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

[Jason Wang <jasowang@redhat.com>]

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
>