kernel/taskstats.c

   1 /*
   2  * taskstats.c - Export per-task statistics to userland
   3  *
   4  * Copyright (C) Shailabh Nagar, IBM Corp. 2006
   5  *           (C) Balbir Singh,   IBM Corp. 2006
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  */
  18
  19 #include <linux/kernel.h>
  20 #include <linux/taskstats_kern.h>
  21 #include <linux/tsacct_kern.h>
  22 #include <linux/delayacct.h>
  23 #include <linux/cpumask.h>
  24 #include <linux/percpu.h>
  25 #include <linux/slab.h>
  26 #include <linux/cgroupstats.h>
  27 #include <linux/cgroup.h>
  28 #include <linux/fs.h>
  29 #include <linux/file.h>
  30 #include <net/genetlink.h>
  31 #include <asm/atomic.h>
  32
  33 /*
  34  * Maximum length of a cpumask that can be specified in
  35  * the TASKSTATS_CMD_ATTR_REGISTER/DEREGISTER_CPUMASK attribute
  36  */
  37 #define TASKSTATS_CPUMASK_MAXLEN        (100+6*NR_CPUS)
  38
  39 static DEFINE_PER_CPU(__u32, taskstats_seqnum);
  40 static int family_registered;
  41 struct kmem_cache *taskstats_cache;
  42
  43 static struct genl_family family = {
  44         .id             = GENL_ID_GENERATE,
  45         .name           = TASKSTATS_GENL_NAME,
  46         .version        = TASKSTATS_GENL_VERSION,
  47         .maxattr        = TASKSTATS_CMD_ATTR_MAX,
  48 };
  49
  50 static const struct nla_policy taskstats_cmd_get_policy[TASKSTATS_CMD_ATTR_MAX+1] = {
  51         [TASKSTATS_CMD_ATTR_PID]  = { .type = NLA_U32 },
  52         [TASKSTATS_CMD_ATTR_TGID] = { .type = NLA_U32 },
  53         [TASKSTATS_CMD_ATTR_REGISTER_CPUMASK] = { .type = NLA_STRING },
  54         [TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK] = { .type = NLA_STRING },};
  55
  56 static const struct nla_policy cgroupstats_cmd_get_policy[CGROUPSTATS_CMD_ATTR_MAX+1] = {
  57         [CGROUPSTATS_CMD_ATTR_FD] = { .type = NLA_U32 },
  58 };
  59
  60 struct listener {
  61         struct list_head list;
  62         pid_t pid;
  63         char valid;
  64 };
  65
  66 struct listener_list {
  67         struct rw_semaphore sem;
  68         struct list_head list;
  69 };
  70 static DEFINE_PER_CPU(struct listener_list, listener_array);
  71
  72 enum actions {
  73         REGISTER,
  74         DEREGISTER,
  75         CPU_DONT_CARE
  76 };
  77
  78 static int prepare_reply(struct genl_info *info, u8 cmd, struct sk_buff **skbp,
  79                                 size_t size)
  80 {
  81         struct sk_buff *skb;
  82         void *reply;
  83
  84         /*
  85          * If new attributes are added, please revisit this allocation
  86          */
  87         skb = genlmsg_new(size, GFP_KERNEL);
  88         if (!skb)
  89                 return -ENOMEM;
  90
  91         if (!info) {
  92                 int seq = get_cpu_var(taskstats_seqnum)++;
  93                 put_cpu_var(taskstats_seqnum);
  94
  95                 reply = genlmsg_put(skb, 0, seq, &family, 0, cmd);
  96         } else
  97                 reply = genlmsg_put_reply(skb, info, &family, 0, cmd);
  98         if (reply == NULL) {
  99                 nlmsg_free(skb);
 100                 return -EINVAL;
 101         }
 102
 103         *skbp = skb;
 104         return 0;
 105 }
 106
 107 /*
 108  * Send taskstats data in @skb to listener with nl_pid @pid
 109  */
 110 static int send_reply(struct sk_buff *skb, struct genl_info *info)
 111 {
 112         struct genlmsghdr *genlhdr = nlmsg_data(nlmsg_hdr(skb));
 113         void *reply = genlmsg_data(genlhdr);
 114         int rc;
 115
 116         rc = genlmsg_end(skb, reply);
 117         if (rc < 0) {
 118                 nlmsg_free(skb);
 119                 return rc;
 120         }
 121
 122         return genlmsg_reply(skb, info);
 123 }
 124
 125 /*
 126  * Send taskstats data in @skb to listeners registered for @cpu's exit data
 127  */
 128 static void send_cpu_listeners(struct sk_buff *skb,
 129                                         struct listener_list *listeners)
 130 {
 131         struct genlmsghdr *genlhdr = nlmsg_data(nlmsg_hdr(skb));
 132         struct listener *s, *tmp;
 133         struct sk_buff *skb_next, *skb_cur = skb;
 134         void *reply = genlmsg_data(genlhdr);
 135         int rc, delcount = 0;
 136
 137         rc = genlmsg_end(skb, reply);
 138         if (rc < 0) {
 139                 nlmsg_free(skb);
 140                 return;
 141         }
 142
 143         rc = 0;
 144         down_read(&listeners->sem);
 145         list_for_each_entry(s, &listeners->list, list) {
 146                 skb_next = NULL;
 147                 if (!list_is_last(&s->list, &listeners->list)) {
 148                         skb_next = skb_clone(skb_cur, GFP_KERNEL);
 149                         if (!skb_next)
 150                                 break;
 151                 }
 152                 rc = genlmsg_unicast(&init_net, skb_cur, s->pid);
 153                 if (rc == -ECONNREFUSED) {
 154                         s->valid = 0;
 155                         delcount++;
 156                 }
 157                 skb_cur = skb_next;
 158         }
 159         up_read(&listeners->sem);
 160
 161         if (skb_cur)
 162                 nlmsg_free(skb_cur);
 163
 164         if (!delcount)
 165                 return;
 166
 167         /* Delete invalidated entries */
 168         down_write(&listeners->sem);
 169         list_for_each_entry_safe(s, tmp, &listeners->list, list) {
 170                 if (!s->valid) {
 171                         list_del(&s->list);
 172                         kfree(s);
 173                 }
 174         }
 175         up_write(&listeners->sem);
 176 }
 177
 178 static void fill_stats(struct task_struct *tsk, struct taskstats *stats)
 179 {
 180         memset(stats, 0, sizeof(*stats));
 181         /*
 182          * Each accounting subsystem adds calls to its functions to
 183          * fill in relevant parts of struct taskstsats as follows
 184          *
 185          *      per-task-foo(stats, tsk);
 186          */
 187
 188         delayacct_add_tsk(stats, tsk);
 189
 190         /* fill in basic acct fields */
 191         stats->version = TASKSTATS_VERSION;
 192         stats->nvcsw = tsk->nvcsw;
 193         stats->nivcsw = tsk->nivcsw;
 194         bacct_add_tsk(stats, tsk);
 195
 196         /* fill in extended acct fields */
 197         xacct_add_tsk(stats, tsk);
 198 }
 199
 200 static int fill_stats_for_pid(pid_t pid, struct taskstats *stats)
 201 {
 202         struct task_struct *tsk;
 203
 204         rcu_read_lock();
 205         tsk = find_task_by_vpid(pid);
 206         if (tsk)
 207                 get_task_struct(tsk);
 208         rcu_read_unlock();
 209         if (!tsk)
 210                 return -ESRCH;
 211         fill_stats(tsk, stats);
 212         put_task_struct(tsk);
 213         return 0;
 214 }
 215
 216 static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
 217 {
 218         struct task_struct *tsk, *first;
 219         unsigned long flags;
 220         int rc = -ESRCH;
 221
 222         /*
 223          * Add additional stats from live tasks except zombie thread group
 224          * leaders who are already counted with the dead tasks
 225          */
 226         rcu_read_lock();
 227         first = find_task_by_vpid(tgid);
 228
 229         if (!first || !lock_task_sighand(first, &flags))
 230                 goto out;
 231
 232         if (first->signal->stats)
 233                 memcpy(stats, first->signal->stats, sizeof(*stats));
 234         else
 235                 memset(stats, 0, sizeof(*stats));
 236
 237         tsk = first;
 238         do {
 239                 if (tsk->exit_state)
 240                         continue;
 241                 /*
 242                  * Accounting subsystem can call its functions here to
 243                  * fill in relevant parts of struct taskstsats as follows
 244                  *
 245                  *      per-task-foo(stats, tsk);
 246                  */
 247                 delayacct_add_tsk(stats, tsk);
 248
 249                 stats->nvcsw += tsk->nvcsw;
 250                 stats->nivcsw += tsk->nivcsw;
 251         } while_each_thread(first, tsk);
 252
 253         unlock_task_sighand(first, &flags);
 254         rc = 0;
 255 out:
 256         rcu_read_unlock();
 257
 258         stats->version = TASKSTATS_VERSION;
 259         /*
 260          * Accounting subsystems can also add calls here to modify
 261          * fields of taskstats.
 262          */
 263         return rc;
 264 }
 265
 266 static void fill_tgid_exit(struct task_struct *tsk)
 267 {
 268         unsigned long flags;
 269
 270         spin_lock_irqsave(&tsk->sighand->siglock, flags);
 271         if (!tsk->signal->stats)
 272                 goto ret;
 273
 274         /*
 275          * Each accounting subsystem calls its functions here to
 276          * accumalate its per-task stats for tsk, into the per-tgid structure
 277          *
 278          *      per-task-foo(tsk->signal->stats, tsk);
 279          */
 280         delayacct_add_tsk(tsk->signal->stats, tsk);
 281 ret:
 282         spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
 283         return;
 284 }
 285
 286 static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd)
 287 {
 288         struct listener_list *listeners;
 289         struct listener *s, *tmp;
 290         unsigned int cpu;
 291
 292         if (!cpumask_subset(mask, cpu_possible_mask))
 293                 return -EINVAL;
 294
 295         if (isadd == REGISTER) {
 296                 for_each_cpu(cpu, mask) {
 297                         s = kmalloc_node(sizeof(struct listener), GFP_KERNEL,
 298                                          cpu_to_node(cpu));
 299                         if (!s)
 300                                 goto cleanup;
 301                         s->pid = pid;
 302                         INIT_LIST_HEAD(&s->list);
 303                         s->valid = 1;
 304
 305                         listeners = &per_cpu(listener_array, cpu);
 306                         down_write(&listeners->sem);
 307                         list_add(&s->list, &listeners->list);
 308                         up_write(&listeners->sem);
 309                 }
 310                 return 0;
 311         }
 312
 313         /* Deregister or cleanup */
 314 cleanup:
 315         for_each_cpu(cpu, mask) {
 316                 listeners = &per_cpu(listener_array, cpu);
 317                 down_write(&listeners->sem);
 318                 list_for_each_entry_safe(s, tmp, &listeners->list, list) {
 319                         if (s->pid == pid) {
 320                                 list_del(&s->list);
 321                                 kfree(s);
 322                                 break;
 323                         }
 324                 }
 325                 up_write(&listeners->sem);
 326         }
 327         return 0;
 328 }
 329
 330 static int parse(struct nlattr *na, struct cpumask *mask)
 331 {
 332         char *data;
 333         int len;
 334         int ret;
 335
 336         if (na == NULL)
 337                 return 1;
 338         len = nla_len(na);
 339         if (len > TASKSTATS_CPUMASK_MAXLEN)
 340                 return -E2BIG;
 341         if (len < 1)
 342                 return -EINVAL;
 343         data = kmalloc(len, GFP_KERNEL);
 344         if (!data)
 345                 return -ENOMEM;
 346         nla_strlcpy(data, na, len);
 347         ret = cpulist_parse(data, mask);
 348         kfree(data);
 349         return ret;
 350 }
 351
 352 #ifdef CONFIG_IA64
 353 #define TASKSTATS_NEEDS_PADDING 1
 354 #endif
 355
 356 static struct taskstats *mk_reply(struct sk_buff *skb, int type, u32 pid)
 357 {
 358         struct nlattr *na, *ret;
 359         int aggr;
 360
 361         aggr = (type == TASKSTATS_TYPE_PID)
 362                         ? TASKSTATS_TYPE_AGGR_PID
 363                         : TASKSTATS_TYPE_AGGR_TGID;
 364
 365         /*
 366          * The taskstats structure is internally aligned on 8 byte
 367          * boundaries but the layout of the aggregrate reply, with
 368          * two NLA headers and the pid (each 4 bytes), actually
 369          * force the entire structure to be unaligned. This causes
 370          * the kernel to issue unaligned access warnings on some
 371          * architectures like ia64. Unfortunately, some software out there
 372          * doesn't properly unroll the NLA packet and assumes that the start
 373          * of the taskstats structure will always be 20 bytes from the start
 374          * of the netlink payload. Aligning the start of the taskstats
 375          * structure breaks this software, which we don't want. So, for now
 376          * the alignment only happens on architectures that require it
 377          * and those users will have to update to fixed versions of those
 378          * packages. Space is reserved in the packet only when needed.
 379          * This ifdef should be removed in several years e.g. 2012 once
 380          * we can be confident that fixed versions are installed on most
 381          * systems. We add the padding before the aggregate since the
 382          * aggregate is already a defined type.
 383          */
 384 #ifdef TASKSTATS_NEEDS_PADDING
 385         if (nla_put(skb, TASKSTATS_TYPE_NULL, 0, NULL) < 0)
 386                 goto err;
 387 #endif
 388         na = nla_nest_start(skb, aggr);
 389         if (!na)
 390                 goto err;
 391
 392         if (nla_put(skb, type, sizeof(pid), &pid) < 0)
 393                 goto err;
 394         ret = nla_reserve(skb, TASKSTATS_TYPE_STATS, sizeof(struct taskstats));
 395         if (!ret)
 396                 goto err;
 397         nla_nest_end(skb, na);
 398
 399         return nla_data(ret);
 400 err:
 401         return NULL;
 402 }
 403
 404 static int cgroupstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
 405 {
 406         int rc = 0;
 407         struct sk_buff *rep_skb;
 408         struct cgroupstats *stats;
 409         struct nlattr *na;
 410         size_t size;
 411         u32 fd;
 412         struct file *file;
 413         int fput_needed;
 414
 415         na = info->attrs[CGROUPSTATS_CMD_ATTR_FD];
 416         if (!na)
 417                 return -EINVAL;
 418
 419         fd = nla_get_u32(info->attrs[CGROUPSTATS_CMD_ATTR_FD]);
 420         file = fget_light(fd, &fput_needed);
 421         if (!file)
 422                 return 0;
 423
 424         size = nla_total_size(sizeof(struct cgroupstats));
 425
 426         rc = prepare_reply(info, CGROUPSTATS_CMD_NEW, &rep_skb,
 427                                 size);
 428         if (rc < 0)
 429                 goto err;
 430
 431         na = nla_reserve(rep_skb, CGROUPSTATS_TYPE_CGROUP_STATS,
 432                                 sizeof(struct cgroupstats));
 433         stats = nla_data(na);
 434         memset(stats, 0, sizeof(*stats));
 435
 436         rc = cgroupstats_build(stats, file->f_dentry);
 437         if (rc < 0) {
 438                 nlmsg_free(rep_skb);
 439                 goto err;
 440         }
 441
 442         rc = send_reply(rep_skb, info);
 443
 444 err:
 445         fput_light(file, fput_needed);
 446         return rc;
 447 }
 448
 449 static int cmd_attr_register_cpumask(struct genl_info *info)
 450 {
 451         cpumask_var_t mask;
 452         int rc;
 453
 454         if (!alloc_cpumask_var(&mask, GFP_KERNEL))
 455                 return -ENOMEM;
 456         rc = parse(info->attrs[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK], mask);
 457         if (rc < 0)
 458                 goto out;
 459         rc = add_del_listener(info->snd_pid, mask, REGISTER);
 460 out:
 461         free_cpumask_var(mask);
 462         return rc;
 463 }
 464
 465 static int cmd_attr_deregister_cpumask(struct genl_info *info)
 466 {
 467         cpumask_var_t mask;
 468         int rc;
 469
 470         if (!alloc_cpumask_var(&mask, GFP_KERNEL))
 471                 return -ENOMEM;
 472         rc = parse(info->attrs[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK], mask);
 473         if (rc < 0)
 474                 goto out;
 475         rc = add_del_listener(info->snd_pid, mask, DEREGISTER);
 476 out:
 477         free_cpumask_var(mask);
 478         return rc;
 479 }
 480
 481 static size_t taskstats_packet_size(void)
 482 {
 483         size_t size;
 484
 485         size = nla_total_size(sizeof(u32)) +
 486                 nla_total_size(sizeof(struct taskstats)) + nla_total_size(0);
 487 #ifdef TASKSTATS_NEEDS_PADDING
 488         size += nla_total_size(0); /* Padding for alignment */
 489 #endif
 490         return size;
 491 }
 492
 493 static int cmd_attr_pid(struct genl_info *info)
 494 {
 495         struct taskstats *stats;
 496         struct sk_buff *rep_skb;
 497         size_t size;
 498         u32 pid;
 499         int rc;
 500
 501         size = taskstats_packet_size();
 502
 503         rc = prepare_reply(info, TASKSTATS_CMD_NEW, &rep_skb, size);
 504         if (rc < 0)
 505                 return rc;
 506
 507         rc = -EINVAL;
 508         pid = nla_get_u32(info->attrs[TASKSTATS_CMD_ATTR_PID]);
 509         stats = mk_reply(rep_skb, TASKSTATS_TYPE_PID, pid);
 510         if (!stats)
 511                 goto err;
 512
 513         rc = fill_stats_for_pid(pid, stats);
 514         if (rc < 0)
 515                 goto err;
 516         return send_reply(rep_skb, info);
 517 err:
 518         nlmsg_free(rep_skb);
 519         return rc;
 520 }
 521
 522 static int cmd_attr_tgid(struct genl_info *info)
 523 {
 524         struct taskstats *stats;
 525         struct sk_buff *rep_skb;
 526         size_t size;
 527         u32 tgid;
 528         int rc;
 529
 530         size = taskstats_packet_size();
 531
 532         rc = prepare_reply(info, TASKSTATS_CMD_NEW, &rep_skb, size);
 533         if (rc < 0)
 534                 return rc;
 535
 536         rc = -EINVAL;
 537         tgid = nla_get_u32(info->attrs[TASKSTATS_CMD_ATTR_TGID]);
 538         stats = mk_reply(rep_skb, TASKSTATS_TYPE_TGID, tgid);
 539         if (!stats)
 540                 goto err;
 541
 542         rc = fill_stats_for_tgid(tgid, stats);
 543         if (rc < 0)
 544                 goto err;
 545         return send_reply(rep_skb, info);
 546 err:
 547         nlmsg_free(rep_skb);
 548         return rc;
 549 }
 550
 551 static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
 552 {
 553         if (info->attrs[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK])
 554                 return cmd_attr_register_cpumask(info);
 555         else if (info->attrs[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK])
 556                 return cmd_attr_deregister_cpumask(info);
 557         else if (info->attrs[TASKSTATS_CMD_ATTR_PID])
 558                 return cmd_attr_pid(info);
 559         else if (info->attrs[TASKSTATS_CMD_ATTR_TGID])
 560                 return cmd_attr_tgid(info);
 561         else
 562                 return -EINVAL;
 563 }
 564
 565 static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk)
 566 {
 567         struct signal_struct *sig = tsk->signal;
 568         struct taskstats *stats;
 569
 570         if (sig->stats || thread_group_empty(tsk))
 571                 goto ret;
 572
 573         /* No problem if kmem_cache_zalloc() fails */
 574         stats = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
 575
 576         spin_lock_irq(&tsk->sighand->siglock);
 577         if (!sig->stats) {
 578                 sig->stats = stats;
 579                 stats = NULL;
 580         }
 581         spin_unlock_irq(&tsk->sighand->siglock);
 582
 583         if (stats)
 584                 kmem_cache_free(taskstats_cache, stats);
 585 ret:
 586         return sig->stats;
 587 }
 588
 589 /* Send pid data out on exit */
 590 void taskstats_exit(struct task_struct *tsk, int group_dead)
 591 {
 592         int rc;
 593         struct listener_list *listeners;
 594         struct taskstats *stats;
 595         struct sk_buff *rep_skb;
 596         size_t size;
 597         int is_thread_group;
 598
 599         if (!family_registered)
 600                 return;
 601
 602         /*
 603          * Size includes space for nested attributes
 604          */
 605         size = taskstats_packet_size();
 606
 607         is_thread_group = !!taskstats_tgid_alloc(tsk);
 608         if (is_thread_group) {
 609                 /* PID + STATS + TGID + STATS */
 610                 size = 2 * size;
 611                 /* fill the tsk->signal->stats structure */
 612                 fill_tgid_exit(tsk);
 613         }
 614
 615         listeners = &__raw_get_cpu_var(listener_array);
 616         if (list_empty(&listeners->list))
 617                 return;
 618
 619         rc = prepare_reply(NULL, TASKSTATS_CMD_NEW, &rep_skb, size);
 620         if (rc < 0)
 621                 return;
 622
 623         stats = mk_reply(rep_skb, TASKSTATS_TYPE_PID, tsk->pid);
 624         if (!stats)
 625                 goto err;
 626
 627         fill_stats(tsk, stats);
 628
 629         /*
 630          * Doesn't matter if tsk is the leader or the last group member leaving
 631          */
 632         if (!is_thread_group || !group_dead)
 633                 goto send;
 634
 635         stats = mk_reply(rep_skb, TASKSTATS_TYPE_TGID, tsk->tgid);
 636         if (!stats)
 637                 goto err;
 638
 639         memcpy(stats, tsk->signal->stats, sizeof(*stats));
 640
 641 send:
 642         send_cpu_listeners(rep_skb, listeners);
 643         return;
 644 err:
 645         nlmsg_free(rep_skb);
 646 }
 647
 648 static struct genl_ops taskstats_ops = {
 649         .cmd            = TASKSTATS_CMD_GET,
 650         .doit           = taskstats_user_cmd,
 651         .policy         = taskstats_cmd_get_policy,
 652 };
 653
 654 static struct genl_ops cgroupstats_ops = {
 655         .cmd            = CGROUPSTATS_CMD_GET,
 656         .doit           = cgroupstats_user_cmd,
 657         .policy         = cgroupstats_cmd_get_policy,
 658 };
 659
 660 /* Needed early in initialization */
 661 void __init taskstats_init_early(void)
 662 {
 663         unsigned int i;
 664
 665         taskstats_cache = KMEM_CACHE(taskstats, SLAB_PANIC);
 666         for_each_possible_cpu(i) {
 667                 INIT_LIST_HEAD(&(per_cpu(listener_array, i).list));
 668                 init_rwsem(&(per_cpu(listener_array, i).sem));
 669         }
 670 }
 671
 672 static int __init taskstats_init(void)
 673 {
 674         int rc;
 675
 676         rc = genl_register_family(&family);
 677         if (rc)
 678                 return rc;
 679
 680         rc = genl_register_ops(&family, &taskstats_ops);
 681         if (rc < 0)
 682                 goto err;
 683
 684         rc = genl_register_ops(&family, &cgroupstats_ops);
 685         if (rc < 0)
 686                 goto err_cgroup_ops;
 687
 688         family_registered = 1;
 689         printk("registered taskstats version %d\n", TASKSTATS_GENL_VERSION);
 690         return 0;
 691 err_cgroup_ops:
 692         genl_unregister_ops(&family, &taskstats_ops);
 693 err:
 694         genl_unregister_family(&family);
 695         return rc;
 696 }
 697
 698 /*
 699  * late initcall ensures initialization of statistics collection
 700  * mechanisms precedes initialization of the taskstats interface
 701  */
 702 late_initcall(taskstats_init);