[TCP]: Add tcp_for_write_queue_from_safe and use it in mtu_probe

Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -1229,6 +1229,11 @@ static inline struct sk_buff *tcp_write_queue_next(struct sock *sk, struct sk_bu
 		for (; (skb != (struct sk_buff *)&(sk)->sk_write_queue);\
 		     skb = skb->next)
 
+#define tcp_for_write_queue_from_safe(skb, tmp, sk)			\
+		for (tmp = skb->next;					\
+		     (skb != (struct sk_buff *)&(sk)->sk_write_queue);	\
+		     skb = tmp, tmp = skb->next)
+
 static inline struct sk_buff *tcp_send_head(struct sock *sk)
 {
 	return sk->sk_send_head;

net/ipv4/tcp_output.c

@@ -1350,9 +1350,7 @@ static int tcp_mtu_probe(struct sock *sk)
 	tcp_insert_write_queue_before(nskb, skb, sk);
 
 	len = 0;
-	while (len < probe_size) {
-		next = tcp_write_queue_next(sk, skb);
-
+	tcp_for_write_queue_from_safe(skb, next, sk) {
 		copy = min_t(int, skb->len, probe_size - len);
 		if (nskb->ip_summed)
 			skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
@@ -1381,7 +1379,9 @@ static int tcp_mtu_probe(struct sock *sk)
 		}
 
 		len += copy;
-		skb = next;
+
+		if (len >= probe_size)
+			break;
 	}
 	tcp_init_tso_segs(sk, nskb, nskb->len);