Re: bonding: link state question

[Jonathan Toppins]

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