netdev - [PATCH RFC 1/3] net: Prepare GSO return values for fraglist GSO.

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Date:   Fri, 21 Dec 2018 08:53:32 +0100
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     <netdev@...r.kernel.org>
CC:     Steffen Klassert <steffen.klassert@...unet.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH RFC 1/3] net: Prepare GSO return values for fraglist GSO.

On fraglist GSO, we don't need to clone the original
skb. So we don't have anything to return to free.
Prepare GSO that it frees the original skb only
if the return pointer really changed. Fraglist
GSO frees the original skb itself on error and
returns -EREMOTE in this case.

Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>
---
 include/net/udp.h      |  8 ++++++--
 net/core/dev.c         | 11 +++++++----
 net/ipv4/ip_output.c   |  3 ++-
 net/xfrm/xfrm_output.c |  3 ++-
 4 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/include/net/udp.h b/include/net/udp.h
index fd6d948755c8..f89b95c3f91e 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -482,11 +482,15 @@ static inline struct sk_buff *udp_rcv_segment(struct sock *sk,
 
 		atomic_add(segs_nr, &sk->sk_drops);
 		SNMP_ADD_STATS(__UDPX_MIB(sk, ipv4), UDP_MIB_INERRORS, segs_nr);
-		kfree_skb(skb);
+
+		if (PTR_ERR(segs) != -EREMOTE)
+			kfree_skb(skb);
 		return NULL;
 	}
 
-	consume_skb(skb);
+	if (segs != skb)
+		consume_skb(skb);
+
 	return segs;
 }
 
diff --git a/net/core/dev.c b/net/core/dev.c
index 754284873355..53df5ac7c9b2 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3030,7 +3030,8 @@ struct sk_buff *skb_mac_gso_segment(struct sk_buff *skb,
 	}
 	rcu_read_unlock();
 
-	__skb_push(skb, skb->data - skb_mac_header(skb));
+	if (segs != skb)
+		__skb_push(skb, skb->data - skb_mac_header(skb));
 
 	return segs;
 }
@@ -3099,7 +3100,7 @@ struct sk_buff *__skb_gso_segment(struct sk_buff *skb,
 
 	segs = skb_mac_gso_segment(skb, features);
 
-	if (unlikely(skb_needs_check(skb, tx_path) && !IS_ERR(segs)))
+	if (segs != skb && unlikely(skb_needs_check(skb, tx_path) && !IS_ERR(segs)))
 		skb_warn_bad_offload(skb);
 
 	return segs;
@@ -3345,8 +3346,10 @@ static struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct net_device
 
 		segs = skb_gso_segment(skb, features);
 		if (IS_ERR(segs)) {
-			goto out_kfree_skb;
-		} else if (segs) {
+			if (PTR_ERR(segs) != -EREMOTE)
+				goto out_kfree_skb;
+			goto out_null;
+		} else if (segs && segs != skb) {
 			consume_skb(skb);
 			skb = segs;
 		}
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index ab6618036afe..f4cecda6c1e8 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -272,7 +272,8 @@ static int ip_finish_output_gso(struct net *net, struct sock *sk,
 		return -ENOMEM;
 	}
 
-	consume_skb(skb);
+	if (segs != skb)
+		consume_skb(skb);
 
 	do {
 		struct sk_buff *nskb = segs->next;
diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
index 4ae87c5ce2e3..1941dc2a80a0 100644
--- a/net/xfrm/xfrm_output.c
+++ b/net/xfrm/xfrm_output.c
@@ -183,7 +183,8 @@ static int xfrm_output_gso(struct net *net, struct sock *sk, struct sk_buff *skb
 	BUILD_BUG_ON(sizeof(*IPCB(skb)) > SKB_SGO_CB_OFFSET);
 	BUILD_BUG_ON(sizeof(*IP6CB(skb)) > SKB_SGO_CB_OFFSET);
 	segs = skb_gso_segment(skb, 0);
-	kfree_skb(skb);
+	if (segs != skb)
+		kfree_skb(skb);
 	if (IS_ERR(segs))
 		return PTR_ERR(segs);
 	if (segs == NULL)
-- 
2.17.1