// 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/aligned_data.h>
#include <net/rps.h>
#include <net/sock.h>
#include <net/inet_common.h>
#include <net/inet_hashtables.h>
#include <net/protocol.h>
#include <net/tcp_states.h>
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
#include <net/transp_v6.h>
#endif
#include <net/mptcp.h>
#include <net/hotdata.h>
#include <net/xfrm.h>
#include <asm/ioctls.h>
#include "protocol.h"
#include "mib.h"

static unsigned int mptcp_inq_hint(const struct sock *sk);

#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

enum {
        MPTCP_CMSG_TS = BIT(0),
        MPTCP_CMSG_INQ = BIT(1),
};

static struct percpu_counter mptcp_sockets_allocated ____cacheline_aligned_in_smp;

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) = {
        .bh_lock = INIT_LOCAL_LOCK(bh_lock),
};
static struct net_device *mptcp_napi_dev;

/* 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 const struct proto_ops *mptcp_fallback_tcp_ops(const struct sock *sk)
{
        unsigned short family = READ_ONCE(sk->sk_family);

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        if (family == AF_INET6)
                return &inet6_stream_ops;
#endif
        WARN_ON_ONCE(family != AF_INET);
        return &inet_stream_ops;
}

bool __mptcp_try_fallback(struct mptcp_sock *msk, int fb_mib)
{
        struct net *net = sock_net((struct sock *)msk);

        if (__mptcp_check_fallback(msk))
                return true;

        /* The caller possibly is not holding the msk socket lock, but
         * in the fallback case only the current subflow is touching
         * the OoO queue.
         */
        if (!RB_EMPTY_ROOT(&msk->out_of_order_queue))
                return false;

        spin_lock_bh(&msk->fallback_lock);
        if (!msk->allow_infinite_fallback) {
                spin_unlock_bh(&msk->fallback_lock);
                return false;
        }

        msk->allow_subflows = false;
        set_bit(MPTCP_FALLBACK_DONE, &msk->flags);
        __MPTCP_INC_STATS(net, fb_mib);
        spin_unlock_bh(&msk->fallback_lock);
        return true;
}

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, sk->sk_family, &ssock);
        if (err)
                return err;

        msk->scaling_ratio = tcp_sk(ssock->sk)->scaling_ratio;
        WRITE_ONCE(msk->first, ssock->sk);
        subflow = mptcp_subflow_ctx(ssock->sk);
        list_add(&subflow->node, &msk->conn_list);
        sock_hold(ssock->sk);
        subflow->request_mptcp = 1;
        subflow->subflow_id = msk->subflow_id++;

        /* This is the first subflow, always with id 0 */
        WRITE_ONCE(subflow->local_id, 0);
        mptcp_sock_graft(msk->first, sk->sk_socket);
        iput(SOCK_INODE(ssock));

        return 0;
}

/* If the MPC handshake is not started, returns the first subflow,
 * eventually allocating it.
 */
struct sock *__mptcp_nmpc_sk(struct mptcp_sock *msk)
{
        struct sock *sk = (struct sock *)msk;
        int ret;

        if (!((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
                return ERR_PTR(-EINVAL);

        if (!msk->first) {
                ret = __mptcp_socket_create(msk);
                if (ret)
                        return ERR_PTR(ret);
        }

        return msk->first;
}

static void mptcp_drop(struct sock *sk, struct sk_buff *skb)
{
        sk_drops_skbadd(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)
{
        int limit = READ_ONCE(sk->sk_rcvbuf);

        if (unlikely(MPTCP_SKB_CB(to)->cant_coalesce) ||
            MPTCP_SKB_CB(from)->offset ||
            ((to->len + from->len) > (limit >> 3)) ||
            !skb_try_coalesce(to, from, fragstolen, delta))
                return false;

        pr_debug("colesced seq %llx into %llx new len %d new end seq %llx\n",
                 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;
        return true;
}

static bool mptcp_try_coalesce(struct sock *sk, struct sk_buff *to,
                               struct sk_buff *from)
{
        bool fragstolen;
        int delta;

        if (!__mptcp_try_coalesce(sk, to, from, &fragstolen, &delta))
                return false;

        /* note the fwd memory can reach a negative value after accounting
         * for the delta, but the later skb free will restore a non
         * negative one
         */
        atomic_add(delta, &sk->sk_rmem_alloc);
        sk_mem_charge(sk, delta);
        kfree_skb_partial(from, fragstolen);

        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_rcvbuf_grow(), main difference:
 * - mptcp does not maintain a msk-level window clamp
 * - returns true when  the receive buffer is actually updated
 */
static bool mptcp_rcvbuf_grow(struct sock *sk, u32 newval)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        const struct net *net = sock_net(sk);
        u32 rcvwin, rcvbuf, cap, oldval;
        u64 grow;

        oldval = msk->rcvq_space.space;
        msk->rcvq_space.space = newval;
        if (!READ_ONCE(net->ipv4.sysctl_tcp_moderate_rcvbuf) ||
            (sk->sk_userlocks & SOCK_RCVBUF_LOCK))
                return false;

        /* DRS is always one RTT late. */
        rcvwin = newval << 1;

        /* slow start: allow the sender to double its rate. */
        grow = (u64)rcvwin * (newval - oldval);
        do_div(grow, oldval);
        rcvwin += grow << 1;

        cap = READ_ONCE(net->ipv4.sysctl_tcp_rmem[2]);

        rcvbuf = min_t(u32, mptcp_space_from_win(sk, rcvwin), cap);
        if (rcvbuf > sk->sk_rcvbuf) {
                WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
                return true;
        }
        return false;
}

/* "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 = atomic64_read(&msk->rcv_wnd_sent);

        pr_debug("msk=%p seq=%llx limit=%llx empty=%d\n", 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)atomic64_read(&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 void mptcp_init_skb(struct sock *ssk, struct sk_buff *skb, int offset,
                           int copy_len)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        bool has_rxtstamp = TCP_SKB_CB(skb)->has_rxtstamp;

        /* the skb map_seq accounts for the skb offset:
         * mptcp_subflow_get_mapped_dsn() is based on the current tp->copied_seq
         * value
         */
        MPTCP_SKB_CB(skb)->map_seq = mptcp_subflow_get_mapped_dsn(subflow);
        MPTCP_SKB_CB(skb)->end_seq = MPTCP_SKB_CB(skb)->map_seq + copy_len;
        MPTCP_SKB_CB(skb)->offset = offset;
        MPTCP_SKB_CB(skb)->has_rxtstamp = has_rxtstamp;
        MPTCP_SKB_CB(skb)->cant_coalesce = 0;

        __skb_unlink(skb, &ssk->sk_receive_queue);

        skb_ext_reset(skb);
        skb_dst_drop(skb);
}

static bool __mptcp_move_skb(struct sock *sk, struct sk_buff *skb)
{
        u64 copy_len = MPTCP_SKB_CB(skb)->end_seq - MPTCP_SKB_CB(skb)->map_seq;
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct sk_buff *tail;

        mptcp_borrow_fwdmem(sk, skb);

        if (MPTCP_SKB_CB(skb)->map_seq == msk->ack_seq) {
                /* in sequence */
                msk->bytes_received += copy_len;
                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);
        mptcp_drop(sk, skb);
        return false;
}

static void mptcp_stop_rtx_timer(struct sock *sk)
{
        sk_stop_timer(sk, &sk->mptcp_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 void mptcp_shutdown_subflows(struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow;

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

                slow = lock_sock_fast(ssk);
                tcp_shutdown(ssk, SEND_SHUTDOWN);
                unlock_sock_fast(ssk, slow);
        }
}

/* called under the msk socket lock */
static bool mptcp_pending_data_fin_ack(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        return ((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:
                        mptcp_set_state(sk, TCP_FIN_WAIT2);
                        break;
                case TCP_CLOSING:
                case TCP_LAST_ACK:
                        mptcp_shutdown_subflows(msk);
                        mptcp_set_state(sk, TCP_CLOSE);
                        break;
                }

                mptcp_close_wake_up(sk);
        }
}

/* can be called with no lock acquired */
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 << inet_sk_state_load(sk)) &
             (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_FIN_WAIT2))) {
                u64 rcv_data_fin_seq = READ_ONCE(msk->rcv_data_fin_seq);

                if (READ_ONCE(msk->ack_seq) == rcv_data_fin_seq) {
                        if (seq)
                                *seq = rcv_data_fin_seq;

                        return true;
                }
        }

        return false;
}

static void mptcp_set_datafin_timeout(struct sock *sk)
{
        struct inet_connection_sock *icsk = inet_csk(sk);
        u32 retransmits;

        retransmits = min_t(u32, icsk->icsk_retransmits,
                            ilog2(TCP_RTO_MAX / TCP_RTO_MIN));

        mptcp_sk(sk)->timer_ival = TCP_RTO_MIN << retransmits;
}

static void __mptcp_set_timeout(struct sock *sk, long tout)
{
        mptcp_sk(sk)->timer_ival = tout > 0 ? tout : TCP_RTO_MIN;
}

static long mptcp_timeout_from_subflow(const struct mptcp_subflow_context *subflow)
{
        const struct sock *ssk = mptcp_subflow_tcp_sock(subflow);

        return inet_csk(ssk)->icsk_pending && !subflow->stale_count ?
               tcp_timeout_expires(ssk) - jiffies : 0;
}

static void mptcp_set_timeout(struct sock *sk)
{
        struct mptcp_subflow_context *subflow;
        long tout = 0;

        mptcp_for_each_subflow(mptcp_sk(sk), subflow)
                tout = max(tout, mptcp_timeout_from_subflow(subflow));
        __mptcp_set_timeout(sk, tout);
}

static inline bool tcp_can_send_ack(const struct sock *ssk)
{
        return !((1 << inet_sk_state_load(ssk)) &
               (TCPF_SYN_SENT | TCPF_SYN_RECV | TCPF_TIME_WAIT | TCPF_CLOSE | TCPF_LISTEN));
}

void __mptcp_subflow_send_ack(struct sock *ssk)
{
        if (tcp_can_send_ack(ssk))
                tcp_send_ack(ssk);
}

static void mptcp_subflow_send_ack(struct sock *ssk)
{
        bool slow;

        slow = lock_sock_fast(ssk);
        __mptcp_subflow_send_ack(ssk);
        unlock_sock_fast(ssk, slow);
}

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

        mptcp_for_each_subflow(msk, subflow)
                mptcp_subflow_send_ack(mptcp_subflow_tcp_sock(subflow));
}

static void mptcp_subflow_cleanup_rbuf(struct sock *ssk, int copied)
{
        bool slow;

        slow = lock_sock_fast(ssk);
        if (tcp_can_send_ack(ssk))
                tcp_cleanup_rbuf(ssk, copied);
        unlock_sock_fast(ssk, slow);
}

static bool mptcp_subflow_could_cleanup(const struct sock *ssk, bool rx_empty)
{
        const struct inet_connection_sock *icsk = inet_csk(ssk);
        u8 ack_pending = READ_ONCE(icsk->icsk_ack.pending);
        const struct tcp_sock *tp = tcp_sk(ssk);

        return (ack_pending & ICSK_ACK_SCHED) &&
                ((READ_ONCE(tp->rcv_nxt) - READ_ONCE(tp->rcv_wup) >
                  READ_ONCE(icsk->icsk_ack.rcv_mss)) ||
                 (rx_empty && ack_pending &
                              (ICSK_ACK_PUSHED2 | ICSK_ACK_PUSHED)));
}

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

        cleanup = (space > 0) && (space >= (old_space << 1)) && copied;
        rx_empty = !sk_rmem_alloc_get(sk) && copied;

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

                if (cleanup || mptcp_subflow_could_cleanup(ssk, rx_empty))
                        mptcp_subflow_cleanup_rbuf(ssk, copied);
        }
}

static void mptcp_check_data_fin(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        u64 rcv_data_fin_seq;

        /* 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);

                WRITE_ONCE(sk->sk_shutdown, sk->sk_shutdown | RCV_SHUTDOWN);
                smp_mb__before_atomic(); /* SHUTDOWN must be visible first */

                switch (sk->sk_state) {
                case TCP_ESTABLISHED:
                        mptcp_set_state(sk, TCP_CLOSE_WAIT);
                        break;
                case TCP_FIN_WAIT1:
                        mptcp_set_state(sk, TCP_CLOSING);
                        break;
                case TCP_FIN_WAIT2:
                        mptcp_shutdown_subflows(msk);
                        mptcp_set_state(sk, TCP_CLOSE);
                        break;
                default:
                        /* Other states not expected */
                        WARN_ON_ONCE(1);
                        break;
                }

                if (!__mptcp_check_fallback(msk))
                        mptcp_send_ack(msk);
                mptcp_close_wake_up(sk);
        }
}

static void mptcp_dss_corruption(struct mptcp_sock *msk, struct sock *ssk)
{
        if (!mptcp_try_fallback(ssk, MPTCP_MIB_DSSCORRUPTIONFALLBACK)) {
                MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DSSCORRUPTIONRESET);
                mptcp_subflow_reset(ssk);
        }
}

static void __mptcp_add_backlog(struct sock *sk,
                                struct mptcp_subflow_context *subflow,
                                struct sk_buff *skb)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct sk_buff *tail = NULL;
        struct sock *ssk = skb->sk;
        bool fragstolen;
        int delta;

        if (unlikely(sk->sk_state == TCP_CLOSE)) {
                kfree_skb_reason(skb, SKB_DROP_REASON_SOCKET_CLOSE);
                return;
        }

        /* Try to coalesce with the last skb in our backlog */
        if (!list_empty(&msk->backlog_list))
                tail = list_last_entry(&msk->backlog_list, struct sk_buff, list);

        if (tail && MPTCP_SKB_CB(skb)->map_seq == MPTCP_SKB_CB(tail)->end_seq &&
            ssk == tail->sk &&
            __mptcp_try_coalesce(sk, tail, skb, &fragstolen, &delta)) {
                skb->truesize -= delta;
                kfree_skb_partial(skb, fragstolen);
                __mptcp_subflow_lend_fwdmem(subflow, delta);
                goto account;
        }

        list_add_tail(&skb->list, &msk->backlog_list);
        mptcp_subflow_lend_fwdmem(subflow, skb);
        delta = skb->truesize;

account:
        WRITE_ONCE(msk->backlog_len, msk->backlog_len + delta);

        /* Possibly not accept()ed yet, keep track of memory not CG
         * accounted, mptcp_graft_subflows() will handle it.
         */
        if (!mem_cgroup_from_sk(ssk))
                msk->backlog_unaccounted += delta;
}

static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
                                           struct sock *ssk, bool own_msk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        struct sock *sk = (struct sock *)msk;
        bool more_data_avail;
        struct tcp_sock *tp;
        bool ret = false;

        pr_debug("msk=%p ssk=%p\n", 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 (unlikely(!skb))
                        break;

                if (__mptcp_check_fallback(msk)) {
                        /* Under fallback skbs have no MPTCP extension and TCP could
                         * collapse them between the dummy map creation and the
                         * current dequeue. Be sure to adjust the map 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)
                        seq++;

                if (offset < skb->len) {
                        size_t len = skb->len - offset;

                        mptcp_init_skb(ssk, skb, offset, len);

                        if (own_msk && sk_rmem_alloc_get(sk) < sk->sk_rcvbuf) {
                                mptcp_subflow_lend_fwdmem(subflow, skb);
                                ret |= __mptcp_move_skb(sk, skb);
                        } else {
                                __mptcp_add_backlog(sk, subflow, skb);
                        }
                        seq += len;

                        if (unlikely(map_remaining < len)) {
                                DEBUG_NET_WARN_ON_ONCE(1);
                                mptcp_dss_corruption(msk, ssk);
                        }
                } else {
                        if (unlikely(!fin)) {
                                DEBUG_NET_WARN_ON_ONCE(1);
                                mptcp_dss_corruption(msk, ssk);
                        }

                        sk_eat_skb(ssk, skb);
                }

                WRITE_ONCE(tp->copied_seq, seq);
                more_data_avail = mptcp_subflow_data_available(ssk);

        } while (more_data_avail);

        if (ret)
                msk->last_data_recv = tcp_jiffies32;
        return ret;
}

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\n", 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\n",
                                 MPTCP_SKB_CB(skb)->map_seq, msk->ack_seq,
                                 delta);
                        MPTCP_SKB_CB(skb)->offset += delta;
                        MPTCP_SKB_CB(skb)->map_seq += delta;
                        __skb_queue_tail(&sk->sk_receive_queue, skb);
                }
                msk->bytes_received += end_seq - msk->ack_seq;
                WRITE_ONCE(msk->ack_seq, end_seq);
                moved = true;
        }
        return moved;
}

static bool __mptcp_subflow_error_report(struct sock *sk, struct sock *ssk)
{
        int ssk_state;
        int err;

        /* only propagate errors on fallen-back sockets or
         * on MPC connect
         */
        if (sk->sk_state != TCP_SYN_SENT && !__mptcp_check_fallback(mptcp_sk(sk)))
                return false;

        err = sock_error(ssk);
        if (!err)
                return false;

        /* We need to propagate only transition to CLOSE state.
         * Orphaned socket will see such state change via
         * subflow_sched_work_if_closed() and that path will properly
         * destroy the msk as needed.
         */
        ssk_state = inet_sk_state_load(ssk);
        if (ssk_state == TCP_CLOSE && !sock_flag(sk, SOCK_DEAD))
                mptcp_set_state(sk, ssk_state);
        WRITE_ONCE(sk->sk_err, -err);

        /* This barrier is coupled with smp_rmb() in mptcp_poll() */
        smp_wmb();
        sk_error_report(sk);
        return true;
}

void __mptcp_error_report(struct sock *sk)
{
        struct mptcp_subflow_context *subflow;
        struct mptcp_sock *msk = mptcp_sk(sk);

        mptcp_for_each_subflow(msk, subflow)
                if (__mptcp_subflow_error_report(sk, mptcp_subflow_tcp_sock(subflow)))
                        break;
}

/* 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;
        bool moved;

        moved = __mptcp_move_skbs_from_subflow(msk, ssk, true);
        __mptcp_ofo_queue(msk);
        if (unlikely(ssk->sk_err))
                __mptcp_subflow_error_report(sk, ssk);

        /* 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;
}

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);

        /* The peer can send data while we are shutting down this
         * subflow at subflow destruction time, but we must avoid enqueuing
         * more data to the msk receive queue
         */
        if (unlikely(subflow->closing))
                return;

        mptcp_data_lock(sk);
        if (!sock_owned_by_user(sk)) {
                /* Wake-up the reader only for in-sequence data */
                if (move_skbs_to_msk(msk, ssk) && mptcp_epollin_ready(sk))
                        sk->sk_data_ready(sk);
        } else {
                __mptcp_move_skbs_from_subflow(msk, ssk, false);
        }
        mptcp_data_unlock(sk);
}

static void mptcp_subflow_joined(struct mptcp_sock *msk, struct sock *ssk)
{
        mptcp_subflow_ctx(ssk)->map_seq = READ_ONCE(msk->ack_seq);
        msk->allow_infinite_fallback = false;
        mptcp_event(MPTCP_EVENT_SUB_ESTABLISHED, msk, ssk, GFP_ATOMIC);
}

static bool __mptcp_finish_join(struct mptcp_sock *msk, struct sock *ssk)
{
        struct sock *sk = (struct sock *)msk;

        if (sk->sk_state != TCP_ESTABLISHED)
                return false;

        spin_lock_bh(&msk->fallback_lock);
        if (!msk->allow_subflows) {
                spin_unlock_bh(&msk->fallback_lock);
                return false;
        }
        mptcp_subflow_joined(msk, ssk);
        spin_unlock_bh(&msk->fallback_lock);

        mptcp_subflow_ctx(ssk)->subflow_id = msk->subflow_id++;
        mptcp_sockopt_sync_locked(msk, ssk);
        mptcp_stop_tout_timer(sk);
        __mptcp_propagate_sndbuf(sk, ssk);
        return true;
}

static void __mptcp_flush_join_list(struct sock *sk, struct list_head *join_list)
{
        struct mptcp_subflow_context *tmp, *subflow;
        struct mptcp_sock *msk = mptcp_sk(sk);

        list_for_each_entry_safe(subflow, tmp, join_list, node) {
                struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
                bool slow = lock_sock_fast(ssk);

                list_move_tail(&subflow->node, &msk->conn_list);
                if (!__mptcp_finish_join(msk, ssk))
                        mptcp_subflow_reset(ssk);
                unlock_sock_fast(ssk, slow);
        }
}

static bool mptcp_rtx_timer_pending(struct sock *sk)
{
        return timer_pending(&sk->mptcp_retransmit_timer);
}

static void mptcp_reset_rtx_timer(struct sock *sk)
{
        unsigned long tout;

        /* prevent rescheduling on close */
        if (unlikely(inet_sk_state_load(sk) == TCP_CLOSE))
                return;

        tout = mptcp_sk(sk)->timer_ival;
        sk_reset_timer(sk, &sk->mptcp_retransmit_timer, jiffies + tout);
}

bool mptcp_schedule_work(struct sock *sk)
{
        if (inet_sk_state_load(sk) == TCP_CLOSE)
                return false;

        /* Get a reference on this socket, mptcp_worker() will release it.
         * As mptcp_worker() might complete before us, we can not avoid
         * a sock_hold()/sock_put() if schedule_work() returns false.
         */
        sock_hold(sk);

        if (schedule_work(&mptcp_sk(sk)->work))
                return true;

        sock_put(sk);
        return false;
}

static bool mptcp_skb_can_collapse_to(u64 write_seq,
                                      const struct sk_buff *skb,
                                      const struct mptcp_ext *mpext)
{
        if (!tcp_skb_can_collapse_to(skb))
                return false;

        /* can collapse only if MPTCP level sequence is in order and this
         * mapping has not been xmitted yet
         */
        return mpext && mpext->data_seq + mpext->data_len == write_seq &&
               !mpext->frozen;
}

/* we can append data to the given data frag if:
 * - there is space available in the backing page_frag
 * - the data frag tail matches the current page_frag free offset
 * - the data frag end sequence number matches the current write seq
 */
static bool mptcp_frag_can_collapse_to(const struct mptcp_sock *msk,
                                       const struct page_frag *pfrag,
                                       const struct mptcp_data_frag *df)
{
        return df && pfrag->page == df->page &&
                pfrag->size - pfrag->offset > 0 &&
                pfrag->offset == (df->offset + df->data_len) &&
                df->data_seq + df->data_len == msk->write_seq;
}

static void 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);
}

/* called under both the msk socket lock and the data lock */
static void __mptcp_clean_una(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct mptcp_data_frag *dtmp, *dfrag;
        u64 snd_una;

        snd_una = msk->snd_una;
        list_for_each_entry_safe(dfrag, dtmp, &msk->rtx_queue, list) {
                if (after64(dfrag->data_seq + dfrag->data_len, snd_una))
                        break;

                if (unlikely(dfrag == msk->first_pending)) {
                        /* in recovery mode can see ack after the current snd head */
                        if (WARN_ON_ONCE(!msk->recovery))
                                break;

                        msk->first_pending = mptcp_send_next(sk);
                }

                dfrag_clear(sk, dfrag);
        }

        dfrag = mptcp_rtx_head(sk);
        if (dfrag && after64(snd_una, dfrag->data_seq)) {
                u64 delta = snd_una - dfrag->data_seq;

                /* prevent wrap around in recovery mode */
                if (unlikely(delta > dfrag->already_sent)) {
                        if (WARN_ON_ONCE(!msk->recovery))
                                goto out;
                        if (WARN_ON_ONCE(delta > dfrag->data_len))
                                goto out;
                        dfrag->already_sent += delta - dfrag->already_sent;
                }

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

                dfrag_uncharge(sk, delta);
        }

        /* all retransmitted data acked, recovery completed */
        if (unlikely(msk->recovery) && after64(msk->snd_una, msk->recovery_snd_nxt))
                msk->recovery = false;

out:
        if (snd_una == msk->snd_nxt && snd_una == msk->write_seq) {
                if (mptcp_rtx_timer_pending(sk) && !mptcp_data_fin_enabled(msk))
                        mptcp_stop_rtx_timer(sk);
        } else {
                mptcp_reset_rtx_timer(sk);
        }

        if (mptcp_pending_data_fin_ack(sk))
                mptcp_schedule_work(sk);
}

static void __mptcp_clean_una_wakeup(struct sock *sk)
{
        lockdep_assert_held_once(&sk->sk_lock.slock);

        __mptcp_clean_una(sk);
        mptcp_write_space(sk);
}

static void mptcp_clean_una_wakeup(struct sock *sk)
{
        mptcp_data_lock(sk);
        __mptcp_clean_una_wakeup(sk);
        mptcp_data_unlock(sk);
}

static void mptcp_enter_memory_pressure(struct sock *sk)
{
        struct mptcp_subflow_context *subflow;
        struct mptcp_sock *msk = mptcp_sk(sk);
        bool first = true;

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

                if (first && !ssk->sk_bypass_prot_mem) {
                        tcp_enter_memory_pressure(ssk);
                        first = false;
                }

                sk_stream_moderate_sndbuf(ssk);
        }
        __mptcp_sync_sndbuf(sk);
}

/* ensure we get enough memory for the frag hdr, beyond some minimal amount of
 * data
 */
static bool mptcp_page_frag_refill(struct sock *sk, struct page_frag *pfrag)
{
        if (likely(skb_page_frag_refill(32U + sizeof(struct mptcp_data_frag),
                                        pfrag, sk->sk_allocation)))
                return true;

        mptcp_enter_memory_pressure(sk);
        return false;
}

static struct mptcp_data_frag *
mptcp_carve_data_frag(const struct mptcp_sock *msk, struct page_frag *pfrag,
                      int orig_offset)
{
        int offset = ALIGN(orig_offset, sizeof(long));
        struct mptcp_data_frag *dfrag;

        dfrag = (struct mptcp_data_frag *)(page_to_virt(pfrag->page) + offset);
        dfrag->data_len = 0;
        dfrag->data_seq = msk->write_seq;
        dfrag->overhead = offset - orig_offset + sizeof(struct mptcp_data_frag);
        dfrag->offset = offset + sizeof(struct mptcp_data_frag);
        dfrag->already_sent = 0;
        dfrag->page = pfrag->page;

        return dfrag;
}

struct mptcp_sendmsg_info {
        int mss_now;
        int size_goal;
        u16 limit;
        u16 sent;
        unsigned int flags;
        bool data_lock_held;
};

static size_t mptcp_check_allowed_size(const struct mptcp_sock *msk,
                                       struct sock *ssk, u64 data_seq,
                                       size_t avail_size)
{
        u64 window_end = mptcp_wnd_end(msk);
        u64 mptcp_snd_wnd;

        if (__mptcp_check_fallback(msk))
                return avail_size;

        mptcp_snd_wnd = window_end - data_seq;
        avail_size = min(mptcp_snd_wnd, avail_size);

        if (unlikely(tcp_sk(ssk)->snd_wnd < mptcp_snd_wnd)) {
                tcp_sk(ssk)->snd_wnd = min_t(u64, U32_MAX, mptcp_snd_wnd);
                MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_SNDWNDSHARED);
        }

        return avail_size;
}

static bool __mptcp_add_ext(struct sk_buff *skb, gfp_t gfp)
{
        struct skb_ext *mpext = __skb_ext_alloc(gfp);

        if (!mpext)
                return false;
        __skb_ext_set(skb, SKB_EXT_MPTCP, mpext);
        return true;
}

static struct sk_buff *__mptcp_do_alloc_tx_skb(struct sock *sk, gfp_t gfp)
{
        struct sk_buff *skb;

        skb = alloc_skb_fclone(MAX_TCP_HEADER, gfp);
        if (likely(skb)) {
                if (likely(__mptcp_add_ext(skb, gfp))) {
                        skb_reserve(skb, MAX_TCP_HEADER);
                        skb->ip_summed = CHECKSUM_PARTIAL;
                        INIT_LIST_HEAD(&skb->tcp_tsorted_anchor);
                        return skb;
                }
                __kfree_skb(skb);
        } else {
                mptcp_enter_memory_pressure(sk);
        }
        return NULL;
}

static struct sk_buff *__mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, gfp_t gfp)
{
        struct sk_buff *skb;

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

        if (likely(sk_wmem_schedule(ssk, skb->truesize))) {
                tcp_skb_entail(ssk, skb);
                return skb;
        }
        tcp_skb_tsorted_anchor_cleanup(skb);
        kfree_skb(skb);
        return NULL;
}

static struct sk_buff *mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, bool data_lock_held)
{
        gfp_t gfp = data_lock_held ? GFP_ATOMIC : sk->sk_allocation;

        return __mptcp_alloc_tx_skb(sk, ssk, gfp);
}

/* note: this always recompute the csum on the whole skb, even
 * if we just appended a single frag. More status info needed
 */
static void mptcp_update_data_checksum(struct sk_buff *skb, int added)
{
        struct mptcp_ext *mpext = mptcp_get_ext(skb);
        __wsum csum = ~csum_unfold(mpext->csum);
        int offset = skb->len - added;

        mpext->csum = csum_fold(csum_block_add(csum, skb_checksum(skb, offset, added, 0), offset));
}

static void mptcp_update_infinite_map(struct mptcp_sock *msk,
                                      struct sock *ssk,
                                      struct mptcp_ext *mpext)
{
        if (!mpext)
                return;

        mpext->infinite_map = 1;
        mpext->data_len = 0;

        if (!mptcp_try_fallback(ssk, MPTCP_MIB_INFINITEMAPTX)) {
                MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_FALLBACKFAILED);
                mptcp_subflow_reset(ssk);
                return;
        }

        mptcp_subflow_ctx(ssk)->send_infinite_map = 0;
}

#define MPTCP_MAX_GSO_SIZE (GSO_LEGACY_MAX_SIZE - (MAX_TCP_HEADER + 1))

static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
                              struct mptcp_data_frag *dfrag,
                              struct mptcp_sendmsg_info *info)
{
        u64 data_seq = dfrag->data_seq + info->sent;
        int offset = dfrag->offset + info->sent;
        struct mptcp_sock *msk = mptcp_sk(sk);
        bool zero_window_probe = false;
        struct mptcp_ext *mpext = NULL;
        bool can_coalesce = false;
        bool reuse_skb = true;
        struct sk_buff *skb;
        size_t copy;
        int i;

        pr_debug("msk=%p ssk=%p sending dfrag at seq=%llu len=%u already sent=%u\n",
                 msk, ssk, dfrag->data_seq, dfrag->data_len, info->sent);

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

        if (unlikely(!__tcp_can_send(ssk)))
                return -EAGAIN;

        /* compute send limit */
        if (unlikely(ssk->sk_gso_max_size > MPTCP_MAX_GSO_SIZE))
                ssk->sk_gso_max_size = MPTCP_MAX_GSO_SIZE;
        info->mss_now = tcp_send_mss(ssk, &info->size_goal, info->flags);
        copy = info->size_goal;

        skb = tcp_write_queue_tail(ssk);
        if (skb && copy > skb->len) {
                /* Limit the write to the size available in the
                 * current skb, if any, so that we create at most a new skb.
                 * Explicitly tells TCP internals to avoid collapsing on later
                 * queue management operation, to avoid breaking the ext <->
                 * SSN association set here
                 */
                mpext = mptcp_get_ext(skb);
                if (!mptcp_skb_can_collapse_to(data_seq, skb, mpext)) {
                        TCP_SKB_CB(skb)->eor = 1;
                        tcp_mark_push(tcp_sk(ssk), skb);
                        goto alloc_skb;
                }

                i = skb_shinfo(skb)->nr_frags;
                can_coalesce = skb_can_coalesce(skb, i, dfrag->page, offset);
                if (!can_coalesce && i >= READ_ONCE(net_hotdata.sysctl_max_skb_frags)) {
                        tcp_mark_push(tcp_sk(ssk), skb);
                        goto alloc_skb;
                }

                copy -= skb->len;
        } else {
alloc_skb:
                skb = mptcp_alloc_tx_skb(sk, ssk, info->data_lock_held);
                if (!skb)
                        return -ENOMEM;

                i = skb_shinfo(skb)->nr_frags;
                reuse_skb = false;
                mpext = mptcp_get_ext(skb);
        }

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

                /* No need for zero probe if there are any data pending
                 * either at the msk or ssk level; skb is the current write
                 * queue tail and can be empty at this point.
                 */
                if (snd_una != msk->snd_nxt || skb->len ||
                    skb != tcp_send_head(ssk)) {
                        tcp_remove_empty_skb(ssk);
                        return 0;
                }

                zero_window_probe = true;
                data_seq = snd_una - 1;
                copy = 1;
        }

        copy = min_t(size_t, copy, info->limit - info->sent);
        if (!sk_wmem_schedule(ssk, copy)) {
                tcp_remove_empty_skb(ssk);
                return -ENOMEM;
        }

        if (can_coalesce) {
                skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
        } else {
                get_page(dfrag->page);
                skb_fill_page_desc(skb, i, dfrag->page, offset, copy);
        }

        skb->len += copy;
        skb->data_len += copy;
        skb->truesize += copy;
        sk_wmem_queued_add(ssk, copy);
        sk_mem_charge(ssk, copy);
        WRITE_ONCE(tcp_sk(ssk)->write_seq, tcp_sk(ssk)->write_seq + copy);
        TCP_SKB_CB(skb)->end_seq += copy;
        tcp_skb_pcount_set(skb, 0);

        /* on skb reuse we just need to update the DSS len */
        if (reuse_skb) {
                TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH;
                mpext->data_len += copy;
                goto out;
        }

        memset(mpext, 0, sizeof(*mpext));
        mpext->data_seq = data_seq;
        mpext->subflow_seq = mptcp_subflow_ctx(ssk)->rel_write_seq;
        mpext->data_len = copy;
        mpext->use_map = 1;
        mpext->dsn64 = 1;

        pr_debug("data_seq=%llu subflow_seq=%u data_len=%u dsn64=%d\n",
                 mpext->data_seq, mpext->subflow_seq, mpext->data_len,
                 mpext->dsn64);

        if (zero_window_probe) {
                MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_WINPROBE);
                mptcp_subflow_ctx(ssk)->rel_write_seq += copy;
                mpext->frozen = 1;
                if (READ_ONCE(msk->csum_enabled))
                        mptcp_update_data_checksum(skb, copy);
                tcp_push_pending_frames(ssk);
                return 0;
        }
out:
        if (READ_ONCE(msk->csum_enabled))
                mptcp_update_data_checksum(skb, copy);
        if (mptcp_subflow_ctx(ssk)->send_infinite_map)
                mptcp_update_infinite_map(msk, ssk, mpext);
        trace_mptcp_sendmsg_frag(mpext);
        mptcp_subflow_ctx(ssk)->rel_write_seq += copy;
        return copy;
}

#define MPTCP_SEND_BURST_SIZE           ((1 << 16) - \
                                         sizeof(struct tcphdr) - \
                                         MAX_TCP_OPTION_SPACE - \
                                         sizeof(struct ipv6hdr) - \
                                         sizeof(struct frag_hdr))

struct subflow_send_info {
        struct sock *ssk;
        u64 linger_time;
};

void mptcp_subflow_set_active(struct mptcp_subflow_context *subflow)
{
        if (!subflow->stale)
                return;

        subflow->stale = 0;
        MPTCP_INC_STATS(sock_net(mptcp_subflow_tcp_sock(subflow)), MPTCP_MIB_SUBFLOWRECOVER);
}

bool mptcp_subflow_active(struct mptcp_subflow_context *subflow)
{
        if (unlikely(subflow->stale)) {
                u32 rcv_tstamp = READ_ONCE(tcp_sk(mptcp_subflow_tcp_sock(subflow))->rcv_tstamp);

                if (subflow->stale_rcv_tstamp == rcv_tstamp)
                        return false;

                mptcp_subflow_set_active(subflow);
        }
        return __mptcp_subflow_active(subflow);
}

#define SSK_MODE_ACTIVE 0
#define SSK_MODE_BACKUP 1
#define SSK_MODE_MAX    2

/* implement the mptcp packet scheduler;
 * returns the subflow that will transmit the next DSS
 * additionally updates the rtx timeout
 */
struct sock *mptcp_subflow_get_send(struct mptcp_sock *msk)
{
        struct subflow_send_info send_info[SSK_MODE_MAX];
        struct mptcp_subflow_context *subflow;
        struct sock *sk = (struct sock *)msk;
        u32 pace, burst, wmem;
        int i, nr_active = 0;
        struct sock *ssk;
        u64 linger_time;
        long tout = 0;

        /* pick the subflow with the lower wmem/wspace ratio */
        for (i = 0; i < SSK_MODE_MAX; ++i) {
                send_info[i].ssk = NULL;
                send_info[i].linger_time = -1;
        }

        mptcp_for_each_subflow(msk, subflow) {
                bool backup = subflow->backup || subflow->request_bkup;

                trace_mptcp_subflow_get_send(subflow);
                ssk =  mptcp_subflow_tcp_sock(subflow);
                if (!mptcp_subflow_active(subflow))
                        continue;

                tout = max(tout, mptcp_timeout_from_subflow(subflow));
                nr_active += !backup;
                pace = subflow->avg_pacing_rate;
                if (unlikely(!pace)) {
                        /* init pacing rate from socket */
                        subflow->avg_pacing_rate = READ_ONCE(ssk->sk_pacing_rate);
                        pace = subflow->avg_pacing_rate;
                        if (!pace)
                                continue;
                }

                linger_time = div_u64((u64)READ_ONCE(ssk->sk_wmem_queued) << 32, pace);
                if (linger_time < send_info[backup].linger_time) {
                        send_info[backup].ssk = ssk;
                        send_info[backup].linger_time = linger_time;
                }
        }
        __mptcp_set_timeout(sk, tout);

        /* pick the best backup if no other subflow is active */
        if (!nr_active)
                send_info[SSK_MODE_ACTIVE].ssk = send_info[SSK_MODE_BACKUP].ssk;

        /* According to the blest algorithm, to avoid HoL blocking for the
         * faster flow, we need to:
         * - estimate the faster flow linger time
         * - use the above to estimate the amount of byte transferred
         *   by the faster flow
         * - check that the amount of queued data is greater than the above,
         *   otherwise do not use the picked, slower, subflow
         * We select the subflow with the shorter estimated time to flush
         * the queued mem, which basically ensure the above. We just need
         * to check that subflow has a non empty cwin.
         */
        ssk = send_info[SSK_MODE_ACTIVE].ssk;
        if (!ssk || !sk_stream_memory_free(ssk))
                return NULL;

        burst = min(MPTCP_SEND_BURST_SIZE, mptcp_wnd_end(msk) - msk->snd_nxt);
        wmem = READ_ONCE(ssk->sk_wmem_queued);
        if (!burst)
                return ssk;

        subflow = mptcp_subflow_ctx(ssk);
        subflow->avg_pacing_rate = div_u64((u64)subflow->avg_pacing_rate * wmem +
                                           READ_ONCE(ssk->sk_pacing_rate) * burst,
                                           burst + wmem);
        msk->snd_burst = burst;
        return ssk;
}

static void mptcp_push_release(struct sock *ssk, struct mptcp_sendmsg_info *info)
{
        tcp_push(ssk, 0, info->mss_now, tcp_sk(ssk)->nonagle, info->size_goal);
        release_sock(ssk);
}

static void mptcp_update_post_push(struct mptcp_sock *msk,
                                   struct mptcp_data_frag *dfrag,
                                   u32 sent)
{
        u64 snd_nxt_new = dfrag->data_seq;

        dfrag->already_sent += sent;

        msk->snd_burst -= sent;

        snd_nxt_new += dfrag->already_sent;

        /* snd_nxt_new can be smaller than snd_nxt in case mptcp
         * is recovering after a failover. In that event, this re-sends
         * old segments.
         *
         * Thus compute snd_nxt_new candidate based on
         * the dfrag->data_seq that was sent and the data
         * that has been handed to the subflow for transmission
         * and skip update in case it was old dfrag.
         */
        if (likely(after64(snd_nxt_new, msk->snd_nxt))) {
                msk->bytes_sent += snd_nxt_new - msk->snd_nxt;
                WRITE_ONCE(msk->snd_nxt, snd_nxt_new);
        }
}

void mptcp_check_and_set_pending(struct sock *sk)
{
        if (mptcp_send_head(sk)) {
                mptcp_data_lock(sk);
                mptcp_sk(sk)->cb_flags |= BIT(MPTCP_PUSH_PENDING);
                mptcp_data_unlock(sk);
        }
}

static int __subflow_push_pending(struct sock *sk, struct sock *ssk,
                                  struct mptcp_sendmsg_info *info)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct mptcp_data_frag *dfrag;
        int len, copied = 0, err = 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;

                        ret = mptcp_sendmsg_frag(sk, ssk, dfrag, info);
                        if (ret <= 0) {
                                err = copied ? : ret;
                                goto out;
                        }

                        info->sent += ret;
                        copied += ret;
                        len -= ret;

                        mptcp_update_post_push(msk, dfrag, ret);
                }
                msk->first_pending = mptcp_send_next(sk);

                if (msk->snd_burst <= 0 ||
                    !sk_stream_memory_free(ssk) ||
                    !mptcp_subflow_active(mptcp_subflow_ctx(ssk))) {
                        err = copied;
                        goto out;
                }
                mptcp_set_timeout(sk);
        }
        err = copied;

out:
        if (err > 0)
                msk->last_data_sent = tcp_jiffies32;
        return err;
}

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,
        };
        bool copied = false;
        int push_count = 1;

        while (mptcp_send_head(sk) && (push_count > 0)) {
                struct mptcp_subflow_context *subflow;
                int ret = 0;

                if (mptcp_sched_get_send(msk))
                        break;

                push_count = 0;

                mptcp_for_each_subflow(msk, subflow) {
                        if (READ_ONCE(subflow->scheduled)) {
                                mptcp_subflow_set_scheduled(subflow, false);

                                prev_ssk = ssk;
                                ssk = mptcp_subflow_tcp_sock(subflow);
                                if (ssk != prev_ssk) {
                                        /* First check. If the ssk has changed since
                                         * the last round, release prev_ssk
                                         */
                                        if (prev_ssk)
                                                mptcp_push_release(prev_ssk, &info);

                                        /* Need to lock the new subflow only if different
                                         * from the previous one, otherwise we are still
                                         * helding the relevant lock
                                         */
                                        lock_sock(ssk);
                                }

                                push_count++;

                                ret = __subflow_push_pending(sk, ssk, &info);
                                if (ret <= 0) {
                                        if (ret != -EAGAIN ||
                                            (1 << ssk->sk_state) &
                                             (TCPF_FIN_WAIT1 | TCPF_FIN_WAIT2 | TCPF_CLOSE))
                                                push_count--;
                                        continue;
                                }
                                copied = true;
                        }
                }
        }

        /* at this point we held the socket lock for the last subflow we used */
        if (ssk)
                mptcp_push_release(ssk, &info);

        /* Avoid scheduling the rtx timer if no data has been pushed; the timer
         * will be updated on positive acks by __mptcp_cleanup_una().
         */
        if (copied) {
                if (!mptcp_rtx_timer_pending(sk))
                        mptcp_reset_rtx_timer(sk);
                mptcp_check_send_data_fin(sk);
        }
}

static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk, bool first)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct mptcp_sendmsg_info info = {
                .data_lock_held = true,
        };
        bool keep_pushing = true;
        struct sock *xmit_ssk;
        int copied = 0;

        info.flags = 0;
        while (mptcp_send_head(sk) && keep_pushing) {
                struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
                int ret = 0;

                /* check for a different subflow usage only after
                 * spooling the first chunk of data
                 */
                if (first) {
                        mptcp_subflow_set_scheduled(subflow, false);
                        ret = __subflow_push_pending(sk, ssk, &info);
                        first = false;
                        if (ret <= 0)
                                break;
                        copied += ret;
                        continue;
                }

                if (mptcp_sched_get_send(msk))
                        goto out;

                if (READ_ONCE(subflow->scheduled)) {
                        mptcp_subflow_set_scheduled(subflow, false);
                        ret = __subflow_push_pending(sk, ssk, &info);
                        if (ret <= 0)
                                keep_pushing = false;
                        copied += ret;
                }

                mptcp_for_each_subflow(msk, subflow) {
                        if (READ_ONCE(subflow->scheduled)) {
                                xmit_ssk = mptcp_subflow_tcp_sock(subflow);
                                if (xmit_ssk != ssk) {
                                        mptcp_subflow_delegate(subflow,
                                                               MPTCP_DELEGATE_SEND);
                                        keep_pushing = false;
                                }
                        }
                }
        }

out:
        /* __mptcp_alloc_tx_skb could have released some wmem and we are
         * not going to flush it via release_sock()
         */
        if (copied) {
                tcp_push(ssk, 0, info.mss_now, tcp_sk(ssk)->nonagle,
                         info.size_goal);
                if (!mptcp_rtx_timer_pending(sk))
                        mptcp_reset_rtx_timer(sk);

                if (msk->snd_data_fin_enable &&
                    msk->snd_nxt + 1 == msk->write_seq)
                        mptcp_schedule_work(sk);
        }
}

static int mptcp_disconnect(struct sock *sk, int flags);

static int mptcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
                                  size_t len, int *copied_syn)
{
        unsigned int saved_flags = msg->msg_flags;
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct sock *ssk;
        int ret;

        /* on flags based fastopen the mptcp is supposed to create the
         * first subflow right now. Otherwise we are in the defer_connect
         * path, and the first subflow must be already present.
         * Since the defer_connect flag is cleared after the first succsful
         * fastopen attempt, no need to check for additional subflow status.
         */
        if (msg->msg_flags & MSG_FASTOPEN) {
                ssk = __mptcp_nmpc_sk(msk);
                if (IS_ERR(ssk))
                        return PTR_ERR(ssk);
        }
        if (!msk->first)
                return -EINVAL;

        ssk = msk->first;

        lock_sock(ssk);
        msg->msg_flags |= MSG_DONTWAIT;
        msk->fastopening = 1;
        ret = tcp_sendmsg_fastopen(ssk, msg, copied_syn, len, NULL);
        msk->fastopening = 0;
        msg->msg_flags = saved_flags;
        release_sock(ssk);

        /* do the blocking bits of inet_stream_connect outside the ssk socket lock */
        if (ret == -EINPROGRESS && !(msg->msg_flags & MSG_DONTWAIT)) {
                ret = __inet_stream_connect(sk->sk_socket, msg->msg_name,
                                            msg->msg_namelen, msg->msg_flags, 1);

                /* Keep the same behaviour of plain TCP: zero the copied bytes in
                 * case of any error, except timeout or signal
                 */
                if (ret && ret != -EINPROGRESS && ret != -ERESTARTSYS && ret != -EINTR)
                        *copied_syn = 0;
        } else if (ret && ret != -EINPROGRESS) {
                /* The disconnect() op called by tcp_sendmsg_fastopen()/
                 * __inet_stream_connect() can fail, due to looking check,
                 * see mptcp_disconnect().
                 * Attempt it again outside the problematic scope.
                 */
                if (!mptcp_disconnect(sk, 0)) {
                        sk->sk_disconnects++;
                        sk->sk_socket->state = SS_UNCONNECTED;
                }
        }
        inet_clear_bit(DEFER_CONNECT, sk);

        return ret;
}

static int do_copy_data_nocache(struct sock *sk, int copy,
                                struct iov_iter *from, char *to)
{
        if (sk->sk_route_caps & NETIF_F_NOCACHE_COPY) {
                if (!copy_from_iter_full_nocache(to, copy, from))
                        return -EFAULT;
        } else if (!copy_from_iter_full(to, copy, from)) {
                return -EFAULT;
        }
        return 0;
}

/* open-code sk_stream_memory_free() plus sent limit computation to
 * avoid indirect calls in fast-path.
 * Called under the msk socket lock, so we can avoid a bunch of ONCE
 * annotations.
 */
static u32 mptcp_send_limit(const struct sock *sk)
{
        const struct mptcp_sock *msk = mptcp_sk(sk);
        u32 limit, not_sent;

        if (sk->sk_wmem_queued >= READ_ONCE(sk->sk_sndbuf))
                return 0;

        limit = mptcp_notsent_lowat(sk);
        if (limit == UINT_MAX)
                return UINT_MAX;

        not_sent = msk->write_seq - msk->snd_nxt;
        if (not_sent >= limit)
                return 0;

        return limit - not_sent;
}

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

        if (!rfs_is_needed())
                return;

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

                sock_rps_record_flow(ssk);
        }
}

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;

        /* silently ignore everything else */
        msg->msg_flags &= MSG_MORE | MSG_DONTWAIT | MSG_NOSIGNAL | MSG_FASTOPEN;

        lock_sock(sk);

        mptcp_rps_record_subflows(msk);

        if (unlikely(inet_test_bit(DEFER_CONNECT, sk) ||
                     msg->msg_flags & MSG_FASTOPEN)) {
                int copied_syn = 0;

                ret = mptcp_sendmsg_fastopen(sk, msg, len, &copied_syn);
                copied += copied_syn;
                if (ret == -EINPROGRESS && copied_syn > 0)
                        goto out;
                else if (ret)
                        goto do_error;
        }

        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 do_error;
        }

        ret = -EPIPE;
        if (unlikely(sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN)))
                goto do_error;

        pfrag = sk_page_frag(sk);

        while (msg_data_left(msg)) {
                int total_ts, frag_truesize = 0;
                struct mptcp_data_frag *dfrag;
                bool dfrag_collapsed;
                size_t psize, offset;
                u32 copy_limit;

                /* ensure fitting the notsent_lowat() constraint */
                copy_limit = mptcp_send_limit(sk);
                if (!copy_limit)
                        goto wait_for_memory;

                /* 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 (!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));
                psize = min_t(size_t, psize, copy_limit);
                total_ts = psize + frag_truesize;

                if (!sk_wmem_schedule(sk, total_ts))
                        goto wait_for_memory;

                ret = do_copy_data_nocache(sk, psize, &msg->msg_iter,
                                           page_address(dfrag->page) + offset);
                if (ret)
                        goto do_error;

                /* data successfully copied into the write queue */
                sk_forward_alloc_add(sk, -total_ts);
                copied += psize;
                dfrag->data_len += psize;
                frag_truesize += psize;
                pfrag->offset += frag_truesize;
                WRITE_ONCE(msk->write_seq, msk->write_seq + psize);

                /* charge data on mptcp pending queue to the msk socket
                 * Note: we charge such data both to sk and ssk
                 */
                sk_wmem_queued_add(sk, frag_truesize);
                if (!dfrag_collapsed) {
                        get_page(dfrag->page);
                        list_add_tail(&dfrag->list, &msk->rtx_queue);
                        if (!msk->first_pending)
                                msk->first_pending = dfrag;
                }
                pr_debug("msk=%p dfrag at seq=%llu len=%u sent=%u new=%d\n", msk,
                         dfrag->data_seq, dfrag->data_len, dfrag->already_sent,
                         !dfrag_collapsed);

                continue;

wait_for_memory:
                set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
                __mptcp_push_pending(sk, msg->msg_flags);
                ret = sk_stream_wait_memory(sk, &timeo);
                if (ret)
                        goto do_error;
        }

        if (copied)
                __mptcp_push_pending(sk, msg->msg_flags);

out:
        release_sock(sk);
        return copied;

do_error:
        if (copied)
                goto out;

        copied = sk_stream_error(sk, msg->msg_flags, ret);
        goto out;
}

static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied);

static void mptcp_eat_recv_skb(struct sock *sk, struct sk_buff *skb)
{
        /* avoid the indirect call, we know the destructor is sock_rfree */
        skb->destructor = NULL;
        skb->sk = NULL;
        atomic_sub(skb->truesize, &sk->sk_rmem_alloc);
        sk_mem_uncharge(sk, skb->truesize);
        __skb_unlink(skb, &sk->sk_receive_queue);
        skb_attempt_defer_free(skb);
}

static int __mptcp_recvmsg_mskq(struct sock *sk, struct msghdr *msg,
                                size_t len, int flags, int copied_total,
                                struct scm_timestamping_internal *tss,
                                int *cmsg_flags, struct sk_buff **last)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct sk_buff *skb, *tmp;
        int total_data_len = 0;
        int copied = 0;

        skb_queue_walk_safe(&sk->sk_receive_queue, skb, tmp) {
                u32 delta, offset = MPTCP_SKB_CB(skb)->offset;
                u32 data_len = skb->len - offset;
                u32 count;
                int err;

                if (flags & MSG_PEEK) {
                        /* skip already peeked skbs */
                        if (total_data_len + data_len <= copied_total) {
                                total_data_len += data_len;
                                *last = skb;
                                continue;
                        }

                        /* skip the already peeked data in the current skb */
                        delta = copied_total - total_data_len;
                        offset += delta;
                        data_len -= delta;
                }

                count = min_t(size_t, len - copied, data_len);
                if (!(flags & MSG_TRUNC)) {
                        err = skb_copy_datagram_msg(skb, offset, msg, count);
                        if (unlikely(err < 0)) {
                                if (!copied)
                                        return err;
                                break;
                        }
                }

                if (MPTCP_SKB_CB(skb)->has_rxtstamp) {
                        tcp_update_recv_tstamps(skb, tss);
                        *cmsg_flags |= MPTCP_CMSG_TS;
                }

                copied += count;

                if (!(flags & MSG_PEEK)) {
                        msk->bytes_consumed += count;
                        if (count < data_len) {
                                MPTCP_SKB_CB(skb)->offset += count;
                                MPTCP_SKB_CB(skb)->map_seq += count;
                                break;
                        }

                        mptcp_eat_recv_skb(sk, skb);
                } else {
                        *last = skb;
                }

                if (copied >= len)
                        break;
        }

        mptcp_rcv_space_adjust(msk, copied);
        return copied;
}

static void mptcp_rcv_space_init(struct mptcp_sock *msk, const struct sock *ssk)
{
        const struct tcp_sock *tp = tcp_sk(ssk);

        msk->rcvspace_init = 1;
        msk->rcvq_space.copied = 0;
        msk->rcvq_space.rtt_us = 0;

        /* 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;
}

/* 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;
        u8 scaling_ratio = U8_MAX;
        u32 time, advmss = 1;
        u64 rtt_us, mstamp;

        msk_owned_by_me(msk);

        if (copied <= 0)
                return;

        if (!msk->rcvspace_init)
                mptcp_rcv_space_init(msk, msk->first);

        msk->rcvq_space.copied += copied;

        mstamp = mptcp_stamp();
        time = tcp_stamp_us_delta(mstamp, READ_ONCE(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);
                scaling_ratio = min(tp->scaling_ratio, scaling_ratio);
        }

        msk->rcvq_space.rtt_us = rtt_us;
        msk->scaling_ratio = scaling_ratio;
        if (time < (rtt_us >> 3) || rtt_us == 0)
                return;

        if (msk->rcvq_space.copied <= msk->rcvq_space.space)
                goto new_measure;

        trace_mptcp_rcvbuf_grow(sk, time);
        if (mptcp_rcvbuf_grow(sk, msk->rcvq_space.copied)) {
                /* 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);
                        /* subflows can be added before tcp_init_transfer() */
                        if (tcp_sk(ssk)->rcvq_space.space)
                                tcp_rcvbuf_grow(ssk, msk->rcvq_space.copied);
                        unlock_sock_fast(ssk, slow);
                }
        }

new_measure:
        msk->rcvq_space.copied = 0;
        msk->rcvq_space.time = mstamp;
}

static bool __mptcp_move_skbs(struct sock *sk, struct list_head *skbs, u32 *delta)
{
        struct sk_buff *skb = list_first_entry(skbs, struct sk_buff, list);
        struct mptcp_sock *msk = mptcp_sk(sk);
        bool moved = false;

        *delta = 0;
        while (1) {
                /* If the msk recvbuf is full stop, don't drop */
                if (sk_rmem_alloc_get(sk) > sk->sk_rcvbuf)
                        break;

                prefetch(skb->next);
                list_del(&skb->list);
                *delta += skb->truesize;

                moved |= __mptcp_move_skb(sk, skb);
                if (list_empty(skbs))
                        break;

                skb = list_first_entry(skbs, struct sk_buff, list);
        }

        __mptcp_ofo_queue(msk);
        if (moved)
                mptcp_check_data_fin((struct sock *)msk);
        return moved;
}

static bool mptcp_can_spool_backlog(struct sock *sk, struct list_head *skbs)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        /* After CG initialization, subflows should never add skb before
         * gaining the CG themself.
         */
        DEBUG_NET_WARN_ON_ONCE(msk->backlog_unaccounted && sk->sk_socket &&
                               mem_cgroup_from_sk(sk));

        /* Don't spool the backlog if the rcvbuf is full. */
        if (list_empty(&msk->backlog_list) ||
            sk_rmem_alloc_get(sk) > sk->sk_rcvbuf)
                return false;

        INIT_LIST_HEAD(skbs);
        list_splice_init(&msk->backlog_list, skbs);
        return true;
}

static void mptcp_backlog_spooled(struct sock *sk, u32 moved,
                                  struct list_head *skbs)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        WRITE_ONCE(msk->backlog_len, msk->backlog_len - moved);
        list_splice(skbs, &msk->backlog_list);
}

static bool mptcp_move_skbs(struct sock *sk)
{
        struct list_head skbs;
        bool enqueued = false;
        u32 moved;

        mptcp_data_lock(sk);
        while (mptcp_can_spool_backlog(sk, &skbs)) {
                mptcp_data_unlock(sk);
                enqueued |= __mptcp_move_skbs(sk, &skbs, &moved);

                mptcp_data_lock(sk);
                mptcp_backlog_spooled(sk, moved, &skbs);
        }
        mptcp_data_unlock(sk);
        return enqueued;
}

static unsigned int mptcp_inq_hint(const struct sock *sk)
{
        const struct mptcp_sock *msk = mptcp_sk(sk);
        const struct sk_buff *skb;

        skb = skb_peek(&sk->sk_receive_queue);
        if (skb) {
                u64 hint_val = READ_ONCE(msk->ack_seq) - MPTCP_SKB_CB(skb)->map_seq;

                if (hint_val >= INT_MAX)
                        return INT_MAX;

                return (unsigned int)hint_val;
        }

        if (sk->sk_state == TCP_CLOSE || (sk->sk_shutdown & RCV_SHUTDOWN))
                return 1;

        return 0;
}

static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
                         int flags, int *addr_len)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct scm_timestamping_internal tss;
        int copied = 0, cmsg_flags = 0;
        int target;
        long timeo;

        /* MSG_ERRQUEUE is really a no-op till we support IP_RECVERR */
        if (unlikely(flags & MSG_ERRQUEUE))
                return inet_recv_error(sk, msg, len, addr_len);

        lock_sock(sk);
        if (unlikely(sk->sk_state == TCP_LISTEN)) {
                copied = -ENOTCONN;
                goto out_err;
        }

        mptcp_rps_record_subflows(msk);

        timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);

        len = min_t(size_t, len, INT_MAX);
        target = sock_rcvlowat(sk, flags & MSG_WAITALL, len);

        if (unlikely(msk->recvmsg_inq))
                cmsg_flags = MPTCP_CMSG_INQ;

        while (copied < len) {
                struct sk_buff *last = NULL;
                int err, bytes_read;

                bytes_read = __mptcp_recvmsg_mskq(sk, msg, len - copied, flags,
                                                  copied, &tss, &cmsg_flags,
                                                  &last);
                if (unlikely(bytes_read < 0)) {
                        if (!copied)
                                copied = bytes_read;
                        goto out_err;
                }

                copied += bytes_read;

                if (!list_empty(&msk->backlog_list) && mptcp_move_skbs(sk))
                        continue;

                /* only the MPTCP 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 (sk->sk_shutdown & RCV_SHUTDOWN)
                                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\n", timeo);
                mptcp_cleanup_rbuf(msk, copied);
                err = sk_wait_data(sk, &timeo, last);
                if (err < 0) {
                        err = copied ? : err;
                        goto out_err;
                }
        }

        mptcp_cleanup_rbuf(msk, copied);

out_err:
        if (cmsg_flags && copied >= 0) {
                if (cmsg_flags & MPTCP_CMSG_TS)
                        tcp_recv_timestamp(msg, sk, &tss);

                if (cmsg_flags & MPTCP_CMSG_INQ) {
                        unsigned int inq = mptcp_inq_hint(sk);

                        put_cmsg(msg, SOL_TCP, TCP_CM_INQ, sizeof(inq), &inq);
                }
        }

        pr_debug("msk=%p rx queue empty=%d copied=%d\n",
                 msk, skb_queue_empty(&sk->sk_receive_queue), copied);

        release_sock(sk);
        return copied;
}

static void mptcp_retransmit_timer(struct timer_list *t)
{
        struct sock *sk = timer_container_of(sk, t, mptcp_retransmit_timer);
        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->cb_flags);
        }
        bh_unlock_sock(sk);
        sock_put(sk);
}

static void mptcp_tout_timer(struct timer_list *t)
{
        struct inet_connection_sock *icsk =
                timer_container_of(icsk, t, mptcp_tout_timer);
        struct sock *sk = &icsk->icsk_inet.sk;

        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.
 */
struct sock *mptcp_subflow_get_retrans(struct mptcp_sock *msk)
{
        struct sock *backup = NULL, *pick = NULL;
        struct mptcp_subflow_context *subflow;
        int min_stale_count = INT_MAX;

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

                if (!__mptcp_subflow_active(subflow))
                        continue;

                /* still data outstanding at TCP level? skip this */
                if (!tcp_rtx_and_write_queues_empty(ssk)) {
                        mptcp_pm_subflow_chk_stale(msk, ssk);
                        min_stale_count = min_t(int, min_stale_count, subflow->stale_count);
                        continue;
                }

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

                if (!pick)
                        pick = ssk;
        }

        if (pick)
                return pick;

        /* use backup only if there are no progresses anywhere */
        return min_stale_count > 1 ? backup : NULL;
}

bool __mptcp_retransmit_pending_data(struct sock *sk)
{
        struct mptcp_data_frag *cur, *rtx_head;
        struct mptcp_sock *msk = mptcp_sk(sk);

        if (__mptcp_check_fallback(msk))
                return false;

        /* the closing socket has some data untransmitted and/or unacked:
         * some data in the mptcp rtx queue has not really xmitted yet.
         * keep it simple and re-inject the whole mptcp level rtx queue
         */
        mptcp_data_lock(sk);
        __mptcp_clean_una_wakeup(sk);
        rtx_head = mptcp_rtx_head(sk);
        if (!rtx_head) {
                mptcp_data_unlock(sk);
                return false;
        }

        msk->recovery_snd_nxt = msk->snd_nxt;
        msk->recovery = true;
        mptcp_data_unlock(sk);

        msk->first_pending = rtx_head;
        msk->snd_burst = 0;

        /* be sure to clear the "sent status" on all re-injected fragments */
        list_for_each_entry(cur, &msk->rtx_queue, list) {
                if (!cur->already_sent)
                        break;
                cur->already_sent = 0;
        }

        return true;
}

/* flags for __mptcp_close_ssk() */
#define MPTCP_CF_PUSH           BIT(1)

/* be sure to send a reset only if the caller asked for it, also
 * clean completely the subflow status when the subflow reaches
 * TCP_CLOSE state
 */
static void __mptcp_subflow_disconnect(struct sock *ssk,
                                       struct mptcp_subflow_context *subflow,
                                       bool fastclosing)
{
        if (((1 << ssk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
            fastclosing) {
                /* The MPTCP code never wait on the subflow sockets, TCP-level
                 * disconnect should never fail
                 */
                WARN_ON_ONCE(tcp_disconnect(ssk, 0));
                mptcp_subflow_ctx_reset(subflow);
        } else {
                tcp_shutdown(ssk, SEND_SHUTDOWN);
        }
}

/* 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,
                              unsigned int flags)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        bool dispose_it, need_push = false;
        int fwd_remaining;

        /* Do not pass RX data to the msk, even if the subflow socket is not
         * going to be freed (i.e. even for the first subflow on graceful
         * subflow close.
         */
        lock_sock_nested(ssk, SINGLE_DEPTH_NESTING);
        subflow->closing = 1;

        /* Borrow the fwd allocated page left-over; fwd memory for the subflow
         * could be negative at this point, but will be reach zero soon - when
         * the data allocated using such fragment will be freed.
         */
        if (subflow->lent_mem_frag) {
                fwd_remaining = PAGE_SIZE - subflow->lent_mem_frag;
                sk_forward_alloc_add(sk, fwd_remaining);
                sk_forward_alloc_add(ssk, -fwd_remaining);
                subflow->lent_mem_frag = 0;
        }

        /* If the first subflow moved to a close state before accept, e.g. due
         * to an incoming reset or listener shutdown, the subflow socket is
         * already deleted by inet_child_forget() and the mptcp socket can't
         * survive too.
         */
        if (msk->in_accept_queue && msk->first == ssk &&
            (sock_flag(sk, SOCK_DEAD) || sock_flag(ssk, SOCK_DEAD))) {
                /* ensure later check in mptcp_worker() will dispose the msk */
                sock_set_flag(sk, SOCK_DEAD);
                mptcp_set_close_tout(sk, tcp_jiffies32 - (mptcp_close_timeout(sk) + 1));
                mptcp_subflow_drop_ctx(ssk);
                goto out_release;
        }

        dispose_it = msk->free_first || ssk != msk->first;
        if (dispose_it)
                list_del(&subflow->node);

        if (subflow->send_fastclose && ssk->sk_state != TCP_CLOSE)
                tcp_set_state(ssk, TCP_CLOSE);

        need_push = (flags & MPTCP_CF_PUSH) && __mptcp_retransmit_pending_data(sk);
        if (!dispose_it) {
                __mptcp_subflow_disconnect(ssk, subflow, msk->fastclosing);
                release_sock(ssk);

                goto out;
        }

        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) {
                WARN_ON_ONCE(!sock_flag(ssk, SOCK_DEAD));
                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);
        }

out_release:
        __mptcp_subflow_error_report(sk, ssk);
        release_sock(ssk);

        sock_put(ssk);

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

out:
        __mptcp_sync_sndbuf(sk);
        if (need_push)
                __mptcp_push_pending(sk, 0);

        /* Catch every 'all subflows closed' scenario, including peers silently
         * closing them, e.g. due to timeout.
         * For established sockets, allow an additional timeout before closing,
         * as the protocol can still create more subflows.
         */
        if (list_is_singular(&msk->conn_list) && msk->first &&
            inet_sk_state_load(msk->first) == TCP_CLOSE) {
                if (sk->sk_state != TCP_ESTABLISHED ||
                    msk->in_accept_queue || sock_flag(sk, SOCK_DEAD)) {
                        mptcp_set_state(sk, TCP_CLOSE);
                        mptcp_close_wake_up(sk);
                } else {
                        mptcp_start_tout_timer(sk);
                }
        }
}

void mptcp_close_ssk(struct sock *sk, struct sock *ssk,
                     struct mptcp_subflow_context *subflow)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct sk_buff *skb;

        /* The first subflow can already be closed or disconnected */
        if (subflow->close_event_done || READ_ONCE(subflow->local_id) < 0)
                return;

        subflow->close_event_done = true;

        if (sk->sk_state == TCP_ESTABLISHED)
                mptcp_event(MPTCP_EVENT_SUB_CLOSED, mptcp_sk(sk), ssk, GFP_KERNEL);

        /* Remove any reference from the backlog to this ssk; backlog skbs consume
         * space in the msk receive queue, no need to touch sk->sk_rmem_alloc
         */
        list_for_each_entry(skb, &msk->backlog_list, list) {
                if (skb->sk != ssk)
                        continue;

                atomic_sub(skb->truesize, &skb->sk->sk_rmem_alloc);
                skb->sk = NULL;
        }

        /* subflow aborted before reaching the fully_established status
         * attempt the creation of the next subflow
         */
        mptcp_pm_subflow_check_next(mptcp_sk(sk), subflow);

        __mptcp_close_ssk(sk, ssk, subflow, MPTCP_CF_PUSH);
}

static unsigned int mptcp_sync_mss(struct sock *sk, u32 pmtu)
{
        return 0;
}

static void __mptcp_close_subflow(struct sock *sk)
{
        struct mptcp_subflow_context *subflow, *tmp;
        struct mptcp_sock *msk = mptcp_sk(sk);

        might_sleep();

        mptcp_for_each_subflow_safe(msk, subflow, tmp) {
                struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
                int ssk_state = inet_sk_state_load(ssk);

                if (ssk_state != TCP_CLOSE &&
                    (ssk_state != TCP_CLOSE_WAIT ||
                     inet_sk_state_load(sk) != TCP_ESTABLISHED ||
                     __mptcp_check_fallback(msk)))
                        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(sk, ssk, subflow);
        }

}

static bool mptcp_close_tout_expired(const struct sock *sk)
{
        if (!inet_csk(sk)->icsk_mtup.probe_timestamp ||
            sk->sk_state == TCP_CLOSE)
                return false;

        return time_after32(tcp_jiffies32,
                  inet_csk(sk)->icsk_mtup.probe_timestamp + mptcp_close_timeout(sk));
}

static void mptcp_check_fastclose(struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow, *tmp;
        struct sock *sk = (struct sock *)msk;

        if (likely(!READ_ONCE(msk->rcv_fastclose)))
                return;

        mptcp_token_destroy(msk);

        mptcp_for_each_subflow_safe(msk, subflow, tmp) {
                struct sock *tcp_sk = mptcp_subflow_tcp_sock(subflow);
                bool slow;

                slow = lock_sock_fast(tcp_sk);
                if (tcp_sk->sk_state != TCP_CLOSE) {
                        mptcp_send_active_reset_reason(tcp_sk);
                        tcp_set_state(tcp_sk, TCP_CLOSE);
                }
                unlock_sock_fast(tcp_sk, slow);
        }

        /* Mirror the tcp_reset() error propagation */
        switch (sk->sk_state) {
        case TCP_SYN_SENT:
                WRITE_ONCE(sk->sk_err, ECONNREFUSED);
                break;
        case TCP_CLOSE_WAIT:
                WRITE_ONCE(sk->sk_err, EPIPE);
                break;
        case TCP_CLOSE:
                return;
        default:
                WRITE_ONCE(sk->sk_err, ECONNRESET);
        }

        mptcp_set_state(sk, TCP_CLOSE);
        WRITE_ONCE(sk->sk_shutdown, SHUTDOWN_MASK);
        smp_mb__before_atomic(); /* SHUTDOWN must be visible first */
        set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags);

        /* the calling mptcp_worker will properly destroy the socket */
        if (sock_flag(sk, SOCK_DEAD))
                return;

        sk->sk_state_change(sk);
        sk_error_report(sk);
}

static void __mptcp_retrans(struct sock *sk)
{
        struct mptcp_sendmsg_info info = { .data_lock_held = true, };
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct mptcp_subflow_context *subflow;
        struct mptcp_data_frag *dfrag;
        struct sock *ssk;
        int ret, err;
        u16 len = 0;

        mptcp_clean_una_wakeup(sk);

        /* first check ssk: need to kick "stale" logic */
        err = mptcp_sched_get_retrans(msk);
        dfrag = mptcp_rtx_head(sk);
        if (!dfrag) {
                if (mptcp_data_fin_enabled(msk)) {
                        struct inet_connection_sock *icsk = inet_csk(sk);

                        WRITE_ONCE(icsk->icsk_retransmits,
                                   icsk->icsk_retransmits + 1);
                        mptcp_set_datafin_timeout(sk);
                        mptcp_send_ack(msk);

                        goto reset_timer;
                }

                if (!mptcp_send_head(sk))
                        goto clear_scheduled;

                goto reset_timer;
        }

        if (err)
                goto reset_timer;

        mptcp_for_each_subflow(msk, subflow) {
                if (READ_ONCE(subflow->scheduled)) {
                        u16 copied = 0;

                        mptcp_subflow_set_scheduled(subflow, false);

                        ssk = mptcp_subflow_tcp_sock(subflow);

                        lock_sock(ssk);

                        /* limit retransmission to the bytes already sent on some subflows */
                        info.sent = 0;
                        info.limit = READ_ONCE(msk->csum_enabled) ? dfrag->data_len :
                                                                    dfrag->already_sent;

                        /*
                         * make the whole retrans decision, xmit, disallow
                         * fallback atomic, note that we can't retrans even
                         * when an infinite fallback is in progress, i.e. new
                         * subflows are disallowed.
                         */
                        spin_lock_bh(&msk->fallback_lock);
                        if (__mptcp_check_fallback(msk) ||
                            !msk->allow_subflows) {
                                spin_unlock_bh(&msk->fallback_lock);
                                release_sock(ssk);
                                goto clear_scheduled;
                        }

                        while (info.sent < info.limit) {
                                ret = mptcp_sendmsg_frag(sk, ssk, dfrag, &info);
                                if (ret <= 0)
                                        break;

                                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_RETRANSSEGS);
                                copied += ret;
                                info.sent += ret;
                        }
                        if (copied) {
                                len = max(copied, len);
                                tcp_push(ssk, 0, info.mss_now, tcp_sk(ssk)->nonagle,
                                         info.size_goal);
                                msk->allow_infinite_fallback = false;
                        }
                        spin_unlock_bh(&msk->fallback_lock);

                        release_sock(ssk);
                }
        }

        msk->bytes_retrans += len;
        dfrag->already_sent = max(dfrag->already_sent, len);

reset_timer:
        mptcp_check_and_set_pending(sk);

        if (!mptcp_rtx_timer_pending(sk))
                mptcp_reset_rtx_timer(sk);

clear_scheduled:
        /* If no rtx data was available or in case of fallback, there
         * could be left-over scheduled subflows; clear them all
         * or later xmit could use bad ones
         */
        mptcp_for_each_subflow(msk, subflow)
                if (READ_ONCE(subflow->scheduled))
                        mptcp_subflow_set_scheduled(subflow, false);
}

/* schedule the timeout timer for the relevant event: either close timeout
 * or mp_fail timeout. The close timeout takes precedence on the mp_fail one
 */
void mptcp_reset_tout_timer(struct mptcp_sock *msk, unsigned long fail_tout)
{
        struct sock *sk = (struct sock *)msk;
        unsigned long timeout, close_timeout;

        if (!fail_tout && !inet_csk(sk)->icsk_mtup.probe_timestamp)
                return;

        close_timeout = (unsigned long)inet_csk(sk)->icsk_mtup.probe_timestamp -
                        tcp_jiffies32 + jiffies + mptcp_close_timeout(sk);

        /* the close timeout takes precedence on the fail one, and here at least one of
         * them is active
         */
        timeout = inet_csk(sk)->icsk_mtup.probe_timestamp ? close_timeout : fail_tout;

        sk_reset_timer(sk, &inet_csk(sk)->mptcp_tout_timer, timeout);
}

static void mptcp_mp_fail_no_response(struct mptcp_sock *msk)
{
        struct sock *ssk = msk->first;
        bool slow;

        if (!ssk)
                return;

        pr_debug("MP_FAIL doesn't respond, reset the subflow\n");

        slow = lock_sock_fast(ssk);
        mptcp_subflow_reset(ssk);
        WRITE_ONCE(mptcp_subflow_ctx(ssk)->fail_tout, 0);
        unlock_sock_fast(ssk, slow);
}

static void mptcp_backlog_purge(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct sk_buff *tmp, *skb;
        LIST_HEAD(backlog);

        mptcp_data_lock(sk);
        list_splice_init(&msk->backlog_list, &backlog);
        msk->backlog_len = 0;
        mptcp_data_unlock(sk);

        list_for_each_entry_safe(skb, tmp, &backlog, list) {
                mptcp_borrow_fwdmem(sk, skb);
                kfree_skb_reason(skb, SKB_DROP_REASON_SOCKET_CLOSE);
        }
        sk_mem_reclaim(sk);
}

static void mptcp_do_fastclose(struct sock *sk)
{
        struct mptcp_subflow_context *subflow, *tmp;
        struct mptcp_sock *msk = mptcp_sk(sk);

        mptcp_set_state(sk, TCP_CLOSE);
        mptcp_backlog_purge(sk);
        msk->fastclosing = 1;

        /* Explicitly send the fastclose reset as need */
        if (__mptcp_check_fallback(msk))
                return;

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

                lock_sock(ssk);

                /* Some subflow socket states don't allow/need a reset.*/
                if ((1 << ssk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
                        goto unlock;

                subflow->send_fastclose = 1;

                /* Initialize rcv_mss to TCP_MIN_MSS to avoid division by 0
                 * issue in __tcp_select_window(), see tcp_disconnect().
                 */
                inet_csk(ssk)->icsk_ack.rcv_mss = TCP_MIN_MSS;

                tcp_send_active_reset(ssk, ssk->sk_allocation,
                                      SK_RST_REASON_TCP_ABORT_ON_CLOSE);
unlock:
                release_sock(ssk);
        }
}

static void mptcp_worker(struct work_struct *work)
{
        struct mptcp_sock *msk = container_of(work, struct mptcp_sock, work);
        struct sock *sk = (struct sock *)msk;
        unsigned long fail_tout;
        int state;

        lock_sock(sk);
        state = sk->sk_state;
        if (unlikely((1 << state) & (TCPF_CLOSE | TCPF_LISTEN)))
                goto unlock;

        mptcp_check_fastclose(msk);

        mptcp_pm_worker(msk);

        mptcp_check_send_data_fin(sk);
        mptcp_check_data_fin_ack(sk);
        mptcp_check_data_fin(sk);

        if (test_and_clear_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags))
                __mptcp_close_subflow(sk);

        if (mptcp_close_tout_expired(sk)) {
                struct mptcp_subflow_context *subflow, *tmp;

                mptcp_do_fastclose(sk);
                mptcp_for_each_subflow_safe(msk, subflow, tmp)
                        __mptcp_close_ssk(sk, subflow->tcp_sock, subflow, 0);
                mptcp_close_wake_up(sk);
        }

        if (sock_flag(sk, SOCK_DEAD) && sk->sk_state == TCP_CLOSE) {
                __mptcp_destroy_sock(sk);
                goto unlock;
        }

        if (test_and_clear_bit(MPTCP_WORK_RTX, &msk->flags))
                __mptcp_retrans(sk);

        fail_tout = msk->first ? READ_ONCE(mptcp_subflow_ctx(msk->first)->fail_tout) : 0;
        if (fail_tout && time_after(jiffies, fail_tout))
                mptcp_mp_fail_no_response(msk);

unlock:
        release_sock(sk);
        sock_put(sk);
}

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

        INIT_LIST_HEAD(&msk->conn_list);
        INIT_LIST_HEAD(&msk->join_list);
        INIT_LIST_HEAD(&msk->rtx_queue);
        INIT_LIST_HEAD(&msk->backlog_list);
        INIT_WORK(&msk->work, mptcp_worker);
        msk->out_of_order_queue = RB_ROOT;
        msk->first_pending = NULL;
        msk->timer_ival = TCP_RTO_MIN;
        msk->scaling_ratio = TCP_DEFAULT_SCALING_RATIO;
        msk->backlog_len = 0;

        WRITE_ONCE(msk->first, NULL);
        inet_csk(sk)->icsk_sync_mss = mptcp_sync_mss;
        WRITE_ONCE(msk->csum_enabled, mptcp_is_checksum_enabled(sock_net(sk)));
        msk->allow_infinite_fallback = true;
        msk->allow_subflows = true;
        msk->recovery = false;
        msk->subflow_id = 1;
        msk->last_data_sent = tcp_jiffies32;
        msk->last_data_recv = tcp_jiffies32;
        msk->last_ack_recv = tcp_jiffies32;

        mptcp_pm_data_init(msk);
        spin_lock_init(&msk->fallback_lock);

        /* re-use the csk retrans timer for MPTCP-level retrans */
        timer_setup(&sk->mptcp_retransmit_timer, mptcp_retransmit_timer, 0);
        timer_setup(&msk->sk.mptcp_tout_timer, mptcp_tout_timer, 0);
}

static void mptcp_ca_reset(struct sock *sk)
{
        struct inet_connection_sock *icsk = inet_csk(sk);

        tcp_assign_congestion_control(sk);
        strscpy(mptcp_sk(sk)->ca_name, icsk->icsk_ca_ops->name,
                sizeof(mptcp_sk(sk)->ca_name));

        /* no need to keep a reference to the ops, the name will suffice */
        tcp_cleanup_congestion_control(sk);
        icsk->icsk_ca_ops = NULL;
}

static int mptcp_init_sock(struct sock *sk)
{
        struct net *net = sock_net(sk);
        int ret;

        __mptcp_init_sock(sk);

        if (!mptcp_is_enabled(net))
                return -ENOPROTOOPT;

        if (unlikely(!net->mib.mptcp_statistics) && !mptcp_mib_alloc(net))
                return -ENOMEM;

        rcu_read_lock();
        ret = mptcp_init_sched(mptcp_sk(sk),
                               mptcp_sched_find(mptcp_get_scheduler(net)));
        rcu_read_unlock();
        if (ret)
                return ret;

        set_bit(SOCK_CUSTOM_SOCKOPT, &sk->sk_socket->flags);

        /* fetch the ca name; do it outside __mptcp_init_sock(), so that clone will
         * propagate the correct value
         */
        mptcp_ca_reset(sk);

        sk_sockets_allocated_inc(sk);
        sk->sk_rcvbuf = READ_ONCE(net->ipv4.sysctl_tcp_rmem[1]);
        sk->sk_sndbuf = READ_ONCE(net->ipv4.sysctl_tcp_wmem[1]);
        sk->sk_write_space = sk_stream_write_space;

        return 0;
}

static void __mptcp_clear_xmit(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct mptcp_data_frag *dtmp, *dfrag;

        msk->first_pending = NULL;
        list_for_each_entry_safe(dfrag, dtmp, &msk->rtx_queue, list)
                dfrag_clear(sk, dfrag);
}

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:
                WARN_ON_ONCE(tcp_disconnect(ssk, O_NONBLOCK));
                break;
        default:
                if (__mptcp_check_fallback(mptcp_sk(sk))) {
                        pr_debug("Fallback\n");
                        ssk->sk_shutdown |= how;
                        tcp_shutdown(ssk, how);

                        /* simulate the data_fin ack reception to let the state
                         * machine move forward
                         */
                        WRITE_ONCE(mptcp_sk(sk)->snd_una, mptcp_sk(sk)->snd_nxt);
                        mptcp_schedule_work(sk);
                } else {
                        pr_debug("Sending DATA_FIN on subflow %p\n", ssk);
                        tcp_send_ack(ssk);
                        if (!mptcp_rtx_timer_pending(sk))
                                mptcp_reset_rtx_timer(sk);
                }
                break;
        }

        release_sock(ssk);
}

void mptcp_set_state(struct sock *sk, int state)
{
        int oldstate = sk->sk_state;

        switch (state) {
        case TCP_ESTABLISHED:
                if (oldstate != TCP_ESTABLISHED)
                        MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_CURRESTAB);
                break;
        case TCP_CLOSE_WAIT:
                /* Unlike TCP, MPTCP sk would not have the TCP_SYN_RECV state:
                 * MPTCP "accepted" sockets will be created later on. So no
                 * transition from TCP_SYN_RECV to TCP_CLOSE_WAIT.
                 */
                break;
        default:
                if (oldstate == TCP_ESTABLISHED || oldstate == TCP_CLOSE_WAIT)
                        MPTCP_DEC_STATS(sock_net(sk), MPTCP_MIB_CURRESTAB);
        }

        inet_sk_state_store(sk, state);
}

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;

        mptcp_set_state(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\n",
                 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);

        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\n",
                 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_sock *msk = mptcp_sk(sk);

        pr_debug("msk=%p\n", msk);

        might_sleep();

        mptcp_stop_rtx_timer(sk);
        sk_stop_timer(sk, &inet_csk(sk)->mptcp_tout_timer);
        msk->pm.status = 0;
        mptcp_release_sched(msk);

        sk->sk_prot->destroy(sk);

        sk_stream_kill_queues(sk);
        xfrm_sk_free_policy(sk);

        sock_put(sk);
}

void __mptcp_unaccepted_force_close(struct sock *sk)
{
        sock_set_flag(sk, SOCK_DEAD);
        mptcp_do_fastclose(sk);
        __mptcp_destroy_sock(sk);
}

static __poll_t mptcp_check_readable(struct sock *sk)
{
        return mptcp_epollin_ready(sk) ? EPOLLIN | EPOLLRDNORM : 0;
}

static void mptcp_check_listen_stop(struct sock *sk)
{
        struct sock *ssk;

        if (inet_sk_state_load(sk) != TCP_LISTEN)
                return;

        sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
        ssk = mptcp_sk(sk)->first;
        if (WARN_ON_ONCE(!ssk || inet_sk_state_load(ssk) != TCP_LISTEN))
                return;

        lock_sock_nested(ssk, SINGLE_DEPTH_NESTING);
        tcp_set_state(ssk, TCP_CLOSE);
        mptcp_subflow_queue_clean(sk, ssk);
        inet_csk_listen_stop(ssk);
        mptcp_event_pm_listener(ssk, MPTCP_EVENT_LISTENER_CLOSED);
        release_sock(ssk);
}

bool __mptcp_close(struct sock *sk, long timeout)
{
        struct mptcp_subflow_context *subflow;
        struct mptcp_sock *msk = mptcp_sk(sk);
        bool do_cancel_work = false;
        int subflows_alive = 0;

        WRITE_ONCE(sk->sk_shutdown, SHUTDOWN_MASK);

        if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE)) {
                mptcp_check_listen_stop(sk);
                mptcp_set_state(sk, TCP_CLOSE);
                goto cleanup;
        }

        if (mptcp_data_avail(msk) || timeout < 0) {
                /* If the msk has read data, or the caller explicitly ask it,
                 * do the MPTCP equivalent of TCP reset, aka MPTCP fastclose
                 */
                mptcp_do_fastclose(sk);
                timeout = 0;
        } else if (mptcp_close_state(sk)) {
                __mptcp_wr_shutdown(sk);
        }

        sk_stream_wait_close(sk, timeout);

cleanup:
        /* orphan all the subflows */
        mptcp_for_each_subflow(msk, subflow) {
                struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
                bool slow = lock_sock_fast_nested(ssk);

                subflows_alive += ssk->sk_state != TCP_CLOSE;

                /* since the close timeout takes precedence on the fail one,
                 * cancel the latter
                 */
                if (ssk == msk->first)
                        subflow->fail_tout = 0;

                /* detach from the parent socket, but allow data_ready to
                 * push incoming data into the mptcp stack, to properly ack it
                 */
                ssk->sk_socket = NULL;
                ssk->sk_wq = NULL;
                unlock_sock_fast(ssk, slow);
        }
        sock_orphan(sk);

        /* all the subflows are closed, only timeout can change the msk
         * state, let's not keep resources busy for no reasons
         */
        if (subflows_alive == 0)
                mptcp_set_state(sk, TCP_CLOSE);

        sock_hold(sk);
        pr_debug("msk=%p state=%d\n", sk, sk->sk_state);
        mptcp_pm_connection_closed(msk);

        if (sk->sk_state == TCP_CLOSE) {
                __mptcp_destroy_sock(sk);
                do_cancel_work = true;
        } else {
                mptcp_start_tout_timer(sk);
        }

        return do_cancel_work;
}

static void mptcp_close(struct sock *sk, long timeout)
{
        bool do_cancel_work;

        lock_sock(sk);

        do_cancel_work = __mptcp_close(sk, timeout);
        release_sock(sk);
        if (do_cancel_work)
                mptcp_cancel_work(sk);

        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 void mptcp_destroy_common(struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow, *tmp;
        struct sock *sk = (struct sock *)msk;

        __mptcp_clear_xmit(sk);
        mptcp_backlog_purge(sk);

        /* join list will be eventually flushed (with rst) at sock lock release time */
        mptcp_for_each_subflow_safe(msk, subflow, tmp)
                __mptcp_close_ssk(sk, mptcp_subflow_tcp_sock(subflow), subflow, 0);

        __skb_queue_purge(&sk->sk_receive_queue);
        skb_rbtree_purge(&msk->out_of_order_queue);

        /* move all the rx fwd alloc into the sk_mem_reclaim_final in
         * inet_sock_destruct() will dispose it
         */
        mptcp_token_destroy(msk);
        mptcp_pm_destroy(msk);
}

static int mptcp_disconnect(struct sock *sk, int flags)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        /* We are on the fastopen error path. We can't call straight into the
         * subflows cleanup code due to lock nesting (we are already under
         * msk->firstsocket lock).
         */
        if (msk->fastopening)
                return -EBUSY;

        mptcp_check_listen_stop(sk);
        mptcp_set_state(sk, TCP_CLOSE);

        mptcp_stop_rtx_timer(sk);
        mptcp_stop_tout_timer(sk);

        mptcp_pm_connection_closed(msk);

        /* msk->subflow is still intact, the following will not free the first
         * subflow
         */
        mptcp_do_fastclose(sk);
        mptcp_destroy_common(msk);

        /* The first subflow is already in TCP_CLOSE status, the following
         * can't overlap with a fallback anymore
         */
        spin_lock_bh(&msk->fallback_lock);
        msk->allow_subflows = true;
        msk->allow_infinite_fallback = true;
        WRITE_ONCE(msk->flags, 0);
        spin_unlock_bh(&msk->fallback_lock);

        msk->cb_flags = 0;
        msk->recovery = false;
        WRITE_ONCE(msk->can_ack, false);
        WRITE_ONCE(msk->fully_established, false);
        WRITE_ONCE(msk->rcv_data_fin, false);
        WRITE_ONCE(msk->snd_data_fin_enable, false);
        WRITE_ONCE(msk->rcv_fastclose, false);
        WRITE_ONCE(msk->use_64bit_ack, false);
        WRITE_ONCE(msk->csum_enabled, mptcp_is_checksum_enabled(sock_net(sk)));
        mptcp_pm_data_reset(msk);
        mptcp_ca_reset(sk);
        msk->bytes_consumed = 0;
        msk->bytes_acked = 0;
        msk->bytes_received = 0;
        msk->bytes_sent = 0;
        msk->bytes_retrans = 0;
        msk->rcvspace_init = 0;
        msk->fastclosing = 0;

        /* for fallback's sake */
        WRITE_ONCE(msk->ack_seq, 0);

        WRITE_ONCE(sk->sk_shutdown, 0);
        sk_error_report(sk);
        return 0;
}

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
static struct ipv6_pinfo *mptcp_inet6_sk(const struct sock *sk)
{
        struct mptcp6_sock *msk6 = container_of(mptcp_sk(sk), struct mptcp6_sock, msk);

        return &msk6->np;
}

static void mptcp_copy_ip6_options(struct sock *newsk, const struct sock *sk)
{
        const struct ipv6_pinfo *np = inet6_sk(sk);
        struct ipv6_txoptions *opt;
        struct ipv6_pinfo *newnp;

        newnp = inet6_sk(newsk);

        rcu_read_lock();
        opt = rcu_dereference(np->opt);
        if (opt) {
                opt = ipv6_dup_options(newsk, opt);
                if (!opt)
                        net_warn_ratelimited("%s: Failed to copy ip6 options\n", __func__);
        }
        RCU_INIT_POINTER(newnp->opt, opt);
        rcu_read_unlock();
}
#endif

static void mptcp_copy_ip_options(struct sock *newsk, const struct sock *sk)
{
        struct ip_options_rcu *inet_opt, *newopt = NULL;
        const struct inet_sock *inet = inet_sk(sk);
        struct inet_sock *newinet;

        newinet = inet_sk(newsk);

        rcu_read_lock();
        inet_opt = rcu_dereference(inet->inet_opt);
        if (inet_opt) {
                newopt = sock_kmemdup(newsk, inet_opt, sizeof(*inet_opt) +
                                      inet_opt->opt.optlen, GFP_ATOMIC);
                if (!newopt)
                        net_warn_ratelimited("%s: Failed to copy ip options\n", __func__);
        }
        RCU_INIT_POINTER(newinet->inet_opt, newopt);
        rcu_read_unlock();
}

struct sock *mptcp_sk_clone_init(const struct sock *sk,
                                 const struct mptcp_options_received *mp_opt,
                                 struct sock *ssk,
                                 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_subflow_context *subflow;
        struct mptcp_sock *msk;

        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);

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        if (nsk->sk_family == AF_INET6)
                mptcp_copy_ip6_options(nsk, sk);
        else
#endif
                mptcp_copy_ip_options(nsk, sk);

        msk = mptcp_sk(nsk);
        WRITE_ONCE(msk->local_key, subflow_req->local_key);
        WRITE_ONCE(msk->token, subflow_req->token);
        msk->in_accept_queue = 1;
        WRITE_ONCE(msk->fully_established, false);
        if (mp_opt->suboptions & OPTION_MPTCP_CSUMREQD)
                WRITE_ONCE(msk->csum_enabled, true);

        WRITE_ONCE(msk->write_seq, subflow_req->idsn + 1);
        WRITE_ONCE(msk->snd_nxt, msk->write_seq);
        WRITE_ONCE(msk->snd_una, msk->write_seq);
        WRITE_ONCE(msk->wnd_end, msk->snd_nxt + tcp_sk(ssk)->snd_wnd);
        msk->setsockopt_seq = mptcp_sk(sk)->setsockopt_seq;
        mptcp_init_sched(msk, mptcp_sk(sk)->sched);

        /* passive msk is created after the first/MPC subflow */
        msk->subflow_id = 2;

        sock_reset_flag(nsk, SOCK_RCU_FREE);
        security_inet_csk_clone(nsk, req);

        /* this can't race with mptcp_close(), as the msk is
         * not yet exposted to user-space
         */
        mptcp_set_state(nsk, TCP_ESTABLISHED);

        /* The msk maintain a ref to each subflow in the connections list */
        WRITE_ONCE(msk->first, ssk);
        subflow = mptcp_subflow_ctx(ssk);
        list_add(&subflow->node, &msk->conn_list);
        sock_hold(ssk);

        /* new mpc subflow takes ownership of the newly
         * created mptcp socket
         */
        mptcp_token_accept(subflow_req, msk);

        /* set msk addresses early to ensure mptcp_pm_get_local_id()
         * uses the correct data
         */
        mptcp_copy_inaddrs(nsk, ssk);
        __mptcp_propagate_sndbuf(nsk, ssk);

        mptcp_rcv_space_init(msk, ssk);
        msk->rcvq_space.time = mptcp_stamp();

        if (mp_opt->suboptions & OPTION_MPTCP_MPC_ACK)
                __mptcp_subflow_fully_established(msk, subflow, mp_opt);
        bh_unlock_sock(nsk);

        /* note: the newly allocated socket refcount is 2 now */
        return nsk;
}

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

        /* allow the following to close even the initial subflow */
        msk->free_first = 1;
        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)->cb_flags);
}

void __mptcp_check_push(struct sock *sk, struct sock *ssk)
{
        if (!sock_owned_by_user(sk))
                __mptcp_subflow_push_pending(sk, ssk, false);
        else
                __set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->cb_flags);
}

#define MPTCP_FLAGS_PROCESS_CTX_NEED (BIT(MPTCP_PUSH_PENDING) | \
                                      BIT(MPTCP_RETRANSMIT) | \
                                      BIT(MPTCP_FLUSH_JOIN_LIST))

/* processes deferred events and flush wmem */
static void mptcp_release_cb(struct sock *sk)
        __must_hold(&sk->sk_lock.slock)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        for (;;) {
                unsigned long flags = (msk->cb_flags & MPTCP_FLAGS_PROCESS_CTX_NEED);
                struct list_head join_list, skbs;
                bool spool_bl;
                u32 moved;

                spool_bl = mptcp_can_spool_backlog(sk, &skbs);
                if (!flags && !spool_bl)
                        break;

                INIT_LIST_HEAD(&join_list);
                list_splice_init(&msk->join_list, &join_list);

                /* 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
                 */
                msk->cb_flags &= ~flags;
                spin_unlock_bh(&sk->sk_lock.slock);

                if (flags & BIT(MPTCP_FLUSH_JOIN_LIST))
                        __mptcp_flush_join_list(sk, &join_list);
                if (flags & BIT(MPTCP_PUSH_PENDING))
                        __mptcp_push_pending(sk, 0);
                if (flags & BIT(MPTCP_RETRANSMIT))
                        __mptcp_retrans(sk);
                if (spool_bl && __mptcp_move_skbs(sk, &skbs, &moved)) {
                        /* notify ack seq update */
                        mptcp_cleanup_rbuf(msk, 0);
                        sk->sk_data_ready(sk);
                }

                cond_resched();
                spin_lock_bh(&sk->sk_lock.slock);
                if (spool_bl)
                        mptcp_backlog_spooled(sk, moved, &skbs);
        }

        if (__test_and_clear_bit(MPTCP_CLEAN_UNA, &msk->cb_flags))
                __mptcp_clean_una_wakeup(sk);
        if (unlikely(msk->cb_flags)) {
                /* be sure to sync the msk state before taking actions
                 * depending on sk_state (MPTCP_ERROR_REPORT)
                 * On sk release avoid actions depending on the first subflow
                 */
                if (__test_and_clear_bit(MPTCP_SYNC_STATE, &msk->cb_flags) && msk->first)
                        __mptcp_sync_state(sk, msk->pending_state);
                if (__test_and_clear_bit(MPTCP_ERROR_REPORT, &msk->cb_flags))
                        __mptcp_error_report(sk);
                if (__test_and_clear_bit(MPTCP_SYNC_SNDBUF, &msk->cb_flags))
                        __mptcp_sync_sndbuf(sk);
        }
}

/* MP_JOIN client subflow must wait for 4th ack before sending any data:
 * TCP can't schedule delack timer before the subflow is fully established.
 * MPTCP uses the delack timer to do 3rd ack retransmissions
 */
static void schedule_3rdack_retransmission(struct sock *ssk)
{
        struct inet_connection_sock *icsk = inet_csk(ssk);
        struct tcp_sock *tp = tcp_sk(ssk);
        unsigned long timeout;

        if (READ_ONCE(mptcp_subflow_ctx(ssk)->fully_established))
                return;

        /* reschedule with a timeout above RTT, as we must look only for drop */
        if (tp->srtt_us)
                timeout = usecs_to_jiffies(tp->srtt_us >> (3 - 1));
        else
                timeout = TCP_TIMEOUT_INIT;
        timeout += jiffies;

        WARN_ON_ONCE(icsk->icsk_ack.pending & ICSK_ACK_TIMER);
        smp_store_release(&icsk->icsk_ack.pending,
                          icsk->icsk_ack.pending | ICSK_ACK_SCHED | ICSK_ACK_TIMER);
        sk_reset_timer(ssk, &icsk->icsk_delack_timer, timeout);
}

void mptcp_subflow_process_delegated(struct sock *ssk, long status)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        struct sock *sk = subflow->conn;

        if (status & BIT(MPTCP_DELEGATE_SEND)) {
                mptcp_data_lock(sk);
                if (!sock_owned_by_user(sk))
                        __mptcp_subflow_push_pending(sk, ssk, true);
                else
                        __set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->cb_flags);
                mptcp_data_unlock(sk);
        }
        if (status & BIT(MPTCP_DELEGATE_SNDBUF)) {
                mptcp_data_lock(sk);
                if (!sock_owned_by_user(sk))
                        __mptcp_sync_sndbuf(sk);
                else
                        __set_bit(MPTCP_SYNC_SNDBUF, &mptcp_sk(sk)->cb_flags);
                mptcp_data_unlock(sk);
        }
        if (status & BIT(MPTCP_DELEGATE_ACK))
                schedule_3rdack_retransmission(ssk);
}

static int mptcp_hash(struct sock *sk)
{
        /* should never be called,
         * we hash the TCP subflows not the MPTCP 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);

        pr_debug("msk=%p, ssk=%p\n", msk, msk->first);
        if (WARN_ON_ONCE(!msk->first))
                return -EINVAL;

        return inet_csk_get_port(msk->first, snum);
}

void mptcp_finish_connect(struct sock *ssk)
{
        struct mptcp_subflow_context *subflow;
        struct mptcp_sock *msk;
        struct sock *sk;

        subflow = mptcp_subflow_ctx(ssk);
        sk = subflow->conn;
        msk = mptcp_sk(sk);

        pr_debug("msk=%p, token=%u\n", sk, subflow->token);

        subflow->map_seq = subflow->iasn;
        subflow->map_subflow_seq = 1;

        /* the socket is not connected yet, no msk/subflow ops can access/race
         * accessing the field below
         */
        WRITE_ONCE(msk->local_key, subflow->local_key);
        WRITE_ONCE(msk->rcvq_space.time, mptcp_stamp());

        mptcp_pm_new_connection(msk, ssk, 0);
}

void mptcp_sock_graft(struct sock *sk, struct socket *parent)
{
        write_lock_bh(&sk->sk_callback_lock);
        rcu_assign_pointer(sk->sk_wq, &parent->wq);
        sk_set_socket(sk, parent);
        write_unlock_bh(&sk->sk_callback_lock);
}

/* Can be called without holding the msk socket lock; use the callback lock
 * to avoid {READ_,WRITE_}ONCE annotations on sk_socket.
 */
static void mptcp_sock_check_graft(struct sock *sk, struct sock *ssk)
{
        struct socket *sock;

        write_lock_bh(&sk->sk_callback_lock);
        sock = sk->sk_socket;
        write_unlock_bh(&sk->sk_callback_lock);
        if (sock) {
                mptcp_sock_graft(ssk, sock);
                __mptcp_inherit_cgrp_data(sk, ssk);
                __mptcp_inherit_memcg(sk, ssk, GFP_ATOMIC);
        }
}

bool mptcp_finish_join(struct sock *ssk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        struct mptcp_sock *msk = mptcp_sk(subflow->conn);
        struct sock *parent = (void *)msk;
        bool ret = true;

        pr_debug("msk=%p, subflow=%p\n", msk, subflow);

        /* mptcp socket already closing? */
        if (!mptcp_is_fully_established(parent)) {
                subflow->reset_reason = MPTCP_RST_EMPTCP;
                return false;
        }

        /* Active subflow, already present inside the conn_list; is grafted
         * either by __mptcp_subflow_connect() or accept.
         */
        if (!list_empty(&subflow->node)) {
                spin_lock_bh(&msk->fallback_lock);
                if (!msk->allow_subflows) {
                        spin_unlock_bh(&msk->fallback_lock);
                        return false;
                }
                mptcp_subflow_joined(msk, ssk);
                spin_unlock_bh(&msk->fallback_lock);
                mptcp_propagate_sndbuf(parent, ssk);
                return true;
        }

        if (!mptcp_pm_allow_new_subflow(msk)) {
                MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_JOINREJECTED);
                goto err_prohibited;
        }

        /* If we can't acquire msk socket lock here, let the release callback
         * handle it
         */
        mptcp_data_lock(parent);
        if (!sock_owned_by_user(parent)) {
                ret = __mptcp_finish_join(msk, ssk);
                if (ret) {
                        sock_hold(ssk);
                        list_add_tail(&subflow->node, &msk->conn_list);
                        mptcp_sock_check_graft(parent, ssk);
                }
        } else {
                sock_hold(ssk);
                list_add_tail(&subflow->node, &msk->join_list);
                __set_bit(MPTCP_FLUSH_JOIN_LIST, &msk->cb_flags);

                /* In case of later failures, __mptcp_flush_join_list() will
                 * properly orphan the ssk via mptcp_close_ssk().
                 */
                mptcp_sock_check_graft(parent, ssk);
        }
        mptcp_data_unlock(parent);

        if (!ret) {
err_prohibited:
                subflow->reset_reason = MPTCP_RST_EPROHIBIT;
                return false;
        }

        return true;
}

static void mptcp_shutdown(struct sock *sk, int how)
{
        pr_debug("sk=%p, how=%d\n", sk, how);

        if ((how & SEND_SHUTDOWN) && mptcp_close_state(sk))
                __mptcp_wr_shutdown(sk);
}

static int mptcp_ioctl_outq(const struct mptcp_sock *msk, u64 v)
{
        const struct sock *sk = (void *)msk;
        u64 delta;

        if (sk->sk_state == TCP_LISTEN)
                return -EINVAL;

        if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))
                return 0;

        delta = msk->write_seq - v;
        if (__mptcp_check_fallback(msk) && msk->first) {
                struct tcp_sock *tp = tcp_sk(msk->first);

                /* the first subflow is disconnected after close - see
                 * __mptcp_close_ssk(). tcp_disconnect() moves the write_seq
                 * so ignore that status, too.
                 */
                if (!((1 << msk->first->sk_state) &
                      (TCPF_SYN_SENT | TCPF_SYN_RECV | TCPF_CLOSE)))
                        delta += READ_ONCE(tp->write_seq) - tp->snd_una;
        }
        if (delta > INT_MAX)
                delta = INT_MAX;

        return (int)delta;
}

static int mptcp_ioctl(struct sock *sk, int cmd, int *karg)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        bool slow;

        switch (cmd) {
        case SIOCINQ:
                if (sk->sk_state == TCP_LISTEN)
                        return -EINVAL;

                lock_sock(sk);
                if (mptcp_move_skbs(sk))
                        mptcp_cleanup_rbuf(msk, 0);
                *karg = mptcp_inq_hint(sk);
                release_sock(sk);
                break;
        case SIOCOUTQ:
                slow = lock_sock_fast(sk);
                *karg = mptcp_ioctl_outq(msk, READ_ONCE(msk->snd_una));
                unlock_sock_fast(sk, slow);
                break;
        case SIOCOUTQNSD:
                slow = lock_sock_fast(sk);
                *karg = mptcp_ioctl_outq(msk, msk->snd_nxt);
                unlock_sock_fast(sk, slow);
                break;
        default:
                return -ENOIOCTLCMD;
        }

        return 0;
}

static int mptcp_connect(struct sock *sk, struct sockaddr_unsized *uaddr,
                         int addr_len)
{
        struct mptcp_subflow_context *subflow;
        struct mptcp_sock *msk = mptcp_sk(sk);
        int err = -EINVAL;
        struct sock *ssk;

        ssk = __mptcp_nmpc_sk(msk);
        if (IS_ERR(ssk))
                return PTR_ERR(ssk);

        mptcp_set_state(sk, TCP_SYN_SENT);
        subflow = mptcp_subflow_ctx(ssk);
#ifdef CONFIG_TCP_MD5SIG
        /* no MPTCP if MD5SIG is enabled on this socket or we may run out of
         * TCP option space.
         */
        if (rcu_access_pointer(tcp_sk(ssk)->md5sig_info))
                mptcp_early_fallback(msk, subflow, MPTCP_MIB_MD5SIGFALLBACK);
#endif
        if (subflow->request_mptcp) {
                if (mptcp_active_should_disable(sk))
                        mptcp_early_fallback(msk, subflow,
                                             MPTCP_MIB_MPCAPABLEACTIVEDISABLED);
                else if (mptcp_token_new_connect(ssk) < 0)
                        mptcp_early_fallback(msk, subflow,
                                             MPTCP_MIB_TOKENFALLBACKINIT);
        }

        WRITE_ONCE(msk->write_seq, subflow->idsn);
        WRITE_ONCE(msk->snd_nxt, subflow->idsn);
        WRITE_ONCE(msk->snd_una, subflow->idsn);
        if (likely(!__mptcp_check_fallback(msk)))
                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPCAPABLEACTIVE);

        /* if reaching here via the fastopen/sendmsg path, the caller already
         * acquired the subflow socket lock, too.
         */
        if (!msk->fastopening)
                lock_sock(ssk);

        /* the following mirrors closely a very small chunk of code from
         * __inet_stream_connect()
         */
        if (ssk->sk_state != TCP_CLOSE)
                goto out;

        if (BPF_CGROUP_PRE_CONNECT_ENABLED(ssk)) {
                err = ssk->sk_prot->pre_connect(ssk, uaddr, addr_len);
                if (err)
                        goto out;
        }

        err = ssk->sk_prot->connect(ssk, uaddr, addr_len);
        if (err < 0)
                goto out;

        inet_assign_bit(DEFER_CONNECT, sk, inet_test_bit(DEFER_CONNECT, ssk));

out:
        if (!msk->fastopening)
                release_sock(ssk);

        /* on successful connect, the msk state will be moved to established by
         * subflow_finish_connect()
         */
        if (unlikely(err)) {
                /* avoid leaving a dangling token in an unconnected socket */
                mptcp_token_destroy(msk);
                mptcp_set_state(sk, TCP_CLOSE);
                return err;
        }

        mptcp_copy_inaddrs(sk, ssk);
        return 0;
}

static struct proto mptcp_prot = {
        .name           = "MPTCP",
        .owner          = THIS_MODULE,
        .init           = mptcp_init_sock,
        .connect        = mptcp_connect,
        .disconnect     = mptcp_disconnect,
        .close          = mptcp_close,
        .setsockopt     = mptcp_setsockopt,
        .getsockopt     = mptcp_getsockopt,
        .shutdown       = mptcp_shutdown,
        .destroy        = mptcp_destroy,
        .sendmsg        = mptcp_sendmsg,
        .ioctl          = mptcp_ioctl,
        .recvmsg        = mptcp_recvmsg,
        .release_cb     = mptcp_release_cb,
        .hash           = mptcp_hash,
        .unhash         = mptcp_unhash,
        .get_port       = mptcp_get_port,
        .stream_memory_free     = mptcp_stream_memory_free,
        .sockets_allocated      = &mptcp_sockets_allocated,

        .memory_allocated       = &net_aligned_data.tcp_memory_allocated,
        .per_cpu_fw_alloc       = &tcp_memory_per_cpu_fw_alloc,

        .memory_pressure        = &tcp_memory_pressure,
        .sysctl_wmem_offset     = offsetof(struct net, ipv4.sysctl_tcp_wmem),
        .sysctl_rmem_offset     = offsetof(struct net, ipv4.sysctl_tcp_rmem),
        .sysctl_mem     = sysctl_tcp_mem,
        .obj_size       = sizeof(struct mptcp_sock),
        .slab_flags     = SLAB_TYPESAFE_BY_RCU,
        .no_autobind    = true,
};

static int mptcp_bind(struct socket *sock, struct sockaddr_unsized *uaddr, int addr_len)
{
        struct mptcp_sock *msk = mptcp_sk(sock->sk);
        struct sock *ssk, *sk = sock->sk;
        int err = -EINVAL;

        lock_sock(sk);
        ssk = __mptcp_nmpc_sk(msk);
        if (IS_ERR(ssk)) {
                err = PTR_ERR(ssk);
                goto unlock;
        }

        if (sk->sk_family == AF_INET)
                err = inet_bind_sk(ssk, uaddr, addr_len);
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        else if (sk->sk_family == AF_INET6)
                err = inet6_bind_sk(ssk, uaddr, addr_len);
#endif
        if (!err)
                mptcp_copy_inaddrs(sk, ssk);

unlock:
        release_sock(sk);
        return err;
}

static int mptcp_listen(struct socket *sock, int backlog)
{
        struct mptcp_sock *msk = mptcp_sk(sock->sk);
        struct sock *sk = sock->sk;
        struct sock *ssk;
        int err;

        pr_debug("msk=%p\n", msk);

        lock_sock(sk);

        err = -EINVAL;
        if (sock->state != SS_UNCONNECTED || sock->type != SOCK_STREAM)
                goto unlock;

        ssk = __mptcp_nmpc_sk(msk);
        if (IS_ERR(ssk)) {
                err = PTR_ERR(ssk);
                goto unlock;
        }

        mptcp_set_state(sk, TCP_LISTEN);
        sock_set_flag(sk, SOCK_RCU_FREE);

        lock_sock(ssk);
        err = __inet_listen_sk(ssk, backlog);
        release_sock(ssk);
        mptcp_set_state(sk, inet_sk_state_load(ssk));

        if (!err) {
                sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
                mptcp_copy_inaddrs(sk, ssk);
                mptcp_event_pm_listener(ssk, MPTCP_EVENT_LISTENER_CREATED);
        }

unlock:
        release_sock(sk);
        return err;
}

static void mptcp_graft_subflows(struct sock *sk)
{
        struct mptcp_subflow_context *subflow;
        struct mptcp_sock *msk = mptcp_sk(sk);

        if (mem_cgroup_sockets_enabled) {
                LIST_HEAD(join_list);

                /* Subflows joining after __inet_accept() will get the
                 * mem CG properly initialized at mptcp_finish_join() time,
                 * but subflows pending in join_list need explicit
                 * initialization before flushing `backlog_unaccounted`
                 * or MPTCP can later unexpectedly observe unaccounted memory.
                 */
                mptcp_data_lock(sk);
                list_splice_init(&msk->join_list, &join_list);
                mptcp_data_unlock(sk);

                __mptcp_flush_join_list(sk, &join_list);
        }

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

                lock_sock(ssk);

                /* Set ssk->sk_socket of accept()ed flows to mptcp socket.
                 * This is needed so NOSPACE flag can be set from tcp stack.
                 */
                if (!ssk->sk_socket)
                        mptcp_sock_graft(ssk, sk->sk_socket);

                if (!mem_cgroup_sk_enabled(sk))
                        goto unlock;

                __mptcp_inherit_cgrp_data(sk, ssk);
                __mptcp_inherit_memcg(sk, ssk, GFP_KERNEL);

unlock:
                release_sock(ssk);
        }

        if (mem_cgroup_sk_enabled(sk)) {
                gfp_t gfp = GFP_KERNEL | __GFP_NOFAIL;
                int amt;

                /* Account the backlog memory; prior accept() is aware of
                 * fwd and rmem only.
                 */
                mptcp_data_lock(sk);
                amt = sk_mem_pages(sk->sk_forward_alloc +
                                   msk->backlog_unaccounted +
                                   atomic_read(&sk->sk_rmem_alloc)) -
                      sk_mem_pages(sk->sk_forward_alloc +
                                   atomic_read(&sk->sk_rmem_alloc));
                msk->backlog_unaccounted = 0;
                mptcp_data_unlock(sk);

                if (amt)
                        mem_cgroup_sk_charge(sk, amt, gfp);
        }
}

static int mptcp_stream_accept(struct socket *sock, struct socket *newsock,
                               struct proto_accept_arg *arg)
{
        struct mptcp_sock *msk = mptcp_sk(sock->sk);
        struct sock *ssk, *newsk;

        pr_debug("msk=%p\n", msk);

        /* Buggy applications can call accept on socket states other then LISTEN
         * but no need to allocate the first subflow just to error out.
         */
        ssk = READ_ONCE(msk->first);
        if (!ssk)
                return -EINVAL;

        pr_debug("ssk=%p, listener=%p\n", ssk, mptcp_subflow_ctx(ssk));
        newsk = inet_csk_accept(ssk, arg);
        if (!newsk)
                return arg->err;

        pr_debug("newsk=%p, subflow is mptcp=%d\n", newsk, 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;
                        goto tcpfallback;
                }

                newsk = new_mptcp_sock;
                MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_MPCAPABLEPASSIVEACK);

                newsk->sk_kern_sock = arg->kern;
                lock_sock(newsk);
                __inet_accept(sock, newsock, newsk);

                set_bit(SOCK_CUSTOM_SOCKOPT, &newsock->flags);
                msk = mptcp_sk(newsk);
                msk->in_accept_queue = 0;

                mptcp_graft_subflows(newsk);
                mptcp_rps_record_subflows(msk);

                /* Do late cleanup for the first subflow as necessary. Also
                 * deal with bad peers not doing a complete shutdown.
                 */
                if (unlikely(inet_sk_state_load(msk->first) == TCP_CLOSE)) {
                        if (unlikely(list_is_singular(&msk->conn_list)))
                                mptcp_set_state(newsk, TCP_CLOSE);
                        mptcp_close_ssk(newsk, msk->first,
                                        mptcp_subflow_ctx(msk->first));
                }
        } else {
tcpfallback:
                newsk->sk_kern_sock = arg->kern;
                lock_sock(newsk);
                __inet_accept(sock, newsock, newsk);
                /* we are being invoked after accepting 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.
                 */
                WRITE_ONCE(newsock->sk->sk_socket->ops,
                           mptcp_fallback_tcp_ops(newsock->sk));
        }
        release_sock(newsk);

        return 0;
}

static __poll_t mptcp_check_writeable(struct mptcp_sock *msk)
{
        struct sock *sk = (struct sock *)msk;

        if (__mptcp_stream_is_writeable(sk, 1))
                return EPOLLOUT | EPOLLWRNORM;

        set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
        smp_mb__after_atomic(); /* NOSPACE is changed by mptcp_write_space() */
        if (__mptcp_stream_is_writeable(sk, 1))
                return EPOLLOUT | EPOLLWRNORM;

        return 0;
}

static __poll_t mptcp_poll(struct file *file, struct socket *sock,
                           struct poll_table_struct *wait)
{
        struct sock *sk = sock->sk;
        struct mptcp_sock *msk;
        __poll_t mask = 0;
        u8 shutdown;
        int state;

        msk = mptcp_sk(sk);
        sock_poll_wait(file, sock, wait);

        state = inet_sk_state_load(sk);
        pr_debug("msk=%p state=%d flags=%lx\n", msk, state, msk->flags);
        if (state == TCP_LISTEN) {
                struct sock *ssk = READ_ONCE(msk->first);

                if (WARN_ON_ONCE(!ssk))
                        return 0;

                return inet_csk_listen_poll(ssk);
        }

        shutdown = READ_ONCE(sk->sk_shutdown);
        if (shutdown == SHUTDOWN_MASK || state == TCP_CLOSE)
                mask |= EPOLLHUP;
        if (shutdown & RCV_SHUTDOWN)
                mask |= EPOLLIN | EPOLLRDNORM | EPOLLRDHUP;

        if (state != TCP_SYN_SENT && state != TCP_SYN_RECV) {
                mask |= mptcp_check_readable(sk);
                if (shutdown & SEND_SHUTDOWN)
                        mask |= EPOLLOUT | EPOLLWRNORM;
                else
                        mask |= mptcp_check_writeable(msk);
        } else if (state == TCP_SYN_SENT &&
                   inet_test_bit(DEFER_CONNECT, sk)) {
                /* cf tcp_poll() note about TFO */
                mask |= EPOLLOUT | EPOLLWRNORM;
        }

        /* This barrier is coupled with smp_wmb() in __mptcp_error_report() */
        smp_rmb();
        if (READ_ONCE(sk->sk_err))
                mask |= EPOLLERR;

        return mask;
}

static struct sk_buff *mptcp_recv_skb(struct sock *sk, u32 *off)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct sk_buff *skb;
        u32 offset;

        if (!list_empty(&msk->backlog_list))
                mptcp_move_skbs(sk);

        while ((skb = skb_peek(&sk->sk_receive_queue)) != NULL) {
                offset = MPTCP_SKB_CB(skb)->offset;
                if (offset < skb->len) {
                        *off = offset;
                        return skb;
                }
                mptcp_eat_recv_skb(sk, skb);
        }
        return NULL;
}

/*
 * Note:
 *      - It is assumed that the socket was locked by the caller.
 */
static int __mptcp_read_sock(struct sock *sk, read_descriptor_t *desc,
                             sk_read_actor_t recv_actor, bool noack)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct sk_buff *skb;
        int copied = 0;
        u32 offset;

        msk_owned_by_me(msk);

        if (sk->sk_state == TCP_LISTEN)
                return -ENOTCONN;
        while ((skb = mptcp_recv_skb(sk, &offset)) != NULL) {
                u32 data_len = skb->len - offset;
                int count;
                u32 size;

                size = min_t(size_t, data_len, INT_MAX);
                count = recv_actor(desc, skb, offset, size);
                if (count <= 0) {
                        if (!copied)
                                copied = count;
                        break;
                }

                copied += count;

                msk->bytes_consumed += count;
                if (count < data_len) {
                        MPTCP_SKB_CB(skb)->offset += count;
                        MPTCP_SKB_CB(skb)->map_seq += count;
                        break;
                }

                mptcp_eat_recv_skb(sk, skb);
        }

        if (noack)
                goto out;

        mptcp_rcv_space_adjust(msk, copied);

        if (copied > 0) {
                mptcp_recv_skb(sk, &offset);
                mptcp_cleanup_rbuf(msk, copied);
        }
out:
        return copied;
}

static int mptcp_read_sock(struct sock *sk, read_descriptor_t *desc,
                           sk_read_actor_t recv_actor)
{
        return __mptcp_read_sock(sk, desc, recv_actor, false);
}

static int __mptcp_splice_read(struct sock *sk, struct tcp_splice_state *tss)
{
        /* Store TCP splice context information in read_descriptor_t. */
        read_descriptor_t rd_desc = {
                .arg.data = tss,
                .count    = tss->len,
        };

        return mptcp_read_sock(sk, &rd_desc, tcp_splice_data_recv);
}

/**
 *  mptcp_splice_read - splice data from MPTCP socket to a pipe
 * @sock:       socket to splice from
 * @ppos:       position (not valid)
 * @pipe:       pipe to splice to
 * @len:        number of bytes to splice
 * @flags:      splice modifier flags
 *
 * Description:
 *    Will read pages from given socket and fill them into a pipe.
 *
 * Return:
 *    Amount of bytes that have been spliced.
 *
 **/
static ssize_t mptcp_splice_read(struct socket *sock, loff_t *ppos,
                                 struct pipe_inode_info *pipe, size_t len,
                                 unsigned int flags)
{
        struct tcp_splice_state tss = {
                .pipe   = pipe,
                .len    = len,
                .flags  = flags,
        };
        struct sock *sk = sock->sk;
        ssize_t spliced = 0;
        int ret = 0;
        long timeo;

        /*
         * We can't seek on a socket input
         */
        if (unlikely(*ppos))
                return -ESPIPE;

        lock_sock(sk);

        mptcp_rps_record_subflows(mptcp_sk(sk));

        timeo = sock_rcvtimeo(sk, sock->file->f_flags & O_NONBLOCK);
        while (tss.len) {
                ret = __mptcp_splice_read(sk, &tss);
                if (ret < 0) {
                        break;
                } else if (!ret) {
                        if (spliced)
                                break;
                        if (sock_flag(sk, SOCK_DONE))
                                break;
                        if (sk->sk_err) {
                                ret = sock_error(sk);
                                break;
                        }
                        if (sk->sk_shutdown & RCV_SHUTDOWN)
                                break;
                        if (sk->sk_state == TCP_CLOSE) {
                                /*
                                 * This occurs when user tries to read
                                 * from never connected socket.
                                 */
                                ret = -ENOTCONN;
                                break;
                        }
                        if (!timeo) {
                                ret = -EAGAIN;
                                break;
                        }
                        /* if __mptcp_splice_read() got nothing while we have
                         * an skb in receive queue, we do not want to loop.
                         * This might happen with URG data.
                         */
                        if (!skb_queue_empty(&sk->sk_receive_queue))
                                break;
                        ret = sk_wait_data(sk, &timeo, NULL);
                        if (ret < 0)
                                break;
                        if (signal_pending(current)) {
                                ret = sock_intr_errno(timeo);
                                break;
                        }
                        continue;
                }
                tss.len -= ret;
                spliced += ret;

                if (!tss.len || !timeo)
                        break;
                release_sock(sk);
                lock_sock(sk);

                if (sk->sk_err || sk->sk_state == TCP_CLOSE ||
                    (sk->sk_shutdown & RCV_SHUTDOWN) ||
                    signal_pending(current))
                        break;
        }

        release_sock(sk);

        if (spliced)
                return spliced;

        return ret;
}

static const struct proto_ops mptcp_stream_ops = {
        .family            = PF_INET,
        .owner             = THIS_MODULE,
        .release           = inet_release,
        .bind              = mptcp_bind,
        .connect           = inet_stream_connect,
        .socketpair        = sock_no_socketpair,
        .accept            = mptcp_stream_accept,
        .getname           = inet_getname,
        .poll              = mptcp_poll,
        .ioctl             = inet_ioctl,
        .gettstamp         = sock_gettstamp,
        .listen            = mptcp_listen,
        .shutdown          = inet_shutdown,
        .setsockopt        = sock_common_setsockopt,
        .getsockopt        = sock_common_getsockopt,
        .sendmsg           = inet_sendmsg,
        .recvmsg           = inet_recvmsg,
        .mmap              = sock_no_mmap,
        .set_rcvlowat      = mptcp_set_rcvlowat,
        .read_sock         = mptcp_read_sock,
        .splice_read       = mptcp_splice_read,
};

static struct inet_protosw mptcp_protosw = {
        .type           = SOCK_STREAM,
        .protocol       = IPPROTO_MPTCP,
        .prot           = &mptcp_prot,
        .ops            = &mptcp_stream_ops,
        .flags          = INET_PROTOSW_ICSK,
};

static int mptcp_napi_poll(struct napi_struct *napi, int budget)
{
        struct mptcp_delegated_action *delegated;
        struct mptcp_subflow_context *subflow;
        int work_done = 0;

        delegated = container_of(napi, struct mptcp_delegated_action, napi);
        while ((subflow = mptcp_subflow_delegated_next(delegated)) != NULL) {
                struct sock *ssk = mptcp_subflow_tcp_sock(subflow);

                bh_lock_sock_nested(ssk);
                if (!sock_owned_by_user(ssk)) {
                        mptcp_subflow_process_delegated(ssk, xchg(&subflow->delegated_status, 0));
                } else {
                        /* tcp_release_cb_override already processed
                         * the action or will do at next release_sock().
                         * In both case must dequeue the subflow here - on the same
                         * CPU that scheduled it.
                         */
                        smp_wmb();
                        clear_bit(MPTCP_DELEGATE_SCHEDULED, &subflow->delegated_status);
                }
                bh_unlock_sock(ssk);
                sock_put(ssk);

                if (++work_done == budget)
                        return budget;
        }

        /* always provide a 0 'work_done' argument, so that napi_complete_done
         * will not try accessing the NULL napi->dev ptr
         */
        napi_complete_done(napi, 0);
        return work_done;
}

void __init mptcp_proto_init(void)
{
        struct mptcp_delegated_action *delegated;
        int cpu;

        mptcp_prot.h.hashinfo = tcp_prot.h.hashinfo;

        if (percpu_counter_init(&mptcp_sockets_allocated, 0, GFP_KERNEL))
                panic("Failed to allocate MPTCP pcpu counter\n");

        mptcp_napi_dev = alloc_netdev_dummy(0);
        if (!mptcp_napi_dev)
                panic("Failed to allocate MPTCP dummy netdev\n");
        for_each_possible_cpu(cpu) {
                delegated = per_cpu_ptr(&mptcp_delegated_actions, cpu);
                INIT_LIST_HEAD(&delegated->head);
                netif_napi_add_tx(mptcp_napi_dev, &delegated->napi,
                                  mptcp_napi_poll);
                napi_enable(&delegated->napi);
        }

        mptcp_subflow_init();
        mptcp_pm_init();
        mptcp_sched_init();
        mptcp_token_init();

        if (proto_register(&mptcp_prot, 1) != 0)
                panic("Failed to register MPTCP proto.\n");

        inet_register_protosw(&mptcp_protosw);

        BUILD_BUG_ON(sizeof(struct mptcp_skb_cb) > sizeof_field(struct sk_buff, cb));
}

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
static const struct proto_ops mptcp_v6_stream_ops = {
        .family            = PF_INET6,
        .owner             = THIS_MODULE,
        .release           = inet6_release,
        .bind              = mptcp_bind,
        .connect           = inet_stream_connect,
        .socketpair        = sock_no_socketpair,
        .accept            = mptcp_stream_accept,
        .getname           = inet6_getname,
        .poll              = mptcp_poll,
        .ioctl             = inet6_ioctl,
        .gettstamp         = sock_gettstamp,
        .listen            = mptcp_listen,
        .shutdown          = inet_shutdown,
        .setsockopt        = sock_common_setsockopt,
        .getsockopt        = sock_common_getsockopt,
        .sendmsg           = inet6_sendmsg,
        .recvmsg           = inet6_recvmsg,
        .mmap              = sock_no_mmap,
#ifdef CONFIG_COMPAT
        .compat_ioctl      = inet6_compat_ioctl,
#endif
        .set_rcvlowat      = mptcp_set_rcvlowat,
        .read_sock         = mptcp_read_sock,
        .splice_read       = mptcp_splice_read,
};

static struct proto mptcp_v6_prot;

static struct inet_protosw mptcp_v6_protosw = {
        .type           = SOCK_STREAM,
        .protocol       = IPPROTO_MPTCP,
        .prot           = &mptcp_v6_prot,
        .ops            = &mptcp_v6_stream_ops,
        .flags          = INET_PROTOSW_ICSK,
};

int __init mptcp_proto_v6_init(void)
{
        int err;

        mptcp_v6_prot = mptcp_prot;
        strscpy(mptcp_v6_prot.name, "MPTCPv6", sizeof(mptcp_v6_prot.name));
        mptcp_v6_prot.slab = NULL;
        mptcp_v6_prot.obj_size = sizeof(struct mptcp6_sock);
        mptcp_v6_prot.ipv6_pinfo_offset = offsetof(struct mptcp6_sock, np);

        err = proto_register(&mptcp_v6_prot, 1);
        if (err)
                return err;

        err = inet6_register_protosw(&mptcp_v6_protosw);
        if (err)
                proto_unregister(&mptcp_v6_prot);

        return err;
}
#endif