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
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
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
/*
 * Implement CPU time clocks for the POSIX clock interface.
 */

#include <linux/sched.h>
#include <linux/posix-timers.h>
#include <linux/errno.h>
#include <linux/math64.h>
#include <asm/uaccess.h>
#include <linux/kernel_stat.h>
#include <trace/events/timer.h>

/*
 * Called after updating RLIMIT_CPU to run cpu timer and update
 * tsk->signal->cputime_expires expiration cache if necessary. Needs
 * siglock protection since other code may update expiration cache as
 * well.
 */
void update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new)
{
	cputime_t cputime = secs_to_cputime(rlim_new);

	spin_lock_irq(&task->sighand->siglock);
	set_process_cpu_timer(task, CPUCLOCK_PROF, &cputime, NULL);
	spin_unlock_irq(&task->sighand->siglock);
}

static int check_clock(const clockid_t which_clock)
{
	int error = 0;
	struct task_struct *p;
	const pid_t pid = CPUCLOCK_PID(which_clock);

	if (CPUCLOCK_WHICH(which_clock) >= CPUCLOCK_MAX)
		return -EINVAL;

	if (pid == 0)
		return 0;

	rcu_read_lock();
	p = find_task_by_vpid(pid);
	if (!p || !(CPUCLOCK_PERTHREAD(which_clock) ?
		   same_thread_group(p, current) : has_group_leader_pid(p))) {
		error = -EINVAL;
	}
	rcu_read_unlock();

	return error;
}

static inline union cpu_time_count
timespec_to_sample(const clockid_t which_clock, const struct timespec *tp)
{
	union cpu_time_count ret;
	ret.sched = 0;		/* high half always zero when .cpu used */
	if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
		ret.sched = (unsigned long long)tp->tv_sec * NSEC_PER_SEC + tp->tv_nsec;
	} else {
		ret.cpu = timespec_to_cputime(tp);
	}
	return ret;
}

static void sample_to_timespec(const clockid_t which_clock,
			       union cpu_time_count cpu,
			       struct timespec *tp)
{
	if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED)
		*tp = ns_to_timespec(cpu.sched);
	else
		cputime_to_timespec(cpu.cpu, tp);
}

static inline int cpu_time_before(const clockid_t which_clock,
				  union cpu_time_count now,
				  union cpu_time_count then)
{
	if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
		return now.sched < then.sched;
	}  else {
		return cputime_lt(now.cpu, then.cpu);
	}
}
static inline void cpu_time_add(const clockid_t which_clock,
				union cpu_time_count *acc,
			        union cpu_time_count val)
{
	if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
		acc->sched += val.sched;
	}  else {
		acc->cpu = cputime_add(acc->cpu, val.cpu);
	}
}
static inline union cpu_time_count cpu_time_sub(const clockid_t which_clock,
						union cpu_time_count a,
						union cpu_time_count b)
{
	if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
		a.sched -= b.sched;
	}  else {
		a.cpu = cputime_sub(a.cpu, b.cpu);
	}
	return a;
}

/*
 * Divide and limit the result to res >= 1
 *
 * This is necessary to prevent signal delivery starvation, when the result of
 * the division would be rounded down to 0.
 */
static inline cputime_t cputime_div_non_zero(cputime_t time, unsigned long div)
{
	cputime_t res = cputime_div(time, div);

	return max_t(cputime_t, res, 1);
}

/*
 * Update expiry time from increment, and increase overrun count,
 * given the current clock sample.
 */
static void bump_cpu_timer(struct k_itimer *timer,
				  union cpu_time_count now)
{
	int i;

	if (timer->it.cpu.incr.sched == 0)
		return;

	if (CPUCLOCK_WHICH(timer->it_clock) == CPUCLOCK_SCHED) {
		unsigned long long delta, incr;

		if (now.sched < timer->it.cpu.expires.sched)
			return;
		incr = timer->it.cpu.incr.sched;
		delta = now.sched + incr - timer->it.cpu.expires.sched;
		/* Don't use (incr*2 < delta), incr*2 might overflow. */
		for (i = 0; incr < delta - incr; i++)
			incr = incr << 1;
		for (; i >= 0; incr >>= 1, i--) {
			if (delta < incr)
				continue;
			timer->it.cpu.expires.sched += incr;
			timer->it_overrun += 1 << i;
			delta -= incr;
		}
	} else {
		cputime_t delta, incr;

		if (cputime_lt(now.cpu, timer->it.cpu.expires.cpu))
			return;
		incr = timer->it.cpu.incr.cpu;
		delta = cputime_sub(cputime_add(now.cpu, incr),
				    timer->it.cpu.expires.cpu);
		/* Don't use (incr*2 < delta), incr*2 might overflow. */
		for (i = 0; cputime_lt(incr, cputime_sub(delta, incr)); i++)
			     incr = cputime_add(incr, incr);
		for (; i >= 0; incr = cputime_halve(incr), i--) {
			if (cputime_lt(delta, incr))
				continue;
			timer->it.cpu.expires.cpu =
				cputime_add(timer->it.cpu.expires.cpu, incr);
			timer->it_overrun += 1 << i;
			delta = cputime_sub(delta, incr);
		}
	}
}

static inline cputime_t prof_ticks(struct task_struct *p)
{
	return cputime_add(p->utime, p->stime);
}
static inline cputime_t virt_ticks(struct task_struct *p)
{
	return p->utime;
}

int posix_cpu_clock_getres(const clockid_t which_clock, struct timespec *tp)
{
	int error = check_clock(which_clock);
	if (!error) {
		tp->tv_sec = 0;
		tp->tv_nsec = ((NSEC_PER_SEC + HZ - 1) / HZ);
		if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
			/*
			 * If sched_clock is using a cycle counter, we
			 * don't have any idea of its true resolution
			 * exported, but it is much more than 1s/HZ.
			 */
			tp->tv_nsec = 1;
		}
	}
	return error;
}

int posix_cpu_clock_set(const clockid_t which_clock, const struct timespec *tp)
{
	/*
	 * You can never reset a CPU clock, but we check for other errors
	 * in the call before failing with EPERM.
	 */
	int error = check_clock(which_clock);
	if (error == 0) {
		error = -EPERM;
	}
	return error;
}


/*
 * Sample a per-thread clock for the given task.
 */
static int cpu_clock_sample(const clockid_t which_clock, struct task_struct *p,
			    union cpu_time_count *cpu)
{
	switch (CPUCLOCK_WHICH(which_clock)) {
	default:
		return -EINVAL;
	case CPUCLOCK_PROF:
		cpu->cpu = prof_ticks(p);
		break;
	case CPUCLOCK_VIRT:
		cpu->cpu = virt_ticks(p);
		break;
	case CPUCLOCK_SCHED:
		cpu->sched = task_sched_runtime(p);
		break;
	}
	return 0;
}

void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
{
	struct signal_struct *sig = tsk->signal;
	struct task_struct *t;

	times->utime = sig->utime;
	times->stime = sig->stime;
	times->sum_exec_runtime = sig->sum_sched_runtime;

	rcu_read_lock();
	/* make sure we can trust tsk->thread_group list */
	if (!likely(pid_alive(tsk)))
		goto out;

	t = tsk;
	do {
		times->utime = cputime_add(times->utime, t->utime);
		times->stime = cputime_add(times->stime, t->stime);
		times->sum_exec_runtime += t->se.sum_exec_runtime;
	} while_each_thread(tsk, t);
out:
	rcu_read_unlock();
}

static void update_gt_cputime(struct task_cputime *a, struct task_cputime *b)
{
	if (cputime_gt(b->utime, a->utime))
		a->utime = b->utime;

	if (cputime_gt(b->stime, a->stime))
		a->stime = b->stime;

	if (b->sum_exec_runtime > a->sum_exec_runtime)
		a->sum_exec_runtime = b->sum_exec_runtime;
}

void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
{
	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
	struct task_cputime sum;
	unsigned long flags;

	spin_lock_irqsave(&cputimer->lock, flags);
	if (!cputimer->running) {
		cputimer->running = 1;
		/*
		 * The POSIX timer interface allows for absolute time expiry
		 * values through the TIMER_ABSTIME flag, therefore we have
		 * to synchronize the timer to the clock every time we start
		 * it.
		 */
		thread_group_cputime(tsk, &sum);
		update_gt_cputime(&cputimer->cputime, &sum);
	}
	*times = cputimer->cputime;
	spin_unlock_irqrestore(&cputimer->lock, flags);
}

/*
 * Sample a process (thread group) clock for the given group_leader task.
 * Must be called with tasklist_lock held for reading.
 */
static int cpu_clock_sample_group(const clockid_t which_clock,
				  struct task_struct *p,
				  union cpu_time_count *cpu)
{
	struct task_cputime cputime;

	switch (CPUCLOCK_WHICH(which_clock)) {
	default:
		return -EINVAL;
	case CPUCLOCK_PROF:
		thread_group_cputime(p, &cputime);
		cpu->cpu = cputime_add(cputime.utime, cputime.stime);
		break;
	case CPUCLOCK_VIRT:
		thread_group_cputime(p, &cputime);
		cpu->cpu = cputime.utime;
		break;
	case CPUCLOCK_SCHED:
		cpu->sched = thread_group_sched_runtime(p);
		break;
	}
	return 0;
}


int posix_cpu_clock_get(const clockid_t which_clock, struct timespec *tp)
{
	const pid_t pid = CPUCLOCK_PID(which_clock);
	int error = -EINVAL;
	union cpu_time_count rtn;

	if (pid == 0) {
		/*
		 * Special case constant value for our own clocks.
		 * We don't have to do any lookup to find ourselves.
		 */
		if (CPUCLOCK_PERTHREAD(which_clock)) {
			/*
			 * Sampling just ourselves we can do with no locking.
			 */
			error = cpu_clock_sample(which_clock,
						 current, &rtn);
		} else {
			read_lock(&tasklist_lock);
			error = cpu_clock_sample_group(which_clock,
						       current, &rtn);
			read_unlock(&tasklist_lock);
		}
	} else {
		/*
		 * Find the given PID, and validate that the caller
		 * should be able to see it.
		 */
		struct task_struct *p;
		rcu_read_lock();
		p = find_task_by_vpid(pid);
		if (p) {
			if (CPUCLOCK_PERTHREAD(which_clock)) {
				if (same_thread_group(p, current)) {
					error = cpu_clock_sample(which_clock,
								 p, &rtn);
				}
			} else {
				read_lock(&tasklist_lock);
				if (thread_group_leader(p) && p->sighand) {
					error =
					    cpu_clock_sample_group(which_clock,
							           p, &rtn);
				}
				read_unlock(&tasklist_lock);
			}
		}
		rcu_read_unlock();
	}

	if (error)
		return error;
	sample_to_timespec(which_clock, rtn, tp);
	return 0;
}


/*
 * Validate the clockid_t for a new CPU-clock timer, and initialize the timer.
 * This is called from sys_timer_create() and do_cpu_nanosleep() with the
 * new timer already all-zeros initialized.
 */
int posix_cpu_timer_create(struct k_itimer *new_timer)
{
	int ret = 0;
	const pid_t pid = CPUCLOCK_PID(new_timer->it_clock);
	struct task_struct *p;

	if (CPUCLOCK_WHICH(new_timer->it_clock) >= CPUCLOCK_MAX)
		return -EINVAL;

	INIT_LIST_HEAD(&new_timer->it.cpu.entry);

	rcu_read_lock();
	if (CPUCLOCK_PERTHREAD(new_timer->it_clock)) {
		if (pid == 0) {
			p = current;
		} else {
			p = find_task_by_vpid(pid);
			if (p && !same_thread_group(p, current))
				p = NULL;
		}
	} else {
		if (pid == 0) {
			p = current->group_leader;
		} else {
			p = find_task_by_vpid(pid);
			if (p && !has_group_leader_pid(p))
				p = NULL;
		}
	}
	new_timer->it.cpu.task = p;
	if (p) {
		get_task_struct(p);
	} else {
		ret = -EINVAL;
	}
	rcu_read_unlock();

	return ret;
}

/*
 * Clean up a CPU-clock timer that is about to be destroyed.
 * This is called from timer deletion with the timer already locked.
 * If we return TIMER_RETRY, it's necessary to release the timer's lock
 * and try again.  (This happens when the timer is in the middle of firing.)
 */
int posix_cpu_timer_del(struct k_itimer *timer)
{
	struct task_struct *p = timer->it.cpu.task;
	int ret = 0;

	if (likely(p != NULL)) {
		read_lock(&tasklist_lock);
		if (unlikely(p->sighand == NULL)) {
			/*
			 * We raced with the reaping of the task.
			 * The deletion should have cleared us off the list.
			 */
			BUG_ON(!list_empty(&timer->it.cpu.entry));
		} else {
			spin_lock(&p->sighand->siglock);
			if (timer->it.cpu.firing)
				ret = TIMER_RETRY;
			else
				list_del(&timer->it.cpu.entry);
			spin_unlock(&p->sighand->siglock);
		}
		read_unlock(&tasklist_lock);

		if (!ret)
			put_task_struct(p);
	}

	return ret;
}

/*
 * Clean out CPU timers still ticking when a thread exited.  The task
 * pointer is cleared, and the expiry time is replaced with the residual
 * time for later timer_gettime calls to return.
 * This must be called with the siglock held.
 */
static void cleanup_timers(struct list_head *head,
			   cputime_t utime, cputime_t stime,
			   unsigned long long sum_exec_runtime)
{
	struct cpu_timer_list *timer, *next;
	cputime_t ptime = cputime_add(utime, stime);

	list_for_each_entry_safe(timer, next, head, entry) {
		list_del_init(&timer->entry);
		if (cputime_lt(timer->expires.cpu, ptime)) {
			timer->expires.cpu = cputime_zero;
		} else {
			timer->expires.cpu = cputime_sub(timer->expires.cpu,
							 ptime);
		}
	}

	++head;
	list_for_each_entry_safe(timer, next, head, entry) {
		list_del_init(&timer->entry);
		if (cputime_lt(timer->expires.cpu, utime)) {
			timer->expires.cpu = cputime_zero;
		} else {
			timer->expires.cpu = cputime_sub(timer->expires.cpu,
							 utime);
		}
	}

	++head;
	list_for_each_entry_safe(timer, next, head, entry) {
		list_del_init(&timer->entry);
		if (timer->expires.sched < sum_exec_runtime) {
			timer->expires.sched = 0;
		} else {
			timer->expires.sched -= sum_exec_runtime;
		}
	}
}

/*
 * These are both called with the siglock held, when the current thread
 * is being reaped.  When the final (leader) thread in the group is reaped,
 * posix_cpu_timers_exit_group will be called after posix_cpu_timers_exit.
 */
void posix_cpu_timers_exit(struct task_struct *tsk)
{
	cleanup_timers(tsk->cpu_timers,
		       tsk->utime, tsk->stime, tsk->se.sum_exec_runtime);

}
void posix_cpu_timers_exit_group(struct task_struct *tsk)
{
	struct signal_struct *const sig = tsk->signal;

	cleanup_timers(tsk->signal->cpu_timers,
		       cputime_add(tsk->utime, sig->utime),
		       cputime_add(tsk->stime, sig->stime),
		       tsk->se.sum_exec_runtime + sig->sum_sched_runtime);
}

static void clear_dead_task(struct k_itimer *timer, union cpu_time_count now)
{
	/*
	 * That's all for this thread or process.
	 * We leave our residual in expires to be reported.
	 */
	put_task_struct(timer->it.cpu.task);
	timer->it.cpu.task = NULL;
	timer->it.cpu.expires = cpu_time_sub(timer->it_clock,
					     timer->it.cpu.expires,
					     now);
}

static inline int expires_gt(cputime_t expires, cputime_t new_exp)
{
	return cputime_eq(expires, cputime_zero) ||
	       cputime_gt(expires, new_exp);
}

/*
 * Insert the timer on the appropriate list before any timers that
 * expire later.  This must be called with the tasklist_lock held
 * for reading, interrupts disabled and p->sighand->siglock taken.
 */
static void arm_timer(struct k_itimer *timer)
{
	struct task_struct *p = timer->it.cpu.task;
	struct list_head *head, *listpos;
	struct task_cputime *cputime_expires;
	struct cpu_timer_list *const nt = &timer->it.cpu;
	struct cpu_timer_list *next;

	if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
		head = p->cpu_timers;
		cputime_expires = &p->cputime_expires;
	} else {
		head = p->signal->cpu_timers;
		cputime_expires = &p->signal->cputime_expires;
	}
	head += CPUCLOCK_WHICH(timer->it_clock);

	listpos = head;
	list_for_each_entry(next, head, entry) {
		if (cpu_time_before(timer->it_clock, nt->expires, next->expires))
			break;
		listpos = &next->entry;
	}
	list_add(&nt->entry, listpos);

	if (listpos == head) {
		union cpu_time_count *exp = &nt->expires;

		/*
		 * We are the new earliest-expiring POSIX 1.b timer, hence
		 * need to update expiration cache. Take into account that
		 * for process timers we share expiration cache with itimers
		 * and RLIMIT_CPU and for thread timers with RLIMIT_RTTIME.
		 */

		switch (CPUCLOCK_WHICH(timer->it_clock)) {
		case CPUCLOCK_PROF:
			if (expires_gt(cputime_expires->prof_exp, exp->cpu))
				cputime_expires->prof_exp = exp->cpu;
			break;
		case CPUCLOCK_VIRT:
			if (expires_gt(cputime_expires->virt_exp, exp->cpu))
				cputime_expires->virt_exp = exp->cpu;
			break;
		case CPUCLOCK_SCHED:
			if (cputime_expires->sched_exp == 0 ||
			    cputime_expires->sched_exp > exp->sched)
				cputime_expires->sched_exp = exp->sched;
			break;
		}
	}
}

/*
 * The timer is locked, fire it and arrange for its reload.
 */
static void cpu_timer_fire(struct k_itimer *timer)
{
	if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
		/*
		 * User don't want any signal.
		 */
		timer->it.cpu.expires.sched = 0;
	} else if (unlikely(timer->sigq == NULL)) {
		/*
		 * This a special case for clock_nanosleep,
		 * not a normal timer from sys_timer_create.
		 */
		wake_up_process(timer->it_process);
		timer->it.cpu.expires.sched = 0;
	} else if (timer->it.cpu.incr.sched == 0) {
		/*
		 * One-shot timer.  Clear it as soon as it's fired.
		 */
		posix_timer_event(timer, 0);
		timer->it.cpu.expires.sched = 0;
	} else if (posix_timer_event(timer, ++timer->it_requeue_pending)) {
		/*
		 * The signal did not get queued because the signal
		 * was ignored, so we won't get any callback to
		 * reload the timer.  But we need to keep it
		 * ticking in case the signal is deliverable next time.
		 */
		posix_cpu_timer_schedule(timer);
	}
}

/*
 * Sample a process (thread group) timer for the given group_leader task.
 * Must be called with tasklist_lock held for reading.
 */
static int cpu_timer_sample_group(const clockid_t which_clock,
				  struct task_struct *p,
				  union cpu_time_count *cpu)
{
	struct task_cputime cputime;

	thread_group_cputimer(p, &cputime);
	switch (CPUCLOCK_WHICH(which_clock)) {
	default:
		return -EINVAL;
	case CPUCLOCK_PROF:
		cpu->cpu = cputime_add(cputime.utime, cputime.stime);
		break;
	case CPUCLOCK_VIRT:
		cpu->cpu = cputime.utime;
		break;
	case CPUCLOCK_SCHED:
		cpu->sched = cputime.sum_exec_runtime + task_delta_exec(p);
		break;
	}
	return 0;
}

/*
 * Guts of sys_timer_settime for CPU timers.
 * This is called with the timer locked and interrupts disabled.
 * If we return TIMER_RETRY, it's necessary to release the timer's lock
 * and try again.  (This happens when the timer is in the middle of firing.)
 */
int posix_cpu_timer_set(struct k_itimer *timer, int flags,
			struct itimerspec *new, struct itimerspec *old)
{
	struct task_struct *p = timer->it.cpu.task;
	union cpu_time_count old_expires, new_expires, old_incr, val;
	int ret;

	if (unlikely(p == NULL)) {
		/*
		 * Timer refers to a dead task's clock.
		 */
		return -ESRCH;
	}

	new_expires = timespec_to_sample(timer->it_clock, &new->it_value);

	read_lock(&tasklist_lock);
	/*
	 * We need the tasklist_lock to protect against reaping that
	 * clears p->sighand.  If p has just been reaped, we can no
	 * longer get any information about it at all.
	 */
	if (unlikely(p->sighand == NULL)) {
		read_unlock(&tasklist_lock);
		put_task_struct(p);
		timer->it.cpu.task = NULL;
		return -ESRCH;
	}

	/*
	 * Disarm any old timer after extracting its expiry time.
	 */
	BUG_ON(!irqs_disabled());

	ret = 0;
	old_incr = timer->it.cpu.incr;
	spin_lock(&p->sighand->siglock);
	old_expires = timer->it.cpu.expires;
	if (unlikely(timer->it.cpu.firing)) {
		timer->it.cpu.firing = -1;
		ret = TIMER_RETRY;
	} else
		list_del_init(&timer->it.cpu.entry);

	/*
	 * We need to sample the current value to convert the new
	 * value from to relative and absolute, and to convert the
	 * old value from absolute to relative.  To set a process
	 * timer, we need a sample to balance the thread expiry
	 * times (in arm_timer).  With an absolute time, we must
	 * check if it's already passed.  In short, we need a sample.
	 */
	if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
		cpu_clock_sample(timer->it_clock, p, &val);
	} else {
		cpu_timer_sample_group(timer->it_clock, p, &val);
	}

	if (old) {
		if (old_expires.sched == 0) {
			old->it_value.tv_sec = 0;
			old->it_value.tv_nsec = 0;
		} else {
			/*
			 * Update the timer in case it has
			 * overrun already.  If it has,
			 * we'll report it as having overrun
			 * and with the next reloaded timer
			 * already ticking, though we are
			 * swallowing that pending
			 * notification here to install the
			 * new setting.
			 */
			bump_cpu_timer(timer, val);
			if (cpu_time_before(timer->it_clock, val,
					    timer->it.cpu.expires)) {
				old_expires = cpu_time_sub(
					timer->it_clock,
					timer->it.cpu.expires, val);
				sample_to_timespec(timer->it_clock,
						   old_expires,
						   &old->it_value);
			} else {
				old->it_value.tv_nsec = 1;
				old->it_value.tv_sec = 0;
			}
		}
	}

	if (unlikely(ret)) {
		/*
		 * We are colliding with the timer actually firing.
		 * Punt after filling in the timer's old value, and
		 * disable this firing since we are already reporting
		 * it as an overrun (thanks to bump_cpu_timer above).
		 */
		spin_unlock(&p->sighand->siglock);
		read_unlock(&tasklist_lock);
		goto out;
	}

	if (new_expires.sched != 0 && !(flags & TIMER_ABSTIME)) {
		cpu_time_add(timer->it_clock, &new_expires, val);
	}

	/*
	 * Install the new expiry time (or zero).
	 * For a timer with no notification action, we don't actually
	 * arm the timer (we'll just fake it for timer_gettime).
	 */
	timer->it.cpu.expires = new_expires;
	if (new_expires.sched != 0 &&
	    cpu_time_before(timer->it_clock, val, new_expires)) {
		arm_timer(timer);
	}

	spin_unlock(&p->sighand->siglock);
	read_unlock(&tasklist_lock);

	/*
	 * Install the new reload setting, and
	 * set up the signal and overrun bookkeeping.
	 */
	timer->it.cpu.incr = timespec_to_sample(timer->it_clock,
						&new->it_interval);

	/*
	 * This acts as a modification timestamp for the timer,
	 * so any automatic reload attempt will punt on seeing
	 * that we have reset the timer manually.
	 */
	timer->it_requeue_pending = (timer->it_requeue_pending + 2) &
		~REQUEUE_PENDING;
	timer->it_overrun_last = 0;
	timer->it_overrun = -1;

	if (new_expires.sched != 0 &&
	    !cpu_time_before(timer->it_clock, val, new_expires)) {
		/*
		 * The designated time already passed, so we notify
		 * immediately, even if the thread never runs to
		 * accumulate more time on this clock.
		 */
		cpu_timer_fire(timer);
	}

	ret = 0;
 out:
	if (old) {
		sample_to_timespec(timer->it_clock,
				   old_incr, &old->it_interval);
	}
	return ret;
}

void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec *itp)
{
	union cpu_time_count now;
	struct task_struct *p = timer->it.cpu.task;
	int clear_dead;

	/*
	 * Easy part: convert the reload time.
	 */
	sample_to_timespec(timer->it_clock,
			   timer->it.cpu.incr, &itp->it_interval);

	if (timer->it.cpu.expires.sched == 0) {	/* Timer not armed at all.  */
		itp->it_value.tv_sec = itp->it_value.tv_nsec = 0;
		return;
	}

	if (unlikely(p == NULL)) {
		/*
		 * This task already died and the timer will never fire.
		 * In this case, expires is actually the dead value.
		 */
	dead:
		sample_to_timespec(timer->it_clock, timer->it.cpu.expires,
				   &itp->it_value);
		return;
	}

	/*
	 * Sample the clock to take the difference with the expiry time.
	 */
	if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
		cpu_clock_sample(timer->it_clock, p, &now);
		clear_dead = p->exit_state;
	} else {
		read_lock(&tasklist_lock);
		if (unlikely(p->sighand == NULL)) {
			/*
			 * The process has been reaped.
			 * We can't even collect a sample any more.
			 * Call the timer disarmed, nothing else to do.
			 */
			put_task_struct(p);
			timer->it.cpu.task = NULL;
			timer->it.cpu.expires.sched = 0;
			read_unlock(&tasklist_lock);
			goto dead;
		} else {
			cpu_timer_sample_group(timer->it_clock, p, &now);
			clear_dead = (unlikely(p->exit_state) &&
				      thread_group_empty(p));
		}
		read_unlock(&tasklist_lock);
	}

	if (unlikely(clear_dead)) {
		/*
		 * We've noticed that the thread is dead, but
		 * not yet reaped.  Take this opportunity to
		 * drop our task ref.
		 */
		clear_dead_task(timer, now);
		goto dead;
	}

	if (cpu_time_before(timer->it_clock, now, timer->it.cpu.expires)) {
		sample_to_timespec(timer->it_clock,
				   cpu_time_sub(timer->it_clock,
						timer->it.cpu.expires, now),
				   &itp->it_value);
	} else {
		/*
		 * The timer should have expired already, but the firing
		 * hasn't taken place yet.  Say it's just about to expire.
		 */
		itp->it_value.tv_nsec = 1;
		itp->it_value.tv_sec = 0;
	}
}

/*
 * Check for any per-thread CPU timers that have fired and move them off
 * the tsk->cpu_timers[N] list onto the firing list.  Here we update the
 * tsk->it_*_expires values to reflect the remaining thread CPU timers.
 */
static void check_thread_timers(struct task_struct *tsk,
				struct list_head *firing)
{
	int maxfire;
	struct list_head *timers = tsk->cpu_timers;
	struct signal_struct *const sig = tsk->signal;
	unsigned long soft;

	maxfire = 20;
	tsk->cputime_expires.prof_exp = cputime_zero;
	while (!list_empty(timers)) {
		struct cpu_timer_list *t = list_first_entry(timers,
						      struct cpu_timer_list,
						      entry);
		if (!--maxfire || cputime_lt(prof_ticks(tsk), t->expires.cpu)) {
			tsk->cputime_expires.prof_exp = t->expires.cpu;
			break;
		}
		t->firing = 1;
		list_move_tail(&t->entry, firing);
	}

	++timers;
	maxfire = 20;
	tsk->cputime_expires.virt_exp = cputime_zero;
	while (!list_empty(timers)) {
		struct cpu_timer_list *t = list_first_entry(timers,
						      struct cpu_timer_list,
						      entry);
		if (!--maxfire || cputime_lt(virt_ticks(tsk), t->expires.cpu)) {
			tsk->cputime_expires.virt_exp = t->expires.cpu;
			break;
		}
		t->firing = 1;
		list_move_tail(&t->entry, firing);
	}

	++timers;
	maxfire = 20;
	tsk->cputime_expires.sched_exp = 0;
	while (!list_empty(timers)) {
		struct cpu_timer_list *t = list_first_entry(timers,
						      struct cpu_timer_list,
						      entry);
		if (!--maxfire || tsk->se.sum_exec_runtime < t->expires.sched) {
			tsk->cputime_expires.sched_exp = t->expires.sched;
			break;
		}
		t->firing = 1;
		list_move_tail(&t->entry, firing);
	}

	/*
	 * Check for the special case thread timers.
	 */
	soft = ACCESS_ONCE(sig->rlim[RLIMIT_RTTIME].rlim_cur);
	if (soft != RLIM_INFINITY) {
		unsigned long hard =
			ACCESS_ONCE(sig->rlim[RLIMIT_RTTIME].rlim_max);

		if (hard != RLIM_INFINITY &&
		    tsk->rt.timeout > DIV_ROUND_UP(hard, USEC_PER_SEC/HZ)) {
			/*
			 * At the hard limit, we just die.
			 * No need to calculate anything else now.
			 */
			__group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
			return;
		}
		if (tsk->rt.timeout > DIV_ROUND_UP(soft, USEC_PER_SEC/HZ)) {
			/*
			 * At the soft limit, send a SIGXCPU every second.
			 */
			if (soft < hard) {
				soft += USEC_PER_SEC;
				sig->rlim[RLIMIT_RTTIME].rlim_cur = soft;
			}
			printk(KERN_INFO
				"RT Watchdog Timeout: %s[%d]\n",
				tsk->comm, task_pid_nr(tsk));
			__group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
		}
	}
}

static void stop_process_timers(struct signal_struct *sig)
{
	struct thread_group_cputimer *cputimer = &sig->cputimer;
	unsigned long flags;

	spin_lock_irqsave(&cputimer->lock, flags);
	cputimer->running = 0;
	spin_unlock_irqrestore(&cputimer->lock, flags);
}

static u32 onecputick;

static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
			     cputime_t *expires, cputime_t cur_time, int signo)
{
	if (cputime_eq(it->expires, cputime_zero))
		return;

	if (cputime_ge(cur_time, it->expires)) {
		if (!cputime_eq(it->incr, cputime_zero)) {
			it->expires = cputime_add(it->expires, it->incr);
			it->error += it->incr_error;
			if (it->error >= onecputick) {
				it->expires = cputime_sub(it->expires,
							  cputime_one_jiffy);
				it->error -= onecputick;
			}
		} else {
			it->expires = cputime_zero;
		}

		trace_itimer_expire(signo == SIGPROF ?
				    ITIMER_PROF : ITIMER_VIRTUAL,
				    tsk->signal->leader_pid, cur_time);
		__group_send_sig_info(signo, SEND_SIG_PRIV, tsk);
	}

	if (!cputime_eq(it->expires, cputime_zero) &&
	    (cputime_eq(*expires, cputime_zero) ||
	     cputime_lt(it->expires, *expires))) {
		*expires = it->expires;
	}
}

/**
 * task_cputime_zero - Check a task_cputime struct for all zero fields.
 *
 * @cputime:	The struct to compare.
 *
 * Checks @cputime to see if all fields are zero.  Returns true if all fields
 * are zero, false if any field is nonzero.
 */
static inline int task_cputime_zero(const struct task_cputime *cputime)
{
	if (cputime_eq(cputime->utime, cputime_zero) &&
	    cputime_eq(cputime->stime, cputime_zero) &&
	    cputime->sum_exec_runtime == 0)
		return 1;
	return 0;
}

/*
 * Check for any per-thread CPU timers that have fired and move them
 * off the tsk->*_timers list onto the firing list.  Per-thread timers
 * have already been taken off.
 */
static void check_process_timers(struct task_struct *tsk,
				 struct list_head *firing)
{
	int maxfire;
	struct signal_struct *const sig = tsk->signal;
	cputime_t utime, ptime, virt_expires, prof_expires;
	unsigned long long sum_sched_runtime, sched_expires;
	struct list_head *timers = sig->cpu_timers;
	struct task_cputime cputime;
	unsigned long soft;

	/*
	 * Collect the current process totals.
	 */
	thread_group_cputimer(tsk, &cputime);
	utime = cputime.utime;
	ptime = cputime_add(utime, cputime.stime);
	sum_sched_runtime = cputime.sum_exec_runtime;
	maxfire = 20;
	prof_expires = cputime_zero;
	while (!list_empty(timers)) {
		struct cpu_timer_list *tl = list_first_entry(timers,
						      struct cpu_timer_list,
						      entry);
		if (!--maxfire || cputime_lt(ptime, tl->expires.cpu)) {
			prof_expires = tl->expires.cpu;
			break;
		}
		tl->firing = 1;
		list_move_tail(&tl->entry, firing);
	}

	++timers;
	maxfire = 20;
	virt_expires = cputime_zero;
	while (!list_empty(timers)) {
		struct cpu_timer_list *tl = list_first_entry(timers,
						      struct cpu_timer_list,
						      entry);
		if (!--maxfire || cputime_lt(utime, tl->expires.cpu)) {
			virt_expires = tl->expires.cpu;
			break;
		}
		tl->firing = 1;
		list_move_tail(&tl->entry, firing);
	}

	++timers;
	maxfire = 20;
	sched_expires = 0;
	while (!list_empty(timers)) {
		struct cpu_timer_list *tl = list_first_entry(timers,
						      struct cpu_timer_list,
						      entry);
		if (!--maxfire || sum_sched_runtime < tl->expires.sched) {
			sched_expires = tl->expires.sched;
			break;
		}
		tl->firing = 1;
		list_move_tail(&tl->entry, firing);
	}

	/*
	 * Check for the special case process timers.
	 */
	check_cpu_itimer(tsk, &sig->it[CPUCLOCK_PROF], &prof_expires, ptime,
			 SIGPROF);
	check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT], &virt_expires, utime,
			 SIGVTALRM);
	soft = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
	if (soft != RLIM_INFINITY) {
		unsigned long psecs = cputime_to_secs(ptime);
		unsigned long hard =
			ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_max);
		cputime_t x;
		if (psecs >= hard) {
			/*
			 * At the hard limit, we just die.
			 * No need to calculate anything else now.
			 */
			__group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
			return;
		}
		if (psecs >= soft) {
			/*
			 * At the soft limit, send a SIGXCPU every second.
			 */
			__group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
			if (soft < hard) {
				soft++;
				sig->rlim[RLIMIT_CPU].rlim_cur = soft;
			}
		}
		x = secs_to_cputime(soft);
		if (cputime_eq(prof_expires, cputime_zero) ||
		    cputime_lt(x, prof_expires)) {
			prof_expires = x;
		}
	}

	sig->cputime_expires.prof_exp = prof_expires;
	sig->cputime_expires.virt_exp = virt_expires;
	sig->cputime_expires.sched_exp = sched_expires;
	if (task_cputime_zero(&sig->cputime_expires))
		stop_process_timers(sig);
}

/*
 * This is called from the signal code (via do_schedule_next_timer)
 * when the last timer signal was delivered and we have to reload the timer.
 */
void posix_cpu_timer_schedule(struct k_itimer *timer)
{
	struct task_struct *p = timer->it.cpu.task;
	union cpu_time_count now;

	if (unlikely(p == NULL))
		/*
		 * The task was cleaned up already, no future firings.
		 */
		goto out;

	/*
	 * Fetch the current sample and update the timer's expiry time.
	 */
	if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
		cpu_clock_sample(timer->it_clock, p, &now);
		bump_cpu_timer(timer, now);
		if (unlikely(p->exit_state)) {
			clear_dead_task(timer, now);
			goto out;
		}
		read_lock(&tasklist_lock); /* arm_timer needs it.  */
		spin_lock(&p->sighand->siglock);
	} else {
		read_lock(&tasklist_lock);
		if (unlikely(p->sighand == NULL)) {
			/*
			 * The process has been reaped.
			 * We can't even collect a sample any more.
			 */
			put_task_struct(p);
			timer->it.cpu.task = p = NULL;
			timer->it.cpu.expires.sched = 0;
			goto out_unlock;
		} else if (unlikely(p->exit_state) && thread_group_empty(p)) {
			/*
			 * We've noticed that the thread is dead, but
			 * not yet reaped.  Take this opportunity to
			 * drop our task ref.
			 */
			clear_dead_task(timer, now);
			goto out_unlock;
		}
		spin_lock(&p->sighand->siglock);
		cpu_timer_sample_group(timer->it_clock, p, &now);
		bump_cpu_timer(timer, now);
		/* Leave the tasklist_lock locked for the call below.  */
	}

	/*
	 * Now re-arm for the new expiry time.
	 */
	BUG_ON(!irqs_disabled());
	arm_timer(timer);
	spin_unlock(&p->sighand->siglock);

out_unlock:
	read_unlock(&tasklist_lock);

out:
	timer->it_overrun_last = timer->it_overrun;
	timer->it_overrun = -1;
	++timer->it_requeue_pending;
}

/**
 * task_cputime_expired - Compare two task_cputime entities.
 *
 * @sample:	The task_cputime structure to be checked for expiration.
 * @expires:	Expiration times, against which @sample will be checked.
 *
 * Checks @sample against @expires to see if any field of @sample has expired.
 * Returns true if any field of the former is greater than the corresponding
 * field of the latter if the latter field is set.  Otherwise returns false.
 */
static inline int task_cputime_expired(const struct task_cputime *sample,
					const struct task_cputime *expires)
{
	if (!cputime_eq(expires->utime, cputime_zero) &&
	    cputime_ge(sample->utime, expires->utime))
		return 1;
	if (!cputime_eq(expires->stime, cputime_zero) &&
	    cputime_ge(cputime_add(sample->utime, sample->stime),
		       expires->stime))
		return 1;
	if (expires->sum_exec_runtime != 0 &&
	    sample->sum_exec_runtime >= expires->sum_exec_runtime)
		return 1;
	return 0;
}

/**
 * fastpath_timer_check - POSIX CPU timers fast path.
 *
 * @tsk:	The task (thread) being checked.
 *
 * Check the task and thread group timers.  If both are zero (there are no
 * timers set) return false.  Otherwise snapshot the task and thread group
 * timers and compare them with the corresponding expiration times.  Return
 * true if a timer has expired, else return false.
 */
static inline int fastpath_timer_check(struct task_struct *tsk)
{
	struct signal_struct *sig;

	if (!task_cputime_zero(&tsk->cputime_expires)) {
		struct task_cputime task_sample = {
			.utime = tsk->utime,
			.stime = tsk->stime,
			.sum_exec_runtime = tsk->se.sum_exec_runtime
		};

		if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
			return 1;
	}

	sig = tsk->signal;
	if (sig->cputimer.running) {
		struct task_cputime group_sample;

		spin_lock(&sig->cputimer.lock);
		group_sample = sig->cputimer.cputime;
		spin_unlock(&sig->cputimer.lock);

		if (task_cputime_expired(&group_sample, &sig->cputime_expires))
			return 1;
	}

	return 0;
}

/*
 * This is called from the timer interrupt handler.  The irq handler has
 * already updated our counts.  We need to check if any timers fire now.
 * Interrupts are disabled.
 */
void run_posix_cpu_timers(struct task_struct *tsk)
{
	LIST_HEAD(firing);
	struct k_itimer *timer, *next;
	unsigned long flags;

	BUG_ON(!irqs_disabled());

	/*
	 * The fast path checks that there are no expired thread or thread
	 * group timers.  If that's so, just return.
	 */
	if (!fastpath_timer_check(tsk))
		return;

	if (!lock_task_sighand(tsk, &flags))
		return;
	/*
	 * Here we take off tsk->signal->cpu_timers[N] and
	 * tsk->cpu_timers[N] all the timers that are firing, and
	 * put them on the firing list.
	 */
	check_thread_timers(tsk, &firing);
	/*
	 * If there are any active process wide timers (POSIX 1.b, itimers,
	 * RLIMIT_CPU) cputimer must be running.
	 */
	if (tsk->signal->cputimer.running)
		check_process_timers(tsk, &firing);

	/*
	 * We must release these locks before taking any timer's lock.
	 * There is a potential race with timer deletion here, as the
	 * siglock now protects our private firing list.  We have set
	 * the firing flag in each timer, so that a deletion attempt
	 * that gets the timer lock before we do will give it up and
	 * spin until we've taken care of that timer below.
	 */
	unlock_task_sighand(tsk, &flags);

	/*
	 * Now that all the timers on our list have the firing flag,
	 * noone will touch their list entries but us.  We'll take
	 * each timer's lock before clearing its firing flag, so no
	 * timer call will interfere.
	 */
	list_for_each_entry_safe(timer, next, &firing, it.cpu.entry) {
		int cpu_firing;

		spin_lock(&timer->it_lock);
		list_del_init(&timer->it.cpu.entry);
		cpu_firing = timer->it.cpu.firing;
		timer->it.cpu.firing = 0;
		/*
		 * The firing flag is -1 if we collided with a reset
		 * of the timer, which already reported this
		 * almost-firing as an overrun.  So don't generate an event.
		 */
		if (likely(cpu_firing >= 0))
			cpu_timer_fire(timer);
		spin_unlock(&timer->it_lock);
	}
}

/*
 * Set one of the process-wide special case CPU timers or RLIMIT_CPU.
 * The tsk->sighand->siglock must be held by the caller.
 */
void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
			   cputime_t *newval, cputime_t *oldval)
{
	union cpu_time_count now;

	BUG_ON(clock_idx == CPUCLOCK_SCHED);
	cpu_timer_sample_group(clock_idx, tsk, &now);

	if (oldval) {
		/*
		 * We are setting itimer. The *oldval is absolute and we update
		 * it to be relative, *newval argument is relative and we update
		 * it to be absolute.
		 */
		if (!cputime_eq(*oldval, cputime_zero)) {
			if (cputime_le(*oldval, now.cpu)) {
				/* Just about to fire. */
				*oldval = cputime_one_jiffy;
			} else {
				*oldval = cputime_sub(*oldval, now.cpu);
			}
		}

		if (cputime_eq(*newval, cputime_zero))
			return;
		*newval = cputime_add(*newval, now.cpu);
	}

	/*
	 * Update expiration cache if we are the earliest timer, or eventually
	 * RLIMIT_CPU limit is earlier than prof_exp cpu timer expire.
	 */
	switch (clock_idx) {
	case CPUCLOCK_PROF:
		if (expires_gt(tsk->signal->cputime_expires.prof_exp, *newval))
			tsk->signal->cputime_expires.prof_exp = *newval;
		break;
	case CPUCLOCK_VIRT:
		if (expires_gt(tsk->signal->cputime_expires.virt_exp, *newval))
			tsk->signal->cputime_expires.virt_exp = *newval;
		break;
	}
}

static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
			    struct timespec *rqtp, struct itimerspec *it)
{
	struct k_itimer timer;
	int error;

	/*
	 * Set up a temporary timer and then wait for it to go off.
	 */
	memset(&timer, 0, sizeof timer);
	spin_lock_init(&timer.it_lock);
	timer.it_clock = which_clock;
	timer.it_overrun = -1;
	error = posix_cpu_timer_create(&timer);
	timer.it_process = current;
	if (!error) {
		static struct itimerspec zero_it;

		memset(it, 0, sizeof *it);
		it->it_value = *rqtp;

		spin_lock_irq(&timer.it_lock);
		error = posix_cpu_timer_set(&timer, flags, it, NULL);
		if (error) {
			spin_unlock_irq(&timer.it_lock);
			return error;
		}

		while (!signal_pending(current)) {
			if (timer.it.cpu.expires.sched == 0) {
				/*
				 * Our timer fired and was reset.
				 */
				spin_unlock_irq(&timer.it_lock);
				return 0;
			}

			/*
			 * Block until cpu_timer_fire (or a signal) wakes us.
			 */
			__set_current_state(TASK_INTERRUPTIBLE);
			spin_unlock_irq(&timer.it_lock);
			schedule();
			spin_lock_irq(&timer.it_lock);
		}

		/*
		 * We were interrupted by a signal.
		 */
		sample_to_timespec(which_clock, timer.it.cpu.expires, rqtp);
		posix_cpu_timer_set(&timer, 0, &zero_it, it);
		spin_unlock_irq(&timer.it_lock);

		if ((it->it_value.tv_sec | it->it_value.tv_nsec) == 0) {
			/*
			 * It actually did fire already.
			 */
			return 0;
		}

		error = -ERESTART_RESTARTBLOCK;
	}

	return error;
}

int posix_cpu_nsleep(const clockid_t which_clock, int flags,
		     struct timespec *rqtp, struct timespec __user *rmtp)
{
	struct restart_block *restart_block =
	    &current_thread_info()->restart_block;
	struct itimerspec it;
	int error;

	/*
	 * Diagnose required errors first.
	 */
	if (CPUCLOCK_PERTHREAD(which_clock) &&
	    (CPUCLOCK_PID(which_clock) == 0 ||
	     CPUCLOCK_PID(which_clock) == current->pid))
		return -EINVAL;

	error = do_cpu_nanosleep(which_clock, flags, rqtp, &it);

	if (error == -ERESTART_RESTARTBLOCK) {

	       	if (flags & TIMER_ABSTIME)
			return -ERESTARTNOHAND;
		/*
	 	 * Report back to the user the time still remaining.
	 	 */
		if (rmtp != NULL && copy_to_user(rmtp, &it.it_value, sizeof *rmtp))
			return -EFAULT;

		restart_block->fn = posix_cpu_nsleep_restart;
		restart_block->arg0 = which_clock;
		restart_block->arg1 = (unsigned long) rmtp;
		restart_block->arg2 = rqtp->tv_sec;
		restart_block->arg3 = rqtp->tv_nsec;
	}
	return error;
}

long posix_cpu_nsleep_restart(struct restart_block *restart_block)
{
	clockid_t which_clock = restart_block->arg0;
	struct timespec __user *rmtp;
	struct timespec t;
	struct itimerspec it;
	int error;

	rmtp = (struct timespec __user *) restart_block->arg1;
	t.tv_sec = restart_block->arg2;
	t.tv_nsec = restart_block->arg3;

	restart_block->fn = do_no_restart_syscall;
	error = do_cpu_nanosleep(which_clock, TIMER_ABSTIME, &t, &it);

	if (error == -ERESTART_RESTARTBLOCK) {
		/*
	 	 * Report back to the user the time still remaining.
	 	 */
		if (rmtp != NULL && copy_to_user(rmtp, &it.it_value, sizeof *rmtp))
			return -EFAULT;

		restart_block->fn = posix_cpu_nsleep_restart;
		restart_block->arg0 = which_clock;
		restart_block->arg1 = (unsigned long) rmtp;
		restart_block->arg2 = t.tv_sec;
		restart_block->arg3 = t.tv_nsec;
	}
	return error;

}


#define PROCESS_CLOCK	MAKE_PROCESS_CPUCLOCK(0, CPUCLOCK_SCHED)
#define THREAD_CLOCK	MAKE_THREAD_CPUCLOCK(0, CPUCLOCK_SCHED)

static int process_cpu_clock_getres(const clockid_t which_clock,
				    struct timespec *tp)
{
	return posix_cpu_clock_getres(PROCESS_CLOCK, tp);
}
static int process_cpu_clock_get(const clockid_t which_clock,
				 struct timespec *tp)
{
	return posix_cpu_clock_get(PROCESS_CLOCK, tp);
}
static int process_cpu_timer_create(struct k_itimer *timer)
{
	timer->it_clock = PROCESS_CLOCK;
	return posix_cpu_timer_create(timer);
}
static int process_cpu_nsleep(const clockid_t which_clock, int flags,
			      struct timespec *rqtp,
			      struct timespec __user *rmtp)
{
	return posix_cpu_nsleep(PROCESS_CLOCK, flags, rqtp, rmtp);
}
static long process_cpu_nsleep_restart(struct restart_block *restart_block)
{
	return -EINVAL;
}
static int thread_cpu_clock_getres(const clockid_t which_clock,
				   struct timespec *tp)
{
	return posix_cpu_clock_getres(THREAD_CLOCK, tp);
}
static int thread_cpu_clock_get(const clockid_t which_clock,
				struct timespec *tp)
{
	return posix_cpu_clock_get(THREAD_CLOCK, tp);
}
static int thread_cpu_timer_create(struct k_itimer *timer)
{
	timer->it_clock = THREAD_CLOCK;
	return posix_cpu_timer_create(timer);
}
static int thread_cpu_nsleep(const clockid_t which_clock, int flags,
			      struct timespec *rqtp, struct timespec __user *rmtp)
{
	return -EINVAL;
}
static long thread_cpu_nsleep_restart(struct restart_block *restart_block)
{
	return -EINVAL;
}

static __init int init_posix_cpu_timers(void)
{
	struct k_clock process = {
		.clock_getres = process_cpu_clock_getres,
		.clock_get = process_cpu_clock_get,
		.clock_set = do_posix_clock_nosettime,
		.timer_create = process_cpu_timer_create,
		.nsleep = process_cpu_nsleep,
		.nsleep_restart = process_cpu_nsleep_restart,
	};
	struct k_clock thread = {
		.clock_getres = thread_cpu_clock_getres,
		.clock_get = thread_cpu_clock_get,
		.clock_set = do_posix_clock_nosettime,
		.timer_create = thread_cpu_timer_create,
		.nsleep = thread_cpu_nsleep,
		.nsleep_restart = thread_cpu_nsleep_restart,
	};
	struct timespec ts;

	register_posix_clock(CLOCK_PROCESS_CPUTIME_ID, &process);
	register_posix_clock(CLOCK_THREAD_CPUTIME_ID, &thread);

	cputime_to_timespec(cputime_one_jiffy, &ts);
	onecputick = ts.tv_nsec;
	WARN_ON(ts.tv_sec != 0);

	return 0;
}
__initcall(init_posix_cpu_timers);