[PATCH v3] xen-netfront: Improve error handling during initialization

[PATCH v3] xen-netfront: Improve error handling during initialization

[Ross Lagerwall]

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@citrix.com>
---

Changed in V3:
* If xennet_create_queues returns < 0, it will not have created any
  queues so there's no need to go to destroy_ring.

 drivers/net/xen-netfront.c | 29 +++++++++++------------------
 1 file changed, 11 insertions(+), 18 deletions(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 722fe9f..f90fc72 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1823,27 +1823,19 @@ 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");
+		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:
@@ -1933,9 +1925,10 @@ 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;
 }
 
-- 
2.7.4

Re: [PATCH v3] xen-netfront: Improve error handling during initialization

[Boris Ostrovsky]

On 02/08/2017 05:57 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@citrix.com>
> ---
>
> Changed in V3:
> * If xennet_create_queues returns < 0, it will not have created any
>   queues so there's no need to go to destroy_ring.
>
>  drivers/net/xen-netfront.c | 29 +++++++++++------------------
>  1 file changed, 11 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index 722fe9f..f90fc72 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -1823,27 +1823,19 @@ 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");
> +		kfree(info->queues);
> +		info->queues = NULL;
> +		goto out;
> +	}

I think it might be better to kfree() in xennet_create_queues() (and set
num_queues to zero, while at it). But either way:

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>


>  
>  	/* 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:
> @@ -1933,9 +1925,10 @@ 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;
>  }
>  

Re: [PATCH v3] xen-netfront: Improve error handling during initialization

[David Miller]

From: Ross Lagerwall <ross.lagerwall@citrix.com>
Date: Wed, 8 Feb 2017 10:57:37 +0000

> 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@citrix.com>

Applied.