced by
>>
>> commit 29c4948293bfc426e52a921f4259eb3676961e81
>> Author: sfeldma@...ulusnetworks.com <sfeldma@...ulusnetworks.com>
>> Date:   Thu Dec 12 14:10:38 2013 -0800
>>
>>      bonding: add arp_validate netlink support
>
>I wasn't entirely sure that was the best choice for Fixes either, it was
>sort of more "Augments the Fix in", so I'd certainly have no objection to
>changing the Fixes tag to the earlier commit instead.

	That would be my preference, as the 29c4948293bf commit looks to
be the change actually being fixed.

	-J

---
	-Jay Vosburgh, jay.vosburgh@...onical.com