[v2,net-next,5/5] mptcp: implement delegated actions

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 8cb582eee2862..a033bf9c26ee1 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -45,6 +45,9 @@  static struct percpu_counter mptcp_sockets_allocated;
 static void __mptcp_destroy_sock(struct sock *sk);
 static void __mptcp_check_send_data_fin(struct sock *sk);
 
+DEFINE_PER_CPU(struct mptcp_delegated_action, mptcp_delegated_actions);
+static struct net_device mptcp_napi_dev;
+
 /* If msk has an initial subflow socket, and the MP_CAPABLE handshake has not
  * completed yet or has failed, return the subflow socket.
  * Otherwise return NULL.
@@ -1506,7 +1509,9 @@  static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk)
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	struct mptcp_sendmsg_info info;
 	struct mptcp_data_frag *dfrag;
+	struct sock *xmit_ssk;
 	int len, copied = 0;
+	bool first = true;
 
 	info.flags = 0;
 	while ((dfrag = mptcp_send_head(sk))) {
@@ -1516,6 +1521,18 @@  static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk)
 		while (len > 0) {
 			int ret = 0;
 
+			/* the caller already invoked the packet scheduler,
+			 * check for a different subflow usage only after
+			 * spooling the first chunk of data
+			 */
+			xmit_ssk = first ? ssk : mptcp_subflow_get_send(mptcp_sk(sk));
+			if (!xmit_ssk)
+				goto out;
+			if (xmit_ssk != ssk) {
+				mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk));
+				goto out;
+			}
+
 			if (unlikely(mptcp_must_reclaim_memory(sk, ssk))) {
 				__mptcp_update_wmem(sk);
 				sk_mem_reclaim_partial(sk);
@@ -1534,6 +1551,7 @@  static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk)
 			msk->tx_pending_data -= ret;
 			copied += ret;
 			len -= ret;
+			first = false;
 		}
 		WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
 	}
@@ -2242,7 +2260,6 @@  static void mptcp_worker(struct work_struct *work)
 	if (unlikely(state == TCP_CLOSE))
 		goto unlock;
 
-	mptcp_push_pending(sk, 0);
 	mptcp_check_data_fin_ack(sk);
 	__mptcp_flush_join_list(msk);
 
@@ -2901,10 +2918,12 @@  void __mptcp_check_push(struct sock *sk, struct sock *ssk)
 		return;
 
 	if (!sock_owned_by_user(sk)) {
-		if (mptcp_subflow_get_send(mptcp_sk(sk)) == ssk)
+		struct sock *xmit_ssk = mptcp_subflow_get_send(mptcp_sk(sk));
+
+		if (xmit_ssk == ssk)
 			__mptcp_subflow_push_pending(sk, ssk);
-		else
-			mptcp_schedule_work(sk);
+		else if (xmit_ssk)
+			mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk));
 	} else {
 		set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->flags);
 	}
@@ -2955,6 +2974,20 @@  static void mptcp_release_cb(struct sock *sk)
 	}
 }
 
+void mptcp_subflow_process_delegated(struct sock *ssk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	struct sock *sk = subflow->conn;
+
+	mptcp_data_lock(sk);
+	if (!sock_owned_by_user(sk))
+		__mptcp_subflow_push_pending(sk, ssk);
+	else
+		set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->flags);
+	mptcp_data_unlock(sk);
+	mptcp_subflow_delegated_done(subflow);
+}
+
 static int mptcp_hash(struct sock *sk)
 {
 	/* should never be called,
@@ -3365,13 +3398,58 @@  static struct inet_protosw mptcp_protosw = {
 	.flags		= INET_PROTOSW_ICSK,
 };
 
+static int mptcp_napi_poll(struct napi_struct *napi, int budget)
+{
+	struct mptcp_delegated_action *delegated;
+	struct mptcp_subflow_context *subflow;
+	int work_done = 0;
+
+	delegated = container_of(napi, struct mptcp_delegated_action, napi);
+	while ((subflow = mptcp_subflow_delegated_next(delegated)) != NULL) {
+		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
+
+		bh_lock_sock_nested(ssk);
+		if (!sock_owned_by_user(ssk) &&
+		    mptcp_subflow_has_delegated_action(subflow))
+			mptcp_subflow_process_delegated(ssk);
+		/* ... elsewhere tcp_release_cb_override already processed
+		 * the action or will do at next release_sock().
+		 * In both case must dequeue the subflow here - on the same
+		 * CPU that scheduled it.
+		 */
+		bh_unlock_sock(ssk);
+		sock_put(ssk);
+
+		if (++work_done == budget)
+			return budget;
+	}
+
+	/* always provide a 0 'work_done' argument, so that napi_complete_done
+	 * will not try accessing the NULL napi->dev ptr
+	 */
+	napi_complete_done(napi, 0);
+	return work_done;
+}
+
 void __init mptcp_proto_init(void)
 {
+	struct mptcp_delegated_action *delegated;
+	int cpu;
+
 	mptcp_prot.h.hashinfo = tcp_prot.h.hashinfo;
 
 	if (percpu_counter_init(&mptcp_sockets_allocated, 0, GFP_KERNEL))
 		panic("Failed to allocate MPTCP pcpu counter\n");
 
+	init_dummy_netdev(&mptcp_napi_dev);
+	for_each_possible_cpu(cpu) {
+		delegated = per_cpu_ptr(&mptcp_delegated_actions, cpu);
+		INIT_LIST_HEAD(&delegated->head);
+		netif_tx_napi_add(&mptcp_napi_dev, &delegated->napi, mptcp_napi_poll,
+				  NAPI_POLL_WEIGHT);
+		napi_enable(&delegated->napi);
+	}
+
 	mptcp_subflow_init();
 	mptcp_pm_init();
 	mptcp_token_init();
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 871534df6140f..1460705aaad05 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -378,6 +378,15 @@  enum mptcp_data_avail {
 	MPTCP_SUBFLOW_OOO_DATA
 };
 
+struct mptcp_delegated_action {
+	struct napi_struct napi;
+	struct list_head head;
+};
+
+DECLARE_PER_CPU(struct mptcp_delegated_action, mptcp_delegated_actions);
+
+#define MPTCP_DELEGATE_SEND		0
+
 /* MPTCP subflow context */
 struct mptcp_subflow_context {
 	struct	list_head node;/* conn_list of subflows */
@@ -415,6 +424,9 @@  struct mptcp_subflow_context {
 	u8	local_id;
 	u8	remote_id;
 
+	long	delegated_status;
+	struct	list_head delegated_node;   /* link into delegated_action, protected by local BH */
+
 	struct	sock *tcp_sock;	    /* tcp sk backpointer */
 	struct	sock *conn;	    /* parent mptcp_sock */
 	const	struct inet_connection_sock_af_ops *icsk_af_ops;
@@ -463,6 +475,61 @@  static inline void mptcp_add_pending_subflow(struct mptcp_sock *msk,
 	spin_unlock_bh(&msk->join_list_lock);
 }
 
+void mptcp_subflow_process_delegated(struct sock *ssk);
+
+static inline void mptcp_subflow_delegate(struct mptcp_subflow_context *subflow)
+{
+	struct mptcp_delegated_action *delegated;
+	bool schedule;
+
+	/* The implied barrier pairs with mptcp_subflow_delegated_done(), and
+	 * ensures the below list check sees list updates done prior to status
+	 * bit changes
+	 */
+	if (!test_and_set_bit(MPTCP_DELEGATE_SEND, &subflow->delegated_status)) {
+		/* still on delegated list from previous scheduling */
+		if (!list_empty(&subflow->delegated_node))
+			return;
+
+		/* the caller held the subflow bh socket lock */
+		lockdep_assert_in_softirq();
+
+		delegated = this_cpu_ptr(&mptcp_delegated_actions);
+		schedule = list_empty(&delegated->head);
+		list_add_tail(&subflow->delegated_node, &delegated->head);
+		sock_hold(mptcp_subflow_tcp_sock(subflow));
+		if (schedule)
+			napi_schedule(&delegated->napi);
+	}
+}
+
+static inline struct mptcp_subflow_context *
+mptcp_subflow_delegated_next(struct mptcp_delegated_action *delegated)
+{
+	struct mptcp_subflow_context *ret;
+
+	if (list_empty(&delegated->head))
+		return NULL;
+
+	ret = list_first_entry(&delegated->head, struct mptcp_subflow_context, delegated_node);
+	list_del_init(&ret->delegated_node);
+	return ret;
+}
+
+static inline bool mptcp_subflow_has_delegated_action(const struct mptcp_subflow_context *subflow)
+{
+	return test_bit(MPTCP_DELEGATE_SEND, &subflow->delegated_status);
+}
+
+static inline void mptcp_subflow_delegated_done(struct mptcp_subflow_context *subflow)
+{
+	/* pairs with mptcp_subflow_delegate, ensures delegate_node is updated before
+	 * touching the status bit
+	 */
+	smp_wmb();
+	clear_bit(MPTCP_DELEGATE_SEND, &subflow->delegated_status);
+}
+
 int mptcp_is_enabled(struct net *net);
 unsigned int mptcp_get_add_addr_timeout(struct net *net);
 void mptcp_subflow_fully_established(struct mptcp_subflow_context *subflow,
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 1ca0c82b0dbde..721059916c968 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -18,12 +18,15 @@ 
 #include <net/tcp.h>
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
 #include <net/ip6_route.h>
+#include <net/transp_v6.h>
 #endif
 #include <net/mptcp.h>
 #include <uapi/linux/mptcp.h>
 #include "protocol.h"
 #include "mib.h"
 
+static void mptcp_subflow_ops_undo_override(struct sock *ssk);
+
 static void SUBFLOW_REQ_INC_STATS(struct request_sock *req,
 				  enum linux_mptcp_mib_field field)
 {
@@ -428,6 +431,7 @@  static int subflow_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 static struct tcp_request_sock_ops subflow_request_sock_ipv6_ops;
 static struct inet_connection_sock_af_ops subflow_v6_specific;
 static struct inet_connection_sock_af_ops subflow_v6m_specific;
+static struct proto tcpv6_prot_override;
 
 static int subflow_v6_conn_request(struct sock *sk, struct sk_buff *skb)
 {
@@ -509,6 +513,8 @@  static void subflow_ulp_fallback(struct sock *sk,
 	icsk->icsk_ulp_ops = NULL;
 	rcu_assign_pointer(icsk->icsk_ulp_data, NULL);
 	tcp_sk(sk)->is_mptcp = 0;
+
+	mptcp_subflow_ops_undo_override(sk);
 }
 
 static void subflow_drop_ctx(struct sock *ssk)
@@ -682,6 +688,7 @@  static struct sock *subflow_syn_recv_sock(const struct sock *sk,
 }
 
 static struct inet_connection_sock_af_ops subflow_specific;
+static struct proto tcp_prot_override;
 
 enum mapping_status {
 	MAPPING_OK,
@@ -1203,6 +1210,25 @@  static void mptcp_attach_cgroup(struct sock *parent, struct sock *child)
 #endif /* CONFIG_SOCK_CGROUP_DATA */
 }
 
+static void mptcp_subflow_ops_override(struct sock *ssk)
+{
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	if (ssk->sk_prot == &tcpv6_prot)
+		ssk->sk_prot = &tcpv6_prot_override;
+	else
+#endif
+		ssk->sk_prot = &tcp_prot_override;
+}
+
+static void mptcp_subflow_ops_undo_override(struct sock *ssk)
+{
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	if (ssk->sk_prot == &tcpv6_prot_override)
+		ssk->sk_prot = &tcpv6_prot;
+	else
+#endif
+		ssk->sk_prot = &tcp_prot;
+}
 int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock)
 {
 	struct mptcp_subflow_context *subflow;
@@ -1258,6 +1284,7 @@  int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock)
 	*new_sock = sf;
 	sock_hold(sk);
 	subflow->conn = sk;
+	mptcp_subflow_ops_override(sf->sk);
 
 	return 0;
 }
@@ -1274,6 +1301,7 @@  static struct mptcp_subflow_context *subflow_create_ctx(struct sock *sk,
 
 	rcu_assign_pointer(icsk->icsk_ulp_data, ctx);
 	INIT_LIST_HEAD(&ctx->node);
+	INIT_LIST_HEAD(&ctx->delegated_node);
 
 	pr_debug("subflow=%p", ctx);
 
@@ -1386,6 +1414,7 @@  static void subflow_ulp_release(struct sock *ssk)
 		sock_put(sk);
 	}
 
+	mptcp_subflow_ops_undo_override(ssk);
 	if (release)
 		kfree_rcu(ctx, rcu);
 }
@@ -1439,6 +1468,16 @@  static void subflow_ulp_clone(const struct request_sock *req,
 	}
 }
 
+static void tcp_release_cb_override(struct sock *ssk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+
+	if (mptcp_subflow_has_delegated_action(subflow))
+		mptcp_subflow_process_delegated(ssk);
+
+	tcp_release_cb(ssk);
+}
+
 static struct tcp_ulp_ops subflow_ulp_ops __read_mostly = {
 	.name		= "mptcp",
 	.owner		= THIS_MODULE,
@@ -1479,6 +1518,9 @@  void __init mptcp_subflow_init(void)
 	subflow_specific.syn_recv_sock = subflow_syn_recv_sock;
 	subflow_specific.sk_rx_dst_set = subflow_finish_connect;
 
+	tcp_prot_override = tcp_prot;
+	tcp_prot_override.release_cb = tcp_release_cb_override;
+
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
 	subflow_request_sock_ipv6_ops = tcp_request_sock_ipv6_ops;
 	subflow_request_sock_ipv6_ops.route_req = subflow_v6_route_req;
@@ -1494,6 +1536,9 @@  void __init mptcp_subflow_init(void)
 	subflow_v6m_specific.net_header_len = ipv4_specific.net_header_len;
 	subflow_v6m_specific.mtu_reduced = ipv4_specific.mtu_reduced;
 	subflow_v6m_specific.net_frag_header_len = 0;
+
+	tcpv6_prot_override = tcpv6_prot;
+	tcpv6_prot_override.release_cb = tcp_release_cb_override;
 #endif
 
 	mptcp_diag_subflow_init(&subflow_ulp_ops);