[PATCH RFC net-next 1/7] sock: add sk_dst_pending_confirm flag

[Julian Anastasov <ja@ssi.bg>]

Add new sock flag to allow sockets to confirm neighbour.
When same struct dst_entry can be used for many different
neighbours we can not use it for pending confirmations.
As not all call paths lock the socket use full word for
the flag.

Add sk_dst_confirm as replacement for dst_confirm when
called for received packets.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
---
 include/net/sock.h | 14 +++++++++++++-
 net/core/sock.c    |  2 ++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 282d065..e83bb01 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -239,6 +239,7 @@ struct sock_common {
   *	@sk_wq: sock wait queue and async head
   *	@sk_rx_dst: receive input route used by early demux
   *	@sk_dst_cache: destination cache
+  *	@sk_dst_pending_confirm: need to confirm neighbour
   *	@sk_policy: flow policy
   *	@sk_receive_queue: incoming packets
   *	@sk_wmem_alloc: transmit queue bytes committed
@@ -381,7 +382,7 @@ struct sock {
 #endif
 	struct dst_entry	*sk_rx_dst;
 	struct dst_entry __rcu	*sk_dst_cache;
-	atomic_t		sk_omem_alloc;
+	int			sk_dst_pending_confirm;
 	int			sk_sndbuf;
 
 	/* ===== cache line for TX ===== */
@@ -405,6 +406,8 @@ struct sock {
 	unsigned int		sk_gso_max_size;
 	gfp_t			sk_allocation;
 	__u32			sk_txhash;
+	atomic_t		sk_omem_alloc;
+	/* Note: 32bit hole on 64bit arches */
 
 	/*
 	 * Because of non atomicity rules, all
@@ -1761,6 +1764,7 @@ static inline void dst_negative_advice(struct sock *sk)
 		if (ndst != dst) {
 			rcu_assign_pointer(sk->sk_dst_cache, ndst);
 			sk_tx_queue_clear(sk);
+			sk->sk_dst_pending_confirm = 0;
 		}
 	}
 }
@@ -1771,6 +1775,7 @@ static inline void dst_negative_advice(struct sock *sk)
 	struct dst_entry *old_dst;
 
 	sk_tx_queue_clear(sk);
+	sk->sk_dst_pending_confirm = 0;
 	/*
 	 * This can be called while sk is owned by the caller only,
 	 * with no state that can be checked in a rcu_dereference_check() cond
@@ -1786,6 +1791,7 @@ static inline void dst_negative_advice(struct sock *sk)
 	struct dst_entry *old_dst;
 
 	sk_tx_queue_clear(sk);
+	sk->sk_dst_pending_confirm = 0;
 	old_dst = xchg((__force struct dst_entry **)&sk->sk_dst_cache, dst);
 	dst_release(old_dst);
 }
@@ -1806,6 +1812,12 @@ static inline void dst_negative_advice(struct sock *sk)
 
 struct dst_entry *sk_dst_check(struct sock *sk, u32 cookie);
 
+static inline void sk_dst_confirm(struct sock *sk)
+{
+	if (!sk->sk_dst_pending_confirm)
+		sk->sk_dst_pending_confirm = 1;
+}
+
 bool sk_mc_loop(struct sock *sk);
 
 static inline bool sk_can_gso(const struct sock *sk)
diff --git a/net/core/sock.c b/net/core/sock.c
index 9fa46b9..8af5296 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -502,6 +502,7 @@ struct dst_entry *__sk_dst_check(struct sock *sk, u32 cookie)
 
 	if (dst && dst->obsolete && dst->ops->check(dst, cookie) == NULL) {
 		sk_tx_queue_clear(sk);
+		sk->sk_dst_pending_confirm = 0;
 		RCU_INIT_POINTER(sk->sk_dst_cache, NULL);
 		dst_release(dst);
 		return NULL;
@@ -1522,6 +1523,7 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
 				af_family_clock_key_strings[newsk->sk_family]);
 
 		newsk->sk_dst_cache	= NULL;
+		newsk->sk_dst_pending_confirm = 0;
 		newsk->sk_wmem_queued	= 0;
 		newsk->sk_forward_alloc = 0;
 		atomic_set(&newsk->sk_drops, 0);
-- 
1.9.3