xref: /linux/fs/proc/array.c (revision 93df8a1ed6231727c5db94a80b1a6bd5ee67cec3)
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/string_helpers.h>
85 #include <linux/user_namespace.h>
86 
87 #include <asm/pgtable.h>
88 #include <asm/processor.h>
89 #include "internal.h"
90 
91 static inline void task_name(struct seq_file *m, struct task_struct *p)
92 {
93 	char *buf;
94 	char tcomm[sizeof(p->comm)];
95 
96 	get_task_comm(tcomm, p);
97 
98 	seq_puts(m, "Name:\t");
99 	buf = m->buf + m->count;
100 
101 	/* Ignore error for now */
102 	buf += string_escape_str(tcomm, buf, m->size - m->count,
103 				 ESCAPE_SPACE | ESCAPE_SPECIAL, "\n\\");
104 
105 	m->count = buf - m->buf;
106 	seq_putc(m, '\n');
107 }
108 
109 /*
110  * The task state array is a strange "bitmap" of
111  * reasons to sleep. Thus "running" is zero, and
112  * you can test for combinations of others with
113  * simple bit tests.
114  */
115 static const char * const task_state_array[] = {
116 	"R (running)",		/*   0 */
117 	"S (sleeping)",		/*   1 */
118 	"D (disk sleep)",	/*   2 */
119 	"T (stopped)",		/*   4 */
120 	"t (tracing stop)",	/*   8 */
121 	"X (dead)",		/*  16 */
122 	"Z (zombie)",		/*  32 */
123 };
124 
125 static inline const char *get_task_state(struct task_struct *tsk)
126 {
127 	unsigned int state = (tsk->state | tsk->exit_state) & TASK_REPORT;
128 
129 	/*
130 	 * Parked tasks do not run; they sit in __kthread_parkme().
131 	 * Without this check, we would report them as running, which is
132 	 * clearly wrong, so we report them as sleeping instead.
133 	 */
134 	if (tsk->state == TASK_PARKED)
135 		state = TASK_INTERRUPTIBLE;
136 
137 	BUILD_BUG_ON(1 + ilog2(TASK_REPORT) != ARRAY_SIZE(task_state_array)-1);
138 
139 	return task_state_array[fls(state)];
140 }
141 
142 static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
143 				struct pid *pid, struct task_struct *p)
144 {
145 	struct user_namespace *user_ns = seq_user_ns(m);
146 	struct group_info *group_info;
147 	int g;
148 	struct task_struct *tracer;
149 	const struct cred *cred;
150 	pid_t ppid, tpid = 0, tgid, ngid;
151 	unsigned int max_fds = 0;
152 
153 	rcu_read_lock();
154 	ppid = pid_alive(p) ?
155 		task_tgid_nr_ns(rcu_dereference(p->real_parent), ns) : 0;
156 
157 	tracer = ptrace_parent(p);
158 	if (tracer)
159 		tpid = task_pid_nr_ns(tracer, ns);
160 
161 	tgid = task_tgid_nr_ns(p, ns);
162 	ngid = task_numa_group_id(p);
163 	cred = get_task_cred(p);
164 
165 	task_lock(p);
166 	if (p->files)
167 		max_fds = files_fdtable(p->files)->max_fds;
168 	task_unlock(p);
169 	rcu_read_unlock();
170 
171 	seq_printf(m,
172 		"State:\t%s\n"
173 		"Tgid:\t%d\n"
174 		"Ngid:\t%d\n"
175 		"Pid:\t%d\n"
176 		"PPid:\t%d\n"
177 		"TracerPid:\t%d\n"
178 		"Uid:\t%d\t%d\t%d\t%d\n"
179 		"Gid:\t%d\t%d\t%d\t%d\n"
180 		"FDSize:\t%d\nGroups:\t",
181 		get_task_state(p),
182 		tgid, ngid, pid_nr_ns(pid, ns), ppid, tpid,
183 		from_kuid_munged(user_ns, cred->uid),
184 		from_kuid_munged(user_ns, cred->euid),
185 		from_kuid_munged(user_ns, cred->suid),
186 		from_kuid_munged(user_ns, cred->fsuid),
187 		from_kgid_munged(user_ns, cred->gid),
188 		from_kgid_munged(user_ns, cred->egid),
189 		from_kgid_munged(user_ns, cred->sgid),
190 		from_kgid_munged(user_ns, cred->fsgid),
191 		max_fds);
192 
193 	group_info = cred->group_info;
194 	for (g = 0; g < group_info->ngroups; g++)
195 		seq_printf(m, "%d ",
196 			   from_kgid_munged(user_ns, GROUP_AT(group_info, g)));
197 	put_cred(cred);
198 
199 #ifdef CONFIG_PID_NS
200 	seq_puts(m, "\nNStgid:");
201 	for (g = ns->level; g <= pid->level; g++)
202 		seq_printf(m, "\t%d",
203 			task_tgid_nr_ns(p, pid->numbers[g].ns));
204 	seq_puts(m, "\nNSpid:");
205 	for (g = ns->level; g <= pid->level; g++)
206 		seq_printf(m, "\t%d",
207 			task_pid_nr_ns(p, pid->numbers[g].ns));
208 	seq_puts(m, "\nNSpgid:");
209 	for (g = ns->level; g <= pid->level; g++)
210 		seq_printf(m, "\t%d",
211 			task_pgrp_nr_ns(p, pid->numbers[g].ns));
212 	seq_puts(m, "\nNSsid:");
213 	for (g = ns->level; g <= pid->level; g++)
214 		seq_printf(m, "\t%d",
215 			task_session_nr_ns(p, pid->numbers[g].ns));
216 #endif
217 	seq_putc(m, '\n');
218 }
219 
220 void render_sigset_t(struct seq_file *m, const char *header,
221 				sigset_t *set)
222 {
223 	int i;
224 
225 	seq_puts(m, header);
226 
227 	i = _NSIG;
228 	do {
229 		int x = 0;
230 
231 		i -= 4;
232 		if (sigismember(set, i+1)) x |= 1;
233 		if (sigismember(set, i+2)) x |= 2;
234 		if (sigismember(set, i+3)) x |= 4;
235 		if (sigismember(set, i+4)) x |= 8;
236 		seq_printf(m, "%x", x);
237 	} while (i >= 4);
238 
239 	seq_putc(m, '\n');
240 }
241 
242 static void collect_sigign_sigcatch(struct task_struct *p, sigset_t *ign,
243 				    sigset_t *catch)
244 {
245 	struct k_sigaction *k;
246 	int i;
247 
248 	k = p->sighand->action;
249 	for (i = 1; i <= _NSIG; ++i, ++k) {
250 		if (k->sa.sa_handler == SIG_IGN)
251 			sigaddset(ign, i);
252 		else if (k->sa.sa_handler != SIG_DFL)
253 			sigaddset(catch, i);
254 	}
255 }
256 
257 static inline void task_sig(struct seq_file *m, struct task_struct *p)
258 {
259 	unsigned long flags;
260 	sigset_t pending, shpending, blocked, ignored, caught;
261 	int num_threads = 0;
262 	unsigned long qsize = 0;
263 	unsigned long qlim = 0;
264 
265 	sigemptyset(&pending);
266 	sigemptyset(&shpending);
267 	sigemptyset(&blocked);
268 	sigemptyset(&ignored);
269 	sigemptyset(&caught);
270 
271 	if (lock_task_sighand(p, &flags)) {
272 		pending = p->pending.signal;
273 		shpending = p->signal->shared_pending.signal;
274 		blocked = p->blocked;
275 		collect_sigign_sigcatch(p, &ignored, &caught);
276 		num_threads = get_nr_threads(p);
277 		rcu_read_lock();  /* FIXME: is this correct? */
278 		qsize = atomic_read(&__task_cred(p)->user->sigpending);
279 		rcu_read_unlock();
280 		qlim = task_rlimit(p, RLIMIT_SIGPENDING);
281 		unlock_task_sighand(p, &flags);
282 	}
283 
284 	seq_printf(m, "Threads:\t%d\n", num_threads);
285 	seq_printf(m, "SigQ:\t%lu/%lu\n", qsize, qlim);
286 
287 	/* render them all */
288 	render_sigset_t(m, "SigPnd:\t", &pending);
289 	render_sigset_t(m, "ShdPnd:\t", &shpending);
290 	render_sigset_t(m, "SigBlk:\t", &blocked);
291 	render_sigset_t(m, "SigIgn:\t", &ignored);
292 	render_sigset_t(m, "SigCgt:\t", &caught);
293 }
294 
295 static void render_cap_t(struct seq_file *m, const char *header,
296 			kernel_cap_t *a)
297 {
298 	unsigned __capi;
299 
300 	seq_puts(m, header);
301 	CAP_FOR_EACH_U32(__capi) {
302 		seq_printf(m, "%08x",
303 			   a->cap[CAP_LAST_U32 - __capi]);
304 	}
305 	seq_putc(m, '\n');
306 }
307 
308 static inline void task_cap(struct seq_file *m, struct task_struct *p)
309 {
310 	const struct cred *cred;
311 	kernel_cap_t cap_inheritable, cap_permitted, cap_effective, cap_bset;
312 
313 	rcu_read_lock();
314 	cred = __task_cred(p);
315 	cap_inheritable	= cred->cap_inheritable;
316 	cap_permitted	= cred->cap_permitted;
317 	cap_effective	= cred->cap_effective;
318 	cap_bset	= cred->cap_bset;
319 	rcu_read_unlock();
320 
321 	render_cap_t(m, "CapInh:\t", &cap_inheritable);
322 	render_cap_t(m, "CapPrm:\t", &cap_permitted);
323 	render_cap_t(m, "CapEff:\t", &cap_effective);
324 	render_cap_t(m, "CapBnd:\t", &cap_bset);
325 }
326 
327 static inline void task_seccomp(struct seq_file *m, struct task_struct *p)
328 {
329 #ifdef CONFIG_SECCOMP
330 	seq_printf(m, "Seccomp:\t%d\n", p->seccomp.mode);
331 #endif
332 }
333 
334 static inline void task_context_switch_counts(struct seq_file *m,
335 						struct task_struct *p)
336 {
337 	seq_printf(m,	"voluntary_ctxt_switches:\t%lu\n"
338 			"nonvoluntary_ctxt_switches:\t%lu\n",
339 			p->nvcsw,
340 			p->nivcsw);
341 }
342 
343 static void task_cpus_allowed(struct seq_file *m, struct task_struct *task)
344 {
345 	seq_printf(m, "Cpus_allowed:\t%*pb\n",
346 		   cpumask_pr_args(&task->cpus_allowed));
347 	seq_printf(m, "Cpus_allowed_list:\t%*pbl\n",
348 		   cpumask_pr_args(&task->cpus_allowed));
349 }
350 
351 int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
352 			struct pid *pid, struct task_struct *task)
353 {
354 	struct mm_struct *mm = get_task_mm(task);
355 
356 	task_name(m, task);
357 	task_state(m, ns, pid, task);
358 
359 	if (mm) {
360 		task_mem(m, mm);
361 		mmput(mm);
362 	}
363 	task_sig(m, task);
364 	task_cap(m, task);
365 	task_seccomp(m, task);
366 	task_cpus_allowed(m, task);
367 	cpuset_task_status_allowed(m, task);
368 	task_context_switch_counts(m, task);
369 	return 0;
370 }
371 
372 static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
373 			struct pid *pid, struct task_struct *task, int whole)
374 {
375 	unsigned long vsize, eip, esp, wchan = ~0UL;
376 	int priority, nice;
377 	int tty_pgrp = -1, tty_nr = 0;
378 	sigset_t sigign, sigcatch;
379 	char state;
380 	pid_t ppid = 0, pgid = -1, sid = -1;
381 	int num_threads = 0;
382 	int permitted;
383 	struct mm_struct *mm;
384 	unsigned long long start_time;
385 	unsigned long cmin_flt = 0, cmaj_flt = 0;
386 	unsigned long  min_flt = 0,  maj_flt = 0;
387 	cputime_t cutime, cstime, utime, stime;
388 	cputime_t cgtime, gtime;
389 	unsigned long rsslim = 0;
390 	char tcomm[sizeof(task->comm)];
391 	unsigned long flags;
392 
393 	state = *get_task_state(task);
394 	vsize = eip = esp = 0;
395 	permitted = ptrace_may_access(task, PTRACE_MODE_READ | PTRACE_MODE_NOAUDIT);
396 	mm = get_task_mm(task);
397 	if (mm) {
398 		vsize = task_vsize(mm);
399 		if (permitted) {
400 			eip = KSTK_EIP(task);
401 			esp = KSTK_ESP(task);
402 		}
403 	}
404 
405 	get_task_comm(tcomm, task);
406 
407 	sigemptyset(&sigign);
408 	sigemptyset(&sigcatch);
409 	cutime = cstime = utime = stime = 0;
410 	cgtime = gtime = 0;
411 
412 	if (lock_task_sighand(task, &flags)) {
413 		struct signal_struct *sig = task->signal;
414 
415 		if (sig->tty) {
416 			struct pid *pgrp = tty_get_pgrp(sig->tty);
417 			tty_pgrp = pid_nr_ns(pgrp, ns);
418 			put_pid(pgrp);
419 			tty_nr = new_encode_dev(tty_devnum(sig->tty));
420 		}
421 
422 		num_threads = get_nr_threads(task);
423 		collect_sigign_sigcatch(task, &sigign, &sigcatch);
424 
425 		cmin_flt = sig->cmin_flt;
426 		cmaj_flt = sig->cmaj_flt;
427 		cutime = sig->cutime;
428 		cstime = sig->cstime;
429 		cgtime = sig->cgtime;
430 		rsslim = ACCESS_ONCE(sig->rlim[RLIMIT_RSS].rlim_cur);
431 
432 		/* add up live thread stats at the group level */
433 		if (whole) {
434 			struct task_struct *t = task;
435 			do {
436 				min_flt += t->min_flt;
437 				maj_flt += t->maj_flt;
438 				gtime += task_gtime(t);
439 			} while_each_thread(task, t);
440 
441 			min_flt += sig->min_flt;
442 			maj_flt += sig->maj_flt;
443 			thread_group_cputime_adjusted(task, &utime, &stime);
444 			gtime += sig->gtime;
445 		}
446 
447 		sid = task_session_nr_ns(task, ns);
448 		ppid = task_tgid_nr_ns(task->real_parent, ns);
449 		pgid = task_pgrp_nr_ns(task, ns);
450 
451 		unlock_task_sighand(task, &flags);
452 	}
453 
454 	if (permitted && (!whole || num_threads < 2))
455 		wchan = get_wchan(task);
456 	if (!whole) {
457 		min_flt = task->min_flt;
458 		maj_flt = task->maj_flt;
459 		task_cputime_adjusted(task, &utime, &stime);
460 		gtime = task_gtime(task);
461 	}
462 
463 	/* scale priority and nice values from timeslices to -20..20 */
464 	/* to make it look like a "normal" Unix priority/nice value  */
465 	priority = task_prio(task);
466 	nice = task_nice(task);
467 
468 	/* convert nsec -> ticks */
469 	start_time = nsec_to_clock_t(task->real_start_time);
470 
471 	seq_printf(m, "%d (%s) %c", pid_nr_ns(pid, ns), tcomm, state);
472 	seq_put_decimal_ll(m, ' ', ppid);
473 	seq_put_decimal_ll(m, ' ', pgid);
474 	seq_put_decimal_ll(m, ' ', sid);
475 	seq_put_decimal_ll(m, ' ', tty_nr);
476 	seq_put_decimal_ll(m, ' ', tty_pgrp);
477 	seq_put_decimal_ull(m, ' ', task->flags);
478 	seq_put_decimal_ull(m, ' ', min_flt);
479 	seq_put_decimal_ull(m, ' ', cmin_flt);
480 	seq_put_decimal_ull(m, ' ', maj_flt);
481 	seq_put_decimal_ull(m, ' ', cmaj_flt);
482 	seq_put_decimal_ull(m, ' ', cputime_to_clock_t(utime));
483 	seq_put_decimal_ull(m, ' ', cputime_to_clock_t(stime));
484 	seq_put_decimal_ll(m, ' ', cputime_to_clock_t(cutime));
485 	seq_put_decimal_ll(m, ' ', cputime_to_clock_t(cstime));
486 	seq_put_decimal_ll(m, ' ', priority);
487 	seq_put_decimal_ll(m, ' ', nice);
488 	seq_put_decimal_ll(m, ' ', num_threads);
489 	seq_put_decimal_ull(m, ' ', 0);
490 	seq_put_decimal_ull(m, ' ', start_time);
491 	seq_put_decimal_ull(m, ' ', vsize);
492 	seq_put_decimal_ull(m, ' ', mm ? get_mm_rss(mm) : 0);
493 	seq_put_decimal_ull(m, ' ', rsslim);
494 	seq_put_decimal_ull(m, ' ', mm ? (permitted ? mm->start_code : 1) : 0);
495 	seq_put_decimal_ull(m, ' ', mm ? (permitted ? mm->end_code : 1) : 0);
496 	seq_put_decimal_ull(m, ' ', (permitted && mm) ? mm->start_stack : 0);
497 	seq_put_decimal_ull(m, ' ', esp);
498 	seq_put_decimal_ull(m, ' ', eip);
499 	/* The signal information here is obsolete.
500 	 * It must be decimal for Linux 2.0 compatibility.
501 	 * Use /proc/#/status for real-time signals.
502 	 */
503 	seq_put_decimal_ull(m, ' ', task->pending.signal.sig[0] & 0x7fffffffUL);
504 	seq_put_decimal_ull(m, ' ', task->blocked.sig[0] & 0x7fffffffUL);
505 	seq_put_decimal_ull(m, ' ', sigign.sig[0] & 0x7fffffffUL);
506 	seq_put_decimal_ull(m, ' ', sigcatch.sig[0] & 0x7fffffffUL);
507 	seq_put_decimal_ull(m, ' ', wchan);
508 	seq_put_decimal_ull(m, ' ', 0);
509 	seq_put_decimal_ull(m, ' ', 0);
510 	seq_put_decimal_ll(m, ' ', task->exit_signal);
511 	seq_put_decimal_ll(m, ' ', task_cpu(task));
512 	seq_put_decimal_ull(m, ' ', task->rt_priority);
513 	seq_put_decimal_ull(m, ' ', task->policy);
514 	seq_put_decimal_ull(m, ' ', delayacct_blkio_ticks(task));
515 	seq_put_decimal_ull(m, ' ', cputime_to_clock_t(gtime));
516 	seq_put_decimal_ll(m, ' ', cputime_to_clock_t(cgtime));
517 
518 	if (mm && permitted) {
519 		seq_put_decimal_ull(m, ' ', mm->start_data);
520 		seq_put_decimal_ull(m, ' ', mm->end_data);
521 		seq_put_decimal_ull(m, ' ', mm->start_brk);
522 		seq_put_decimal_ull(m, ' ', mm->arg_start);
523 		seq_put_decimal_ull(m, ' ', mm->arg_end);
524 		seq_put_decimal_ull(m, ' ', mm->env_start);
525 		seq_put_decimal_ull(m, ' ', mm->env_end);
526 	} else
527 		seq_printf(m, " 0 0 0 0 0 0 0");
528 
529 	if (permitted)
530 		seq_put_decimal_ll(m, ' ', task->exit_code);
531 	else
532 		seq_put_decimal_ll(m, ' ', 0);
533 
534 	seq_putc(m, '\n');
535 	if (mm)
536 		mmput(mm);
537 	return 0;
538 }
539 
540 int proc_tid_stat(struct seq_file *m, struct pid_namespace *ns,
541 			struct pid *pid, struct task_struct *task)
542 {
543 	return do_task_stat(m, ns, pid, task, 0);
544 }
545 
546 int proc_tgid_stat(struct seq_file *m, struct pid_namespace *ns,
547 			struct pid *pid, struct task_struct *task)
548 {
549 	return do_task_stat(m, ns, pid, task, 1);
550 }
551 
552 int proc_pid_statm(struct seq_file *m, struct pid_namespace *ns,
553 			struct pid *pid, struct task_struct *task)
554 {
555 	unsigned long size = 0, resident = 0, shared = 0, text = 0, data = 0;
556 	struct mm_struct *mm = get_task_mm(task);
557 
558 	if (mm) {
559 		size = task_statm(mm, &shared, &text, &data, &resident);
560 		mmput(mm);
561 	}
562 	/*
563 	 * For quick read, open code by putting numbers directly
564 	 * expected format is
565 	 * seq_printf(m, "%lu %lu %lu %lu 0 %lu 0\n",
566 	 *               size, resident, shared, text, data);
567 	 */
568 	seq_put_decimal_ull(m, 0, size);
569 	seq_put_decimal_ull(m, ' ', resident);
570 	seq_put_decimal_ull(m, ' ', shared);
571 	seq_put_decimal_ull(m, ' ', text);
572 	seq_put_decimal_ull(m, ' ', 0);
573 	seq_put_decimal_ull(m, ' ', data);
574 	seq_put_decimal_ull(m, ' ', 0);
575 	seq_putc(m, '\n');
576 
577 	return 0;
578 }
579 
580 #ifdef CONFIG_PROC_CHILDREN
581 static struct pid *
582 get_children_pid(struct inode *inode, struct pid *pid_prev, loff_t pos)
583 {
584 	struct task_struct *start, *task;
585 	struct pid *pid = NULL;
586 
587 	read_lock(&tasklist_lock);
588 
589 	start = pid_task(proc_pid(inode), PIDTYPE_PID);
590 	if (!start)
591 		goto out;
592 
593 	/*
594 	 * Lets try to continue searching first, this gives
595 	 * us significant speedup on children-rich processes.
596 	 */
597 	if (pid_prev) {
598 		task = pid_task(pid_prev, PIDTYPE_PID);
599 		if (task && task->real_parent == start &&
600 		    !(list_empty(&task->sibling))) {
601 			if (list_is_last(&task->sibling, &start->children))
602 				goto out;
603 			task = list_first_entry(&task->sibling,
604 						struct task_struct, sibling);
605 			pid = get_pid(task_pid(task));
606 			goto out;
607 		}
608 	}
609 
610 	/*
611 	 * Slow search case.
612 	 *
613 	 * We might miss some children here if children
614 	 * are exited while we were not holding the lock,
615 	 * but it was never promised to be accurate that
616 	 * much.
617 	 *
618 	 * "Just suppose that the parent sleeps, but N children
619 	 *  exit after we printed their tids. Now the slow paths
620 	 *  skips N extra children, we miss N tasks." (c)
621 	 *
622 	 * So one need to stop or freeze the leader and all
623 	 * its children to get a precise result.
624 	 */
625 	list_for_each_entry(task, &start->children, sibling) {
626 		if (pos-- == 0) {
627 			pid = get_pid(task_pid(task));
628 			break;
629 		}
630 	}
631 
632 out:
633 	read_unlock(&tasklist_lock);
634 	return pid;
635 }
636 
637 static int children_seq_show(struct seq_file *seq, void *v)
638 {
639 	struct inode *inode = seq->private;
640 	pid_t pid;
641 
642 	pid = pid_nr_ns(v, inode->i_sb->s_fs_info);
643 	seq_printf(seq, "%d ", pid);
644 
645 	return 0;
646 }
647 
648 static void *children_seq_start(struct seq_file *seq, loff_t *pos)
649 {
650 	return get_children_pid(seq->private, NULL, *pos);
651 }
652 
653 static void *children_seq_next(struct seq_file *seq, void *v, loff_t *pos)
654 {
655 	struct pid *pid;
656 
657 	pid = get_children_pid(seq->private, v, *pos + 1);
658 	put_pid(v);
659 
660 	++*pos;
661 	return pid;
662 }
663 
664 static void children_seq_stop(struct seq_file *seq, void *v)
665 {
666 	put_pid(v);
667 }
668 
669 static const struct seq_operations children_seq_ops = {
670 	.start	= children_seq_start,
671 	.next	= children_seq_next,
672 	.stop	= children_seq_stop,
673 	.show	= children_seq_show,
674 };
675 
676 static int children_seq_open(struct inode *inode, struct file *file)
677 {
678 	struct seq_file *m;
679 	int ret;
680 
681 	ret = seq_open(file, &children_seq_ops);
682 	if (ret)
683 		return ret;
684 
685 	m = file->private_data;
686 	m->private = inode;
687 
688 	return ret;
689 }
690 
691 int children_seq_release(struct inode *inode, struct file *file)
692 {
693 	seq_release(inode, file);
694 	return 0;
695 }
696 
697 const struct file_operations proc_tid_children_operations = {
698 	.open    = children_seq_open,
699 	.read    = seq_read,
700 	.llseek  = seq_lseek,
701 	.release = children_seq_release,
702 };
703 #endif /* CONFIG_PROC_CHILDREN */
704