netdev - Re: [PATCH v4 net-next 09/15] net: dsa: Never offload FDB entries on standalone ports

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Date:   Wed, 16 Mar 2022 00:42:05 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Tobias Waldekranz <tobias@...dekranz.com>
Cc:     davem@...emloft.net, kuba@...nel.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>,
        Russell King <linux@...linux.org.uk>,
        Petr Machata <petrm@...dia.com>,
        Ido Schimmel <idosch@...dia.com>,
        Matt Johnston <matt@...econstruct.com.au>,
        Cooper Lees <me@...perlees.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bridge@...ts.linux-foundation.org
Subject: Re: [PATCH v4 net-next 09/15] net: dsa: Never offload FDB entries on
 standalone ports

On Tue, Mar 15, 2022 at 11:26:59PM +0100, Tobias Waldekranz wrote:
> On Tue, Mar 15, 2022 at 18:33, Vladimir Oltean <olteanv@...il.com> wrote:
> > On Tue, Mar 15, 2022 at 01:25:37AM +0100, Tobias Waldekranz wrote:
> >> If a port joins a bridge that it can't offload, it will fallback to
> >> standalone mode and software bridging. In this case, we never want to
> >> offload any FDB entries to hardware either.
> >> 
> >> Signed-off-by: Tobias Waldekranz <tobias@...dekranz.com>
> >> ---
> >
> > When you resend, please send this patch separately, unless something
> > breaks really ugly with your MST series in place.
> 
> Sure. I found this while testing the software fallback. It prevents a
> segfault in dsa_port_bridge_host_fdb_add, which (rightly, I think)
> assumes that dp->bridge is valid. I feel like this should have a Fixes:
> tag, but I'm not sure which commit to blame. Any suggestions?

Ok, makes sense. So far, unoffloaded bridge ports meant that the DSA
switch driver didn't have a ->port_bridge_join() implementation.
Presumably that also came along with a missing ->port_fdb_add()
implementation. So probably no NPD for the existing code paths, it is
just your unoffloaded MST support that opens up new possibilities.

Anyway, the dereference of dp->bridge first appeared in commit
c26933639b54 ("net: dsa: request drivers to perform FDB isolation")
which is still just in net-next.

> >>  net/dsa/slave.c | 3 +++
> >>  1 file changed, 3 insertions(+)
> >> 
> >> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> >> index a61a7c54af20..647adee97f7f 100644
> >> --- a/net/dsa/slave.c
> >> +++ b/net/dsa/slave.c
> >> @@ -2624,6 +2624,9 @@ static int dsa_slave_fdb_event(struct net_device *dev,
> >>  	if (ctx && ctx != dp)
> >>  		return 0;
> >>  
> >> +	if (!dp->bridge)
> >> +		return 0;
> >> +
> >>  	if (switchdev_fdb_is_dynamically_learned(fdb_info)) {
> >>  		if (dsa_port_offloads_bridge_port(dp, orig_dev))
> >>  			return 0;
> >> -- 
> >> 2.25.1
> >>