Re: [PATCH v2] xen-netfront: Improve error handling during initialization

[Ross Lagerwall]

On 02/07/2017 11:33 PM, Boris Ostrovsky wrote:
> On 02/07/2017 09:55 AM, Ross Lagerwall wrote:
> > This fixes a crash when running out of grant refs when creating many
> > queues across many netdevs.
> >
> > * If creating queues fails (i.e. there are no grant refs available),
> > call xenbus_dev_fatal() to ensure that the xenbus device is set to the
> > closed state.
> > * If no queues are created, don't call xennet_disconnect_backend as
> > netdev->real_num_tx_queues will not have been set correctly.
> > * If setup_netfront() fails, ensure that all the queues created are
> > cleaned up, not just those that have been set up.
> > * If any queues were set up and an error occurs, call
> > xennet_destroy_queues() to clean up the napi context.
> > * If any fatal error occurs, unregister and destroy the netdev to avoid
> > leaving around a half setup network device.
> >
> > Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> > ---
> >
> > Changed in V2:
> > * Retested on top of v4.10-rc7 + "xen-netfront: Delete rx_refill_timer
> >   in xennet_disconnect_backend()".
> > * Don't move setup_timer as it is not necessary.
> >
> >  drivers/net/xen-netfront.c | 33 +++++++++++++++------------------
> >  1 file changed, 15 insertions(+), 18 deletions(-)
> >
> > diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> > index 722fe9f..5399a86 100644
> > --- a/drivers/net/xen-netfront.c
> > +++ b/drivers/net/xen-netfront.c
> > @@ -1823,27 +1823,23 @@ static int talk_to_netback(struct xenbus_device *dev,
> >  		xennet_destroy_queues(info);
> >
> >  	err = xennet_create_queues(info, &num_queues);
> > -	if (err < 0)
> > -		goto destroy_ring;
> > +	if (err < 0) {
> > +		xenbus_dev_fatal(dev, err, "creating queues");
> > +		if (num_queues > 0) {
> > +			goto destroy_ring;
>
> The only way for us to have (err<0) && (num_queues>0) is when we get a
> -ENOMEM right at the top, isn't it? So there is nothing to disconnect or
> destroy, it seems to me. And if that's true you can directly 'goto out'.

You're right, although that might make it a bit more fragile if 
something in xennet_create_queues() changes in the future. Nevertheless, 
I'll update the patch.

--
Ross Lagerwall