netdev - RE: [PATCH v2] smsc95xx: Use skb_cow

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Message-ID: <9235D6609DB808459E95D78E17F2E43D40A477A5@CHN-SV-EXMX02.mchp-main.com>
Date:   Tue, 18 Apr 2017 22:09:41 +0000
From:   <Woojung.Huh@...rochip.com>
To:     <eric.dumazet@...il.com>, <james.hughes@...pberrypi.org>
CC:     <netdev@...r.kernel.org>, <steve.glendinning@...well.net>,
        <UNGLinuxDriver@...rochip.com>
Subject: RE: [PATCH v2] smsc95xx: Use skb_cow_head to deal with cloned skbs

> > @@ -2067,13 +2067,9 @@ static struct sk_buff *smsc95xx_tx_fixup(struct
> usbnet *dev,
> >  	/* We do not advertise SG, so skbs should be already linearized */
> >  	BUG_ON(skb_shinfo(skb)->nr_frags);
> >
> > -	if (skb_headroom(skb) < overhead) {
> > -		struct sk_buff *skb2 = skb_copy_expand(skb,
> > -			overhead, 0, flags);
> > -		dev_kfree_skb_any(skb);
> > -		skb = skb2;
> > -		if (!skb)
> > -			return NULL;
> > +	/* Make writable and expand header space by overhead if required
> */
> > +	if (skb_cow_head(skb, overhead)) {
> 
> I believe you still need to
> 		dev_kfree_skb_any(skb);
> 
I think caller of usbnet_start_xmit() takes care of free when return NULL.

- Woojung