[PATCHv1,net] xen-netback: fix guest Rx stall detection (after guest Rx refactor)

If a VIF has been ready for rx_stall_timeout (60s by default) and an
Rx ring is drained of all requests an Rx stall will be incorrectly
detected.  When this occurs and the guest Rx queue is empty, the Rx
ring's event index will not be set and the frontend will not raise an
event when new requests are placed on the ring, permanently stalling
the VIF.

This is a regression introduced by eb1723a29b9a7 (xen-netback:
refactor guest rx).

Fix this by reinstating the setting of queue->last_rx_time when
placing a packet onto the guest Rx ring.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
 drivers/net/xen-netback/rx.c | 2 ++
 1 file changed, 2 insertions(+)

> -----Original Message-----
> From: David Vrabel [mailto:david.vrabel@citrix.com]
> Sent: 11 October 2016 16:48
> To: netdev@vger.kernel.org
> Cc: David Vrabel <david.vrabel@citrix.com>; xen-devel@lists.xenproject.org;
> Paul Durrant <Paul.Durrant@citrix.com>; Wei Liu <wei.liu2@citrix.com>
> Subject: [PATCHv1 net] xen-netback: fix guest Rx stall detection (after guest
> Rx refactor)
> 
> If a VIF has been ready for rx_stall_timeout (60s by default) and an
> Rx ring is drained of all requests an Rx stall will be incorrectly
> detected.  When this occurs and the guest Rx queue is empty, the Rx
> ring's event index will not be set and the frontend will not raise an
> event when new requests are placed on the ring, permanently stalling
> the VIF.
> 
> This is a regression introduced by eb1723a29b9a7 (xen-netback:
> refactor guest rx).
> 
> Fix this by reinstating the setting of queue->last_rx_time when
> placing a packet onto the guest Rx ring.
> 
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>

> ---
>  drivers/net/xen-netback/rx.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/net/xen-netback/rx.c b/drivers/net/xen-netback/rx.c
> index 8e9ade6..d69f2a9 100644
> --- a/drivers/net/xen-netback/rx.c
> +++ b/drivers/net/xen-netback/rx.c
> @@ -425,6 +425,8 @@ void xenvif_rx_skb(struct xenvif_queue *queue)
> 
>  	xenvif_rx_next_skb(queue, &pkt);
> 
> +	queue->last_rx_time = jiffies;
> +
>  	do {
>  		struct xen_netif_rx_request *req;
>  		struct xen_netif_rx_response *rsp;
> --
> 2.1.4

From: David Vrabel <david.vrabel@citrix.com>
Date: Tue, 11 Oct 2016 16:48:27 +0100

> If a VIF has been ready for rx_stall_timeout (60s by default) and an
> Rx ring is drained of all requests an Rx stall will be incorrectly
> detected.  When this occurs and the guest Rx queue is empty, the Rx
> ring's event index will not be set and the frontend will not raise an
> event when new requests are placed on the ring, permanently stalling
> the VIF.
> 
> This is a regression introduced by eb1723a29b9a7 (xen-netback:
> refactor guest rx).
> 
> Fix this by reinstating the setting of queue->last_rx_time when
> placing a packet onto the guest Rx ring.
> 
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Applied.