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 = this_cpu_inc_return(taskstats_seqnum) - 1;
  93
  94                 reply = genlmsg_put(skb, 0, seq, &family, 0, cmd);
  95         } else
  96                 reply = genlmsg_put_reply(skb, info, &family, 0, cmd);
  97         if (reply == NULL) {
  98                 nlmsg_free(skb);
  99                 return -EINVAL;
 100         }
 101
 102         *skbp = skb;
 103         return 0;
 104 }
 105
 106 /*
 107  * Send taskstats data in @skb to listener with nl_pid @pid
 108  */
 109 static int send_reply(struct sk_buff *skb, struct genl_info *info)
 110 {
 111         struct genlmsghdr *genlhdr = nlmsg_data(nlmsg_hdr(skb));
 112         void *reply = genlmsg_data(genlhdr);
 113         int rc;
 114
 115         rc = genlmsg_end(skb, reply);
 116         if (rc < 0) {
 117                 nlmsg_free(skb);
 118                 return rc;
 119         }
 120
 121         return genlmsg_reply(skb, info);
 122 }
 123
 124 /*
 125  * Send taskstats data in @skb to listeners registered for @cpu's exit data
 126  */
 127 static void send_cpu_listeners(struct sk_buff *skb,
 128                                         struct listener_list *listeners)
 129 {
 130         struct genlmsghdr *genlhdr = nlmsg_data(nlmsg_hdr(skb));
 131         struct listener *s, *tmp;
 132         struct sk_buff *skb_next, *skb_cur = skb;
 133         void *reply = genlmsg_data(genlhdr);
 134         int rc, delcount = 0;
 135
 136         rc = genlmsg_end(skb, reply);
 137         if (rc < 0) {
 138                 nlmsg_free(skb);
 139                 return;
 140         }
 141
 142         rc = 0;
 143         down_read(&listeners->sem);
 144         list_for_each_entry(s, &listeners->list, list) {
 145                 skb_next = NULL;
 146                 if (!list_is_last(&s->list, &listeners->list)) {
 147                         skb_next = skb_clone(skb_cur, GFP_KERNEL);
 148                         if (!skb_next)
 149                                 break;
 150                 }
 151                 rc = genlmsg_unicast(&init_net, skb_cur, s->pid);
 152                 if (rc == -ECONNREFUSED) {
 153                         s->valid = 0;
 154                         delcount++;
 155                 }
 156                 skb_cur = skb_next;
 157         }
 158         up_read(&listeners->sem);
 159
 160         if (skb_cur)
 161                 nlmsg_free(skb_cur);
 162
 163         if (!delcount)
 164                 return;
 165
 166         /* Delete invalidated entries */
 167         down_write(&listeners->sem);
 168         list_for_each_entry_safe(s, tmp, &listeners->list, list) {
 169                 if (!s->valid) {
 170                         list_del(&s->list);
 171                         kfree(s);
 172                 }
 173         }
 174         up_write(&listeners->sem);
 175 }
 176
 177 static void fill_stats(struct task_struct *tsk, struct taskstats *stats)
 178 {
 179         memset(stats, 0, sizeof(*stats));
 180         /*
 181          * Each accounting subsystem adds calls to its functions to
 182          * fill in relevant parts of struct taskstsats as follows
 183          *
 184          *      per-task-foo(stats, tsk);
 185          */
 186
 187         delayacct_add_tsk(stats, tsk);
 188
 189         /* fill in basic acct fields */
 190         stats->version = TASKSTATS_VERSION;
 191         stats->nvcsw = tsk->nvcsw;
 192         stats->nivcsw = tsk->nivcsw;
 193         bacct_add_tsk(stats, tsk);
 194
 195         /* fill in extended acct fields */
 196         xacct_add_tsk(stats, tsk);
 197 }
 198
 199 static int fill_stats_for_pid(pid_t pid, struct taskstats *stats)
 200 {
 201         struct task_struct *tsk;
 202
 203         rcu_read_lock();
 204         tsk = find_task_by_vpid(pid);
 205         if (tsk)
 206                 get_task_struct(tsk);
 207         rcu_read_unlock();
 208         if (!tsk)
 209                 return -ESRCH;
 210         fill_stats(tsk, stats);
 211         put_task_struct(tsk);
 212         return 0;
 213 }
 214
 215 static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
 216 {
 217         struct task_struct *tsk, *first;
 218         unsigned long flags;
 219         int rc = -ESRCH;
 220
 221         /*
 222          * Add additional stats from live tasks except zombie thread group
 223          * leaders who are already counted with the dead tasks
 224          */
 225         rcu_read_lock();
 226         first = find_task_by_vpid(tgid);
 227
 228         if (!first || !lock_task_sighand(first, &flags))
 229                 goto out;
 230
 231         if (first->signal->stats)
 232                 memcpy(stats, first->signal->stats, sizeof(*stats));
 233         else
 234                 memset(stats, 0, sizeof(*stats));
 235
 236         tsk = first;
 237         do {
 238                 if (tsk->exit_state)
 239                         continue;
 240                 /*
 241                  * Accounting subsystem can call its functions here to
 242                  * fill in relevant parts of struct taskstsats as follows
 243                  *
 244                  *      per-task-foo(stats, tsk);
 245                  */
 246                 delayacct_add_tsk(stats, tsk);
 247
 248                 stats->nvcsw += tsk->nvcsw;
 249                 stats->nivcsw += tsk->nivcsw;
 250         } while_each_thread(first, tsk);
 251
 252         unlock_task_sighand(first, &flags);
 253         rc = 0;
 254 out:
 255         rcu_read_unlock();
 256
 257         stats->version = TASKSTATS_VERSION;
 258         /*
 259          * Accounting subsystems can also add calls here to modify
 260          * fields of taskstats.
 261          */
 262         return rc;
 263 }
 264
 265 static void fill_tgid_exit(struct task_struct *tsk)
 266 {
 267         unsigned long flags;
 268
 269         spin_lock_irqsave(&tsk->sighand->siglock, flags);
 270         if (!tsk->signal->stats)
 271                 goto ret;
 272
 273         /*
 274          * Each accounting subsystem calls its functions here to
 275          * accumalate its per-task stats for tsk, into the per-tgid structure
 276          *
 277          *      per-task-foo(tsk->signal->stats, tsk);
 278          */
 279         delayacct_add_tsk(tsk->signal->stats, tsk);
 280 ret:
 281         spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
 282         return;
 283 }
 284
 285 static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd)
 286 {
 287         struct listener_list *listeners;
 288         struct listener *s, *tmp;
 289         unsigned int cpu;
 290
 291         if (!cpumask_subset(mask, cpu_possible_mask))
 292                 return -EINVAL;
 293
 294         if (isadd == REGISTER) {
 295                 for_each_cpu(cpu, mask) {
 296                         s = kmalloc_node(sizeof(struct listener), GFP_KERNEL,
 297                                          cpu_to_node(cpu));
 298                         if (!s)
 299                                 goto cleanup;
 300                         s->pid = pid;
 301                         INIT_LIST_HEAD(&s->list);
 302                         s->valid = 1;
 303
 304                         listeners = &per_cpu(listener_array, cpu);
 305                         down_write(&listeners->sem);
 306                         list_add(&s->list, &listeners->list);
 307                         up_write(&listeners->sem);
 308                 }
 309                 return 0;
 310         }
 311
 312         /* Deregister or cleanup */
 313 cleanup:
 314         for_each_cpu(cpu, mask) {
 315                 listeners = &per_cpu(listener_array, cpu);
 316                 down_write(&listeners->sem);
 317                 list_for_each_entry_safe(s, tmp, &listeners->list, list) {
 318                         if (s->pid == pid) {
 319                                 list_del(&s->list);
 320                                 kfree(s);
 321                                 break;
 322                         }
 323                 }
 324                 up_write(&listeners->sem);
 325         }
 326         return 0;
 327 }
 328
 329 static int parse(struct nlattr *na, struct cpumask *mask)
 330 {
 331         char *data;
 332         int len;
 333         int ret;
 334
 335         if (na == NULL)
 336                 return 1;
 337         len = nla_len(na);
 338         if (len > TASKSTATS_CPUMASK_MAXLEN)
 339                 return -E2BIG;
 340         if (len < 1)
 341                 return -EINVAL;
 342         data = kmalloc(len, GFP_KERNEL);
 343         if (!data)
 344                 return -ENOMEM;
 345         nla_strlcpy(data, na, len);
 346         ret = cpulist_parse(data, mask);
 347         kfree(data);
 348         return ret;
 349 }
 350
 351 #if defined(CONFIG_64BIT) && !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
 352 #define TASKSTATS_NEEDS_PADDING 1
 353 #endif
 354
 355 static struct taskstats *mk_reply(struct sk_buff *skb, int type, u32 pid)
 356 {
 357         struct nlattr *na, *ret;
 358         int aggr;
 359
 360         aggr = (type == TASKSTATS_TYPE_PID)
 361                         ? TASKSTATS_TYPE_AGGR_PID
 362                         : TASKSTATS_TYPE_AGGR_TGID;
 363
 364         /*
 365          * The taskstats structure is internally aligned on 8 byte
 366          * boundaries but the layout of the aggregrate reply, with
 367          * two NLA headers and the pid (each 4 bytes), actually
 368          * force the entire structure to be unaligned. This causes
 369          * the kernel to issue unaligned access warnings on some
 370          * architectures like ia64. Unfortunately, some software out there
 371          * doesn't properly unroll the NLA packet and assumes that the start
 372          * of the taskstats structure will always be 20 bytes from the start
 373          * of the netlink payload. Aligning the start of the taskstats
 374          * structure breaks this software, which we don't want. So, for now
 375          * the alignment only happens on architectures that require it
 376          * and those users will have to update to fixed versions of those
 377          * packages. Space is reserved in the packet only when needed.
 378          * This ifdef should be removed in several years e.g. 2012 once
 379          * we can be confident that fixed versions are installed on most
 380          * systems. We add the padding before the aggregate since the
 381          * aggregate is already a defined type.
 382          */
 383 #ifdef TASKSTATS_NEEDS_PADDING
 384         if (nla_put(skb, TASKSTATS_TYPE_NULL, 0, NULL) < 0)
 385                 goto err;
 386 #endif
 387         na = nla_nest_start(skb, aggr);
 388         if (!na)
 389                 goto err;
 390
 391         if (nla_put(skb, type, sizeof(pid), &pid) < 0)
 392                 goto err;
 393         ret = nla_reserve(skb, TASKSTATS_TYPE_STATS, sizeof(struct taskstats));
 394         if (!ret)
 395                 goto err;
 396         nla_nest_end(skb, na);
 397
 398         return nla_data(ret);
 399 err:
 400         return NULL;
 401 }
 402
 403 static int cgroupstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
 404 {
 405         int rc = 0;
 406         struct sk_buff *rep_skb;
 407         struct cgroupstats *stats;
 408         struct nlattr *na;
 409         size_t size;
 410         u32 fd;
 411         struct file *file;
 412         int fput_needed;
 413
 414         na = info->attrs[CGROUPSTATS_CMD_ATTR_FD];
 415         if (!na)
 416                 return -EINVAL;
 417
 418         fd = nla_get_u32(info->attrs[CGROUPSTATS_CMD_ATTR_FD]);
 419         file = fget_light(fd, &fput_needed);
 420         if (!file)
 421                 return 0;
 422
 423         size = nla_total_size(sizeof(struct cgroupstats));
 424
 425         rc = prepare_reply(info, CGROUPSTATS_CMD_NEW, &rep_skb,
 426                                 size);
 427         if (rc < 0)
 428                 goto err;
 429
 430         na = nla_reserve(rep_skb, CGROUPSTATS_TYPE_CGROUP_STATS,
 431                                 sizeof(struct cgroupstats));
 432         stats = nla_data(na);
 433         memset(stats, 0, sizeof(*stats));
 434
 435         rc = cgroupstats_build(stats, file->f_dentry);
 436         if (rc < 0) {
 437                 nlmsg_free(rep_skb);
 438                 goto err;
 439         }
 440
 441         rc = send_reply(rep_skb, info);
 442
 443 err:
 444         fput_light(file, fput_needed);
 445         return rc;
 446 }
 447
 448 static int cmd_attr_register_cpumask(struct genl_info *info)
 449 {
 450         cpumask_var_t mask;
 451         int rc;
 452
 453         if (!alloc_cpumask_var(&mask, GFP_KERNEL))
 454                 return -ENOMEM;
 455         rc = parse(info->attrs[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK], mask);
 456         if (rc < 0)
 457                 goto out;
 458         rc = add_del_listener(info->snd_pid, mask, REGISTER);
 459 out:
 460         free_cpumask_var(mask);
 461         return rc;
 462 }
 463
 464 static int cmd_attr_deregister_cpumask(struct genl_info *info)
 465 {
 466         cpumask_var_t mask;
 467         int rc;
 468
 469         if (!alloc_cpumask_var(&mask, GFP_KERNEL))
 470                 return -ENOMEM;
 471         rc = parse(info->attrs[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK], mask);
 472         if (rc < 0)
 473                 goto out;
 474         rc = add_del_listener(info->snd_pid, mask, DEREGISTER);
 475 out:
 476         free_cpumask_var(mask);
 477         return rc;
 478 }
 479
 480 static size_t taskstats_packet_size(void)
 481 {
 482         size_t size;
 483
 484         size = nla_total_size(sizeof(u32)) +
 485                 nla_total_size(sizeof(struct taskstats)) + nla_total_size(0);
 486 #ifdef TASKSTATS_NEEDS_PADDING
 487         size += nla_total_size(0); /* Padding for alignment */
 488 #endif
 489         return size;
 490 }
 491
 492 static int cmd_attr_pid(struct genl_info *info)
 493 {
 494         struct taskstats *stats;
 495         struct sk_buff *rep_skb;
 496         size_t size;
 497         u32 pid;
 498         int rc;
 499
 500         size = taskstats_packet_size();
 501
 502         rc = prepare_reply(info, TASKSTATS_CMD_NEW, &rep_skb, size);
 503         if (rc < 0)
 504                 return rc;
 505
 506         rc = -EINVAL;
 507         pid = nla_get_u32(info->attrs[TASKSTATS_CMD_ATTR_PID]);
 508         stats = mk_reply(rep_skb, TASKSTATS_TYPE_PID, pid);
 509         if (!stats)
 510                 goto err;
 511
 512         rc = fill_stats_for_pid(pid, stats);
 513         if (rc < 0)
 514                 goto err;
 515         return send_reply(rep_skb, info);
 516 err:
 517         nlmsg_free(rep_skb);
 518         return rc;
 519 }
 520
 521 static int cmd_attr_tgid(struct genl_info *info)
 522 {
 523         struct taskstats *stats;
 524         struct sk_buff *rep_skb;
 525         size_t size;
 526         u32 tgid;
 527         int rc;
 528
 529         size = taskstats_packet_size();
 530
 531         rc = prepare_reply(info, TASKSTATS_CMD_NEW, &rep_skb, size);
 532         if (rc < 0)
 533                 return rc;
 534
 535         rc = -EINVAL;
 536         tgid = nla_get_u32(info->attrs[TASKSTATS_CMD_ATTR_TGID]);
 537         stats = mk_reply(rep_skb, TASKSTATS_TYPE_TGID, tgid);
 538         if (!stats)
 539                 goto err;
 540
 541         rc = fill_stats_for_tgid(tgid, stats);
 542         if (rc < 0)
 543                 goto err;
 544         return send_reply(rep_skb, info);
 545 err:
 546         nlmsg_free(rep_skb);
 547         return rc;
 548 }
 549
 550 static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
 551 {
 552         if (info->attrs[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK])
 553                 return cmd_attr_register_cpumask(info);
 554         else if (info->attrs[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK])
 555                 return cmd_attr_deregister_cpumask(info);
 556         else if (info->attrs[TASKSTATS_CMD_ATTR_PID])
 557                 return cmd_attr_pid(info);
 558         else if (info->attrs[TASKSTATS_CMD_ATTR_TGID])
 559                 return cmd_attr_tgid(info);
 560         else
 561                 return -EINVAL;
 562 }
 563
 564 static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk)
 565 {
 566         struct signal_struct *sig = tsk->signal;
 567         struct taskstats *stats;
 568
 569         if (sig->stats || thread_group_empty(tsk))
 570                 goto ret;
 571
 572         /* No problem if kmem_cache_zalloc() fails */
 573         stats = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
 574
 575         spin_lock_irq(&tsk->sighand->siglock);
 576         if (!sig->stats) {
 577                 sig->stats = stats;
 578                 stats = NULL;
 579         }
 580         spin_unlock_irq(&tsk->sighand->siglock);
 581
 582         if (stats)
 583                 kmem_cache_free(taskstats_cache, stats);
 584 ret:
 585         return sig->stats;
 586 }
 587
 588 /* Send pid data out on exit */
 589 void taskstats_exit(struct task_struct *tsk, int group_dead)
 590 {
 591         int rc;
 592         struct listener_list *listeners;
 593         struct taskstats *stats;
 594         struct sk_buff *rep_skb;
 595         size_t size;
 596         int is_thread_group;
 597
 598         if (!family_registered)
 599                 return;
 600
 601         /*
 602          * Size includes space for nested attributes
 603          */
 604         size = taskstats_packet_size();
 605
 606         is_thread_group = !!taskstats_tgid_alloc(tsk);
 607         if (is_thread_group) {
 608                 /* PID + STATS + TGID + STATS */
 609                 size = 2 * size;
 610                 /* fill the tsk->signal->stats structure */
 611                 fill_tgid_exit(tsk);
 612         }
 613
 614         listeners = __this_cpu_ptr(&listener_array);
 615         if (list_empty(&listeners->list))
 616                 return;
 617
 618         rc = prepare_reply(NULL, TASKSTATS_CMD_NEW, &rep_skb, size);
 619         if (rc < 0)
 620                 return;
 621
 622         stats = mk_reply(rep_skb, TASKSTATS_TYPE_PID, tsk->pid);
 623         if (!stats)
 624                 goto err;
 625
 626         fill_stats(tsk, stats);
 627
 628         /*
 629          * Doesn't matter if tsk is the leader or the last group member leaving
 630          */
 631         if (!is_thread_group || !group_dead)
 632                 goto send;
 633
 634         stats = mk_reply(rep_skb, TASKSTATS_TYPE_TGID, tsk->tgid);
 635         if (!stats)
 636                 goto err;
 637
 638         memcpy(stats, tsk->signal->stats, sizeof(*stats));
 639
 640 send:
 641         send_cpu_listeners(rep_skb, listeners);
 642         return;
 643 err:
 644         nlmsg_free(rep_skb);
 645 }
 646
 647 static struct genl_ops taskstats_ops = {
 648         .cmd            = TASKSTATS_CMD_GET,
 649         .doit           = taskstats_user_cmd,
 650         .policy         = taskstats_cmd_get_policy,
 651 };
 652
 653 static struct genl_ops cgroupstats_ops = {
 654         .cmd            = CGROUPSTATS_CMD_GET,
 655         .doit           = cgroupstats_user_cmd,
 656         .policy         = cgroupstats_cmd_get_policy,
 657 };
 658
 659 /* Needed early in initialization */
 660 void __init taskstats_init_early(void)
 661 {
 662         unsigned int i;
 663
 664         taskstats_cache = KMEM_CACHE(taskstats, SLAB_PANIC);
 665         for_each_possible_cpu(i) {
 666                 INIT_LIST_HEAD(&(per_cpu(listener_array, i).list));
 667                 init_rwsem(&(per_cpu(listener_array, i).sem));
 668         }
 669 }
 670
 671 static int __init taskstats_init(void)
 672 {
 673         int rc;
 674
 675         rc = genl_register_family(&family);
 676         if (rc)
 677                 return rc;
 678
 679         rc = genl_register_ops(&family, &taskstats_ops);
 680         if (rc < 0)
 681                 goto err;
 682
 683         rc = genl_register_ops(&family, &cgroupstats_ops);
 684         if (rc < 0)
 685                 goto err_cgroup_ops;
 686
 687         family_registered = 1;
 688         printk("registered taskstats version %d\n", TASKSTATS_GENL_VERSION);
 689         return 0;
 690 err_cgroup_ops:
 691         genl_unregister_ops(&family, &taskstats_ops);
 692 err:
 693         genl_unregister_family(&family);
 694         return rc;
 695 }
 696
 697 /*
 698  * late initcall ensures initialization of statistics collection
 699  * mechanisms precedes initialization of the taskstats interface
 700  */
 701 late_initcall(taskstats_init);