Subject: Re: [PATCH net-next 3/3] net: dsa: mv88e6xxx: mac-auth/MAB implementation

From: Hans Schultz <[email-masked]>
Date: Tue, 22 Mar 2022 15:47:05 +0100

On tis, mar 22, 2022 at 14:21, Hans Schultz <[email-masked]> wrote:
> On tis, mar 22, 2022 at 13:08, Vladimir Oltean <[email-masked]> wrote:
>> On Tue, Mar 22, 2022 at 12:01:13PM +0100, Hans Schultz wrote:
>>> On fre, mar 18, 2022 at 15:19, Vladimir Oltean <[email-masked]> wrote:
>>> > On Fri, Mar 18, 2022 at 02:10:26PM +0100, Hans Schultz wrote:
>>> >> In the offloaded case there is no difference between static and dynamic
>>> >> flags, which I see as a general issue. (The resulting ATU entry is static
>>> >> in either case.)
>>> >
>>> > It _is_ a problem. We had the same problem with the is_local bit.
>>> > Independently of this series, you can add the dynamic bit to struct
>>> > switchdev_notifier_fdb_info and make drivers reject it.
>>> >
>>> >> These FDB entries are removed when link goes down (soft or hard). The
>>> >> zero DPV entries that the new code introduces age out after 5 minutes,
>>> >> while the locked flagged FDB entries are removed by link down (thus the
>>> >> FDB and the ATU are not in sync in this case).
>>> >
>>> > Ok, so don't let them disappear from hardware, refresh them from the
>>> > driver, since user space and the bridge driver expect that they are
>>> > still there.
>>> 
>>> I have now tested with two extra unmanaged switches (each connected to a
>>> seperate port on our managed switch, and when migrating from one port to
>>> another, there is member violations, but as the initial entry ages out,
>>> a new miss violation occurs and the new port adds the locked entry. In
>>> this case I only see one locked entry, either on the initial port or
>>> later on the port the host migrated to (via switch).
>>> 
>>> If I refresh the ATU entries indefinitly, then this migration will for
>>> sure not work, and with the member violation suppressed, it will be
>>> silent about it.
>>
>> Manual says that migrations should trigger miss violations if configured
>> adequately, is this not the case?
>>
> Yes, but that depends on the ATU entries ageing out. As it is now, it works.
>
>>> So I don't think it is a good idea to refresh the ATU entries
>>> indefinitely.
>>> 
>>> Another issue I see, is that there is a deadlock or similar issue when
>>> receiving violations and running 'bridge fdb show' (it seemed that
>>> member violations also caused this, but not sure yet...), as the unit
>>> freezes, not to return...

I have now verified that it is only on miss violations that the problem
occurs, so it seems that there is a deadlock (with 'bridge fdb show')
somehow with the nl lock that the handling of ATU miss violations
acquires.

>>
>> Have you enabled lockdep, debug atomic sleep, detect hung tasks, things
>> like that?
>
> No, I haven't looked deeper into it yet. Maybe I was hoping someone had
> an idea... but I guess it cannot be a netlink deadlock?