[PATCHv2 net-next] ip_gre: remove CRC flag from dev features in gre_gso_segment

[Xin Long <lucien.xin@gmail.com>]

This patch is to let it always do CRC checksum in sctp_gso_segment()
by removing CRC flag from the dev features in gre_gso_segment() for
SCTP over GRE, just as it does in Commit 527beb8ef9c0 ("udp: support
sctp over udp in skb_udp_tunnel_segment") for SCTP over UDP.

It could set csum/csum_start in GSO CB properly in sctp_gso_segment()
after that commit, so it would do checksum with gso_make_checksum()
in gre_gso_segment(), and Commit 622e32b7d4a6 ("net: gre: recompute
gre csum for sctp over gre tunnels") can be reverted now.

Note that the current HWs like igb NIC can only handle the SCTP CRC
when it's in the outer packet, not in the inner packet like in this
case, so here it removes CRC flag from the dev features even when
need_csum is false.

v1->v2:
  - improve the changelog.
  - fix "rev xmas tree" in varibles declaration.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/ipv4/gre_offload.c | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
index e0a2465..a681306 100644
--- a/net/ipv4/gre_offload.c
+++ b/net/ipv4/gre_offload.c
@@ -15,10 +15,10 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
 				       netdev_features_t features)
 {
 	int tnl_hlen = skb_inner_mac_header(skb) - skb_transport_header(skb);
-	bool need_csum, need_recompute_csum, gso_partial;
 	struct sk_buff *segs = ERR_PTR(-EINVAL);
 	u16 mac_offset = skb->mac_header;
 	__be16 protocol = skb->protocol;
+	bool need_csum, gso_partial;
 	u16 mac_len = skb->mac_len;
 	int gre_offset, outer_hlen;
 
@@ -41,10 +41,11 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
 	skb->protocol = skb->inner_protocol;
 
 	need_csum = !!(skb_shinfo(skb)->gso_type & SKB_GSO_GRE_CSUM);
-	need_recompute_csum = skb->csum_not_inet;
 	skb->encap_hdr_csum = need_csum;
 
 	features &= skb->dev->hw_enc_features;
+	/* CRC checksum can't be handled by HW when SCTP is the inner proto. */
+	features &= ~NETIF_F_SCTP_CRC;
 
 	/* segment inner packet. */
 	segs = skb_mac_gso_segment(skb, features);
@@ -99,15 +100,7 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
 		}
 
 		*(pcsum + 1) = 0;
-		if (need_recompute_csum && !skb_is_gso(skb)) {
-			__wsum csum;
-
-			csum = skb_checksum(skb, gre_offset,
-					    skb->len - gre_offset, 0);
-			*pcsum = csum_fold(csum);
-		} else {
-			*pcsum = gso_make_checksum(skb, 0);
-		}
+		*pcsum = gso_make_checksum(skb, 0);
 	} while ((skb = skb->next));
 out:
 	return segs;
-- 
2.1.0