linux-kernel - Re: [PATCH v8 net-next 2/2] net: dsa: mv88e6xxx: mac-auth/MAB implementation

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Message-ID: <5a8195cfa02a95d614e782b9ae55546b@kapio-technology.com>
Date:   Tue, 15 Nov 2022 16:24:02 +0100
From:   netdev@...io-technology.com
To:     Ido Schimmel <idosch@...sch.org>
Cc:     davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 net-next 2/2] net: dsa: mv88e6xxx: mac-auth/MAB
 implementation

On 2022-11-15 16:12, Ido Schimmel wrote:
> On Tue, Nov 15, 2022 at 11:36:38AM +0100, netdev@...io-technology.com 
> wrote:
>> On 2022-11-15 10:58, Ido Schimmel wrote:
>> > On Sat, Nov 12, 2022 at 09:37:48PM +0100, Hans J. Schultz wrote:
>> > > diff --git a/drivers/net/dsa/mv88e6xxx/global1_atu.c
>> > > b/drivers/net/dsa/mv88e6xxx/global1_atu.c
>> > > index 8a874b6fc8e1..0a57f4e7dd46 100644
>> > > --- a/drivers/net/dsa/mv88e6xxx/global1_atu.c
>> > > +++ b/drivers/net/dsa/mv88e6xxx/global1_atu.c
>> > > @@ -12,6 +12,7 @@
>> > >
>> > >  #include "chip.h"
>> > >  #include "global1.h"
>> > > +#include "switchdev.h"
>> > >
>> > >  /* Offset 0x01: ATU FID Register */
>> > >
>> > > @@ -426,6 +427,8 @@ static irqreturn_t
>> > > mv88e6xxx_g1_atu_prob_irq_thread_fn(int irq, void *dev_id)
>> > >  	if (err)
>> > >  		goto out;
>> > >
>> > > +	mv88e6xxx_reg_unlock(chip);
>> >
>> > Why? At minimum such a change needs to be explained in the commit
>> > message and probably split to a separate preparatory patch, assuming the
>> > change is actually required.
>> 
>> This was a change done long time ago related to that the violation 
>> handle
>> function takes the NL lock,
>> which could lead to a double-lock deadlock afair if the chip lock is 
>> taken
>> throughout the handler.
> 
> Why do you need to take RTNL lock? br_switchdev_event() which receives
> the 'SWITCHDEV_FDB_ADD_TO_BRIDGE' event has this comment:
> "/* called with RTNL or RCU */"
> And it's using br_port_get_rtnl_rcu(), so looks like RCU is enough.

As I understand, dsa_port_to_bridge_port() needs to be called with the 
NL lock taken...