Free Electrons

Embedded Linux Experts

   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
/*
 * Copyright (c) 2006 Oracle.  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/kernel.h>
#include <net/sock.h>
#include <linux/in.h>
#include <linux/list.h>

#include "rds.h"
#include "rdma.h"

/* When transmitting messages in rds_send_xmit, we need to emerge from
 * time to time and briefly release the CPU. Otherwise the softlock watchdog
 * will kick our shin.
 * Also, it seems fairer to not let one busy connection stall all the
 * others.
 *
 * send_batch_count is the number of times we'll loop in send_xmit. Setting
 * it to 0 will restore the old behavior (where we looped until we had
 * drained the queue).
 */
static int send_batch_count = 64;
module_param(send_batch_count, int, 0444);
MODULE_PARM_DESC(send_batch_count, " batch factor when working the send queue");

/*
 * Reset the send state. Caller must hold c_send_lock when calling here.
 */
void rds_send_reset(struct rds_connection *conn)
{
	struct rds_message *rm, *tmp;
	unsigned long flags;

	if (conn->c_xmit_rm) {
		/* Tell the user the RDMA op is no longer mapped by the
		 * transport. This isn't entirely true (it's flushed out
		 * independently) but as the connection is down, there's
		 * no ongoing RDMA to/from that memory */
		rds_message_unmapped(conn->c_xmit_rm);
		rds_message_put(conn->c_xmit_rm);
		conn->c_xmit_rm = NULL;
	}
	conn->c_xmit_sg = 0;
	conn->c_xmit_hdr_off = 0;
	conn->c_xmit_data_off = 0;
	conn->c_xmit_rdma_sent = 0;

	conn->c_map_queued = 0;

	conn->c_unacked_packets = rds_sysctl_max_unacked_packets;
	conn->c_unacked_bytes = rds_sysctl_max_unacked_bytes;

	/* Mark messages as retransmissions, and move them to the send q */
	spin_lock_irqsave(&conn->c_lock, flags);
	list_for_each_entry_safe(rm, tmp, &conn->c_retrans, m_conn_item) {
		set_bit(RDS_MSG_ACK_REQUIRED, &rm->m_flags);
		set_bit(RDS_MSG_RETRANSMITTED, &rm->m_flags);
	}
	list_splice_init(&conn->c_retrans, &conn->c_send_queue);
	spin_unlock_irqrestore(&conn->c_lock, flags);
}

/*
 * We're making the concious trade-off here to only send one message
 * down the connection at a time.
 *   Pro:
 *      - tx queueing is a simple fifo list
 *   	- reassembly is optional and easily done by transports per conn
 *      - no per flow rx lookup at all, straight to the socket
 *   	- less per-frag memory and wire overhead
 *   Con:
 *      - queued acks can be delayed behind large messages
 *   Depends:
 *      - small message latency is higher behind queued large messages
 *      - large message latency isn't starved by intervening small sends
 */
int rds_send_xmit(struct rds_connection *conn)
{
	struct rds_message *rm;
	unsigned long flags;
	unsigned int tmp;
	unsigned int send_quota = send_batch_count;
	struct scatterlist *sg;
	int ret = 0;
	int was_empty = 0;
	LIST_HEAD(to_be_dropped);

	/*
	 * sendmsg calls here after having queued its message on the send
	 * queue.  We only have one task feeding the connection at a time.  If
	 * another thread is already feeding the queue then we back off.  This
	 * avoids blocking the caller and trading per-connection data between
	 * caches per message.
	 *
	 * The sem holder will issue a retry if they notice that someone queued
	 * a message after they stopped walking the send queue but before they
	 * dropped the sem.
	 */
	if (!mutex_trylock(&conn->c_send_lock)) {
		rds_stats_inc(s_send_sem_contention);
		ret = -ENOMEM;
		goto out;
	}

	if (conn->c_trans->xmit_prepare)
		conn->c_trans->xmit_prepare(conn);

	/*
	 * spin trying to push headers and data down the connection until
	 * the connection doens't make forward progress.
	 */
	while (--send_quota) {
		/*
		 * See if need to send a congestion map update if we're
		 * between sending messages.  The send_sem protects our sole
		 * use of c_map_offset and _bytes.
		 * Note this is used only by transports that define a special
		 * xmit_cong_map function. For all others, we create allocate
		 * a cong_map message and treat it just like any other send.
		 */
		if (conn->c_map_bytes) {
			ret = conn->c_trans->xmit_cong_map(conn, conn->c_lcong,
						conn->c_map_offset);
			if (ret <= 0)
				break;

			conn->c_map_offset += ret;
			conn->c_map_bytes -= ret;
			if (conn->c_map_bytes)
				continue;
		}

		/* If we're done sending the current message, clear the
		 * offset and S/G temporaries.
		 */
		rm = conn->c_xmit_rm;
		if (rm != NULL &&
		    conn->c_xmit_hdr_off == sizeof(struct rds_header) &&
		    conn->c_xmit_sg == rm->m_nents) {
			conn->c_xmit_rm = NULL;
			conn->c_xmit_sg = 0;
			conn->c_xmit_hdr_off = 0;
			conn->c_xmit_data_off = 0;
			conn->c_xmit_rdma_sent = 0;

			/* Release the reference to the previous message. */
			rds_message_put(rm);
			rm = NULL;
		}

		/* If we're asked to send a cong map update, do so.
		 */
		if (rm == NULL && test_and_clear_bit(0, &conn->c_map_queued)) {
			if (conn->c_trans->xmit_cong_map != NULL) {
				conn->c_map_offset = 0;
				conn->c_map_bytes = sizeof(struct rds_header) +
					RDS_CONG_MAP_BYTES;
				continue;
			}

			rm = rds_cong_update_alloc(conn);
			if (IS_ERR(rm)) {
				ret = PTR_ERR(rm);
				break;
			}

			conn->c_xmit_rm = rm;
		}

		/*
		 * Grab the next message from the send queue, if there is one.
		 *
		 * c_xmit_rm holds a ref while we're sending this message down
		 * the connction.  We can use this ref while holding the
		 * send_sem.. rds_send_reset() is serialized with it.
		 */
		if (rm == NULL) {
			unsigned int len;

			spin_lock_irqsave(&conn->c_lock, flags);

			if (!list_empty(&conn->c_send_queue)) {
				rm = list_entry(conn->c_send_queue.next,
						struct rds_message,
						m_conn_item);
				rds_message_addref(rm);

				/*
				 * Move the message from the send queue to the retransmit
				 * list right away.
				 */
				list_move_tail(&rm->m_conn_item, &conn->c_retrans);
			}

			spin_unlock_irqrestore(&conn->c_lock, flags);

			if (rm == NULL) {
				was_empty = 1;
				break;
			}

			/* Unfortunately, the way Infiniband deals with
			 * RDMA to a bad MR key is by moving the entire
			 * queue pair to error state. We cold possibly
			 * recover from that, but right now we drop the
			 * connection.
			 * Therefore, we never retransmit messages with RDMA ops.
			 */
			if (rm->m_rdma_op
			 && test_bit(RDS_MSG_RETRANSMITTED, &rm->m_flags)) {
				spin_lock_irqsave(&conn->c_lock, flags);
				if (test_and_clear_bit(RDS_MSG_ON_CONN, &rm->m_flags))
					list_move(&rm->m_conn_item, &to_be_dropped);
				spin_unlock_irqrestore(&conn->c_lock, flags);
				rds_message_put(rm);
				continue;
			}

			/* Require an ACK every once in a while */
			len = ntohl(rm->m_inc.i_hdr.h_len);
			if (conn->c_unacked_packets == 0
			 || conn->c_unacked_bytes < len) {
				__set_bit(RDS_MSG_ACK_REQUIRED, &rm->m_flags);

				conn->c_unacked_packets = rds_sysctl_max_unacked_packets;
				conn->c_unacked_bytes = rds_sysctl_max_unacked_bytes;
				rds_stats_inc(s_send_ack_required);
			} else {
				conn->c_unacked_bytes -= len;
				conn->c_unacked_packets--;
			}

			conn->c_xmit_rm = rm;
		}

		/*
		 * Try and send an rdma message.  Let's see if we can
		 * keep this simple and require that the transport either
		 * send the whole rdma or none of it.
		 */
		if (rm->m_rdma_op && !conn->c_xmit_rdma_sent) {
			ret = conn->c_trans->xmit_rdma(conn, rm->m_rdma_op);
			if (ret)
				break;
			conn->c_xmit_rdma_sent = 1;
			/* The transport owns the mapped memory for now.
			 * You can't unmap it while it's on the send queue */
			set_bit(RDS_MSG_MAPPED, &rm->m_flags);
		}

		if (conn->c_xmit_hdr_off < sizeof(struct rds_header) ||
		    conn->c_xmit_sg < rm->m_nents) {
			ret = conn->c_trans->xmit(conn, rm,
						  conn->c_xmit_hdr_off,
						  conn->c_xmit_sg,
						  conn->c_xmit_data_off);
			if (ret <= 0)
				break;

			if (conn->c_xmit_hdr_off < sizeof(struct rds_header)) {
				tmp = min_t(int, ret,
					    sizeof(struct rds_header) -
					    conn->c_xmit_hdr_off);
				conn->c_xmit_hdr_off += tmp;
				ret -= tmp;
			}

			sg = &rm->m_sg[conn->c_xmit_sg];
			while (ret) {
				tmp = min_t(int, ret, sg->length -
						      conn->c_xmit_data_off);
				conn->c_xmit_data_off += tmp;
				ret -= tmp;
				if (conn->c_xmit_data_off == sg->length) {
					conn->c_xmit_data_off = 0;
					sg++;
					conn->c_xmit_sg++;
					BUG_ON(ret != 0 &&
					       conn->c_xmit_sg == rm->m_nents);
				}
			}
		}
	}

	/* Nuke any messages we decided not to retransmit. */
	if (!list_empty(&to_be_dropped))
		rds_send_remove_from_sock(&to_be_dropped, RDS_RDMA_DROPPED);

	if (conn->c_trans->xmit_complete)
		conn->c_trans->xmit_complete(conn);

	/*
	 * We might be racing with another sender who queued a message but
	 * backed off on noticing that we held the c_send_lock.  If we check
	 * for queued messages after dropping the sem then either we'll
	 * see the queued message or the queuer will get the sem.  If we
	 * notice the queued message then we trigger an immediate retry.
	 *
	 * We need to be careful only to do this when we stopped processing
	 * the send queue because it was empty.  It's the only way we
	 * stop processing the loop when the transport hasn't taken
	 * responsibility for forward progress.
	 */
	mutex_unlock(&conn->c_send_lock);

	if (conn->c_map_bytes || (send_quota == 0 && !was_empty)) {
		/* We exhausted the send quota, but there's work left to
		 * do. Return and (re-)schedule the send worker.
		 */
		ret = -EAGAIN;
	}

	if (ret == 0 && was_empty) {
		/* A simple bit test would be way faster than taking the
		 * spin lock */
		spin_lock_irqsave(&conn->c_lock, flags);
		if (!list_empty(&conn->c_send_queue)) {
			rds_stats_inc(s_send_sem_queue_raced);
			ret = -EAGAIN;
		}
		spin_unlock_irqrestore(&conn->c_lock, flags);
	}
out:
	return ret;
}

static void rds_send_sndbuf_remove(struct rds_sock *rs, struct rds_message *rm)
{
	u32 len = be32_to_cpu(rm->m_inc.i_hdr.h_len);

	assert_spin_locked(&rs->rs_lock);

	BUG_ON(rs->rs_snd_bytes < len);
	rs->rs_snd_bytes -= len;

	if (rs->rs_snd_bytes == 0)
		rds_stats_inc(s_send_queue_empty);
}

static inline int rds_send_is_acked(struct rds_message *rm, u64 ack,
				    is_acked_func is_acked)
{
	if (is_acked)
		return is_acked(rm, ack);
	return be64_to_cpu(rm->m_inc.i_hdr.h_sequence) <= ack;
}

/*
 * Returns true if there are no messages on the send and retransmit queues
 * which have a sequence number greater than or equal to the given sequence
 * number.
 */
int rds_send_acked_before(struct rds_connection *conn, u64 seq)
{
	struct rds_message *rm, *tmp;
	int ret = 1;

	spin_lock(&conn->c_lock);

	list_for_each_entry_safe(rm, tmp, &conn->c_retrans, m_conn_item) {
		if (be64_to_cpu(rm->m_inc.i_hdr.h_sequence) < seq)
			ret = 0;
		break;
	}

	list_for_each_entry_safe(rm, tmp, &conn->c_send_queue, m_conn_item) {
		if (be64_to_cpu(rm->m_inc.i_hdr.h_sequence) < seq)
			ret = 0;
		break;
	}

	spin_unlock(&conn->c_lock);

	return ret;
}

/*
 * This is pretty similar to what happens below in the ACK
 * handling code - except that we call here as soon as we get
 * the IB send completion on the RDMA op and the accompanying
 * message.
 */
void rds_rdma_send_complete(struct rds_message *rm, int status)
{
	struct rds_sock *rs = NULL;
	struct rds_rdma_op *ro;
	struct rds_notifier *notifier;

	spin_lock(&rm->m_rs_lock);

	ro = rm->m_rdma_op;
	if (test_bit(RDS_MSG_ON_SOCK, &rm->m_flags)
	 && ro && ro->r_notify && ro->r_notifier) {
		notifier = ro->r_notifier;
		rs = rm->m_rs;
		sock_hold(rds_rs_to_sk(rs));

		notifier->n_status = status;
		spin_lock(&rs->rs_lock);
		list_add_tail(&notifier->n_list, &rs->rs_notify_queue);
		spin_unlock(&rs->rs_lock);

		ro->r_notifier = NULL;
	}

	spin_unlock(&rm->m_rs_lock);

	if (rs) {
		rds_wake_sk_sleep(rs);
		sock_put(rds_rs_to_sk(rs));
	}
}
EXPORT_SYMBOL_GPL(rds_rdma_send_complete);

/*
 * This is the same as rds_rdma_send_complete except we
 * don't do any locking - we have all the ingredients (message,
 * socket, socket lock) and can just move the notifier.
 */
static inline void
__rds_rdma_send_complete(struct rds_sock *rs, struct rds_message *rm, int status)
{
	struct rds_rdma_op *ro;

	ro = rm->m_rdma_op;
	if (ro && ro->r_notify && ro->r_notifier) {
		ro->r_notifier->n_status = status;
		list_add_tail(&ro->r_notifier->n_list, &rs->rs_notify_queue);
		ro->r_notifier = NULL;
	}

	/* No need to wake the app - caller does this */
}

/*
 * This is called from the IB send completion when we detect
 * a RDMA operation that failed with remote access error.
 * So speed is not an issue here.
 */
struct rds_message *rds_send_get_message(struct rds_connection *conn,
					 struct rds_rdma_op *op)
{
	struct rds_message *rm, *tmp, *found = NULL;
	unsigned long flags;

	spin_lock_irqsave(&conn->c_lock, flags);

	list_for_each_entry_safe(rm, tmp, &conn->c_retrans, m_conn_item) {
		if (rm->m_rdma_op == op) {
			atomic_inc(&rm->m_refcount);
			found = rm;
			goto out;
		}
	}

	list_for_each_entry_safe(rm, tmp, &conn->c_send_queue, m_conn_item) {
		if (rm->m_rdma_op == op) {
			atomic_inc(&rm->m_refcount);
			found = rm;
			break;
		}
	}

out:
	spin_unlock_irqrestore(&conn->c_lock, flags);

	return found;
}
EXPORT_SYMBOL_GPL(rds_send_get_message);

/*
 * This removes messages from the socket's list if they're on it.  The list
 * argument must be private to the caller, we must be able to modify it
 * without locks.  The messages must have a reference held for their
 * position on the list.  This function will drop that reference after
 * removing the messages from the 'messages' list regardless of if it found
 * the messages on the socket list or not.
 */
void rds_send_remove_from_sock(struct list_head *messages, int status)
{
	unsigned long flags = 0; /* silence gcc :P */
	struct rds_sock *rs = NULL;
	struct rds_message *rm;

	local_irq_save(flags);
	while (!list_empty(messages)) {
		rm = list_entry(messages->next, struct rds_message,
				m_conn_item);
		list_del_init(&rm->m_conn_item);

		/*
		 * If we see this flag cleared then we're *sure* that someone
		 * else beat us to removing it from the sock.  If we race
		 * with their flag update we'll get the lock and then really
		 * see that the flag has been cleared.
		 *
		 * The message spinlock makes sure nobody clears rm->m_rs
		 * while we're messing with it. It does not prevent the
		 * message from being removed from the socket, though.
		 */
		spin_lock(&rm->m_rs_lock);
		if (!test_bit(RDS_MSG_ON_SOCK, &rm->m_flags))
			goto unlock_and_drop;

		if (rs != rm->m_rs) {
			if (rs) {
				spin_unlock(&rs->rs_lock);
				rds_wake_sk_sleep(rs);
				sock_put(rds_rs_to_sk(rs));
			}
			rs = rm->m_rs;
			spin_lock(&rs->rs_lock);
			sock_hold(rds_rs_to_sk(rs));
		}

		if (test_and_clear_bit(RDS_MSG_ON_SOCK, &rm->m_flags)) {
			struct rds_rdma_op *ro = rm->m_rdma_op;
			struct rds_notifier *notifier;

			list_del_init(&rm->m_sock_item);
			rds_send_sndbuf_remove(rs, rm);

			if (ro && ro->r_notifier
			   && (status || ro->r_notify)) {
				notifier = ro->r_notifier;
				list_add_tail(&notifier->n_list,
						&rs->rs_notify_queue);
				if (!notifier->n_status)
					notifier->n_status = status;
				rm->m_rdma_op->r_notifier = NULL;
			}
			rds_message_put(rm);
			rm->m_rs = NULL;
		}

unlock_and_drop:
		spin_unlock(&rm->m_rs_lock);
		rds_message_put(rm);
	}

	if (rs) {
		spin_unlock(&rs->rs_lock);
		rds_wake_sk_sleep(rs);
		sock_put(rds_rs_to_sk(rs));
	}
	local_irq_restore(flags);
}

/*
 * Transports call here when they've determined that the receiver queued
 * messages up to, and including, the given sequence number.  Messages are
 * moved to the retrans queue when rds_send_xmit picks them off the send
 * queue. This means that in the TCP case, the message may not have been
 * assigned the m_ack_seq yet - but that's fine as long as tcp_is_acked
 * checks the RDS_MSG_HAS_ACK_SEQ bit.
 *
 * XXX It's not clear to me how this is safely serialized with socket
 * destruction.  Maybe it should bail if it sees SOCK_DEAD.
 */
void rds_send_drop_acked(struct rds_connection *conn, u64 ack,
			 is_acked_func is_acked)
{
	struct rds_message *rm, *tmp;
	unsigned long flags;
	LIST_HEAD(list);

	spin_lock_irqsave(&conn->c_lock, flags);

	list_for_each_entry_safe(rm, tmp, &conn->c_retrans, m_conn_item) {
		if (!rds_send_is_acked(rm, ack, is_acked))
			break;

		list_move(&rm->m_conn_item, &list);
		clear_bit(RDS_MSG_ON_CONN, &rm->m_flags);
	}

	/* order flag updates with spin locks */
	if (!list_empty(&list))
		smp_mb__after_clear_bit();

	spin_unlock_irqrestore(&conn->c_lock, flags);

	/* now remove the messages from the sock list as needed */
	rds_send_remove_from_sock(&list, RDS_RDMA_SUCCESS);
}
EXPORT_SYMBOL_GPL(rds_send_drop_acked);

void rds_send_drop_to(struct rds_sock *rs, struct sockaddr_in *dest)
{
	struct rds_message *rm, *tmp;
	struct rds_connection *conn;
	unsigned long flags, flags2;
	LIST_HEAD(list);
	int wake = 0;

	/* get all the messages we're dropping under the rs lock */
	spin_lock_irqsave(&rs->rs_lock, flags);

	list_for_each_entry_safe(rm, tmp, &rs->rs_send_queue, m_sock_item) {
		if (dest && (dest->sin_addr.s_addr != rm->m_daddr ||
			     dest->sin_port != rm->m_inc.i_hdr.h_dport))
			continue;

		wake = 1;
		list_move(&rm->m_sock_item, &list);
		rds_send_sndbuf_remove(rs, rm);
		clear_bit(RDS_MSG_ON_SOCK, &rm->m_flags);

		/* If this is a RDMA operation, notify the app. */
		__rds_rdma_send_complete(rs, rm, RDS_RDMA_CANCELED);
	}

	/* order flag updates with the rs lock */
	if (wake)
		smp_mb__after_clear_bit();

	spin_unlock_irqrestore(&rs->rs_lock, flags);

	if (wake)
		rds_wake_sk_sleep(rs);

	conn = NULL;

	/* now remove the messages from the conn list as needed */
	list_for_each_entry(rm, &list, m_sock_item) {
		/* We do this here rather than in the loop above, so that
		 * we don't have to nest m_rs_lock under rs->rs_lock */
		spin_lock_irqsave(&rm->m_rs_lock, flags2);
		rm->m_rs = NULL;
		spin_unlock_irqrestore(&rm->m_rs_lock, flags2);

		/*
		 * If we see this flag cleared then we're *sure* that someone
		 * else beat us to removing it from the conn.  If we race
		 * with their flag update we'll get the lock and then really
		 * see that the flag has been cleared.
		 */
		if (!test_bit(RDS_MSG_ON_CONN, &rm->m_flags))
			continue;

		if (conn != rm->m_inc.i_conn) {
			if (conn)
				spin_unlock_irqrestore(&conn->c_lock, flags);
			conn = rm->m_inc.i_conn;
			spin_lock_irqsave(&conn->c_lock, flags);
		}

		if (test_and_clear_bit(RDS_MSG_ON_CONN, &rm->m_flags)) {
			list_del_init(&rm->m_conn_item);
			rds_message_put(rm);
		}
	}

	if (conn)
		spin_unlock_irqrestore(&conn->c_lock, flags);

	while (!list_empty(&list)) {
		rm = list_entry(list.next, struct rds_message, m_sock_item);
		list_del_init(&rm->m_sock_item);

		rds_message_wait(rm);
		rds_message_put(rm);
	}
}

/*
 * we only want this to fire once so we use the callers 'queued'.  It's
 * possible that another thread can race with us and remove the
 * message from the flow with RDS_CANCEL_SENT_TO.
 */
static int rds_send_queue_rm(struct rds_sock *rs, struct rds_connection *conn,
			     struct rds_message *rm, __be16 sport,
			     __be16 dport, int *queued)
{
	unsigned long flags;
	u32 len;

	if (*queued)
		goto out;

	len = be32_to_cpu(rm->m_inc.i_hdr.h_len);

	/* this is the only place which holds both the socket's rs_lock
	 * and the connection's c_lock */
	spin_lock_irqsave(&rs->rs_lock, flags);

	/*
	 * If there is a little space in sndbuf, we don't queue anything,
	 * and userspace gets -EAGAIN. But poll() indicates there's send
	 * room. This can lead to bad behavior (spinning) if snd_bytes isn't
	 * freed up by incoming acks. So we check the *old* value of
	 * rs_snd_bytes here to allow the last msg to exceed the buffer,
	 * and poll() now knows no more data can be sent.
	 */
	if (rs->rs_snd_bytes < rds_sk_sndbuf(rs)) {
		rs->rs_snd_bytes += len;

		/* let recv side know we are close to send space exhaustion.
		 * This is probably not the optimal way to do it, as this
		 * means we set the flag on *all* messages as soon as our
		 * throughput hits a certain threshold.
		 */
		if (rs->rs_snd_bytes >= rds_sk_sndbuf(rs) / 2)
			__set_bit(RDS_MSG_ACK_REQUIRED, &rm->m_flags);

		list_add_tail(&rm->m_sock_item, &rs->rs_send_queue);
		set_bit(RDS_MSG_ON_SOCK, &rm->m_flags);
		rds_message_addref(rm);
		rm->m_rs = rs;

		/* The code ordering is a little weird, but we're
		   trying to minimize the time we hold c_lock */
		rds_message_populate_header(&rm->m_inc.i_hdr, sport, dport, 0);
		rm->m_inc.i_conn = conn;
		rds_message_addref(rm);

		spin_lock(&conn->c_lock);
		rm->m_inc.i_hdr.h_sequence = cpu_to_be64(conn->c_next_tx_seq++);
		list_add_tail(&rm->m_conn_item, &conn->c_send_queue);
		set_bit(RDS_MSG_ON_CONN, &rm->m_flags);
		spin_unlock(&conn->c_lock);

		rdsdebug("queued msg %p len %d, rs %p bytes %d seq %llu\n",
			 rm, len, rs, rs->rs_snd_bytes,
			 (unsigned long long)be64_to_cpu(rm->m_inc.i_hdr.h_sequence));

		*queued = 1;
	}

	spin_unlock_irqrestore(&rs->rs_lock, flags);
out:
	return *queued;
}

static int rds_cmsg_send(struct rds_sock *rs, struct rds_message *rm,
			 struct msghdr *msg, int *allocated_mr)
{
	struct cmsghdr *cmsg;
	int ret = 0;

	for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg)) {
		if (!CMSG_OK(msg, cmsg))
			return -EINVAL;

		if (cmsg->cmsg_level != SOL_RDS)
			continue;

		/* As a side effect, RDMA_DEST and RDMA_MAP will set
		 * rm->m_rdma_cookie and rm->m_rdma_mr.
		 */
		switch (cmsg->cmsg_type) {
		case RDS_CMSG_RDMA_ARGS:
			ret = rds_cmsg_rdma_args(rs, rm, cmsg);
			break;

		case RDS_CMSG_RDMA_DEST:
			ret = rds_cmsg_rdma_dest(rs, rm, cmsg);
			break;

		case RDS_CMSG_RDMA_MAP:
			ret = rds_cmsg_rdma_map(rs, rm, cmsg);
			if (!ret)
				*allocated_mr = 1;
			break;

		default:
			return -EINVAL;
		}

		if (ret)
			break;
	}

	return ret;
}

int rds_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
		size_t payload_len)
{
	struct sock *sk = sock->sk;
	struct rds_sock *rs = rds_sk_to_rs(sk);
	struct sockaddr_in *usin = (struct sockaddr_in *)msg->msg_name;
	__be32 daddr;
	__be16 dport;
	struct rds_message *rm = NULL;
	struct rds_connection *conn;
	int ret = 0;
	int queued = 0, allocated_mr = 0;
	int nonblock = msg->msg_flags & MSG_DONTWAIT;
	long timeo = sock_rcvtimeo(sk, nonblock);

	/* Mirror Linux UDP mirror of BSD error message compatibility */
	/* XXX: Perhaps MSG_MORE someday */
	if (msg->msg_flags & ~(MSG_DONTWAIT | MSG_CMSG_COMPAT)) {
		printk(KERN_INFO "msg_flags 0x%08X\n", msg->msg_flags);
		ret = -EOPNOTSUPP;
		goto out;
	}

	if (msg->msg_namelen) {
		/* XXX fail non-unicast destination IPs? */
		if (msg->msg_namelen < sizeof(*usin) || usin->sin_family != AF_INET) {
			ret = -EINVAL;
			goto out;
		}
		daddr = usin->sin_addr.s_addr;
		dport = usin->sin_port;
	} else {
		/* We only care about consistency with ->connect() */
		lock_sock(sk);
		daddr = rs->rs_conn_addr;
		dport = rs->rs_conn_port;
		release_sock(sk);
	}

	/* racing with another thread binding seems ok here */
	if (daddr == 0 || rs->rs_bound_addr == 0) {
		ret = -ENOTCONN; /* XXX not a great errno */
		goto out;
	}

	rm = rds_message_copy_from_user(msg->msg_iov, payload_len);
	if (IS_ERR(rm)) {
		ret = PTR_ERR(rm);
		rm = NULL;
		goto out;
	}

	rm->m_daddr = daddr;

	/* rds_conn_create has a spinlock that runs with IRQ off.
	 * Caching the conn in the socket helps a lot. */
	if (rs->rs_conn && rs->rs_conn->c_faddr == daddr)
		conn = rs->rs_conn;
	else {
		conn = rds_conn_create_outgoing(rs->rs_bound_addr, daddr,
					rs->rs_transport,
					sock->sk->sk_allocation);
		if (IS_ERR(conn)) {
			ret = PTR_ERR(conn);
			goto out;
		}
		rs->rs_conn = conn;
	}

	/* Parse any control messages the user may have included. */
	ret = rds_cmsg_send(rs, rm, msg, &allocated_mr);
	if (ret)
		goto out;

	if ((rm->m_rdma_cookie || rm->m_rdma_op)
	 && conn->c_trans->xmit_rdma == NULL) {
		if (printk_ratelimit())
			printk(KERN_NOTICE "rdma_op %p conn xmit_rdma %p\n",
				rm->m_rdma_op, conn->c_trans->xmit_rdma);
		ret = -EOPNOTSUPP;
		goto out;
	}

	/* If the connection is down, trigger a connect. We may
	 * have scheduled a delayed reconnect however - in this case
	 * we should not interfere.
	 */
	if (rds_conn_state(conn) == RDS_CONN_DOWN
	 && !test_and_set_bit(RDS_RECONNECT_PENDING, &conn->c_flags))
		queue_delayed_work(rds_wq, &conn->c_conn_w, 0);

	ret = rds_cong_wait(conn->c_fcong, dport, nonblock, rs);
	if (ret)
		goto out;

	while (!rds_send_queue_rm(rs, conn, rm, rs->rs_bound_port,
				  dport, &queued)) {
		rds_stats_inc(s_send_queue_full);
		/* XXX make sure this is reasonable */
		if (payload_len > rds_sk_sndbuf(rs)) {
			ret = -EMSGSIZE;
			goto out;
		}
		if (nonblock) {
			ret = -EAGAIN;
			goto out;
		}

		timeo = wait_event_interruptible_timeout(*sk->sk_sleep,
					rds_send_queue_rm(rs, conn, rm,
							  rs->rs_bound_port,
							  dport,
							  &queued),
					timeo);
		rdsdebug("sendmsg woke queued %d timeo %ld\n", queued, timeo);
		if (timeo > 0 || timeo == MAX_SCHEDULE_TIMEOUT)
			continue;

		ret = timeo;
		if (ret == 0)
			ret = -ETIMEDOUT;
		goto out;
	}

	/*
	 * By now we've committed to the send.  We reuse rds_send_worker()
	 * to retry sends in the rds thread if the transport asks us to.
	 */
	rds_stats_inc(s_send_queued);

	if (!test_bit(RDS_LL_SEND_FULL, &conn->c_flags))
		rds_send_worker(&conn->c_send_w.work);

	rds_message_put(rm);
	return payload_len;

out:
	/* If the user included a RDMA_MAP cmsg, we allocated a MR on the fly.
	 * If the sendmsg goes through, we keep the MR. If it fails with EAGAIN
	 * or in any other way, we need to destroy the MR again */
	if (allocated_mr)
		rds_rdma_unuse(rs, rds_rdma_cookie_key(rm->m_rdma_cookie), 1);

	if (rm)
		rds_message_put(rm);
	return ret;
}

/*
 * Reply to a ping packet.
 */
int
rds_send_pong(struct rds_connection *conn, __be16 dport)
{
	struct rds_message *rm;
	unsigned long flags;
	int ret = 0;

	rm = rds_message_alloc(0, GFP_ATOMIC);
	if (rm == NULL) {
		ret = -ENOMEM;
		goto out;
	}

	rm->m_daddr = conn->c_faddr;

	/* If the connection is down, trigger a connect. We may
	 * have scheduled a delayed reconnect however - in this case
	 * we should not interfere.
	 */
	if (rds_conn_state(conn) == RDS_CONN_DOWN
	 && !test_and_set_bit(RDS_RECONNECT_PENDING, &conn->c_flags))
		queue_delayed_work(rds_wq, &conn->c_conn_w, 0);

	ret = rds_cong_wait(conn->c_fcong, dport, 1, NULL);
	if (ret)
		goto out;

	spin_lock_irqsave(&conn->c_lock, flags);
	list_add_tail(&rm->m_conn_item, &conn->c_send_queue);
	set_bit(RDS_MSG_ON_CONN, &rm->m_flags);
	rds_message_addref(rm);
	rm->m_inc.i_conn = conn;

	rds_message_populate_header(&rm->m_inc.i_hdr, 0, dport,
				    conn->c_next_tx_seq);
	conn->c_next_tx_seq++;
	spin_unlock_irqrestore(&conn->c_lock, flags);

	rds_stats_inc(s_send_queued);
	rds_stats_inc(s_send_pong);

	queue_delayed_work(rds_wq, &conn->c_send_w, 0);
	rds_message_put(rm);
	return 0;

out:
	if (rm)
		rds_message_put(rm);
	return ret;
}