linux-kernel - Re: [PATCH 0/5] Call netif_carrier_off() after register

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Message-Id: <1345190143-12050-1-git-send-email-shchepetkov@ispras.ru>
Date:	Fri, 17 Aug 2012 11:55:43 +0400
From:	Ilya Shchepetkov <shchepetkov@...ras.ru>
To:	<bjorn@...k.no>
Cc:	Ilya Shchepetkov <shchepetkov@...ras.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Ben Hutchings <bhutchings@...arflare.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	ldv-project@...ras.ru
Subject: Re: [PATCH 0/5] Call netif_carrier_off() after	register_netdev()

>> Ben Hutchings <bhutchings@...arflare.com> writes:
>>> But if you do it beforehand then it doesn't have the intended effect.
>>> (Supposed to be fixed by 22604c866889c4b2e12b73cbf1683bda1b72a313, which
>>> had to be reverted: c276e098d3ee33059b4a1c747354226cec58487c.)
>>>
>>> So you have to do it after, but without dropping the RTNL lock in
>>> between.
>> So you may want to add something like
>>
>> int register_netdev_carrier_off(struct net_device *dev)
>> {
>>      int err;
>>
>>      rtnl_lock();
>>      err = register_netdevice(dev);
>>         if (!err)
>>                 set_bit(__LINK_STATE_NOCARRIER, &dev->state)
>>      rtnl_unlock();
>>      return err;
>> }
>>
>>
>> for these drivers?

t looks like this variant is equivalent to the existing code:

	netif_carrier_off(dev);
	err = register_netdev(dev);
	if (err)
		goto out;

According to explanation in commit 22604c866889c4b2e12b73cbf1683bda1b72a313,
in this case "this causes these drivers to incorrectly report their
link status as IF_OPER_UNKNOWN which can falsely set the IFF_RUNNING
flag when the interface is first brought up".

As far as I understand, to fix the issue it is required to call
netif_carrier_off() itself:

int register_netdev_carrier_off(struct net_device *dev)
{
	int err;

	rtnl_lock();
	err = register_netdevice(dev);
	if (!err)
		netif_carrier_off(dev);
	rtnl_unlock();
	return err;
}

What do you think?
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