Subject: Re: [Xen-devel] [PATCH net V2] xen-netback: disable rogue vif in kthread context

From: David Vrabel <[email-masked]>
Date: Tue, 25 Mar 2014 13:04:10 +0000

On 25/03/14 12:20, Wei Liu wrote:
> When netback discovers frontend is sending malformed packet it will
> disables the interface which serves that frontend.
> 
> However disabling a network interface involving taking a mutex which
> cannot be done in softirq context, so we need to defer this process to
> kthread context.
> 
> This patch does the following:
> 1. introduce a flag to indicate the interface is disabled.
> 2. check that flag in TX path, don't do any work if it's true.
> 3. check that flag in RX path, turn off that interface if it's true.
> 
> The reason to disable it in RX path is because RX uses kthread. After
> this change the behavior of netback is still consistent -- it won't do
> any TX work for a rogue frontend, and the interface will be eventually
> turned off.
[...]
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -61,12 +61,23 @@ static int xenvif_poll(struct napi_struct *napi, int budget)
>  {
>  	struct xenvif *vif = container_of(napi, struct xenvif, napi);
>  	int work_done;
> +	unsigned long flags;
> +
> +	/* This vif is rogue, we pretend we've there is nothing to do
> +	 * for this vif to deschedule it from NAPI. But this interface
> +	 * will be turned off in thread context later.
> +	 */
> +	if (unlikely(vif->disabled)) {
> +		local_irq_save(flags);
> +		__napi_complete(napi);
> +		local_irq_restore(flags);

Why isn't this napi_complete(napi) (which uses local_irq_save/restore()
internally)?

David