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

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

On 24/03/14 12:49, David Vrabel wrote:
> On 24/03/14 12:13, Wei Liu wrote:
> > --- a/drivers/net/xen-netback/interface.c
> > +++ b/drivers/net/xen-netback/interface.c
> > @@ -62,6 +62,13 @@ static int xenvif_poll(struct napi_struct *napi, int budget)
> >         struct xenvif *vif = container_of(napi, struct xenvif, napi);
> >         int work_done;
> >
> > +       /* This vif is rogue, we pretend we've used up all budget to
> > +        * deschedule it from NAPI. But this interface will be turned
> > +        * off in thread context later.
> > +        */
> > +       if (unlikely(vif->disabled))
> > +               return budget;
> Shouldn't you call __napi_complete() and return 0?  Returning budget
> will make NAPI poll repeatedly (since you're pretending to do work).
The comment in net_rx_action:

                /* Drivers must not modify the NAPI state if they
                 * consume the entire weight.  In such cases this code
                 * still "owns" the NAPI instance and therefore can
                 * move the instance around on the list at-will.
                 */



> > diff --git a/drivers/net/xen-netback/netback.c 
> > b/drivers/net/xen-netback/netback.c
> > index 438d0c0..94e7261 100644
> > --- a/drivers/net/xen-netback/netback.c
> > +++ b/drivers/net/xen-netback/netback.c
> > @@ -655,7 +655,7 @@ static void xenvif_tx_err(struct xenvif *vif,
> >   static void xenvif_fatal_tx_err(struct xenvif *vif)
> >   {
> >         netdev_err(vif->dev, "fatal error; disabling device\n");
> > -       xenvif_carrier_off(vif);
> > +       vif->disabled = true;
> Do you need to wake the thread here?
>
> > @@ -1549,6 +1549,16 @@ int xenvif_kthread(void *data)
> >                 wait_event_interruptible(vif->wq,
> >                                          rx_work_todo(vif) ||
> >                                          kthread_should_stop());
>                                           || vif->disabled ?
>
> > +
> > +               /* This frontend is found to be rogue, disable it in
> > +                * kthread context. Currently this is only set when
> > +                * netback finds out frontend sends malformed packet,
> > +                * but we cannot disable the interface in softirq
> > +                * context so we defer it here.
> > +                */
> > +               if (unlikely(vif->disabled) && netif_carrier_ok(vif->dev))
> > +                       xenvif_carrier_off(vif);
> > +
> >                 if (kthread_should_stop())
> >                         break;
> As an aside, since I happened to be looking at xenvif_poll(), disabling
> local irqs to avoid problems with concurrent events looks unsafe as the
> event may occur on another VCPU.
>
>     __napi_complete(napi);
>     RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, more_to_do);
>     if (more_to_do)
>         napi_schedule(napi);
>
> Would work I think.
>
> David

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