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

[Boris Ostrovsky]

On 02/01/2017 10:50 AM, Ross Lagerwall wrote:
> Improve error handling during initialization. This fixes a crash when
> running out of grant refs when creating many queues across many netdevs.
>
> * Delay timer creation so that if initializing a queue fails, the timer
> has not been setup yet.
> * 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 stop the timer and clean up the napi context.

We need to stop the timer in xennet_disconnect_backend(). I sent a patch
a couple of day ago

https://lists.xenproject.org/archives/html/xen-devel/2017-01/msg03269.html

but was about to resend it with del_timer_sync() moved after
napi_synchronize().



-boris

> * 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>
> ---
>  drivers/net/xen-netfront.c | 39 ++++++++++++++++++---------------------
>  1 file changed, 18 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index 8315fe7..8ca85af 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -1596,9 +1596,6 @@ static int xennet_init_queue(struct netfront_queue *queue)
>  	spin_lock_init(&queue->tx_lock);
>  	spin_lock_init(&queue->rx_lock);
>  
> -	setup_timer(&queue->rx_refill_timer, rx_refill_timeout,
> -		    (unsigned long)queue);
> -
>  	snprintf(queue->name, sizeof(queue->name), "%s-q%u",
>  		 queue->info->netdev->name, queue->id);
>  
> @@ -1632,6 +1629,9 @@ static int xennet_init_queue(struct netfront_queue *queue)
>  		goto exit_free_tx;
>  	}
>  
> +	setup_timer(&queue->rx_refill_timer, rx_refill_timeout,
> +		    (unsigned long)queue);
> +
>  	return 0;
>  
>   exit_free_tx:
> @@ -1822,27 +1822,23 @@ 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;
> +		} else {
> +			kfree(info->queues);
> +			info->queues = NULL;
> +			goto out;
> +		}
> +	}
>  
>  	/* Create shared ring, alloc event channel -- for each queue */
>  	for (i = 0; i < num_queues; ++i) {
>  		queue = &info->queues[i];
>  		err = setup_netfront(dev, queue, feature_split_evtchn);
> -		if (err) {
> -			/* setup_netfront() will tidy up the current
> -			 * queue on error, but we need to clean up
> -			 * those already allocated.
> -			 */
> -			if (i > 0) {
> -				rtnl_lock();
> -				netif_set_real_num_tx_queues(info->netdev, i);
> -				rtnl_unlock();
> -				goto destroy_ring;
> -			} else {
> -				goto out;
> -			}
> -		}
> +		if (err)
> +			goto destroy_ring;
>  	}
>  
>  again:
> @@ -1932,9 +1928,10 @@ static int talk_to_netback(struct xenbus_device *dev,
>  	xenbus_transaction_end(xbt, 1);
>   destroy_ring:
>  	xennet_disconnect_backend(info);
> -	kfree(info->queues);
> -	info->queues = NULL;
> +	xennet_destroy_queues(info);
>   out:
> +	unregister_netdev(info->netdev);
> +	xennet_free_netdev(info->netdev);
>  	return err;
>  }
>