text: // SPDX-License-Identifier: GPL-2.0
  /* Multipath TCP
   *
   * Copyright (c) 2017 - 2019, Intel Corporation.
   */
  
  #define pr_fmt(fmt) "MPTCP: " fmt
  
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/netdevice.h>
  #include <linux/sched/signal.h>
  #include <linux/atomic.h>
  #include <net/sock.h>
  #include <net/inet_common.h>
  #include <net/inet_hashtables.h>
  #include <net/protocol.h>
  #include <net/tcp.h>
  #include <net/tcp_states.h>
  #if IS_ENABLED(CONFIG_MPTCP_IPV6)
  #include <net/transp_v6.h>
  #endif
  #include <net/mptcp.h>
  #include <net/xfrm.h>
  #include "protocol.h"
  #include "mib.h"
  
  #define CREATE_TRACE_POINTS
  #include <trace/events/mptcp.h>
  
  #if IS_ENABLED(CONFIG_MPTCP_IPV6)
  struct mptcp6_sock {
  	struct mptcp_sock msk;
  	struct ipv6_pinfo np;
  };
  #endif
  
  struct mptcp_skb_cb {
  	u64 map_seq;
  	u64 end_seq;
  	u32 offset;
  	u8  has_rxtstamp:1;
  };
  
  #define MPTCP_SKB_CB(__skb)	((struct mptcp_skb_cb *)&((__skb)->cb[0]))
  
  enum {
  	MPTCP_CMSG_TS = BIT(0),
  };
  
  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.
   */
  struct socket *__mptcp_nmpc_socket(const struct mptcp_sock *msk)
  {
  	if (!msk->subflow || READ_ONCE(msk->can_ack))
  		return NULL;
  
  	return msk->subflow;
  }
  
  /* Returns end sequence number of the receiver's advertised window */
  static u64 mptcp_wnd_end(const struct mptcp_sock *msk)
  {
  	return READ_ONCE(msk->wnd_end);
  }
  
  static bool mptcp_is_tcpsk(struct sock *sk)
  {
  	struct socket *sock = sk->sk_socket;
  
  	if (unlikely(sk->sk_prot == &tcp_prot)) {
  		/* we are being invoked after mptcp_accept() has
  		 * accepted a non-mp-capable flow: sk is a tcp_sk,
  		 * not an mptcp one.
  		 *
  		 * Hand the socket over to tcp so all further socket ops
  		 * bypass mptcp.
  		 */
  		sock->ops = &inet_stream_ops;
  		return true;
  #if IS_ENABLED(CONFIG_MPTCP_IPV6)
  	} else if (unlikely(sk->sk_prot == &tcpv6_prot)) {
  		sock->ops = &inet6_stream_ops;
  		return true;
  #endif
  	}
  
  	return false;
  }
  
  static int __mptcp_socket_create(struct mptcp_sock *msk)
  {
  	struct mptcp_subflow_context *subflow;
  	struct sock *sk = (struct sock *)msk;
  	struct socket *ssock;
  	int err;
  
  	err = mptcp_subflow_create_socket(sk, &ssock);
  	if (err)
  		return err;
  
  	msk->first = ssock->sk;
  	msk->subflow = ssock;
  	subflow = mptcp_subflow_ctx(ssock->sk);
  	list_add(&subflow->node, &msk->conn_list);
  	sock_hold(ssock->sk);
  	subflow->request_mptcp = 1;
  	mptcp_sock_graft(msk->first, sk->sk_socket);
  
  	return 0;
  }
  
  static void mptcp_drop(struct sock *sk, struct sk_buff *skb)
  {
  	sk_drops_add(sk, skb);
  	__kfree_skb(skb);
  }
  
  static void mptcp_rmem_charge(struct sock *sk, int size)
  {
  	mptcp_sk(sk)->rmem_fwd_alloc -= size;
  }
  
  static bool mptcp_try_coalesce(struct sock *sk, struct sk_buff *to,
  			       struct sk_buff *from)
  {
  	bool fragstolen;
  	int delta;
  
  	if (MPTCP_SKB_CB(from)->offset ||
  	    !skb_try_coalesce(to, from, &fragstolen, &delta))
  		return false;
  
  	pr_debug("colesced seq %llx into %llx new len %d new end seq %llx",
  		 MPTCP_SKB_CB(from)->map_seq, MPTCP_SKB_CB(to)->map_seq,
  		 to->len, MPTCP_SKB_CB(from)->end_seq);
  	MPTCP_SKB_CB(to)->end_seq = MPTCP_SKB_CB(from)->end_seq;
  	kfree_skb_partial(from, fragstolen);
  	atomic_add(delta, &sk->sk_rmem_alloc);
  	mptcp_rmem_charge(sk, delta);
  	return true;
  }
  
  static bool mptcp_ooo_try_coalesce(struct mptcp_sock *msk, struct sk_buff *to,
  				   struct sk_buff *from)
  {
  	if (MPTCP_SKB_CB(from)->map_seq != MPTCP_SKB_CB(to)->end_seq)
  		return false;
  
  	return mptcp_try_coalesce((struct sock *)msk, to, from);
  }
  
  static void __mptcp_rmem_reclaim(struct sock *sk, int amount)
  {
  	amount >>= SK_MEM_QUANTUM_SHIFT;
  	mptcp_sk(sk)->rmem_fwd_alloc -= amount << SK_MEM_QUANTUM_SHIFT;
  	__sk_mem_reduce_allocated(sk, amount);
  }
  
  static void mptcp_rmem_uncharge(struct sock *sk, int size)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	int reclaimable;
  
  	msk->rmem_fwd_alloc += size;
  	reclaimable = msk->rmem_fwd_alloc - sk_unused_reserved_mem(sk);
  
  	/* see sk_mem_uncharge() for the rationale behind the following schema */
  	if (unlikely(reclaimable >= SK_RECLAIM_THRESHOLD))
  		__mptcp_rmem_reclaim(sk, SK_RECLAIM_CHUNK);
  }
  
  static void mptcp_rfree(struct sk_buff *skb)
  {
  	unsigned int len = skb->truesize;
  	struct sock *sk = skb->sk;
  
  	atomic_sub(len, &sk->sk_rmem_alloc);
  	mptcp_rmem_uncharge(sk, len);
  }
  
  static void mptcp_set_owner_r(struct sk_buff *skb, struct sock *sk)
  {
  	skb_orphan(skb);
  	skb->sk = sk;
  	skb->destructor = mptcp_rfree;
  	atomic_add(skb->truesize, &sk->sk_rmem_alloc);
  	mptcp_rmem_charge(sk, skb->truesize);
  }
  
  /* "inspired" by tcp_data_queue_ofo(), main differences:
   * - use mptcp seqs
   * - don't cope with sacks
   */
  static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb)
  {
  	struct sock *sk = (struct sock *)msk;
  	struct rb_node **p, *parent;
  	u64 seq, end_seq, max_seq;
  	struct sk_buff *skb1;
  
  	seq = MPTCP_SKB_CB(skb)->map_seq;
  	end_seq = MPTCP_SKB_CB(skb)->end_seq;
  	max_seq = READ_ONCE(msk->rcv_wnd_sent);
  
  	pr_debug("msk=%p seq=%llx limit=%llx empty=%d", msk, seq, max_seq,
  		 RB_EMPTY_ROOT(&msk->out_of_order_queue));
  	if (after64(end_seq, max_seq)) {
  		/* out of window */
  		mptcp_drop(sk, skb);
  		pr_debug("oow by %lld, rcv_wnd_sent %llu\n",
  			 (unsigned long long)end_seq - (unsigned long)max_seq,
  			 (unsigned long long)msk->rcv_wnd_sent);
  		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_NODSSWINDOW);
  		return;
  	}
  
  	p = &msk->out_of_order_queue.rb_node;
  	MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOQUEUE);
  	if (RB_EMPTY_ROOT(&msk->out_of_order_queue)) {
  		rb_link_node(&skb->rbnode, NULL, p);
  		rb_insert_color(&skb->rbnode, &msk->out_of_order_queue);
  		msk->ooo_last_skb = skb;
  		goto end;
  	}
  
  	/* with 2 subflows, adding at end of ooo queue is quite likely
  	 * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
  	 */
  	if (mptcp_ooo_try_coalesce(msk, msk->ooo_last_skb, skb)) {
  		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOMERGE);
  		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOQUEUETAIL);
  		return;
  	}
  
  	/* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
  	if (!before64(seq, MPTCP_SKB_CB(msk->ooo_last_skb)->end_seq)) {
  		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOQUEUETAIL);
  		parent = &msk->ooo_last_skb->rbnode;
  		p = &parent->rb_right;
  		goto insert;
  	}
  
  	/* Find place to insert this segment. Handle overlaps on the way. */
  	parent = NULL;
  	while (*p) {
  		parent = *p;
  		skb1 = rb_to_skb(parent);
  		if (before64(seq, MPTCP_SKB_CB(skb1)->map_seq)) {
  			p = &parent->rb_left;
  			continue;
  		}
  		if (before64(seq, MPTCP_SKB_CB(skb1)->end_seq)) {
  			if (!after64(end_seq, MPTCP_SKB_CB(skb1)->end_seq)) {
  				/* All the bits are present. Drop. */
  				mptcp_drop(sk, skb);
  				MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
  				return;
  			}
  			if (after64(seq, MPTCP_SKB_CB(skb1)->map_seq)) {
  				/* partial overlap:
  				 *     |     skb      |
  				 *  |     skb1    |
  				 * continue traversing
  				 */
  			} else {
  				/* skb's seq == skb1's seq and skb covers skb1.
  				 * Replace skb1 with skb.
  				 */
  				rb_replace_node(&skb1->rbnode, &skb->rbnode,
  						&msk->out_of_order_queue);
  				mptcp_drop(sk, skb1);
  				MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
  				goto merge_right;
  			}
  		} else if (mptcp_ooo_try_coalesce(msk, skb1, skb)) {
  			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOMERGE);
  			return;
  		}
  		p = &parent->rb_right;
  	}
  
  insert:
  	/* Insert segment into RB tree. */
  	rb_link_node(&skb->rbnode, parent, p);
  	rb_insert_color(&skb->rbnode, &msk->out_of_order_queue);
  
  merge_right:
  	/* Remove other segments covered by skb. */
  	while ((skb1 = skb_rb_next(skb)) != NULL) {
  		if (before64(end_seq, MPTCP_SKB_CB(skb1)->end_seq))
  			break;
  		rb_erase(&skb1->rbnode, &msk->out_of_order_queue);
  		mptcp_drop(sk, skb1);
  		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
  	}
  	/* If there is no skb after us, we are the last_skb ! */
  	if (!skb1)
  		msk->ooo_last_skb = skb;
  
  end:
  	skb_condense(skb);
  	mptcp_set_owner_r(skb, sk);
  }
  
  static bool mptcp_rmem_schedule(struct sock *sk, struct sock *ssk, int size)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	int amt, amount;
  
  	if (size < msk->rmem_fwd_alloc)
  		return true;
  
  	amt = sk_mem_pages(size);
  	amount = amt << SK_MEM_QUANTUM_SHIFT;
  	msk->rmem_fwd_alloc += amount;
  	if (!__sk_mem_raise_allocated(sk, size, amt, SK_MEM_RECV)) {
  		if (ssk->sk_forward_alloc < amount) {
  			msk->rmem_fwd_alloc -= amount;
  			return false;
  		}
  
  		ssk->sk_forward_alloc -= amount;
  	}
  	return true;
  }
  
  static bool __mptcp_move_skb(struct mptcp_sock *msk, struct sock *ssk,
  			     struct sk_buff *skb, unsigned int offset,
  			     size_t copy_len)
  {
  	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
  	struct sock *sk = (struct sock *)msk;
  	struct sk_buff *tail;
  	bool has_rxtstamp;
  
  	__skb_unlink(skb, &ssk->sk_receive_queue);
  
  	skb_ext_reset(skb);
  	skb_orphan(skb);
  
  	/* try to fetch required memory from subflow */
  	if (!mptcp_rmem_schedule(sk, ssk, skb->truesize))
  		goto drop;
  
  	has_rxtstamp = TCP_SKB_CB(skb)->has_rxtstamp;
  
  	/* the skb map_seq accounts for the skb offset:
  	 * mptcp_subflow_get_mapped_dsn() is based on the current tp->copied_seq
  	 * value
  	 */
  	MPTCP_SKB_CB(skb)->map_seq = mptcp_subflow_get_mapped_dsn(subflow);
  	MPTCP_SKB_CB(skb)->end_seq = MPTCP_SKB_CB(skb)->map_seq + copy_len;
  	MPTCP_SKB_CB(skb)->offset = offset;
  	MPTCP_SKB_CB(skb)->has_rxtstamp = has_rxtstamp;
  
  	if (MPTCP_SKB_CB(skb)->map_seq == msk->ack_seq) {
  		/* in sequence */
  		WRITE_ONCE(msk->ack_seq, msk->ack_seq + copy_len);
  		tail = skb_peek_tail(&sk->sk_receive_queue);
  		if (tail && mptcp_try_coalesce(sk, tail, skb))
  			return true;
  
  		mptcp_set_owner_r(skb, sk);
  		__skb_queue_tail(&sk->sk_receive_queue, skb);
  		return true;
  	} else if (after64(MPTCP_SKB_CB(skb)->map_seq, msk->ack_seq)) {
  		mptcp_data_queue_ofo(msk, skb);
  		return false;
  	}
  
  	/* old data, keep it simple and drop the whole pkt, sender
  	 * will retransmit as needed, if needed.
  	 */
  	MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
  drop:
  	mptcp_drop(sk, skb);
  	return false;
  }
  
  static void mptcp_stop_timer(struct sock *sk)
  {
  	struct inet_connection_sock *icsk = inet_csk(sk);
  
  	sk_stop_timer(sk, &icsk->icsk_retransmit_timer);
  	mptcp_sk(sk)->timer_ival = 0;
  }
  
  static void mptcp_close_wake_up(struct sock *sk)
  {
  	if (sock_flag(sk, SOCK_DEAD))
  		return;
  
  	sk->sk_state_change(sk);
  	if (sk->sk_shutdown == SHUTDOWN_MASK ||
  	    sk->sk_state == TCP_CLOSE)
  		sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
  	else
  		sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
  }
  
  static bool mptcp_pending_data_fin_ack(struct sock *sk)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  
  	return !__mptcp_check_fallback(msk) &&
  	       ((1 << sk->sk_state) &
  		(TCPF_FIN_WAIT1 | TCPF_CLOSING | TCPF_LAST_ACK)) &&
  	       msk->write_seq == READ_ONCE(msk->snd_una);
  }
  
  static void mptcp_check_data_fin_ack(struct sock *sk)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  
  	/* Look for an acknowledged DATA_FIN */
  	if (mptcp_pending_data_fin_ack(sk)) {
  		WRITE_ONCE(msk->snd_data_fin_enable, 0);
  
  		switch (sk->sk_state) {
  		case TCP_FIN_WAIT1:
  			inet_sk_state_store(sk, TCP_FIN_WAIT2);
  			break;
  		case TCP_CLOSING:
  		case TCP_LAST_ACK:
  			inet_sk_state_store(sk, TCP_CLOSE);
  			break;
  		}
  
  		mptcp_close_wake_up(sk);
  	}
  }
  
  static bool mptcp_pending_data_fin(struct sock *sk, u64 *seq)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  
  	if (READ_ONCE(msk->rcv_data_fin) &&
  	    ((1 << sk->sk_state) &
  	     (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_FIN_WAIT2))) {
  		u64 rcv_data_fin_seq = READ_ONCE(msk->rcv_data_fin_seq);
  
  		if (msk->ack_seq == rcv_data_fin_seq) {
  			if (seq)
  				*seq = rcv_data_fin_seq;
  
  			return true;
  		}
  	}
  
  	return false;
  }
  
  static void mptcp_set_datafin_timeout(const struct sock *sk)
  {
  	struct inet_connection_sock *icsk = inet_csk(sk);
  
  	mptcp_sk(sk)->timer_ival = min(TCP_RTO_MAX,
  				       TCP_RTO_MIN << icsk->icsk_retransmits);
  }
  
  static void __mptcp_set_timeout(struct sock *sk, long tout)
  {
  	mptcp_sk(sk)->timer_ival = tout > 0 ? tout : TCP_RTO_MIN;
  }
  
  static long mptcp_timeout_from_subflow(const struct mptcp_subflow_context *subflow)
  {
  	const struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
  
  	return inet_csk(ssk)->icsk_pending && !subflow->stale_count ?
  	       inet_csk(ssk)->icsk_timeout - jiffies : 0;
  }
  
  static void mptcp_set_timeout(struct sock *sk)
  {
  	struct mptcp_subflow_context *subflow;
  	long tout = 0;
  
  	mptcp_for_each_subflow(mptcp_sk(sk), subflow)
  		tout = max(tout, mptcp_timeout_from_subflow(subflow));
  	__mptcp_set_timeout(sk, tout);
  }
  
  static bool tcp_can_send_ack(const struct sock *ssk)
  {
  	return !((1 << inet_sk_state_load(ssk)) &
  	       (TCPF_SYN_SENT | TCPF_SYN_RECV | TCPF_TIME_WAIT | TCPF_CLOSE | TCPF_LISTEN));
  }
  
  void mptcp_subflow_send_ack(struct sock *ssk)
  {
  	bool slow;
  
  	slow = lock_sock_fast(ssk);
  	if (tcp_can_send_ack(ssk))
  		tcp_send_ack(ssk);
  	unlock_sock_fast(ssk, slow);
  }
  
  static void mptcp_send_ack(struct mptcp_sock *msk)
  {
  	struct mptcp_subflow_context *subflow;
  
  	mptcp_for_each_subflow(msk, subflow)
  		mptcp_subflow_send_ack(mptcp_subflow_tcp_sock(subflow));
  }
  
  static void mptcp_subflow_cleanup_rbuf(struct sock *ssk)
  {
  	bool slow;
  
  	slow = lock_sock_fast(ssk);
  	if (tcp_can_send_ack(ssk))
  		tcp_cleanup_rbuf(ssk, 1);
  	unlock_sock_fast(ssk, slow);
  }
  
  static bool mptcp_subflow_could_cleanup(const struct sock *ssk, bool rx_empty)
  {
  	const struct inet_connection_sock *icsk = inet_csk(ssk);
  	u8 ack_pending = READ_ONCE(icsk->icsk_ack.pending);
  	const struct tcp_sock *tp = tcp_sk(ssk);
  
  	return (ack_pending & ICSK_ACK_SCHED) &&
  		((READ_ONCE(tp->rcv_nxt) - READ_ONCE(tp->rcv_wup) >
  		  READ_ONCE(icsk->icsk_ack.rcv_mss)) ||
  		 (rx_empty && ack_pending &
  			      (ICSK_ACK_PUSHED2 | ICSK_ACK_PUSHED)));
  }
  
  static void mptcp_cleanup_rbuf(struct mptcp_sock *msk)
  {
  	int old_space = READ_ONCE(msk->old_wspace);
  	struct mptcp_subflow_context *subflow;
  	struct sock *sk = (struct sock *)msk;
  	int space =  __mptcp_space(sk);
  	bool cleanup, rx_empty;
  
  	cleanup = (space > 0) && (space >= (old_space << 1));
  	rx_empty = !__mptcp_rmem(sk);
  
  	mptcp_for_each_subflow(msk, subflow) {
  		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
  
  		if (cleanup || mptcp_subflow_could_cleanup(ssk, rx_empty))
  			mptcp_subflow_cleanup_rbuf(ssk);
  	}
  }
  
  static bool mptcp_check_data_fin(struct sock *sk)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	u64 rcv_data_fin_seq;
  	bool ret = false;
  
  	if (__mptcp_check_fallback(msk))
  		return ret;
  
  	/* Need to ack a DATA_FIN received from a peer while this side
  	 * of the connection is in ESTABLISHED, FIN_WAIT1, or FIN_WAIT2.
  	 * msk->rcv_data_fin was set when parsing the incoming options
  	 * at the subflow level and the msk lock was not held, so this
  	 * is the first opportunity to act on the DATA_FIN and change
  	 * the msk state.
  	 *
  	 * If we are caught up to the sequence number of the incoming
  	 * DATA_FIN, send the DATA_ACK now and do state transition.  If
  	 * not caught up, do nothing and let the recv code send DATA_ACK
  	 * when catching up.
  	 */
  
  	if (mptcp_pending_data_fin(sk, &rcv_data_fin_seq)) {
  		WRITE_ONCE(msk->ack_seq, msk->ack_seq + 1);
  		WRITE_ONCE(msk->rcv_data_fin, 0);
  
  		sk->sk_shutdown |= RCV_SHUTDOWN;
  		smp_mb__before_atomic(); /* SHUTDOWN must be visible first */
  
  		switch (sk->sk_state) {
  		case TCP_ESTABLISHED:
  			inet_sk_state_store(sk, TCP_CLOSE_WAIT);
  			break;
  		case TCP_FIN_WAIT1:
  			inet_sk_state_store(sk, TCP_CLOSING);
  			break;
  		case TCP_FIN_WAIT2:
  			inet_sk_state_store(sk, TCP_CLOSE);
  			break;
  		default:
  			/* Other states not expected */
  			WARN_ON_ONCE(1);
  			break;
  		}
  
  		ret = true;
  		mptcp_send_ack(msk);
  		mptcp_close_wake_up(sk);
  	}
  	return ret;
  }
  
  static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
  					   struct sock *ssk,
  					   unsigned int *bytes)
  {
  	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
  	struct sock *sk = (struct sock *)msk;
  	unsigned int moved = 0;
  	bool more_data_avail;
  	struct tcp_sock *tp;
  	bool done = false;
  	int sk_rbuf;
  
  	sk_rbuf = READ_ONCE(sk->sk_rcvbuf);
  
  	if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
  		int ssk_rbuf = READ_ONCE(ssk->sk_rcvbuf);
  
  		if (unlikely(ssk_rbuf > sk_rbuf)) {
  			WRITE_ONCE(sk->sk_rcvbuf, ssk_rbuf);
  			sk_rbuf = ssk_rbuf;
  		}
  	}
  
  	pr_debug("msk=%p ssk=%p", msk, ssk);
  	tp = tcp_sk(ssk);
  	do {
  		u32 map_remaining, offset;
  		u32 seq = tp->copied_seq;
  		struct sk_buff *skb;
  		bool fin;
  
  		/* try to move as much data as available */
  		map_remaining = subflow->map_data_len -
  				mptcp_subflow_get_map_offset(subflow);
  
  		skb = skb_peek(&ssk->sk_receive_queue);
  		if (!skb) {
  			/* if no data is found, a racing workqueue/recvmsg
  			 * already processed the new data, stop here or we
  			 * can enter an infinite loop
  			 */
  			if (!moved)
  				done = true;
  			break;
  		}
  
  		if (__mptcp_check_fallback(msk)) {
  			/* if we are running under the workqueue, TCP could have
  			 * collapsed skbs between dummy map creation and now
  			 * be sure to adjust the size
  			 */
  			map_remaining = skb->len;
  			subflow->map_data_len = skb->len;
  		}
  
  		offset = seq - TCP_SKB_CB(skb)->seq;
  		fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
  		if (fin) {
  			done = true;
  			seq++;
  		}
  
  		if (offset < skb->len) {
  			size_t len = skb->len - offset;
  
  			if (tp->urg_data)
  				done = true;
  
  			if (__mptcp_move_skb(msk, ssk, skb, offset, len))
  				moved += len;
  			seq += len;
  
  			if (WARN_ON_ONCE(map_remaining < len))
  				break;
  		} else {
  			WARN_ON_ONCE(!fin);
  			sk_eat_skb(ssk, skb);
  			done = true;
  		}
  
  		WRITE_ONCE(tp->copied_seq, seq);
  		more_data_avail = mptcp_subflow_data_available(ssk);
  
  		if (atomic_read(&sk->sk_rmem_alloc) > sk_rbuf) {
  			done = true;
  			break;
  		}
  	} while (more_data_avail);
  
  	*bytes += moved;
  	return done;
  }
  
  static bool __mptcp_ofo_queue(struct mptcp_sock *msk)
  {
  	struct sock *sk = (struct sock *)msk;
  	struct sk_buff *skb, *tail;
  	bool moved = false;
  	struct rb_node *p;
  	u64 end_seq;
  
  	p = rb_first(&msk->out_of_order_queue);
  	pr_debug("msk=%p empty=%d", msk, RB_EMPTY_ROOT(&msk->out_of_order_queue));
  	while (p) {
  		skb = rb_to_skb(p);
  		if (after64(MPTCP_SKB_CB(skb)->map_seq, msk->ack_seq))
  			break;
  
  		p = rb_next(p);
  		rb_erase(&skb->rbnode, &msk->out_of_order_queue);
  
  		if (unlikely(!after64(MPTCP_SKB_CB(skb)->end_seq,
  				      msk->ack_seq))) {
  			mptcp_drop(sk, skb);
  			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
  			continue;
  		}
  
  		end_seq = MPTCP_SKB_CB(skb)->end_seq;
  		tail = skb_peek_tail(&sk->sk_receive_queue);
  		if (!tail || !mptcp_ooo_try_coalesce(msk, tail, skb)) {
  			int delta = msk->ack_seq - MPTCP_SKB_CB(skb)->map_seq;
  
  			/* skip overlapping data, if any */
  			pr_debug("uncoalesced seq=%llx ack seq=%llx delta=%d",
  				 MPTCP_SKB_CB(skb)->map_seq, msk->ack_seq,
  				 delta);
  			MPTCP_SKB_CB(skb)->offset += delta;
  			__skb_queue_tail(&sk->sk_receive_queue, skb);
  		}
  		msk->ack_seq = end_seq;
  		moved = true;
  	}
  	return moved;
  }
  
  /* In most cases we will be able to lock the mptcp socket.  If its already
   * owned, we need to defer to the work queue to avoid ABBA deadlock.
   */
  static bool move_skbs_to_msk(struct mptcp_sock *msk, struct sock *ssk)
  {
  	struct sock *sk = (struct sock *)msk;
  	unsigned int moved = 0;
  
  	__mptcp_move_skbs_from_subflow(msk, ssk, &moved);
  	__mptcp_ofo_queue(msk);
  	if (unlikely(ssk->sk_err)) {
  		if (!sock_owned_by_user(sk))
  			__mptcp_error_report(sk);
  		else
  			set_bit(MPTCP_ERROR_REPORT,  &msk->flags);
  	}
  
  	/* If the moves have caught up with the DATA_FIN sequence number
  	 * it's time to ack the DATA_FIN and change socket state, but
  	 * this is not a good place to change state. Let the workqueue
  	 * do it.
  	 */
  	if (mptcp_pending_data_fin(sk, NULL))
  		mptcp_schedule_work(sk);
  	return moved > 0;
  }
  
  void mptcp_data_ready(struct sock *sk, struct sock *ssk)
  {
  	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	int sk_rbuf, ssk_rbuf;
  
  	/* The peer can send data while we are shutting down this
  	 * subflow at msk destruction time, but we must avoid enqueuing
  	 * more data to the msk receive queue
  	 */
  	if (unlikely(subflow->disposable))
  		return;
  
  	ssk_rbuf = READ_ONCE(ssk->sk_rcvbuf);
  	sk_rbuf = READ_ONCE(sk->sk_rcvbuf);
  	if (unlikely(ssk_rbuf > sk_rbuf))
  		sk_rbuf = ssk_rbuf;
  
  	/* over limit? can't append more skbs to msk, Also, no need to wake-up*/
  	if (__mptcp_rmem(sk) > sk_rbuf) {
  		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_RCVPRUNED);
  		return;
  	}
  
  	/* Wake-up the reader only for in-sequence data */
  	mptcp_data_lock(sk);
  	if (move_skbs_to_msk(msk, ssk))
  		sk->sk_data_ready(sk);
  
  	mptcp_data_unlock(sk);
  }
  
  static bool mptcp_do_flush_join_list(struct mptcp_sock *msk)
  {
  	struct mptcp_subflow_context *subflow;
  	bool ret = false;
  
  	if (likely(list_empty(&msk->join_list)))
  		return false;
  
  	spin_lock_bh(&msk->join_list_lock);
  	list_for_each_entry(subflow, &msk->join_list, node) {
  		u32 sseq = READ_ONCE(subflow->setsockopt_seq);
  
  		mptcp_propagate_sndbuf((struct sock *)msk, mptcp_subflow_tcp_sock(subflow));
  		if (READ_ONCE(msk->setsockopt_seq) != sseq)
  			ret = true;
  	}
  	list_splice_tail_init(&msk->join_list, &msk->conn_list);
  	spin_unlock_bh(&msk->join_list_lock);
  
  	return ret;
  }
  
  void __mptcp_flush_join_list(struct mptcp_sock *msk)
  {
  	if (likely(!mptcp_do_flush_join_list(msk)))
  		return;
  
  	if (!test_and_set_bit(MPTCP_WORK_SYNC_SETSOCKOPT, &msk->flags))
  		mptcp_schedule_work((struct sock *)msk);
  }
  
  static void mptcp_flush_join_list(struct mptcp_sock *msk)
  {
  	bool sync_needed = test_and_clear_bit(MPTCP_WORK_SYNC_SETSOCKOPT, &msk->flags);
  
  	might_sleep();
  
  	if (!mptcp_do_flush_join_list(msk) && !sync_needed)
  		return;
  
  	mptcp_sockopt_sync_all(msk);
  }
  
  static bool mptcp_timer_pending(struct sock *sk)
  {
  	return timer_pending(&inet_csk(sk)->icsk_retransmit_timer);
  }
  
  static void mptcp_reset_timer(struct sock *sk)
  {
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	unsigned long tout;
  
  	/* prevent rescheduling on close */
  	if (unlikely(inet_sk_state_load(sk) == TCP_CLOSE))
  		return;
  
  	tout = mptcp_sk(sk)->timer_ival;
  	sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + tout);
  }
  
  bool mptcp_schedule_work(struct sock *sk)
  {
  	if (inet_sk_state_load(sk) != TCP_CLOSE &&
  	    schedule_work(&mptcp_sk(sk)->work)) {
  		/* each subflow already holds a reference to the sk, and the
  		 * workqueue is invoked by a subflow, so sk can't go away here.
  		 */
  		sock_hold(sk);
  		return true;
  	}
  	return false;
  }
  
  void mptcp_subflow_eof(struct sock *sk)
  {
  	if (!test_and_set_bit(MPTCP_WORK_EOF, &mptcp_sk(sk)->flags))
  		mptcp_schedule_work(sk);
  }
  
  static void mptcp_check_for_eof(struct mptcp_sock *msk)
  {
  	struct mptcp_subflow_context *subflow;
  	struct sock *sk = (struct sock *)msk;
  	int receivers = 0;
  
  	mptcp_for_each_subflow(msk, subflow)
  		receivers += !subflow->rx_eof;
  	if (receivers)
  		return;
  
  	if (!(sk->sk_shutdown & RCV_SHUTDOWN)) {
  		/* hopefully temporary hack: propagate shutdown status
  		 * to msk, when all subflows agree on it
  		 */
  		sk->sk_shutdown |= RCV_SHUTDOWN;
  
  		smp_mb__before_atomic(); /* SHUTDOWN must be visible first */
  		sk->sk_data_ready(sk);
  	}
  
  	switch (sk->sk_state) {
  	case TCP_ESTABLISHED:
  		inet_sk_state_store(sk, TCP_CLOSE_WAIT);
  		break;
  	case TCP_FIN_WAIT1:
  		inet_sk_state_store(sk, TCP_CLOSING);
  		break;
  	case TCP_FIN_WAIT2:
  		inet_sk_state_store(sk, TCP_CLOSE);
  		break;
  	default:
  		return;
  	}
  	mptcp_close_wake_up(sk);
  }
  
  static struct sock *mptcp_subflow_recv_lookup(const struct mptcp_sock *msk)
  {
  	struct mptcp_subflow_context *subflow;
  	struct sock *sk = (struct sock *)msk;
  
  	sock_owned_by_me(sk);
  
  	mptcp_for_each_subflow(msk, subflow) {
  		if (READ_ONCE(subflow->data_avail))
  			return mptcp_subflow_tcp_sock(subflow);
  	}
  
  	return NULL;
  }
  
  static bool mptcp_skb_can_collapse_to(u64 write_seq,
  				      const struct sk_buff *skb,
  				      const struct mptcp_ext *mpext)
  {
  	if (!tcp_skb_can_collapse_to(skb))
  		return false;
  
  	/* can collapse only if MPTCP level sequence is in order and this
  	 * mapping has not been xmitted yet
  	 */
  	return mpext && mpext->data_seq + mpext->data_len == write_seq &&
  	       !mpext->frozen;
  }
  
  /* we can append data to the given data frag if:
   * - there is space available in the backing page_frag
   * - the data frag tail matches the current page_frag free offset
   * - the data frag end sequence number matches the current write seq
   */
  static bool mptcp_frag_can_collapse_to(const struct mptcp_sock *msk,
  				       const struct page_frag *pfrag,
  				       const struct mptcp_data_frag *df)
  {
  	return df && pfrag->page == df->page &&
  		pfrag->size - pfrag->offset > 0 &&
  		pfrag->offset == (df->offset + df->data_len) &&
  		df->data_seq + df->data_len == msk->write_seq;
  }
  
  static void __mptcp_mem_reclaim_partial(struct sock *sk)
  {
  	int reclaimable = mptcp_sk(sk)->rmem_fwd_alloc - sk_unused_reserved_mem(sk);
  
  	lockdep_assert_held_once(&sk->sk_lock.slock);
  
  	__mptcp_rmem_reclaim(sk, reclaimable - 1);
  	sk_mem_reclaim_partial(sk);
  }
  
  static void mptcp_mem_reclaim_partial(struct sock *sk)
  {
  	mptcp_data_lock(sk);
  	__mptcp_mem_reclaim_partial(sk);
  	mptcp_data_unlock(sk);
  }
  
  static void dfrag_uncharge(struct sock *sk, int len)
  {
  	sk_mem_uncharge(sk, len);
  	sk_wmem_queued_add(sk, -len);
  }
  
  static void dfrag_clear(struct sock *sk, struct mptcp_data_frag *dfrag)
  {
  	int len = dfrag->data_len + dfrag->overhead;
  
  	list_del(&dfrag->list);
  	dfrag_uncharge(sk, len);
  	put_page(dfrag->page);
  }
  
  static void __mptcp_clean_una(struct sock *sk)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	struct mptcp_data_frag *dtmp, *dfrag;
  	bool cleaned = false;
  	u64 snd_una;
  
  	/* on fallback we just need to ignore snd_una, as this is really
  	 * plain TCP
  	 */
  	if (__mptcp_check_fallback(msk))
  		msk->snd_una = READ_ONCE(msk->snd_nxt);
  
  	snd_una = msk->snd_una;
  	list_for_each_entry_safe(dfrag, dtmp, &msk->rtx_queue, list) {
  		if (after64(dfrag->data_seq + dfrag->data_len, snd_una))
  			break;
  
  		if (unlikely(dfrag == msk->first_pending)) {
  			/* in recovery mode can see ack after the current snd head */
  			if (WARN_ON_ONCE(!msk->recovery))
  				break;
  
  			WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
  		}
  
  		dfrag_clear(sk, dfrag);
  		cleaned = true;
  	}
  
  	dfrag = mptcp_rtx_head(sk);
  	if (dfrag && after64(snd_una, dfrag->data_seq)) {
  		u64 delta = snd_una - dfrag->data_seq;
  
  		/* prevent wrap around in recovery mode */
  		if (unlikely(delta > dfrag->already_sent)) {
  			if (WARN_ON_ONCE(!msk->recovery))
  				goto out;
  			if (WARN_ON_ONCE(delta > dfrag->data_len))
  				goto out;
  			dfrag->already_sent += delta - dfrag->already_sent;
  		}
  
  		dfrag->data_seq += delta;
  		dfrag->offset += delta;
  		dfrag->data_len -= delta;
  		dfrag->already_sent -= delta;
  
  		dfrag_uncharge(sk, delta);
  		cleaned = true;
  	}
  
  	/* all retransmitted data acked, recovery completed */
  	if (unlikely(msk->recovery) && after64(msk->snd_una, msk->recovery_snd_nxt))
  		msk->recovery = false;
  
  out:
  	if (cleaned && tcp_under_memory_pressure(sk))
  		__mptcp_mem_reclaim_partial(sk);
  
  	if (snd_una == READ_ONCE(msk->snd_nxt) &&
  	    snd_una == READ_ONCE(msk->write_seq)) {
  		if (mptcp_timer_pending(sk) && !mptcp_data_fin_enabled(msk))
  			mptcp_stop_timer(sk);
  	} else {
  		mptcp_reset_timer(sk);
  	}
  }
  
  static void __mptcp_clean_una_wakeup(struct sock *sk)
  {
  	lockdep_assert_held_once(&sk->sk_lock.slock);
  
  	__mptcp_clean_una(sk);
  	mptcp_write_space(sk);
  }
  
  static void mptcp_clean_una_wakeup(struct sock *sk)
  {
  	mptcp_data_lock(sk);
  	__mptcp_clean_una_wakeup(sk);
  	mptcp_data_unlock(sk);
  }
  
  static void mptcp_enter_memory_pressure(struct sock *sk)
  {
  	struct mptcp_subflow_context *subflow;
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	bool first = true;
  
  	sk_stream_moderate_sndbuf(sk);
  	mptcp_for_each_subflow(msk, subflow) {
  		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
  
  		if (first)
  			tcp_enter_memory_pressure(ssk);
  		sk_stream_moderate_sndbuf(ssk);
  		first = false;
  	}
  }
  
  /* ensure we get enough memory for the frag hdr, beyond some minimal amount of
   * data
   */
  static bool mptcp_page_frag_refill(struct sock *sk, struct page_frag *pfrag)
  {
  	if (likely(skb_page_frag_refill(32U + sizeof(struct mptcp_data_frag),
  					pfrag, sk->sk_allocation)))
  		return true;
  
  	mptcp_enter_memory_pressure(sk);
  	return false;
  }
  
  static struct mptcp_data_frag *
  mptcp_carve_data_frag(const struct mptcp_sock *msk, struct page_frag *pfrag,
  		      int orig_offset)
  {
  	int offset = ALIGN(orig_offset, sizeof(long));
  	struct mptcp_data_frag *dfrag;
  
  	dfrag = (struct mptcp_data_frag *)(page_to_virt(pfrag->page) + offset);
  	dfrag->data_len = 0;
  	dfrag->data_seq = msk->write_seq;
  	dfrag->overhead = offset - orig_offset + sizeof(struct mptcp_data_frag);
  	dfrag->offset = offset + sizeof(struct mptcp_data_frag);
  	dfrag->already_sent = 0;
  	dfrag->page = pfrag->page;
  
  	return dfrag;
  }
  
  struct mptcp_sendmsg_info {
  	int mss_now;
  	int size_goal;
  	u16 limit;
  	u16 sent;
  	unsigned int flags;
  	bool data_lock_held;
  };
  
  static int mptcp_check_allowed_size(struct mptcp_sock *msk, u64 data_seq,
  				    int avail_size)
  {
  	u64 window_end = mptcp_wnd_end(msk);
  
  	if (__mptcp_check_fallback(msk))
  		return avail_size;
  
  	if (!before64(data_seq + avail_size, window_end)) {
  		u64 allowed_size = window_end - data_seq;
  
  		return min_t(unsigned int, allowed_size, avail_size);
  	}
  
  	return avail_size;
  }
  
  static bool __mptcp_add_ext(struct sk_buff *skb, gfp_t gfp)
  {
  	struct skb_ext *mpext = __skb_ext_alloc(gfp);
  
  	if (!mpext)
  		return false;
  	__skb_ext_set(skb, SKB_EXT_MPTCP, mpext);
  	return true;
  }
  
  static struct sk_buff *__mptcp_do_alloc_tx_skb(struct sock *sk, gfp_t gfp)
  {
  	struct sk_buff *skb;
  
  	skb = alloc_skb_fclone(MAX_TCP_HEADER, gfp);
  	if (likely(skb)) {
  		if (likely(__mptcp_add_ext(skb, gfp))) {
  			skb_reserve(skb, MAX_TCP_HEADER);
  			skb->ip_summed = CHECKSUM_PARTIAL;
  			INIT_LIST_HEAD(&skb->tcp_tsorted_anchor);
  			return skb;
  		}
  		__kfree_skb(skb);
  	} else {
  		mptcp_enter_memory_pressure(sk);
  	}
  	return NULL;
  }
  
  static struct sk_buff *__mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, gfp_t gfp)
  {
  	struct sk_buff *skb;
  
  	skb = __mptcp_do_alloc_tx_skb(sk, gfp);
  	if (!skb)
  		return NULL;
  
  	if (likely(sk_wmem_schedule(ssk, skb->truesize))) {
  		tcp_skb_entail(ssk, skb);
  		return skb;
  	}
  	kfree_skb(skb);
  	return NULL;
  }
  
  static struct sk_buff *mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, bool data_lock_held)
  {
  	gfp_t gfp = data_lock_held ? GFP_ATOMIC : sk->sk_allocation;
  
  	if (unlikely(tcp_under_memory_pressure(sk))) {
  		if (data_lock_held)
  			__mptcp_mem_reclaim_partial(sk);
  		else
  			mptcp_mem_reclaim_partial(sk);
  	}
  	return __mptcp_alloc_tx_skb(sk, ssk, gfp);
  }
  
  /* note: this always recompute the csum on the whole skb, even
   * if we just appended a single frag. More status info needed
   */
  static void mptcp_update_data_checksum(struct sk_buff *skb, int added)
  {
  	struct mptcp_ext *mpext = mptcp_get_ext(skb);
  	__wsum csum = ~csum_unfold(mpext->csum);
  	int offset = skb->len - added;
  
  	mpext->csum = csum_fold(csum_block_add(csum, skb_checksum(skb, offset, added, 0), offset));
  }
  
  static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
  			      struct mptcp_data_frag *dfrag,
  			      struct mptcp_sendmsg_info *info)
  {
  	u64 data_seq = dfrag->data_seq + info->sent;
  	int offset = dfrag->offset + info->sent;
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	bool zero_window_probe = false;
  	struct mptcp_ext *mpext = NULL;
  	bool can_coalesce = false;
  	bool reuse_skb = true;
  	struct sk_buff *skb;
  	size_t copy;
  	int i;
  
  	pr_debug("msk=%p ssk=%p sending dfrag at seq=%llu len=%u already sent=%u",
  		 msk, ssk, dfrag->data_seq, dfrag->data_len, info->sent);
  
  	if (WARN_ON_ONCE(info->sent > info->limit ||
  			 info->limit > dfrag->data_len))
  		return 0;
  
  	/* compute send limit */
  	info->mss_now = tcp_send_mss(ssk, &info->size_goal, info->flags);
  	copy = info->size_goal;
  
  	skb = tcp_write_queue_tail(ssk);
  	if (skb && copy > skb->len) {
  		/* Limit the write to the size available in the
  		 * current skb, if any, so that we create at most a new skb.
  		 * Explicitly tells TCP internals to avoid collapsing on later
  		 * queue management operation, to avoid breaking the ext <->
  		 * SSN association set here
  		 */
  		mpext = skb_ext_find(skb, SKB_EXT_MPTCP);
  		if (!mptcp_skb_can_collapse_to(data_seq, skb, mpext)) {
  			TCP_SKB_CB(skb)->eor = 1;
  			goto alloc_skb;
  		}
  
  		i = skb_shinfo(skb)->nr_frags;
  		can_coalesce = skb_can_coalesce(skb, i, dfrag->page, offset);
  		if (!can_coalesce && i >= sysctl_max_skb_frags) {
  			tcp_mark_push(tcp_sk(ssk), skb);
  			goto alloc_skb;
  		}
  
  		copy -= skb->len;
  	} else {
  alloc_skb:
  		skb = mptcp_alloc_tx_skb(sk, ssk, info->data_lock_held);
  		if (!skb)
  			return -ENOMEM;
  
  		i = skb_shinfo(skb)->nr_frags;
  		reuse_skb = false;
  		mpext = skb_ext_find(skb, SKB_EXT_MPTCP);
  	}
  
  	/* Zero window and all data acked? Probe. */
  	copy = mptcp_check_allowed_size(msk, data_seq, copy);
  	if (copy == 0) {
  		u64 snd_una = READ_ONCE(msk->snd_una);
  
  		if (snd_una != msk->snd_nxt) {
  			tcp_remove_empty_skb(ssk);
  			return 0;
  		}
  
  		zero_window_probe = true;
  		data_seq = snd_una - 1;
  		copy = 1;
  
  		/* all mptcp-level data is acked, no skbs should be present into the
  		 * ssk write queue
  		 */
  		WARN_ON_ONCE(reuse_skb);
  	}
  
  	copy = min_t(size_t, copy, info->limit - info->sent);
  	if (!sk_wmem_schedule(ssk, copy)) {
  		tcp_remove_empty_skb(ssk);
  		return -ENOMEM;
  	}
  
  	if (can_coalesce) {
  		skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
  	} else {
  		get_page(dfrag->page);
  		skb_fill_page_desc(skb, i, dfrag->page, offset, copy);
  	}
  
  	skb->len += copy;
  	skb->data_len += copy;
  	skb->truesize += copy;
  	sk_wmem_queued_add(ssk, copy);
  	sk_mem_charge(ssk, copy);
  	WRITE_ONCE(tcp_sk(ssk)->write_seq, tcp_sk(ssk)->write_seq + copy);
  	TCP_SKB_CB(skb)->end_seq += copy;
  	tcp_skb_pcount_set(skb, 0);
  
  	/* on skb reuse we just need to update the DSS len */
  	if (reuse_skb) {
  		TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH;
  		mpext->data_len += copy;
  		WARN_ON_ONCE(zero_window_probe);
  		goto out;
  	}
  
  	memset(mpext, 0, sizeof(*mpext));
  	mpext->data_seq = data_seq;
  	mpext->subflow_seq = mptcp_subflow_ctx(ssk)->rel_write_seq;
  	mpext->data_len = copy;
  	mpext->use_map = 1;
  	mpext->dsn64 = 1;
  
  	pr_debug("data_seq=%llu subflow_seq=%u data_len=%u dsn64=%d",
  		 mpext->data_seq, mpext->subflow_seq, mpext->data_len,
  		 mpext->dsn64);
  
  	if (zero_window_probe) {
  		mptcp_subflow_ctx(ssk)->rel_write_seq += copy;
  		mpext->frozen = 1;
  		if (READ_ONCE(msk->csum_enabled))
  			mptcp_update_data_checksum(skb, copy);
  		tcp_push_pending_frames(ssk);
  		return 0;
  	}
  out:
  	if (READ_ONCE(msk->csum_enabled))
  		mptcp_update_data_checksum(skb, copy);
  	mptcp_subflow_ctx(ssk)->rel_write_seq += copy;
  	return copy;
  }
  
  #define MPTCP_SEND_BURST_SIZE		((1 << 16) - \
  					 sizeof(struct tcphdr) - \
  					 MAX_TCP_OPTION_SPACE - \
  					 sizeof(struct ipv6hdr) - \
  					 sizeof(struct frag_hdr))
  
  struct subflow_send_info {
  	struct sock *ssk;
  	u64 ratio;
  };
  
  void mptcp_subflow_set_active(struct mptcp_subflow_context *subflow)
  {
  	if (!subflow->stale)
  		return;
  
  	subflow->stale = 0;
  	MPTCP_INC_STATS(sock_net(mptcp_subflow_tcp_sock(subflow)), MPTCP_MIB_SUBFLOWRECOVER);
  }
  
  bool mptcp_subflow_active(struct mptcp_subflow_context *subflow)
  {
  	if (unlikely(subflow->stale)) {
  		u32 rcv_tstamp = READ_ONCE(tcp_sk(mptcp_subflow_tcp_sock(subflow))->rcv_tstamp);
  
  		if (subflow->stale_rcv_tstamp == rcv_tstamp)
  			return false;
  
  		mptcp_subflow_set_active(subflow);
  	}
  	return __mptcp_subflow_active(subflow);
  }
  
  /* implement the mptcp packet scheduler;
   * returns the subflow that will transmit the next DSS
   * additionally updates the rtx timeout
   */
  static struct sock *mptcp_subflow_get_send(struct mptcp_sock *msk)
  {
  	struct subflow_send_info send_info[2];
  	struct mptcp_subflow_context *subflow;
  	struct sock *sk = (struct sock *)msk;
  	int i, nr_active = 0;
  	struct sock *ssk;
  	long tout = 0;
  	u64 ratio;
  	u32 pace;
  
  	sock_owned_by_me(sk);
  
  	if (__mptcp_check_fallback(msk)) {
  		if (!msk->first)
  			return NULL;
  		return sk_stream_memory_free(msk->first) ? msk->first : NULL;
  	}
  
  	/* re-use last subflow, if the burst allow that */
  	if (msk->last_snd && msk->snd_burst > 0 &&
  	    sk_stream_memory_free(msk->last_snd) &&
  	    mptcp_subflow_active(mptcp_subflow_ctx(msk->last_snd))) {
  		mptcp_set_timeout(sk);
  		return msk->last_snd;
  	}
  
  	/* pick the subflow with the lower wmem/wspace ratio */
  	for (i = 0; i < 2; ++i) {
  		send_info[i].ssk = NULL;
  		send_info[i].ratio = -1;
  	}
  	mptcp_for_each_subflow(msk, subflow) {
  		trace_mptcp_subflow_get_send(subflow);
  		ssk =  mptcp_subflow_tcp_sock(subflow);
  		if (!mptcp_subflow_active(subflow))
  			continue;
  
  		tout = max(tout, mptcp_timeout_from_subflow(subflow));
  		nr_active += !subflow->backup;
  		if (!sk_stream_memory_free(subflow->tcp_sock) || !tcp_sk(ssk)->snd_wnd)
  			continue;
  
  		pace = READ_ONCE(ssk->sk_pacing_rate);
  		if (!pace)
  			continue;
  
  		ratio = div_u64((u64)READ_ONCE(ssk->sk_wmem_queued) << 32,
  				pace);
  		if (ratio < send_info[subflow->backup].ratio) {
  			send_info[subflow->backup].ssk = ssk;
  			send_info[subflow->backup].ratio = ratio;
  		}
  	}
  	__mptcp_set_timeout(sk, tout);
  
  	/* pick the best backup if no other subflow is active */
  	if (!nr_active)
  		send_info[0].ssk = send_info[1].ssk;
  
  	if (send_info[0].ssk) {
  		msk->last_snd = send_info[0].ssk;
  		msk->snd_burst = min_t(int, MPTCP_SEND_BURST_SIZE,
  				       tcp_sk(msk->last_snd)->snd_wnd);
  		return msk->last_snd;
  	}
  
  	return NULL;
  }
  
  static void mptcp_push_release(struct sock *ssk, struct mptcp_sendmsg_info *info)
  {
  	tcp_push(ssk, 0, info->mss_now, tcp_sk(ssk)->nonagle, info->size_goal);
  	release_sock(ssk);
  }
  
  static void mptcp_update_post_push(struct mptcp_sock *msk,
  				   struct mptcp_data_frag *dfrag,
  				   u32 sent)
  {
  	u64 snd_nxt_new = dfrag->data_seq;
  
  	dfrag->already_sent += sent;
  
  	msk->snd_burst -= sent;
  
  	snd_nxt_new += dfrag->already_sent;
  
  	/* snd_nxt_new can be smaller than snd_nxt in case mptcp
  	 * is recovering after a failover. In that event, this re-sends
  	 * old segments.
  	 *
  	 * Thus compute snd_nxt_new candidate based on
  	 * the dfrag->data_seq that was sent and the data
  	 * that has been handed to the subflow for transmission
  	 * and skip update in case it was old dfrag.
  	 */
  	if (likely(after64(snd_nxt_new, msk->snd_nxt)))
  		msk->snd_nxt = snd_nxt_new;
  }
  
  static void mptcp_check_and_set_pending(struct sock *sk)
  {
  	if (mptcp_send_head(sk) &&
  	    !test_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->flags))
  		set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->flags);
  }
  
  void __mptcp_push_pending(struct sock *sk, unsigned int flags)
  {
  	struct sock *prev_ssk = NULL, *ssk = NULL;
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	struct mptcp_sendmsg_info info = {
  				.flags = flags,
  	};
  	struct mptcp_data_frag *dfrag;
  	int len, copied = 0;
  
  	while ((dfrag = mptcp_send_head(sk))) {
  		info.sent = dfrag->already_sent;
  		info.limit = dfrag->data_len;
  		len = dfrag->data_len - dfrag->already_sent;
  		while (len > 0) {
  			int ret = 0;
  
  			prev_ssk = ssk;
  			mptcp_flush_join_list(msk);
  			ssk = mptcp_subflow_get_send(msk);
  
  			/* First check. If the ssk has changed since
  			 * the last round, release prev_ssk
  			 */
  			if (ssk != prev_ssk && prev_ssk)
  				mptcp_push_release(prev_ssk, &info);
  			if (!ssk)
  				goto out;
  
  			/* Need to lock the new subflow only if different
  			 * from the previous one, otherwise we are still
  			 * helding the relevant lock
  			 */
  			if (ssk != prev_ssk)
  				lock_sock(ssk);
  
  			ret = mptcp_sendmsg_frag(sk, ssk, dfrag, &info);
  			if (ret <= 0) {
  				mptcp_push_release(ssk, &info);
  				goto out;
  			}
  
  			info.sent += ret;
  			copied += ret;
  			len -= ret;
  
  			mptcp_update_post_push(msk, dfrag, ret);
  		}
  		WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
  	}
  
  	/* at this point we held the socket lock for the last subflow we used */
  	if (ssk)
  		mptcp_push_release(ssk, &info);
  
  out:
  	/* ensure the rtx timer is running */
  	if (!mptcp_timer_pending(sk))
  		mptcp_reset_timer(sk);
  	if (copied)
  		__mptcp_check_send_data_fin(sk);
  }
  
  static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	struct mptcp_sendmsg_info info = {
  		.data_lock_held = true,
  	};
  	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))) {
  		info.sent = dfrag->already_sent;
  		info.limit = dfrag->data_len;
  		len = dfrag->data_len - dfrag->already_sent;
  		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;
  			}
  
  			ret = mptcp_sendmsg_frag(sk, ssk, dfrag, &info);
  			if (ret <= 0)
  				goto out;
  
  			info.sent += ret;
  			copied += ret;
  			len -= ret;
  			first = false;
  
  			mptcp_update_post_push(msk, dfrag, ret);
  		}
  		WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
  	}
  
  out:
  	/* __mptcp_alloc_tx_skb could have released some wmem and we are
  	 * not going to flush it via release_sock()
  	 */
  	if (copied) {
  		tcp_push(ssk, 0, info.mss_now, tcp_sk(ssk)->nonagle,
  			 info.size_goal);
  		if (!mptcp_timer_pending(sk))
  			mptcp_reset_timer(sk);
  
  		if (msk->snd_data_fin_enable &&
  		    msk->snd_nxt + 1 == msk->write_seq)
  			mptcp_schedule_work(sk);
  	}
  }
  
  static void mptcp_set_nospace(struct sock *sk)
  {
  	/* enable autotune */
  	set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
  
  	/* will be cleared on avail space */
  	set_bit(MPTCP_NOSPACE, &mptcp_sk(sk)->flags);
  }
  
  static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	struct page_frag *pfrag;
  	size_t copied = 0;
  	int ret = 0;
  	long timeo;
  
  	/* we don't support FASTOPEN yet */
  	if (msg->msg_flags & MSG_FASTOPEN)
  		return -EOPNOTSUPP;
  
  	/* silently ignore everything else */
  	msg->msg_flags &= MSG_MORE | MSG_DONTWAIT | MSG_NOSIGNAL;
  
  	lock_sock(sk);
  
  	timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
  
  	if ((1 << sk->sk_state) & ~(TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)) {
  		ret = sk_stream_wait_connect(sk, &timeo);
  		if (ret)
  			goto out;
  	}
  
  	pfrag = sk_page_frag(sk);
  
  	while (msg_data_left(msg)) {
  		int total_ts, frag_truesize = 0;
  		struct mptcp_data_frag *dfrag;
  		bool dfrag_collapsed;
  		size_t psize, offset;
  
  		if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN)) {
  			ret = -EPIPE;
  			goto out;
  		}
  
  		/* reuse tail pfrag, if possible, or carve a new one from the
  		 * page allocator
  		 */
  		dfrag = mptcp_pending_tail(sk);
  		dfrag_collapsed = mptcp_frag_can_collapse_to(msk, pfrag, dfrag);
  		if (!dfrag_collapsed) {
  			if (!sk_stream_memory_free(sk))
  				goto wait_for_memory;
  
  			if (!mptcp_page_frag_refill(sk, pfrag))
  				goto wait_for_memory;
  
  			dfrag = mptcp_carve_data_frag(msk, pfrag, pfrag->offset);
  			frag_truesize = dfrag->overhead;
  		}
  
  		/* we do not bound vs wspace, to allow a single packet.
  		 * memory accounting will prevent execessive memory usage
  		 * anyway
  		 */
  		offset = dfrag->offset + dfrag->data_len;
  		psize = pfrag->size - offset;
  		psize = min_t(size_t, psize, msg_data_left(msg));
  		total_ts = psize + frag_truesize;
  
  		if (!sk_wmem_schedule(sk, total_ts))
  			goto wait_for_memory;
  
  		if (copy_page_from_iter(dfrag->page, offset, psize,
  					&msg->msg_iter) != psize) {
  			ret = -EFAULT;
  			goto out;
  		}
  
  		/* data successfully copied into the write queue */
  		sk->sk_forward_alloc -= total_ts;
  		copied += psize;
  		dfrag->data_len += psize;
  		frag_truesize += psize;
  		pfrag->offset += frag_truesize;
  		WRITE_ONCE(msk->write_seq, msk->write_seq + psize);
  
  		/* charge data on mptcp pending queue to the msk socket
  		 * Note: we charge such data both to sk and ssk
  		 */
  		sk_wmem_queued_add(sk, frag_truesize);
  		if (!dfrag_collapsed) {
  			get_page(dfrag->page);
  			list_add_tail(&dfrag->list, &msk->rtx_queue);
  			if (!msk->first_pending)
  				WRITE_ONCE(msk->first_pending, dfrag);
  		}
  		pr_debug("msk=%p dfrag at seq=%llu len=%u sent=%u new=%d", msk,
  			 dfrag->data_seq, dfrag->data_len, dfrag->already_sent,
  			 !dfrag_collapsed);
  
  		continue;
  
  wait_for_memory:
  		mptcp_set_nospace(sk);
  		__mptcp_push_pending(sk, msg->msg_flags);
  		ret = sk_stream_wait_memory(sk, &timeo);
  		if (ret)
  			goto out;
  	}
  
  	if (copied)
  		__mptcp_push_pending(sk, msg->msg_flags);
  
  out:
  	release_sock(sk);
  	return copied ? : ret;
  }
  
  static int __mptcp_recvmsg_mskq(struct mptcp_sock *msk,
  				struct msghdr *msg,
  				size_t len, int flags,
  				struct scm_timestamping_internal *tss,
  				int *cmsg_flags)
  {
  	struct sk_buff *skb, *tmp;
  	int copied = 0;
  
  	skb_queue_walk_safe(&msk->receive_queue, skb, tmp) {
  		u32 offset = MPTCP_SKB_CB(skb)->offset;
  		u32 data_len = skb->len - offset;
  		u32 count = min_t(size_t, len - copied, data_len);
  		int err;
  
  		if (!(flags & MSG_TRUNC)) {
  			err = skb_copy_datagram_msg(skb, offset, msg, count);
  			if (unlikely(err < 0)) {
  				if (!copied)
  					return err;
  				break;
  			}
  		}
  
  		if (MPTCP_SKB_CB(skb)->has_rxtstamp) {
  			tcp_update_recv_tstamps(skb, tss);
  			*cmsg_flags |= MPTCP_CMSG_TS;
  		}
  
  		copied += count;
  
  		if (count < data_len) {
  			if (!(flags & MSG_PEEK))
  				MPTCP_SKB_CB(skb)->offset += count;
  			break;
  		}
  
  		if (!(flags & MSG_PEEK)) {
  			/* we will bulk release the skb memory later */
  			skb->destructor = NULL;
  			WRITE_ONCE(msk->rmem_released, msk->rmem_released + skb->truesize);
  			__skb_unlink(skb, &msk->receive_queue);
  			__kfree_skb(skb);
  		}
  
  		if (copied >= len)
  			break;
  	}
  
  	return copied;
  }
  
  /* receive buffer autotuning.  See tcp_rcv_space_adjust for more information.
   *
   * Only difference: Use highest rtt estimate of the subflows in use.
   */
  static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied)
  {
  	struct mptcp_subflow_context *subflow;
  	struct sock *sk = (struct sock *)msk;
  	u32 time, advmss = 1;
  	u64 rtt_us, mstamp;
  
  	sock_owned_by_me(sk);
  
  	if (copied <= 0)
  		return;
  
  	msk->rcvq_space.copied += copied;
  
  	mstamp = div_u64(tcp_clock_ns(), NSEC_PER_USEC);
  	time = tcp_stamp_us_delta(mstamp, msk->rcvq_space.time);
  
  	rtt_us = msk->rcvq_space.rtt_us;
  	if (rtt_us && time < (rtt_us >> 3))
  		return;
  
  	rtt_us = 0;
  	mptcp_for_each_subflow(msk, subflow) {
  		const struct tcp_sock *tp;
  		u64 sf_rtt_us;
  		u32 sf_advmss;
  
  		tp = tcp_sk(mptcp_subflow_tcp_sock(subflow));
  
  		sf_rtt_us = READ_ONCE(tp->rcv_rtt_est.rtt_us);
  		sf_advmss = READ_ONCE(tp->advmss);
  
  		rtt_us = max(sf_rtt_us, rtt_us);
  		advmss = max(sf_advmss, advmss);
  	}
  
  	msk->rcvq_space.rtt_us = rtt_us;
  	if (time < (rtt_us >> 3) || rtt_us == 0)
  		return;
  
  	if (msk->rcvq_space.copied <= msk->rcvq_space.space)
  		goto new_measure;
  
  	if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf &&
  	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
  		int rcvmem, rcvbuf;
  		u64 rcvwin, grow;
  
  		rcvwin = ((u64)msk->rcvq_space.copied << 1) + 16 * advmss;
  
  		grow = rcvwin * (msk->rcvq_space.copied - msk->rcvq_space.space);
  
  		do_div(grow, msk->rcvq_space.space);
  		rcvwin += (grow << 1);
  
  		rcvmem = SKB_TRUESIZE(advmss + MAX_TCP_HEADER);
  		while (tcp_win_from_space(sk, rcvmem) < advmss)
  			rcvmem += 128;
  
  		do_div(rcvwin, advmss);
  		rcvbuf = min_t(u64, rcvwin * rcvmem,
  			       sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
  
  		if (rcvbuf > sk->sk_rcvbuf) {
  			u32 window_clamp;
  
  			window_clamp = tcp_win_from_space(sk, rcvbuf);
  			WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
  
  			/* Make subflows follow along.  If we do not do this, we
  			 * get drops at subflow level if skbs can't be moved to
  			 * the mptcp rx queue fast enough (announced rcv_win can
  			 * exceed ssk->sk_rcvbuf).
  			 */
  			mptcp_for_each_subflow(msk, subflow) {
  				struct sock *ssk;
  				bool slow;
  
  				ssk = mptcp_subflow_tcp_sock(subflow);
  				slow = lock_sock_fast(ssk);
  				WRITE_ONCE(ssk->sk_rcvbuf, rcvbuf);
  				tcp_sk(ssk)->window_clamp = window_clamp;
  				tcp_cleanup_rbuf(ssk, 1);
  				unlock_sock_fast(ssk, slow);
  			}
  		}
  	}
  
  	msk->rcvq_space.space = msk->rcvq_space.copied;
  new_measure:
  	msk->rcvq_space.copied = 0;
  	msk->rcvq_space.time = mstamp;
  }
  
  static void __mptcp_update_rmem(struct sock *sk)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  
  	if (!msk->rmem_released)
  		return;
  
  	atomic_sub(msk->rmem_released, &sk->sk_rmem_alloc);
  	mptcp_rmem_uncharge(sk, msk->rmem_released);
  	WRITE_ONCE(msk->rmem_released, 0);
  }
  
  static void __mptcp_splice_receive_queue(struct sock *sk)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  
  	skb_queue_splice_tail_init(&sk->sk_receive_queue, &msk->receive_queue);
  }
  
  static bool __mptcp_move_skbs(struct mptcp_sock *msk)
  {
  	struct sock *sk = (struct sock *)msk;
  	unsigned int moved = 0;
  	bool ret, done;
  
  	mptcp_flush_join_list(msk);
  	do {
  		struct sock *ssk = mptcp_subflow_recv_lookup(msk);
  		bool slowpath;
  
  		/* we can have data pending in the subflows only if the msk
  		 * receive buffer was full at subflow_data_ready() time,
  		 * that is an unlikely slow path.
  		 */
  		if (likely(!ssk))
  			break;
  
  		slowpath = lock_sock_fast(ssk);
  		mptcp_data_lock(sk);
  		__mptcp_update_rmem(sk);
  		done = __mptcp_move_skbs_from_subflow(msk, ssk, &moved);
  		mptcp_data_unlock(sk);
  
  		if (unlikely(ssk->sk_err))
  			__mptcp_error_report(sk);
  		unlock_sock_fast(ssk, slowpath);
  	} while (!done);
  
  	/* acquire the data lock only if some input data is pending */
  	ret = moved > 0;
  	if (!RB_EMPTY_ROOT(&msk->out_of_order_queue) ||
  	    !skb_queue_empty_lockless(&sk->sk_receive_queue)) {
  		mptcp_data_lock(sk);
  		__mptcp_update_rmem(sk);
  		ret |= __mptcp_ofo_queue(msk);
  		__mptcp_splice_receive_queue(sk);
  		mptcp_data_unlock(sk);
  	}
  	if (ret)
  		mptcp_check_data_fin((struct sock *)msk);
  	return !skb_queue_empty(&msk->receive_queue);
  }
  
  static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
  			 int nonblock, int flags, int *addr_len)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	struct scm_timestamping_internal tss;
  	int copied = 0, cmsg_flags = 0;
  	int target;
  	long timeo;
  
  	/* MSG_ERRQUEUE is really a no-op till we support IP_RECVERR */
  	if (unlikely(flags & MSG_ERRQUEUE))
  		return inet_recv_error(sk, msg, len, addr_len);
  
  	lock_sock(sk);
  	if (unlikely(sk->sk_state == TCP_LISTEN)) {
  		copied = -ENOTCONN;
  		goto out_err;
  	}
  
  	timeo = sock_rcvtimeo(sk, nonblock);
  
  	len = min_t(size_t, len, INT_MAX);
  	target = sock_rcvlowat(sk, flags & MSG_WAITALL, len);
  
  	while (copied < len) {
  		int bytes_read;
  
  		bytes_read = __mptcp_recvmsg_mskq(msk, msg, len - copied, flags, &tss, &cmsg_flags);
  		if (unlikely(bytes_read < 0)) {
  			if (!copied)
  				copied = bytes_read;
  			goto out_err;
  		}
  
  		copied += bytes_read;
  
  		/* be sure to advertise window change */
  		mptcp_cleanup_rbuf(msk);
  
  		if (skb_queue_empty(&msk->receive_queue) && __mptcp_move_skbs(msk))
  			continue;
  
  		/* only the master socket status is relevant here. The exit
  		 * conditions mirror closely tcp_recvmsg()
  		 */
  		if (copied >= target)
  			break;
  
  		if (copied) {
  			if (sk->sk_err ||
  			    sk->sk_state == TCP_CLOSE ||
  			    (sk->sk_shutdown & RCV_SHUTDOWN) ||
  			    !timeo ||
  			    signal_pending(current))
  				break;
  		} else {
  			if (sk->sk_err) {
  				copied = sock_error(sk);
  				break;
  			}
  
  			if (test_and_clear_bit(MPTCP_WORK_EOF, &msk->flags))
  				mptcp_check_for_eof(msk);
  
  			if (sk->sk_shutdown & RCV_SHUTDOWN) {
  				/* race breaker: the shutdown could be after the
  				 * previous receive queue check
  				 */
  				if (__mptcp_move_skbs(msk))
  					continue;
  				break;
  			}
  
  			if (sk->sk_state == TCP_CLOSE) {
  				copied = -ENOTCONN;
  				break;
  			}
  
  			if (!timeo) {
  				copied = -EAGAIN;
  				break;
  			}
  
  			if (signal_pending(current)) {
  				copied = sock_intr_errno(timeo);
  				break;
  			}
  		}
  
  		pr_debug("block timeout %ld", timeo);
  		sk_wait_data(sk, &timeo, NULL);
  	}
  
  out_err:
  	if (cmsg_flags && copied >= 0) {
  		if (cmsg_flags & MPTCP_CMSG_TS)
  			tcp_recv_timestamp(msg, sk, &tss);
  	}
  
  	pr_debug("msk=%p rx queue empty=%d:%d copied=%d",
  		 msk, skb_queue_empty_lockless(&sk->sk_receive_queue),
  		 skb_queue_empty(&msk->receive_queue), copied);
  	if (!(flags & MSG_PEEK))
  		mptcp_rcv_space_adjust(msk, copied);
  
  	release_sock(sk);
  	return copied;
  }
  
  static void mptcp_retransmit_timer(struct timer_list *t)
  {
  	struct inet_connection_sock *icsk = from_timer(icsk, t,
  						       icsk_retransmit_timer);
  	struct sock *sk = &icsk->icsk_inet.sk;
  	struct mptcp_sock *msk = mptcp_sk(sk);
  
  	bh_lock_sock(sk);
  	if (!sock_owned_by_user(sk)) {
  		/* we need a process context to retransmit */
  		if (!test_and_set_bit(MPTCP_WORK_RTX, &msk->flags))
  			mptcp_schedule_work(sk);
  	} else {
  		/* delegate our work to tcp_release_cb() */
  		set_bit(MPTCP_RETRANSMIT, &msk->flags);
  	}
  	bh_unlock_sock(sk);
  	sock_put(sk);
  }
  
  static void mptcp_timeout_timer(struct timer_list *t)
  {
  	struct sock *sk = from_timer(sk, t, sk_timer);
  
  	mptcp_schedule_work(sk);
  	sock_put(sk);
  }
  
  /* Find an idle subflow.  Return NULL if there is unacked data at tcp
   * level.
   *
   * A backup subflow is returned only if that is the only kind available.
   */
  static struct sock *mptcp_subflow_get_retrans(struct mptcp_sock *msk)
  {
  	struct sock *backup = NULL, *pick = NULL;
  	struct mptcp_subflow_context *subflow;
  	int min_stale_count = INT_MAX;
  
  	sock_owned_by_me((const struct sock *)msk);
  
  	if (__mptcp_check_fallback(msk))
  		return NULL;
  
  	mptcp_for_each_subflow(msk, subflow) {
  		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
  
  		if (!__mptcp_subflow_active(subflow))
  			continue;
  
  		/* still data outstanding at TCP level? skip this */
  		if (!tcp_rtx_and_write_queues_empty(ssk)) {
  			mptcp_pm_subflow_chk_stale(msk, ssk);
  			min_stale_count = min_t(int, min_stale_count, subflow->stale_count);
  			continue;
  		}
  
  		if (subflow->backup) {
  			if (!backup)
  				backup = ssk;
  			continue;
  		}
  
  		if (!pick)
  			pick = ssk;
  	}
  
  	if (pick)
  		return pick;
  
  	/* use backup only if there are no progresses anywhere */
  	return min_stale_count > 1 ? backup : NULL;
  }
  
  static void mptcp_dispose_initial_subflow(struct mptcp_sock *msk)
  {
  	if (msk->subflow) {
  		iput(SOCK_INODE(msk->subflow));
  		msk->subflow = NULL;
  	}
  }
  
  bool __mptcp_retransmit_pending_data(struct sock *sk)
  {
  	struct mptcp_data_frag *cur, *rtx_head;
  	struct mptcp_sock *msk = mptcp_sk(sk);
  
  	if (__mptcp_check_fallback(mptcp_sk(sk)))
  		return false;
  
  	if (tcp_rtx_and_write_queues_empty(sk))
  		return false;
  
  	/* the closing socket has some data untransmitted and/or unacked:
  	 * some data in the mptcp rtx queue has not really xmitted yet.
  	 * keep it simple and re-inject the whole mptcp level rtx queue
  	 */
  	mptcp_data_lock(sk);
  	__mptcp_clean_una_wakeup(sk);
  	rtx_head = mptcp_rtx_head(sk);
  	if (!rtx_head) {
  		mptcp_data_unlock(sk);
  		return false;
  	}
  
  	msk->recovery_snd_nxt = msk->snd_nxt;
  	msk->recovery = true;
  	mptcp_data_unlock(sk);
  
  	msk->first_pending = rtx_head;
  	msk->snd_burst = 0;
  
  	/* be sure to clear the "sent status" on all re-injected fragments */
  	list_for_each_entry(cur, &msk->rtx_queue, list) {
  		if (!cur->already_sent)
  			break;
  		cur->already_sent = 0;
  	}
  
  	return true;
  }
  
  /* subflow sockets can be either outgoing (connect) or incoming
   * (accept).
   *
   * Outgoing subflows use in-kernel sockets.
   * Incoming subflows do not have their own 'struct socket' allocated,
   * so we need to use tcp_close() after detaching them from the mptcp
   * parent socket.
   */
  static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
  			      struct mptcp_subflow_context *subflow)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	bool need_push;
  
  	list_del(&subflow->node);
  
  	lock_sock_nested(ssk, SINGLE_DEPTH_NESTING);
  
  	/* if we are invoked by the msk cleanup code, the subflow is
  	 * already orphaned
  	 */
  	if (ssk->sk_socket)
  		sock_orphan(ssk);
  
  	need_push = __mptcp_retransmit_pending_data(sk);
  	subflow->disposable = 1;
  
  	/* if ssk hit tcp_done(), tcp_cleanup_ulp() cleared the related ops
  	 * the ssk has been already destroyed, we just need to release the
  	 * reference owned by msk;
  	 */
  	if (!inet_csk(ssk)->icsk_ulp_ops) {
  		kfree_rcu(subflow, rcu);
  	} else {
  		/* otherwise tcp will dispose of the ssk and subflow ctx */
  		__tcp_close(ssk, 0);
  
  		/* close acquired an extra ref */
  		__sock_put(ssk);
  	}
  	release_sock(ssk);
  
  	sock_put(ssk);
  
  	if (ssk == msk->last_snd)
  		msk->last_snd = NULL;
  
  	if (ssk == msk->first)
  		msk->first = NULL;
  
  	if (msk->subflow && ssk == msk->subflow->sk)
  		mptcp_dispose_initial_subflow(msk);
  
  	if (need_push)
  		__mptcp_push_pending(sk, 0);
  }
  
  void mptcp_close_ssk(struct sock *sk, struct sock *ssk,
  		     struct mptcp_subflow_context *subflow)
  {
  	if (sk->sk_state == TCP_ESTABLISHED)
  		mptcp_event(MPTCP_EVENT_SUB_CLOSED, mptcp_sk(sk), ssk, GFP_KERNEL);
  	__mptcp_close_ssk(sk, ssk, subflow);
  }
  
  static unsigned int mptcp_sync_mss(struct sock *sk, u32 pmtu)
  {
  	return 0;
  }
  
  static void __mptcp_close_subflow(struct mptcp_sock *msk)
  {
  	struct mptcp_subflow_context *subflow, *tmp;
  
  	might_sleep();
  
  	list_for_each_entry_safe(subflow, tmp, &msk->conn_list, node) {
  		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
  
  		if (inet_sk_state_load(ssk) != TCP_CLOSE)
  			continue;
  
  		/* 'subflow_data_ready' will re-sched once rx queue is empty */
  		if (!skb_queue_empty_lockless(&ssk->sk_receive_queue))
  			continue;
  
  		mptcp_close_ssk((struct sock *)msk, ssk, subflow);
  	}
  }
  
  static bool mptcp_check_close_timeout(const struct sock *sk)
  {
  	s32 delta = tcp_jiffies32 - inet_csk(sk)->icsk_mtup.probe_timestamp;
  	struct mptcp_subflow_context *subflow;
  
  	if (delta >= TCP_TIMEWAIT_LEN)
  		return true;
  
  	/* if all subflows are in closed status don't bother with additional
  	 * timeout
  	 */
  	mptcp_for_each_subflow(mptcp_sk(sk), subflow) {
  		if (inet_sk_state_load(mptcp_subflow_tcp_sock(subflow)) !=
  		    TCP_CLOSE)
  			return false;
  	}
  	return true;
  }
  
  static void mptcp_check_fastclose(struct mptcp_sock *msk)
  {
  	struct mptcp_subflow_context *subflow, *tmp;
  	struct sock *sk = &msk->sk.icsk_inet.sk;
  
  	if (likely(!READ_ONCE(msk->rcv_fastclose)))
  		return;
  
  	mptcp_token_destroy(msk);
  
  	list_for_each_entry_safe(subflow, tmp, &msk->conn_list, node) {
  		struct sock *tcp_sk = mptcp_subflow_tcp_sock(subflow);
  		bool slow;
  
  		slow = lock_sock_fast(tcp_sk);
  		if (tcp_sk->sk_state != TCP_CLOSE) {
  			tcp_send_active_reset(tcp_sk, GFP_ATOMIC);
  			tcp_set_state(tcp_sk, TCP_CLOSE);
  		}
  		unlock_sock_fast(tcp_sk, slow);
  	}
  
  	inet_sk_state_store(sk, TCP_CLOSE);
  	sk->sk_shutdown = SHUTDOWN_MASK;
  	smp_mb__before_atomic(); /* SHUTDOWN must be visible first */
  	set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags);
  
  	mptcp_close_wake_up(sk);
  }
  
  static void __mptcp_retrans(struct sock *sk)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	struct mptcp_sendmsg_info info = {};
  	struct mptcp_data_frag *dfrag;
  	size_t copied = 0;
  	struct sock *ssk;
  	int ret;
  
  	mptcp_clean_una_wakeup(sk);
  
  	/* first check ssk: need to kick "stale" logic */
  	ssk = mptcp_subflow_get_retrans(msk);
  	dfrag = mptcp_rtx_head(sk);
  	if (!dfrag) {
  		if (mptcp_data_fin_enabled(msk)) {
  			struct inet_connection_sock *icsk = inet_csk(sk);
  
  			icsk->icsk_retransmits++;
  			mptcp_set_datafin_timeout(sk);
  			mptcp_send_ack(msk);
  
  			goto reset_timer;
  		}
  
  		if (!mptcp_send_head(sk))
  			return;
  
  		goto reset_timer;
  	}
  
  	if (!ssk)
  		goto reset_timer;
  
  	lock_sock(ssk);
  
  	/* limit retransmission to the bytes already sent on some subflows */
  	info.sent = 0;
  	info.limit = READ_ONCE(msk->csum_enabled) ? dfrag->data_len : dfrag->already_sent;
  	while (info.sent < info.limit) {
  		ret = mptcp_sendmsg_frag(sk, ssk, dfrag, &info);
  		if (ret <= 0)
  			break;
  
  		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_RETRANSSEGS);
  		copied += ret;
  		info.sent += ret;
  	}
  	if (copied) {
  		dfrag->already_sent = max(dfrag->already_sent, info.sent);
  		tcp_push(ssk, 0, info.mss_now, tcp_sk(ssk)->nonagle,
  			 info.size_goal);
  	}
  
  	release_sock(ssk);
  
  reset_timer:
  	mptcp_check_and_set_pending(sk);
  
  	if (!mptcp_timer_pending(sk))
  		mptcp_reset_timer(sk);
  }
  
  static void mptcp_worker(struct work_struct *work)
  {
  	struct mptcp_sock *msk = container_of(work, struct mptcp_sock, work);
  	struct sock *sk = &msk->sk.icsk_inet.sk;
  	int state;
  
  	lock_sock(sk);
  	state = sk->sk_state;
  	if (unlikely(state == TCP_CLOSE))
  		goto unlock;
  
  	mptcp_check_data_fin_ack(sk);
  	mptcp_flush_join_list(msk);
  
  	mptcp_check_fastclose(msk);
  
  	if (msk->pm.status)
  		mptcp_pm_nl_work(msk);
  
  	if (test_and_clear_bit(MPTCP_WORK_EOF, &msk->flags))
  		mptcp_check_for_eof(msk);
  
  	__mptcp_check_send_data_fin(sk);
  	mptcp_check_data_fin(sk);
  
  	/* There is no point in keeping around an orphaned sk timedout or
  	 * closed, but we need the msk around to reply to incoming DATA_FIN,
  	 * even if it is orphaned and in FIN_WAIT2 state
  	 */
  	if (sock_flag(sk, SOCK_DEAD) &&
  	    (mptcp_check_close_timeout(sk) || sk->sk_state == TCP_CLOSE)) {
  		inet_sk_state_store(sk, TCP_CLOSE);
  		__mptcp_destroy_sock(sk);
  		goto unlock;
  	}
  
  	if (test_and_clear_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags))
  		__mptcp_close_subflow(msk);
  
  	if (test_and_clear_bit(MPTCP_WORK_RTX, &msk->flags))
  		__mptcp_retrans(sk);
  
  unlock:
  	release_sock(sk);
  	sock_put(sk);
  }
  
  static int __mptcp_init_sock(struct sock *sk)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  
  	spin_lock_init(&msk->join_list_lock);
  
  	INIT_LIST_HEAD(&msk->conn_list);
  	INIT_LIST_HEAD(&msk->join_list);
  	INIT_LIST_HEAD(&msk->rtx_queue);
  	INIT_WORK(&msk->work, mptcp_worker);
  	__skb_queue_head_init(&msk->receive_queue);
  	msk->out_of_order_queue = RB_ROOT;
  	msk->first_pending = NULL;
  	msk->rmem_fwd_alloc = 0;
  	WRITE_ONCE(msk->rmem_released, 0);
  	msk->timer_ival = TCP_RTO_MIN;
  
  	msk->first = NULL;
  	inet_csk(sk)->icsk_sync_mss = mptcp_sync_mss;
  	WRITE_ONCE(msk->csum_enabled, mptcp_is_checksum_enabled(sock_net(sk)));
  	msk->recovery = false;
  
  	mptcp_pm_data_init(msk);
  
  	/* re-use the csk retrans timer for MPTCP-level retrans */
  	timer_setup(&msk->sk.icsk_retransmit_timer, mptcp_retransmit_timer, 0);
  	timer_setup(&sk->sk_timer, mptcp_timeout_timer, 0);
  
  	return 0;
  }
  
  static int mptcp_init_sock(struct sock *sk)
  {
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	struct net *net = sock_net(sk);
  	int ret;
  
  	ret = __mptcp_init_sock(sk);
  	if (ret)
  		return ret;
  
  	if (!mptcp_is_enabled(net))
  		return -ENOPROTOOPT;
  
  	if (unlikely(!net->mib.mptcp_statistics) && !mptcp_mib_alloc(net))
  		return -ENOMEM;
  
  	ret = __mptcp_socket_create(mptcp_sk(sk));
  	if (ret)
  		return ret;
  
  	/* fetch the ca name; do it outside __mptcp_init_sock(), so that clone will
  	 * propagate the correct value
  	 */
  	tcp_assign_congestion_control(sk);
  	strcpy(mptcp_sk(sk)->ca_name, icsk->icsk_ca_ops->name);
  
  	/* no need to keep a reference to the ops, the name will suffice */
  	tcp_cleanup_congestion_control(sk);
  	icsk->icsk_ca_ops = NULL;
  
  	sk_sockets_allocated_inc(sk);
  	sk->sk_rcvbuf = sock_net(sk)->ipv4.sysctl_tcp_rmem[1];
  	sk->sk_sndbuf = sock_net(sk)->ipv4.sysctl_tcp_wmem[1];
  
  	return 0;
  }
  
  static void __mptcp_clear_xmit(struct sock *sk)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	struct mptcp_data_frag *dtmp, *dfrag;
  
  	WRITE_ONCE(msk->first_pending, NULL);
  	list_for_each_entry_safe(dfrag, dtmp, &msk->rtx_queue, list)
  		dfrag_clear(sk, dfrag);
  }
  
  static void mptcp_cancel_work(struct sock *sk)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  
  	if (cancel_work_sync(&msk->work))
  		__sock_put(sk);
  }
  
  void mptcp_subflow_shutdown(struct sock *sk, struct sock *ssk, int how)
  {
  	lock_sock(ssk);
  
  	switch (ssk->sk_state) {
  	case TCP_LISTEN:
  		if (!(how & RCV_SHUTDOWN))
  			break;
  		fallthrough;
  	case TCP_SYN_SENT:
  		tcp_disconnect(ssk, O_NONBLOCK);
  		break;
  	default:
  		if (__mptcp_check_fallback(mptcp_sk(sk))) {
  			pr_debug("Fallback");
  			ssk->sk_shutdown |= how;
  			tcp_shutdown(ssk, how);
  		} else {
  			pr_debug("Sending DATA_FIN on subflow %p", ssk);
  			tcp_send_ack(ssk);
  			if (!mptcp_timer_pending(sk))
  				mptcp_reset_timer(sk);
  		}
  		break;
  	}
  
  	release_sock(ssk);
  }
  
  static const unsigned char new_state[16] = {
  	/* current state:     new state:      action:	*/
  	[0 /* (Invalid) */] = TCP_CLOSE,
  	[TCP_ESTABLISHED]   = TCP_FIN_WAIT1 | TCP_ACTION_FIN,
  	[TCP_SYN_SENT]      = TCP_CLOSE,
  	[TCP_SYN_RECV]      = TCP_FIN_WAIT1 | TCP_ACTION_FIN,
  	[TCP_FIN_WAIT1]     = TCP_FIN_WAIT1,
  	[TCP_FIN_WAIT2]     = TCP_FIN_WAIT2,
  	[TCP_TIME_WAIT]     = TCP_CLOSE,	/* should not happen ! */
  	[TCP_CLOSE]         = TCP_CLOSE,
  	[TCP_CLOSE_WAIT]    = TCP_LAST_ACK  | TCP_ACTION_FIN,
  	[TCP_LAST_ACK]      = TCP_LAST_ACK,
  	[TCP_LISTEN]        = TCP_CLOSE,
  	[TCP_CLOSING]       = TCP_CLOSING,
  	[TCP_NEW_SYN_RECV]  = TCP_CLOSE,	/* should not happen ! */
  };
  
  static int mptcp_close_state(struct sock *sk)
  {
  	int next = (int)new_state[sk->sk_state];
  	int ns = next & TCP_STATE_MASK;
  
  	inet_sk_state_store(sk, ns);
  
  	return next & TCP_ACTION_FIN;
  }
  
  static void __mptcp_check_send_data_fin(struct sock *sk)
  {
  	struct mptcp_subflow_context *subflow;
  	struct mptcp_sock *msk = mptcp_sk(sk);
  
  	pr_debug("msk=%p snd_data_fin_enable=%d pending=%d snd_nxt=%llu write_seq=%llu",
  		 msk, msk->snd_data_fin_enable, !!mptcp_send_head(sk),
  		 msk->snd_nxt, msk->write_seq);
  
  	/* we still need to enqueue subflows or not really shutting down,
  	 * skip this
  	 */
  	if (!msk->snd_data_fin_enable || msk->snd_nxt + 1 != msk->write_seq ||
  	    mptcp_send_head(sk))
  		return;
  
  	WRITE_ONCE(msk->snd_nxt, msk->write_seq);
  
  	/* fallback socket will not get data_fin/ack, can move to the next
  	 * state now
  	 */
  	if (__mptcp_check_fallback(msk)) {
  		if ((1 << sk->sk_state) & (TCPF_CLOSING | TCPF_LAST_ACK)) {
  			inet_sk_state_store(sk, TCP_CLOSE);
  			mptcp_close_wake_up(sk);
  		} else if (sk->sk_state == TCP_FIN_WAIT1) {
  			inet_sk_state_store(sk, TCP_FIN_WAIT2);
  		}
  	}
  
  	mptcp_flush_join_list(msk);
  	mptcp_for_each_subflow(msk, subflow) {
  		struct sock *tcp_sk = mptcp_subflow_tcp_sock(subflow);
  
  		mptcp_subflow_shutdown(sk, tcp_sk, SEND_SHUTDOWN);
  	}
  }
  
  static void __mptcp_wr_shutdown(struct sock *sk)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  
  	pr_debug("msk=%p snd_data_fin_enable=%d shutdown=%x state=%d pending=%d",
  		 msk, msk->snd_data_fin_enable, sk->sk_shutdown, sk->sk_state,
  		 !!mptcp_send_head(sk));
  
  	/* will be ignored by fallback sockets */
  	WRITE_ONCE(msk->write_seq, msk->write_seq + 1);
  	WRITE_ONCE(msk->snd_data_fin_enable, 1);
  
  	__mptcp_check_send_data_fin(sk);
  }
  
  static void __mptcp_destroy_sock(struct sock *sk)
  {
  	struct mptcp_subflow_context *subflow, *tmp;
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	LIST_HEAD(conn_list);
  
  	pr_debug("msk=%p", msk);
  
  	might_sleep();
  
  	/* be sure to always acquire the join list lock, to sync vs
  	 * mptcp_finish_join().
  	 */
  	spin_lock_bh(&msk->join_list_lock);
  	list_splice_tail_init(&msk->join_list, &msk->conn_list);
  	spin_unlock_bh(&msk->join_list_lock);
  	list_splice_init(&msk->conn_list, &conn_list);
  
  	sk_stop_timer(sk, &msk->sk.icsk_retransmit_timer);
  	sk_stop_timer(sk, &sk->sk_timer);
  	msk->pm.status = 0;
  
  	list_for_each_entry_safe(subflow, tmp, &conn_list, node) {
  		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
  		__mptcp_close_ssk(sk, ssk, subflow);
  	}
  
  	sk->sk_prot->destroy(sk);
  
  	WARN_ON_ONCE(msk->rmem_fwd_alloc);
  	WARN_ON_ONCE(msk->rmem_released);
  	sk_stream_kill_queues(sk);
  	xfrm_sk_free_policy(sk);
  
  	sk_refcnt_debug_release(sk);
  	mptcp_dispose_initial_subflow(msk);
  	sock_put(sk);
  }
  
  static void mptcp_close(struct sock *sk, long timeout)
  {
  	struct mptcp_subflow_context *subflow;
  	bool do_cancel_work = false;
  
  	lock_sock(sk);
  	sk->sk_shutdown = SHUTDOWN_MASK;
  
  	if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE)) {
  		inet_sk_state_store(sk, TCP_CLOSE);
  		goto cleanup;
  	}
  
  	if (mptcp_close_state(sk))
  		__mptcp_wr_shutdown(sk);
  
  	sk_stream_wait_close(sk, timeout);
  
  cleanup:
  	/* orphan all the subflows */
  	inet_csk(sk)->icsk_mtup.probe_timestamp = tcp_jiffies32;
  	mptcp_for_each_subflow(mptcp_sk(sk), subflow) {
  		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
  		bool slow = lock_sock_fast_nested(ssk);
  
  		sock_orphan(ssk);
  		unlock_sock_fast(ssk, slow);
  	}
  	sock_orphan(sk);
  
  	sock_hold(sk);
  	pr_debug("msk=%p state=%d", sk, sk->sk_state);
  	if (sk->sk_state == TCP_CLOSE) {
  		__mptcp_destroy_sock(sk);
  		do_cancel_work = true;
  	} else {
  		sk_reset_timer(sk, &sk->sk_timer, jiffies + TCP_TIMEWAIT_LEN);
  	}
  	release_sock(sk);
  	if (do_cancel_work)
  		mptcp_cancel_work(sk);
  
  	if (mptcp_sk(sk)->token)
  		mptcp_event(MPTCP_EVENT_CLOSED, mptcp_sk(sk), NULL, GFP_KERNEL);
  
  	sock_put(sk);
  }
  
  static void mptcp_copy_inaddrs(struct sock *msk, const struct sock *ssk)
  {
  #if IS_ENABLED(CONFIG_MPTCP_IPV6)
  	const struct ipv6_pinfo *ssk6 = inet6_sk(ssk);
  	struct ipv6_pinfo *msk6 = inet6_sk(msk);
  
  	msk->sk_v6_daddr = ssk->sk_v6_daddr;
  	msk->sk_v6_rcv_saddr = ssk->sk_v6_rcv_saddr;
  
  	if (msk6 && ssk6) {
  		msk6->saddr = ssk6->saddr;
  		msk6->flow_label = ssk6->flow_label;
  	}
  #endif
  
  	inet_sk(msk)->inet_num = inet_sk(ssk)->inet_num;
  	inet_sk(msk)->inet_dport = inet_sk(ssk)->inet_dport;
  	inet_sk(msk)->inet_sport = inet_sk(ssk)->inet_sport;
  	inet_sk(msk)->inet_daddr = inet_sk(ssk)->inet_daddr;
  	inet_sk(msk)->inet_saddr = inet_sk(ssk)->inet_saddr;
  	inet_sk(msk)->inet_rcv_saddr = inet_sk(ssk)->inet_rcv_saddr;
  }
  
  static int mptcp_disconnect(struct sock *sk, int flags)
  {
  	struct mptcp_subflow_context *subflow;
  	struct mptcp_sock *msk = mptcp_sk(sk);
  
  	mptcp_do_flush_join_list(msk);
  
  	mptcp_for_each_subflow(msk, subflow) {
  		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
  
  		lock_sock(ssk);
  		tcp_disconnect(ssk, flags);
  		release_sock(ssk);
  	}
  	return 0;
  }
  
  #if IS_ENABLED(CONFIG_MPTCP_IPV6)
  static struct ipv6_pinfo *mptcp_inet6_sk(const struct sock *sk)
  {
  	unsigned int offset = sizeof(struct mptcp6_sock) - sizeof(struct ipv6_pinfo);
  
  	return (struct ipv6_pinfo *)(((u8 *)sk) + offset);
  }
  #endif
  
  struct sock *mptcp_sk_clone(const struct sock *sk,
  			    const struct mptcp_options_received *mp_opt,
  			    struct request_sock *req)
  {
  	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
  	struct sock *nsk = sk_clone_lock(sk, GFP_ATOMIC);
  	struct mptcp_sock *msk;
  	u64 ack_seq;
  
  	if (!nsk)
  		return NULL;
  
  #if IS_ENABLED(CONFIG_MPTCP_IPV6)
  	if (nsk->sk_family == AF_INET6)
  		inet_sk(nsk)->pinet6 = mptcp_inet6_sk(nsk);
  #endif
  
  	__mptcp_init_sock(nsk);
  
  	msk = mptcp_sk(nsk);
  	msk->local_key = subflow_req->local_key;
  	msk->token = subflow_req->token;
  	msk->subflow = NULL;
  	WRITE_ONCE(msk->fully_established, false);
  	if (mp_opt->suboptions & OPTION_MPTCP_CSUMREQD)
  		WRITE_ONCE(msk->csum_enabled, true);
  
  	msk->write_seq = subflow_req->idsn + 1;
  	msk->snd_nxt = msk->write_seq;
  	msk->snd_una = msk->write_seq;
  	msk->wnd_end = msk->snd_nxt + req->rsk_rcv_wnd;
  	msk->setsockopt_seq = mptcp_sk(sk)->setsockopt_seq;
  
  	if (mp_opt->suboptions & OPTIONS_MPTCP_MPC) {
  		msk->can_ack = true;
  		msk->remote_key = mp_opt->sndr_key;
  		mptcp_crypto_key_sha(msk->remote_key, NULL, &ack_seq);
  		ack_seq++;
  		WRITE_ONCE(msk->ack_seq, ack_seq);
  		WRITE_ONCE(msk->rcv_wnd_sent, ack_seq);
  	}
  
  	sock_reset_flag(nsk, SOCK_RCU_FREE);
  	/* will be fully established after successful MPC subflow creation */
  	inet_sk_state_store(nsk, TCP_SYN_RECV);
  
  	security_inet_csk_clone(nsk, req);
  	bh_unlock_sock(nsk);
  
  	/* keep a single reference */
  	__sock_put(nsk);
  	return nsk;
  }
  
  void mptcp_rcv_space_init(struct mptcp_sock *msk, const struct sock *ssk)
  {
  	const struct tcp_sock *tp = tcp_sk(ssk);
  
  	msk->rcvq_space.copied = 0;
  	msk->rcvq_space.rtt_us = 0;
  
  	msk->rcvq_space.time = tp->tcp_mstamp;
  
  	/* initial rcv_space offering made to peer */
  	msk->rcvq_space.space = min_t(u32, tp->rcv_wnd,
  				      TCP_INIT_CWND * tp->advmss);
  	if (msk->rcvq_space.space == 0)
  		msk->rcvq_space.space = TCP_INIT_CWND * TCP_MSS_DEFAULT;
  
  	WRITE_ONCE(msk->wnd_end, msk->snd_nxt + tcp_sk(ssk)->snd_wnd);
  }
  
  static struct sock *mptcp_accept(struct sock *sk, int flags, int *err,
  				 bool kern)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	struct socket *listener;
  	struct sock *newsk;
  
  	listener = __mptcp_nmpc_socket(msk);
  	if (WARN_ON_ONCE(!listener)) {
  		*err = -EINVAL;
  		return NULL;
  	}
  
  	pr_debug("msk=%p, listener=%p", msk, mptcp_subflow_ctx(listener->sk));
  	newsk = inet_csk_accept(listener->sk, flags, err, kern);
  	if (!newsk)
  		return NULL;
  
  	pr_debug("msk=%p, subflow is mptcp=%d", msk, sk_is_mptcp(newsk));
  	if (sk_is_mptcp(newsk)) {
  		struct mptcp_subflow_context *subflow;
  		struct sock *new_mptcp_sock;
  
  		subflow = mptcp_subflow_ctx(newsk);
  		new_mptcp_sock = subflow->conn;
  
  		/* is_mptcp should be false if subflow->conn is missing, see
  		 * subflow_syn_recv_sock()
  		 */
  		if (WARN_ON_ONCE(!new_mptcp_sock)) {
  			tcp_sk(newsk)->is_mptcp = 0;
  			return newsk;
  		}
  
  		/* acquire the 2nd reference for the owning socket */
  		sock_hold(new_mptcp_sock);
  		newsk = new_mptcp_sock;
  		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPCAPABLEPASSIVEACK);
  	} else {
  		MPTCP_INC_STATS(sock_net(sk),
  				MPTCP_MIB_MPCAPABLEPASSIVEFALLBACK);
  	}
  
  	return newsk;
  }
  
  void mptcp_destroy_common(struct mptcp_sock *msk)
  {
  	struct sock *sk = (struct sock *)msk;
  
  	__mptcp_clear_xmit(sk);
  
  	/* move to sk_receive_queue, sk_stream_kill_queues will purge it */
  	skb_queue_splice_tail_init(&msk->receive_queue, &sk->sk_receive_queue);
  	__skb_queue_purge(&sk->sk_receive_queue);
  	skb_rbtree_purge(&msk->out_of_order_queue);
  
  	/* move all the rx fwd alloc into the sk_mem_reclaim_final in
  	 * inet_sock_destruct() will dispose it
  	 */
  	sk->sk_forward_alloc += msk->rmem_fwd_alloc;
  	msk->rmem_fwd_alloc = 0;
  	mptcp_token_destroy(msk);
  	mptcp_pm_free_anno_list(msk);
  }
  
  static void mptcp_destroy(struct sock *sk)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  
  	mptcp_destroy_common(msk);
  	sk_sockets_allocated_dec(sk);
  }
  
  void __mptcp_data_acked(struct sock *sk)
  {
  	if (!sock_owned_by_user(sk))
  		__mptcp_clean_una(sk);
  	else
  		set_bit(MPTCP_CLEAN_UNA, &mptcp_sk(sk)->flags);
  
  	if (mptcp_pending_data_fin_ack(sk))
  		mptcp_schedule_work(sk);
  }
  
  void __mptcp_check_push(struct sock *sk, struct sock *ssk)
  {
  	if (!mptcp_send_head(sk))
  		return;
  
  	if (!sock_owned_by_user(sk)) {
  		struct sock *xmit_ssk = mptcp_subflow_get_send(mptcp_sk(sk));
  
  		if (xmit_ssk == ssk)
  			__mptcp_subflow_push_pending(sk, ssk);
  		else if (xmit_ssk)
  			mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk));
  	} else {
  		set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->flags);
  	}
  }
  
  /* processes deferred events and flush wmem */
  static void mptcp_release_cb(struct sock *sk)
  {
  	for (;;) {
  		unsigned long flags = 0;
  
  		if (test_and_clear_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->flags))
  			flags |= BIT(MPTCP_PUSH_PENDING);
  		if (test_and_clear_bit(MPTCP_RETRANSMIT, &mptcp_sk(sk)->flags))
  			flags |= BIT(MPTCP_RETRANSMIT);
  		if (!flags)
  			break;
  
  		/* the following actions acquire the subflow socket lock
  		 *
  		 * 1) can't be invoked in atomic scope
  		 * 2) must avoid ABBA deadlock with msk socket spinlock: the RX
  		 *    datapath acquires the msk socket spinlock while helding
  		 *    the subflow socket lock
  		 */
  
  		spin_unlock_bh(&sk->sk_lock.slock);
  		if (flags & BIT(MPTCP_PUSH_PENDING))
  			__mptcp_push_pending(sk, 0);
  		if (flags & BIT(MPTCP_RETRANSMIT))
  			__mptcp_retrans(sk);
  
  		cond_resched();
  		spin_lock_bh(&sk->sk_lock.slock);
  	}
  
  	/* be sure to set the current sk state before tacking actions
  	 * depending on sk_state
  	 */
  	if (test_and_clear_bit(MPTCP_CONNECTED, &mptcp_sk(sk)->flags))
  		__mptcp_set_connected(sk);
  	if (test_and_clear_bit(MPTCP_CLEAN_UNA, &mptcp_sk(sk)->flags))
  		__mptcp_clean_una_wakeup(sk);
  	if (test_and_clear_bit(MPTCP_ERROR_REPORT, &mptcp_sk(sk)->flags))
  		__mptcp_error_report(sk);
  
  	__mptcp_update_rmem(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,
  	 * we hash the TCP subflows not the master socket
  	 */
  	WARN_ON_ONCE(1);
  	return 0;
  }
  
  static void mptcp_unhash(struct sock *sk)
  {
  	/* called from sk_common_release(), but nothing to do here */
  }
  
  static int mptcp_get_port(struct sock *sk, unsigned short snum)
  {
  	struct mptcp_sock *msk = mptcp_sk(sk);
  	struct socket *ssock;
  
  	ssock = __mptcp_nmpc_socket(msk);
  	pr_debug("msk=%p, subflow=%p", msk, ssock);
  	if (WARN_ON_ONCE(!ssock))
  		return -EINVAL;
  
  	return inet_csk_get_port(ssock->sk, snum);
  }
  
  void mptcp_finish_connect(struct sock *ssk)
  {
  	struct mptcp_subflow_context *subflow;
  	struct mptcp_sock *msk;
  	struct sock *sk;
  	u64 ack_seq;
  
  	subflow = mptcp_subflow_ctx(ssk);
  	sk = subflow->conn;
  	msk = mptcp_sk(sk);
  
  	pr_debug("msk=%p, token=%u", sk, subflow->token);
  
  	mptcp_crypto_key_sha(subflow->remote_key, NULL, &ack_seq);
  	ack_seq++;
  	subflow->map_seq = ack_seq;
  	subflow->map_subflow_seq = 1;
  
  	/* the socket is not connected yet, no msk/subflow ops can access/race
  	 * accessing the field below
  	 */
  	WRITE_ONCE(msk->remote_key, subflow->remote_key);
  	WRITE_ONCE(msk->local_key, subflow->local_key);
  	WRITE_ONCE(msk->write_seq, subflow->idsn + 1);
  	WRITE_ONCE(msk->snd_nxt, msk->write_seq);
  	WRITE_ONCE(msk->ack_seq, ack_seq);
  	WRITE_ONCE(msk->rcv_wnd_sent, ack_seq);
  	WRITE_ONCE(msk->can_ack, 1);
  	WRITE_ONCE(msk->snd_una, msk->write_seq);
  
  	mptcp_pm_new_connection(msk, ssk, 0);
  
  	mptcp_rcv_space_init(msk, ssk);
  }
  
  void mptcp_sock_graft(struct sock *sk, struct socket *parent)
  {
  	write_lock_bh(&sk->sk_callback_lock);
  	rcu_assign_pointer(sk->sk_wq, &parent->wq);
  	sk_set_socket(sk, parent);
  	sk->sk_uid = SOCK_INODE(parent)->i_uid;
  	write_unlock_bh(&sk->sk_callback_lock);
  }
  
  bool mptcp_finish_join(struct sock *ssk)
  {
  	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
  	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
  	struct sock *parent = (void *)msk;
  	struct socket *parent_sock;
  	bool ret;
  
  	pr_debug("msk=%p, subflow=%p", msk, subflow);
  
  	/* mptcp socket already closing? */
  	if (!mptcp_is_fully_established(parent)) {
  		subflow->reset_reason = MPTCP_RST_EMPTCP;
  		return false;
  	}
  
  	if (!msk->pm.server_side)
  		goto out;
  
  	if (!mptcp_pm_allow_new_subflow(msk)) {
  		subflow->reset_reason = MPTCP_RST_EPROHIBIT;
  		return false;
  	}
  
  	/* active connections are already on conn_list, and we can't acquire
  	 * msk lock here.
  	 * use the join list lock as synchronization point and double-check
  	 * msk status to avoid racing with __mptcp_destroy_sock()
  	 */
  	spin_lock_bh(&msk->join_list_lock);
  	ret = inet_sk_state_load(parent) == TCP_ESTABLISHED;
  	if (ret && !WARN_ON_ONCE(!list_empty(&subflow->node))) {
  		list_add_tail(&subflow->node, &msk->join_list);
  		sock_hold(ssk);
  	}
  	spin_unlock_bh(&msk->join_list_lock);
  	if (!ret) {
  		subflow->reset_reason = MPTCP_RST_EPROHIBIT;
  		return false;
  	}
  
  	/* attach to msk socket only after we are sure he will deal with us
  	 * at close time
  	 */
  	parent_sock = READ_ONCE(parent->sk_socket);
  	if (parent_sock && !ssk->sk_socket)
  		mptcp_sock_graft(ssk, parent_sock);
  	subflow->map_seq = READ_ONCE(msk->ack_seq);
  out:
  	mptcp_event(MPTCP_EVENT_SUB_ESTABLISHED, msk, ssk, GFP_ATOMIC);
  	return true;
  }
  
  static void mptcp_shutdown(struct sock *sk, int how)
  {
  	pr_debug("sk=%p, how=%d", sk, how);
  
  	if ((how & SEND_SHUTDOWN) && mptcp_close_state(sk))
  		__mptcp_wr_shutdown(sk);
  }
  
  static int mptcp_forward_alloc_get(const struct sock *sk)
  {
  	return sk->sk_forward_alloc + mptcp_sk(sk)->rmem_fwd_alloc;
  }
  
  static struct proto mptcp_prot = {
  	.name		= "MPTCP",
  	.owner		= THIS_MODULE,
  	.init		= mptcp_init_sock,
  	.disconnect	= mptcp_disconnect,
  	.close		= mptcp_close,
  	.accept		= mptcp_accept,
  	.setsockopt	= mptcp_setsockopt,
  	.getsockopt	= mptcp_getsockopt,
  	.shutdown	= mptcp_shutdown,
  	.destroy	= mptcp_destroy,
  	.sendmsg	= mptcp_sendmsg,
  	.recvmsg	= mptcp_recvmsg,
  	.release_cb	= mptcp_release_cb,
  	.hash		= mptcp_hash,
  	.unhash		= mptcp_unhash,
  	.get_port	= mptcp_get_port,
  	.forward_alloc_get	= mptcp_forward_alloc_get,
  	.sockets_allocated	= &mptcp_sockets_allocated,
  	.memory_allocated	= &tcp_memory_allocated,
  	.memory_pressure	= &tcp_memory_pressure,
  	.sysctl_wmem_offset	= offsetof(struct net, ipv4.sysctl_tcp_wmem),
  	.sysctl_rmem_offset	= offsetof(struct net, ipv4.sysctl_tcp_rmem),
  	.sysctl_mem	= sysctl_tcp_mem,
  	.obj_size	= sizeof(struct mptcp_sock),
  	.slab_flags	= SLAB_TYPESAFE_BY_RCU,
  	.no_autobind	= true,
  };
  
  static int mptcp_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
  {
  	struct mptcp_sock *msk = mptcp_sk(sock->sk);
  	struct socket *ssock;
  	int err;
  
  	lock_sock(sock->sk);
  	ssock = __mptcp_nmpc_socket(msk);
  	if (!ssock) {
  		err = -EINVAL;
  		goto unlock;
  	}
  
  	err = ssock->ops->bind(ssock, uaddr, addr_len);
  	if (!err)
  		mptcp_copy_inaddrs(sock->sk, ssock->sk);
  
  unlock:
  	release_sock(sock->sk);
  	return err;
  }
  
  static void mptcp_subflow_early_fallback(struct mptcp_sock *msk,
  					 struct mptcp_subflow_context *subflow)
  {
  	subflow->request_mptcp = 0;
  	__mptcp_do_fallback(msk);
  }
  
  static int mptcp_stream_connect(struct socket *sock, struct sockaddr *uaddr,
  				int addr_len, int flags)
  {
  	struct mptcp_sock *msk = mptcp_sk(sock->sk);
  	struct mptcp_subflow_context *subflow;
  	struct socket *ssock;
  	int err;
  
  	lock_sock(sock->sk);
  	if (sock->state != SS_UNCONNECTED && msk->subflow) {
  		/* pending connection or invalid state, let existing subflow
  		 * cope with that
  		 */
  		ssock = msk->subflow;
  		goto do_connect;
  	}
  
  	ssock = __mptcp_nmpc_socket(msk);
  	if (!ssock) {
  		err = -EINVAL;
  		goto unlock;
  	}
  
  	mptcp_token_destroy(msk);
  	inet_sk_state_store(sock->sk, TCP_SYN_SENT);
  	subflow = mptcp_subflow_ctx(ssock->sk);
  #ifdef CONFIG_TCP_MD5SIG
  	/* no MPTCP if MD5SIG is enabled on this socket or we may run out of
  	 * TCP option space.
  	 */
  	if (rcu_access_pointer(tcp_sk(ssock->sk)->md5sig_info))
  		mptcp_subflow_early_fallback(msk, subflow);
  #endif
  	if (subflow->request_mptcp && mptcp_token_new_connect(ssock->sk)) {
  		MPTCP_INC_STATS(sock_net(ssock->sk), MPTCP_MIB_TOKENFALLBACKINIT);
  		mptcp_subflow_early_fallback(msk, subflow);
  	}
  	if (likely(!__mptcp_check_fallback(msk)))
  		MPTCP_INC_STATS(sock_net(sock->sk), MPTCP_MIB_MPCAPABLEACTIVE);
  
  do_connect:
  	err = ssock->ops->connect(ssock, uaddr, addr_len, flags);
  	sock->state = ssock->state;
  
  	/* on successful connect, the msk state will be moved to established by
  	 * subflow_finish_connect()
  	 */
  	if (!err || err == -EINPROGRESS)
  		mptcp_copy_inaddrs(sock->sk, ssock->sk);
  	else
  		inet_sk_state_store(sock->sk, inet_sk_state_load(ssock->sk));
  
  unlock:
  	release_sock(sock->sk);
  	return err;
  }
  
  static int mptcp_listen(struct socket *sock, int backlog)
  {
  	struct mptcp_sock *msk = mptcp_sk(sock->sk);
  	struct socket *ssock;
  	int err;
  
  	pr_debug("msk=%p", msk);
  
  	lock_sock(sock->sk);
  	ssock = __mptcp_nmpc_socket(msk);
  	if (!ssock) {
  		err = -EINVAL;
  		goto unlock;
  	}
  
  	mptcp_token_destroy(msk);
  	inet_sk_state_store(sock->sk, TCP_LISTEN);
  	sock_set_flag(sock->sk, SOCK_RCU_FREE);
  
  	err = ssock->ops->listen(ssock, backlog);
  	inet_sk_state_store(sock->sk, inet_sk_state_load(ssock->sk));
  	if (!err)
  		mptcp_copy_inaddrs(sock->sk, ssock->sk);
  
  unlock:
  	release_sock(sock->sk);
  	return err;
  }
  
  static int mptcp_stream_accept(struct socket *sock, struct socket *newsock,
  			       int flags, bool kern)
  {
  	struct mptcp_sock *msk = mptcp_sk(sock->sk);
  	struct socket *ssock;
  	int err;
  
  	pr_debug("msk=%p", msk);
  
  	lock_sock(sock->sk);
  	if (sock->sk->sk_state != TCP_LISTEN)
  		goto unlock_fail;
  
  	ssock = __mptcp_nmpc_socket(msk);
  	if (!ssock)
  		goto unlock_fail;
  
  	clear_bit(MPTCP_DATA_READY, &msk->flags);
  	sock_hold(ssock->sk);
  	release_sock(sock->sk);
  
  	err = ssock->ops->accept(sock, newsock, flags, kern);
  	if (err == 0 && !mptcp_is_tcpsk(newsock->sk)) {
  		struct mptcp_sock *msk = mptcp_sk(newsock->sk);
  		struct mptcp_subflow_context *subflow;
  		struct sock *newsk = newsock->sk;
  
  		lock_sock(newsk);
  
  		/* PM/worker can now acquire the first subflow socket
  		 * lock without racing with listener queue cleanup,
  		 * we can notify it, if needed.
  		 *
  		 * Even if remote has reset the initial subflow by now
  		 * the refcnt is still at least one.
  		 */
  		subflow = mptcp_subflow_ctx(msk->first);
  		list_add(&subflow->node, &msk->conn_list);
  		sock_hold(msk->first);
  		if (mptcp_is_fully_established(newsk))
  			mptcp_pm_fully_established(msk, msk->first, GFP_KERNEL);
  
  		mptcp_copy_inaddrs(newsk, msk->first);
  		mptcp_rcv_space_init(msk, msk->first);
  		mptcp_propagate_sndbuf(newsk, msk->first);
  
  		/* set ssk->sk_socket of accept()ed flows to mptcp socket.
  		 * This is needed so NOSPACE flag can be set from tcp stack.
  		 */
  		mptcp_flush_join_list(msk);
  		mptcp_for_each_subflow(msk, subflow) {
  			struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
  
  			if (!ssk->sk_socket)
  				mptcp_sock_graft(ssk, newsock);
  		}
  		release_sock(newsk);
  	}
  
  	if (inet_csk_listen_poll(ssock->sk))
  		set_bit(MPTCP_DATA_READY, &msk->flags);
  	sock_put(ssock->sk);
  	return err;
  
  unlock_fail:
  	release_sock(sock->sk);
  	return -EINVAL;
  }
  
  static __poll_t mptcp_check_readable(struct mptcp_sock *msk)
  {
  	/* Concurrent splices from sk_receive_queue into receive_queue will
  	 * always show at least one non-empty queue when checked in this order.
  	 */
  	if (skb_queue_empty_lockless(&((struct sock *)msk)->sk_receive_queue) &&
  	    skb_queue_empty_lockless(&msk->receive_queue))
  		return 0;
  
  	return EPOLLIN | EPOLLRDNORM;
  }
  
  static __poll_t mptcp_check_writeable(struct mptcp_sock *msk)
  {
  	struct sock *sk = (struct sock *)msk;
  
  	if (unlikely(sk->sk_shutdown & SEND_SHUTDOWN))
  		return EPOLLOUT | EPOLLWRNORM;
  
  	if (sk_stream_is_writeable(sk))
  		return EPOLLOUT | EPOLLWRNORM;
  
  	mptcp_set_nospace(sk);
  	smp_mb__after_atomic(); /* msk->flags is changed by write_space cb */
  	if (sk_stream_is_writeable(sk))
  		return EPOLLOUT | EPOLLWRNORM;
  
  	return 0;
  }
  
  static __poll_t mptcp_poll(struct file *file, struct socket *sock,
  			   struct poll_table_struct *wait)
  {
  	struct sock *sk = sock->sk;
  	struct mptcp_sock *msk;
  	__poll_t mask = 0;
  	int state;
  
  	msk = mptcp_sk(sk);
  	sock_poll_wait(file, sock, wait);
  
  	state = inet_sk_state_load(sk);
  	pr_debug("msk=%p state=%d flags=%lx", msk, state, msk->flags);
  	if (state == TCP_LISTEN)
  		return test_bit(MPTCP_DATA_READY, &msk->flags) ? EPOLLIN | EPOLLRDNORM : 0;
  
  	if (state != TCP_SYN_SENT && state != TCP_SYN_RECV) {
  		mask |= mptcp_check_readable(msk);
  		mask |= mptcp_check_writeable(msk);
  	}
  	if (sk->sk_shutdown == SHUTDOWN_MASK || state == TCP_CLOSE)
  		mask |= EPOLLHUP;
  	if (sk->sk_shutdown & RCV_SHUTDOWN)
  		mask |= EPOLLIN | EPOLLRDNORM | EPOLLRDHUP;
  
  	/* This barrier is coupled with smp_wmb() in tcp_reset() */
  	smp_rmb();
  	if (sk->sk_err)
  		mask |= EPOLLERR;
  
  	return mask;
  }
  
  static const struct proto_ops mptcp_stream_ops = {
  	.family		   = PF_INET,
  	.owner		   = THIS_MODULE,
  	.release	   = inet_release,
  	.bind		   = mptcp_bind,
  	.connect	   = mptcp_stream_connect,
  	.socketpair	   = sock_no_socketpair,
  	.accept		   = mptcp_stream_accept,
  	.getname	   = inet_getname,
  	.poll		   = mptcp_poll,
  	.ioctl		   = inet_ioctl,
  	.gettstamp	   = sock_gettstamp,
  	.listen		   = mptcp_listen,
  	.shutdown	   = inet_shutdown,
  	.setsockopt	   = sock_common_setsockopt,
  	.getsockopt	   = sock_common_getsockopt,
  	.sendmsg	   = inet_sendmsg,
  	.recvmsg	   = inet_recvmsg,
  	.mmap		   = sock_no_mmap,
  	.sendpage	   = inet_sendpage,
  };
  
  static struct inet_protosw mptcp_protosw = {
  	.type		= SOCK_STREAM,
  	.protocol	= IPPROTO_MPTCP,
  	.prot		= &mptcp_prot,
  	.ops		= &mptcp_stream_ops,
  	.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();
  
  	if (proto_register(&mptcp_prot, 1) != 0)
  		panic("Failed to register MPTCP proto.\n");
  
  	inet_register_protosw(&mptcp_protosw);
  
  	BUILD_BUG_ON(sizeof(struct mptcp_skb_cb) > sizeof_field(struct sk_buff, cb));
  }
  
  #if IS_ENABLED(CONFIG_MPTCP_IPV6)
  static const struct proto_ops mptcp_v6_stream_ops = {
  	.family		   = PF_INET6,
  	.owner		   = THIS_MODULE,
  	.release	   = inet6_release,
  	.bind		   = mptcp_bind,
  	.connect	   = mptcp_stream_connect,
  	.socketpair	   = sock_no_socketpair,
  	.accept		   = mptcp_stream_accept,
  	.getname	   = inet6_getname,
  	.poll		   = mptcp_poll,
  	.ioctl		   = inet6_ioctl,
  	.gettstamp	   = sock_gettstamp,
  	.listen		   = mptcp_listen,
  	.shutdown	   = inet_shutdown,
  	.setsockopt	   = sock_common_setsockopt,
  	.getsockopt	   = sock_common_getsockopt,
  	.sendmsg	   = inet6_sendmsg,
  	.recvmsg	   = inet6_recvmsg,
  	.mmap		   = sock_no_mmap,
  	.sendpage	   = inet_sendpage,
  #ifdef CONFIG_COMPAT
  	.compat_ioctl	   = inet6_compat_ioctl,
  #endif
  };
  
  static struct proto mptcp_v6_prot;
  
  static void mptcp_v6_destroy(struct sock *sk)
  {
  	mptcp_destroy(sk);
  	inet6_destroy_sock(sk);
  }
  
  static struct inet_protosw mptcp_v6_protosw = {
  	.type		= SOCK_STREAM,
  	.protocol	= IPPROTO_MPTCP,
  	.prot		= &mptcp_v6_prot,
  	.ops		= &mptcp_v6_stream_ops,
  	.flags		= INET_PROTOSW_ICSK,
  };
  
  int __init mptcp_proto_v6_init(void)
  {
  	int err;
  
  	mptcp_v6_prot = mptcp_prot;
  	strcpy(mptcp_v6_prot.name, "MPTCPv6");
  	mptcp_v6_prot.slab = NULL;
  	mptcp_v6_prot.destroy = mptcp_v6_destroy;
  	mptcp_v6_prot.obj_size = sizeof(struct mptcp6_sock);
  
  	err = proto_register(&mptcp_v6_prot, 1);
  	if (err)
  		return err;
  
  	err = inet6_register_protosw(&mptcp_v6_protosw);
  	if (err)
  		proto_unregister(&mptcp_v6_prot);
  
  	return err;
  }
  #endif
  