netdev - Re: [PATCH net] bonding: fix event handling for stacked bonds

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Message-ID: <20190412141218.GA29605@bistromath.localdomain>
Date:   Fri, 12 Apr 2019 16:12:18 +0200
From:   Sabrina Dubroca <sd@...asysnail.net>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        Jarod Wilson <jarod@...hat.com>
Subject: Re: [PATCH net] bonding: fix event handling for stacked bonds

2019-04-12, 15:57:55 +0200, Jiri Pirko wrote:
> Fri, Apr 12, 2019 at 03:04:10PM CEST, sd@...asysnail.net wrote:
> >When a bond is enslaved to another bond, bond_netdev_event() only
> >handles the event as if the bond is a master, and skips treating the
> >bond as a slave.
> >
> >This leads to a refcount leak on the slave, since we don't remove the
> >adjacency to its master and the master holds a reference on the slave.
> >
> >Reproducer:
> >  ip link add bondL type bond
> >  ip link add bondU type bond
> >  ip link set bondL master bondU
> >  ip link del bondL
> 
> Out of curiosity, what is a usecase of stacked bonds? I don't see any.

I don't have one, but nothing is preventing that setup. It's just
something I accidentally ran into while testing other things. If you
want to prevent bond-bond, you also need to prevent things like
bond-macvlan-bond for example. The set of rules of what types of
stacking make sense seems a bit hairy.

-- 
Sabrina