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

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Date:   Wed, 23 Mar 2022 13:21:16 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     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 Wed, Mar 23, 2022 at 11:57:16AM +0100, Hans Schultz wrote:
> >> >> 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?

The cleanest way to go about this would be to have the call_switchdev_notifiers()
portion of the ATU interrupt handling at the very end of mv88e6xxx_g1_atu_prob_irq_thread_fn(),
with no hardware access needed, and therefore no reg_lock() held.