netdev - Re: bonding: link state question

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Date:   Sun, 8 Aug 2021 21:31:39 -0400
From:   Jonathan Toppins <jtoppins@...hat.com>
To:     Willy Tarreau <w@....eu>
Cc:     Jay Vosburgh <jay.vosburgh@...onical.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: bonding: link state question

On 8/8/21 12:49 AM, Willy Tarreau wrote:
> On Sat, Aug 07, 2021 at 08:09:31PM -0400, Jonathan Toppins wrote:
>> setting miimon = 100 does appear to fix it.
>>
>> It is interesting that there is no link monitor on by default. For example
>> when I enslave enp0s31f6 to a new bond with miimon == 0, enp0s31f6 starts
>> admin down and will never de-assert NO-CARRIER the bond always results in an
>> operstate of up. It seems like miimon = 100 should be the default since some
>> modes cannot use arpmon.
> 
> Historically when miimon was implemented, not all NICs nor drivers had
> support for link state checking at all! In addition, there are certain
> deployments where you could rely on many devices by having a bond device
> on top of a vlan or similar device, and where monitoring could cost a
> lot of resources and you'd prefer to rely on external monitoring to set
> all of them up or down at once.
> 
> I do think however that there remains a case with a missing state
> transition in the driver: on my laptop I have a bond interface attached
> to eth0, and I noticed that if I suspend the laptop with the link up,
> when I wake it up with no interface connected, the bond will not turn
> down, regardless of miimon. I have not looked closer yet, but I
> suspect that we're relying too much on a state change between previous
> and current and that one historically impossible transition does not
> exist there and/or used to work because it was handled as part of
> another change. I'll eventually have a look.
> 
> Willy
> 

I am likely very wrong but the lack of a recalculation of the bond 
carrier state after a lower notifies of an up/down event seemed 
incorrect. Maybe a place to start?

diff --git i/drivers/net/bonding/bond_main.c 
w/drivers/net/bonding/bond_main.c
index 9018fcc59f78..2b2c4b937142 100644
--- i/drivers/net/bonding/bond_main.c
+++ w/drivers/net/bonding/bond_main.c
@@ -3308,6 +3308,7 @@ static int bond_slave_netdev_event(unsigned long 
event,
                  */
                 if (bond_mode_can_use_xmit_hash(bond))
                         bond_update_slave_arr(bond, NULL);
+               bond_set_carrier(bond);
                 break;
         case NETDEV_CHANGEMTU:
                 /* TODO: Should slaves be allowed to