inet: add rsk_listener field to struct request_sock

Once we'll be able to lookup request sockets in ehash table,
we'll need to get access to listener which created this request.

This avoid doing a lookup to find the listener, which benefits
for a more solid SO_REUSEPORT, and is needed once we no
longer queue request sock into a listener private queue.

Note that 'struct tcp_request_sock'->listener could be reduced
to a single bit, as TFO listener should match req->rsk_listener.
TFO will no longer need to hold a reference on the listener.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/request_sock.h

@@ -52,6 +52,7 @@ struct request_sock {
 #define rsk_refcnt			__req_common.skc_refcnt
 
 	struct request_sock		*dl_next;
+	struct sock			*rsk_listener;
 	u16				mss;
 	u8				num_retrans; /* number of retransmits */
 	u8				cookie_ts:1; /* syncookie: encode tcpopts in timestamp */
@@ -67,13 +68,16 @@ struct request_sock {
 	u32				peer_secid;
 };
 
-static inline struct request_sock *reqsk_alloc(const struct request_sock_ops *ops)
+static inline struct request_sock *
+reqsk_alloc(const struct request_sock_ops *ops, struct sock *sk_listener)
 {
 	struct request_sock *req = kmem_cache_alloc(ops->slab, GFP_ATOMIC);
 
-	if (req != NULL)
+	if (req) {
 		req->rsk_ops = ops;
-
+		sock_hold(sk_listener);
+		req->rsk_listener = sk_listener;
+	}
 	return req;
 }
 
@@ -88,6 +92,8 @@ static inline void reqsk_free(struct request_sock *req)
 	WARN_ON_ONCE(atomic_read(&req->rsk_refcnt) != 0);
 
 	req->rsk_ops->destructor(req);
+	if (req->rsk_listener)
+		sock_put(req->rsk_listener);
 	kmem_cache_free(req->rsk_ops->slab, req);
 }
 

net/ipv4/tcp_input.c

@@ -5970,7 +5970,7 @@ static void tcp_openreq_init(struct request_sock *req,
 struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
 				      struct sock *sk_listener)
 {
-	struct request_sock *req = reqsk_alloc(ops);
+	struct request_sock *req = reqsk_alloc(ops, sk_listener);
 
 	if (req) {
 		struct inet_request_sock *ireq = inet_rsk(req);