Re: [Xen-devel] [PATCH 2/2] xen-netback: cancel the credit timer when taking the vif down

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, 2013-02-14 at 13:18 +0000, David Vrabel wrote:
> From: David Vrabel <david.vrabel@xxxxxxxxxx>
> 
> If the credit timer is left armed after calling
> xen_netbk_remove_xenvif(), then it may fire and attempt to schedule
> the vif which will then oops as vif->netbk == NULL.
> 
> This may happen both in the fatal error path and during normal
> disconnection from the front end.
> 
> The sequencing during shutdown is critical to ensure that: a)
> vif->netbk doesn't become unexpectedly NULL; and b) the net device/vif
> is not freed.
> 
> 1. Mark as unschedulable (netif_carrier_off()).
> 2. Synchronously cancel the timer.
> 3. Remove the vif from the schedule list.
> 4. Remove it from it netback thread group.
> 5. Wait for vif->refcnt to become 0.
> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>

You would need to reinitialize the timer in xenvif_up, given that user
might `ifconfig vifX.X down; ifconfig vifX.X up`.

Another less desired but simpler fix would be leave the timer alone but
check for vif->netbk != NULL in the timer callback.


Wei.

> ---
>  drivers/net/xen-netback/interface.c |    3 +--
>  1 files changed, 1 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/interface.c 
> b/drivers/net/xen-netback/interface.c
> index b8c5193..221f426 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -132,6 +132,7 @@ static void xenvif_up(struct xenvif *vif)
>  static void xenvif_down(struct xenvif *vif)
>  {
>       disable_irq(vif->irq);
> +     del_timer_sync(&vif->credit_timeout);
>       xen_netbk_deschedule_xenvif(vif);
>       xen_netbk_remove_xenvif(vif);
>  }
> @@ -363,8 +364,6 @@ void xenvif_disconnect(struct xenvif *vif)
>       atomic_dec(&vif->refcnt);
>       wait_event(vif->waiting_to_free, atomic_read(&vif->refcnt) == 0);
>  
> -     del_timer_sync(&vif->credit_timeout);
> -
>       if (vif->irq)
>               unbind_from_irqhandler(vif->irq, vif);
>  



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