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

[David Miller <davem@davemloft.net>]

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

> From: Li Fengmao <li.fengmao@zte.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@zte.com.cn>
> Reviewed-by: Long Chun <long.chun@zte.com.cn>
> Reviewed-by: Wang Liang <wang.liang82@zte.com.cn>
> Reviewed-by: Cai Qu <cai.qu@zte.com.cn>
> Reviewed-by: Jiang Biao <jiang.biao2@zte.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.