netdev - Re: [PATCH] Revert "net: linkwatch: add check for netdevice being present to linkwatch_do

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Message-ID: <e6f50a85-aa25-5fb7-7fd2-158668d55378@gmail.com>
Date:   Wed, 23 Sep 2020 22:44:30 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     saeed@...nel.org, geert+renesas@...der.be, f.fainelli@...il.com,
        andrew@...n.ch, kuba@...nel.org, gaku.inami.xh@...esas.com,
        yoshihiro.shimoda.uh@...esas.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "net: linkwatch: add check for netdevice being
 present to linkwatch_do_dev"

On 23.09.2020 22:15, David Miller wrote:
> From: Heiner Kallweit <hkallweit1@...il.com>
> Date: Wed, 23 Sep 2020 21:58:59 +0200
> 
>> On 23.09.2020 20:35, Saeed Mahameed wrote:
>>> Why would a driver detach the device on ndo_stop() ?
>>> seems like this is the bug you need to be chasing ..
>>> which driver is doing this ? 
>>>
>> Some drivers set the device to PCI D3hot at the end of ndo_stop()
>> to save power (using e.g. Runtime PM). Marking the device as detached
>> makes clear to to the net core that the device isn't accessible any
>> longer.
> 
> That being the case, the problem is that IFF_UP+!present is not a
> valid netdev state.
> 
If this combination is invalid, then netif_device_detach() should
clear IFF_UP? At a first glance this should be sufficient to avoid
the issue I was dealing with.

> Is it simply the issue that, upon resume, IFF_UP is marked true before
> the device is brought out from D3hot state and thus marked as present
> again?
> 
I can't really comment on that. The issue I was dealing with at the
time I submitted this change was about an async linkwatch event
(caused by powering down the PHY in ndo_stop) trying to access the
device when it was powered down already.