Message-ID: <CAMEtUuyEw81g8+68HUMpR1RERAA9rjL=WHRE58se83cdur67eg@mail.gmail.com>
Date:	Thu, 10 Oct 2013 17:47:26 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Pravin Shelar <pshelar@...ira.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Jesse Gross <jesse@...ira.com>, Jiri Pirko <jiri@...nulli.us>,
	"dev@...nvswitch.org" <dev@...nvswitch.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] openvswitch: fix vport-netdev unregister

On Thu, Oct 10, 2013 at 3:38 PM, Pravin Shelar <pshelar@...ira.com> wrote:
> On Thu, Oct 10, 2013 at 1:48 PM, Alexei Starovoitov <ast@...mgrid.com> wrote:
>> On Thu, Oct 10, 2013 at 11:21 AM, Pravin Shelar <pshelar@...ira.com> wrote:
>>> On Wed, Oct 9, 2013 at 11:26 PM, Alexei Starovoitov <ast@...mgrid.com> wrote:
>>>> On Wed, Oct 9, 2013 at 11:07 PM, Pravin Shelar <pshelar@...ira.com> wrote:
>>>>> On Wed, Oct 9, 2013 at 9:11 PM, Alexei Starovoitov <ast@...mgrid.com> wrote:
>>>>>> On Wed, Oct 9, 2013 at 8:02 PM, Pravin Shelar <pshelar@...ira.com> wrote:
>>>>>>> On Tue, Oct 8, 2013 at 8:07 PM, Alexei Starovoitov <ast@...mgrid.com> wrote:
>>>>>>>> The combination of two commits
>>>>>>>>
>>>>>>>> commit 8e4e1713e4
>>>>>>>> ("openvswitch: Simplify datapath locking.")
>>>>>>>>
>>>>>>>> and
>>>>>>>>
>>>>>>>> commit 2537b4dd0a
>>>>>>>> ("openvswitch:: link upper device for port devices")
>>>>>>>>
>>>>>>>> introduced a bug where upper_dev wasn't unlinked upon
>>>>>>>> netdev_unregister notification
>>>>>>>>
>>>>>>>> The following steps:
>>>>>>>>
>>>>>>>>   modprobe openvswitch
>>>>>>>>   ovs-dpctl add-dp test
>>>>>>>>   ip tuntap add dev tap1 mode tap
>>>>>>>>   ovs-dpctl add-if test tap1
>>>>>>>>   ip tuntap del dev tap1 mode tap
>>>>>>>>
>>>>>>>> are causing multiple warnings:
>>>>>>>> diff --git a/net/openvswitch/dp_notify.c b/net/openvswitch/dp_notify.c
>>>>>>>> index c323567..e9380bd 100644
>>>>>>>> --- a/net/openvswitch/dp_notify.c
>>>>>>>> +++ b/net/openvswitch/dp_notify.c
>>>>>>>> @@ -88,6 +88,11 @@ static int dp_device_event(struct notifier_block *unused, unsigned long event,
>>>>>>>>                 return NOTIFY_DONE;
>>>>>>>>
>>>>>>>>         if (event == NETDEV_UNREGISTER) {
>>>>>>>> +               /* rx_handler_unregister and upper_dev_unlink immediately */
>>>>>>>> +               if (dev->reg_state == NETREG_UNREGISTERING)
>>>>>>>> +                       ovs_netdev_unlink_dev(vport);
>>>>>>>> +
>>>>>>>
>>>>>>> Rather than doing vport destroy here, we can just unlink upper device
>>>>>>> and let workq do rest of work.
>>>>>>
>>>>>> isn't it what it's doing?
>>>>>
>>>>> I meant just call netdev_upper_dev_unlink() here in event handler and
>>>>> rest of vport destroy can be done in workq.
>>>>
>>>> netdev_upper_dev_unlink() without netdev_rx_handler_unregister() ?!
>>>> that's dangerous.
>>> why is it dangerous? ovs already had ref to net-device.
>>
>> comment from dev.c:
>>                 /* Notify protocols, that we are about to destroy
>>                    this device. They should clean all the things.
>>                 */
>>                 call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
>>
>> so here you're suggesting to just netdev_upper_dev_unlink() to silence
>> the warning,
>> but then do dev_set_promisc(-1) in workqueue?
>>
> promiscuity setting is different issue. If you want to have discussion
> then you can post separate patch for same. Lets fix the warning here.
>
>> well, as a minimum audit of promiscuity will be wrong.
>> ndo_change_rx_flags will be called after ndo_uninit,
>> all sorts of other cleanups are done.
>
> change_rx_flags() checks for UP flag for given device.
>
>> I cannot track all possible scenarios, but it seems much safer to
>> cleanup everything possible
>> as soon as ovs received NETDEV_UNREGISTER event.
>>
>> May be all these risks are worth taking, then please explain what is
>> the problem with the proposed patch?
>>
> Problem is that this is causing layering issues in OVS. dp_notify is
> suppose to work at dp layer. your patch directly calls vport-netdev
> implementation function from dp_notify.
> I could not think of a simple approach that will do this in completely
> clean manner. Therefore I am trying to minimize layering issues. So
> just calling netdev_upper_dev_unlink() looks better than doing
> anything extra.

dp_notify is per net, not per dp.
notifier can only be called for net_device and the first thing it does:
        if (!ovs_is_internal_dev(dev))
                vport = ovs_netdev_get_vport(dev);
where ovs_netdev_get_vport() is defined in vport-netdev.c

once it gets into workq, it checks for:
       if (vport->ops->type != OVS_VPORT_TYPE_NETDEV)
             continue;
and
        netdev_vport = netdev_vport_priv(vport);
where netdev_vport_priv() is defined in netdev-vport.h

only then it proceeds with generic ovs_dp_detach_port().

Is that the layering you talking about?

So to minimize layering issues you want to call 'upper_dev_link' from
netdev_create() in vport-netdev.c
and 'upper_dev_unlink' directly from dp_device_event() in dp_notify.c?

That will look better than calling ovs_netdev_unlink_dev() ?

Having both register+link and unregister+unlink in the same
vport-netdev.c, is not an advantage?

I'm still missing something here.
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