tcp: increment sk_drops for listeners

Goal: packets dropped by a listener are accounted for.

This adds tcp_listendrop() helper, and clears sk_drops in sk_clone_lock()
so that children do not inherit their parent drop count.

Note that we no longer increment LINUX_MIB_LISTENDROPS counter when
sending a SYNCOOKIE, since the SYN packet generated a SYNACK.
We already have a separate LINUX_MIB_SYNCOOKIESSENT

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 0 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index a23282996ca9..74d3ed5eb219 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1836,4 +1836,17 @@ static inline void tcp_segs_in(struct tcp_sock *tp, const struct sk_buff *skb)
 		tp->data_segs_in += segs_in;
 }
 
+/*
+ * TCP listen path runs lockless.
+ * We forced "struct sock" to be const qualified to make sure
+ * we don't modify one of its field by mistake.
+ * Here, we increment sk_drops which is an atomic_t, so we can safely
+ * make sock writable again.
+ */
+static inline void tcp_listendrop(const struct sock *sk)
+{
+	atomic_inc(&((struct sock *)sk)->sk_drops);
+	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);
+}
+
 #endif	/* _TCP_H */