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 /*
  * Copyright (c) 2007, 2017 Oracle and/or its affiliates. All rights reserved.
  *
  * This software is available to you under a choice of one of two
  * licenses.  You may choose to be licensed under the terms of the GNU
  * General Public License (GPL) Version 2, available from the file
  * COPYING in the main directory of this source tree, or the
  * OpenIB.org BSD license below:
  *
  *     Redistribution and use in source and binary forms, with or
  *     without modification, are permitted provided that the following
  *     conditions are met:
  *
  *      - Redistributions of source code must retain the above
  *        copyright notice, this list of conditions and the following
  *        disclaimer.
  *
  *      - Redistributions in binary form must reproduce the above
  *        copyright notice, this list of conditions and the following
  *        disclaimer in the documentation and/or other materials
  *        provided with the distribution.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE.
  *
  */
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/rbtree.h>
 #include <linux/bitops.h>
 #include <linux/export.h>
 
 #include "rds.h"
 
 /*
  * This file implements the receive side of the unconventional congestion
  * management in RDS.
  *
  * Messages waiting in the receive queue on the receiving socket are accounted
  * against the sockets SO_RCVBUF option value.  Only the payload bytes in the
  * message are accounted for.  If the number of bytes queued equals or exceeds
  * rcvbuf then the socket is congested.  All sends attempted to this socket's
  * address should return block or return -EWOULDBLOCK.
  *
  * Applications are expected to be reasonably tuned such that this situation
  * very rarely occurs.  An application encountering this "back-pressure" is
  * considered a bug.
  *
  * This is implemented by having each node maintain bitmaps which indicate
  * which ports on bound addresses are congested.  As the bitmap changes it is
  * sent through all the connections which terminate in the local address of the
  * bitmap which changed.
  *
  * The bitmaps are allocated as connections are brought up.  This avoids
  * allocation in the interrupt handling path which queues messages on sockets.
  * The dense bitmaps let transports send the entire bitmap on any bitmap change
  * reasonably efficiently.  This is much easier to implement than some
  * finer-grained communication of per-port congestion.  The sender does a very
  * inexpensive bit test to test if the port it's about to send to is congested
  * or not.
  */
 
 /*
  * Interaction with poll is a tad tricky. We want all processes stuck in
  * poll to wake up and check whether a congested destination became uncongested.
  * The really sad thing is we have no idea which destinations the application
  * wants to send to - we don't even know which rds_connections are involved.
  * So until we implement a more flexible rds poll interface, we have to make
  * do with this:
  * We maintain a global counter that is incremented each time a congestion map
  * update is received. Each rds socket tracks this value, and if rds_poll
  * finds that the saved generation number is smaller than the global generation
  * number, it wakes up the process.
  */
 static atomic_t     rds_cong_generation = ATOMIC_INIT(0);
 
 /*
  * Congestion monitoring
  */
 static LIST_HEAD(rds_cong_monitor);
 static DEFINE_RWLOCK(rds_cong_monitor_lock);
 
 /*
  * Yes, a global lock.  It's used so infrequently that it's worth keeping it
  * global to simplify the locking.  It's only used in the following
  * circumstances:
  *
  *  - on connection buildup to associate a conn with its maps
  *  - on map changes to inform conns of a new map to send
  *
  *  It's sadly ordered under the socket callback lock and the connection lock.
  *  Receive paths can mark ports congested from interrupt context so the
  *  lock masks interrupts.
  */
 static DEFINE_SPINLOCK(rds_cong_lock);
 static struct rb_root rds_cong_tree = RB_ROOT;
 
 static struct rds_cong_map *rds_cong_tree_walk(const struct in6_addr *addr,
                            struct rds_cong_map *insert)
 {
     struct rb_node **p = &rds_cong_tree.rb_node;
     struct rb_node *parent = NULL;
     struct rds_cong_map *map;
 
     while (*p) {
         int diff;
 
         parent = *p;
         map = rb_entry(parent, struct rds_cong_map, m_rb_node);
 
         diff = rds_addr_cmp(addr, &map->m_addr);
         if (diff < 0)
             p = &(*p)->rb_left;
         else if (diff > 0)
             p = &(*p)->rb_right;
         else
             return map;
     }
 
     if (insert) {
         rb_link_node(&insert->m_rb_node, parent, p);
         rb_insert_color(&insert->m_rb_node, &rds_cong_tree);
     }
     return NULL;
 }
 
 /*
  * There is only ever one bitmap for any address.  Connections try and allocate
  * these bitmaps in the process getting pointers to them.  The bitmaps are only
  * ever freed as the module is removed after all connections have been freed.
  */
 static struct rds_cong_map *rds_cong_from_addr(const struct in6_addr *addr)
 {
     struct rds_cong_map *map;
     struct rds_cong_map *ret = NULL;
     unsigned long zp;
     unsigned long i;
     unsigned long flags;
 
     map = kzalloc(sizeof(struct rds_cong_map), GFP_KERNEL);
     if (!map)
         return NULL;
 
     map->m_addr = *addr;
     init_waitqueue_head(&map->m_waitq);
     INIT_LIST_HEAD(&map->m_conn_list);
 
     for (i = 0; i < RDS_CONG_MAP_PAGES; i++) {
         zp = get_zeroed_page(GFP_KERNEL);
         if (zp == 0)
             goto out;
         map->m_page_addrs[i] = zp;
     }
 
     spin_lock_irqsave(&rds_cong_lock, flags);
     ret = rds_cong_tree_walk(addr, map);
     spin_unlock_irqrestore(&rds_cong_lock, flags);
 
     if (!ret) {
         ret = map;
         map = NULL;
     }
 
 out:
     if (map) {
         for (i = 0; i < RDS_CONG_MAP_PAGES && map->m_page_addrs[i]; i++)
             free_page(map->m_page_addrs[i]);
         kfree(map);
     }
 
     rdsdebug("map %p for addr %pI6c\n", ret, addr);
 
     return ret;
 }
 
 /*
  * Put the conn on its local map's list.  This is called when the conn is
  * really added to the hash.  It's nested under the rds_conn_lock, sadly.
  */
 void rds_cong_add_conn(struct rds_connection *conn)
 {
     unsigned long flags;
 
     rdsdebug("conn %p now on map %p\n", conn, conn->c_lcong);
     spin_lock_irqsave(&rds_cong_lock, flags);
     list_add_tail(&conn->c_map_item, &conn->c_lcong->m_conn_list);
     spin_unlock_irqrestore(&rds_cong_lock, flags);
 }
 
 void rds_cong_remove_conn(struct rds_connection *conn)
 {
     unsigned long flags;
 
     rdsdebug("removing conn %p from map %p\n", conn, conn->c_lcong);
     spin_lock_irqsave(&rds_cong_lock, flags);
     list_del_init(&conn->c_map_item);
     spin_unlock_irqrestore(&rds_cong_lock, flags);
 }
 
 int rds_cong_get_maps(struct rds_connection *conn)
 {
     conn->c_lcong = rds_cong_from_addr(&conn->c_laddr);
     conn->c_fcong = rds_cong_from_addr(&conn->c_faddr);
 
     if (!(conn->c_lcong && conn->c_fcong))
         return -ENOMEM;
 
     return 0;
 }
 
 void rds_cong_queue_updates(struct rds_cong_map *map)
 {
     struct rds_connection *conn;
     unsigned long flags;
 
     spin_lock_irqsave(&rds_cong_lock, flags);
 
     list_for_each_entry(conn, &map->m_conn_list, c_map_item) {
         struct rds_conn_path *cp = &conn->c_path[0];
 
         rcu_read_lock();
         if (!test_and_set_bit(0, &conn->c_map_queued) &&
             !rds_destroy_pending(cp->cp_conn)) {
             rds_stats_inc(s_cong_update_queued);
             /* We cannot inline the call to rds_send_xmit() here
              * for two reasons (both pertaining to a TCP transport):
              * 1. When we get here from the receive path, we
              *    are already holding the sock_lock (held by
              *    tcp_v4_rcv()). So inlining calls to
              *    tcp_setsockopt and/or tcp_sendmsg will deadlock
              *    when it tries to get the sock_lock())
              * 2. Interrupts are masked so that we can mark the
              *    port congested from both send and recv paths.
              *    (See comment around declaration of rdc_cong_lock).
              *    An attempt to get the sock_lock() here will
              *    therefore trigger warnings.
              * Defer the xmit to rds_send_worker() instead.
              */
             queue_delayed_work(rds_wq, &cp->cp_send_w, 0);
         }
         rcu_read_unlock();
     }
 
     spin_unlock_irqrestore(&rds_cong_lock, flags);
 }
 
 void rds_cong_map_updated(struct rds_cong_map *map, uint64_t portmask)
 {
     rdsdebug("waking map %p for %pI4\n",
       map, &map->m_addr);
     rds_stats_inc(s_cong_update_received);
     atomic_inc(&rds_cong_generation);
     if (waitqueue_active(&map->m_waitq))
         wake_up(&map->m_waitq);
     if (waitqueue_active(&rds_poll_waitq))
         wake_up_all(&rds_poll_waitq);
 
     if (portmask && !list_empty(&rds_cong_monitor)) {
         unsigned long flags;
         struct rds_sock *rs;
 
         read_lock_irqsave(&rds_cong_monitor_lock, flags);
         list_for_each_entry(rs, &rds_cong_monitor, rs_cong_list) {
             spin_lock(&rs->rs_lock);
             rs->rs_cong_notify |= (rs->rs_cong_mask & portmask);
             rs->rs_cong_mask &= ~portmask;
             spin_unlock(&rs->rs_lock);
             if (rs->rs_cong_notify)
                 rds_wake_sk_sleep(rs);
         }
         read_unlock_irqrestore(&rds_cong_monitor_lock, flags);
     }
 }
 EXPORT_SYMBOL_GPL(rds_cong_map_updated);
 
 int rds_cong_updated_since(unsigned long *recent)
 {
     unsigned long gen = atomic_read(&rds_cong_generation);
 
     if (likely(*recent == gen))
         return 0;
     *recent = gen;
     return 1;
 }
 
 /*
  * We're called under the locking that protects the sockets receive buffer
  * consumption.  This makes it a lot easier for the caller to only call us
  * when it knows that an existing set bit needs to be cleared, and vice versa.
  * We can't block and we need to deal with concurrent sockets working against
  * the same per-address map.
  */
 void rds_cong_set_bit(struct rds_cong_map *map, __be16 port)
 {
     unsigned long i;
     unsigned long off;
 
     rdsdebug("setting congestion for %pI4:%u in map %p\n",
       &map->m_addr, ntohs(port), map);
 
     i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
     off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
 
     set_bit_le(off, (void *)map->m_page_addrs[i]);
 }
 
 void rds_cong_clear_bit(struct rds_cong_map *map, __be16 port)
 {
     unsigned long i;
     unsigned long off;
 
     rdsdebug("clearing congestion for %pI4:%u in map %p\n",
       &map->m_addr, ntohs(port), map);
 
     i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
     off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
 
     clear_bit_le(off, (void *)map->m_page_addrs[i]);
 }
 
 static int rds_cong_test_bit(struct rds_cong_map *map, __be16 port)
 {
     unsigned long i;
     unsigned long off;
 
     i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
     off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
 
     return test_bit_le(off, (void *)map->m_page_addrs[i]);
 }
 
 void rds_cong_add_socket(struct rds_sock *rs)
 {
     unsigned long flags;
 
     write_lock_irqsave(&rds_cong_monitor_lock, flags);
     if (list_empty(&rs->rs_cong_list))
         list_add(&rs->rs_cong_list, &rds_cong_monitor);
     write_unlock_irqrestore(&rds_cong_monitor_lock, flags);
 }
 
 void rds_cong_remove_socket(struct rds_sock *rs)
 {
     unsigned long flags;
     struct rds_cong_map *map;
 
     write_lock_irqsave(&rds_cong_monitor_lock, flags);
     list_del_init(&rs->rs_cong_list);
     write_unlock_irqrestore(&rds_cong_monitor_lock, flags);
 
     /* update congestion map for now-closed port */
     spin_lock_irqsave(&rds_cong_lock, flags);
     map = rds_cong_tree_walk(&rs->rs_bound_addr, NULL);
     spin_unlock_irqrestore(&rds_cong_lock, flags);
 
     if (map && rds_cong_test_bit(map, rs->rs_bound_port)) {
         rds_cong_clear_bit(map, rs->rs_bound_port);
         rds_cong_queue_updates(map);
     }
 }
 
 int rds_cong_wait(struct rds_cong_map *map, __be16 port, int nonblock,
           struct rds_sock *rs)
 {
     if (!rds_cong_test_bit(map, port))
         return 0;
     if (nonblock) {
         if (rs && rs->rs_cong_monitor) {
             unsigned long flags;
 
             /* It would have been nice to have an atomic set_bit on
              * a uint64_t. */
             spin_lock_irqsave(&rs->rs_lock, flags);
             rs->rs_cong_mask |= RDS_CONG_MONITOR_MASK(ntohs(port));
             spin_unlock_irqrestore(&rs->rs_lock, flags);
 
             /* Test again - a congestion update may have arrived in
              * the meantime. */
             if (!rds_cong_test_bit(map, port))
                 return 0;
         }
         rds_stats_inc(s_cong_send_error);
         return -ENOBUFS;
     }
 
     rds_stats_inc(s_cong_send_blocked);
     rdsdebug("waiting on map %p for port %u\n", map, be16_to_cpu(port));
 
     return wait_event_interruptible(map->m_waitq,
                     !rds_cong_test_bit(map, port));
 }
 
 void rds_cong_exit(void)
 {
     struct rb_node *node;
     struct rds_cong_map *map;
     unsigned long i;
 
     while ((node = rb_first(&rds_cong_tree))) {
         map = rb_entry(node, struct rds_cong_map, m_rb_node);
         rdsdebug("freeing map %p\n", map);
         rb_erase(&map->m_rb_node, &rds_cong_tree);
         for (i = 0; i < RDS_CONG_MAP_PAGES && map->m_page_addrs[i]; i++)
             free_page(map->m_page_addrs[i]);
         kfree(map);
     }
 }
 
 /*
  * Allocate a RDS message containing a congestion update.
  */
 struct rds_message *rds_cong_update_alloc(struct rds_connection *conn)
 {
     struct rds_cong_map *map = conn->c_lcong;
     struct rds_message *rm;
 
     rm = rds_message_map_pages(map->m_page_addrs, RDS_CONG_MAP_BYTES);
     if (!IS_ERR(rm))
         rm->m_inc.i_hdr.h_flags = RDS_FLAG_CONG_BITMAP;
 
     return rm;
 }

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