netdev - Re: [PATCH v2 net-next 10/10] net: dsa: mv88e6xxx: MST Offloading

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Date:   Thu, 10 Mar 2022 17:33:53 +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>,
        Cooper Lees <me@...perlees.com>,
        Ido Schimmel <idosch@...dia.com>,
        Matt Johnston <matt@...econstruct.com.au>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        bridge@...ts.linux-foundation.org
Subject: Re: [PATCH v2 net-next 10/10] net: dsa: mv88e6xxx: MST Offloading

On Thu, Mar 10, 2022 at 05:25:47PM +0200, Vladimir Oltean wrote:
> > >> +	err = mv88e6xxx_sid_get(chip, attr->orig_dev, vattr->msti, &new_sid);
> > >> +	if (err)
> > >> +		goto unlock;
> > >> +
> > >> +	if (vlan.sid) {
> > >> +		err = mv88e6xxx_sid_put(chip, vlan.sid);
> > >> +		if (err)
> > >> +			goto unlock;
> > >> +	}
> > >> +
> > >> +	vlan.sid = new_sid;
> > >> +	err = mv88e6xxx_vtu_loadpurge(chip, &vlan);
> > >
> > > Maybe you could move mv88e6xxx_sid_put() after this succeeds?
> > 
> > Yep. Also made sure to avoid needless updates of the VTU entry if it
> > already belonged to the correct SID.
> 
> I realize I gave you conflicting advice here, first with inverting the
> refcount_inc() with the refcount_dec(), then with having fast handling
> of noop-changes to vlan.sid. I hope you're able to make some sense out
> of that and avoid the obvious issue with the refcount temporarily
> dropping to zero before going back to 1, which makes the sanity checker
> complain.

Oh wow... I didn't look at the code again, and commented based on a
false memory. Disregard, sorry. You aren't reversing sid_get with sid_put,
nor did I suggest that. There's a lot that happened just in my head,
apparently.