netdev - Re: [Patch] netxen_nic: Bugfix for wrong RUNNING status of NX3031 NICs with no link

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Message-ID: <1388685624.9947.7.camel@bwh-desktop.uk.level5networks.com>
Date:	Thu, 2 Jan 2014 18:00:24 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	<jiang.biao2@....com.cn>
CC:	David Miller <davem@...emloft.net>, <li.fengmao@....com.cn>,
	<manish.chopra@...gic.com>, <netdev@...r.kernel.org>,
	<rajesh.borundia@...gic.com>, <sony.chacko@...gic.com>
Subject: Re: [Patch] netxen_nic: Bugfix for wrong RUNNING status of NX3031
 NICs with no link

On Thu, 2014-01-02 at 17:16 +0800, jiang.biao2@....com.cn wrote:
> > You cannot do this, because at the very exact moment you call
> > register_netdevice() the device can be brought up and once the
> > device is up the link can be brought up.
> 
> > Therefore if you invoke netif_carrier_off() right after
> > register_netdevice(), it can cancel out a legitimate
> > netif_carrier_on() call.
> 
> register_netdevice() should be call in probe(), at that time, is
> it impossible to bring up device because the driver loading has
> not finished?

So far as the networking core is concerned, when register_netdevice() is
called the device is ready to use.  But you can do:

rtnl_lock();
register_netdevice();
netif_carrier_off();
rtnl_unlock();

However, as I said before, the current order in netxen_nic works and
only older kernel versions require you to call netif_carrier_off() after
registering the device.

> Even that, the netif_carrier_off() will be called before
> netif_carrier_on(), and that will not be a problem.
> 
> Besides, the other net drivers(e.g igb, e1000, e1000e) I saw all
> call netif_carrier_off() after register_netdev(). There is no such
> problems in these drivers.

It is not easy to hit the race condition but it is real.

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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