netdev - Re: [PATCH net] net/ibmvnic: Report last valid speed and duplex values to ethtool

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Message-Id: <20190702.140134.1769484209181791824.davem@davemloft.net>
Date:   Tue, 02 Jul 2019 14:01:34 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     tlfalcon@...ux.ibm.com
Cc:     netdev@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        bjking1@...ibm.com, pradeep@...ibm.com, dnbanerg@...ibm.com
Subject: Re: [PATCH net] net/ibmvnic: Report last valid speed and duplex
 values to ethtool

From: Thomas Falcon <tlfalcon@...ux.ibm.com>
Date: Thu, 27 Jun 2019 12:09:13 -0500

> This patch resolves an issue with sensitive bonding modes
> that require valid speed and duplex settings to function
> properly. Currently, the adapter will report that device
> speed and duplex is unknown if the communication link
> with firmware is unavailable. This decision can break LACP
> configurations if the timing is right.
> 
> For example, if invalid speeds are reported, the slave
> device's link state is set to a transitional "fail" state
> and the LACP port is disabled. However, if valid speeds
> are reported later but the link state has not been altered,
> the LACP port will remain disabled. If the link state then
> transitions back to "up" from "fail," it results in a state
> such that the slave reports valid speed/duplex and is up,
> but the LACP port will remain disabled.
> 
> Workaround this by reporting the last recorded speed
> and duplex settings unless the device has never been
> activated. In that case or when the hypervisor gives
> invalid values, continue to report unknown speed or
> duplex to ethtool.
> 
> Signed-off-by: Thomas Falcon <tlfalcon@...ux.ibm.com>

Like Andrew, I have my conerns about this.

If the firmware is unavailable, the link is effectively down.  So
you should report link down and unknown link parameters.

Bonding and LACP should do the right thing when the firwmare is
reachable again after the migration and the link goes back up.

If bonding/LACP isn't doing that, then the bug is there.