Subject: Re: [PATCH] net: Disable queueing when carrier is lost (take 2)

From: Thomas Graf <[email-masked]>
Date: Tue, 3 May 2005 13:18:44 +0200

* Herbert Xu <[email-masked]> 2005-05-03 20:03
> On Tue, May 03, 2005 at 01:01:19AM +0200, Tommy Christensen wrote:
> > Some network drivers call netif_stop_queue() when detecting loss of
> > carrier. This leads to packets being queued up at the qdisc level for
> > an unbound period of time. In order to prevent this effect, the core
> > networking stack will now seize to queue packets for any device, that
> > is operationally down (i.e. the queue is flushed and disabled).
> 
> This looks great.
> 
> > @@ -552,15 +560,18 @@
> >  {
> >  	struct Qdisc *qdisc;
> >  
> > -	spin_lock_bh(&dev->queue_lock);
> > -	qdisc = dev->qdisc;
> > -	dev->qdisc = &noop_qdisc;
> > +	if (dev->flags & IFF_RUNNING) {
> > +		spin_lock_bh(&dev->queue_lock);
> > +		qdisc = dev->qdisc;
> > +		dev->qdisc = &noop_qdisc;
> >  
> > -	qdisc_reset(qdisc);
> > +		qdisc_reset(qdisc);
> >  
> > -	spin_unlock_bh(&dev->queue_lock);
> > +		spin_unlock_bh(&dev->queue_lock);
> >  
> > -	dev_watchdog_down(dev);
> > +		dev_watchdog_down(dev);
> > +	}
> > +	dev->flags &= ~IFF_RUNNING;
> >  
> >  	while (test_bit(__LINK_STATE_SCHED, &dev->state))
> >  		yield();
> 
> Doing the wait when IFF_RUNNING is off isn't necessary though.  If
> IFF_RUNNING isn't set, then either the device has never been activated
> or we've already carried out those waits the last time we were in
> dev_deactivate.

I do like the patch, no question but IFF_RUNNING is still abused
by drivers and some subsystems. So I'm not sure how reliable the
above code will be without those cases fixed. I submitted a
patchset once to fix some of them, not sure about the status. Also,
what about those drivers that do not support or do not use
netif_carrier_(on|off)?