netdev - RE: net/usb/ax88179_178a driver broken in linux-3.12

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Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6026B7433@saturn3.aculab.com>
Date:	Tue, 19 Nov 2013 13:56:43 -0000
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Mark Lord" <mlord@...ox.com>,
	"Eric Dumazet" <eric.dumazet@...il.com>,
	"Ming Lei" <ming.lei@...onical.com>, <davem@...emloft.net>,
	<netdev@...r.kernel.org>
Subject: RE: net/usb/ax88179_178a driver broken in linux-3.12

> From: Mark Lord [mailto:mlord@...ox.com]
> On 13-11-19 05:04 AM, David Laight wrote:
> >
> > Which changes did you revert?
> 
> Just the bits that changed how the headroom/tailroom sizes
> were checked and adjusted.  See attachment for the revert patch
> I am using here.  My mailer unfortunately likes to mangle inline patches.
> 
> =========snip===========
> Revert USB 3.0 network driver changes that break the adapter (lockups)
> in 3.12.  This just puts back the original code from previous kernels.
> 
> Signed-off-by: Mark Lord <mlord@...ox.com>
> 
> --- linux/drivers/net/usb/ax88179_178a.c.orig   2013-11-03 18:41:51.000000000 -0500
> +++ linux/drivers/net/usb/ax88179_178a.c        2013-11-17 13:23:39.525734277 -0500
> @@ -1177,18 +1177,31 @@
>         int frame_size = dev->maxpacket;
>         int mss = skb_shinfo(skb)->gso_size;
>         int headroom;
> +       int tailroom;
> 
>         tx_hdr1 = skb->len;
>         tx_hdr2 = mss;
>         if (((skb->len + 8) % frame_size) == 0)
>                 tx_hdr2 |= 0x80008000;  /* Enable padding */
> 
> -       headroom = skb_headroom(skb) - 8;
> +       headroom = skb_headroom(skb);
> +       tailroom = skb_tailroom(skb);
> 
> -       if ((skb_header_cloned(skb) || headroom < 0) &&
> -           pskb_expand_head(skb, headroom < 0 ? 8 : 0, 0, GFP_ATOMIC)) {
> +       if (!skb_header_cloned(skb) &&
> +           !skb_cloned(skb) &&
> +           (headroom + tailroom) >= 8) {
> +               if (headroom < 8) {
> +                       skb->data = memmove(skb->head + 8, skb->data, skb->len);
> +                       skb_set_tail_pointer(skb, skb->len);
> +               }
> +       } else {
> +               struct sk_buff *skb2;
> +
> +               skb2 = skb_copy_expand(skb, 8, 0, flags);
>                 dev_kfree_skb_any(skb);
> -               return NULL;
> +               skb = skb2;
> +               if (!skb)
> +                       return NULL;
>         }
> 
>         skb_push(skb, 4);

At a guess it will be a difference between pskb_expand_head() and
skb_copy_expand(). The latter probably generates a linear skb.
The extra check for skb_cloned() probably also applies - and forces
a data copy.

Have you tried the patch to xhci-ring.c?

	David