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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * NET      Generic infrastructure for Network protocols.
  *
  * Authors: Arnaldo Carvalho de Melo <acme@conectiva.com.br>
  *
  *      From code originally in include/net/tcp.h
  */
 
 #include <linux/module.h>
 #include <linux/random.h>
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/tcp.h>
 #include <linux/vmalloc.h>
 
 #include <net/request_sock.h>
 
 /*
  * Maximum number of SYN_RECV sockets in queue per LISTEN socket.
  * One SYN_RECV socket costs about 80bytes on a 32bit machine.
  * It would be better to replace it with a global counter for all sockets
  * but then some measure against one socket starving all other sockets
  * would be needed.
  *
  * The minimum value of it is 128. Experiments with real servers show that
  * it is absolutely not enough even at 100conn/sec. 256 cures most
  * of problems.
  * This value is adjusted to 128 for low memory machines,
  * and it will increase in proportion to the memory of machine.
  * Note : Dont forget somaxconn that may limit backlog too.
  */
 
 void reqsk_queue_alloc(struct request_sock_queue *queue)
 {
     spin_lock_init(&queue->rskq_lock);
 
     spin_lock_init(&queue->fastopenq.lock);
     queue->fastopenq.rskq_rst_head = NULL;
     queue->fastopenq.rskq_rst_tail = NULL;
     queue->fastopenq.qlen = 0;
 
     queue->rskq_accept_head = NULL;
 }
 
 /*
  * This function is called to set a Fast Open socket's "fastopen_rsk" field
  * to NULL when a TFO socket no longer needs to access the request_sock.
  * This happens only after 3WHS has been either completed or aborted (e.g.,
  * RST is received).
  *
  * Before TFO, a child socket is created only after 3WHS is completed,
  * hence it never needs to access the request_sock. things get a lot more
  * complex with TFO. A child socket, accepted or not, has to access its
  * request_sock for 3WHS processing, e.g., to retransmit SYN-ACK pkts,
  * until 3WHS is either completed or aborted. Afterwards the req will stay
  * until either the child socket is accepted, or in the rare case when the
  * listener is closed before the child is accepted.
  *
  * In short, a request socket is only freed after BOTH 3WHS has completed
  * (or aborted) and the child socket has been accepted (or listener closed).
  * When a child socket is accepted, its corresponding req->sk is set to
  * NULL since it's no longer needed. More importantly, "req->sk == NULL"
  * will be used by the code below to determine if a child socket has been
  * accepted or not, and the check is protected by the fastopenq->lock
  * described below.
  *
  * Note that fastopen_rsk is only accessed from the child socket's context
  * with its socket lock held. But a request_sock (req) can be accessed by
  * both its child socket through fastopen_rsk, and a listener socket through
  * icsk_accept_queue.rskq_accept_head. To protect the access a simple spin
  * lock per listener "icsk->icsk_accept_queue.fastopenq->lock" is created.
  * only in the rare case when both the listener and the child locks are held,
  * e.g., in inet_csk_listen_stop() do we not need to acquire the lock.
  * The lock also protects other fields such as fastopenq->qlen, which is
  * decremented by this function when fastopen_rsk is no longer needed.
  *
  * Note that another solution was to simply use the existing socket lock
  * from the listener. But first socket lock is difficult to use. It is not
  * a simple spin lock - one must consider sock_owned_by_user() and arrange
  * to use sk_add_backlog() stuff. But what really makes it infeasible is the
  * locking hierarchy violation. E.g., inet_csk_listen_stop() may try to
  * acquire a child's lock while holding listener's socket lock. A corner
  * case might also exist in tcp_v4_hnd_req() that will trigger this locking
  * order.
  *
  * This function also sets "treq->tfo_listener" to false.
  * treq->tfo_listener is used by the listener so it is protected by the
  * fastopenq->lock in this function.
  */
 void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
                bool reset)
 {
     struct sock *lsk = req->rsk_listener;
     struct fastopen_queue *fastopenq;
 
     fastopenq = &inet_csk(lsk)->icsk_accept_queue.fastopenq;
 
     RCU_INIT_POINTER(tcp_sk(sk)->fastopen_rsk, NULL);
     spin_lock_bh(&fastopenq->lock);
     fastopenq->qlen--;
     tcp_rsk(req)->tfo_listener = false;
     if (req->sk)    /* the child socket hasn't been accepted yet */
         goto out;
 
     if (!reset || lsk->sk_state != TCP_LISTEN) {
         /* If the listener has been closed don't bother with the
          * special RST handling below.
          */
         spin_unlock_bh(&fastopenq->lock);
         reqsk_put(req);
         return;
     }
     /* Wait for 60secs before removing a req that has triggered RST.
      * This is a simple defense against TFO spoofing attack - by
      * counting the req against fastopen.max_qlen, and disabling
      * TFO when the qlen exceeds max_qlen.
      *
      * For more details see CoNext'11 "TCP Fast Open" paper.
      */
     req->rsk_timer.expires = jiffies + 60*HZ;
     if (fastopenq->rskq_rst_head == NULL)
         fastopenq->rskq_rst_head = req;
     else
         fastopenq->rskq_rst_tail->dl_next = req;
 
     req->dl_next = NULL;
     fastopenq->rskq_rst_tail = req;
     fastopenq->qlen++;
 out:
     spin_unlock_bh(&fastopenq->lock);
 }

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