tcp: tcp_make_synack() consumes dst parameter
tcp_make_synack() clones the dst, and callers release it.
We can avoid two atomic operations per SYNACK if tcp_make_synack()
consumes dst instead of cloning it.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index f0b0e44..c465d3e 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2442,7 +2442,16 @@
return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
}
-/* Prepare a SYN-ACK. */
+/**
+ * tcp_make_synack - Prepare a SYN-ACK.
+ * sk: listener socket
+ * dst: dst entry attached to the SYNACK
+ * req: request_sock pointer
+ * rvp: request_values pointer
+ *
+ * Allocate one skb and build a SYNACK packet.
+ * @dst is consumed : Caller should not use it again.
+ */
struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
struct request_sock *req,
struct request_values *rvp)
@@ -2462,13 +2471,14 @@
if (cvp != NULL && cvp->s_data_constant && cvp->s_data_desired)
s_data_desired = cvp->s_data_desired;
skb = alloc_skb(MAX_TCP_HEADER + 15 + s_data_desired, GFP_ATOMIC);
- if (skb == NULL)
+ if (unlikely(!skb)) {
+ dst_release(dst);
return NULL;
-
+ }
/* Reserve space for headers. */
skb_reserve(skb, MAX_TCP_HEADER);
- skb_dst_set(skb, dst_clone(dst));
+ skb_dst_set(skb, dst);
mss = dst_metric_advmss(dst);
if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
