Linux Ethernet Bridging - Mar 2022 - [Bridge] [PATCH net-next 3/3] net: dsa: mv88e6xxx: mac-auth/MAB implementation

On Tue, Mar 22, 2022 at 12:01:13PM +0100, Hans Schultz
wrote:
> On fre, mar 18, 2022 at 15:19, Vladimir Oltean <olteanv at gmail.com>
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?
> 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...
Have you enabled lockdep, debug atomic sleep, detect hung tasks, things
like that?

On tis, mar 22, 2022 at 13:08, Vladimir Oltean <olteanv at gmail.com>
wrote:
> On Tue, Mar 22, 2022 at 12:01:13PM +0100, Hans Schultz wrote:
>> On fre, mar 18, 2022 at 15:19, Vladimir Oltean <olteanv at
gmail.com> 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...
>
> 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?

On tis, mar 22, 2022 at 13:08, Vladimir Oltean <olteanv at gmail.com>
wrote:
> On Tue, Mar 22, 2022 at 12:01:13PM +0100, Hans Schultz wrote:
>> On fre, mar 18, 2022 at 15:19, Vladimir Oltean <olteanv at
gmail.com> 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?
>
>> 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...
>
> Have you enabled lockdep, debug atomic sleep, detect hung tasks, things
> like that?
I have now determined that it is the rtnl_lock() that causes the
"deadlock". The doit() in rtnetlink.c is under rtnl_lock() and is what
takes care of getting the fdb entries when running 'bridge fdb show'. In
principle there should be no problem with this, but I don't know if some
interrupt queue is getting jammed as they are blocked from rtnetlink.c?