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From: Hans Schultz <schultz.hans@gmail.com>
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 <20220310142836.m5onuelv4jej5gvs@skbuf> <865yolg8d7.fsf@gmail.com>
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Date: Thu, 10 Mar 2022 16:51:15 +0100
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Subject: Re: [Bridge] [PATCH net-next 3/3] net: dsa: mv88e6xxx: mac-auth/MAB
 implementation
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To: Vladimir Oltean <olteanv@gmail.com>, Hans Schultz <schultz.hans@gmail.com>
Cc: Ivan Vecera <ivecera@redhat.com>, Andrew Lunn <andrew@lunn.ch>, Florian Fainelli <f.fainelli@gmail.com>, Jiri Pirko <jiri@resnulli.us>, Daniel Borkmann <daniel@iogearbox.net>, netdev@vger.kernel.org, Nikolay Aleksandrov <razor@blackwall.org>, bridge@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Vivien Didelot <vivien.didelot@gmail.com>, Ido Schimmel <idosch@nvidia.com>, Roopa Prabhu <roopa@nvidia.com>, kuba@kernel.org, davem@davemloft.net

On tor, mar 10, 2022 at 17:07, Vladimir Oltean <olteanv@gmail.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?