Explanation sought for a check in ip_finish_output2() function
 

Could someone please explain why there is a following check in ip_finish_output2() function as sk_buff in question should have already headroom space accounted for in the original allocation. In what scenario we can hit this leg.


/* Be paranoid, rather than too clever. */
if (unlikely(skb_headroom(skb) < hh_len && dev->hard_header)) {
struct sk_buff *skb2;

skb2 = skb_realloc_headroom(skb, LL_RESERVED_SPACE(dev));
if (skb2 == NULL) {
kfree_skb(skb);
return -ENOMEM;
}
if (skb->sk)
skb_set_owner_w(skb2, skb->sk);
kfree_skb(skb);
skb = skb2;
}