Subject: Re: [v1 PATCH] ucc_geth: fix ethtool set ring param bug

From: Liang Li <[email-masked]>
Date: Thu, 2 Sep 2010 08:50:34 +0800

On Wed, Sep 01, 2010 at 02:42:30PM +0100, Ben Hutchings wrote:
> On Wed, 2010-09-01 at 09:43 +0800, Liang Li wrote:
> > It's common sense that when we should do change to driver ring
> > desc/buffer etc only after 'stop/shutdown' the device. When we
> > do change while devices/driver is running, kernel oops occur:
> [...]
> > -	ug_info->bdRingLenRx[queue] = ring->rx_pending;
> > -	ug_info->bdRingLenTx[queue] = ring->tx_pending;
> > -
> >  	if (netif_running(netdev)) {
> > -		/* FIXME: restart automatically */
> > -		printk(KERN_INFO
> > -			"Please re-open the interface.\n");
> > +		u16 rx_t;
> > +		u16 tx_t;
> > +		printk(KERN_INFO "Stopping interface %s.\n", netdev->name);
> > +		ucc_geth_close(netdev);
> > +
> > +		rx_t = ug_info->bdRingLenRx[queue];
> > +		tx_t = ug_info->bdRingLenTx[queue];
> > +
> > +		ug_info->bdRingLenRx[queue] = ring->rx_pending;
> > +		ug_info->bdRingLenTx[queue] = ring->tx_pending;
> > +
> > +		printk(KERN_INFO "Reactivating interface %s.\n", netdev->name);
> > +		ret = ucc_geth_open(netdev);
> > +		if (ret) {
> > +			printk(KERN_WARNING "uec_set_ringparam: set ring param for running"
> > +					" interface %s failed. Please try to make the interface "
> > +					" down, then try again.\n", netdev->name);
> > +			ug_info->bdRingLenRx[queue] = rx_t;
> > +			ug_info->bdRingLenTx[queue] = tx_t;
> > +		}
> [...]
> 
> Bringing the interface down will call ucc_geth_close(), which will try
> to free resources that have not been allocated!

Sorry, I did not understand you on this point. There is no
ucc_geth_close when 'open fail'. What you mean here exactly?

> 
> If you cannot roll back a failed change then at least use dev_close()
> and dev_open() rather than calling ucc_geth_{close,open}() directly, so
> that the interface state is updated correctly.  Or just refuse to make
> the change if the interface is up.

That make things more simply but I do not think that is necessary.
Since there is no such restriction exist in most NIC drivers. :)
Actually I did not see the 'fail of reopen' case. So I assume you
may witnessed similar 'open fail' case in some rare cases. May you
please give more input on this then I can 'make re-open safer' here.

Thanks,
				-Liang Li

> 
> Ben.
> 
> -- 
> Ben Hutchings, Senior Software Engineer, Solarflare Communications
> Not speaking for my employer; that's the marketing department's job.
> They asked us to note that Solarflare product names are trademarked.