netdev - Re: [patch net-next 0/3] devlink: fix order of port and netdev register in drivers

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Message-ID: <Yz03Cm/OBMae5IVT@nanopsycho>
Date:   Wed, 5 Oct 2022 09:49:30 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     "Lucero Palau, Alejandro" <alejandro.lucero-palau@....com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "dmichail@...gible.com" <dmichail@...gible.com>,
        "jesse.brandeburg@...el.com" <jesse.brandeburg@...el.com>,
        "anthony.l.nguyen@...el.com" <anthony.l.nguyen@...el.com>,
        "snelson@...sando.io" <snelson@...sando.io>,
        "drivers@...sando.io" <drivers@...sando.io>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "yangyingliang@...wei.com" <yangyingliang@...wei.com>
Subject: Re: [patch net-next 0/3] devlink: fix order of port and netdev
 register in drivers

Tue, Oct 04, 2022 at 05:31:10PM CEST, alejandro.lucero-palau@....com wrote:
>Hi Jiri,

I don't understand why you send this as a reply to this patchset. I
don't see the relation to it.


>
>I think we have another issue with devlink_unregister and related 
>devlink_port_unregister. It is likely not an issue with current drivers 
>because the devlink ports are managed by netdev register/unregister 
>code, and with your patch that will be fine.
>
>But by definition, devlink does exist for those things not matching 
>smoothly to netdevs, so it is expected devlink ports not related to 
>existing netdevs at all. That is the case in a patch I'm working on for 
>sfc ef100, where devlink ports are created at PF initialization, so 
>related netdevs will not be there at that point, and they can not exist 
>when the devlink ports are removed when the driver is removed.
>
>So the question in this case is, should the devlink ports unregister 
>before or after their devlink unregisters?

Before. If devlink instance should be unregistered only after all other
related instances are gone.

Also, the devlink ports come and go during the devlink lifetime. When
you add a VF, split a port for example. There are many other cases.


>
>Since the ports are in a list owned by the devlink struct, I think it 
>seems logical to unregister the ports first, and that is what I did. It 
>works but there exists a potential concurrency issue with devlink user 

What concurrency issue are you talking about?


>space operations. The devlink code takes care of race conditions involving the 
>devlink struct with rcu plus get/put operations, but that is not the 
>case for devlink ports.
>
>Interestingly, unregistering the devlink first, and doing so with the 
>ports without touching/releasing the devlink struct would solve the 
>problem, but not sure this is the right approach here. It does not seem 

It is not. As I wrote above, the devlink ports come and go.


>clean, and it would require documenting the right unwinding order and 
>to add a check for DEVLINK_REGISTERED in devlink_port_unregister.
>
>I think the right solution would be to add protection to devlink ports 
>and likely other devlink objects with similar concurrency issues.
>
>
>Let me know what you think about it.
>
>
>
>On 9/26/22 13:09, Jiri Pirko wrote:
>> CAUTION: This message has originated from an External Source. Please use proper judgment and caution when opening attachments, clicking links, or responding to this email.
>>
>>
>> From: Jiri Pirko <jiri@...dia.com>
>>
>> Some of the drivers use wrong order in registering devlink port and
>> netdev, registering netdev first. That was not intended as the devlink
>> port is some sort of parent for the netdev. Fix the ordering.
>>
>> Note that the follow-up patchset is going to make this ordering
>> mandatory.
>>
>> Jiri Pirko (3):
>>    funeth: unregister devlink port after netdevice unregister
>>    ice: reorder PF/representor devlink port register/unregister flows
>>    ionic: change order of devlink port register and netdev register
>>
>>   .../net/ethernet/fungible/funeth/funeth_main.c   |  2 +-
>>   drivers/net/ethernet/intel/ice/ice_lib.c         |  6 +++---
>>   drivers/net/ethernet/intel/ice/ice_main.c        | 12 ++++++------
>>   drivers/net/ethernet/intel/ice/ice_repr.c        |  2 +-
>>   .../net/ethernet/pensando/ionic/ionic_bus_pci.c  | 16 ++++++++--------
>>   5 files changed, 19 insertions(+), 19 deletions(-)
>>
>> --
>> 2.37.1
>>
>