Re: [Patch net-next 1/3] net: introduce helper dev_change_tx_queue_len()

[John Fastabend <john.fastabend@gmail.com>]

On 01/19/2018 03:09 PM, Cong Wang wrote:
> This patch promotes the local change_tx_queue_len() to a core
> helper function, dev_change_tx_queue_len(), so that rtnetlink
> and net-sysfs could share the code. This also prepares for the
> following patch.
> 
> Note, the -EFAULT in the original code doesn't make sense,
> we should propagate the errno from notifiers.
> 
> Cc: John Fastabend <john.fastabend@gmail.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
> ---


[...]

>  static ssize_t tx_queue_len_store(struct device *dev,
>  				  struct device_attribute *attr,
>  				  const char *buf, size_t len)
> @@ -355,7 +332,7 @@ static ssize_t tx_queue_len_store(struct device *dev,
>  	if (!capable(CAP_NET_ADMIN))
>  		return -EPERM;
>  
> -	return netdev_store(dev, attr, buf, len, change_tx_queue_len);
> +	return netdev_store(dev, attr, buf, len, dev_change_tx_queue_len);
>  }

Is this protected by RTNL lock? If not what happens if this and do_setlink
both try to change tx queue length at the same time? Seems we could get
a race with multiple dev_deactivate/dev_activate sequences in-flight in
the following 2/3 patch.

Thanks,
John

>  NETDEVICE_SHOW_RW(tx_queue_len, fmt_dec);
>