netdev - Re: [PATCH net-next v3 1/2] macsec: add support for IFLA_MACSEC_OFFLOAD in macsec

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Date:   Wed, 7 Dec 2022 23:03:45 +0100
From:   Sabrina Dubroca <sd@...asysnail.net>
To:     Emeel Hakim <ehakim@...dia.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Raed Salem <raeds@...dia.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "atenart@...nel.org" <atenart@...nel.org>,
        "jiri@...nulli.us" <jiri@...nulli.us>
Subject: Re: [PATCH net-next v3 1/2] macsec: add support for
 IFLA_MACSEC_OFFLOAD in macsec_changelink

2022-12-07, 15:52:15 +0000, Emeel Hakim wrote:
> 
> 
> > -----Original Message-----
> > From: Sabrina Dubroca <sd@...asysnail.net>
> > Sent: Wednesday, 7 December 2022 17:46
> > To: Emeel Hakim <ehakim@...dia.com>
> > Cc: linux-kernel@...r.kernel.org; Raed Salem <raeds@...dia.com>;
> > davem@...emloft.net; edumazet@...gle.com; kuba@...nel.org;
> > pabeni@...hat.com; netdev@...r.kernel.org; atenart@...nel.org; jiri@...nulli.us
> > Subject: Re: [PATCH net-next v3 1/2] macsec: add support for
> > IFLA_MACSEC_OFFLOAD in macsec_changelink
> > 
> > External email: Use caution opening links or attachments
> > 
> > 
> > 2022-12-07, 12:10:16 +0200, ehakim@...dia.com wrote:
> > [...]
> > > +static int macsec_changelink_upd_offload(struct net_device *dev,
> > > +struct nlattr *data[]) {
> > > +     enum macsec_offload offload;
> > > +     struct macsec_dev *macsec;
> > > +
> > > +     macsec = macsec_priv(dev);
> > > +     offload = nla_get_u8(data[IFLA_MACSEC_OFFLOAD]);
> > 
> > All those checks are also present in macsec_upd_offload, why not move them into
> > macsec_update_offload as well? (and then you don't really need
> > macsec_changelink_upd_offload anymore)
> > 
> 
> Right, I thought about it , but I realized that those checks are done before holding the lock in macsec_upd_offload
> and if I move them to macsec_update_offload I will hold the lock for a longer time , I want to minimize the time
> of holding the lock.

Those couple of tests are probably lost in the noise compared to what
mdo_add_secy ends up doing. It also looks like a race condition
between the "macsec->offload == offload" test in macsec_upd_offload
(outside rtnl_lock) and updating macsec->offload via macsec_changelink
is possible. (Currently we can only change it with macsec_upd_offload
(called under genl_lock) so there's no issue until we add this patch)


> > > +     if (macsec->offload == offload)
> > > +             return 0;
> > > +
> > > +     /* Check if the offloading mode is supported by the underlying layers */
> > > +     if (offload != MACSEC_OFFLOAD_OFF &&
> > > +         !macsec_check_offload(offload, macsec))
> > > +             return -EOPNOTSUPP;
> > > +
> > > +     /* Check if the net device is busy. */
> > > +     if (netif_running(dev))
> > > +             return -EBUSY;
> > > +
> > > +     return macsec_update_offload(macsec, offload); }
> > > +
> > 
> > --
> > Sabrina
> 

-- 
Sabrina