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

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Message-ID: <864k3p5437.fsf@gmail.com>
Date:   Wed, 23 Mar 2022 11:57:16 +0100
From:   Hans Schultz <schultz.hans@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>,
        Hans Schultz <schultz.hans@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, davem@...emloft.net, kuba@...nel.org,
        netdev@...r.kernel.org, Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Ido Schimmel <idosch@...dia.com>, linux-kernel@...r.kernel.org,
        bridge@...ts.linux-foundation.org
Subject: Re: [PATCH net-next 3/3] net: dsa: mv88e6xxx: mac-auth/MAB
 implementation

On ons, mar 23, 2022 at 12:16, Vladimir Oltean <olteanv@...il.com> wrote:
> On Wed, Mar 23, 2022 at 11:13:51AM +0100, Hans Schultz wrote:
>> On tis, mar 22, 2022 at 13:08, Vladimir Oltean <olteanv@...il.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@...il.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?
>
> Sorry, I forgot to respond yesterday to this.
> By any chance do you maybe have an AB/BA lock inversion, where from the
> ATU interrupt handler you do mv88e6xxx_reg_lock() -> rtnl_lock(), while
> from the port_fdb_dump() handler you do rtnl_lock() -> mv88e6xxx_reg_lock()?

If I release the mv88e6xxx_reg_lock() before calling the handler, I need
to get it again for the mv88e6xxx_g1_atu_loadpurge() call at least. But
maybe the vtu_walk also needs the mv88e6xxx_reg_lock()?
I could also just release the mv88e6xxx_reg_lock() before the
call_switchdev_notifiers() call and reacquire it immediately after?