netdev - Re: RFC: netdev: allow ethtool physical id to drop rtnl

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Date:	Fri, 30 Oct 2009 11:30:02 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: RFC: netdev: allow ethtool physical id to drop rtnl_lock

On Fri, 30 Oct 2009 18:47:39 +0100
Eric Dumazet <eric.dumazet@...il.com> wrote:

> 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 <shemminger@...tta.com>
> > 
> > 
> > --- 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 ?
> 

Because that is what old behaviour was (one blink at a time).


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