[PATCHv3 net-next 1/2] net: move the hsize check to the else block in skb_segment

[Xin Long]

After commit 89319d3801d1 ("net: Add frag_list support to skb_segment"),
it goes to process frag_list when !hsize in skb_segment(). However, when
using skb frag_list, sg normally should not be set. In this case, hsize
will be set with len right before !hsize check, then it won't go to
frag_list processing code.

So the right thing to do is move the hsize check to the else block, so
that it won't affect the !hsize check for frag_list processing.

v1->v2:
  - change to do "hsize <= 0" check instead of "!hsize", and also move
    "hsize < 0" into else block, to save some cycles, as Alex suggested.

Signed-off-by: Xin Long <lucien....@gmail.com>
---
 net/core/skbuff.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 6039069..e835193 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3894,12 +3894,8 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
                }
 
                hsize = skb_headlen(head_skb) - offset;
-               if (hsize < 0)
-                       hsize = 0;
-               if (hsize > len || !sg)
-                       hsize = len;
 
-               if (!hsize && i >= nfrags && skb_headlen(list_skb) &&
+               if (hsize <= 0 && i >= nfrags && skb_headlen(list_skb) &&
                    (skb_headlen(list_skb) == len || sg)) {
                        BUG_ON(skb_headlen(list_skb) > len);
 
@@ -3942,6 +3938,11 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
                        skb_release_head_state(nskb);
                        __skb_push(nskb, doffset);
                } else {
+                       if (hsize > len || !sg)
+                               hsize = len;
+                       else if (hsize < 0)
+                               hsize = 0;
+
                        nskb = __alloc_skb(hsize + doffset + headroom,
                                           GFP_ATOMIC, 
skb_alloc_rx_flag(head_skb),
                                           NUMA_NO_NODE);
-- 
2.1.0