Re: [Xen-devel] [PATCHv1 net] xen-netback: stop the guest rx thread after a fatal error

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Feb 02, 2015 at 04:57:51PM +0000, David Vrabel wrote:
> After commit e9d8b2c2968499c1f96563e6522c56958d5a1d0d (xen-netback:
> disable rogue vif in kthread context), a fatal (protocol) error would
> leave the guest Rx thread spinning, wasting CPU time.  Commit
> ecf08d2dbb96d5a4b4bcc53a39e8d29cc8fef02e (xen-netback: reintroduce
> guest Rx stall detection) made this even worse by removing a
> cond_resched() from this path.
> 
> Since a fatal error is non-recoverable, just allow the guest Rx thread
> to exit.  This requires taking additional refs to the task so the
> thread exiting early is handled safely.
> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> Reported-by: Julien Grall <julien.grall@xxxxxxxxxx>
> Tested-by: Julien Grall <julien.grall@xxxxxxxxxx>

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

> ---
>  drivers/net/xen-netback/interface.c |    2 ++
>  drivers/net/xen-netback/netback.c   |    3 +--
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/interface.c 
> b/drivers/net/xen-netback/interface.c
> index 9259a73..037f74f 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -578,6 +578,7 @@ int xenvif_connect(struct xenvif_queue *queue, unsigned 
> long tx_ring_ref,
>               goto err_rx_unbind;
>       }
>       queue->task = task;
> +     get_task_struct(task);
>  
>       task = kthread_create(xenvif_dealloc_kthread,
>                             (void *)queue, "%s-dealloc", queue->name);
> @@ -634,6 +635,7 @@ void xenvif_disconnect(struct xenvif *vif)
>  
>               if (queue->task) {
>                       kthread_stop(queue->task);
> +                     put_task_struct(queue->task);
>                       queue->task = NULL;
>               }
>  
> diff --git a/drivers/net/xen-netback/netback.c 
> b/drivers/net/xen-netback/netback.c
> index 908e65e..c8ce701 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -2109,8 +2109,7 @@ int xenvif_kthread_guest_rx(void *data)
>                */
>               if (unlikely(vif->disabled && queue->id == 0)) {
>                       xenvif_carrier_off(vif);
> -                     xenvif_rx_queue_purge(queue);
> -                     continue;
> +                     break;
>               }
>  
>               if (!skb_queue_empty(&queue->rx_queue))
> -- 
> 1.7.10.4

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