netdev - Re: [PATCH net-next] openvswitch: fix vport-netdev unregister

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Date:	Thu, 10 Oct 2013 15:38:36 -0700
From:	Pravin Shelar <pshelar@...ira.com>
To:	Alexei Starovoitov <ast@...mgrid.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 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.
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