RE: [PATCH net,v4, 2/3] hv_netvsc: Fix race of register_netdevice_notifier and VF register

[Haiyang Zhang]

> -----Original Message-----
> From: Simon Horman <horms@xxxxxxxxxx>
> Sent: Sunday, November 12, 2023 4:41 AM
> To: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> Cc: linux-hyperv@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; KY Srinivasan
> <kys@xxxxxxxxxxxxx>; wei.liu@xxxxxxxxxx; Dexuan Cui
> <decui@xxxxxxxxxxxxx>; edumazet@xxxxxxxxxx; kuba@xxxxxxxxxx;
> pabeni@xxxxxxxxxx; davem@xxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> stable@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH net,v4, 2/3] hv_netvsc: Fix race of
> register_netdevice_notifier and VF register
> 
> On Fri, Nov 10, 2023 at 06:38:59AM -0800, Haiyang Zhang wrote:
> > If VF NIC is registered earlier, NETDEV_REGISTER event is replayed,
> > but NETDEV_POST_INIT is not.
> >
> > Move register_netdevice_notifier() earlier, so the call back
> > function is set before probing.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Fixes: e04e7a7bbd4b ("hv_netvsc: Fix a deadlock by getting rtnl lock earlier
> in netvsc_probe()")
> > Reported-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> > Signed-off-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> > Reviewed-by: Wojciech Drewek <wojciech.drewek@xxxxxxxxx>
> >
> > ---
> > v3:
> >   Divide it into two patches, suggested by Jakub Kicinski.
> > v2:
> >   Fix rtnl_unlock() in error handling as found by Wojciech Drewek.
> > ---
> >  drivers/net/hyperv/netvsc_drv.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/hyperv/netvsc_drv.c
> b/drivers/net/hyperv/netvsc_drv.c
> > index 5e528a76f5f5..1d1491da303b 100644
> > --- a/drivers/net/hyperv/netvsc_drv.c
> > +++ b/drivers/net/hyperv/netvsc_drv.c
> > @@ -2793,11 +2793,14 @@ static int __init netvsc_drv_init(void)
> >  	}
> >  	netvsc_ring_bytes = ring_size * PAGE_SIZE;
> >
> > +	register_netdevice_notifier(&netvsc_netdev_notifier);
> > +
> >  	ret = vmbus_driver_register(&netvsc_drv);
> > -	if (ret)
> > +	if (ret) {
> > +		unregister_netdevice_notifier(&netvsc_netdev_notifier);
> >  		return ret;
> > +	}
> >
> > -	register_netdevice_notifier(&netvsc_netdev_notifier);
> >  	return 0;
> >  }
> 
> Hi Haiyang Zhang,
> 
> functionally this change looks good to me, thanks!
> 
> I'm wondering if we could improve things slightly by using a more idiomatic
> form for the error path. Something like the following (completely untested!).
> 
> My reasoning is that this way things are less likely go to wrong if more
> error conditions are added to this function later.
> 
> 	...
> 
> 	register_netdevice_notifier(&netvsc_netdev_notifier);
> 
> 	ret = vmbus_driver_register(&netvsc_drv);
> 	if (ret)
> 		goto err_unregister_netdevice_notifier;
> 
> 	return 0;
> 
> err_unregister_netdevice_notifier:
> 	unregister_netdevice_notifier(&netvsc_netdev_notifier);
> 	return ret;
> }

Thanks for the suggested idiomatic form. I will update it.

- Haiyang