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

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Date:   Thu, 10 Mar 2022 16:51:15 +0100
From:   Hans Schultz <schultz.hans@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>,
        Hans Schultz <schultz.hans@...il.com>
Cc:     davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        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 tor, mar 10, 2022 at 17:07, Vladimir Oltean <olteanv@...il.com> wrote:
> On Thu, Mar 10, 2022 at 04:00:52PM +0100, Hans Schultz wrote:
>> >> +	brport = dsa_port_to_bridge_port(dp);
>> >
>> > Since this is threaded interrupt context, I suppose it could race with
>> > dsa_port_bridge_leave(). So it is best to check whether "brport" is NULL
>> > or not.
>> >
>> Would something like:
>> if (dsa_is_unused_port(chip->ds, port))
>>         return -ENODATA;
>> 
>> be appropriate and sufficient for that?
>
> static inline
> struct net_device *dsa_port_to_bridge_port(const struct dsa_port *dp)
> {
> 	if (!dp->bridge)
> 		return NULL;
>
> 	if (dp->lag)
> 		return dp->lag->dev;
> 	else if (dp->hsr_dev)
> 		return dp->hsr_dev;
>
> 	return dp->slave;
> }
>
> Notice the "dp->bridge" check. The assignments are in dsa_port_bridge_create()
> and in dsa_port_bridge_destroy(). These functions assume rtnl_mutex protection.
> The question was how do you serialize with that, and why do you assume
> that dsa_port_to_bridge_port() returns non-NULL.
>
> So no, dsa_is_unused_port() would do absolutely nothing to help.

I was thinking in indirect terms (dangerous I know :-).

But wrt the nl lock, I wonder when other threads could pull the carpet
away under this, and so I might have to wait till after the last call
(mv88e6xxx_g1_atu_loadpurge) to free the nl lock?