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

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Message-ID: <Yz7NkPIWItRy0hkC@nanopsycho>
Date:   Thu, 6 Oct 2022 14:44:00 +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

Wed, Oct 05, 2022 at 10:18:29AM CEST, alejandro.lucero-palau@....com wrote:
>
>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.

devl_lock is taken here.


>
>3) driver is removed. devlink port is removed. devlink is not because 

devl_lock taken before port is removed and will block there.

I don't see any problem. Did you actually encoutered any problem?


>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
>>>>
>