Subject: Re: [[PATCH stable <3.12]] xen-netback: fix refcnt unbalance for 3.11 and earlier versions

From: Luis Henriques <[email-masked]>
Date: Fri, 20 Dec 2013 10:02:56 +0000

On Thu, Nov 28, 2013 at 12:48:09PM +0000, Wei Liu wrote:
> With the introduction of "xen-netback: Don't destroy the netdev until
> the vif is shut down" (upstream commit id 279f438e36), vif disconnect
> and free are separated. However in the backported verion reference
> counting code was not correctly modified, and the reset of vif->tx_irq
> was lost. If frontend goes through vif life cycle more than once the
> reference counting is skewed.
> 
> This patch adds back the missing tx_irq reset line. It also moves
> several lines of the reference counting code to vif_free, so the moved
> code corresponds to the counterpart in vif_alloc, thus the reference
> counting is balanced.
> 
> 3.12 and onward versions are not affected by this bug, because reference
> counting code was removed due to the introduction of 1:1 model.
> 
> This pacth should be backported to all stable verions which are lower
> than 3.12 and have 279f438e36.

For some reason, I missed this patch.  I'm queuing it now for the 3.11
kernel.  Thank you!

Cheers,
--
Luis

> 
> Reported-and-tested-by: Tomasz Wroblewski <[email-masked]>
> Signed-off-by: Wei Liu <[email-masked]>
> Cc: Ian Campbell <[email-masked]>
> Cc: Konrad Wilk <[email-masked]>
> Cc: David Vrabel <[email-masked]>
> ---
>  drivers/net/xen-netback/interface.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
> index d28324a..342d4e5 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -418,9 +418,6 @@ void xenvif_disconnect(struct xenvif *vif)
>  	if (netif_carrier_ok(vif->dev))
>  		xenvif_carrier_off(vif);
>  
> -	atomic_dec(&vif->refcnt);
> -	wait_event(vif->waiting_to_free, atomic_read(&vif->refcnt) == 0);
> -
>  	if (vif->tx_irq) {
>  		if (vif->tx_irq == vif->rx_irq)
>  			unbind_from_irqhandler(vif->tx_irq, vif);
> @@ -428,6 +425,7 @@ void xenvif_disconnect(struct xenvif *vif)
>  			unbind_from_irqhandler(vif->tx_irq, vif);
>  			unbind_from_irqhandler(vif->rx_irq, vif);
>  		}
> +		vif->tx_irq = 0;
>  	}
>  
>  	xen_netbk_unmap_frontend_rings(vif);
> @@ -435,6 +433,9 @@ void xenvif_disconnect(struct xenvif *vif)
>  
>  void xenvif_free(struct xenvif *vif)
>  {
> +	atomic_dec(&vif->refcnt);
> +	wait_event(vif->waiting_to_free, atomic_read(&vif->refcnt) == 0);
> +
>  	unregister_netdev(vif->dev);
>  
>  	free_netdev(vif->dev);
> -- 
> 1.7.10.4
> 
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