fs/proc/array.c

   1 /*
   2  *  linux/fs/proc/array.c
   3  *
   4  *  Copyright (C) 1992  by Linus Torvalds
   5  *  based on ideas by Darren Senn
   6  *
   7  * Fixes:
   8  * Michael. K. Johnson: stat,statm extensions.
   9  *                      <johnsonm@stolaf.edu>
  10  *
  11  * Pauline Middelink :  Made cmdline,envline only break at '\0's, to
  12  *                      make sure SET_PROCTITLE works. Also removed
  13  *                      bad '!' which forced address recalculation for
  14  *                      EVERY character on the current page.
  15  *                      <middelin@polyware.iaf.nl>
  16  *
  17  * Danny ter Haar    :  added cpuinfo
  18  *                      <dth@cistron.nl>
  19  *
  20  * Alessandro Rubini :  profile extension.
  21  *                      <rubini@ipvvis.unipv.it>
  22  *
  23  * Jeff Tranter      :  added BogoMips field to cpuinfo
  24  *                      <Jeff_Tranter@Mitel.COM>
  25  *
  26  * Bruno Haible      :  remove 4K limit for the maps file
  27  *                      <haible@ma2s2.mathematik.uni-karlsruhe.de>
  28  *
  29  * Yves Arrouye      :  remove removal of trailing spaces in get_array.
  30  *                      <Yves.Arrouye@marin.fdn.fr>
  31  *
  32  * Jerome Forissier  :  added per-CPU time information to /proc/stat
  33  *                      and /proc/<pid>/cpu extension
  34  *                      <forissier@isia.cma.fr>
  35  *                      - Incorporation and non-SMP safe operation
  36  *                      of forissier patch in 2.1.78 by
  37  *                      Hans Marcus <crowbar@concepts.nl>
  38  *
  39  * aeb@cwi.nl        :  /proc/partitions
  40  *
  41  *
  42  * Alan Cox          :  security fixes.
  43  *                      <alan@lxorguk.ukuu.org.uk>
  44  *
  45  * Al Viro           :  safe handling of mm_struct
  46  *
  47  * Gerhard Wichert   :  added BIGMEM support
  48  * Siemens AG           <Gerhard.Wichert@pdb.siemens.de>
  49  *
  50  * Al Viro & Jeff Garzik :  moved most of the thing into base.c and
  51  *                       :  proc_misc.c. The rest may eventually go into
  52  *                       :  base.c too.
  53  */
  54
  55 #include <linux/types.h>
  56 #include <linux/errno.h>
  57 #include <linux/time.h>
  58 #include <linux/kernel.h>
  59 #include <linux/kernel_stat.h>
  60 #include <linux/tty.h>
  61 #include <linux/string.h>
  62 #include <linux/mman.h>
  63 #include <linux/proc_fs.h>
  64 #include <linux/ioport.h>
  65 #include <linux/uaccess.h>
  66 #include <linux/io.h>
  67 #include <linux/mm.h>
  68 #include <linux/hugetlb.h>
  69 #include <linux/pagemap.h>
  70 #include <linux/swap.h>
  71 #include <linux/smp.h>
  72 #include <linux/signal.h>
  73 #include <linux/highmem.h>
  74 #include <linux/file.h>
  75 #include <linux/fdtable.h>
  76 #include <linux/times.h>
  77 #include <linux/cpuset.h>
  78 #include <linux/rcupdate.h>
  79 #include <linux/delayacct.h>
  80 #include <linux/seq_file.h>
  81 #include <linux/pid_namespace.h>
  82 #include <linux/ptrace.h>
  83 #include <linux/tracehook.h>
  84 #include <linux/user_namespace.h>
  85
  86 #include <asm/pgtable.h>
  87 #include <asm/processor.h>
  88 #include "internal.h"
  89
  90 static inline void task_name(struct seq_file *m, struct task_struct *p)
  91 {
  92         int i;
  93         char *buf, *end;
  94         char *name;
  95         char tcomm[sizeof(p->comm)];
  96
  97         get_task_comm(tcomm, p);
  98
  99         seq_puts(m, "Name:\t");
 100         end = m->buf + m->size;
 101         buf = m->buf + m->count;
 102         name = tcomm;
 103         i = sizeof(tcomm);
 104         while (i && (buf < end)) {
 105                 unsigned char c = *name;
 106                 name++;
 107                 i--;
 108                 *buf = c;
 109                 if (!c)
 110                         break;
 111                 if (c == '\\') {
 112                         buf++;
 113                         if (buf < end)
 114                                 *buf++ = c;
 115                         continue;
 116                 }
 117                 if (c == '\n') {
 118                         *buf++ = '\\';
 119                         if (buf < end)
 120                                 *buf++ = 'n';
 121                         continue;
 122                 }
 123                 buf++;
 124         }
 125         m->count = buf - m->buf;
 126         seq_putc(m, '\n');
 127 }
 128
 129 /*
 130  * The task state array is a strange "bitmap" of
 131  * reasons to sleep. Thus "running" is zero, and
 132  * you can test for combinations of others with
 133  * simple bit tests.
 134  */
 135 static const char * const task_state_array[] = {
 136         "R (running)",          /*   0 */
 137         "S (sleeping)",         /*   1 */
 138         "D (disk sleep)",       /*   2 */
 139         "T (stopped)",          /*   4 */
 140         "t (tracing stop)",     /*   8 */
 141         "Z (zombie)",           /*  16 */
 142         "X (dead)",             /*  32 */
 143         "x (dead)",             /*  64 */
 144         "K (wakekill)",         /* 128 */
 145         "W (waking)",           /* 256 */
 146 };
 147
 148 static inline const char *get_task_state(struct task_struct *tsk)
 149 {
 150         unsigned int state = (tsk->state & TASK_REPORT) | tsk->exit_state;
 151         const char * const *p = &task_state_array[0];
 152
 153         BUILD_BUG_ON(1 + ilog2(TASK_STATE_MAX) != ARRAY_SIZE(task_state_array));
 154
 155         while (state) {
 156                 p++;
 157                 state >>= 1;
 158         }
 159         return *p;
 160 }
 161
 162 static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 163                                 struct pid *pid, struct task_struct *p)
 164 {
 165         struct user_namespace *user_ns = current_user_ns();
 166         struct group_info *group_info;
 167         int g;
 168         struct fdtable *fdt = NULL;
 169         const struct cred *cred;
 170         pid_t ppid, tpid;
 171
 172         rcu_read_lock();
 173         ppid = pid_alive(p) ?
 174                 task_tgid_nr_ns(rcu_dereference(p->real_parent), ns) : 0;
 175         tpid = 0;
 176         if (pid_alive(p)) {
 177                 struct task_struct *tracer = ptrace_parent(p);
 178                 if (tracer)
 179                         tpid = task_pid_nr_ns(tracer, ns);
 180         }
 181         cred = get_task_cred(p);
 182         seq_printf(m,
 183                 "State:\t%s\n"
 184                 "Tgid:\t%d\n"
 185                 "Pid:\t%d\n"
 186                 "PPid:\t%d\n"
 187                 "TracerPid:\t%d\n"
 188                 "Uid:\t%d\t%d\t%d\t%d\n"
 189                 "Gid:\t%d\t%d\t%d\t%d\n",
 190                 get_task_state(p),
 191                 task_tgid_nr_ns(p, ns),
 192                 pid_nr_ns(pid, ns),
 193                 ppid, tpid,
 194                 from_kuid_munged(user_ns, cred->uid),
 195                 from_kuid_munged(user_ns, cred->euid),
 196                 from_kuid_munged(user_ns, cred->suid),
 197                 from_kuid_munged(user_ns, cred->fsuid),
 198                 from_kgid_munged(user_ns, cred->gid),
 199                 from_kgid_munged(user_ns, cred->egid),
 200                 from_kgid_munged(user_ns, cred->sgid),
 201                 from_kgid_munged(user_ns, cred->fsgid));
 202
 203         task_lock(p);
 204         if (p->files)
 205                 fdt = files_fdtable(p->files);
 206         seq_printf(m,
 207                 "FDSize:\t%d\n"
 208                 "Groups:\t",
 209                 fdt ? fdt->max_fds : 0);
 210         rcu_read_unlock();
 211
 212         group_info = cred->group_info;
 213         task_unlock(p);
 214
 215         for (g = 0; g < min(group_info->ngroups, NGROUPS_SMALL); g++)
 216                 seq_printf(m, "%d ",
 217                            from_kgid_munged(user_ns, GROUP_AT(group_info, g)));
 218         put_cred(cred);
 219
 220         seq_putc(m, '\n');
 221 }
 222
 223 static void render_sigset_t(struct seq_file *m, const char *header,
 224                                 sigset_t *set)
 225 {
 226         int i;
 227
 228         seq_puts(m, header);
 229
 230         i = _NSIG;
 231         do {
 232                 int x = 0;
 233
 234                 i -= 4;
 235                 if (sigismember(set, i+1)) x |= 1;
 236                 if (sigismember(set, i+2)) x |= 2;
 237                 if (sigismember(set, i+3)) x |= 4;
 238                 if (sigismember(set, i+4)) x |= 8;
 239                 seq_printf(m, "%x", x);
 240         } while (i >= 4);
 241
 242         seq_putc(m, '\n');
 243 }
 244
 245 static void collect_sigign_sigcatch(struct task_struct *p, sigset_t *ign,
 246                                     sigset_t *catch)
 247 {
 248         struct k_sigaction *k;
 249         int i;
 250
 251         k = p->sighand->action;
 252         for (i = 1; i <= _NSIG; ++i, ++k) {
 253                 if (k->sa.sa_handler == SIG_IGN)
 254                         sigaddset(ign, i);
 255                 else if (k->sa.sa_handler != SIG_DFL)
 256                         sigaddset(catch, i);
 257         }
 258 }
 259
 260 static inline void task_sig(struct seq_file *m, struct task_struct *p)
 261 {
 262         unsigned long flags;
 263         sigset_t pending, shpending, blocked, ignored, caught;
 264         int num_threads = 0;
 265         unsigned long qsize = 0;
 266         unsigned long qlim = 0;
 267
 268         sigemptyset(&pending);
 269         sigemptyset(&shpending);
 270         sigemptyset(&blocked);
 271         sigemptyset(&ignored);
 272         sigemptyset(&caught);
 273
 274         if (lock_task_sighand(p, &flags)) {
 275                 pending = p->pending.signal;
 276                 shpending = p->signal->shared_pending.signal;
 277                 blocked = p->blocked;
 278                 collect_sigign_sigcatch(p, &ignored, &caught);
 279                 num_threads = get_nr_threads(p);
 280                 rcu_read_lock();  /* FIXME: is this correct? */
 281                 qsize = atomic_read(&__task_cred(p)->user->sigpending);
 282                 rcu_read_unlock();
 283                 qlim = task_rlimit(p, RLIMIT_SIGPENDING);
 284                 unlock_task_sighand(p, &flags);
 285         }
 286
 287         seq_printf(m, "Threads:\t%d\n", num_threads);
 288         seq_printf(m, "SigQ:\t%lu/%lu\n", qsize, qlim);
 289
 290         /* render them all */
 291         render_sigset_t(m, "SigPnd:\t", &pending);
 292         render_sigset_t(m, "ShdPnd:\t", &shpending);
 293         render_sigset_t(m, "SigBlk:\t", &blocked);
 294         render_sigset_t(m, "SigIgn:\t", &ignored);
 295         render_sigset_t(m, "SigCgt:\t", &caught);
 296 }
 297
 298 static void render_cap_t(struct seq_file *m, const char *header,
 299                         kernel_cap_t *a)
 300 {
 301         unsigned __capi;
 302
 303         seq_puts(m, header);
 304         CAP_FOR_EACH_U32(__capi) {
 305                 seq_printf(m, "%08x",
 306                            a->cap[(_KERNEL_CAPABILITY_U32S-1) - __capi]);
 307         }
 308         seq_putc(m, '\n');
 309 }
 310
 311 static inline void task_cap(struct seq_file *m, struct task_struct *p)
 312 {
 313         const struct cred *cred;
 314         kernel_cap_t cap_inheritable, cap_permitted, cap_effective, cap_bset;
 315
 316         rcu_read_lock();
 317         cred = __task_cred(p);
 318         cap_inheritable = cred->cap_inheritable;
 319         cap_permitted   = cred->cap_permitted;
 320         cap_effective   = cred->cap_effective;
 321         cap_bset        = cred->cap_bset;
 322         rcu_read_unlock();
 323
 324         render_cap_t(m, "CapInh:\t", &cap_inheritable);
 325         render_cap_t(m, "CapPrm:\t", &cap_permitted);
 326         render_cap_t(m, "CapEff:\t", &cap_effective);
 327         render_cap_t(m, "CapBnd:\t", &cap_bset);
 328 }
 329
 330 static inline void task_context_switch_counts(struct seq_file *m,
 331                                                 struct task_struct *p)
 332 {
 333         seq_printf(m,   "voluntary_ctxt_switches:\t%lu\n"
 334                         "nonvoluntary_ctxt_switches:\t%lu\n",
 335                         p->nvcsw,
 336                         p->nivcsw);
 337 }
 338
 339 static void task_cpus_allowed(struct seq_file *m, struct task_struct *task)
 340 {
 341         seq_puts(m, "Cpus_allowed:\t");
 342         seq_cpumask(m, &task->cpus_allowed);
 343         seq_putc(m, '\n');
 344         seq_puts(m, "Cpus_allowed_list:\t");
 345         seq_cpumask_list(m, &task->cpus_allowed);
 346         seq_putc(m, '\n');
 347 }
 348
 349 int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
 350                         struct pid *pid, struct task_struct *task)
 351 {
 352         struct mm_struct *mm = get_task_mm(task);
 353
 354         task_name(m, task);
 355         task_state(m, ns, pid, task);
 356
 357         if (mm) {
 358                 task_mem(m, mm);
 359                 mmput(mm);
 360         }
 361         task_sig(m, task);
 362         task_cap(m, task);
 363         task_cpus_allowed(m, task);
 364         cpuset_task_status_allowed(m, task);
 365         task_context_switch_counts(m, task);
 366         return 0;
 367 }
 368
 369 static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 370                         struct pid *pid, struct task_struct *task, int whole)
 371 {
 372         unsigned long vsize, eip, esp, wchan = ~0UL;
 373         int priority, nice;
 374         int tty_pgrp = -1, tty_nr = 0;
 375         sigset_t sigign, sigcatch;
 376         char state;
 377         pid_t ppid = 0, pgid = -1, sid = -1;
 378         int num_threads = 0;
 379         int permitted;
 380         struct mm_struct *mm;
 381         unsigned long long start_time;
 382         unsigned long cmin_flt = 0, cmaj_flt = 0;
 383         unsigned long  min_flt = 0,  maj_flt = 0;
 384         cputime_t cutime, cstime, utime, stime;
 385         cputime_t cgtime, gtime;
 386         unsigned long rsslim = 0;
 387         char tcomm[sizeof(task->comm)];
 388         unsigned long flags;
 389
 390         state = *get_task_state(task);
 391         vsize = eip = esp = 0;
 392         permitted = ptrace_may_access(task, PTRACE_MODE_READ | PTRACE_MODE_NOAUDIT);
 393         mm = get_task_mm(task);
 394         if (mm) {
 395                 vsize = task_vsize(mm);
 396                 if (permitted) {
 397                         eip = KSTK_EIP(task);
 398                         esp = KSTK_ESP(task);
 399                 }
 400         }
 401
 402         get_task_comm(tcomm, task);
 403
 404         sigemptyset(&sigign);
 405         sigemptyset(&sigcatch);
 406         cutime = cstime = utime = stime = 0;
 407         cgtime = gtime = 0;
 408
 409         if (lock_task_sighand(task, &flags)) {
 410                 struct signal_struct *sig = task->signal;
 411
 412                 if (sig->tty) {
 413                         struct pid *pgrp = tty_get_pgrp(sig->tty);
 414                         tty_pgrp = pid_nr_ns(pgrp, ns);
 415                         put_pid(pgrp);
 416                         tty_nr = new_encode_dev(tty_devnum(sig->tty));
 417                 }
 418
 419                 num_threads = get_nr_threads(task);
 420                 collect_sigign_sigcatch(task, &sigign, &sigcatch);
 421
 422                 cmin_flt = sig->cmin_flt;
 423                 cmaj_flt = sig->cmaj_flt;
 424                 cutime = sig->cutime;
 425                 cstime = sig->cstime;
 426                 cgtime = sig->cgtime;
 427                 rsslim = ACCESS_ONCE(sig->rlim[RLIMIT_RSS].rlim_cur);
 428
 429                 /* add up live thread stats at the group level */
 430                 if (whole) {
 431                         struct task_struct *t = task;
 432                         do {
 433                                 min_flt += t->min_flt;
 434                                 maj_flt += t->maj_flt;
 435                                 gtime += t->gtime;
 436                                 t = next_thread(t);
 437                         } while (t != task);
 438
 439                         min_flt += sig->min_flt;
 440                         maj_flt += sig->maj_flt;
 441                         thread_group_times(task, &utime, &stime);
 442                         gtime += sig->gtime;
 443                 }
 444
 445                 sid = task_session_nr_ns(task, ns);
 446                 ppid = task_tgid_nr_ns(task->real_parent, ns);
 447                 pgid = task_pgrp_nr_ns(task, ns);
 448
 449                 unlock_task_sighand(task, &flags);
 450         }
 451
 452         if (permitted && (!whole || num_threads < 2))
 453                 wchan = get_wchan(task);
 454         if (!whole) {
 455                 min_flt = task->min_flt;
 456                 maj_flt = task->maj_flt;
 457                 task_times(task, &utime, &stime);
 458                 gtime = task->gtime;
 459         }
 460
 461         /* scale priority and nice values from timeslices to -20..20 */
 462         /* to make it look like a "normal" Unix priority/nice value  */
 463         priority = task_prio(task);
 464         nice = task_nice(task);
 465
 466         /* Temporary variable needed for gcc-2.96 */
 467         /* convert timespec -> nsec*/
 468         start_time =
 469                 (unsigned long long)task->real_start_time.tv_sec * NSEC_PER_SEC
 470                                 + task->real_start_time.tv_nsec;
 471         /* convert nsec -> ticks */
 472         start_time = nsec_to_clock_t(start_time);
 473
 474         seq_printf(m, "%d (%s) %c", pid_nr_ns(pid, ns), tcomm, state);
 475         seq_put_decimal_ll(m, ' ', ppid);
 476         seq_put_decimal_ll(m, ' ', pgid);
 477         seq_put_decimal_ll(m, ' ', sid);
 478         seq_put_decimal_ll(m, ' ', tty_nr);
 479         seq_put_decimal_ll(m, ' ', tty_pgrp);
 480         seq_put_decimal_ull(m, ' ', task->flags);
 481         seq_put_decimal_ull(m, ' ', min_flt);
 482         seq_put_decimal_ull(m, ' ', cmin_flt);
 483         seq_put_decimal_ull(m, ' ', maj_flt);
 484         seq_put_decimal_ull(m, ' ', cmaj_flt);
 485         seq_put_decimal_ull(m, ' ', cputime_to_clock_t(utime));
 486         seq_put_decimal_ull(m, ' ', cputime_to_clock_t(stime));
 487         seq_put_decimal_ll(m, ' ', cputime_to_clock_t(cutime));
 488         seq_put_decimal_ll(m, ' ', cputime_to_clock_t(cstime));
 489         seq_put_decimal_ll(m, ' ', priority);
 490         seq_put_decimal_ll(m, ' ', nice);
 491         seq_put_decimal_ll(m, ' ', num_threads);
 492         seq_put_decimal_ull(m, ' ', 0);
 493         seq_put_decimal_ull(m, ' ', start_time);
 494         seq_put_decimal_ull(m, ' ', vsize);
 495         seq_put_decimal_ull(m, ' ', mm ? get_mm_rss(mm) : 0);
 496         seq_put_decimal_ull(m, ' ', rsslim);
 497         seq_put_decimal_ull(m, ' ', mm ? (permitted ? mm->start_code : 1) : 0);
 498         seq_put_decimal_ull(m, ' ', mm ? (permitted ? mm->end_code : 1) : 0);
 499         seq_put_decimal_ull(m, ' ', (permitted && mm) ? mm->start_stack : 0);
 500         seq_put_decimal_ull(m, ' ', esp);
 501         seq_put_decimal_ull(m, ' ', eip);
 502         /* The signal information here is obsolete.
 503          * It must be decimal for Linux 2.0 compatibility.
 504          * Use /proc/#/status for real-time signals.
 505          */
 506         seq_put_decimal_ull(m, ' ', task->pending.signal.sig[0] & 0x7fffffffUL);
 507         seq_put_decimal_ull(m, ' ', task->blocked.sig[0] & 0x7fffffffUL);
 508         seq_put_decimal_ull(m, ' ', sigign.sig[0] & 0x7fffffffUL);
 509         seq_put_decimal_ull(m, ' ', sigcatch.sig[0] & 0x7fffffffUL);
 510         seq_put_decimal_ull(m, ' ', wchan);
 511         seq_put_decimal_ull(m, ' ', 0);
 512         seq_put_decimal_ull(m, ' ', 0);
 513         seq_put_decimal_ll(m, ' ', task->exit_signal);
 514         seq_put_decimal_ll(m, ' ', task_cpu(task));
 515         seq_put_decimal_ull(m, ' ', task->rt_priority);
 516         seq_put_decimal_ull(m, ' ', task->policy);
 517         seq_put_decimal_ull(m, ' ', delayacct_blkio_ticks(task));
 518         seq_put_decimal_ull(m, ' ', cputime_to_clock_t(gtime));
 519         seq_put_decimal_ll(m, ' ', cputime_to_clock_t(cgtime));
 520         seq_put_decimal_ull(m, ' ', (mm && permitted) ? mm->start_data : 0);
 521         seq_put_decimal_ull(m, ' ', (mm && permitted) ? mm->end_data : 0);
 522         seq_put_decimal_ull(m, ' ', (mm && permitted) ? mm->start_brk : 0);
 523         seq_putc(m, '\n');
 524         if (mm)
 525                 mmput(mm);
 526         return 0;
 527 }
 528
 529 int proc_tid_stat(struct seq_file *m, struct pid_namespace *ns,
 530                         struct pid *pid, struct task_struct *task)
 531 {
 532         return do_task_stat(m, ns, pid, task, 0);
 533 }
 534
 535 int proc_tgid_stat(struct seq_file *m, struct pid_namespace *ns,
 536                         struct pid *pid, struct task_struct *task)
 537 {
 538         return do_task_stat(m, ns, pid, task, 1);
 539 }
 540
 541 int proc_pid_statm(struct seq_file *m, struct pid_namespace *ns,
 542                         struct pid *pid, struct task_struct *task)
 543 {
 544         unsigned long size = 0, resident = 0, shared = 0, text = 0, data = 0;
 545         struct mm_struct *mm = get_task_mm(task);
 546
 547         if (mm) {
 548                 size = task_statm(mm, &shared, &text, &data, &resident);
 549                 mmput(mm);
 550         }
 551         /*
 552          * For quick read, open code by putting numbers directly
 553          * expected format is
 554          * seq_printf(m, "%lu %lu %lu %lu 0 %lu 0\n",
 555          *               size, resident, shared, text, data);
 556          */
 557         seq_put_decimal_ull(m, 0, size);
 558         seq_put_decimal_ull(m, ' ', resident);
 559         seq_put_decimal_ull(m, ' ', shared);
 560         seq_put_decimal_ull(m, ' ', text);
 561         seq_put_decimal_ull(m, ' ', 0);
 562         seq_put_decimal_ull(m, ' ', data);
 563         seq_put_decimal_ull(m, ' ', 0);
 564         seq_putc(m, '\n');
 565
 566         return 0;
 567 }
 568
 569 #ifdef CONFIG_CHECKPOINT_RESTORE
 570 static struct pid *
 571 get_children_pid(struct inode *inode, struct pid *pid_prev, loff_t pos)
 572 {
 573         struct task_struct *start, *task;
 574         struct pid *pid = NULL;
 575
 576         read_lock(&tasklist_lock);
 577
 578         start = pid_task(proc_pid(inode), PIDTYPE_PID);
 579         if (!start)
 580                 goto out;
 581
 582         /*
 583          * Lets try to continue searching first, this gives
 584          * us significant speedup on children-rich processes.
 585          */
 586         if (pid_prev) {
 587                 task = pid_task(pid_prev, PIDTYPE_PID);
 588                 if (task && task->real_parent == start &&
 589                     !(list_empty(&task->sibling))) {
 590                         if (list_is_last(&task->sibling, &start->children))
 591                                 goto out;
 592                         task = list_first_entry(&task->sibling,
 593                                                 struct task_struct, sibling);
 594                         pid = get_pid(task_pid(task));
 595                         goto out;
 596                 }
 597         }
 598
 599         /*
 600          * Slow search case.
 601          *
 602          * We might miss some children here if children
 603          * are exited while we were not holding the lock,
 604          * but it was never promised to be accurate that
 605          * much.
 606          *
 607          * "Just suppose that the parent sleeps, but N children
 608          *  exit after we printed their tids. Now the slow paths
 609          *  skips N extra children, we miss N tasks." (c)
 610          *
 611          * So one need to stop or freeze the leader and all
 612          * its children to get a precise result.
 613          */
 614         list_for_each_entry(task, &start->children, sibling) {
 615                 if (pos-- == 0) {
 616                         pid = get_pid(task_pid(task));
 617                         break;
 618                 }
 619         }
 620
 621 out:
 622         read_unlock(&tasklist_lock);
 623         return pid;
 624 }
 625
 626 static int children_seq_show(struct seq_file *seq, void *v)
 627 {
 628         struct inode *inode = seq->private;
 629         pid_t pid;
 630
 631         pid = pid_nr_ns(v, inode->i_sb->s_fs_info);
 632         return seq_printf(seq, "%d ", pid);
 633 }
 634
 635 static void *children_seq_start(struct seq_file *seq, loff_t *pos)
 636 {
 637         return get_children_pid(seq->private, NULL, *pos);
 638 }
 639
 640 static void *children_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 641 {
 642         struct pid *pid;
 643
 644         pid = get_children_pid(seq->private, v, *pos + 1);
 645         put_pid(v);
 646
 647         ++*pos;
 648         return pid;
 649 }
 650
 651 static void children_seq_stop(struct seq_file *seq, void *v)
 652 {
 653         put_pid(v);
 654 }
 655
 656 static const struct seq_operations children_seq_ops = {
 657         .start  = children_seq_start,
 658         .next   = children_seq_next,
 659         .stop   = children_seq_stop,
 660         .show   = children_seq_show,
 661 };
 662
 663 static int children_seq_open(struct inode *inode, struct file *file)
 664 {
 665         struct seq_file *m;
 666         int ret;
 667
 668         ret = seq_open(file, &children_seq_ops);
 669         if (ret)
 670                 return ret;
 671
 672         m = file->private_data;
 673         m->private = inode;
 674
 675         return ret;
 676 }
 677
 678 int children_seq_release(struct inode *inode, struct file *file)
 679 {
 680         seq_release(inode, file);
 681         return 0;
 682 }
 683
 684 const struct file_operations proc_tid_children_operations = {
 685         .open    = children_seq_open,
 686         .read    = seq_read,
 687         .llseek  = seq_lseek,
 688         .release = children_seq_release,
 689 };
 690 #endif /* CONFIG_CHECKPOINT_RESTORE */