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

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Message-Id: <20140102.032423.2130522873875479421.davem@davemloft.net>
Date:	Thu, 02 Jan 2014 03:24:23 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	jiang.biao2@....com.cn
Cc:	manish.chopra@...gic.com, sony.chacko@...gic.com,
	rajesh.borundia@...gic.com, netdev@...r.kernel.org,
	li.fengmao@....com.cn
Subject: Re: [Patch] netxen_nic: Bugfix for wrong RUNNING status of NX3031
 NICs with no link

From: jiang.biao2@....com.cn
Date: Thu, 2 Jan 2014 14:32:32 +0800

> From: Li Fengmao <li.fengmao@....com.cn>
> 
> Ifconfig command displays RUNNING status when there is no link on
> NX3031 NICs. The problem is caused by the wrong calling order of
> netif_carrier_off() and register_netdev() in netxen_setup_netdev(),
> dev->reg_state is initialized to NETREG_UNINITIALIZED before
> registering network device, so the linkwatch_fire_event() will not
> be called to notify the link change event in netif_carrier_off(),
> and the operational status of network device will be set to
> IF_OPER_UNKNOWN. In that case, the IFF_RUNNING flags will be set,
> which result in the wrong RUNNING status in the result of ifconfig
> command.
> 
> It can be solved by calling netif_carrier_off() after
> register_netdev() in netxen_setup_netdev() to ensure the
> notification of the link change event. And then the operational
> status of device will be set to IF_OPER_DOWN correctly.
> 
> Steps to reproduce the bug:
> 1. Prepare a NX3031 NIC with no network cable on it.
> 2. Reboot the system. (e.g exec reboot command)
> 3. Activate the interface. (e.g ifconfig eth0 up)
> 4. The operstatus of the NX3031 NIC will be RUNNING in the result of
> ifconfig command.
> 
> Signed-off-by: Li Fengmao <li.fengmao@....com.cn>
> Reviewed-by: Long Chun <long.chun@....com.cn>
> Reviewed-by: Wang Liang <wang.liang82@....com.cn>
> Reviewed-by: Cai Qu <cai.qu@....com.cn>
> Reviewed-by: Jiang Biao <jiang.biao2@....com.cn>

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.
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