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

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

On 25/03/14 13:04, David Vrabel wrote:
> 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)?
I guess we don't need napi_gro_flush, so you can spare a few cycles, and 
I don't know if we need to check for netpoll, I'm not sure it's a 
sensible thing to run debug console from a guest towards the backend (or 
do I misunderstand what's the purpose here?)
> David

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