summaryrefslogtreecommitdiffstats
path: root/kernel/cpuset.c
blob: 6a6e87b2f2fd0d245aaf48a9a42a07e4bbe9dd83 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
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
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
/*
 *  kernel/cpuset.c
 *
 *  Processor and Memory placement constraints for sets of tasks.
 *
 *  Copyright (C) 2003 BULL SA.
 *  Copyright (C) 2004 Silicon Graphics, Inc.
 *
 *  Portions derived from Patrick Mochel's sysfs code.
 *  sysfs is Copyright (c) 2001-3 Patrick Mochel
 *  Portions Copyright (c) 2004 Silicon Graphics, Inc.
 *
 *  2003-10-10 Written by Simon Derr <simon.derr@bull.net>
 *  2003-10-22 Updates by Stephen Hemminger.
 *  2004 May-July Rework by Paul Jackson <pj@sgi.com>
 *
 *  This file is subject to the terms and conditions of the GNU General Public
 *  License.  See the file COPYING in the main directory of the Linux
 *  distribution for more details.
 */

#include <linux/config.h>
#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <linux/cpuset.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/kmod.h>
#include <linux/list.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/pagemap.h>
#include <linux/proc_fs.h>
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/smp_lock.h>
#include <linux/spinlock.h>
#include <linux/stat.h>
#include <linux/string.h>
#include <linux/time.h>
#include <linux/backing-dev.h>
#include <linux/sort.h>

#include <asm/uaccess.h>
#include <asm/atomic.h>
#include <asm/semaphore.h>

#define CPUSET_SUPER_MAGIC 		0x27e0eb

struct cpuset {
	unsigned long flags;		/* "unsigned long" so bitops work */
	cpumask_t cpus_allowed;		/* CPUs allowed to tasks in cpuset */
	nodemask_t mems_allowed;	/* Memory Nodes allowed to tasks */

	atomic_t count;			/* count tasks using this cpuset */

	/*
	 * We link our 'sibling' struct into our parents 'children'.
	 * Our children link their 'sibling' into our 'children'.
	 */
	struct list_head sibling;	/* my parents children */
	struct list_head children;	/* my children */

	struct cpuset *parent;		/* my parent */
	struct dentry *dentry;		/* cpuset fs entry */

	/*
	 * Copy of global cpuset_mems_generation as of the most
	 * recent time this cpuset changed its mems_allowed.
	 */
	 int mems_generation;
};

/* bits in struct cpuset flags field */
typedef enum {
	CS_CPU_EXCLUSIVE,
	CS_MEM_EXCLUSIVE,
	CS_REMOVED,
	CS_NOTIFY_ON_RELEASE
} cpuset_flagbits_t;

/* convenient tests for these bits */
static inline int is_cpu_exclusive(const struct cpuset *cs)
{
	return !!test_bit(CS_CPU_EXCLUSIVE, &cs->flags);
}

static inline int is_mem_exclusive(const struct cpuset *cs)
{
	return !!test_bit(CS_MEM_EXCLUSIVE, &cs->flags);
}

static inline int is_removed(const struct cpuset *cs)
{
	return !!test_bit(CS_REMOVED, &cs->flags);
}

static inline int notify_on_release(const struct cpuset *cs)
{
	return !!test_bit(CS_NOTIFY_ON_RELEASE, &cs->flags);
}

/*
 * Increment this atomic integer everytime any cpuset changes its
 * mems_allowed value.  Users of cpusets can track this generation
 * number, and avoid having to lock and reload mems_allowed unless
 * the cpuset they're using changes generation.
 *
 * A single, global generation is needed because attach_task() could
 * reattach a task to a different cpuset, which must not have its
 * generation numbers aliased with those of that tasks previous cpuset.
 *
 * Generations are needed for mems_allowed because one task cannot
 * modify anothers memory placement.  So we must enable every task,
 * on every visit to __alloc_pages(), to efficiently check whether
 * its current->cpuset->mems_allowed has changed, requiring an update
 * of its current->mems_allowed.
 */
static atomic_t cpuset_mems_generation = ATOMIC_INIT(1);

static struct cpuset top_cpuset = {
	.flags = ((1 << CS_CPU_EXCLUSIVE) | (1 << CS_MEM_EXCLUSIVE)),
	.cpus_allowed = CPU_MASK_ALL,
	.mems_allowed = NODE_MASK_ALL,
	.count = ATOMIC_INIT(0),
	.sibling = LIST_HEAD_INIT(top_cpuset.sibling),
	.children = LIST_HEAD_INIT(top_cpuset.children),
	.parent = NULL,
	.dentry = NULL,
	.mems_generation = 0,
};

static struct vfsmount *cpuset_mount;
static struct super_block *cpuset_sb = NULL;

/*
 * cpuset_sem should be held by anyone who is depending on the children
 * or sibling lists of any cpuset, or performing non-atomic operations
 * on the flags or *_allowed values of a cpuset, such as raising the
 * CS_REMOVED flag bit iff it is not already raised, or reading and
 * conditionally modifying the *_allowed values.  One kernel global
 * cpuset semaphore should be sufficient - these things don't change
 * that much.
 *
 * The code that modifies cpusets holds cpuset_sem across the entire
 * operation, from cpuset_common_file_write() down, single threading
 * all cpuset modifications (except for counter manipulations from
 * fork and exit) across the system.  This presumes that cpuset
 * modifications are rare - better kept simple and safe, even if slow.
 *
 * The code that reads cpusets, such as in cpuset_common_file_read()
 * and below, only holds cpuset_sem across small pieces of code, such
 * as when reading out possibly multi-word cpumasks and nodemasks, as
 * the risks are less, and the desire for performance a little greater.
 * The proc_cpuset_show() routine needs to hold cpuset_sem to insure
 * that no cs->dentry is NULL, as it walks up the cpuset tree to root.
 *
 * The hooks from fork and exit, cpuset_fork() and cpuset_exit(), don't
 * (usually) grab cpuset_sem.  These are the two most performance
 * critical pieces of code here.  The exception occurs on exit(),
 * when a task in a notify_on_release cpuset exits.  Then cpuset_sem
 * is taken, and if the cpuset count is zero, a usermode call made
 * to /sbin/cpuset_release_agent with the name of the cpuset (path
 * relative to the root of cpuset file system) as the argument.
 *
 * A cpuset can only be deleted if both its 'count' of using tasks is
 * zero, and its list of 'children' cpusets is empty.  Since all tasks
 * in the system use _some_ cpuset, and since there is always at least
 * one task in the system (init, pid == 1), therefore, top_cpuset
 * always has either children cpusets and/or using tasks.  So no need
 * for any special hack to ensure that top_cpuset cannot be deleted.
 */

static DECLARE_MUTEX(cpuset_sem);
static struct task_struct *cpuset_sem_owner;
static int cpuset_sem_depth;

/*
 * The global cpuset semaphore cpuset_sem can be needed by the
 * memory allocator to update a tasks mems_allowed (see the calls
 * to cpuset_update_current_mems_allowed()) or to walk up the
 * cpuset hierarchy to find a mem_exclusive cpuset see the calls
 * to cpuset_excl_nodes_overlap()).
 *
 * But if the memory allocation is being done by cpuset.c code, it
 * usually already holds cpuset_sem.  Double tripping on a kernel
 * semaphore deadlocks the current task, and any other task that
 * subsequently tries to obtain the lock.
 *
 * Run all up's and down's on cpuset_sem through the following
 * wrappers, which will detect this nested locking, and avoid
 * deadlocking.
 */

static inline void cpuset_down(struct semaphore *psem)
{
	if (cpuset_sem_owner != current) {
		down(psem);
		cpuset_sem_owner = current;
	}
	cpuset_sem_depth++;
}

static inline void cpuset_up(struct semaphore *psem)
{
	if (--cpuset_sem_depth == 0) {
		cpuset_sem_owner = NULL;
		up(psem);
	}
}

/*
 * A couple of forward declarations required, due to cyclic reference loop:
 *  cpuset_mkdir -> cpuset_create -> cpuset_populate_dir -> cpuset_add_file
 *  -> cpuset_create_file -> cpuset_dir_inode_operations -> cpuset_mkdir.
 */

static int cpuset_mkdir(struct inode *dir, struct dentry *dentry, int mode);
static int cpuset_rmdir(struct inode *unused_dir, struct dentry *dentry);

static struct backing_dev_info cpuset_backing_dev_info = {
	.ra_pages = 0,		/* No readahead */
	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
};

static struct inode *cpuset_new_inode(mode_t mode)
{
	struct inode *inode = new_inode(cpuset_sb);

	if (inode) {
		inode->i_mode = mode;
		inode->i_uid = current->fsuid;
		inode->i_gid = current->fsgid;
		inode->i_blksize = PAGE_CACHE_SIZE;
		inode->i_blocks = 0;
		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
		inode->i_mapping->backing_dev_info = &cpuset_backing_dev_info;
	}
	return inode;
}

static void cpuset_diput(struct dentry *dentry, struct inode *inode)
{
	/* is dentry a directory ? if so, kfree() associated cpuset */
	if (S_ISDIR(inode->i_mode)) {
		struct cpuset *cs = dentry->d_fsdata;
		BUG_ON(!(is_removed(cs)));
		kfree(cs);
	}
	iput(inode);
}

static struct dentry_operations cpuset_dops = {
	.d_iput = cpuset_diput,
};

static struct dentry *cpuset_get_dentry(struct dentry *parent, const char *name)
{
	struct dentry *d = lookup_one_len(name, parent, strlen(name));
	if (!IS_ERR(d))
		d->d_op = &cpuset_dops;
	return d;
}

static void remove_dir(struct dentry *d)
{
	struct dentry *parent = dget(d->d_parent);

	d_delete(d);
	simple_rmdir(parent->d_inode, d);
	dput(parent);
}

/*
 * NOTE : the dentry must have been dget()'ed
 */
static void cpuset_d_remove_dir(struct dentry *dentry)
{
	struct list_head *node;

	spin_lock(&dcache_lock);
	node = dentry->d_subdirs.next;
	while (node != &dentry->d_subdirs) {
		struct dentry *d = list_entry(node, struct dentry, d_child);
		list_del_init(node);
		if (d->d_inode) {
			d = dget_locked(d);
			spin_unlock(&dcache_lock);
			d_delete(d);
			simple_unlink(dentry->d_inode, d);
			dput(d);
			spin_lock(&dcache_lock);
		}
		node = dentry->d_subdirs.next;
	}
	list_del_init(&dentry->d_child);
	spin_unlock(&dcache_lock);
	remove_dir(dentry);
}

static struct super_operations cpuset_ops = {
	.statfs = simple_statfs,
	.drop_inode = generic_delete_inode,
};

static int cpuset_fill_super(struct super_block *sb, void *unused_data,
							int unused_silent)
{
	struct inode *inode;
	struct dentry *root;

	sb->s_blocksize = PAGE_CACHE_SIZE;
	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
	sb->s_magic = CPUSET_SUPER_MAGIC;
	sb->s_op = &cpuset_ops;
	cpuset_sb = sb;

	inode = cpuset_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR);
	if (inode) {
		inode->i_op = &simple_dir_inode_operations;
		inode->i_fop = &simple_dir_operations;
		/* directories start off with i_nlink == 2 (for "." entry) */
		inode->i_nlink++;
	} else {
		return -ENOMEM;
	}

	root = d_alloc_root(inode);
	if (!root) {
		iput(inode);
		return -ENOMEM;
	}
	sb->s_root = root;
	return 0;
}

static struct super_block *cpuset_get_sb(struct file_system_type *fs_type,
					int flags, const char *unused_dev_name,
					void *data)
{
	return get_sb_single(fs_type, flags, data, cpuset_fill_super);
}

static struct file_system_type cpuset_fs_type = {
	.name = "cpuset",
	.get_sb = cpuset_get_sb,
	.kill_sb = kill_litter_super,
};

/* struct cftype:
 *
 * The files in the cpuset filesystem mostly have a very simple read/write
 * handling, some common function will take care of it. Nevertheless some cases
 * (read tasks) are special and therefore I define this structure for every
 * kind of file.
 *
 *
 * When reading/writing to a file:
 *	- the cpuset to use in file->f_dentry->d_parent->d_fsdata
 *	- the 'cftype' of the file is file->f_dentry->d_fsdata
 */

struct cftype {
	char *name;
	int private;
	int (*open) (struct inode *inode, struct file *file);
	ssize_t (*read) (struct file *file, char __user *buf, size_t nbytes,
							loff_t *ppos);
	int (*write) (struct file *file, const char __user *buf, size_t nbytes,
							loff_t *ppos);
	int (*release) (struct inode *inode, struct file *file);
};

static inline struct cpuset *__d_cs(struct dentry *dentry)
{
	return dentry->d_fsdata;
}

static inline struct cftype *__d_cft(struct dentry *dentry)
{
	return dentry->d_fsdata;
}

/*
 * Call with cpuset_sem held.  Writes path of cpuset into buf.
 * Returns 0 on success, -errno on error.
 */

static int cpuset_path(const struct cpuset *cs, char *buf, int buflen)
{
	char *start;

	start = buf + buflen;

	*--start = '\0';
	for (;;) {
		int len = cs->dentry->d_name.len;
		if ((start -= len) < buf)
			return -ENAMETOOLONG;
		memcpy(start, cs->dentry->d_name.name, len);
		cs = cs->parent;
		if (!cs)
			break;
		if (!cs->parent)
			continue;
		if (--start < buf)
			return -ENAMETOOLONG;
		*start = '/';
	}
	memmove(buf, start, buf + buflen - start);
	return 0;
}

/*
 * Notify userspace when a cpuset is released, by running
 * /sbin/cpuset_release_agent with the name of the cpuset (path
 * relative to the root of cpuset file system) as the argument.
 *
 * Most likely, this user command will try to rmdir this cpuset.
 *
 * This races with the possibility that some other task will be
 * attached to this cpuset before it is removed, or that some other
 * user task will 'mkdir' a child cpuset of this cpuset.  That's ok.
 * The presumed 'rmdir' will fail quietly if this cpuset is no longer
 * unused, and this cpuset will be reprieved from its death sentence,
 * to continue to serve a useful existence.  Next time it's released,
 * we will get notified again, if it still has 'notify_on_release' set.
 *
 * The final arg to call_usermodehelper() is 0, which means don't
 * wait.  The separate /sbin/cpuset_release_agent task is forked by
 * call_usermodehelper(), then control in this thread returns here,
 * without waiting for the release agent task.  We don't bother to
 * wait because the caller of this routine has no use for the exit
 * status of the /sbin/cpuset_release_agent task, so no sense holding
 * our caller up for that.
 *
 * The simple act of forking that task might require more memory,
 * which might need cpuset_sem.  So this routine must be called while
 * cpuset_sem is not held, to avoid a possible deadlock.  See also
 * comments for check_for_release(), below.
 */

static void cpuset_release_agent(const char *pathbuf)
{
	char *argv[3], *envp[3];
	int i;

	if (!pathbuf)
		return;

	i = 0;
	argv[i++] = "/sbin/cpuset_release_agent";
	argv[i++] = (char *)pathbuf;
	argv[i] = NULL;

	i = 0;
	/* minimal command environment */
	envp[i++] = "HOME=/";
	envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
	envp[i] = NULL;

	call_usermodehelper(argv[0], argv, envp, 0);
	kfree(pathbuf);
}

/*
 * Either cs->count of using tasks transitioned to zero, or the
 * cs->children list of child cpusets just became empty.  If this
 * cs is notify_on_release() and now both the user count is zero and
 * the list of children is empty, prepare cpuset path in a kmalloc'd
 * buffer, to be returned via ppathbuf, so that the caller can invoke
 * cpuset_release_agent() with it later on, once cpuset_sem is dropped.
 * Call here with cpuset_sem held.
 *
 * This check_for_release() routine is responsible for kmalloc'ing
 * pathbuf.  The above cpuset_release_agent() is responsible for
 * kfree'ing pathbuf.  The caller of these routines is responsible
 * for providing a pathbuf pointer, initialized to NULL, then
 * calling check_for_release() with cpuset_sem held and the address
 * of the pathbuf pointer, then dropping cpuset_sem, then calling
 * cpuset_release_agent() with pathbuf, as set by check_for_release().
 */

static void check_for_release(struct cpuset *cs, char **ppathbuf)
{
	if (notify_on_release(cs) && atomic_read(&cs->count) == 0 &&
	    list_empty(&cs->children)) {
		char *buf;

		buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
		if (!buf)
			return;
		if (cpuset_path(cs, buf, PAGE_SIZE) < 0)
			kfree(buf);
		else
			*ppathbuf = buf;
	}
}

/*
 * Return in *pmask the portion of a cpusets's cpus_allowed that
 * are online.  If none are online, walk up the cpuset hierarchy
 * until we find one that does have some online cpus.  If we get
 * all the way to the top and still haven't found any online cpus,
 * return cpu_online_map.  Or if passed a NULL cs from an exit'ing
 * task, return cpu_online_map.
 *
 * One way or another, we guarantee to return some non-empty subset
 * of cpu_online_map.
 *
 * Call with cpuset_sem held.
 */

static void guarantee_online_cpus(const struct cpuset *cs, cpumask_t *pmask)
{
	while (cs && !cpus_intersects(cs->cpus_allowed, cpu_online_map))
		cs = cs->parent;
	if (cs)
		cpus_and(*pmask, cs->cpus_allowed, cpu_online_map);
	else
		*pmask = cpu_online_map;
	BUG_ON(!cpus_intersects(*pmask, cpu_online_map));
}

/*
 * Return in *pmask the portion of a cpusets's mems_allowed that
 * are online.  If none are online, walk up the cpuset hierarchy
 * until we find one that does have some online mems.  If we get
 * all the way to the top and still haven't found any online mems,
 * return node_online_map.
 *
 * One way or another, we guarantee to return some non-empty subset
 * of node_online_map.
 *
 * Call with cpuset_sem held.
 */

static void guarantee_online_mems(const struct cpuset *cs, nodemask_t *pmask)
{
	while (cs && !nodes_intersects(cs->mems_allowed, node_online_map))
		cs = cs->parent;
	if (cs)
		nodes_and(*pmask, cs->mems_allowed, node_online_map);
	else
		*pmask = node_online_map;
	BUG_ON(!nodes_intersects(*pmask, node_online_map));
}

/*
 * Refresh current tasks mems_allowed and mems_generation from
 * current tasks cpuset.  Call with cpuset_sem held.
 *
 * This routine is needed to update the per-task mems_allowed
 * data, within the tasks context, when it is trying to allocate
 * memory (in various mm/mempolicy.c routines) and notices
 * that some other task has been modifying its cpuset.
 */

static void refresh_mems(void)
{
	struct cpuset *cs = current->cpuset;

	if (current->cpuset_mems_generation != cs->mems_generation) {
		guarantee_online_mems(cs, &current->mems_allowed);
		current->cpuset_mems_generation = cs->mems_generation;
	}
}

/*
 * is_cpuset_subset(p, q) - Is cpuset p a subset of cpuset q?
 *
 * One cpuset is a subset of another if all its allowed CPUs and
 * Memory Nodes are a subset of the other, and its exclusive flags
 * are only set if the other's are set.
 */

static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
{
	return	cpus_subset(p->cpus_allowed, q->cpus_allowed) &&
		nodes_subset(p->mems_allowed, q->mems_allowed) &&
		is_cpu_exclusive(p) <= is_cpu_exclusive(q) &&
		is_mem_exclusive(p) <= is_mem_exclusive(q);
}

/*
 * validate_change() - Used to validate that any proposed cpuset change
 *		       follows the structural rules for cpusets.
 *
 * If we replaced the flag and mask values of the current cpuset
 * (cur) with those values in the trial cpuset (trial), would
 * our various subset and exclusive rules still be valid?  Presumes
 * cpuset_sem held.
 *
 * 'cur' is the address of an actual, in-use cpuset.  Operations
 * such as list traversal that depend on the actual address of the
 * cpuset in the list must use cur below, not trial.
 *
 * 'trial' is the address of bulk structure copy of cur, with
 * perhaps one or more of the fields cpus_allowed, mems_allowed,
 * or flags changed to new, trial values.
 *
 * Return 0 if valid, -errno if not.
 */

static int validate_change(const struct cpuset *cur, const struct cpuset *trial)
{
	struct cpuset *c, *par;

	/* Each of our child cpusets must be a subset of us */
	list_for_each_entry(c, &cur->children, sibling) {
		if (!is_cpuset_subset(c, trial))
			return -EBUSY;
	}

	/* Remaining checks don't apply to root cpuset */
	if ((par = cur->parent) == NULL)
		return 0;

	/* We must be a subset of our parent cpuset */
	if (!is_cpuset_subset(trial, par))
		return -EACCES;

	/* If either I or some sibling (!= me) is exclusive, we can't overlap */
	list_for_each_entry(c, &par->children, sibling) {
		if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
		    c != cur &&
		    cpus_intersects(trial->cpus_allowed, c->cpus_allowed))
			return -EINVAL;
		if ((is_mem_exclusive(trial) || is_mem_exclusive(c)) &&
		    c != cur &&
		    nodes_intersects(trial->mems_allowed, c->mems_allowed))
			return -EINVAL;
	}

	return 0;
}

/*
 * For a given cpuset cur, partition the system as follows
 * a. All cpus in the parent cpuset's cpus_allowed that are not part of any
 *    exclusive child cpusets
 * b. All cpus in the current cpuset's cpus_allowed that are not part of any
 *    exclusive child cpusets
 * Build these two partitions by calling partition_sched_domains
 *
 * Call with cpuset_sem held.  May nest a call to the
 * lock_cpu_hotplug()/unlock_cpu_hotplug() pair.
 */

static void update_cpu_domains(struct cpuset *cur)
{
	struct cpuset *c, *par = cur->parent;
	cpumask_t pspan, cspan;

	if (par == NULL || cpus_empty(cur->cpus_allowed))
		return;

	/*
	 * Get all cpus from parent's cpus_allowed not part of exclusive
	 * children
	 */
	pspan = par->cpus_allowed;
	list_for_each_entry(c, &par->children, sibling) {
		if (is_cpu_exclusive(c))
			cpus_andnot(pspan, pspan, c->cpus_allowed);
	}
	if (is_removed(cur) || !is_cpu_exclusive(cur)) {
		cpus_or(pspan, pspan, cur->cpus_allowed);
		if (cpus_equal(pspan, cur->cpus_allowed))
			return;
		cspan = CPU_MASK_NONE;
	} else {
		if (cpus_empty(pspan))
			return;
		cspan = cur->cpus_allowed;
		/*
		 * Get all cpus from current cpuset's cpus_allowed not part
		 * of exclusive children
		 */
		list_for_each_entry(c, &cur->children, sibling) {
			if (is_cpu_exclusive(c))
				cpus_andnot(cspan, cspan, c->cpus_allowed);
		}
	}

	lock_cpu_hotplug();
	partition_sched_domains(&pspan, &cspan);
	unlock_cpu_hotplug();
}

static int update_cpumask(struct cpuset *cs, char *buf)
{
	struct cpuset trialcs;
	int retval, cpus_unchanged;

	trialcs = *cs;
	retval = cpulist_parse(buf, trialcs.cpus_allowed);
	if (retval < 0)
		return retval;
	cpus_and(trialcs.cpus_allowed, trialcs.cpus_allowed, cpu_online_map);
	if (cpus_empty(trialcs.cpus_allowed))
		return -ENOSPC;
	retval = validate_change(cs, &trialcs);
	if (retval < 0)
		return retval;
	cpus_unchanged = cpus_equal(cs->cpus_allowed, trialcs.cpus_allowed);
	cs->cpus_allowed = trialcs.cpus_allowed;
	if (is_cpu_exclusive(cs) && !cpus_unchanged)
		update_cpu_domains(cs);
	return 0;
}

static int update_nodemask(struct cpuset *cs, char *buf)
{
	struct cpuset trialcs;
	int retval;

	trialcs = *cs;
	retval = nodelist_parse(buf, trialcs.mems_allowed);
	if (retval < 0)
		return retval;
	nodes_and(trialcs.mems_allowed, trialcs.mems_allowed, node_online_map);
	if (nodes_empty(trialcs.mems_allowed))
		return -ENOSPC;
	retval = validate_change(cs, &trialcs);
	if (retval == 0) {
		cs->mems_allowed = trialcs.mems_allowed;
		atomic_inc(&cpuset_mems_generation);
		cs->mems_generation = atomic_read(&cpuset_mems_generation);
	}
	return retval;
}

/*
 * update_flag - read a 0 or a 1 in a file and update associated flag
 * bit:	the bit to update (CS_CPU_EXCLUSIVE, CS_MEM_EXCLUSIVE,
 *						CS_NOTIFY_ON_RELEASE)
 * cs:	the cpuset to update
 * buf:	the buffer where we read the 0 or 1
 */

static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, char *buf)
{
	int turning_on;
	struct cpuset trialcs;
	int err, cpu_exclusive_changed;

	turning_on = (simple_strtoul(buf, NULL, 10) != 0);

	trialcs = *cs;
	if (turning_on)
		set_bit(bit, &trialcs.flags);
	else
		clear_bit(bit, &trialcs.flags);

	err = validate_change(cs, &trialcs);
	if (err < 0)
		return err;
	cpu_exclusive_changed =
		(is_cpu_exclusive(cs) != is_cpu_exclusive(&trialcs));
	if (turning_on)
		set_bit(bit, &cs->flags);
	else
		clear_bit(bit, &cs->flags);

	if (cpu_exclusive_changed)
                update_cpu_domains(cs);
	return 0;
}

static int attach_task(struct cpuset *cs, char *pidbuf, char **ppathbuf)
{
	pid_t pid;
	struct task_struct *tsk;
	struct cpuset *oldcs;
	cpumask_t cpus;

	if (sscanf(pidbuf, "%d", &pid) != 1)
		return -EIO;
	if (cpus_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
		return -ENOSPC;

	if (pid) {
		read_lock(&tasklist_lock);

		tsk = find_task_by_pid(pid);
		if (!tsk) {
			read_unlock(&tasklist_lock);
			return -ESRCH;
		}

		get_task_struct(tsk);
		read_unlock(&tasklist_lock);

		if ((current->euid) && (current->euid != tsk->uid)
		    && (current->euid != tsk->suid)) {
			put_task_struct(tsk);
			return -EACCES;
		}
	} else {
		tsk = current;
		get_task_struct(tsk);
	}

	task_lock(tsk);
	oldcs = tsk->cpuset;
	if (!oldcs) {
		task_unlock(tsk);
		put_task_struct(tsk);
		return -ESRCH;
	}
	atomic_inc(&cs->count);
	tsk->cpuset = cs;
	task_unlock(tsk);

	guarantee_online_cpus(cs, &cpus);
	set_cpus_allowed(tsk, cpus);

	put_task_struct(tsk);
	if (atomic_dec_and_test(&oldcs->count))
		check_for_release(oldcs, ppathbuf);
	return 0;
}

/* The various types of files and directories in a cpuset file system */

typedef enum {
	FILE_ROOT,
	FILE_DIR,
	FILE_CPULIST,
	FILE_MEMLIST,
	FILE_CPU_EXCLUSIVE,
	FILE_MEM_EXCLUSIVE,
	FILE_NOTIFY_ON_RELEASE,
	FILE_TASKLIST,
} cpuset_filetype_t;

static ssize_t cpuset_common_file_write(struct file *file, const char __user *userbuf,
					size_t nbytes, loff_t *unused_ppos)
{
	struct cpuset *cs = __d_cs(file->f_dentry->d_parent);
	struct cftype *cft = __d_cft(file->f_dentry);
	cpuset_filetype_t type = cft->private;
	char *buffer;
	char *pathbuf = NULL;
	int retval = 0;

	/* Crude upper limit on largest legitimate cpulist user might write. */
	if (nbytes > 100 + 6 * NR_CPUS)
		return -E2BIG;

	/* +1 for nul-terminator */
	if ((buffer = kmalloc(nbytes + 1, GFP_KERNEL)) == 0)
		return -ENOMEM;

	if (copy_from_user(buffer, userbuf, nbytes)) {
		retval = -EFAULT;
		goto out1;
	}
	buffer[nbytes] = 0;	/* nul-terminate */

	cpuset_down(&cpuset_sem);

	if (is_removed(cs)) {
		retval = -ENODEV;
		goto out2;
	}

	switch (type) {
	case FILE_CPULIST:
		retval = update_cpumask(cs, buffer);
		break;
	case FILE_MEMLIST:
		retval = update_nodemask(cs, buffer);
		break;
	case FILE_CPU_EXCLUSIVE:
		retval = update_flag(CS_CPU_EXCLUSIVE, cs, buffer);
		break;
	case FILE_MEM_EXCLUSIVE:
		retval = update_flag(CS_MEM_EXCLUSIVE, cs, buffer);
		break;
	case FILE_NOTIFY_ON_RELEASE:
		retval = update_flag(CS_NOTIFY_ON_RELEASE, cs, buffer);
		break;
	case FILE_TASKLIST:
		retval = attach_task(cs, buffer, &pathbuf);
		break;
	default:
		retval = -EINVAL;
		goto out2;
	}

	if (retval == 0)
		retval = nbytes;
out2:
	cpuset_up(&cpuset_sem);
	cpuset_release_agent(pathbuf);
out1:
	kfree(buffer);
	return retval;
}

static ssize_t cpuset_file_write(struct file *file, const char __user *buf,
						size_t nbytes, loff_t *ppos)
{
	ssize_t retval = 0;
	struct cftype *cft = __d_cft(file->f_dentry);
	if (!cft)
		return -ENODEV;

	/* special function ? */
	if (cft->write)
		retval = cft->write(file, buf, nbytes, ppos);
	else
		retval = cpuset_common_file_write(file, buf, nbytes, ppos);

	return retval;
}

/*
 * These ascii lists should be read in a single call, by using a user
 * buffer large enough to hold the entire map.  If read in smaller
 * chunks, there is no guarantee of atomicity.  Since the display format
 * used, list of ranges of sequential numbers, is variable length,
 * and since these maps can change value dynamically, one could read
 * gibberish by doing partial reads while a list was changing.
 * A single large read to a buffer that crosses a page boundary is
 * ok, because the result being copied to user land is not recomputed
 * across a page fault.
 */

static int cpuset_sprintf_cpulist(char *page, struct cpuset *cs)
{
	cpumask_t mask;

	cpuset_down(&cpuset_sem);
	mask = cs->cpus_allowed;
	cpuset_up(&cpuset_sem);

	return cpulist_scnprintf(page, PAGE_SIZE, mask);
}

static int cpuset_sprintf_memlist(char *page, struct cpuset *cs)
{
	nodemask_t mask;

	cpuset_down(&cpuset_sem);
	mask = cs->mems_allowed;
	cpuset_up(&cpuset_sem);

	return nodelist_scnprintf(page, PAGE_SIZE, mask);
}

static ssize_t cpuset_common_file_read(struct file *file, char __user *buf,
				size_t nbytes, loff_t *ppos)
{
	struct cftype *cft = __d_cft(file->f_dentry);
	struct cpuset *cs = __d_cs(file->f_dentry->d_parent);
	cpuset_filetype_t type = cft->private;
	char *page;
	ssize_t retval = 0;
	char *s;
	char *start;
	ssize_t n;

	if (!(page = (char *)__get_free_page(GFP_KERNEL)))
		return -ENOMEM;

	s = page;

	switch (type) {
	case FILE_CPULIST:
		s += cpuset_sprintf_cpulist(s, cs);
		break;
	case FILE_MEMLIST:
		s += cpuset_sprintf_memlist(s, cs);
		break;
	case FILE_CPU_EXCLUSIVE:
		*s++ = is_cpu_exclusive(cs) ? '1' : '0';
		break;
	case FILE_MEM_EXCLUSIVE:
		*s++ = is_mem_exclusive(cs) ? '1' : '0';
		break;
	case FILE_NOTIFY_ON_RELEASE:
		*s++ = notify_on_release(cs) ? '1' : '0';
		break;
	default:
		retval = -EINVAL;
		goto out;
	}
	*s++ = '\n';
	*s = '\0';

	start = page + *ppos;
	n = s - start;

	/* Do nothing if *ppos is at the eof or beyond the eof. */
	if (n <= 0)
		goto out;

	retval = n - copy_to_user(buf, start, min(n, nbytes));
	*ppos += retval;
out:
	free_page((unsigned long)page);
	return retval;
}

static ssize_t cpuset_file_read(struct file *file, char __user *buf, size_t nbytes,
								loff_t *ppos)
{
	ssize_t retval = 0;
	struct cftype *cft = __d_cft(file->f_dentry);
	if (!cft)
		return -ENODEV;

	/* special function ? */
	if (cft->read)
		retval = cft->read(file, buf, nbytes, ppos);
	else
		retval = cpuset_common_file_read(file, buf, nbytes, ppos);

	return retval;
}

static int cpuset_file_open(struct inode *inode, struct file *file)
{
	int err;
	struct cftype *cft;

	err = generic_file_open(inode, file);
	if (err)
		return err;

	cft = __d_cft(file->f_dentry);
	if (!cft)
		return -ENODEV;
	if (cft->open)
		err = cft->open(inode, file);
	else
		err = 0;

	return err;
}

static int cpuset_file_release(struct inode *inode, struct file *file)
{
	struct cftype *cft = __d_cft(file->f_dentry);
	if (cft->release)
		return cft->release(inode, file);
	return 0;
}

static struct file_operations cpuset_file_operations = {
	.read = cpuset_file_read,
	.write = cpuset_file_write,
	.llseek = generic_file_llseek,
	.open = cpuset_file_open,
	.release = cpuset_file_release,
};

static struct inode_operations cpuset_dir_inode_operations = {
	.lookup = simple_lookup,
	.mkdir = cpuset_mkdir,
	.rmdir = cpuset_rmdir,
};

static int cpuset_create_file(struct dentry *dentry, int mode)
{
	struct inode *inode;

	if (!dentry)
		return -ENOENT;
	if (dentry->d_inode)
		return -EEXIST;

	inode = cpuset_new_inode(mode);
	if (!inode)
		return -ENOMEM;

	if (S_ISDIR(mode)) {
		inode->i_op = &cpuset_dir_inode_operations;
		inode->i_fop = &simple_dir_operations;

		/* start off with i_nlink == 2 (for "." entry) */
		inode->i_nlink++;
	} else if (S_ISREG(mode)) {
		inode->i_size = 0;
		inode->i_fop = &cpuset_file_operations;
	}

	d_instantiate(dentry, inode);
	dget(dentry);	/* Extra count - pin the dentry in core */
	return 0;
}

/*
 *	cpuset_create_dir - create a directory for an object.
 *	cs: 	the cpuset we create the directory for.
 *		It must have a valid ->parent field
 *		And we are going to fill its ->dentry field.
 *	name:	The name to give to the cpuset directory. Will be copied.
 *	mode:	mode to set on new directory.
 */

static int cpuset_create_dir(struct cpuset *cs, const char *name, int mode)
{
	struct dentry *dentry = NULL;
	struct dentry *parent;
	int error = 0;

	parent = cs->parent->dentry;
	dentry = cpuset_get_dentry(parent, name);
	if (IS_ERR(dentry))
		return PTR_ERR(dentry);
	error = cpuset_create_file(dentry, S_IFDIR | mode);
	if (!error) {
		dentry->d_fsdata = cs;
		parent->d_inode->i_nlink++;
		cs->dentry = dentry;
	}
	dput(dentry);

	return error;
}

static int cpuset_add_file(struct dentry *dir, const struct cftype *cft)
{
	struct dentry *dentry;
	int error;

	down(&dir->d_inode->i_sem);
	dentry = cpuset_get_dentry(dir, cft->name);
	if (!IS_ERR(dentry)) {
		error = cpuset_create_file(dentry, 0644 | S_IFREG);
		if (!error)
			dentry->d_fsdata = (void *)cft;
		dput(dentry);
	} else
		error = PTR_ERR(dentry);
	up(&dir->d_inode->i_sem);
	return error;
}

/*
 * Stuff for reading the 'tasks' file.
 *
 * Reading this file can return large amounts of data if a cpuset has
 * *lots* of attached tasks. So it may need several calls to read(),
 * but we cannot guarantee that the information we produce is correct
 * unless we produce it entirely atomically.
 *
 * Upon tasks file open(), a struct ctr_struct is allocated, that
 * will have a pointer to an array (also allocated here).  The struct
 * ctr_struct * is stored in file->private_data.  Its resources will
 * be freed by release() when the file is closed.  The array is used
 * to sprintf the PIDs and then used by read().
 */

/* cpusets_tasks_read array */

struct ctr_struct {
	char *buf;
	int bufsz;
};

/*
 * Load into 'pidarray' up to 'npids' of the tasks using cpuset 'cs'.
 * Return actual number of pids loaded.
 */
static inline int pid_array_load(pid_t *pidarray, int npids, struct cpuset *cs)
{
	int n = 0;
	struct task_struct *g, *p;

	read_lock(&tasklist_lock);

	do_each_thread(g, p) {
		if (p->cpuset == cs) {
			pidarray[n++] = p->pid;
			if (unlikely(n == npids))
				goto array_full;
		}
	} while_each_thread(g, p);

array_full:
	read_unlock(&tasklist_lock);
	return n;
}

static int cmppid(const void *a, const void *b)
{
	return *(pid_t *)a - *(pid_t *)b;
}

/*
 * Convert array 'a' of 'npids' pid_t's to a string of newline separated
 * decimal pids in 'buf'.  Don't write more than 'sz' chars, but return
 * count 'cnt' of how many chars would be written if buf were large enough.
 */
static int pid_array_to_buf(char *buf, int sz, pid_t *a, int npids)
{
	int cnt = 0;
	int i;

	for (i = 0; i < npids; i++)
		cnt += snprintf(buf + cnt, max(sz - cnt, 0), "%d\n", a[i]);
	return cnt;
}

static int cpuset_tasks_open(struct inode *unused, struct file *file)
{
	struct cpuset *cs = __d_cs(file->f_dentry->d_parent);
	struct ctr_struct *ctr;
	pid_t *pidarray;
	int npids;
	char c;

	if (!(file->f_mode & FMODE_READ))
		return 0;

	ctr = kmalloc(sizeof(*ctr), GFP_KERNEL);
	if (!ctr)
		goto err0;

	/*
	 * If cpuset gets more users after we read count, we won't have
	 * enough space - tough.  This race is indistinguishable to the
	 * caller from the case that the additional cpuset users didn't
	 * show up until sometime later on.
	 */
	npids = atomic_read(&cs->count);
	pidarray = kmalloc(npids * sizeof(pid_t), GFP_KERNEL);
	if (!pidarray)
		goto err1;

	npids = pid_array_load(pidarray, npids, cs);
	sort(pidarray, npids, sizeof(pid_t), cmppid, NULL);

	/* Call pid_array_to_buf() twice, first just to get bufsz */
	ctr->bufsz = pid_array_to_buf(&c, sizeof(c), pidarray, npids) + 1;
	ctr->buf = kmalloc(ctr->bufsz, GFP_KERNEL);
	if (!ctr->buf)
		goto err2;
	ctr->bufsz = pid_array_to_buf(ctr->buf, ctr->bufsz, pidarray, npids);

	kfree(pidarray);
	file->private_data = ctr;
	return 0;

err2:
	kfree(pidarray);
err1:
	kfree(ctr);
err0:
	return -ENOMEM;
}

static ssize_t cpuset_tasks_read(struct file *file, char __user *buf,
						size_t nbytes, loff_t *ppos)
{
	struct ctr_struct *ctr = file->private_data;

	if (*ppos + nbytes > ctr->bufsz)
		nbytes = ctr->bufsz - *ppos;
	if (copy_to_user(buf, ctr->buf + *ppos, nbytes))
		return -EFAULT;
	*ppos += nbytes;
	return nbytes;
}

static int cpuset_tasks_release(struct inode *unused_inode, struct file *file)
{
	struct ctr_struct *ctr;

	if (file->f_mode & FMODE_READ) {
		ctr = file->private_data;
		kfree(ctr->buf);
		kfree(ctr);
	}
	return 0;
}

/*
 * for the common functions, 'private' gives the type of file
 */

static struct cftype cft_tasks = {
	.name = "tasks",
	.open = cpuset_tasks_open,
	.read = cpuset_tasks_read,
	.release = cpuset_tasks_release,
	.private = FILE_TASKLIST,
};

static struct cftype cft_cpus = {
	.name = "cpus",
	.private = FILE_CPULIST,
};

static struct cftype cft_mems = {
	.name = "mems",
	.private = FILE_MEMLIST,
};

static struct cftype cft_cpu_exclusive = {
	.name = "cpu_exclusive",
	.private = FILE_CPU_EXCLUSIVE,
};

static struct cftype cft_mem_exclusive = {
	.name = "mem_exclusive",
	.private = FILE_MEM_EXCLUSIVE,
};

static struct cftype cft_notify_on_release = {
	.name = "notify_on_release",
	.private = FILE_NOTIFY_ON_RELEASE,
};

static int cpuset_populate_dir(struct dentry *cs_dentry)
{
	int err;

	if ((err = cpuset_add_file(cs_dentry, &cft_cpus)) < 0)
		return err;
	if ((err = cpuset_add_file(cs_dentry, &cft_mems)) < 0)
		return err;
	if ((err = cpuset_add_file(cs_dentry, &cft_cpu_exclusive)) < 0)
		return err;
	if ((err = cpuset_add_file(cs_dentry, &cft_mem_exclusive)) < 0)
		return err;
	if ((err = cpuset_add_file(cs_dentry, &cft_notify_on_release)) < 0)
		return err;
	if ((err = cpuset_add_file(cs_dentry, &cft_tasks)) < 0)
		return err;
	return 0;
}

/*
 *	cpuset_create - create a cpuset
 *	parent:	cpuset that will be parent of the new cpuset.
 *	name:		name of the new cpuset. Will be strcpy'ed.
 *	mode:		mode to set on new inode
 *
 *	Must be called with the semaphore on the parent inode held
 */

static long cpuset_create(struct cpuset *parent, const char *name, int mode)
{
	struct cpuset *cs;
	int err;

	cs = kmalloc(sizeof(*cs), GFP_KERNEL);
	if (!cs)
		return -ENOMEM;

	cpuset_down(&cpuset_sem);
	cs->flags = 0;
	if (notify_on_release(parent))
		set_bit(CS_NOTIFY_ON_RELEASE, &cs->flags);
	cs->cpus_allowed = CPU_MASK_NONE;
	cs->mems_allowed = NODE_MASK_NONE;
	atomic_set(&cs->count, 0);
	INIT_LIST_HEAD(&cs->sibling);
	INIT_LIST_HEAD(&cs->children);
	atomic_inc(&cpuset_mems_generation);
	cs->mems_generation = atomic_read(&cpuset_mems_generation);

	cs->parent = parent;

	list_add(&cs->sibling, &cs->parent->children);

	err = cpuset_create_dir(cs, name, mode);
	if (err < 0)
		goto err;

	/*
	 * Release cpuset_sem before cpuset_populate_dir() because it
	 * will down() this new directory's i_sem and if we race with
	 * another mkdir, we might deadlock.
	 */
	cpuset_up(&cpuset_sem);

	err = cpuset_populate_dir(cs->dentry);
	/* If err < 0, we have a half-filled directory - oh well ;) */
	return 0;
err:
	list_del(&cs->sibling);
	cpuset_up(&cpuset_sem);
	kfree(cs);
	return err;
}

static int cpuset_mkdir(struct inode *dir, struct dentry *dentry, int mode)
{
	struct cpuset *c_parent = dentry->d_parent->d_fsdata;

	/* the vfs holds inode->i_sem already */
	return cpuset_create(c_parent, dentry->d_name.name, mode | S_IFDIR);
}

static int cpuset_rmdir(struct inode *unused_dir, struct dentry *dentry)
{
	struct cpuset *cs = dentry->d_fsdata;
	struct dentry *d;
	struct cpuset *parent;
	char *pathbuf = NULL;

	/* the vfs holds both inode->i_sem already */

	cpuset_down(&cpuset_sem);
	if (atomic_read(&cs->count) > 0) {
		cpuset_up(&cpuset_sem);
		return -EBUSY;
	}
	if (!list_empty(&cs->children)) {
		cpuset_up(&cpuset_sem);
		return -EBUSY;
	}
	parent = cs->parent;
	set_bit(CS_REMOVED, &cs->flags);
	if (is_cpu_exclusive(cs))
		update_cpu_domains(cs);
	list_del(&cs->sibling);	/* delete my sibling from parent->children */
	if (list_empty(&parent->children))
		check_for_release(parent, &pathbuf);
	spin_lock(&cs->dentry->d_lock);
	d = dget(cs->dentry);
	cs->dentry = NULL;
	spin_unlock(&d->d_lock);
	cpuset_d_remove_dir(d);
	dput(d);
	cpuset_up(&cpuset_sem);
	cpuset_release_agent(pathbuf);
	return 0;
}

/**
 * cpuset_init - initialize cpusets at system boot
 *
 * Description: Initialize top_cpuset and the cpuset internal file system,
 **/

int __init cpuset_init(void)
{
	struct dentry *root;
	int err;

	top_cpuset.cpus_allowed = CPU_MASK_ALL;
	top_cpuset.mems_allowed = NODE_MASK_ALL;

	atomic_inc(&cpuset_mems_generation);
	top_cpuset.mems_generation = atomic_read(&cpuset_mems_generation);

	init_task.cpuset = &top_cpuset;

	err = register_filesystem(&cpuset_fs_type);
	if (err < 0)
		goto out;
	cpuset_mount = kern_mount(&cpuset_fs_type);
	if (IS_ERR(cpuset_mount)) {
		printk(KERN_ERR "cpuset: could not mount!\n");
		err = PTR_ERR(cpuset_mount);
		cpuset_mount = NULL;
		goto out;
	}
	root = cpuset_mount->mnt_sb->s_root;
	root->d_fsdata = &top_cpuset;
	root->d_inode->i_nlink++;
	top_cpuset.dentry = root;
	root->d_inode->i_op = &cpuset_dir_inode_operations;
	err = cpuset_populate_dir(root);
out:
	return err;
}

/**
 * cpuset_init_smp - initialize cpus_allowed
 *
 * Description: Finish top cpuset after cpu, node maps are initialized
 **/

void __init cpuset_init_smp(void)
{
	top_cpuset.cpus_allowed = cpu_online_map;
	top_cpuset.mems_allowed = node_online_map;
}

/**
 * cpuset_fork - attach newly forked task to its parents cpuset.
 * @tsk: pointer to task_struct of forking parent process.
 *
 * Description: By default, on fork, a task inherits its
 * parent's cpuset.  The pointer to the shared cpuset is
 * automatically copied in fork.c by dup_task_struct().
 * This cpuset_fork() routine need only increment the usage
 * counter in that cpuset.
 **/

void cpuset_fork(struct task_struct *tsk)
{
	atomic_inc(&tsk->cpuset->count);
}

/**
 * cpuset_exit - detach cpuset from exiting task
 * @tsk: pointer to task_struct of exiting process
 *
 * Description: Detach cpuset from @tsk and release it.
 *
 * Note that cpusets marked notify_on_release force every task
 * in them to take the global cpuset_sem semaphore when exiting.
 * This could impact scaling on very large systems.  Be reluctant
 * to use notify_on_release cpusets where very high task exit
 * scaling is required on large systems.
 *
 * Don't even think about derefencing 'cs' after the cpuset use
 * count goes to zero, except inside a critical section guarded
 * by the cpuset_sem semaphore.  If you don't hold cpuset_sem,
 * then a zero cpuset use count is a license to any other task to
 * nuke the cpuset immediately.
 **/

void cpuset_exit(struct task_struct *tsk)
{
	struct cpuset *cs;

	task_lock(tsk);
	cs = tsk->cpuset;
	tsk->cpuset = NULL;
	task_unlock(tsk);

	if (notify_on_release(cs)) {
		char *pathbuf = NULL;

		cpuset_down(&cpuset_sem);
		if (atomic_dec_and_test(&cs->count))
			check_for_release(cs, &pathbuf);
		cpuset_up(&cpuset_sem);
		cpuset_release_agent(pathbuf);
	} else {
		atomic_dec(&cs->count);
	}
}

/**
 * cpuset_cpus_allowed - return cpus_allowed mask from a tasks cpuset.
 * @tsk: pointer to task_struct from which to obtain cpuset->cpus_allowed.
 *
 * Description: Returns the cpumask_t cpus_allowed of the cpuset
 * attached to the specified @tsk.  Guaranteed to return some non-empty
 * subset of cpu_online_map, even if this means going outside the
 * tasks cpuset.
 **/

cpumask_t cpuset_cpus_allowed(const struct task_struct *tsk)
{
	cpumask_t mask;

	cpuset_down(&cpuset_sem);
	task_lock((struct task_struct *)tsk);
	guarantee_online_cpus(tsk->cpuset, &mask);
	task_unlock((struct task_struct *)tsk);
	cpuset_up(&cpuset_sem);

	return mask;
}

void cpuset_init_current_mems_allowed(void)
{
	current->mems_allowed = NODE_MASK_ALL;
}

/**
 * cpuset_update_current_mems_allowed - update mems parameters to new values
 *
 * If the current tasks cpusets mems_allowed changed behind our backs,
 * update current->mems_allowed and mems_generation to the new value.
 * Do not call this routine if in_interrupt().
 */

void cpuset_update_current_mems_allowed(void)
{
	struct cpuset *cs = current->cpuset;

	if (!cs)
		return;		/* task is exiting */
	if (current->cpuset_mems_generation != cs->mems_generation) {
		cpuset_down(&cpuset_sem);
		refresh_mems();
		cpuset_up(&cpuset_sem);
	}
}

/**
 * cpuset_restrict_to_mems_allowed - limit nodes to current mems_allowed
 * @nodes: pointer to a node bitmap that is and-ed with mems_allowed
 */
void cpuset_restrict_to_mems_allowed(unsigned long *nodes)
{
	bitmap_and(nodes, nodes, nodes_addr(current->mems_allowed),
							MAX_NUMNODES);
}

/**
 * cpuset_zonelist_valid_mems_allowed - check zonelist vs. curremt mems_allowed
 * @zl: the zonelist to be checked
 *
 * Are any of the nodes on zonelist zl allowed in current->mems_allowed?
 */
int cpuset_zonelist_valid_mems_allowed(struct zonelist *zl)
{
	int i;

	for (i = 0; zl->zones[i]; i++) {
		int nid = zl->zones[i]->zone_pgdat->node_id;

		if (node_isset(nid, current->mems_allowed))
			return 1;
	}
	return 0;
}

/*
 * nearest_exclusive_ancestor() - Returns the nearest mem_exclusive
 * ancestor to the specified cpuset.  Call while holding cpuset_sem.
 * If no ancestor is mem_exclusive (an unusual configuration), then
 * returns the root cpuset.
 */
static const struct cpuset *nearest_exclusive_ancestor(const struct cpuset *cs)
{
	while (!is_mem_exclusive(cs) && cs->parent)
		cs = cs->parent;
	return cs;
}

/**
 * cpuset_zone_allowed - Can we allocate memory on zone z's memory node?
 * @z: is this zone on an allowed node?
 * @gfp_mask: memory allocation flags (we use __GFP_HARDWALL)
 *
 * If we're in interrupt, yes, we can always allocate.  If zone
 * z's node is in our tasks mems_allowed, yes.  If it's not a
 * __GFP_HARDWALL request and this zone's nodes is in the nearest
 * mem_exclusive cpuset ancestor to this tasks cpuset, yes.
 * Otherwise, no.
 *
 * GFP_USER allocations are marked with the __GFP_HARDWALL bit,
 * and do not allow allocations outside the current tasks cpuset.
 * GFP_KERNEL allocations are not so marked, so can escape to the
 * nearest mem_exclusive ancestor cpuset.
 *
 * Scanning up parent cpusets requires cpuset_sem.  The __alloc_pages()
 * routine only calls here with __GFP_HARDWALL bit _not_ set if
 * it's a GFP_KERNEL allocation, and all nodes in the current tasks
 * mems_allowed came up empty on the first pass over the zonelist.
 * So only GFP_KERNEL allocations, if all nodes in the cpuset are
 * short of memory, might require taking the cpuset_sem semaphore.
 *
 * The first loop over the zonelist in mm/page_alloc.c:__alloc_pages()
 * calls here with __GFP_HARDWALL always set in gfp_mask, enforcing
 * hardwall cpusets - no allocation on a node outside the cpuset is
 * allowed (unless in interrupt, of course).
 *
 * The second loop doesn't even call here for GFP_ATOMIC requests
 * (if the __alloc_pages() local variable 'wait' is set).  That check
 * and the checks below have the combined affect in the second loop of
 * the __alloc_pages() routine that:
 *	in_interrupt - any node ok (current task context irrelevant)
 *	GFP_ATOMIC   - any node ok
 *	GFP_KERNEL   - any node in enclosing mem_exclusive cpuset ok
 *	GFP_USER     - only nodes in current tasks mems allowed ok.
 **/

int cpuset_zone_allowed(struct zone *z, unsigned int __nocast gfp_mask)
{
	int node;			/* node that zone z is on */
	const struct cpuset *cs;	/* current cpuset ancestors */
	int allowed = 1;		/* is allocation in zone z allowed? */

	if (in_interrupt())
		return 1;
	node = z->zone_pgdat->node_id;
	if (node_isset(node, current->mems_allowed))
		return 1;
	if (gfp_mask & __GFP_HARDWALL)	/* If hardwall request, stop here */
		return 0;

	/* Not hardwall and node outside mems_allowed: scan up cpusets */
	cpuset_down(&cpuset_sem);
	cs = current->cpuset;
	if (!cs)
		goto done;		/* current task exiting */
	cs = nearest_exclusive_ancestor(cs);
	allowed = node_isset(node, cs->mems_allowed);
done:
	cpuset_up(&cpuset_sem);
	return allowed;
}

/**
 * cpuset_excl_nodes_overlap - Do we overlap @p's mem_exclusive ancestors?
 * @p: pointer to task_struct of some other task.
 *
 * Description: Return true if the nearest mem_exclusive ancestor
 * cpusets of tasks @p and current overlap.  Used by oom killer to
 * determine if task @p's memory usage might impact the memory
 * available to the current task.
 *
 * Acquires cpuset_sem - not suitable for calling from a fast path.
 **/

int cpuset_excl_nodes_overlap(const struct task_struct *p)
{
	const struct cpuset *cs1, *cs2;	/* my and p's cpuset ancestors */
	int overlap = 0;		/* do cpusets overlap? */

	cpuset_down(&cpuset_sem);
	cs1 = current->cpuset;
	if (!cs1)
		goto done;		/* current task exiting */
	cs2 = p->cpuset;
	if (!cs2)
		goto done;		/* task p is exiting */
	cs1 = nearest_exclusive_ancestor(cs1);
	cs2 = nearest_exclusive_ancestor(cs2);
	overlap = nodes_intersects(cs1->mems_allowed, cs2->mems_allowed);
done:
	cpuset_up(&cpuset_sem);

	return overlap;
}

/*
 * proc_cpuset_show()
 *  - Print tasks cpuset path into seq_file.
 *  - Used for /proc/<pid>/cpuset.
 */

static int proc_cpuset_show(struct seq_file *m, void *v)
{
	struct cpuset *cs;
	struct task_struct *tsk;
	char *buf;
	int retval = 0;

	buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
	if (!buf)
		return -ENOMEM;

	tsk = m->private;
	cpuset_down(&cpuset_sem);
	task_lock(tsk);
	cs = tsk->cpuset;
	task_unlock(tsk);
	if (!cs) {
		retval = -EINVAL;
		goto out;
	}

	retval = cpuset_path(cs, buf, PAGE_SIZE);
	if (retval < 0)
		goto out;
	seq_puts(m, buf);
	seq_putc(m, '\n');
out:
	cpuset_up(&cpuset_sem);
	kfree(buf);
	return retval;
}

static int cpuset_open(struct inode *inode, struct file *file)
{
	struct task_struct *tsk = PROC_I(inode)->task;
	return single_open(file, proc_cpuset_show, tsk);
}

struct file_operations proc_cpuset_operations = {
	.open		= cpuset_open,
	.read		= seq_read,
	.llseek		= seq_lseek,
	.release	= single_release,
};

/* Display task cpus_allowed, mems_allowed in /proc/<pid>/status file. */
char *cpuset_task_status_allowed(struct task_struct *task, char *buffer)
{
	buffer += sprintf(buffer, "Cpus_allowed:\t");
	buffer += cpumask_scnprintf(buffer, PAGE_SIZE, task->cpus_allowed);
	buffer += sprintf(buffer, "\n");
	buffer += sprintf(buffer, "Mems_allowed:\t");
	buffer += nodemask_scnprintf(buffer, PAGE_SIZE, task->mems_allowed);
	buffer += sprintf(buffer, "\n");
	return buffer;
}