From: Wei Liu <wei.liu2@citrix•com>
To: David Vrabel <david.vrabel@citrix•com>
Cc: Wei Liu <wei.liu2@citrix•com>, <netdev@vger•kernel.org>,
<xen-devel@lists•xen.org>, <paul.durrant@citrix•com>,
<edwin@etorok•net>, Ian Campbell <ian.campbell@citrix•com>,
<zoltan.kiss@citrix•com>
Subject: Re: [Xen-devel] [PATCH net] xen-netback: disable rogue vif in kthread context
Date: Tue, 25 Mar 2014 00:55:03 +0000 [thread overview]
Message-ID: <20140325005503.GA22245@zion.uk.xensource.com> (raw)
In-Reply-To: <533029C7.1080006@citrix.com>
On Mon, Mar 24, 2014 at 12:49:11PM +0000, David Vrabel wrote:
> On 24/03/14 12:13, 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.
> >
> > Also change a "continue" to "break" after xenvif_fatal_tx_err, as it
> > doesn't make sense to continue processing packets if frontend is rogue.
> [...]
> > --- 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).
>
Yes. You're right.
> > 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?
>
That's a better approach.
> > @@ -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.
>
Are you seeing any problem? If this is not related to this fix we should
probably discuss this in another thread.
> __napi_complete(napi);
> RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, more_to_do);
> if (more_to_do)
> napi_schedule(napi);
>
> Would work I think.
>
Not sure I get your suggestion. Sorry. If you're talking about the code
in xenvif_poll, there's comment up there describing a race. Again, this
should be discussed in separate thread.
Wei.
> David
next prev parent reply other threads:[~2014-03-25 0:55 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-24 12:13 [PATCH net] xen-netback: disable rogue vif in kthread context Wei Liu
2014-03-24 12:22 ` Ian Campbell
2014-03-24 12:33 ` David Laight
2014-03-24 12:49 ` [Xen-devel] " David Vrabel
2014-03-24 13:17 ` Zoltan Kiss
2014-03-25 0:55 ` Wei Liu [this message]
2014-03-24 19:29 ` David Miller
2014-03-25 0:44 ` [Xen-devel] " Wei Liu
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