aboutsummaryrefslogtreecommitdiff
path: root/net/rxrpc/conn_client.c
blob: 4b213bc0f55467a71a955a6839b985331debbb7d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
/* Client connection-specific management code.
 *
 * Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 *
 *
 * Client connections need to be cached for a little while after they've made a
 * call so as to handle retransmitted DATA packets in case the server didn't
 * receive the final ACK or terminating ABORT we sent it.
 *
 * Client connections can be in one of a number of cache states:
 *
 *  (1) INACTIVE - The connection is not held in any list and may not have been
 *      exposed to the world.  If it has been previously exposed, it was
 *      discarded from the idle list after expiring.
 *
 *  (2) WAITING - The connection is waiting for the number of client conns to
 *      drop below the maximum capacity.  Calls may be in progress upon it from
 *      when it was active and got culled.
 *
 *	The connection is on the rxrpc_waiting_client_conns list which is kept
 *	in to-be-granted order.  Culled conns with waiters go to the back of
 *	the queue just like new conns.
 *
 *  (3) ACTIVE - The connection has at least one call in progress upon it, it
 *      may freely grant available channels to new calls and calls may be
 *      waiting on it for channels to become available.
 *
 *	The connection is on the rxrpc_active_client_conns list which is kept
 *	in activation order for culling purposes.
 *
 *	rxrpc_nr_active_client_conns is held incremented also.
 *
 *  (4) CULLED - The connection got summarily culled to try and free up
 *      capacity.  Calls currently in progress on the connection are allowed to
 *      continue, but new calls will have to wait.  There can be no waiters in
 *      this state - the conn would have to go to the WAITING state instead.
 *
 *  (5) IDLE - The connection has no calls in progress upon it and must have
 *      been exposed to the world (ie. the EXPOSED flag must be set).  When it
 *      expires, the EXPOSED flag is cleared and the connection transitions to
 *      the INACTIVE state.
 *
 *	The connection is on the rxrpc_idle_client_conns list which is kept in
 *	order of how soon they'll expire.
 *
 * There are flags of relevance to the cache:
 *
 *  (1) EXPOSED - The connection ID got exposed to the world.  If this flag is
 *      set, an extra ref is added to the connection preventing it from being
 *      reaped when it has no calls outstanding.  This flag is cleared and the
 *      ref dropped when a conn is discarded from the idle list.
 *
 *      This allows us to move terminal call state retransmission to the
 *      connection and to discard the call immediately we think it is done
 *      with.  It also give us a chance to reuse the connection.
 *
 *  (2) DONT_REUSE - The connection should be discarded as soon as possible and
 *      should not be reused.  This is set when an exclusive connection is used
 *      or a call ID counter overflows.
 *
 * The caching state may only be changed if the cache lock is held.
 *
 * There are two idle client connection expiry durations.  If the total number
 * of connections is below the reap threshold, we use the normal duration; if
 * it's above, we use the fast duration.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/slab.h>
#include <linux/idr.h>
#include <linux/timer.h>
#include "ar-internal.h"

__read_mostly unsigned int rxrpc_max_client_connections = 1000;
__read_mostly unsigned int rxrpc_reap_client_connections = 900;
__read_mostly unsigned int rxrpc_conn_idle_client_expiry = 2 * 60 * HZ;
__read_mostly unsigned int rxrpc_conn_idle_client_fast_expiry = 2 * HZ;

static unsigned int rxrpc_nr_client_conns;
static unsigned int rxrpc_nr_active_client_conns;
static __read_mostly bool rxrpc_kill_all_client_conns;

static DEFINE_SPINLOCK(rxrpc_client_conn_cache_lock);
static DEFINE_SPINLOCK(rxrpc_client_conn_discard_mutex);
static LIST_HEAD(rxrpc_waiting_client_conns);
static LIST_HEAD(rxrpc_active_client_conns);
static LIST_HEAD(rxrpc_idle_client_conns);

/*
 * We use machine-unique IDs for our client connections.
 */
DEFINE_IDR(rxrpc_client_conn_ids);
static DEFINE_SPINLOCK(rxrpc_conn_id_lock);

static void rxrpc_cull_active_client_conns(void);
static void rxrpc_discard_expired_client_conns(struct work_struct *);

static DECLARE_DELAYED_WORK(rxrpc_client_conn_reap,
			    rxrpc_discard_expired_client_conns);

/*
 * Get a connection ID and epoch for a client connection from the global pool.
 * The connection struct pointer is then recorded in the idr radix tree.  The
 * epoch is changed if this wraps.
 */
static int rxrpc_get_client_connection_id(struct rxrpc_connection *conn,
					  gfp_t gfp)
{
	u32 epoch;
	int id;

	_enter("");

	idr_preload(gfp);
	spin_lock(&rxrpc_conn_id_lock);

	epoch = rxrpc_epoch;

	/* We could use idr_alloc_cyclic() here, but we really need to know
	 * when the thing wraps so that we can advance the epoch.
	 */
	if (rxrpc_client_conn_ids.cur == 0)
		rxrpc_client_conn_ids.cur = 1;
	id = idr_alloc(&rxrpc_client_conn_ids, conn,
		       rxrpc_client_conn_ids.cur, 0x40000000, GFP_NOWAIT);
	if (id < 0) {
		if (id != -ENOSPC)
			goto error;
		id = idr_alloc(&rxrpc_client_conn_ids, conn,
			       1, 0x40000000, GFP_NOWAIT);
		if (id < 0)
			goto error;
		epoch++;
		rxrpc_epoch = epoch;
	}
	rxrpc_client_conn_ids.cur = id + 1;

	spin_unlock(&rxrpc_conn_id_lock);
	idr_preload_end();

	conn->proto.epoch = epoch;
	conn->proto.cid = id << RXRPC_CIDSHIFT;
	set_bit(RXRPC_CONN_HAS_IDR, &conn->flags);
	_leave(" [CID %x:%x]", epoch, conn->proto.cid);
	return 0;

error:
	spin_unlock(&rxrpc_conn_id_lock);
	idr_preload_end();
	_leave(" = %d", id);
	return id;
}

/*
 * Release a connection ID for a client connection from the global pool.
 */
static void rxrpc_put_client_connection_id(struct rxrpc_connection *conn)
{
	if (test_bit(RXRPC_CONN_HAS_IDR, &conn->flags)) {
		spin_lock(&rxrpc_conn_id_lock);
		idr_remove(&rxrpc_client_conn_ids,
			   conn->proto.cid >> RXRPC_CIDSHIFT);
		spin_unlock(&rxrpc_conn_id_lock);
	}
}

/*
 * Destroy the client connection ID tree.
 */
void rxrpc_destroy_client_conn_ids(void)
{
	struct rxrpc_connection *conn;
	int id;

	if (!idr_is_empty(&rxrpc_client_conn_ids)) {
		idr_for_each_entry(&rxrpc_client_conn_ids, conn, id) {
			pr_err("AF_RXRPC: Leaked client conn %p {%d}\n",
			       conn, atomic_read(&conn->usage));
		}
		BUG();
	}

	idr_destroy(&rxrpc_client_conn_ids);
}

/*
 * Allocate a client connection.
 */
static struct rxrpc_connection *
rxrpc_alloc_client_connection(struct rxrpc_conn_parameters *cp, gfp_t gfp)
{
	struct rxrpc_connection *conn;
	int ret;

	_enter("");

	conn = rxrpc_alloc_connection(gfp);
	if (!conn) {
		_leave(" = -ENOMEM");
		return ERR_PTR(-ENOMEM);
	}

	atomic_set(&conn->usage, 1);
	if (conn->params.exclusive)
		__set_bit(RXRPC_CONN_DONT_REUSE, &conn->flags);

	conn->params		= *cp;
	conn->out_clientflag	= RXRPC_CLIENT_INITIATED;
	conn->state		= RXRPC_CONN_CLIENT;

	ret = rxrpc_get_client_connection_id(conn, gfp);
	if (ret < 0)
		goto error_0;

	ret = rxrpc_init_client_conn_security(conn);
	if (ret < 0)
		goto error_1;

	ret = conn->security->prime_packet_security(conn);
	if (ret < 0)
		goto error_2;

	write_lock(&rxrpc_connection_lock);
	list_add_tail(&conn->proc_link, &rxrpc_connection_proc_list);
	write_unlock(&rxrpc_connection_lock);

	/* We steal the caller's peer ref. */
	cp->peer = NULL;
	rxrpc_get_local(conn->params.local);
	key_get(conn->params.key);

	_leave(" = %p", conn);
	return conn;

error_2:
	conn->security->clear(conn);
error_1:
	rxrpc_put_client_connection_id(conn);
error_0:
	kfree(conn);
	_leave(" = %d", ret);
	return ERR_PTR(ret);
}

/*
 * Determine if a connection may be reused.
 */
static bool rxrpc_may_reuse_conn(struct rxrpc_connection *conn)
{
	int id_cursor, id, distance, limit;

	if (test_bit(RXRPC_CONN_DONT_REUSE, &conn->flags))
		goto dont_reuse;

	if (conn->proto.epoch != rxrpc_epoch)
		goto mark_dont_reuse;

	/* The IDR tree gets very expensive on memory if the connection IDs are
	 * widely scattered throughout the number space, so we shall want to
	 * kill off connections that, say, have an ID more than about four
	 * times the maximum number of client conns away from the current
	 * allocation point to try and keep the IDs concentrated.
	 */
	id_cursor = READ_ONCE(rxrpc_client_conn_ids.cur);
	id = conn->proto.cid >> RXRPC_CIDSHIFT;
	distance = id - id_cursor;
	if (distance < 0)
		distance = -distance;
	limit = round_up(rxrpc_max_client_connections, IDR_SIZE) * 4;
	if (distance > limit)
		goto mark_dont_reuse;

	return true;

mark_dont_reuse:
	set_bit(RXRPC_CONN_DONT_REUSE, &conn->flags);
dont_reuse:
	return false;
}

/*
 * Create or find a client connection to use for a call.
 *
 * If we return with a connection, the call will be on its waiting list.  It's
 * left to the caller to assign a channel and wake up the call.
 */
static int rxrpc_get_client_conn(struct rxrpc_call *call,
				 struct rxrpc_conn_parameters *cp,
				 struct sockaddr_rxrpc *srx,
				 gfp_t gfp)
{
	struct rxrpc_connection *conn, *candidate = NULL;
	struct rxrpc_local *local = cp->local;
	struct rb_node *p, **pp, *parent;
	long diff;
	int ret = -ENOMEM;

	_enter("{%d,%lx},", call->debug_id, call->user_call_ID);

	cp->peer = rxrpc_lookup_peer(cp->local, srx, gfp);
	if (!cp->peer)
		goto error;

	/* If the connection is not meant to be exclusive, search the available
	 * connections to see if the connection we want to use already exists.
	 */
	if (!cp->exclusive) {
		_debug("search 1");
		spin_lock(&local->client_conns_lock);
		p = local->client_conns.rb_node;
		while (p) {
			conn = rb_entry(p, struct rxrpc_connection, client_node);

#define cmp(X) ((long)conn->params.X - (long)cp->X)
			diff = (cmp(peer) ?:
				cmp(key) ?:
				cmp(security_level));
#undef cmp
			if (diff < 0) {
				p = p->rb_left;
			} else if (diff > 0) {
				p = p->rb_right;
			} else {
				if (rxrpc_may_reuse_conn(conn) &&
				    rxrpc_get_connection_maybe(conn))
					goto found_extant_conn;
				/* The connection needs replacing.  It's better
				 * to effect that when we have something to
				 * replace it with so that we don't have to
				 * rebalance the tree twice.
				 */
				break;
			}
		}
		spin_unlock(&local->client_conns_lock);
	}

	/* There wasn't a connection yet or we need an exclusive connection.
	 * We need to create a candidate and then potentially redo the search
	 * in case we're racing with another thread also trying to connect on a
	 * shareable connection.
	 */
	_debug("new conn");
	candidate = rxrpc_alloc_client_connection(cp, gfp);
	if (IS_ERR(candidate)) {
		ret = PTR_ERR(candidate);
		goto error_peer;
	}

	/* Add the call to the new connection's waiting list in case we're
	 * going to have to wait for the connection to come live.  It's our
	 * connection, so we want first dibs on the channel slots.  We would
	 * normally have to take channel_lock but we do this before anyone else
	 * can see the connection.
	 */
	list_add_tail(&call->chan_wait_link, &candidate->waiting_calls);

	if (cp->exclusive) {
		call->conn = candidate;
		_leave(" = 0 [exclusive %d]", candidate->debug_id);
		return 0;
	}

	/* Publish the new connection for userspace to find.  We need to redo
	 * the search before doing this lest we race with someone else adding a
	 * conflicting instance.
	 */
	_debug("search 2");
	spin_lock(&local->client_conns_lock);

	pp = &local->client_conns.rb_node;
	parent = NULL;
	while (*pp) {
		parent = *pp;
		conn = rb_entry(parent, struct rxrpc_connection, client_node);

#define cmp(X) ((long)conn->params.X - (long)candidate->params.X)
		diff = (cmp(peer) ?:
			cmp(key) ?:
			cmp(security_level));
#undef cmp
		if (diff < 0) {
			pp = &(*pp)->rb_left;
		} else if (diff > 0) {
			pp = &(*pp)->rb_right;
		} else {
			if (rxrpc_may_reuse_conn(conn) &&
			    rxrpc_get_connection_maybe(conn))
				goto found_extant_conn;
			/* The old connection is from an outdated epoch. */
			_debug("replace conn");
			clear_bit(RXRPC_CONN_IN_CLIENT_CONNS, &conn->flags);
			rb_replace_node(&conn->client_node,
					&candidate->client_node,
					&local->client_conns);
			goto candidate_published;
		}
	}

	_debug("new conn");
	rb_link_node(&candidate->client_node, parent, pp);
	rb_insert_color(&candidate->client_node, &local->client_conns);

candidate_published:
	set_bit(RXRPC_CONN_IN_CLIENT_CONNS, &candidate->flags);
	call->conn = candidate;
	spin_unlock(&local->client_conns_lock);
	_leave(" = 0 [new %d]", candidate->debug_id);
	return 0;

	/* We come here if we found a suitable connection already in existence.
	 * Discard any candidate we may have allocated, and try to get a
	 * channel on this one.
	 */
found_extant_conn:
	_debug("found conn");
	spin_unlock(&local->client_conns_lock);

	rxrpc_put_connection(candidate);
	candidate = NULL;

	spin_lock(&conn->channel_lock);
	call->conn = conn;
	list_add(&call->chan_wait_link, &conn->waiting_calls);
	spin_unlock(&conn->channel_lock);
	_leave(" = 0 [extant %d]", conn->debug_id);
	return 0;

error_peer:
	rxrpc_put_peer(cp->peer);
	cp->peer = NULL;
error:
	_leave(" = %d", ret);
	return ret;
}

/*
 * Activate a connection.
 */
static void rxrpc_activate_conn(struct rxrpc_connection *conn)
{
	conn->cache_state = RXRPC_CONN_CLIENT_ACTIVE;
	rxrpc_nr_active_client_conns++;
	list_move_tail(&conn->cache_link, &rxrpc_active_client_conns);
}

/*
 * Attempt to animate a connection for a new call.
 *
 * If it's not exclusive, the connection is in the endpoint tree, and we're in
 * the conn's list of those waiting to grab a channel.  There is, however, a
 * limit on the number of live connections allowed at any one time, so we may
 * have to wait for capacity to become available.
 *
 * Note that a connection on the waiting queue might *also* have active
 * channels if it has been culled to make space and then re-requested by a new
 * call.
 */
static void rxrpc_animate_client_conn(struct rxrpc_connection *conn)
{
	unsigned int nr_conns;

	_enter("%d,%d", conn->debug_id, conn->cache_state);

	if (conn->cache_state == RXRPC_CONN_CLIENT_ACTIVE)
		goto out;

	spin_lock(&rxrpc_client_conn_cache_lock);

	nr_conns = rxrpc_nr_client_conns;
	if (!test_and_set_bit(RXRPC_CONN_COUNTED, &conn->flags))
		rxrpc_nr_client_conns = nr_conns + 1;

	switch (conn->cache_state) {
	case RXRPC_CONN_CLIENT_ACTIVE:
	case RXRPC_CONN_CLIENT_WAITING:
		break;

	case RXRPC_CONN_CLIENT_INACTIVE:
	case RXRPC_CONN_CLIENT_CULLED:
	case RXRPC_CONN_CLIENT_IDLE:
		if (nr_conns >= rxrpc_max_client_connections)
			goto wait_for_capacity;
		goto activate_conn;

	default:
		BUG();
	}

out_unlock:
	spin_unlock(&rxrpc_client_conn_cache_lock);
out:
	_leave(" [%d]", conn->cache_state);
	return;

activate_conn:
	_debug("activate");
	rxrpc_activate_conn(conn);
	goto out_unlock;

wait_for_capacity:
	_debug("wait");
	conn->cache_state = RXRPC_CONN_CLIENT_WAITING;
	list_move_tail(&conn->cache_link, &rxrpc_waiting_client_conns);
	goto out_unlock;
}

/*
 * Deactivate a channel.
 */
static void rxrpc_deactivate_one_channel(struct rxrpc_connection *conn,
					 unsigned int channel)
{
	struct rxrpc_channel *chan = &conn->channels[channel];

	rcu_assign_pointer(chan->call, NULL);
	conn->active_chans &= ~(1 << channel);
}

/*
 * Assign a channel to the call at the front of the queue and wake the call up.
 * We don't increment the callNumber counter until this number has been exposed
 * to the world.
 */
static void rxrpc_activate_one_channel(struct rxrpc_connection *conn,
				       unsigned int channel)
{
	struct rxrpc_channel *chan = &conn->channels[channel];
	struct rxrpc_call *call = list_entry(conn->waiting_calls.next,
					     struct rxrpc_call, chan_wait_link);
	u32 call_id = chan->call_counter + 1;

	rxrpc_see_call(call);
	list_del_init(&call->chan_wait_link);
	conn->active_chans |= 1 << channel;
	call->peer	= rxrpc_get_peer(conn->params.peer);
	call->cid	= conn->proto.cid | channel;
	call->call_id	= call_id;

	_net("CONNECT call %08x:%08x as call %d on conn %d",
	     call->cid, call->call_id, call->debug_id, conn->debug_id);

	/* Paired with the read barrier in rxrpc_wait_for_channel().  This
	 * orders cid and epoch in the connection wrt to call_id without the
	 * need to take the channel_lock.
	 *
	 * We provisionally assign a callNumber at this point, but we don't
	 * confirm it until the call is about to be exposed.
	 *
	 * TODO: Pair with a barrier in the data_ready handler when that looks
	 * at the call ID through a connection channel.
	 */
	smp_wmb();
	chan->call_id	= call_id;
	rcu_assign_pointer(chan->call, call);
	wake_up(&call->waitq);
}

/*
 * Assign channels and callNumbers to waiting calls.
 */
static void rxrpc_activate_channels(struct rxrpc_connection *conn)
{
	unsigned char mask;

	_enter("%d", conn->debug_id);

	if (conn->cache_state != RXRPC_CONN_CLIENT_ACTIVE ||
	    conn->active_chans == RXRPC_ACTIVE_CHANS_MASK)
		return;

	spin_lock(&conn->channel_lock);

	while (!list_empty(&conn->waiting_calls) &&
	       (mask = ~conn->active_chans,
		mask &= RXRPC_ACTIVE_CHANS_MASK,
		mask != 0))
		rxrpc_activate_one_channel(conn, __ffs(mask));

	spin_unlock(&conn->channel_lock);
	_leave("");
}

/*
 * Wait for a callNumber and a channel to be granted to a call.
 */
static int rxrpc_wait_for_channel(struct rxrpc_call *call, gfp_t gfp)
{
	int ret = 0;

	_enter("%d", call->debug_id);

	if (!call->call_id) {
		DECLARE_WAITQUEUE(myself, current);

		if (!gfpflags_allow_blocking(gfp)) {
			ret = -EAGAIN;
			goto out;
		}

		add_wait_queue_exclusive(&call->waitq, &myself);
		for (;;) {
			set_current_state(TASK_INTERRUPTIBLE);
			if (call->call_id)
				break;
			if (signal_pending(current)) {
				ret = -ERESTARTSYS;
				break;
			}
			schedule();
		}
		remove_wait_queue(&call->waitq, &myself);
		__set_current_state(TASK_RUNNING);
	}

	/* Paired with the write barrier in rxrpc_activate_one_channel(). */
	smp_rmb();

out:
	_leave(" = %d", ret);
	return ret;
}

/*
 * find a connection for a call
 * - called in process context with IRQs enabled
 */
int rxrpc_connect_call(struct rxrpc_call *call,
		       struct rxrpc_conn_parameters *cp,
		       struct sockaddr_rxrpc *srx,
		       gfp_t gfp)
{
	int ret;

	_enter("{%d,%lx},", call->debug_id, call->user_call_ID);

	rxrpc_discard_expired_client_conns(NULL);
	rxrpc_cull_active_client_conns();

	ret = rxrpc_get_client_conn(call, cp, srx, gfp);
	if (ret < 0)
		return ret;

	rxrpc_animate_client_conn(call->conn);
	rxrpc_activate_channels(call->conn);

	ret = rxrpc_wait_for_channel(call, gfp);
	if (ret < 0)
		rxrpc_disconnect_client_call(call);

	_leave(" = %d", ret);
	return ret;
}

/*
 * Note that a connection is about to be exposed to the world.  Once it is
 * exposed, we maintain an extra ref on it that stops it from being summarily
 * discarded before it's (a) had a chance to deal with retransmission and (b)
 * had a chance at re-use (the per-connection security negotiation is
 * expensive).
 */
static void rxrpc_expose_client_conn(struct rxrpc_connection *conn)
{
	if (!test_and_set_bit(RXRPC_CONN_EXPOSED, &conn->flags))
		rxrpc_get_connection(conn);
}

/*
 * Note that a call, and thus a connection, is about to be exposed to the
 * world.
 */
void rxrpc_expose_client_call(struct rxrpc_call *call)
{
	struct rxrpc_connection *conn = call->conn;
	struct rxrpc_channel *chan =
		&conn->channels[call->cid & RXRPC_CHANNELMASK];

	if (!test_and_set_bit(RXRPC_CALL_EXPOSED, &call->flags)) {
		/* Mark the call ID as being used.  If the callNumber counter
		 * exceeds ~2 billion, we kill the connection after its
		 * outstanding calls have finished so that the counter doesn't
		 * wrap.
		 */
		chan->call_counter++;
		if (chan->call_counter >= INT_MAX)
			set_bit(RXRPC_CONN_DONT_REUSE, &conn->flags);
		rxrpc_expose_client_conn(conn);
	}
}

/*
 * Disconnect a client call.
 */
void rxrpc_disconnect_client_call(struct rxrpc_call *call)
{
	unsigned int channel = call->cid & RXRPC_CHANNELMASK;
	struct rxrpc_connection *conn = call->conn;
	struct rxrpc_channel *chan = &conn->channels[channel];

	call->conn = NULL;

	spin_lock(&conn->channel_lock);

	/* Calls that have never actually been assigned a channel can simply be
	 * discarded.  If the conn didn't get used either, it will follow
	 * immediately unless someone else grabs it in the meantime.
	 */
	if (!list_empty(&call->chan_wait_link)) {
		_debug("call is waiting");
		ASSERTCMP(call->call_id, ==, 0);
		ASSERT(!test_bit(RXRPC_CALL_EXPOSED, &call->flags));
		list_del_init(&call->chan_wait_link);

		/* We must deactivate or idle the connection if it's now
		 * waiting for nothing.
		 */
		spin_lock(&rxrpc_client_conn_cache_lock);
		if (conn->cache_state == RXRPC_CONN_CLIENT_WAITING &&
		    list_empty(&conn->waiting_calls) &&
		    !conn->active_chans)
			goto idle_connection;
		goto out;
	}

	ASSERTCMP(rcu_access_pointer(chan->call), ==, call);
	ASSERTCMP(atomic_read(&conn->usage), >=, 2);

	/* If a client call was exposed to the world, we save the result for
	 * retransmission.
	 *
	 * We use a barrier here so that the call number and abort code can be
	 * read without needing to take a lock.
	 *
	 * TODO: Make the incoming packet handler check this and handle
	 * terminal retransmission without requiring access to the call.
	 */
	if (test_bit(RXRPC_CALL_EXPOSED, &call->flags)) {
		_debug("exposed %u,%u", call->call_id, call->abort_code);
		__rxrpc_disconnect_call(conn, call);
	}

	/* See if we can pass the channel directly to another call. */
	if (conn->cache_state == RXRPC_CONN_CLIENT_ACTIVE &&
	    !list_empty(&conn->waiting_calls)) {
		_debug("pass chan");
		rxrpc_activate_one_channel(conn, channel);
		goto out_2;
	}

	/* Things are more complex and we need the cache lock.  We might be
	 * able to simply idle the conn or it might now be lurking on the wait
	 * list.  It might even get moved back to the active list whilst we're
	 * waiting for the lock.
	 */
	spin_lock(&rxrpc_client_conn_cache_lock);

	switch (conn->cache_state) {
	case RXRPC_CONN_CLIENT_ACTIVE:
		if (list_empty(&conn->waiting_calls)) {
			rxrpc_deactivate_one_channel(conn, channel);
			if (!conn->active_chans) {
				rxrpc_nr_active_client_conns--;
				goto idle_connection;
			}
			goto out;
		}

		_debug("pass chan 2");
		rxrpc_activate_one_channel(conn, channel);
		goto out;

	case RXRPC_CONN_CLIENT_CULLED:
		rxrpc_deactivate_one_channel(conn, channel);
		ASSERT(list_empty(&conn->waiting_calls));
		if (!conn->active_chans)
			goto idle_connection;
		goto out;

	case RXRPC_CONN_CLIENT_WAITING:
		rxrpc_deactivate_one_channel(conn, channel);
		goto out;

	default:
		BUG();
	}

out:
	spin_unlock(&rxrpc_client_conn_cache_lock);
out_2:
	spin_unlock(&conn->channel_lock);
	rxrpc_put_connection(conn);
	_leave("");
	return;

idle_connection:
	/* As no channels remain active, the connection gets deactivated
	 * immediately or moved to the idle list for a short while.
	 */
	if (test_bit(RXRPC_CONN_EXPOSED, &conn->flags)) {
		_debug("make idle");
		conn->idle_timestamp = jiffies;
		conn->cache_state = RXRPC_CONN_CLIENT_IDLE;
		list_move_tail(&conn->cache_link, &rxrpc_idle_client_conns);
		if (rxrpc_idle_client_conns.next == &conn->cache_link &&
		    !rxrpc_kill_all_client_conns)
			queue_delayed_work(rxrpc_workqueue,
					   &rxrpc_client_conn_reap,
					   rxrpc_conn_idle_client_expiry);
	} else {
		_debug("make inactive");
		conn->cache_state = RXRPC_CONN_CLIENT_INACTIVE;
		list_del_init(&conn->cache_link);
	}
	goto out;
}

/*
 * Clean up a dead client connection.
 */
static struct rxrpc_connection *
rxrpc_put_one_client_conn(struct rxrpc_connection *conn)
{
	struct rxrpc_connection *next;
	struct rxrpc_local *local = conn->params.local;
	unsigned int nr_conns;

	if (test_bit(RXRPC_CONN_IN_CLIENT_CONNS, &conn->flags)) {
		spin_lock(&local->client_conns_lock);
		if (test_and_clear_bit(RXRPC_CONN_IN_CLIENT_CONNS,
				       &conn->flags))
			rb_erase(&conn->client_node, &local->client_conns);
		spin_unlock(&local->client_conns_lock);
	}

	rxrpc_put_client_connection_id(conn);

	ASSERTCMP(conn->cache_state, ==, RXRPC_CONN_CLIENT_INACTIVE);

	if (!test_bit(RXRPC_CONN_COUNTED, &conn->flags))
		return NULL;

	spin_lock(&rxrpc_client_conn_cache_lock);
	nr_conns = --rxrpc_nr_client_conns;

	next = NULL;
	if (nr_conns < rxrpc_max_client_connections &&
	    !list_empty(&rxrpc_waiting_client_conns)) {
		next = list_entry(rxrpc_waiting_client_conns.next,
				  struct rxrpc_connection, cache_link);
		rxrpc_get_connection(next);
		rxrpc_activate_conn(next);
	}

	spin_unlock(&rxrpc_client_conn_cache_lock);
	rxrpc_kill_connection(conn);

	if (next)
		rxrpc_activate_channels(next);

	/* We need to get rid of the temporary ref we took upon next, but we
	 * can't call rxrpc_put_connection() recursively.
	 */
	return next;
}

/*
 * Clean up a dead client connections.
 */
void rxrpc_put_client_conn(struct rxrpc_connection *conn)
{
	struct rxrpc_connection *next;

	do {
		_enter("%p{u=%d,d=%d}",
		       conn, atomic_read(&conn->usage), conn->debug_id);

		next = rxrpc_put_one_client_conn(conn);

		if (!next)
			break;
		conn = next;
	} while (atomic_dec_and_test(&conn->usage));

	_leave("");
}

/*
 * Kill the longest-active client connections to make room for new ones.
 */
static void rxrpc_cull_active_client_conns(void)
{
	struct rxrpc_connection *conn;
	unsigned int nr_conns = rxrpc_nr_client_conns;
	unsigned int nr_active, limit;

	_enter("");

	ASSERTCMP(nr_conns, >=, 0);
	if (nr_conns < rxrpc_max_client_connections) {
		_leave(" [ok]");
		return;
	}
	limit = rxrpc_reap_client_connections;

	spin_lock(&rxrpc_client_conn_cache_lock);
	nr_active = rxrpc_nr_active_client_conns;

	while (nr_active > limit) {
		ASSERT(!list_empty(&rxrpc_active_client_conns));
		conn = list_entry(rxrpc_active_client_conns.next,
				  struct rxrpc_connection, cache_link);
		ASSERTCMP(conn->cache_state, ==, RXRPC_CONN_CLIENT_ACTIVE);

		if (list_empty(&conn->waiting_calls)) {
			conn->cache_state = RXRPC_CONN_CLIENT_CULLED;
			list_del_init(&conn->cache_link);
		} else {
			conn->cache_state = RXRPC_CONN_CLIENT_WAITING;
			list_move_tail(&conn->cache_link,
				       &rxrpc_waiting_client_conns);
		}

		nr_active--;
	}

	rxrpc_nr_active_client_conns = nr_active;
	spin_unlock(&rxrpc_client_conn_cache_lock);
	ASSERTCMP(nr_active, >=, 0);
	_leave(" [culled]");
}

/*
 * Discard expired client connections from the idle list.  Each conn in the
 * idle list has been exposed and holds an extra ref because of that.
 *
 * This may be called from conn setup or from a work item so cannot be
 * considered non-reentrant.
 */
static void rxrpc_discard_expired_client_conns(struct work_struct *work)
{
	struct rxrpc_connection *conn;
	unsigned long expiry, conn_expires_at, now;
	unsigned int nr_conns;
	bool did_discard = false;

	_enter("%c", work ? 'w' : 'n');

	if (list_empty(&rxrpc_idle_client_conns)) {
		_leave(" [empty]");
		return;
	}

	/* Don't double up on the discarding */
	if (!spin_trylock(&rxrpc_client_conn_discard_mutex)) {
		_leave(" [already]");
		return;
	}

	/* We keep an estimate of what the number of conns ought to be after
	 * we've discarded some so that we don't overdo the discarding.
	 */
	nr_conns = rxrpc_nr_client_conns;

next:
	spin_lock(&rxrpc_client_conn_cache_lock);

	if (list_empty(&rxrpc_idle_client_conns))
		goto out;

	conn = list_entry(rxrpc_idle_client_conns.next,
			  struct rxrpc_connection, cache_link);
	ASSERT(test_bit(RXRPC_CONN_EXPOSED, &conn->flags));

	if (!rxrpc_kill_all_client_conns) {
		/* If the number of connections is over the reap limit, we
		 * expedite discard by reducing the expiry timeout.  We must,
		 * however, have at least a short grace period to be able to do
		 * final-ACK or ABORT retransmission.
		 */
		expiry = rxrpc_conn_idle_client_expiry;
		if (nr_conns > rxrpc_reap_client_connections)
			expiry = rxrpc_conn_idle_client_fast_expiry;

		conn_expires_at = conn->idle_timestamp + expiry;

		now = READ_ONCE(jiffies);
		if (time_after(conn_expires_at, now))
			goto not_yet_expired;
	}

	_debug("discard conn %d", conn->debug_id);
	if (!test_and_clear_bit(RXRPC_CONN_EXPOSED, &conn->flags))
		BUG();
	conn->cache_state = RXRPC_CONN_CLIENT_INACTIVE;
	list_del_init(&conn->cache_link);

	spin_unlock(&rxrpc_client_conn_cache_lock);

	/* When we cleared the EXPOSED flag, we took on responsibility for the
	 * reference that that had on the usage count.  We deal with that here.
	 * If someone re-sets the flag and re-gets the ref, that's fine.
	 */
	rxrpc_put_connection(conn);
	did_discard = true;
	nr_conns--;
	goto next;

not_yet_expired:
	/* The connection at the front of the queue hasn't yet expired, so
	 * schedule the work item for that point if we discarded something.
	 *
	 * We don't worry if the work item is already scheduled - it can look
	 * after rescheduling itself at a later time.  We could cancel it, but
	 * then things get messier.
	 */
	_debug("not yet");
	if (!rxrpc_kill_all_client_conns)
		queue_delayed_work(rxrpc_workqueue,
				   &rxrpc_client_conn_reap,
				   conn_expires_at - now);

out:
	spin_unlock(&rxrpc_client_conn_cache_lock);
	spin_unlock(&rxrpc_client_conn_discard_mutex);
	_leave("");
}

/*
 * Preemptively destroy all the client connection records rather than waiting
 * for them to time out
 */
void __exit rxrpc_destroy_all_client_connections(void)
{
	_enter("");

	spin_lock(&rxrpc_client_conn_cache_lock);
	rxrpc_kill_all_client_conns = true;
	spin_unlock(&rxrpc_client_conn_cache_lock);

	cancel_delayed_work(&rxrpc_client_conn_reap);

	if (!queue_delayed_work(rxrpc_workqueue, &rxrpc_client_conn_reap, 0))
		_debug("destroy: queue failed");

	_leave("");
}