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

[Emeel Hakim]

> -----Original Message-----
> From: Sabrina Dubroca <sd@xxxxxxxxxxxxxxx>
> Sent: Thursday, 8 December 2022 0:04
> To: Emeel Hakim <ehakim@xxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; Raed Salem <raeds@xxxxxxxxxx>;
> davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx; kuba@xxxxxxxxxx;
> pabeni@xxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; atenart@xxxxxxxxxx; jiri@xxxxxxxxxxx
> 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, 15:52:15 +0000, Emeel Hakim wrote:
> >
> >
> > > -----Original Message-----
> > > From: Sabrina Dubroca <sd@xxxxxxxxxxxxxxx>
> > > Sent: Wednesday, 7 December 2022 17:46
> > > To: Emeel Hakim <ehakim@xxxxxxxxxx>
> > > Cc: linux-kernel@xxxxxxxxxxxxxxx; Raed Salem <raeds@xxxxxxxxxx>;
> > > davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx; kuba@xxxxxxxxxx;
> > > pabeni@xxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; atenart@xxxxxxxxxx;
> > > jiri@xxxxxxxxxxx
> > > 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@xxxxxxxxxx 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)

Ack, 
so getting rid of macsec_changelink_upd_offload and moving the locking inside macsec_update_offload
should handle this issue

> 
> > > > +     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