Subject: Re: RFC: netdev: allow ethtool physical id to drop rtnl_lock

From: Eric Dumazet <[email-masked]>
Date: Fri, 30 Oct 2009 18:47:39 +0100

Stephen Hemminger a écrit :
> The ethtool operation to blink LED can take an indeterminately long time,
> blocking out other operations (via rtnl_lock). This patch is an attempt
> to work around the problem.
> 
> It does need more discussion, because it will mean that drivers that formerly
> were protected from changes during blink aren't.  For example, user could
> start device blinking, and then plug in cable causing change netlink event
> to change state or pull cable and have device come down.
> 
> The other possibility is to do this on a driver by driver basis
> which is more effort.
> 
> Signed-off-by: Stephen Hemminger <[email-masked]>
> 
> 
> --- a/net/core/ethtool.c	2009-10-30 10:27:23.621917624 -0700
> +++ b/net/core/ethtool.c	2009-10-30 10:35:53.787670774 -0700
> @@ -17,6 +17,7 @@
>  #include <linux/errno.h>
>  #include <linux/ethtool.h>
>  #include <linux/netdevice.h>
> +#include <linux/rtnetlink.h>
>  #include <asm/uaccess.h>
>  
>  /*
> @@ -781,6 +782,8 @@ static int ethtool_get_strings(struct ne
>  static int ethtool_phys_id(struct net_device *dev, void __user *useraddr)
>  {
>  	struct ethtool_value id;
> +	int err;
> +	static int busy;
>  
>  	if (!dev->ethtool_ops->phys_id)
>  		return -EOPNOTSUPP;
> @@ -788,7 +791,21 @@ static int ethtool_phys_id(struct net_de
>  	if (copy_from_user(&id, useraddr, sizeof(id)))
>  		return -EFAULT;
>  
> -	return dev->ethtool_ops->phys_id(dev, id.data);
> +	if (busy)
> +		return -EBUSY;
> +
> +	/* This operation may take a long time, drop lock */
> +	busy = 1;
> +	dev_hold(dev);
> +	rtnl_unlock();
> +
> +	err = dev->ethtool_ops->phys_id(dev, id.data);
> +
> +	rtnl_lock();
> +	dev_put(dev);
> +	busy = 0;
> +
> +	return err;
>  }
>  

It seems reasonable, but why have a global 'busy' flag, and not
private to each netdev ?