netdev - Re: [PATCH net] net: hyperv: initialize link status correctly

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Date:	Mon, 27 Jan 2014 18:28:42 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	Ben Hutchings <ben@...adent.org.uk>
CC:	David Miller <davem@...emloft.net>, kys@...rosoft.com,
	haiyangz@...rosoft.com, devel@...uxdriverproject.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: hyperv: initialize link status correctly

On 01/27/2014 06:22 PM, Ben Hutchings wrote:
> On Mon, 2014-01-27 at 17:40 +0800, Jason Wang wrote:
>> On 01/27/2014 04:35 PM, David Miller wrote:
>>> From: Jason Wang <jasowang@...hat.com>
>>> Date: Mon, 27 Jan 2014 15:30:54 +0800
>>>
>>>> Call netif_carrier_on() after register_device(). Otherwise it won't work since
>>>> the device was still in NETREG_UNINITIALIZED state.
>>>>
>>>> Fixes a68f9614614749727286f675d15f1e09d13cb54a
>>>> (hyperv: Fix race between probe and open calls)
>>>>
>>>> Cc: Haiyang Zhang <haiyangz@...rosoft.com>
>>>> Cc: K. Y. Srinivasan <kys@...rosoft.com>
>>>> Reported-by: Di Nie <dnie@...hat.com>
>>>> Tested-by: Di Nie <dnie@...hat.com>
>>>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>>> A device up can occur at the moment you call register_netdevice(),
>>> therefore that up call can see the carrier as down and fail or
>>> similar.  So you really cannot resolve the carrier to be on in this
>>> way.
>> True, we need a workqueue to synchronize them.
> Whatever for?  All you need to do is:
>
> 	rtnl_lock();
> 	register_netdevice();
> 	netif_carrier_on();
> 	rtnl_unlock();
>
> It would be nice if we could make the current code work with a change in
> the core, though.
>
> Ben.
>

Looks like the link status interrupt may happen during this (after
netvsc_device_add() was called by rndis_filter_device_add()) without any
synchronization. This may lead a wrong link status here.
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