// 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;
};

#define MPTCP_SKB_CB(__skb)     ((struct mptcp_skb_cb *)&((__skb)->cb[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 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);
        sk_mem_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);
}

/* "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);
        skb_set_owner_r(skb, sk);
}

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;

        __skb_unlink(skb, &ssk->sk_receive_queue);

        skb_ext_reset(skb);
        skb_orphan(skb);

        /* try to fetch required memory from subflow */
        if (!sk_rmem_schedule(sk, skb, skb->truesize)) {
                int amount = sk_mem_pages(skb->truesize) << SK_MEM_QUANTUM_SHIFT;

                if (ssk->sk_forward_alloc < amount)
                        goto drop;

                ssk->sk_forward_alloc -= amount;
                sk->sk_forward_alloc += amount;
        }

        /* 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;

        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;

                skb_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(const struct sock *sk, const struct sock *ssk)
{
        long tout = ssk && inet_csk(ssk)->icsk_pending ?
                                      inet_csk(ssk)->icsk_timeout - jiffies : 0;

        if (tout <= 0)
                tout = mptcp_sk(sk)->timer_ival;
        mptcp_sk(sk)->timer_ival = tout > 0 ? tout : TCP_RTO_MIN;
}

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));
}

static void mptcp_send_ack(struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow;

        mptcp_for_each_subflow(msk, subflow) {
                struct sock *ssk = mptcp_subflow_tcp_sock(subflow);

                lock_sock(ssk);
                if (tcp_can_send_ack(ssk))
                        tcp_send_ack(ssk);
                release_sock(ssk);
        }
}

static bool mptcp_subflow_cleanup_rbuf(struct sock *ssk)
{
        int ret;

        lock_sock(ssk);
        ret = tcp_can_send_ack(ssk);
        if (ret)
                tcp_cleanup_rbuf(ssk, 1);
        release_sock(ssk);
        return ret;
}

static void mptcp_cleanup_rbuf(struct mptcp_sock *msk)
{
        struct sock *ack_hint = READ_ONCE(msk->ack_hint);
        int old_space = READ_ONCE(msk->old_wspace);
        struct mptcp_subflow_context *subflow;
        struct sock *sk = (struct sock *)msk;
        bool cleanup;

        /* this is a simple superset of what tcp_cleanup_rbuf() implements
         * so that we don't have to acquire the ssk socket lock most of the time
         * to do actually nothing
         */
        cleanup = __mptcp_space(sk) - old_space >= max(0, old_space);
        if (!cleanup)
                return;

        /* if the hinted ssk is still active, try to use it */
        if (likely(ack_hint)) {
                mptcp_for_each_subflow(msk, subflow) {
                        struct sock *ssk = mptcp_subflow_tcp_sock(subflow);

                        if (ack_hint == ssk && mptcp_subflow_cleanup_rbuf(ssk))
                                return;
                }
        }

        /* otherwise pick the first active subflow */
        mptcp_for_each_subflow(msk, subflow)
                if (mptcp_subflow_cleanup_rbuf(mptcp_subflow_tcp_sock(subflow)))
                        return;
}

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 */
                set_bit(MPTCP_DATA_READY, &msk->flags);

                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_set_timeout(sk, NULL);
                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);
        WRITE_ONCE(msk->ack_hint, ssk);

        *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;

        if (inet_sk_state_load(sk) == TCP_CLOSE)
                return false;

        __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 (atomic_read(&sk->sk_rmem_alloc) > sk_rbuf)
                return;

        /* Wake-up the reader only for in-sequence data */
        mptcp_data_lock(sk);
        if (move_skbs_to_msk(msk, ssk)) {
                set_bit(MPTCP_DATA_READY, &msk->flags);
                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;

        /* should never be called with mptcp level timer cleared */
        tout = READ_ONCE(mptcp_sk(sk)->timer_ival);
        if (WARN_ON_ONCE(!tout))
                tout = TCP_RTO_MIN;
        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 */
                set_bit(MPTCP_DATA_READY, &msk->flags);
                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 int mptcp_wmem_with_overhead(struct sock *sk, int size)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        int ret, skbs;

        ret = size + ((sizeof(struct mptcp_data_frag) * size) >> PAGE_SHIFT);
        skbs = (msk->tx_pending_data + size) / msk->size_goal_cache;
        if (skbs < msk->skb_tx_cache.qlen)
                return ret;

        return ret + (skbs - msk->skb_tx_cache.qlen) * SKB_TRUESIZE(MAX_TCP_HEADER);
}

static void __mptcp_wmem_reserve(struct sock *sk, int size)
{
        int amount = mptcp_wmem_with_overhead(sk, size);
        struct mptcp_sock *msk = mptcp_sk(sk);

        WARN_ON_ONCE(msk->wmem_reserved);
        if (WARN_ON_ONCE(amount < 0))
                amount = 0;

        if (amount <= sk->sk_forward_alloc)
                goto reserve;

        /* under memory pressure try to reserve at most a single page
         * otherwise try to reserve the full estimate and fallback
         * to a single page before entering the error path
         */
        if ((tcp_under_memory_pressure(sk) && amount > PAGE_SIZE) ||
            !sk_wmem_schedule(sk, amount)) {
                if (amount <= PAGE_SIZE)
                        goto nomem;

                amount = PAGE_SIZE;
                if (!sk_wmem_schedule(sk, amount))
                        goto nomem;
        }

reserve:
        msk->wmem_reserved = amount;
        sk->sk_forward_alloc -= amount;
        return;

nomem:
        /* we will wait for memory on next allocation */
        msk->wmem_reserved = -1;
}

static void __mptcp_update_wmem(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

#ifdef CONFIG_LOCKDEP
        WARN_ON_ONCE(!lockdep_is_held(&sk->sk_lock.slock));
#endif

        if (!msk->wmem_reserved)
                return;

        if (msk->wmem_reserved < 0)
                msk->wmem_reserved = 0;
        if (msk->wmem_reserved > 0) {
                sk->sk_forward_alloc += msk->wmem_reserved;
                msk->wmem_reserved = 0;
        }
}

static bool mptcp_wmem_alloc(struct sock *sk, int size)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        /* check for pre-existing error condition */
        if (msk->wmem_reserved < 0)
                return false;

        if (msk->wmem_reserved >= size)
                goto account;

        mptcp_data_lock(sk);
        if (!sk_wmem_schedule(sk, size)) {
                mptcp_data_unlock(sk);
                return false;
        }

        sk->sk_forward_alloc -= size;
        msk->wmem_reserved += size;
        mptcp_data_unlock(sk);

account:
        msk->wmem_reserved -= size;
        return true;
}

static void mptcp_wmem_uncharge(struct sock *sk, int size)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        if (msk->wmem_reserved < 0)
                msk->wmem_reserved = 0;
        msk->wmem_reserved += size;
}

static void mptcp_mem_reclaim_partial(struct sock *sk)
{

        struct mptcp_sock *msk = mptcp_sk(sk);

        /* if we are experiencing a transint allocation error,
         * the forward allocation memory has been already
         * released
         */
        if (msk->wmem_reserved < 0)
                return;

        mptcp_data_lock(sk);
        sk->sk_forward_alloc += msk->wmem_reserved;
        sk_mem_reclaim_partial(sk);
        msk->wmem_reserved = sk->sk_forward_alloc;
        sk->sk_forward_alloc = 0;
        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 (WARN_ON_ONCE(dfrag == msk->first_pending))
                        break;
                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;

                if (WARN_ON_ONCE(delta > dfrag->already_sent))
                        goto out;

                dfrag->data_seq += delta;
                dfrag->offset += delta;
                dfrag->data_len -= delta;
                dfrag->already_sent -= delta;

                dfrag_uncharge(sk, delta);
                cleaned = true;
        }

out:
        if (cleaned) {
                if (tcp_under_memory_pressure(sk)) {
                        __mptcp_update_wmem(sk);
                        sk_mem_reclaim_partial(sk);
                }
        }

        if (snd_una == READ_ONCE(msk->snd_nxt)) {
                if (msk->timer_ival && !mptcp_data_fin_enabled(msk))
                        mptcp_stop_timer(sk);
        } else {
                mptcp_reset_timer(sk);
        }
}

static void __mptcp_clean_una_wakeup(struct sock *sk)
{
#ifdef CONFIG_LOCKDEP
        WARN_ON_ONCE(!lockdep_is_held(&sk->sk_lock.slock));
#endif
        __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;
};

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->reserved_tailroom = skb->end - skb->tail;
                        return skb;
                }
                __kfree_skb(skb);
        } else {
                mptcp_enter_memory_pressure(sk);
        }
        return NULL;
}

static bool mptcp_tx_cache_refill(struct sock *sk, int size,
                                  struct sk_buff_head *skbs, int *total_ts)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct sk_buff *skb;
        int space_needed;

        if (unlikely(tcp_under_memory_pressure(sk))) {
                mptcp_mem_reclaim_partial(sk);

                /* under pressure pre-allocate at most a single skb */
                if (msk->skb_tx_cache.qlen)
                        return true;
                space_needed = msk->size_goal_cache;
        } else {
                space_needed = msk->tx_pending_data + size -
                               msk->skb_tx_cache.qlen * msk->size_goal_cache;
        }

        while (space_needed > 0) {
                skb = __mptcp_do_alloc_tx_skb(sk, sk->sk_allocation);
                if (unlikely(!skb)) {
                        /* under memory pressure, try to pass the caller a
                         * single skb to allow forward progress
                         */
                        while (skbs->qlen > 1) {
                                skb = __skb_dequeue_tail(skbs);
                                *total_ts -= skb->truesize;
                                __kfree_skb(skb);
                        }
                        return skbs->qlen > 0;
                }

                *total_ts += skb->truesize;
                __skb_queue_tail(skbs, skb);
                space_needed -= msk->size_goal_cache;
        }
        return true;
}

static bool __mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, gfp_t gfp)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct sk_buff *skb;

        if (ssk->sk_tx_skb_cache) {
                skb = ssk->sk_tx_skb_cache;
                if (unlikely(!skb_ext_find(skb, SKB_EXT_MPTCP) &&
                             !__mptcp_add_ext(skb, gfp)))
                        return false;
                return true;
        }

        skb = skb_peek(&msk->skb_tx_cache);
        if (skb) {
                if (likely(sk_wmem_schedule(ssk, skb->truesize))) {
                        skb = __skb_dequeue(&msk->skb_tx_cache);
                        if (WARN_ON_ONCE(!skb))
                                return false;

                        mptcp_wmem_uncharge(sk, skb->truesize);
                        ssk->sk_tx_skb_cache = skb;
                        return true;
                }

                /* over memory limit, no point to try to allocate a new skb */
                return false;
        }

        skb = __mptcp_do_alloc_tx_skb(sk, gfp);
        if (!skb)
                return false;

        if (likely(sk_wmem_schedule(ssk, skb->truesize))) {
                ssk->sk_tx_skb_cache = skb;
                return true;
        }
        kfree_skb(skb);
        return false;
}

static bool mptcp_must_reclaim_memory(struct sock *sk, struct sock *ssk)
{
        return !ssk->sk_tx_skb_cache &&
               !skb_peek(&mptcp_sk(sk)->skb_tx_cache) &&
               tcp_under_memory_pressure(sk);
}

static bool mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk)
{
        if (unlikely(mptcp_must_reclaim_memory(sk, ssk)))
                mptcp_mem_reclaim_partial(sk);
        return __mptcp_alloc_tx_skb(sk, ssk, sk->sk_allocation);
}

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;
        struct mptcp_sock *msk = mptcp_sk(sk);
        bool zero_window_probe = false;
        struct mptcp_ext *mpext = NULL;
        struct sk_buff *skb, *tail;
        bool can_collapse = false;
        int size_bias = 0;
        int avail_size;
        size_t ret = 0;

        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);

        /* compute send limit */
        info->mss_now = tcp_send_mss(ssk, &info->size_goal, info->flags);
        avail_size = info->size_goal;
        msk->size_goal_cache = info->size_goal;
        skb = tcp_write_queue_tail(ssk);
        if (skb) {
                /* 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);
                can_collapse = (info->size_goal - skb->len > 0) &&
                         mptcp_skb_can_collapse_to(data_seq, skb, mpext);
                if (!can_collapse) {
                        TCP_SKB_CB(skb)->eor = 1;
                } else {
                        size_bias = skb->len;
                        avail_size = info->size_goal - skb->len;
                }
        }

        /* Zero window and all data acked? Probe. */
        avail_size = mptcp_check_allowed_size(msk, data_seq, avail_size);
        if (avail_size == 0) {
                u64 snd_una = READ_ONCE(msk->snd_una);

                if (skb || snd_una != msk->snd_nxt)
                        return 0;
                zero_window_probe = true;
                data_seq = snd_una - 1;
                avail_size = 1;
        }

        if (WARN_ON_ONCE(info->sent > info->limit ||
                         info->limit > dfrag->data_len))
                return 0;

        ret = info->limit - info->sent;
        tail = tcp_build_frag(ssk, avail_size + size_bias, info->flags,
                              dfrag->page, dfrag->offset + info->sent, &ret);
        if (!tail) {
                tcp_remove_empty_skb(sk, tcp_write_queue_tail(ssk));
                return -ENOMEM;
        }

        /* if the tail skb is still the cached one, collapsing really happened.
         */
        if (skb == tail) {
                TCP_SKB_CB(tail)->tcp_flags &= ~TCPHDR_PSH;
                mpext->data_len += ret;
                WARN_ON_ONCE(!can_collapse);
                WARN_ON_ONCE(zero_window_probe);
                goto out;
        }

        mpext = skb_ext_find(tail, SKB_EXT_MPTCP);
        if (WARN_ON_ONCE(!mpext)) {
                /* should never reach here, stream corrupted */
                return -EINVAL;
        }

        memset(mpext, 0, sizeof(*mpext));
        mpext->data_seq = data_seq;
        mpext->subflow_seq = mptcp_subflow_ctx(ssk)->rel_write_seq;
        mpext->data_len = ret;
        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 += ret;
                mpext->frozen = 1;
                ret = 0;
                tcp_push_pending_frames(ssk);
        }
out:
        mptcp_subflow_ctx(ssk)->rel_write_seq += ret;
        return ret;
}

#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;
};

static struct sock *mptcp_subflow_get_send(struct mptcp_sock *msk)
{
        struct subflow_send_info send_info[2];
        struct mptcp_subflow_context *subflow;
        int i, nr_active = 0;
        struct sock *ssk;
        u64 ratio;
        u32 pace;

        sock_owned_by_me((struct sock *)msk);

        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)))
                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;

                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;
                }
        }

        /* 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 *sk, struct sock *ssk,
                               struct mptcp_sendmsg_info *info)
{
        mptcp_set_timeout(sk, ssk);
        tcp_push(ssk, 0, info->mss_now, tcp_sk(ssk)->nonagle, info->size_goal);
        release_sock(ssk);
}

static 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);

                        /* try to keep the subflow socket lock across
                         * consecutive xmit on the same socket
                         */
                        if (ssk != prev_ssk && prev_ssk)
                                mptcp_push_release(sk, prev_ssk, &info);
                        if (!ssk)
                                goto out;

                        if (ssk != prev_ssk || !prev_ssk)
                                lock_sock(ssk);

                        /* keep it simple and always provide a new skb for the
                         * subflow, even if we will not use it when collapsing
                         * on the pending one
                         */
                        if (!mptcp_alloc_tx_skb(sk, ssk)) {
                                mptcp_push_release(sk, ssk, &info);
                                goto out;
                        }

                        ret = mptcp_sendmsg_frag(sk, ssk, dfrag, &info);
                        if (ret <= 0) {
                                mptcp_push_release(sk, ssk, &info);
                                goto out;
                        }

                        info.sent += ret;
                        dfrag->already_sent += ret;
                        msk->snd_nxt += ret;
                        msk->snd_burst -= ret;
                        msk->tx_pending_data -= ret;
                        copied += ret;
                        len -= 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(sk, ssk, &info);

out:
        if (copied) {
                /* start the timer, if it's not pending */
                if (!mptcp_timer_pending(sk))
                        mptcp_reset_timer(sk);
                __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;
        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;
                        }

                        if (unlikely(mptcp_must_reclaim_memory(sk, ssk))) {
                                __mptcp_update_wmem(sk);
                                sk_mem_reclaim_partial(sk);
                        }
                        if (!__mptcp_alloc_tx_skb(sk, ssk, GFP_ATOMIC))
                                goto out;

                        ret = mptcp_sendmsg_frag(sk, ssk, dfrag, &info);
                        if (ret <= 0)
                                goto out;

                        info.sent += ret;
                        dfrag->already_sent += ret;
                        msk->snd_nxt += ret;
                        msk->snd_burst -= ret;
                        msk->tx_pending_data -= ret;
                        copied += ret;
                        len -= ret;
                        first = false;
                }
                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()
         */
        __mptcp_update_wmem(sk);
        if (copied) {
                mptcp_set_timeout(sk, ssk);
                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;

        mptcp_lock_sock(sk, __mptcp_wmem_reserve(sk, min_t(size_t, 1 << 20, len)));

        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;
                struct sk_buff_head skbs;
                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;
                __skb_queue_head_init(&skbs);
                if (!mptcp_tx_cache_refill(sk, psize, &skbs, &total_ts))
                        goto wait_for_memory;

                if (!mptcp_wmem_alloc(sk, total_ts)) {
                        __skb_queue_purge(&skbs);
                        goto wait_for_memory;
                }

                skb_queue_splice_tail(&skbs, &msk->skb_tx_cache);
                if (copy_page_from_iter(dfrag->page, offset, psize,
                                        &msg->msg_iter) != psize) {
                        mptcp_wmem_uncharge(sk, psize + frag_truesize);
                        ret = -EFAULT;
                        goto out;
                }

                /* data successfully copied into the write queue */
                copied += psize;
                dfrag->data_len += psize;
                frag_truesize += psize;
                pfrag->offset += frag_truesize;
                WRITE_ONCE(msk->write_seq, msk->write_seq + psize);
                msk->tx_pending_data += 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 void mptcp_wait_data(struct sock *sk, long *timeo)
{
        DEFINE_WAIT_FUNC(wait, woken_wake_function);
        struct mptcp_sock *msk = mptcp_sk(sk);

        add_wait_queue(sk_sleep(sk), &wait);
        sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);

        sk_wait_event(sk, timeo,
                      test_and_clear_bit(MPTCP_DATA_READY, &msk->flags), &wait);

        sk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk);
        remove_wait_queue(sk_sleep(sk), &wait);
}

static int __mptcp_recvmsg_mskq(struct mptcp_sock *msk,
                                struct msghdr *msg,
                                size_t len, int 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;
                        }
                }

                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;
                        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);
        sk_mem_uncharge(sk, msk->rmem_released);
        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);
                tcp_cleanup_rbuf(ssk, moved);

                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);
                mptcp_cleanup_rbuf(msk);
        }
        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);
        int copied = 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);

        mptcp_lock_sock(sk, __mptcp_splice_receive_queue(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);
                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);
                mptcp_wait_data(sk, &timeo);
        }

        if (skb_queue_empty_lockless(&sk->sk_receive_queue) &&
            skb_queue_empty(&msk->receive_queue)) {
                /* entire backlog drained, clear DATA_READY. */
                clear_bit(MPTCP_DATA_READY, &msk->flags);

                /* .. race-breaker: ssk might have gotten new data
                 * after last __mptcp_move_skbs() returned false.
                 */
                if (unlikely(__mptcp_move_skbs(msk)))
                        set_bit(MPTCP_DATA_READY, &msk->flags);
        } else if (unlikely(!test_bit(MPTCP_DATA_READY, &msk->flags))) {
                /* data to read but mptcp_wait_data() cleared DATA_READY */
                set_bit(MPTCP_DATA_READY, &msk->flags);
        }
out_err:
        pr_debug("msk=%p data_ready=%d rx queue empty=%d copied=%d",
                 msk, test_bit(MPTCP_DATA_READY, &msk->flags),
                 skb_queue_empty_lockless(&sk->sk_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(const struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow;
        struct sock *backup = NULL;

        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?  Don't retransmit. */
                if (!tcp_write_queue_empty(ssk)) {
                        if (inet_csk(ssk)->icsk_ca_state >= TCP_CA_Loss)
                                continue;
                        return NULL;
                }

                if (subflow->backup) {
                        if (!backup)
                                backup = ssk;
                        continue;
                }

                return ssk;
        }

        return backup;
}

static void mptcp_dispose_initial_subflow(struct mptcp_sock *msk)
{
        if (msk->subflow) {
                iput(SOCK_INODE(msk->subflow));
                msk->subflow = NULL;
        }
}

/* 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);

        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);

        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->ack_hint)
                msk->ack_hint = NULL;

        if (ssk == msk->first)
                msk->first = NULL;

        if (msk->subflow && ssk == msk->subflow->sk)
                mptcp_dispose_initial_subflow(msk);
}

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);

                lock_sock(tcp_sk);
                if (tcp_sk->sk_state != TCP_CLOSE) {
                        tcp_send_active_reset(tcp_sk, GFP_ATOMIC);
                        tcp_set_state(tcp_sk, TCP_CLOSE);
                }
                release_sock(tcp_sk);
        }

        inet_sk_state_store(sk, TCP_CLOSE);
        sk->sk_shutdown = SHUTDOWN_MASK;
        smp_mb__before_atomic(); /* SHUTDOWN must be visible first */
        set_bit(MPTCP_DATA_READY, &msk->flags);
        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);
        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;
                }

                return;
        }

        ssk = mptcp_subflow_get_retrans(msk);
        if (!ssk)
                goto reset_timer;

        lock_sock(ssk);

        /* limit retransmission to the bytes already sent on some subflows */
        info.sent = 0;
        info.limit = dfrag->already_sent;
        while (info.sent < dfrag->already_sent) {
                if (!mptcp_alloc_tx_skb(sk, ssk))
                        break;

                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)
                tcp_push(ssk, 0, info.mss_now, tcp_sk(ssk)->nonagle,
                         info.size_goal);

        mptcp_set_timeout(sk, ssk);
        release_sock(ssk);

reset_timer:
        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);
        __skb_queue_head_init(&msk->skb_tx_cache);
        msk->out_of_order_queue = RB_ROOT;
        msk->first_pending = NULL;
        msk->wmem_reserved = 0;
        msk->rmem_released = 0;
        msk->tx_pending_data = 0;
        msk->size_goal_cache = TCP_BASE_MSS;

        msk->ack_hint = NULL;
        msk->first = NULL;
        inet_csk(sk)->icsk_sync_mss = mptcp_sync_mss;

        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;
        struct sk_buff *skb;

        WRITE_ONCE(msk->first_pending, NULL);
        list_for_each_entry_safe(dfrag, dtmp, &msk->rtx_queue, list)
                dfrag_clear(sk, dfrag);
        while ((skb = __skb_dequeue(&msk->skb_tx_cache)) != NULL) {
                sk->sk_forward_alloc += skb->truesize;
                kfree_skb(skb);
        }
}

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);
                        mptcp_set_timeout(sk, 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->wmem_reserved);
        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(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);

        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->mp_capable) {
                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_rbtree_purge(&msk->out_of_order_queue);
        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);
        }

        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);

        /* push_pending may touch wmem_reserved, ensure we do the cleanup
         * later
         */
        __mptcp_update_wmem(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);
}