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

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Message-ID: <c85fb638-77d1-dbbd-51aa-e39b05652e75@amd.com>
Date:   Wed, 5 Oct 2022 08:18:29 +0000
From:   "Lucero Palau, Alejandro" <alejandro.lucero-palau@....com>
To:     Jiri Pirko <jiri@...nulli.us>,
        "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


On 10/5/22 09:49, Jiri Pirko wrote:
> 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 thought there was a relationship with ordering being the issue.

Apologies if this is not the right way for rising my concern.


>
>> 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?
>
1) devlink port function set ...

2) predoit inside devlink obtains devlink then the reference to devlink 
port. Code does a put on devlink but not on the devlink port.

3) driver is removed. devlink port is removed. devlink is not because 
the put.

4) devlink port reference is wrong.


>> 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
>>>