posix-cpu-timers.c 45.2 KB
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 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727
/*
 * 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 set timer expiration if necessary.
 */
void update_rlimit_cpu(unsigned long rlim_new)
{
	cputime_t cputime = secs_to_cputime(rlim_new);
	struct signal_struct *const sig = current->signal;

	if (cputime_eq(sig->it[CPUCLOCK_PROF].expires, cputime_zero) ||
	    cputime_gt(sig->it[CPUCLOCK_PROF].expires, cputime)) {
		spin_lock_irq(&current->sighand->siglock);
		set_process_cpu_timer(current, CPUCLOCK_PROF, &cputime, NULL);
		spin_unlock_irq(&current->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;

	read_lock(&tasklist_lock);
	p = find_task_by_vpid(pid);
	if (!p || !(CPUCLOCK_PERTHREAD(which_clock) ?
		   same_thread_group(p, current) : thread_group_leader(p))) {
		error = -EINVAL;
	}
	read_unlock(&tasklist_lock);

	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 sighand_struct *sighand;
	struct signal_struct *sig;
	struct task_struct *t;

	*times = INIT_CPUTIME;

	rcu_read_lock();
	sighand = rcu_dereference(tsk->sighand);
	if (!sighand)
		goto out;

	sig = tsk->signal;

	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;

		t = next_thread(t);
	} while (t != tsk);

	times->utime = cputime_add(times->utime, sig->utime);
	times->stime = cputime_add(times->stime, sig->stime);
	times->sum_exec_runtime += sig->sum_sched_runtime;
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->signal) {
					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 with the new timer already locked.
 */
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);
	new_timer->it.cpu.incr.sched = 0;
	new_timer->it.cpu.expires.sched = 0;

	read_lock(&tasklist_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 && !thread_group_leader(p))
				p = NULL;
		}
	}
	new_timer->it.cpu.task = p;
	if (p) {
		get_task_struct(p);
	} else {
		ret = -EINVAL;
	}
	read_unlock(&tasklist_lock);

	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->signal == 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);
}

static inline int expires_le(cputime_t expires, cputime_t new_exp)
{
	return !cputime_eq(expires, cputime_zero) &&
	       cputime_le(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, and interrupts disabled.
 */
static void arm_timer(struct k_itimer *timer, union cpu_time_count now)
{
	struct task_struct *p = timer->it.cpu.task;
	struct list_head *head, *listpos;
	struct cpu_timer_list *const nt = &timer->it.cpu;
	struct cpu_timer_list *next;
	unsigned long i;

	head = (CPUCLOCK_PERTHREAD(timer->it_clock) ?
		p->cpu_timers : p->signal->cpu_timers);
	head += CPUCLOCK_WHICH(timer->it_clock);

	BUG_ON(!irqs_disabled());
	spin_lock(&p->sighand->siglock);

	listpos = head;
	if (CPUCLOCK_WHICH(timer->it_clock) == CPUCLOCK_SCHED) {
		list_for_each_entry(next, head, entry) {
			if (next->expires.sched > nt->expires.sched)
				break;
			listpos = &next->entry;
		}
	} else {
		list_for_each_entry(next, head, entry) {
			if (cputime_gt(next->expires.cpu, nt->expires.cpu))
				break;
			listpos = &next->entry;
		}
	}
	list_add(&nt->entry, listpos);

	if (listpos == head) {
		/*
		 * We are the new earliest-expiring timer.
		 * If we are a thread timer, there can always
		 * be a process timer telling us to stop earlier.
		 */

		if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
			union cpu_time_count *exp = &nt->expires;

			switch (CPUCLOCK_WHICH(timer->it_clock)) {
			default:
				BUG();
			case CPUCLOCK_PROF:
				if (expires_gt(p->cputime_expires.prof_exp,
					       exp->cpu))
					p->cputime_expires.prof_exp = exp->cpu;
				break;
			case CPUCLOCK_VIRT:
				if (expires_gt(p->cputime_expires.virt_exp,
					       exp->cpu))
					p->cputime_expires.virt_exp = exp->cpu;
				break;
			case CPUCLOCK_SCHED:
				if (p->cputime_expires.sched_exp == 0 ||
				    p->cputime_expires.sched_exp > exp->sched)
					p->cputime_expires.sched_exp =
								exp->sched;
				break;
			}
		} else {
			struct signal_struct *const sig = p->signal;
			union cpu_time_count *exp = &timer->it.cpu.expires;

			/*
			 * For a process timer, set the cached expiration time.
			 */
			switch (CPUCLOCK_WHICH(timer->it_clock)) {
			default:
				BUG();
			case CPUCLOCK_VIRT:
				if (expires_le(sig->it[CPUCLOCK_VIRT].expires,
					       exp->cpu))
					break;
				sig->cputime_expires.virt_exp = exp->cpu;
				break;
			case CPUCLOCK_PROF:
				if (expires_le(sig->it[CPUCLOCK_PROF].expires,
					       exp->cpu))
					break;
				i = sig->rlim[RLIMIT_CPU].rlim_cur;
				if (i != RLIM_INFINITY &&
				    i <= cputime_to_secs(exp->cpu))
					break;
				sig->cputime_expires.prof_exp = exp->cpu;
				break;
			case CPUCLOCK_SCHED:
				sig->cputime_expires.sched_exp = exp->sched;
				break;
			}
		}
	}

	spin_unlock(&p->sighand->siglock);
}

/*
 * The timer is locked, fire it and arrange for its reload.
 */
static void cpu_timer_fire(struct k_itimer *timer)
{
	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, 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->signal.  If p has just been reaped, we can no
	 * longer get any information about it at all.
	 */
	if (unlikely(p->signal == 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;
	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);
	spin_unlock(&p->sighand->siglock);

	/*
	 * 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).
		 */
		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 &&
	    (timer->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE &&
	    cpu_time_before(timer->it_clock, val, new_expires)) {
		arm_timer(timer, val);
	}

	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 &&
	    (timer->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE &&
	    !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,
				   timer->it.cpu.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->signal == 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 ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
		if (timer->it.cpu.incr.sched == 0 &&
		    cpu_time_before(timer->it_clock,
				    timer->it.cpu.expires, now)) {
			/*
			 * Do-nothing timer expired and has no reload,
			 * so it's as if it was never set.
			 */
			timer->it.cpu.expires.sched = 0;
			itp->it_value.tv_sec = itp->it_value.tv_nsec = 0;
			return;
		}
		/*
		 * Account for any expirations and reloads that should
		 * have happened.
		 */
		bump_cpu_timer(timer, now);
	}

	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;

	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.
	 */
	if (sig->rlim[RLIMIT_RTTIME].rlim_cur != RLIM_INFINITY) {
		unsigned long hard = sig->rlim[RLIMIT_RTTIME].rlim_max;
		unsigned long *soft = &sig->rlim[RLIMIT_RTTIME].rlim_cur;

		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 (sig->rlim[RLIMIT_RTTIME].rlim_cur
			    < sig->rlim[RLIMIT_RTTIME].rlim_max) {
				sig->rlim[RLIMIT_RTTIME].rlim_cur +=
								USEC_PER_SEC;
			}
			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 task_struct *tsk)
{
	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
	unsigned long flags;

	if (!cputimer->running)
		return;

	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;
	}
}

/*
 * 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;

	/*
	 * Don't sample the current process CPU clocks if there are no timers.
	 */
	if (list_empty(&timers[CPUCLOCK_PROF]) &&
	    cputime_eq(sig->it[CPUCLOCK_PROF].expires, cputime_zero) &&
	    sig->rlim[RLIMIT_CPU].rlim_cur == RLIM_INFINITY &&
	    list_empty(&timers[CPUCLOCK_VIRT]) &&
	    cputime_eq(sig->it[CPUCLOCK_VIRT].expires, cputime_zero) &&
	    list_empty(&timers[CPUCLOCK_SCHED])) {
		stop_process_timers(tsk);
		return;
	}

	/*
	 * 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);

	if (sig->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY) {
		unsigned long psecs = cputime_to_secs(ptime);
		cputime_t x;
		if (psecs >= sig->rlim[RLIMIT_CPU].rlim_max) {
			/*
			 * 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 >= sig->rlim[RLIMIT_CPU].rlim_cur) {
			/*
			 * At the soft limit, send a SIGXCPU every second.
			 */
			__group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
			if (sig->rlim[RLIMIT_CPU].rlim_cur
			    < sig->rlim[RLIMIT_CPU].rlim_max) {
				sig->rlim[RLIMIT_CPU].rlim_cur++;
			}
		}
		x = secs_to_cputime(sig->rlim[RLIMIT_CPU].rlim_cur);
		if (cputime_eq(prof_expires, cputime_zero) ||
		    cputime_lt(x, prof_expires)) {
			prof_expires = x;
		}
	}

	if (!cputime_eq(prof_expires, cputime_zero) &&
	    (cputime_eq(sig->cputime_expires.prof_exp, cputime_zero) ||
	     cputime_gt(sig->cputime_expires.prof_exp, prof_expires)))
		sig->cputime_expires.prof_exp = prof_expires;
	if (!cputime_eq(virt_expires, cputime_zero) &&
	    (cputime_eq(sig->cputime_expires.virt_exp, cputime_zero) ||
	     cputime_gt(sig->cputime_expires.virt_exp, virt_expires)))
		sig->cputime_expires.virt_exp = virt_expires;
	if (sched_expires != 0 &&
	    (sig->cputime_expires.sched_exp == 0 ||
	     sig->cputime_expires.sched_exp > sched_expires))
		sig->cputime_expires.sched_exp = sched_expires;
}

/*
 * 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.  */
	} else {
		read_lock(&tasklist_lock);
		if (unlikely(p->signal == 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;
		}
		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.
	 */
	arm_timer(timer, now);

out_unlock:
	read_unlock(&tasklist_lock);

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

/**
 * 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;
}

/**
 * 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;

	/* tsk == current, ensure it is safe to use ->signal/sighand */
	if (unlikely(tsk->exit_state))
		return 0;

	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 (!task_cputime_zero(&sig->cputime_expires)) {
		struct task_cputime group_sample;

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

	return sig->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY;
}

/*
 * 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;

	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;

	spin_lock(&tsk->sighand->siglock);
	/*
	 * 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);
	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.
	 */
	spin_unlock(&tsk->sighand->siglock);

	/*
	 * 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.
 * The tsk->sighand->siglock must be held by the caller.
 * The *newval argument is relative and we update it to be absolute, *oldval
 * is absolute and we update it to be relative.
 */
void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
			   cputime_t *newval, cputime_t *oldval)
{
	union cpu_time_count now;
	struct list_head *head;

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

	if (oldval) {
		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);

		/*
		 * If the RLIMIT_CPU timer will expire before the
		 * ITIMER_PROF timer, we have nothing else to do.
		 */
		if (tsk->signal->rlim[RLIMIT_CPU].rlim_cur
		    < cputime_to_secs(*newval))
			return;
	}

	/*
	 * Check whether there are any process timers already set to fire
	 * before this one.  If so, we don't have anything more to do.
	 */
	head = &tsk->signal->cpu_timers[clock_idx];
	if (list_empty(head) ||
	    cputime_ge(list_first_entry(head,
				  struct cpu_timer_list, entry)->expires.cpu,
		       *newval)) {
		switch (clock_idx) {
		case CPUCLOCK_PROF:
			tsk->signal->cputime_expires.prof_exp = *newval;
			break;
		case CPUCLOCK_VIRT:
			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);