netdev - Re: [PATCH net] xen-netback: clear vif->task on disconnect

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Message-ID: <20131203133854.GE14293@zion.uk.xensource.com>
Date:	Tue, 3 Dec 2013 13:38:54 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Paul Durrant <paul.durrant@...rix.com>
CC:	<xen-devel@...ts.xen.org>, <netdev@...r.kernel.org>,
	Wei Liu <wei.liu2@...rix.com>,
	Ian Campbell <ian.campbell@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>
Subject: Re: [PATCH net] xen-netback: clear vif->task on disconnect

On Tue, Dec 03, 2013 at 09:53:47AM +0000, Paul Durrant wrote:
> xenvif_start_xmit() relies on checking vif->task for NULL to determine
> whether the vif is ready to accept packets. The task thread is stopped in
> xenvif_disconnect() but task is not set to NULL. Thus, on a re-connect the
> check will give a false positive.
> Also since commit ea732dff5cfa10789007bf4a5b935388a0bb2a8f it should not
> be possible for xenvif_connect() to be called if the vif is already connected
> so change the check of vif->tx_irq to a BUG_ON() and also add a
> BUG_ON(vif->task).
> 

The kthread_create in xenvif_alloc can return non-NULL value on error.
You would need to reset vif->task there as well. We should probably
check all allocation / free locations to avoid tripping over this again.

And, please add new line between paragraphs and specify commit summary
as Sergei suggested.

Wei.

> Signed-off-by: Paul Durrant <paul.durrant@...rix.com>
> Cc: Wei Liu <wei.liu2@...rix.com>
> Cc: Ian Campbell <ian.campbell@...rix.com>
> Cc: David Vrabel <david.vrabel@...rix.com>
> ---
>  drivers/net/xen-netback/interface.c |    9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
> index 2329ccc..d42efbf 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -370,9 +370,8 @@ int xenvif_connect(struct xenvif *vif, unsigned long tx_ring_ref,
>  {
>  	int err = -ENOMEM;
>  
> -	/* Already connected through? */
> -	if (vif->tx_irq)
> -		return 0;
> +	BUG_ON(vif->tx_irq);
> +	BUG_ON(vif->task);
>  
>  	err = xenvif_map_frontend_rings(vif, tx_ring_ref, rx_ring_ref);
>  	if (err < 0)
> @@ -461,8 +460,10 @@ void xenvif_disconnect(struct xenvif *vif)
>  	if (netif_carrier_ok(vif->dev))
>  		xenvif_carrier_off(vif);
>  
> -	if (vif->task)
> +	if (vif->task) {
>  		kthread_stop(vif->task);
> +		vif->task = NULL;
> +	}
>  
>  	if (vif->tx_irq) {
>  		if (vif->tx_irq == vif->rx_irq)
> -- 
> 1.7.10.4
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