netdev - Re: [Question]Why a skb with frag_list causes BUG_ON in function skb

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Date:	Thu, 30 Jul 2015 12:26:18 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	"Zhangjie (HZ)" <zhangjie14@...wei.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mst@...hat.com" <mst@...hat.com>
CC:	Qinchuanyu <qinchuanyu@...wei.com>, Yewudi <yewudi@...wei.com>,
	liuyongan 00175866 <l00175866@...esmail.huawei.com.cn>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [Question]Why a skb with frag_list causes BUG_ON in function
 skb_segment

cc netdev for more experts

On 07/28/2015 04:53 PM, Zhangjie (HZ) wrote:
>
> Hi,
>
> I generate a skb as follows:
>
> It has a linear data region, 17 frags and the last fragment is in
> skb_shinfo(skb)->frag_list.
>
> Before this skb is sent to driver, dev_hard_start_xmit() will segment
> it first(skb has frag_list,
>
> so we get true from netif_needs_gso()), then the skb is passed to
> function skb_segment().
>
> Then, BUG_ON() happened.
>
> while (pos < offset + len) {
>
>         if (i >= nfrags) {
>
>                 BUG_ON(skb_headlen(list_skb));    (skbuff.c:3120)
>
>                 …
>
>         }
>
>         …
>
> }
>
> A skb that has no frags but frag_list also causes BUG_ON().
>
> I wonder if skb like follows is legal? Could skb in frag_list have
> linear data region?
>
>  
>
>  
>
> Thanks
>
> Zhangjie
>

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