linux-kernel - Re: [PATCH 3/5] net/mlx4_en: Call netif_carrier_off() after register

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Date:	Tue, 14 Aug 2012 15:56:35 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	<Sathya.Perla@...lex.Com>
CC:	<shchepetkov@...ras.ru>, <yevgenyp@...lanox.co.il>,
	<davem@...emloft.net>, <amirv@...lanox.com>,
	<ogerlitz@...lanox.com>, <alexg@...lanox.com>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<ldv-project@...ras.ru>
Subject: Re: [PATCH 3/5] net/mlx4_en: Call netif_carrier_off() after
 register_netdev()

On Tue, 2012-08-14 at 12:36 +0000, Sathya.Perla@...lex.Com wrote:
> >-----Original Message-----
> >From: netdev-owner@...r.kernel.org [mailto:netdev-owner@...r.kernel.org] On
> >Behalf Of Ilya Shchepetkov
> >
> >For carrier detection to work properly when binding the driver with a
> >cable unplugged, netif_carrier_off() should be called after
> >register_netdev(), not before.
> >
> >Calling netif_carrier_off() before register_netdev() was causing the
> >network interface to miss a linkwatch pending event leading to an
> >inconsistent state if the link is not up when interface is initialized.
> 
> ndo_open() may be called as soon register_netdev() completes...
> When netif_carrier_off() is called *after* register_netdev(), isn't there
> a possibility of a ndo_open()->netif_carrier_on() call racing this call, causing
> incorrect results?

Yes, you should use something like:

	rtnl_lock();
	rc = register_netdevice(dev);
	if (rc)
		goto out_unlock;
	netif_carrier_off(dev);
	rtnl_unlock();

(Why do we even have register_netdev() when it's such an invitation to
races?)

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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