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TOMOYO Linux Cross Reference
Linux/net/rds/cong.c

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  1 /*
  2  * Copyright (c) 2007, 2017 Oracle and/or its affiliates. All rights reserved.
  3  *
  4  * This software is available to you under a choice of one of two
  5  * licenses.  You may choose to be licensed under the terms of the GNU
  6  * General Public License (GPL) Version 2, available from the file
  7  * COPYING in the main directory of this source tree, or the
  8  * OpenIB.org BSD license below:
  9  *
 10  *     Redistribution and use in source and binary forms, with or
 11  *     without modification, are permitted provided that the following
 12  *     conditions are met:
 13  *
 14  *      - Redistributions of source code must retain the above
 15  *        copyright notice, this list of conditions and the following
 16  *        disclaimer.
 17  *
 18  *      - Redistributions in binary form must reproduce the above
 19  *        copyright notice, this list of conditions and the following
 20  *        disclaimer in the documentation and/or other materials
 21  *        provided with the distribution.
 22  *
 23  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 24  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 25  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 26  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 27  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 28  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 29  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 30  * SOFTWARE.
 31  *
 32  */
 33 #include <linux/slab.h>
 34 #include <linux/types.h>
 35 #include <linux/rbtree.h>
 36 #include <linux/bitops.h>
 37 #include <linux/export.h>
 38 
 39 #include "rds.h"
 40 
 41 /*
 42  * This file implements the receive side of the unconventional congestion
 43  * management in RDS.
 44  *
 45  * Messages waiting in the receive queue on the receiving socket are accounted
 46  * against the sockets SO_RCVBUF option value.  Only the payload bytes in the
 47  * message are accounted for.  If the number of bytes queued equals or exceeds
 48  * rcvbuf then the socket is congested.  All sends attempted to this socket's
 49  * address should return block or return -EWOULDBLOCK.
 50  *
 51  * Applications are expected to be reasonably tuned such that this situation
 52  * very rarely occurs.  An application encountering this "back-pressure" is
 53  * considered a bug.
 54  *
 55  * This is implemented by having each node maintain bitmaps which indicate
 56  * which ports on bound addresses are congested.  As the bitmap changes it is
 57  * sent through all the connections which terminate in the local address of the
 58  * bitmap which changed.
 59  *
 60  * The bitmaps are allocated as connections are brought up.  This avoids
 61  * allocation in the interrupt handling path which queues messages on sockets.
 62  * The dense bitmaps let transports send the entire bitmap on any bitmap change
 63  * reasonably efficiently.  This is much easier to implement than some
 64  * finer-grained communication of per-port congestion.  The sender does a very
 65  * inexpensive bit test to test if the port it's about to send to is congested
 66  * or not.
 67  */
 68 
 69 /*
 70  * Interaction with poll is a tad tricky. We want all processes stuck in
 71  * poll to wake up and check whether a congested destination became uncongested.
 72  * The really sad thing is we have no idea which destinations the application
 73  * wants to send to - we don't even know which rds_connections are involved.
 74  * So until we implement a more flexible rds poll interface, we have to make
 75  * do with this:
 76  * We maintain a global counter that is incremented each time a congestion map
 77  * update is received. Each rds socket tracks this value, and if rds_poll
 78  * finds that the saved generation number is smaller than the global generation
 79  * number, it wakes up the process.
 80  */
 81 static atomic_t         rds_cong_generation = ATOMIC_INIT(0);
 82 
 83 /*
 84  * Congestion monitoring
 85  */
 86 static LIST_HEAD(rds_cong_monitor);
 87 static DEFINE_RWLOCK(rds_cong_monitor_lock);
 88 
 89 /*
 90  * Yes, a global lock.  It's used so infrequently that it's worth keeping it
 91  * global to simplify the locking.  It's only used in the following
 92  * circumstances:
 93  *
 94  *  - on connection buildup to associate a conn with its maps
 95  *  - on map changes to inform conns of a new map to send
 96  *
 97  *  It's sadly ordered under the socket callback lock and the connection lock.
 98  *  Receive paths can mark ports congested from interrupt context so the
 99  *  lock masks interrupts.
100  */
101 static DEFINE_SPINLOCK(rds_cong_lock);
102 static struct rb_root rds_cong_tree = RB_ROOT;
103 
104 static struct rds_cong_map *rds_cong_tree_walk(const struct in6_addr *addr,
105                                                struct rds_cong_map *insert)
106 {
107         struct rb_node **p = &rds_cong_tree.rb_node;
108         struct rb_node *parent = NULL;
109         struct rds_cong_map *map;
110 
111         while (*p) {
112                 int diff;
113 
114                 parent = *p;
115                 map = rb_entry(parent, struct rds_cong_map, m_rb_node);
116 
117                 diff = rds_addr_cmp(addr, &map->m_addr);
118                 if (diff < 0)
119                         p = &(*p)->rb_left;
120                 else if (diff > 0)
121                         p = &(*p)->rb_right;
122                 else
123                         return map;
124         }
125 
126         if (insert) {
127                 rb_link_node(&insert->m_rb_node, parent, p);
128                 rb_insert_color(&insert->m_rb_node, &rds_cong_tree);
129         }
130         return NULL;
131 }
132 
133 /*
134  * There is only ever one bitmap for any address.  Connections try and allocate
135  * these bitmaps in the process getting pointers to them.  The bitmaps are only
136  * ever freed as the module is removed after all connections have been freed.
137  */
138 static struct rds_cong_map *rds_cong_from_addr(const struct in6_addr *addr)
139 {
140         struct rds_cong_map *map;
141         struct rds_cong_map *ret = NULL;
142         unsigned long zp;
143         unsigned long i;
144         unsigned long flags;
145 
146         map = kzalloc(sizeof(struct rds_cong_map), GFP_KERNEL);
147         if (!map)
148                 return NULL;
149 
150         map->m_addr = *addr;
151         init_waitqueue_head(&map->m_waitq);
152         INIT_LIST_HEAD(&map->m_conn_list);
153 
154         for (i = 0; i < RDS_CONG_MAP_PAGES; i++) {
155                 zp = get_zeroed_page(GFP_KERNEL);
156                 if (zp == 0)
157                         goto out;
158                 map->m_page_addrs[i] = zp;
159         }
160 
161         spin_lock_irqsave(&rds_cong_lock, flags);
162         ret = rds_cong_tree_walk(addr, map);
163         spin_unlock_irqrestore(&rds_cong_lock, flags);
164 
165         if (!ret) {
166                 ret = map;
167                 map = NULL;
168         }
169 
170 out:
171         if (map) {
172                 for (i = 0; i < RDS_CONG_MAP_PAGES && map->m_page_addrs[i]; i++)
173                         free_page(map->m_page_addrs[i]);
174                 kfree(map);
175         }
176 
177         rdsdebug("map %p for addr %pI6c\n", ret, addr);
178 
179         return ret;
180 }
181 
182 /*
183  * Put the conn on its local map's list.  This is called when the conn is
184  * really added to the hash.  It's nested under the rds_conn_lock, sadly.
185  */
186 void rds_cong_add_conn(struct rds_connection *conn)
187 {
188         unsigned long flags;
189 
190         rdsdebug("conn %p now on map %p\n", conn, conn->c_lcong);
191         spin_lock_irqsave(&rds_cong_lock, flags);
192         list_add_tail(&conn->c_map_item, &conn->c_lcong->m_conn_list);
193         spin_unlock_irqrestore(&rds_cong_lock, flags);
194 }
195 
196 void rds_cong_remove_conn(struct rds_connection *conn)
197 {
198         unsigned long flags;
199 
200         rdsdebug("removing conn %p from map %p\n", conn, conn->c_lcong);
201         spin_lock_irqsave(&rds_cong_lock, flags);
202         list_del_init(&conn->c_map_item);
203         spin_unlock_irqrestore(&rds_cong_lock, flags);
204 }
205 
206 int rds_cong_get_maps(struct rds_connection *conn)
207 {
208         conn->c_lcong = rds_cong_from_addr(&conn->c_laddr);
209         conn->c_fcong = rds_cong_from_addr(&conn->c_faddr);
210 
211         if (!(conn->c_lcong && conn->c_fcong))
212                 return -ENOMEM;
213 
214         return 0;
215 }
216 
217 void rds_cong_queue_updates(struct rds_cong_map *map)
218 {
219         struct rds_connection *conn;
220         unsigned long flags;
221 
222         spin_lock_irqsave(&rds_cong_lock, flags);
223 
224         list_for_each_entry(conn, &map->m_conn_list, c_map_item) {
225                 struct rds_conn_path *cp = &conn->c_path[0];
226 
227                 rcu_read_lock();
228                 if (!test_and_set_bit(0, &conn->c_map_queued) &&
229                     !rds_destroy_pending(cp->cp_conn)) {
230                         rds_stats_inc(s_cong_update_queued);
231                         /* We cannot inline the call to rds_send_xmit() here
232                          * for two reasons (both pertaining to a TCP transport):
233                          * 1. When we get here from the receive path, we
234                          *    are already holding the sock_lock (held by
235                          *    tcp_v4_rcv()). So inlining calls to
236                          *    tcp_setsockopt and/or tcp_sendmsg will deadlock
237                          *    when it tries to get the sock_lock())
238                          * 2. Interrupts are masked so that we can mark the
239                          *    the port congested from both send and recv paths.
240                          *    (See comment around declaration of rdc_cong_lock).
241                          *    An attempt to get the sock_lock() here will
242                          *    therefore trigger warnings.
243                          * Defer the xmit to rds_send_worker() instead.
244                          */
245                         queue_delayed_work(rds_wq, &cp->cp_send_w, 0);
246                 }
247                 rcu_read_unlock();
248         }
249 
250         spin_unlock_irqrestore(&rds_cong_lock, flags);
251 }
252 
253 void rds_cong_map_updated(struct rds_cong_map *map, uint64_t portmask)
254 {
255         rdsdebug("waking map %p for %pI4\n",
256           map, &map->m_addr);
257         rds_stats_inc(s_cong_update_received);
258         atomic_inc(&rds_cong_generation);
259         if (waitqueue_active(&map->m_waitq))
260                 wake_up(&map->m_waitq);
261         if (waitqueue_active(&rds_poll_waitq))
262                 wake_up_all(&rds_poll_waitq);
263 
264         if (portmask && !list_empty(&rds_cong_monitor)) {
265                 unsigned long flags;
266                 struct rds_sock *rs;
267 
268                 read_lock_irqsave(&rds_cong_monitor_lock, flags);
269                 list_for_each_entry(rs, &rds_cong_monitor, rs_cong_list) {
270                         spin_lock(&rs->rs_lock);
271                         rs->rs_cong_notify |= (rs->rs_cong_mask & portmask);
272                         rs->rs_cong_mask &= ~portmask;
273                         spin_unlock(&rs->rs_lock);
274                         if (rs->rs_cong_notify)
275                                 rds_wake_sk_sleep(rs);
276                 }
277                 read_unlock_irqrestore(&rds_cong_monitor_lock, flags);
278         }
279 }
280 EXPORT_SYMBOL_GPL(rds_cong_map_updated);
281 
282 int rds_cong_updated_since(unsigned long *recent)
283 {
284         unsigned long gen = atomic_read(&rds_cong_generation);
285 
286         if (likely(*recent == gen))
287                 return 0;
288         *recent = gen;
289         return 1;
290 }
291 
292 /*
293  * We're called under the locking that protects the sockets receive buffer
294  * consumption.  This makes it a lot easier for the caller to only call us
295  * when it knows that an existing set bit needs to be cleared, and vice versa.
296  * We can't block and we need to deal with concurrent sockets working against
297  * the same per-address map.
298  */
299 void rds_cong_set_bit(struct rds_cong_map *map, __be16 port)
300 {
301         unsigned long i;
302         unsigned long off;
303 
304         rdsdebug("setting congestion for %pI4:%u in map %p\n",
305           &map->m_addr, ntohs(port), map);
306 
307         i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
308         off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
309 
310         set_bit_le(off, (void *)map->m_page_addrs[i]);
311 }
312 
313 void rds_cong_clear_bit(struct rds_cong_map *map, __be16 port)
314 {
315         unsigned long i;
316         unsigned long off;
317 
318         rdsdebug("clearing congestion for %pI4:%u in map %p\n",
319           &map->m_addr, ntohs(port), map);
320 
321         i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
322         off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
323 
324         clear_bit_le(off, (void *)map->m_page_addrs[i]);
325 }
326 
327 static int rds_cong_test_bit(struct rds_cong_map *map, __be16 port)
328 {
329         unsigned long i;
330         unsigned long off;
331 
332         i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
333         off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
334 
335         return test_bit_le(off, (void *)map->m_page_addrs[i]);
336 }
337 
338 void rds_cong_add_socket(struct rds_sock *rs)
339 {
340         unsigned long flags;
341 
342         write_lock_irqsave(&rds_cong_monitor_lock, flags);
343         if (list_empty(&rs->rs_cong_list))
344                 list_add(&rs->rs_cong_list, &rds_cong_monitor);
345         write_unlock_irqrestore(&rds_cong_monitor_lock, flags);
346 }
347 
348 void rds_cong_remove_socket(struct rds_sock *rs)
349 {
350         unsigned long flags;
351         struct rds_cong_map *map;
352 
353         write_lock_irqsave(&rds_cong_monitor_lock, flags);
354         list_del_init(&rs->rs_cong_list);
355         write_unlock_irqrestore(&rds_cong_monitor_lock, flags);
356 
357         /* update congestion map for now-closed port */
358         spin_lock_irqsave(&rds_cong_lock, flags);
359         map = rds_cong_tree_walk(&rs->rs_bound_addr, NULL);
360         spin_unlock_irqrestore(&rds_cong_lock, flags);
361 
362         if (map && rds_cong_test_bit(map, rs->rs_bound_port)) {
363                 rds_cong_clear_bit(map, rs->rs_bound_port);
364                 rds_cong_queue_updates(map);
365         }
366 }
367 
368 int rds_cong_wait(struct rds_cong_map *map, __be16 port, int nonblock,
369                   struct rds_sock *rs)
370 {
371         if (!rds_cong_test_bit(map, port))
372                 return 0;
373         if (nonblock) {
374                 if (rs && rs->rs_cong_monitor) {
375                         unsigned long flags;
376 
377                         /* It would have been nice to have an atomic set_bit on
378                          * a uint64_t. */
379                         spin_lock_irqsave(&rs->rs_lock, flags);
380                         rs->rs_cong_mask |= RDS_CONG_MONITOR_MASK(ntohs(port));
381                         spin_unlock_irqrestore(&rs->rs_lock, flags);
382 
383                         /* Test again - a congestion update may have arrived in
384                          * the meantime. */
385                         if (!rds_cong_test_bit(map, port))
386                                 return 0;
387                 }
388                 rds_stats_inc(s_cong_send_error);
389                 return -ENOBUFS;
390         }
391 
392         rds_stats_inc(s_cong_send_blocked);
393         rdsdebug("waiting on map %p for port %u\n", map, be16_to_cpu(port));
394 
395         return wait_event_interruptible(map->m_waitq,
396                                         !rds_cong_test_bit(map, port));
397 }
398 
399 void rds_cong_exit(void)
400 {
401         struct rb_node *node;
402         struct rds_cong_map *map;
403         unsigned long i;
404 
405         while ((node = rb_first(&rds_cong_tree))) {
406                 map = rb_entry(node, struct rds_cong_map, m_rb_node);
407                 rdsdebug("freeing map %p\n", map);
408                 rb_erase(&map->m_rb_node, &rds_cong_tree);
409                 for (i = 0; i < RDS_CONG_MAP_PAGES && map->m_page_addrs[i]; i++)
410                         free_page(map->m_page_addrs[i]);
411                 kfree(map);
412         }
413 }
414 
415 /*
416  * Allocate a RDS message containing a congestion update.
417  */
418 struct rds_message *rds_cong_update_alloc(struct rds_connection *conn)
419 {
420         struct rds_cong_map *map = conn->c_lcong;
421         struct rds_message *rm;
422 
423         rm = rds_message_map_pages(map->m_page_addrs, RDS_CONG_MAP_BYTES);
424         if (!IS_ERR(rm))
425                 rm->m_inc.i_hdr.h_flags = RDS_FLAG_CONG_BITMAP;
426 
427         return rm;
428 }
429 

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