xref: /openbmc/linux/kernel/taskstats.c (revision 81de3bf3) 
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * taskstats.c - Export per-task statistics to userland
4  *
5  * Copyright (C) Shailabh Nagar, IBM Corp. 2006
6  *           (C) Balbir Singh,   IBM Corp. 2006
7  */
8 
9 #include <linux/kernel.h>
10 #include <linux/taskstats_kern.h>
11 #include <linux/tsacct_kern.h>
12 #include <linux/delayacct.h>
13 #include <linux/cpumask.h>
14 #include <linux/percpu.h>
15 #include <linux/slab.h>
16 #include <linux/cgroupstats.h>
17 #include <linux/cgroup.h>
18 #include <linux/fs.h>
19 #include <linux/file.h>
20 #include <linux/pid_namespace.h>
21 #include <net/genetlink.h>
22 #include <linux/atomic.h>
23 #include <linux/sched/cputime.h>
24 
25 /*
26  * Maximum length of a cpumask that can be specified in
27  * the TASKSTATS_CMD_ATTR_REGISTER/DEREGISTER_CPUMASK attribute
28  */
29 #define TASKSTATS_CPUMASK_MAXLEN	(100+6*NR_CPUS)
30 
31 static DEFINE_PER_CPU(__u32, taskstats_seqnum);
32 static int family_registered;
33 struct kmem_cache *taskstats_cache;
34 
35 static struct genl_family family;
36 
37 static const struct nla_policy taskstats_cmd_get_policy[TASKSTATS_CMD_ATTR_MAX+1] = {
38 	[TASKSTATS_CMD_ATTR_PID]  = { .type = NLA_U32 },
39 	[TASKSTATS_CMD_ATTR_TGID] = { .type = NLA_U32 },
40 	[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK] = { .type = NLA_STRING },
41 	[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK] = { .type = NLA_STRING },};
42 
43 /*
44  * We have to use TASKSTATS_CMD_ATTR_MAX here, it is the maxattr in the family.
45  * Make sure they are always aligned.
46  */
47 static const struct nla_policy cgroupstats_cmd_get_policy[TASKSTATS_CMD_ATTR_MAX+1] = {
48 	[CGROUPSTATS_CMD_ATTR_FD] = { .type = NLA_U32 },
49 };
50 
51 struct listener {
52 	struct list_head list;
53 	pid_t pid;
54 	char valid;
55 };
56 
57 struct listener_list {
58 	struct rw_semaphore sem;
59 	struct list_head list;
60 };
61 static DEFINE_PER_CPU(struct listener_list, listener_array);
62 
63 enum actions {
64 	REGISTER,
65 	DEREGISTER,
66 	CPU_DONT_CARE
67 };
68 
69 static int prepare_reply(struct genl_info *info, u8 cmd, struct sk_buff **skbp,
70 				size_t size)
71 {
72 	struct sk_buff *skb;
73 	void *reply;
74 
75 	/*
76 	 * If new attributes are added, please revisit this allocation
77 	 */
78 	skb = genlmsg_new(size, GFP_KERNEL);
79 	if (!skb)
80 		return -ENOMEM;
81 
82 	if (!info) {
83 		int seq = this_cpu_inc_return(taskstats_seqnum) - 1;
84 
85 		reply = genlmsg_put(skb, 0, seq, &family, 0, cmd);
86 	} else
87 		reply = genlmsg_put_reply(skb, info, &family, 0, cmd);
88 	if (reply == NULL) {
89 		nlmsg_free(skb);
90 		return -EINVAL;
91 	}
92 
93 	*skbp = skb;
94 	return 0;
95 }
96 
97 /*
98  * Send taskstats data in @skb to listener with nl_pid @pid
99  */
100 static int send_reply(struct sk_buff *skb, struct genl_info *info)
101 {
102 	struct genlmsghdr *genlhdr = nlmsg_data(nlmsg_hdr(skb));
103 	void *reply = genlmsg_data(genlhdr);
104 
105 	genlmsg_end(skb, reply);
106 
107 	return genlmsg_reply(skb, info);
108 }
109 
110 /*
111  * Send taskstats data in @skb to listeners registered for @cpu's exit data
112  */
113 static void send_cpu_listeners(struct sk_buff *skb,
114 					struct listener_list *listeners)
115 {
116 	struct genlmsghdr *genlhdr = nlmsg_data(nlmsg_hdr(skb));
117 	struct listener *s, *tmp;
118 	struct sk_buff *skb_next, *skb_cur = skb;
119 	void *reply = genlmsg_data(genlhdr);
120 	int rc, delcount = 0;
121 
122 	genlmsg_end(skb, reply);
123 
124 	rc = 0;
125 	down_read(&listeners->sem);
126 	list_for_each_entry(s, &listeners->list, list) {
127 		skb_next = NULL;
128 		if (!list_is_last(&s->list, &listeners->list)) {
129 			skb_next = skb_clone(skb_cur, GFP_KERNEL);
130 			if (!skb_next)
131 				break;
132 		}
133 		rc = genlmsg_unicast(&init_net, skb_cur, s->pid);
134 		if (rc == -ECONNREFUSED) {
135 			s->valid = 0;
136 			delcount++;
137 		}
138 		skb_cur = skb_next;
139 	}
140 	up_read(&listeners->sem);
141 
142 	if (skb_cur)
143 		nlmsg_free(skb_cur);
144 
145 	if (!delcount)
146 		return;
147 
148 	/* Delete invalidated entries */
149 	down_write(&listeners->sem);
150 	list_for_each_entry_safe(s, tmp, &listeners->list, list) {
151 		if (!s->valid) {
152 			list_del(&s->list);
153 			kfree(s);
154 		}
155 	}
156 	up_write(&listeners->sem);
157 }
158 
159 static void fill_stats(struct user_namespace *user_ns,
160 		       struct pid_namespace *pid_ns,
161 		       struct task_struct *tsk, struct taskstats *stats)
162 {
163 	memset(stats, 0, sizeof(*stats));
164 	/*
165 	 * Each accounting subsystem adds calls to its functions to
166 	 * fill in relevant parts of struct taskstsats as follows
167 	 *
168 	 *	per-task-foo(stats, tsk);
169 	 */
170 
171 	delayacct_add_tsk(stats, tsk);
172 
173 	/* fill in basic acct fields */
174 	stats->version = TASKSTATS_VERSION;
175 	stats->nvcsw = tsk->nvcsw;
176 	stats->nivcsw = tsk->nivcsw;
177 	bacct_add_tsk(user_ns, pid_ns, stats, tsk);
178 
179 	/* fill in extended acct fields */
180 	xacct_add_tsk(stats, tsk);
181 }
182 
183 static int fill_stats_for_pid(pid_t pid, struct taskstats *stats)
184 {
185 	struct task_struct *tsk;
186 
187 	tsk = find_get_task_by_vpid(pid);
188 	if (!tsk)
189 		return -ESRCH;
190 	fill_stats(current_user_ns(), task_active_pid_ns(current), tsk, stats);
191 	put_task_struct(tsk);
192 	return 0;
193 }
194 
195 static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
196 {
197 	struct task_struct *tsk, *first;
198 	unsigned long flags;
199 	int rc = -ESRCH;
200 	u64 delta, utime, stime;
201 	u64 start_time;
202 
203 	/*
204 	 * Add additional stats from live tasks except zombie thread group
205 	 * leaders who are already counted with the dead tasks
206 	 */
207 	rcu_read_lock();
208 	first = find_task_by_vpid(tgid);
209 
210 	if (!first || !lock_task_sighand(first, &flags))
211 		goto out;
212 
213 	if (first->signal->stats)
214 		memcpy(stats, first->signal->stats, sizeof(*stats));
215 	else
216 		memset(stats, 0, sizeof(*stats));
217 
218 	tsk = first;
219 	start_time = ktime_get_ns();
220 	do {
221 		if (tsk->exit_state)
222 			continue;
223 		/*
224 		 * Accounting subsystem can call its functions here to
225 		 * fill in relevant parts of struct taskstsats as follows
226 		 *
227 		 *	per-task-foo(stats, tsk);
228 		 */
229 		delayacct_add_tsk(stats, tsk);
230 
231 		/* calculate task elapsed time in nsec */
232 		delta = start_time - tsk->start_time;
233 		/* Convert to micro seconds */
234 		do_div(delta, NSEC_PER_USEC);
235 		stats->ac_etime += delta;
236 
237 		task_cputime(tsk, &utime, &stime);
238 		stats->ac_utime += div_u64(utime, NSEC_PER_USEC);
239 		stats->ac_stime += div_u64(stime, NSEC_PER_USEC);
240 
241 		stats->nvcsw += tsk->nvcsw;
242 		stats->nivcsw += tsk->nivcsw;
243 	} while_each_thread(first, tsk);
244 
245 	unlock_task_sighand(first, &flags);
246 	rc = 0;
247 out:
248 	rcu_read_unlock();
249 
250 	stats->version = TASKSTATS_VERSION;
251 	/*
252 	 * Accounting subsystems can also add calls here to modify
253 	 * fields of taskstats.
254 	 */
255 	return rc;
256 }
257 
258 static void fill_tgid_exit(struct task_struct *tsk)
259 {
260 	unsigned long flags;
261 
262 	spin_lock_irqsave(&tsk->sighand->siglock, flags);
263 	if (!tsk->signal->stats)
264 		goto ret;
265 
266 	/*
267 	 * Each accounting subsystem calls its functions here to
268 	 * accumalate its per-task stats for tsk, into the per-tgid structure
269 	 *
270 	 *	per-task-foo(tsk->signal->stats, tsk);
271 	 */
272 	delayacct_add_tsk(tsk->signal->stats, tsk);
273 ret:
274 	spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
275 	return;
276 }
277 
278 static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd)
279 {
280 	struct listener_list *listeners;
281 	struct listener *s, *tmp, *s2;
282 	unsigned int cpu;
283 	int ret = 0;
284 
285 	if (!cpumask_subset(mask, cpu_possible_mask))
286 		return -EINVAL;
287 
288 	if (current_user_ns() != &init_user_ns)
289 		return -EINVAL;
290 
291 	if (task_active_pid_ns(current) != &init_pid_ns)
292 		return -EINVAL;
293 
294 	if (isadd == REGISTER) {
295 		for_each_cpu(cpu, mask) {
296 			s = kmalloc_node(sizeof(struct listener),
297 					GFP_KERNEL, cpu_to_node(cpu));
298 			if (!s) {
299 				ret = -ENOMEM;
300 				goto cleanup;
301 			}
302 			s->pid = pid;
303 			s->valid = 1;
304 
305 			listeners = &per_cpu(listener_array, cpu);
306 			down_write(&listeners->sem);
307 			list_for_each_entry(s2, &listeners->list, list) {
308 				if (s2->pid == pid && s2->valid)
309 					goto exists;
310 			}
311 			list_add(&s->list, &listeners->list);
312 			s = NULL;
313 exists:
314 			up_write(&listeners->sem);
315 			kfree(s); /* nop if NULL */
316 		}
317 		return 0;
318 	}
319 
320 	/* Deregister or cleanup */
321 cleanup:
322 	for_each_cpu(cpu, mask) {
323 		listeners = &per_cpu(listener_array, cpu);
324 		down_write(&listeners->sem);
325 		list_for_each_entry_safe(s, tmp, &listeners->list, list) {
326 			if (s->pid == pid) {
327 				list_del(&s->list);
328 				kfree(s);
329 				break;
330 			}
331 		}
332 		up_write(&listeners->sem);
333 	}
334 	return ret;
335 }
336 
337 static int parse(struct nlattr *na, struct cpumask *mask)
338 {
339 	char *data;
340 	int len;
341 	int ret;
342 
343 	if (na == NULL)
344 		return 1;
345 	len = nla_len(na);
346 	if (len > TASKSTATS_CPUMASK_MAXLEN)
347 		return -E2BIG;
348 	if (len < 1)
349 		return -EINVAL;
350 	data = kmalloc(len, GFP_KERNEL);
351 	if (!data)
352 		return -ENOMEM;
353 	nla_strlcpy(data, na, len);
354 	ret = cpulist_parse(data, mask);
355 	kfree(data);
356 	return ret;
357 }
358 
359 static struct taskstats *mk_reply(struct sk_buff *skb, int type, u32 pid)
360 {
361 	struct nlattr *na, *ret;
362 	int aggr;
363 
364 	aggr = (type == TASKSTATS_TYPE_PID)
365 			? TASKSTATS_TYPE_AGGR_PID
366 			: TASKSTATS_TYPE_AGGR_TGID;
367 
368 	na = nla_nest_start_noflag(skb, aggr);
369 	if (!na)
370 		goto err;
371 
372 	if (nla_put(skb, type, sizeof(pid), &pid) < 0) {
373 		nla_nest_cancel(skb, na);
374 		goto err;
375 	}
376 	ret = nla_reserve_64bit(skb, TASKSTATS_TYPE_STATS,
377 				sizeof(struct taskstats), TASKSTATS_TYPE_NULL);
378 	if (!ret) {
379 		nla_nest_cancel(skb, na);
380 		goto err;
381 	}
382 	nla_nest_end(skb, na);
383 
384 	return nla_data(ret);
385 err:
386 	return NULL;
387 }
388 
389 static int cgroupstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
390 {
391 	int rc = 0;
392 	struct sk_buff *rep_skb;
393 	struct cgroupstats *stats;
394 	struct nlattr *na;
395 	size_t size;
396 	u32 fd;
397 	struct fd f;
398 
399 	na = info->attrs[CGROUPSTATS_CMD_ATTR_FD];
400 	if (!na)
401 		return -EINVAL;
402 
403 	fd = nla_get_u32(info->attrs[CGROUPSTATS_CMD_ATTR_FD]);
404 	f = fdget(fd);
405 	if (!f.file)
406 		return 0;
407 
408 	size = nla_total_size(sizeof(struct cgroupstats));
409 
410 	rc = prepare_reply(info, CGROUPSTATS_CMD_NEW, &rep_skb,
411 				size);
412 	if (rc < 0)
413 		goto err;
414 
415 	na = nla_reserve(rep_skb, CGROUPSTATS_TYPE_CGROUP_STATS,
416 				sizeof(struct cgroupstats));
417 	if (na == NULL) {
418 		nlmsg_free(rep_skb);
419 		rc = -EMSGSIZE;
420 		goto err;
421 	}
422 
423 	stats = nla_data(na);
424 	memset(stats, 0, sizeof(*stats));
425 
426 	rc = cgroupstats_build(stats, f.file->f_path.dentry);
427 	if (rc < 0) {
428 		nlmsg_free(rep_skb);
429 		goto err;
430 	}
431 
432 	rc = send_reply(rep_skb, info);
433 
434 err:
435 	fdput(f);
436 	return rc;
437 }
438 
439 static int cmd_attr_register_cpumask(struct genl_info *info)
440 {
441 	cpumask_var_t mask;
442 	int rc;
443 
444 	if (!alloc_cpumask_var(&mask, GFP_KERNEL))
445 		return -ENOMEM;
446 	rc = parse(info->attrs[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK], mask);
447 	if (rc < 0)
448 		goto out;
449 	rc = add_del_listener(info->snd_portid, mask, REGISTER);
450 out:
451 	free_cpumask_var(mask);
452 	return rc;
453 }
454 
455 static int cmd_attr_deregister_cpumask(struct genl_info *info)
456 {
457 	cpumask_var_t mask;
458 	int rc;
459 
460 	if (!alloc_cpumask_var(&mask, GFP_KERNEL))
461 		return -ENOMEM;
462 	rc = parse(info->attrs[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK], mask);
463 	if (rc < 0)
464 		goto out;
465 	rc = add_del_listener(info->snd_portid, mask, DEREGISTER);
466 out:
467 	free_cpumask_var(mask);
468 	return rc;
469 }
470 
471 static size_t taskstats_packet_size(void)
472 {
473 	size_t size;
474 
475 	size = nla_total_size(sizeof(u32)) +
476 		nla_total_size_64bit(sizeof(struct taskstats)) +
477 		nla_total_size(0);
478 
479 	return size;
480 }
481 
482 static int cmd_attr_pid(struct genl_info *info)
483 {
484 	struct taskstats *stats;
485 	struct sk_buff *rep_skb;
486 	size_t size;
487 	u32 pid;
488 	int rc;
489 
490 	size = taskstats_packet_size();
491 
492 	rc = prepare_reply(info, TASKSTATS_CMD_NEW, &rep_skb, size);
493 	if (rc < 0)
494 		return rc;
495 
496 	rc = -EINVAL;
497 	pid = nla_get_u32(info->attrs[TASKSTATS_CMD_ATTR_PID]);
498 	stats = mk_reply(rep_skb, TASKSTATS_TYPE_PID, pid);
499 	if (!stats)
500 		goto err;
501 
502 	rc = fill_stats_for_pid(pid, stats);
503 	if (rc < 0)
504 		goto err;
505 	return send_reply(rep_skb, info);
506 err:
507 	nlmsg_free(rep_skb);
508 	return rc;
509 }
510 
511 static int cmd_attr_tgid(struct genl_info *info)
512 {
513 	struct taskstats *stats;
514 	struct sk_buff *rep_skb;
515 	size_t size;
516 	u32 tgid;
517 	int rc;
518 
519 	size = taskstats_packet_size();
520 
521 	rc = prepare_reply(info, TASKSTATS_CMD_NEW, &rep_skb, size);
522 	if (rc < 0)
523 		return rc;
524 
525 	rc = -EINVAL;
526 	tgid = nla_get_u32(info->attrs[TASKSTATS_CMD_ATTR_TGID]);
527 	stats = mk_reply(rep_skb, TASKSTATS_TYPE_TGID, tgid);
528 	if (!stats)
529 		goto err;
530 
531 	rc = fill_stats_for_tgid(tgid, stats);
532 	if (rc < 0)
533 		goto err;
534 	return send_reply(rep_skb, info);
535 err:
536 	nlmsg_free(rep_skb);
537 	return rc;
538 }
539 
540 static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
541 {
542 	if (info->attrs[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK])
543 		return cmd_attr_register_cpumask(info);
544 	else if (info->attrs[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK])
545 		return cmd_attr_deregister_cpumask(info);
546 	else if (info->attrs[TASKSTATS_CMD_ATTR_PID])
547 		return cmd_attr_pid(info);
548 	else if (info->attrs[TASKSTATS_CMD_ATTR_TGID])
549 		return cmd_attr_tgid(info);
550 	else
551 		return -EINVAL;
552 }
553 
554 static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk)
555 {
556 	struct signal_struct *sig = tsk->signal;
557 	struct taskstats *stats;
558 
559 	if (sig->stats || thread_group_empty(tsk))
560 		goto ret;
561 
562 	/* No problem if kmem_cache_zalloc() fails */
563 	stats = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
564 
565 	spin_lock_irq(&tsk->sighand->siglock);
566 	if (!sig->stats) {
567 		sig->stats = stats;
568 		stats = NULL;
569 	}
570 	spin_unlock_irq(&tsk->sighand->siglock);
571 
572 	if (stats)
573 		kmem_cache_free(taskstats_cache, stats);
574 ret:
575 	return sig->stats;
576 }
577 
578 /* Send pid data out on exit */
579 void taskstats_exit(struct task_struct *tsk, int group_dead)
580 {
581 	int rc;
582 	struct listener_list *listeners;
583 	struct taskstats *stats;
584 	struct sk_buff *rep_skb;
585 	size_t size;
586 	int is_thread_group;
587 
588 	if (!family_registered)
589 		return;
590 
591 	/*
592 	 * Size includes space for nested attributes
593 	 */
594 	size = taskstats_packet_size();
595 
596 	is_thread_group = !!taskstats_tgid_alloc(tsk);
597 	if (is_thread_group) {
598 		/* PID + STATS + TGID + STATS */
599 		size = 2 * size;
600 		/* fill the tsk->signal->stats structure */
601 		fill_tgid_exit(tsk);
602 	}
603 
604 	listeners = raw_cpu_ptr(&listener_array);
605 	if (list_empty(&listeners->list))
606 		return;
607 
608 	rc = prepare_reply(NULL, TASKSTATS_CMD_NEW, &rep_skb, size);
609 	if (rc < 0)
610 		return;
611 
612 	stats = mk_reply(rep_skb, TASKSTATS_TYPE_PID,
613 			 task_pid_nr_ns(tsk, &init_pid_ns));
614 	if (!stats)
615 		goto err;
616 
617 	fill_stats(&init_user_ns, &init_pid_ns, tsk, stats);
618 
619 	/*
620 	 * Doesn't matter if tsk is the leader or the last group member leaving
621 	 */
622 	if (!is_thread_group || !group_dead)
623 		goto send;
624 
625 	stats = mk_reply(rep_skb, TASKSTATS_TYPE_TGID,
626 			 task_tgid_nr_ns(tsk, &init_pid_ns));
627 	if (!stats)
628 		goto err;
629 
630 	memcpy(stats, tsk->signal->stats, sizeof(*stats));
631 
632 send:
633 	send_cpu_listeners(rep_skb, listeners);
634 	return;
635 err:
636 	nlmsg_free(rep_skb);
637 }
638 
639 static const struct genl_ops taskstats_ops[] = {
640 	{
641 		.cmd		= TASKSTATS_CMD_GET,
642 		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
643 		.doit		= taskstats_user_cmd,
644 		/* policy enforced later */
645 		.flags		= GENL_ADMIN_PERM | GENL_CMD_CAP_HASPOL,
646 	},
647 	{
648 		.cmd		= CGROUPSTATS_CMD_GET,
649 		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
650 		.doit		= cgroupstats_user_cmd,
651 		/* policy enforced later */
652 		.flags		= GENL_CMD_CAP_HASPOL,
653 	},
654 };
655 
656 static int taskstats_pre_doit(const struct genl_ops *ops, struct sk_buff *skb,
657 			      struct genl_info *info)
658 {
659 	const struct nla_policy *policy = NULL;
660 
661 	switch (ops->cmd) {
662 	case TASKSTATS_CMD_GET:
663 		policy = taskstats_cmd_get_policy;
664 		break;
665 	case CGROUPSTATS_CMD_GET:
666 		policy = cgroupstats_cmd_get_policy;
667 		break;
668 	default:
669 		return -EINVAL;
670 	}
671 
672 	return nlmsg_validate_deprecated(info->nlhdr, GENL_HDRLEN,
673 					 TASKSTATS_CMD_ATTR_MAX, policy,
674 					 info->extack);
675 }
676 
677 static struct genl_family family __ro_after_init = {
678 	.name		= TASKSTATS_GENL_NAME,
679 	.version	= TASKSTATS_GENL_VERSION,
680 	.maxattr	= TASKSTATS_CMD_ATTR_MAX,
681 	.module		= THIS_MODULE,
682 	.ops		= taskstats_ops,
683 	.n_ops		= ARRAY_SIZE(taskstats_ops),
684 	.pre_doit	= taskstats_pre_doit,
685 };
686 
687 /* Needed early in initialization */
688 void __init taskstats_init_early(void)
689 {
690 	unsigned int i;
691 
692 	taskstats_cache = KMEM_CACHE(taskstats, SLAB_PANIC);
693 	for_each_possible_cpu(i) {
694 		INIT_LIST_HEAD(&(per_cpu(listener_array, i).list));
695 		init_rwsem(&(per_cpu(listener_array, i).sem));
696 	}
697 }
698 
699 static int __init taskstats_init(void)
700 {
701 	int rc;
702 
703 	rc = genl_register_family(&family);
704 	if (rc)
705 		return rc;
706 
707 	family_registered = 1;
708 	pr_info("registered taskstats version %d\n", TASKSTATS_GENL_VERSION);
709 	return 0;
710 }
711 
712 /*
713  * late initcall ensures initialization of statistics collection
714  * mechanisms precedes initialization of the taskstats interface
715  */
716 late_initcall(taskstats_init);
717