1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Implement CPU time clocks for the POSIX clock interface.
   4 */
   5
   6#include <linux/sched/signal.h>
   7#include <linux/sched/cputime.h>
   8#include <linux/posix-timers.h>
   9#include <linux/errno.h>
  10#include <linux/math64.h>
  11#include <linux/uaccess.h>
  12#include <linux/kernel_stat.h>
  13#include <trace/events/timer.h>
  14#include <linux/tick.h>
  15#include <linux/workqueue.h>
  16#include <linux/compat.h>
  17#include <linux/sched/deadline.h>
  18#include <linux/task_work.h>
  19
  20#include "posix-timers.h"
  21
  22static void posix_cpu_timer_rearm(struct k_itimer *timer);
  23
  24void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit)
  25{
  26	posix_cputimers_init(pct);
  27	if (cpu_limit != RLIM_INFINITY) {
  28		pct->bases[CPUCLOCK_PROF].nextevt = cpu_limit * NSEC_PER_SEC;
  29		pct->timers_active = true;
  30	}
  31}
  32
  33/*
  34 * Called after updating RLIMIT_CPU to run cpu timer and update
  35 * tsk->signal->posix_cputimers.bases[clock].nextevt expiration cache if
  36 * necessary. Needs siglock protection since other code may update the
  37 * expiration cache as well.
  38 *
  39 * Returns 0 on success, -ESRCH on failure.  Can fail if the task is exiting and
  40 * we cannot lock_task_sighand.  Cannot fail if task is current.
  41 */
  42int update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new)
  43{
  44	u64 nsecs = rlim_new * NSEC_PER_SEC;
  45	unsigned long irq_fl;
  46
  47	if (!lock_task_sighand(task, &irq_fl))
  48		return -ESRCH;
  49	set_process_cpu_timer(task, CPUCLOCK_PROF, &nsecs, NULL);
  50	unlock_task_sighand(task, &irq_fl);
  51	return 0;
  52}
  53
  54/*
  55 * Functions for validating access to tasks.
  56 */
  57static struct pid *pid_for_clock(const clockid_t clock, bool gettime)
  58{
  59	const bool thread = !!CPUCLOCK_PERTHREAD(clock);
  60	const pid_t upid = CPUCLOCK_PID(clock);
  61	struct pid *pid;
  62
  63	if (CPUCLOCK_WHICH(clock) >= CPUCLOCK_MAX)
  64		return NULL;
  65
  66	/*
  67	 * If the encoded PID is 0, then the timer is targeted at current
  68	 * or the process to which current belongs.
  69	 */
  70	if (upid == 0)
  71		return thread ? task_pid(current) : task_tgid(current);
  72
  73	pid = find_vpid(upid);
  74	if (!pid)
  75		return NULL;
  76
  77	if (thread) {
  78		struct task_struct *tsk = pid_task(pid, PIDTYPE_PID);
  79		return (tsk && same_thread_group(tsk, current)) ? pid : NULL;
  80	}
  81
  82	/*
  83	 * For clock_gettime(PROCESS) allow finding the process by
  84	 * with the pid of the current task.  The code needs the tgid
  85	 * of the process so that pid_task(pid, PIDTYPE_TGID) can be
  86	 * used to find the process.
  87	 */
  88	if (gettime && (pid == task_pid(current)))
  89		return task_tgid(current);
  90
  91	/*
  92	 * For processes require that pid identifies a process.
  93	 */
  94	return pid_has_task(pid, PIDTYPE_TGID) ? pid : NULL;
  95}
  96
  97static inline int validate_clock_permissions(const clockid_t clock)
  98{
  99	int ret;
 100
 101	rcu_read_lock();
 102	ret = pid_for_clock(clock, false) ? 0 : -EINVAL;
 103	rcu_read_unlock();
 104
 105	return ret;
 106}
 107
 108static inline enum pid_type clock_pid_type(const clockid_t clock)
 109{
 110	return CPUCLOCK_PERTHREAD(clock) ? PIDTYPE_PID : PIDTYPE_TGID;
 111}
 112
 113static inline struct task_struct *cpu_timer_task_rcu(struct k_itimer *timer)
 114{
 115	return pid_task(timer->it.cpu.pid, clock_pid_type(timer->it_clock));
 116}
 117
 118/*
 119 * Update expiry time from increment, and increase overrun count,
 120 * given the current clock sample.
 121 */
 122static u64 bump_cpu_timer(struct k_itimer *timer, u64 now)
 123{
 124	u64 delta, incr, expires = timer->it.cpu.node.expires;
 125	int i;
 126
 127	if (!timer->it_interval)
 128		return expires;
 129
 130	if (now < expires)
 131		return expires;
 132
 133	incr = timer->it_interval;
 134	delta = now + incr - expires;
 135
 136	/* Don't use (incr*2 < delta), incr*2 might overflow. */
 137	for (i = 0; incr < delta - incr; i++)
 138		incr = incr << 1;
 139
 140	for (; i >= 0; incr >>= 1, i--) {
 141		if (delta < incr)
 142			continue;
 143
 144		timer->it.cpu.node.expires += incr;
 145		timer->it_overrun += 1LL << i;
 146		delta -= incr;
 147	}
 148	return timer->it.cpu.node.expires;
 149}
 150
 151/* Check whether all cache entries contain U64_MAX, i.e. eternal expiry time */
 152static inline bool expiry_cache_is_inactive(const struct posix_cputimers *pct)
 153{
 154	return !(~pct->bases[CPUCLOCK_PROF].nextevt |
 155		 ~pct->bases[CPUCLOCK_VIRT].nextevt |
 156		 ~pct->bases[CPUCLOCK_SCHED].nextevt);
 157}
 158
 159static int
 160posix_cpu_clock_getres(const clockid_t which_clock, struct timespec64 *tp)
 161{
 162	int error = validate_clock_permissions(which_clock);
 163
 164	if (!error) {
 165		tp->tv_sec = 0;
 166		tp->tv_nsec = ((NSEC_PER_SEC + HZ - 1) / HZ);
 167		if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
 168			/*
 169			 * If sched_clock is using a cycle counter, we
 170			 * don't have any idea of its true resolution
 171			 * exported, but it is much more than 1s/HZ.
 172			 */
 173			tp->tv_nsec = 1;
 174		}
 175	}
 176	return error;
 177}
 178
 179static int
 180posix_cpu_clock_set(const clockid_t clock, const struct timespec64 *tp)
 181{
 182	int error = validate_clock_permissions(clock);
 183
 184	/*
 185	 * You can never reset a CPU clock, but we check for other errors
 186	 * in the call before failing with EPERM.
 187	 */
 188	return error ? : -EPERM;
 189}
 190
 191/*
 192 * Sample a per-thread clock for the given task. clkid is validated.
 193 */
 194static u64 cpu_clock_sample(const clockid_t clkid, struct task_struct *p)
 195{
 196	u64 utime, stime;
 197
 198	if (clkid == CPUCLOCK_SCHED)
 199		return task_sched_runtime(p);
 200
 201	task_cputime(p, &utime, &stime);
 202
 203	switch (clkid) {
 204	case CPUCLOCK_PROF:
 205		return utime + stime;
 206	case CPUCLOCK_VIRT:
 207		return utime;
 208	default:
 209		WARN_ON_ONCE(1);
 210	}
 211	return 0;
 212}
 213
 214static inline void store_samples(u64 *samples, u64 stime, u64 utime, u64 rtime)
 215{
 216	samples[CPUCLOCK_PROF] = stime + utime;
 217	samples[CPUCLOCK_VIRT] = utime;
 218	samples[CPUCLOCK_SCHED] = rtime;
 219}
 220
 221static void task_sample_cputime(struct task_struct *p, u64 *samples)
 222{
 223	u64 stime, utime;
 224
 225	task_cputime(p, &utime, &stime);
 226	store_samples(samples, stime, utime, p->se.sum_exec_runtime);
 227}
 228
 229static void proc_sample_cputime_atomic(struct task_cputime_atomic *at,
 230				       u64 *samples)
 231{
 232	u64 stime, utime, rtime;
 233
 234	utime = atomic64_read(&at->utime);
 235	stime = atomic64_read(&at->stime);
 236	rtime = atomic64_read(&at->sum_exec_runtime);
 237	store_samples(samples, stime, utime, rtime);
 238}
 239
 240/*
 241 * Set cputime to sum_cputime if sum_cputime > cputime. Use cmpxchg
 242 * to avoid race conditions with concurrent updates to cputime.
 243 */
 244static inline void __update_gt_cputime(atomic64_t *cputime, u64 sum_cputime)
 245{
 246	u64 curr_cputime = atomic64_read(cputime);
 247
 248	do {
 249		if (sum_cputime <= curr_cputime)
 250			return;
 251	} while (!atomic64_try_cmpxchg(cputime, &curr_cputime, sum_cputime));
 
 252}
 253
 254static void update_gt_cputime(struct task_cputime_atomic *cputime_atomic,
 255			      struct task_cputime *sum)
 256{
 257	__update_gt_cputime(&cputime_atomic->utime, sum->utime);
 258	__update_gt_cputime(&cputime_atomic->stime, sum->stime);
 259	__update_gt_cputime(&cputime_atomic->sum_exec_runtime, sum->sum_exec_runtime);
 260}
 261
 262/**
 263 * thread_group_sample_cputime - Sample cputime for a given task
 264 * @tsk:	Task for which cputime needs to be started
 265 * @samples:	Storage for time samples
 266 *
 267 * Called from sys_getitimer() to calculate the expiry time of an active
 268 * timer. That means group cputime accounting is already active. Called
 269 * with task sighand lock held.
 270 *
 271 * Updates @times with an uptodate sample of the thread group cputimes.
 272 */
 273void thread_group_sample_cputime(struct task_struct *tsk, u64 *samples)
 274{
 275	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
 276	struct posix_cputimers *pct = &tsk->signal->posix_cputimers;
 277
 278	WARN_ON_ONCE(!pct->timers_active);
 279
 280	proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
 281}
 282
 283/**
 284 * thread_group_start_cputime - Start cputime and return a sample
 285 * @tsk:	Task for which cputime needs to be started
 286 * @samples:	Storage for time samples
 287 *
 288 * The thread group cputime accounting is avoided when there are no posix
 289 * CPU timers armed. Before starting a timer it's required to check whether
 290 * the time accounting is active. If not, a full update of the atomic
 291 * accounting store needs to be done and the accounting enabled.
 292 *
 293 * Updates @times with an uptodate sample of the thread group cputimes.
 294 */
 295static void thread_group_start_cputime(struct task_struct *tsk, u64 *samples)
 296{
 297	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
 298	struct posix_cputimers *pct = &tsk->signal->posix_cputimers;
 299
 300	lockdep_assert_task_sighand_held(tsk);
 301
 302	/* Check if cputimer isn't running. This is accessed without locking. */
 303	if (!READ_ONCE(pct->timers_active)) {
 304		struct task_cputime sum;
 305
 306		/*
 307		 * The POSIX timer interface allows for absolute time expiry
 308		 * values through the TIMER_ABSTIME flag, therefore we have
 309		 * to synchronize the timer to the clock every time we start it.
 310		 */
 311		thread_group_cputime(tsk, &sum);
 312		update_gt_cputime(&cputimer->cputime_atomic, &sum);
 313
 314		/*
 315		 * We're setting timers_active without a lock. Ensure this
 316		 * only gets written to in one operation. We set it after
 317		 * update_gt_cputime() as a small optimization, but
 318		 * barriers are not required because update_gt_cputime()
 319		 * can handle concurrent updates.
 320		 */
 321		WRITE_ONCE(pct->timers_active, true);
 322	}
 323	proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
 324}
 325
 326static void __thread_group_cputime(struct task_struct *tsk, u64 *samples)
 327{
 328	struct task_cputime ct;
 329
 330	thread_group_cputime(tsk, &ct);
 331	store_samples(samples, ct.stime, ct.utime, ct.sum_exec_runtime);
 332}
 333
 334/*
 335 * Sample a process (thread group) clock for the given task clkid. If the
 336 * group's cputime accounting is already enabled, read the atomic
 337 * store. Otherwise a full update is required.  clkid is already validated.
 338 */
 339static u64 cpu_clock_sample_group(const clockid_t clkid, struct task_struct *p,
 340				  bool start)
 341{
 342	struct thread_group_cputimer *cputimer = &p->signal->cputimer;
 343	struct posix_cputimers *pct = &p->signal->posix_cputimers;
 344	u64 samples[CPUCLOCK_MAX];
 345
 346	if (!READ_ONCE(pct->timers_active)) {
 347		if (start)
 348			thread_group_start_cputime(p, samples);
 349		else
 350			__thread_group_cputime(p, samples);
 351	} else {
 352		proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
 353	}
 354
 355	return samples[clkid];
 356}
 357
 358static int posix_cpu_clock_get(const clockid_t clock, struct timespec64 *tp)
 359{
 360	const clockid_t clkid = CPUCLOCK_WHICH(clock);
 361	struct task_struct *tsk;
 362	u64 t;
 363
 364	rcu_read_lock();
 365	tsk = pid_task(pid_for_clock(clock, true), clock_pid_type(clock));
 366	if (!tsk) {
 367		rcu_read_unlock();
 368		return -EINVAL;
 369	}
 370
 371	if (CPUCLOCK_PERTHREAD(clock))
 372		t = cpu_clock_sample(clkid, tsk);
 373	else
 374		t = cpu_clock_sample_group(clkid, tsk, false);
 375	rcu_read_unlock();
 376
 377	*tp = ns_to_timespec64(t);
 378	return 0;
 379}
 380
 381/*
 382 * Validate the clockid_t for a new CPU-clock timer, and initialize the timer.
 383 * This is called from sys_timer_create() and do_cpu_nanosleep() with the
 384 * new timer already all-zeros initialized.
 385 */
 386static int posix_cpu_timer_create(struct k_itimer *new_timer)
 387{
 388	static struct lock_class_key posix_cpu_timers_key;
 389	struct pid *pid;
 390
 391	rcu_read_lock();
 392	pid = pid_for_clock(new_timer->it_clock, false);
 393	if (!pid) {
 394		rcu_read_unlock();
 395		return -EINVAL;
 396	}
 397
 398	/*
 399	 * If posix timer expiry is handled in task work context then
 400	 * timer::it_lock can be taken without disabling interrupts as all
 401	 * other locking happens in task context. This requires a separate
 402	 * lock class key otherwise regular posix timer expiry would record
 403	 * the lock class being taken in interrupt context and generate a
 404	 * false positive warning.
 405	 */
 406	if (IS_ENABLED(CONFIG_POSIX_CPU_TIMERS_TASK_WORK))
 407		lockdep_set_class(&new_timer->it_lock, &posix_cpu_timers_key);
 408
 409	new_timer->kclock = &clock_posix_cpu;
 410	timerqueue_init(&new_timer->it.cpu.node);
 411	new_timer->it.cpu.pid = get_pid(pid);
 412	rcu_read_unlock();
 413	return 0;
 414}
 415
 416static struct posix_cputimer_base *timer_base(struct k_itimer *timer,
 417					      struct task_struct *tsk)
 418{
 419	int clkidx = CPUCLOCK_WHICH(timer->it_clock);
 420
 421	if (CPUCLOCK_PERTHREAD(timer->it_clock))
 422		return tsk->posix_cputimers.bases + clkidx;
 423	else
 424		return tsk->signal->posix_cputimers.bases + clkidx;
 425}
 426
 427/*
 428 * Force recalculating the base earliest expiration on the next tick.
 429 * This will also re-evaluate the need to keep around the process wide
 430 * cputime counter and tick dependency and eventually shut these down
 431 * if necessary.
 432 */
 433static void trigger_base_recalc_expires(struct k_itimer *timer,
 434					struct task_struct *tsk)
 435{
 436	struct posix_cputimer_base *base = timer_base(timer, tsk);
 437
 438	base->nextevt = 0;
 439}
 440
 441/*
 442 * Dequeue the timer and reset the base if it was its earliest expiration.
 443 * It makes sure the next tick recalculates the base next expiration so we
 444 * don't keep the costly process wide cputime counter around for a random
 445 * amount of time, along with the tick dependency.
 446 *
 447 * If another timer gets queued between this and the next tick, its
 448 * expiration will update the base next event if necessary on the next
 449 * tick.
 450 */
 451static void disarm_timer(struct k_itimer *timer, struct task_struct *p)
 452{
 453	struct cpu_timer *ctmr = &timer->it.cpu;
 454	struct posix_cputimer_base *base;
 455
 456	if (!cpu_timer_dequeue(ctmr))
 457		return;
 458
 459	base = timer_base(timer, p);
 460	if (cpu_timer_getexpires(ctmr) == base->nextevt)
 461		trigger_base_recalc_expires(timer, p);
 462}
 463
 464
 465/*
 466 * Clean up a CPU-clock timer that is about to be destroyed.
 467 * This is called from timer deletion with the timer already locked.
 468 * If we return TIMER_RETRY, it's necessary to release the timer's lock
 469 * and try again.  (This happens when the timer is in the middle of firing.)
 470 */
 471static int posix_cpu_timer_del(struct k_itimer *timer)
 472{
 473	struct cpu_timer *ctmr = &timer->it.cpu;
 474	struct sighand_struct *sighand;
 475	struct task_struct *p;
 476	unsigned long flags;
 477	int ret = 0;
 478
 479	rcu_read_lock();
 480	p = cpu_timer_task_rcu(timer);
 481	if (!p)
 482		goto out;
 483
 484	/*
 485	 * Protect against sighand release/switch in exit/exec and process/
 486	 * thread timer list entry concurrent read/writes.
 487	 */
 488	sighand = lock_task_sighand(p, &flags);
 489	if (unlikely(sighand == NULL)) {
 490		/*
 491		 * This raced with the reaping of the task. The exit cleanup
 492		 * should have removed this timer from the timer queue.
 493		 */
 494		WARN_ON_ONCE(ctmr->head || timerqueue_node_queued(&ctmr->node));
 495	} else {
 496		if (timer->it.cpu.firing)
 497			ret = TIMER_RETRY;
 498		else
 499			disarm_timer(timer, p);
 500
 501		unlock_task_sighand(p, &flags);
 502	}
 503
 504out:
 505	rcu_read_unlock();
 506	if (!ret)
 507		put_pid(ctmr->pid);
 508
 509	return ret;
 510}
 511
 512static void cleanup_timerqueue(struct timerqueue_head *head)
 513{
 514	struct timerqueue_node *node;
 515	struct cpu_timer *ctmr;
 516
 517	while ((node = timerqueue_getnext(head))) {
 518		timerqueue_del(head, node);
 519		ctmr = container_of(node, struct cpu_timer, node);
 520		ctmr->head = NULL;
 521	}
 522}
 523
 524/*
 525 * Clean out CPU timers which are still armed when a thread exits. The
 526 * timers are only removed from the list. No other updates are done. The
 527 * corresponding posix timers are still accessible, but cannot be rearmed.
 528 *
 529 * This must be called with the siglock held.
 530 */
 531static void cleanup_timers(struct posix_cputimers *pct)
 532{
 533	cleanup_timerqueue(&pct->bases[CPUCLOCK_PROF].tqhead);
 534	cleanup_timerqueue(&pct->bases[CPUCLOCK_VIRT].tqhead);
 535	cleanup_timerqueue(&pct->bases[CPUCLOCK_SCHED].tqhead);
 536}
 537
 538/*
 539 * These are both called with the siglock held, when the current thread
 540 * is being reaped.  When the final (leader) thread in the group is reaped,
 541 * posix_cpu_timers_exit_group will be called after posix_cpu_timers_exit.
 542 */
 543void posix_cpu_timers_exit(struct task_struct *tsk)
 544{
 545	cleanup_timers(&tsk->posix_cputimers);
 546}
 547void posix_cpu_timers_exit_group(struct task_struct *tsk)
 548{
 549	cleanup_timers(&tsk->signal->posix_cputimers);
 550}
 551
 552/*
 553 * Insert the timer on the appropriate list before any timers that
 554 * expire later.  This must be called with the sighand lock held.
 555 */
 556static void arm_timer(struct k_itimer *timer, struct task_struct *p)
 557{
 558	struct posix_cputimer_base *base = timer_base(timer, p);
 559	struct cpu_timer *ctmr = &timer->it.cpu;
 560	u64 newexp = cpu_timer_getexpires(ctmr);
 
 
 
 
 
 
 561
 562	if (!cpu_timer_enqueue(&base->tqhead, ctmr))
 563		return;
 564
 565	/*
 566	 * We are the new earliest-expiring POSIX 1.b timer, hence
 567	 * need to update expiration cache. Take into account that
 568	 * for process timers we share expiration cache with itimers
 569	 * and RLIMIT_CPU and for thread timers with RLIMIT_RTTIME.
 570	 */
 571	if (newexp < base->nextevt)
 572		base->nextevt = newexp;
 573
 574	if (CPUCLOCK_PERTHREAD(timer->it_clock))
 575		tick_dep_set_task(p, TICK_DEP_BIT_POSIX_TIMER);
 576	else
 577		tick_dep_set_signal(p, TICK_DEP_BIT_POSIX_TIMER);
 578}
 579
 580/*
 581 * The timer is locked, fire it and arrange for its reload.
 582 */
 583static void cpu_timer_fire(struct k_itimer *timer)
 584{
 585	struct cpu_timer *ctmr = &timer->it.cpu;
 586
 587	if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
 588		/*
 589		 * User don't want any signal.
 590		 */
 591		cpu_timer_setexpires(ctmr, 0);
 592	} else if (unlikely(timer->sigq == NULL)) {
 593		/*
 594		 * This a special case for clock_nanosleep,
 595		 * not a normal timer from sys_timer_create.
 596		 */
 597		wake_up_process(timer->it_process);
 598		cpu_timer_setexpires(ctmr, 0);
 599	} else if (!timer->it_interval) {
 600		/*
 601		 * One-shot timer.  Clear it as soon as it's fired.
 602		 */
 603		posix_timer_event(timer, 0);
 604		cpu_timer_setexpires(ctmr, 0);
 605	} else if (posix_timer_event(timer, ++timer->it_requeue_pending)) {
 606		/*
 607		 * The signal did not get queued because the signal
 608		 * was ignored, so we won't get any callback to
 609		 * reload the timer.  But we need to keep it
 610		 * ticking in case the signal is deliverable next time.
 611		 */
 612		posix_cpu_timer_rearm(timer);
 613		++timer->it_requeue_pending;
 614	}
 615}
 616
 617/*
 618 * Guts of sys_timer_settime for CPU timers.
 619 * This is called with the timer locked and interrupts disabled.
 620 * If we return TIMER_RETRY, it's necessary to release the timer's lock
 621 * and try again.  (This happens when the timer is in the middle of firing.)
 622 */
 623static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
 624			       struct itimerspec64 *new, struct itimerspec64 *old)
 625{
 626	clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
 627	u64 old_expires, new_expires, old_incr, val;
 628	struct cpu_timer *ctmr = &timer->it.cpu;
 629	struct sighand_struct *sighand;
 630	struct task_struct *p;
 631	unsigned long flags;
 632	int ret = 0;
 633
 634	rcu_read_lock();
 635	p = cpu_timer_task_rcu(timer);
 636	if (!p) {
 637		/*
 638		 * If p has just been reaped, we can no
 639		 * longer get any information about it at all.
 640		 */
 641		rcu_read_unlock();
 642		return -ESRCH;
 643	}
 644
 645	/*
 646	 * Use the to_ktime conversion because that clamps the maximum
 647	 * value to KTIME_MAX and avoid multiplication overflows.
 648	 */
 649	new_expires = ktime_to_ns(timespec64_to_ktime(new->it_value));
 650
 651	/*
 652	 * Protect against sighand release/switch in exit/exec and p->cpu_timers
 653	 * and p->signal->cpu_timers read/write in arm_timer()
 654	 */
 655	sighand = lock_task_sighand(p, &flags);
 656	/*
 657	 * If p has just been reaped, we can no
 658	 * longer get any information about it at all.
 659	 */
 660	if (unlikely(sighand == NULL)) {
 661		rcu_read_unlock();
 662		return -ESRCH;
 663	}
 664
 665	/*
 666	 * Disarm any old timer after extracting its expiry time.
 667	 */
 668	old_incr = timer->it_interval;
 669	old_expires = cpu_timer_getexpires(ctmr);
 670
 671	if (unlikely(timer->it.cpu.firing)) {
 672		timer->it.cpu.firing = -1;
 673		ret = TIMER_RETRY;
 674	} else {
 675		cpu_timer_dequeue(ctmr);
 676	}
 677
 678	/*
 679	 * We need to sample the current value to convert the new
 680	 * value from to relative and absolute, and to convert the
 681	 * old value from absolute to relative.  To set a process
 682	 * timer, we need a sample to balance the thread expiry
 683	 * times (in arm_timer).  With an absolute time, we must
 684	 * check if it's already passed.  In short, we need a sample.
 685	 */
 686	if (CPUCLOCK_PERTHREAD(timer->it_clock))
 687		val = cpu_clock_sample(clkid, p);
 688	else
 689		val = cpu_clock_sample_group(clkid, p, true);
 690
 691	if (old) {
 692		if (old_expires == 0) {
 693			old->it_value.tv_sec = 0;
 694			old->it_value.tv_nsec = 0;
 695		} else {
 696			/*
 697			 * Update the timer in case it has overrun already.
 698			 * If it has, we'll report it as having overrun and
 699			 * with the next reloaded timer already ticking,
 700			 * though we are swallowing that pending
 701			 * notification here to install the new setting.
 702			 */
 703			u64 exp = bump_cpu_timer(timer, val);
 704
 705			if (val < exp) {
 706				old_expires = exp - val;
 707				old->it_value = ns_to_timespec64(old_expires);
 708			} else {
 709				old->it_value.tv_nsec = 1;
 710				old->it_value.tv_sec = 0;
 711			}
 712		}
 713	}
 714
 715	if (unlikely(ret)) {
 716		/*
 717		 * We are colliding with the timer actually firing.
 718		 * Punt after filling in the timer's old value, and
 719		 * disable this firing since we are already reporting
 720		 * it as an overrun (thanks to bump_cpu_timer above).
 721		 */
 722		unlock_task_sighand(p, &flags);
 723		goto out;
 724	}
 725
 726	if (new_expires != 0 && !(timer_flags & TIMER_ABSTIME)) {
 727		new_expires += val;
 728	}
 729
 730	/*
 731	 * Install the new expiry time (or zero).
 732	 * For a timer with no notification action, we don't actually
 733	 * arm the timer (we'll just fake it for timer_gettime).
 734	 */
 735	cpu_timer_setexpires(ctmr, new_expires);
 736	if (new_expires != 0 && val < new_expires) {
 737		arm_timer(timer, p);
 738	}
 739
 740	unlock_task_sighand(p, &flags);
 741	/*
 742	 * Install the new reload setting, and
 743	 * set up the signal and overrun bookkeeping.
 744	 */
 745	timer->it_interval = timespec64_to_ktime(new->it_interval);
 746
 747	/*
 748	 * This acts as a modification timestamp for the timer,
 749	 * so any automatic reload attempt will punt on seeing
 750	 * that we have reset the timer manually.
 751	 */
 752	timer->it_requeue_pending = (timer->it_requeue_pending + 2) &
 753		~REQUEUE_PENDING;
 754	timer->it_overrun_last = 0;
 755	timer->it_overrun = -1;
 756
 757	if (val >= new_expires) {
 758		if (new_expires != 0) {
 759			/*
 760			 * The designated time already passed, so we notify
 761			 * immediately, even if the thread never runs to
 762			 * accumulate more time on this clock.
 763			 */
 764			cpu_timer_fire(timer);
 765		}
 766
 767		/*
 768		 * Make sure we don't keep around the process wide cputime
 769		 * counter or the tick dependency if they are not necessary.
 
 770		 */
 771		sighand = lock_task_sighand(p, &flags);
 772		if (!sighand)
 773			goto out;
 774
 775		if (!cpu_timer_queued(ctmr))
 776			trigger_base_recalc_expires(timer, p);
 777
 778		unlock_task_sighand(p, &flags);
 779	}
 
 
 780 out:
 781	rcu_read_unlock();
 782	if (old)
 783		old->it_interval = ns_to_timespec64(old_incr);
 784
 785	return ret;
 786}
 787
 788static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp)
 789{
 790	clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
 791	struct cpu_timer *ctmr = &timer->it.cpu;
 792	u64 now, expires = cpu_timer_getexpires(ctmr);
 793	struct task_struct *p;
 794
 795	rcu_read_lock();
 796	p = cpu_timer_task_rcu(timer);
 797	if (!p)
 798		goto out;
 799
 800	/*
 801	 * Easy part: convert the reload time.
 802	 */
 803	itp->it_interval = ktime_to_timespec64(timer->it_interval);
 804
 805	if (!expires)
 806		goto out;
 807
 808	/*
 809	 * Sample the clock to take the difference with the expiry time.
 810	 */
 811	if (CPUCLOCK_PERTHREAD(timer->it_clock))
 812		now = cpu_clock_sample(clkid, p);
 813	else
 814		now = cpu_clock_sample_group(clkid, p, false);
 815
 816	if (now < expires) {
 817		itp->it_value = ns_to_timespec64(expires - now);
 818	} else {
 819		/*
 820		 * The timer should have expired already, but the firing
 821		 * hasn't taken place yet.  Say it's just about to expire.
 822		 */
 823		itp->it_value.tv_nsec = 1;
 824		itp->it_value.tv_sec = 0;
 825	}
 826out:
 827	rcu_read_unlock();
 828}
 829
 830#define MAX_COLLECTED	20
 831
 832static u64 collect_timerqueue(struct timerqueue_head *head,
 833			      struct list_head *firing, u64 now)
 834{
 835	struct timerqueue_node *next;
 836	int i = 0;
 837
 838	while ((next = timerqueue_getnext(head))) {
 839		struct cpu_timer *ctmr;
 840		u64 expires;
 841
 842		ctmr = container_of(next, struct cpu_timer, node);
 843		expires = cpu_timer_getexpires(ctmr);
 844		/* Limit the number of timers to expire at once */
 845		if (++i == MAX_COLLECTED || now < expires)
 846			return expires;
 847
 848		ctmr->firing = 1;
 849		/* See posix_cpu_timer_wait_running() */
 850		rcu_assign_pointer(ctmr->handling, current);
 851		cpu_timer_dequeue(ctmr);
 852		list_add_tail(&ctmr->elist, firing);
 853	}
 854
 855	return U64_MAX;
 856}
 857
 858static void collect_posix_cputimers(struct posix_cputimers *pct, u64 *samples,
 859				    struct list_head *firing)
 860{
 861	struct posix_cputimer_base *base = pct->bases;
 862	int i;
 863
 864	for (i = 0; i < CPUCLOCK_MAX; i++, base++) {
 865		base->nextevt = collect_timerqueue(&base->tqhead, firing,
 866						    samples[i]);
 867	}
 868}
 869
 870static inline void check_dl_overrun(struct task_struct *tsk)
 871{
 872	if (tsk->dl.dl_overrun) {
 873		tsk->dl.dl_overrun = 0;
 874		send_signal_locked(SIGXCPU, SEND_SIG_PRIV, tsk, PIDTYPE_TGID);
 875	}
 876}
 877
 878static bool check_rlimit(u64 time, u64 limit, int signo, bool rt, bool hard)
 879{
 880	if (time < limit)
 881		return false;
 882
 883	if (print_fatal_signals) {
 884		pr_info("%s Watchdog Timeout (%s): %s[%d]\n",
 885			rt ? "RT" : "CPU", hard ? "hard" : "soft",
 886			current->comm, task_pid_nr(current));
 887	}
 888	send_signal_locked(signo, SEND_SIG_PRIV, current, PIDTYPE_TGID);
 889	return true;
 890}
 891
 892/*
 893 * Check for any per-thread CPU timers that have fired and move them off
 894 * the tsk->cpu_timers[N] list onto the firing list.  Here we update the
 895 * tsk->it_*_expires values to reflect the remaining thread CPU timers.
 896 */
 897static void check_thread_timers(struct task_struct *tsk,
 898				struct list_head *firing)
 899{
 900	struct posix_cputimers *pct = &tsk->posix_cputimers;
 901	u64 samples[CPUCLOCK_MAX];
 902	unsigned long soft;
 903
 904	if (dl_task(tsk))
 905		check_dl_overrun(tsk);
 906
 907	if (expiry_cache_is_inactive(pct))
 908		return;
 909
 910	task_sample_cputime(tsk, samples);
 911	collect_posix_cputimers(pct, samples, firing);
 912
 913	/*
 914	 * Check for the special case thread timers.
 915	 */
 916	soft = task_rlimit(tsk, RLIMIT_RTTIME);
 917	if (soft != RLIM_INFINITY) {
 918		/* Task RT timeout is accounted in jiffies. RTTIME is usec */
 919		unsigned long rttime = tsk->rt.timeout * (USEC_PER_SEC / HZ);
 920		unsigned long hard = task_rlimit_max(tsk, RLIMIT_RTTIME);
 921
 922		/* At the hard limit, send SIGKILL. No further action. */
 923		if (hard != RLIM_INFINITY &&
 924		    check_rlimit(rttime, hard, SIGKILL, true, true))
 925			return;
 926
 927		/* At the soft limit, send a SIGXCPU every second */
 928		if (check_rlimit(rttime, soft, SIGXCPU, true, false)) {
 929			soft += USEC_PER_SEC;
 930			tsk->signal->rlim[RLIMIT_RTTIME].rlim_cur = soft;
 931		}
 932	}
 933
 934	if (expiry_cache_is_inactive(pct))
 935		tick_dep_clear_task(tsk, TICK_DEP_BIT_POSIX_TIMER);
 936}
 937
 938static inline void stop_process_timers(struct signal_struct *sig)
 939{
 940	struct posix_cputimers *pct = &sig->posix_cputimers;
 941
 942	/* Turn off the active flag. This is done without locking. */
 943	WRITE_ONCE(pct->timers_active, false);
 944	tick_dep_clear_signal(sig, TICK_DEP_BIT_POSIX_TIMER);
 945}
 946
 947static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
 948			     u64 *expires, u64 cur_time, int signo)
 949{
 950	if (!it->expires)
 951		return;
 952
 953	if (cur_time >= it->expires) {
 954		if (it->incr)
 955			it->expires += it->incr;
 956		else
 957			it->expires = 0;
 958
 959		trace_itimer_expire(signo == SIGPROF ?
 960				    ITIMER_PROF : ITIMER_VIRTUAL,
 961				    task_tgid(tsk), cur_time);
 962		send_signal_locked(signo, SEND_SIG_PRIV, tsk, PIDTYPE_TGID);
 963	}
 964
 965	if (it->expires && it->expires < *expires)
 966		*expires = it->expires;
 967}
 968
 969/*
 970 * Check for any per-thread CPU timers that have fired and move them
 971 * off the tsk->*_timers list onto the firing list.  Per-thread timers
 972 * have already been taken off.
 973 */
 974static void check_process_timers(struct task_struct *tsk,
 975				 struct list_head *firing)
 976{
 977	struct signal_struct *const sig = tsk->signal;
 978	struct posix_cputimers *pct = &sig->posix_cputimers;
 979	u64 samples[CPUCLOCK_MAX];
 980	unsigned long soft;
 981
 982	/*
 983	 * If there are no active process wide timers (POSIX 1.b, itimers,
 984	 * RLIMIT_CPU) nothing to check. Also skip the process wide timer
 985	 * processing when there is already another task handling them.
 986	 */
 987	if (!READ_ONCE(pct->timers_active) || pct->expiry_active)
 988		return;
 989
 990	/*
 991	 * Signify that a thread is checking for process timers.
 992	 * Write access to this field is protected by the sighand lock.
 993	 */
 994	pct->expiry_active = true;
 995
 996	/*
 997	 * Collect the current process totals. Group accounting is active
 998	 * so the sample can be taken directly.
 999	 */
1000	proc_sample_cputime_atomic(&sig->cputimer.cputime_atomic, samples);
1001	collect_posix_cputimers(pct, samples, firing);
1002
1003	/*
1004	 * Check for the special case process timers.
1005	 */
1006	check_cpu_itimer(tsk, &sig->it[CPUCLOCK_PROF],
1007			 &pct->bases[CPUCLOCK_PROF].nextevt,
1008			 samples[CPUCLOCK_PROF], SIGPROF);
1009	check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT],
1010			 &pct->bases[CPUCLOCK_VIRT].nextevt,
1011			 samples[CPUCLOCK_VIRT], SIGVTALRM);
1012
1013	soft = task_rlimit(tsk, RLIMIT_CPU);
1014	if (soft != RLIM_INFINITY) {
1015		/* RLIMIT_CPU is in seconds. Samples are nanoseconds */
1016		unsigned long hard = task_rlimit_max(tsk, RLIMIT_CPU);
1017		u64 ptime = samples[CPUCLOCK_PROF];
1018		u64 softns = (u64)soft * NSEC_PER_SEC;
1019		u64 hardns = (u64)hard * NSEC_PER_SEC;
1020
1021		/* At the hard limit, send SIGKILL. No further action. */
1022		if (hard != RLIM_INFINITY &&
1023		    check_rlimit(ptime, hardns, SIGKILL, false, true))
1024			return;
1025
1026		/* At the soft limit, send a SIGXCPU every second */
1027		if (check_rlimit(ptime, softns, SIGXCPU, false, false)) {
1028			sig->rlim[RLIMIT_CPU].rlim_cur = soft + 1;
1029			softns += NSEC_PER_SEC;
1030		}
1031
1032		/* Update the expiry cache */
1033		if (softns < pct->bases[CPUCLOCK_PROF].nextevt)
1034			pct->bases[CPUCLOCK_PROF].nextevt = softns;
1035	}
1036
1037	if (expiry_cache_is_inactive(pct))
1038		stop_process_timers(sig);
1039
1040	pct->expiry_active = false;
1041}
1042
1043/*
1044 * This is called from the signal code (via posixtimer_rearm)
1045 * when the last timer signal was delivered and we have to reload the timer.
1046 */
1047static void posix_cpu_timer_rearm(struct k_itimer *timer)
1048{
1049	clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
1050	struct task_struct *p;
1051	struct sighand_struct *sighand;
1052	unsigned long flags;
1053	u64 now;
1054
1055	rcu_read_lock();
1056	p = cpu_timer_task_rcu(timer);
1057	if (!p)
1058		goto out;
1059
1060	/* Protect timer list r/w in arm_timer() */
1061	sighand = lock_task_sighand(p, &flags);
1062	if (unlikely(sighand == NULL))
1063		goto out;
1064
1065	/*
1066	 * Fetch the current sample and update the timer's expiry time.
1067	 */
1068	if (CPUCLOCK_PERTHREAD(timer->it_clock))
1069		now = cpu_clock_sample(clkid, p);
1070	else
1071		now = cpu_clock_sample_group(clkid, p, true);
1072
1073	bump_cpu_timer(timer, now);
1074
1075	/*
1076	 * Now re-arm for the new expiry time.
1077	 */
1078	arm_timer(timer, p);
1079	unlock_task_sighand(p, &flags);
1080out:
1081	rcu_read_unlock();
1082}
1083
1084/**
1085 * task_cputimers_expired - Check whether posix CPU timers are expired
1086 *
1087 * @samples:	Array of current samples for the CPUCLOCK clocks
1088 * @pct:	Pointer to a posix_cputimers container
1089 *
1090 * Returns true if any member of @samples is greater than the corresponding
1091 * member of @pct->bases[CLK].nextevt. False otherwise
1092 */
1093static inline bool
1094task_cputimers_expired(const u64 *samples, struct posix_cputimers *pct)
1095{
1096	int i;
1097
1098	for (i = 0; i < CPUCLOCK_MAX; i++) {
1099		if (samples[i] >= pct->bases[i].nextevt)
1100			return true;
1101	}
1102	return false;
1103}
1104
1105/**
1106 * fastpath_timer_check - POSIX CPU timers fast path.
1107 *
1108 * @tsk:	The task (thread) being checked.
1109 *
1110 * Check the task and thread group timers.  If both are zero (there are no
1111 * timers set) return false.  Otherwise snapshot the task and thread group
1112 * timers and compare them with the corresponding expiration times.  Return
1113 * true if a timer has expired, else return false.
1114 */
1115static inline bool fastpath_timer_check(struct task_struct *tsk)
1116{
1117	struct posix_cputimers *pct = &tsk->posix_cputimers;
1118	struct signal_struct *sig;
1119
1120	if (!expiry_cache_is_inactive(pct)) {
1121		u64 samples[CPUCLOCK_MAX];
1122
1123		task_sample_cputime(tsk, samples);
1124		if (task_cputimers_expired(samples, pct))
1125			return true;
1126	}
1127
1128	sig = tsk->signal;
1129	pct = &sig->posix_cputimers;
1130	/*
1131	 * Check if thread group timers expired when timers are active and
1132	 * no other thread in the group is already handling expiry for
1133	 * thread group cputimers. These fields are read without the
1134	 * sighand lock. However, this is fine because this is meant to be
1135	 * a fastpath heuristic to determine whether we should try to
1136	 * acquire the sighand lock to handle timer expiry.
1137	 *
1138	 * In the worst case scenario, if concurrently timers_active is set
1139	 * or expiry_active is cleared, but the current thread doesn't see
1140	 * the change yet, the timer checks are delayed until the next
1141	 * thread in the group gets a scheduler interrupt to handle the
1142	 * timer. This isn't an issue in practice because these types of
1143	 * delays with signals actually getting sent are expected.
1144	 */
1145	if (READ_ONCE(pct->timers_active) && !READ_ONCE(pct->expiry_active)) {
1146		u64 samples[CPUCLOCK_MAX];
1147
1148		proc_sample_cputime_atomic(&sig->cputimer.cputime_atomic,
1149					   samples);
1150
1151		if (task_cputimers_expired(samples, pct))
1152			return true;
1153	}
1154
1155	if (dl_task(tsk) && tsk->dl.dl_overrun)
1156		return true;
1157
1158	return false;
1159}
1160
1161static void handle_posix_cpu_timers(struct task_struct *tsk);
1162
1163#ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK
1164static void posix_cpu_timers_work(struct callback_head *work)
1165{
1166	struct posix_cputimers_work *cw = container_of(work, typeof(*cw), work);
1167
1168	mutex_lock(&cw->mutex);
1169	handle_posix_cpu_timers(current);
1170	mutex_unlock(&cw->mutex);
1171}
1172
1173/*
1174 * Invoked from the posix-timer core when a cancel operation failed because
1175 * the timer is marked firing. The caller holds rcu_read_lock(), which
1176 * protects the timer and the task which is expiring it from being freed.
1177 */
1178static void posix_cpu_timer_wait_running(struct k_itimer *timr)
1179{
1180	struct task_struct *tsk = rcu_dereference(timr->it.cpu.handling);
1181
1182	/* Has the handling task completed expiry already? */
1183	if (!tsk)
1184		return;
1185
1186	/* Ensure that the task cannot go away */
1187	get_task_struct(tsk);
1188	/* Now drop the RCU protection so the mutex can be locked */
1189	rcu_read_unlock();
1190	/* Wait on the expiry mutex */
1191	mutex_lock(&tsk->posix_cputimers_work.mutex);
1192	/* Release it immediately again. */
1193	mutex_unlock(&tsk->posix_cputimers_work.mutex);
1194	/* Drop the task reference. */
1195	put_task_struct(tsk);
1196	/* Relock RCU so the callsite is balanced */
1197	rcu_read_lock();
1198}
1199
1200static void posix_cpu_timer_wait_running_nsleep(struct k_itimer *timr)
1201{
1202	/* Ensure that timr->it.cpu.handling task cannot go away */
1203	rcu_read_lock();
1204	spin_unlock_irq(&timr->it_lock);
1205	posix_cpu_timer_wait_running(timr);
1206	rcu_read_unlock();
1207	/* @timr is on stack and is valid */
1208	spin_lock_irq(&timr->it_lock);
1209}
1210
1211/*
1212 * Clear existing posix CPU timers task work.
1213 */
1214void clear_posix_cputimers_work(struct task_struct *p)
1215{
1216	/*
1217	 * A copied work entry from the old task is not meaningful, clear it.
1218	 * N.B. init_task_work will not do this.
1219	 */
1220	memset(&p->posix_cputimers_work.work, 0,
1221	       sizeof(p->posix_cputimers_work.work));
1222	init_task_work(&p->posix_cputimers_work.work,
1223		       posix_cpu_timers_work);
1224	mutex_init(&p->posix_cputimers_work.mutex);
1225	p->posix_cputimers_work.scheduled = false;
1226}
1227
1228/*
1229 * Initialize posix CPU timers task work in init task. Out of line to
1230 * keep the callback static and to avoid header recursion hell.
1231 */
1232void __init posix_cputimers_init_work(void)
1233{
1234	clear_posix_cputimers_work(current);
 
1235}
1236
1237/*
1238 * Note: All operations on tsk->posix_cputimer_work.scheduled happen either
1239 * in hard interrupt context or in task context with interrupts
1240 * disabled. Aside of that the writer/reader interaction is always in the
1241 * context of the current task, which means they are strict per CPU.
1242 */
1243static inline bool posix_cpu_timers_work_scheduled(struct task_struct *tsk)
1244{
1245	return tsk->posix_cputimers_work.scheduled;
1246}
1247
1248static inline void __run_posix_cpu_timers(struct task_struct *tsk)
1249{
1250	if (WARN_ON_ONCE(tsk->posix_cputimers_work.scheduled))
1251		return;
1252
1253	/* Schedule task work to actually expire the timers */
1254	tsk->posix_cputimers_work.scheduled = true;
1255	task_work_add(tsk, &tsk->posix_cputimers_work.work, TWA_RESUME);
1256}
1257
1258static inline bool posix_cpu_timers_enable_work(struct task_struct *tsk,
1259						unsigned long start)
1260{
1261	bool ret = true;
1262
1263	/*
1264	 * On !RT kernels interrupts are disabled while collecting expired
1265	 * timers, so no tick can happen and the fast path check can be
1266	 * reenabled without further checks.
1267	 */
1268	if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
1269		tsk->posix_cputimers_work.scheduled = false;
1270		return true;
1271	}
1272
1273	/*
1274	 * On RT enabled kernels ticks can happen while the expired timers
1275	 * are collected under sighand lock. But any tick which observes
1276	 * the CPUTIMERS_WORK_SCHEDULED bit set, does not run the fastpath
1277	 * checks. So reenabling the tick work has do be done carefully:
1278	 *
1279	 * Disable interrupts and run the fast path check if jiffies have
1280	 * advanced since the collecting of expired timers started. If
1281	 * jiffies have not advanced or the fast path check did not find
1282	 * newly expired timers, reenable the fast path check in the timer
1283	 * interrupt. If there are newly expired timers, return false and
1284	 * let the collection loop repeat.
1285	 */
1286	local_irq_disable();
1287	if (start != jiffies && fastpath_timer_check(tsk))
1288		ret = false;
1289	else
1290		tsk->posix_cputimers_work.scheduled = false;
1291	local_irq_enable();
1292
1293	return ret;
1294}
1295#else /* CONFIG_POSIX_CPU_TIMERS_TASK_WORK */
1296static inline void __run_posix_cpu_timers(struct task_struct *tsk)
1297{
1298	lockdep_posixtimer_enter();
1299	handle_posix_cpu_timers(tsk);
1300	lockdep_posixtimer_exit();
1301}
1302
1303static void posix_cpu_timer_wait_running(struct k_itimer *timr)
1304{
1305	cpu_relax();
1306}
1307
1308static void posix_cpu_timer_wait_running_nsleep(struct k_itimer *timr)
1309{
1310	spin_unlock_irq(&timr->it_lock);
1311	cpu_relax();
1312	spin_lock_irq(&timr->it_lock);
1313}
1314
1315static inline bool posix_cpu_timers_work_scheduled(struct task_struct *tsk)
1316{
1317	return false;
1318}
1319
1320static inline bool posix_cpu_timers_enable_work(struct task_struct *tsk,
1321						unsigned long start)
1322{
1323	return true;
1324}
1325#endif /* CONFIG_POSIX_CPU_TIMERS_TASK_WORK */
1326
1327static void handle_posix_cpu_timers(struct task_struct *tsk)
1328{
1329	struct k_itimer *timer, *next;
1330	unsigned long flags, start;
1331	LIST_HEAD(firing);
1332
1333	if (!lock_task_sighand(tsk, &flags))
1334		return;
1335
1336	do {
1337		/*
1338		 * On RT locking sighand lock does not disable interrupts,
1339		 * so this needs to be careful vs. ticks. Store the current
1340		 * jiffies value.
1341		 */
1342		start = READ_ONCE(jiffies);
1343		barrier();
1344
1345		/*
1346		 * Here we take off tsk->signal->cpu_timers[N] and
1347		 * tsk->cpu_timers[N] all the timers that are firing, and
1348		 * put them on the firing list.
1349		 */
1350		check_thread_timers(tsk, &firing);
1351
1352		check_process_timers(tsk, &firing);
1353
1354		/*
1355		 * The above timer checks have updated the expiry cache and
1356		 * because nothing can have queued or modified timers after
1357		 * sighand lock was taken above it is guaranteed to be
1358		 * consistent. So the next timer interrupt fastpath check
1359		 * will find valid data.
1360		 *
1361		 * If timer expiry runs in the timer interrupt context then
1362		 * the loop is not relevant as timers will be directly
1363		 * expired in interrupt context. The stub function below
1364		 * returns always true which allows the compiler to
1365		 * optimize the loop out.
1366		 *
1367		 * If timer expiry is deferred to task work context then
1368		 * the following rules apply:
1369		 *
1370		 * - On !RT kernels no tick can have happened on this CPU
1371		 *   after sighand lock was acquired because interrupts are
1372		 *   disabled. So reenabling task work before dropping
1373		 *   sighand lock and reenabling interrupts is race free.
1374		 *
1375		 * - On RT kernels ticks might have happened but the tick
1376		 *   work ignored posix CPU timer handling because the
1377		 *   CPUTIMERS_WORK_SCHEDULED bit is set. Reenabling work
1378		 *   must be done very carefully including a check whether
1379		 *   ticks have happened since the start of the timer
1380		 *   expiry checks. posix_cpu_timers_enable_work() takes
1381		 *   care of that and eventually lets the expiry checks
1382		 *   run again.
1383		 */
1384	} while (!posix_cpu_timers_enable_work(tsk, start));
1385
1386	/*
1387	 * We must release sighand lock before taking any timer's lock.
1388	 * There is a potential race with timer deletion here, as the
1389	 * siglock now protects our private firing list.  We have set
1390	 * the firing flag in each timer, so that a deletion attempt
1391	 * that gets the timer lock before we do will give it up and
1392	 * spin until we've taken care of that timer below.
1393	 */
1394	unlock_task_sighand(tsk, &flags);
1395
1396	/*
1397	 * Now that all the timers on our list have the firing flag,
1398	 * no one will touch their list entries but us.  We'll take
1399	 * each timer's lock before clearing its firing flag, so no
1400	 * timer call will interfere.
1401	 */
1402	list_for_each_entry_safe(timer, next, &firing, it.cpu.elist) {
1403		int cpu_firing;
1404
1405		/*
1406		 * spin_lock() is sufficient here even independent of the
1407		 * expiry context. If expiry happens in hard interrupt
1408		 * context it's obvious. For task work context it's safe
1409		 * because all other operations on timer::it_lock happen in
1410		 * task context (syscall or exit).
1411		 */
1412		spin_lock(&timer->it_lock);
1413		list_del_init(&timer->it.cpu.elist);
1414		cpu_firing = timer->it.cpu.firing;
1415		timer->it.cpu.firing = 0;
1416		/*
1417		 * The firing flag is -1 if we collided with a reset
1418		 * of the timer, which already reported this
1419		 * almost-firing as an overrun.  So don't generate an event.
1420		 */
1421		if (likely(cpu_firing >= 0))
1422			cpu_timer_fire(timer);
1423		/* See posix_cpu_timer_wait_running() */
1424		rcu_assign_pointer(timer->it.cpu.handling, NULL);
1425		spin_unlock(&timer->it_lock);
1426	}
1427}
1428
1429/*
1430 * This is called from the timer interrupt handler.  The irq handler has
1431 * already updated our counts.  We need to check if any timers fire now.
1432 * Interrupts are disabled.
1433 */
1434void run_posix_cpu_timers(void)
1435{
1436	struct task_struct *tsk = current;
1437
1438	lockdep_assert_irqs_disabled();
1439
1440	/*
1441	 * If the actual expiry is deferred to task work context and the
1442	 * work is already scheduled there is no point to do anything here.
1443	 */
1444	if (posix_cpu_timers_work_scheduled(tsk))
1445		return;
1446
1447	/*
1448	 * The fast path checks that there are no expired thread or thread
1449	 * group timers.  If that's so, just return.
1450	 */
1451	if (!fastpath_timer_check(tsk))
1452		return;
1453
1454	__run_posix_cpu_timers(tsk);
1455}
1456
1457/*
1458 * Set one of the process-wide special case CPU timers or RLIMIT_CPU.
1459 * The tsk->sighand->siglock must be held by the caller.
1460 */
1461void set_process_cpu_timer(struct task_struct *tsk, unsigned int clkid,
1462			   u64 *newval, u64 *oldval)
1463{
1464	u64 now, *nextevt;
1465
1466	if (WARN_ON_ONCE(clkid >= CPUCLOCK_SCHED))
1467		return;
1468
1469	nextevt = &tsk->signal->posix_cputimers.bases[clkid].nextevt;
1470	now = cpu_clock_sample_group(clkid, tsk, true);
1471
1472	if (oldval) {
1473		/*
1474		 * We are setting itimer. The *oldval is absolute and we update
1475		 * it to be relative, *newval argument is relative and we update
1476		 * it to be absolute.
1477		 */
1478		if (*oldval) {
1479			if (*oldval <= now) {
1480				/* Just about to fire. */
1481				*oldval = TICK_NSEC;
1482			} else {
1483				*oldval -= now;
1484			}
1485		}
1486
1487		if (*newval)
1488			*newval += now;
 
1489	}
1490
1491	/*
1492	 * Update expiration cache if this is the earliest timer. CPUCLOCK_PROF
1493	 * expiry cache is also used by RLIMIT_CPU!.
1494	 */
1495	if (*newval < *nextevt)
1496		*nextevt = *newval;
1497
1498	tick_dep_set_signal(tsk, TICK_DEP_BIT_POSIX_TIMER);
1499}
1500
1501static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
1502			    const struct timespec64 *rqtp)
1503{
1504	struct itimerspec64 it;
1505	struct k_itimer timer;
1506	u64 expires;
1507	int error;
1508
1509	/*
1510	 * Set up a temporary timer and then wait for it to go off.
1511	 */
1512	memset(&timer, 0, sizeof timer);
1513	spin_lock_init(&timer.it_lock);
1514	timer.it_clock = which_clock;
1515	timer.it_overrun = -1;
1516	error = posix_cpu_timer_create(&timer);
1517	timer.it_process = current;
1518
1519	if (!error) {
1520		static struct itimerspec64 zero_it;
1521		struct restart_block *restart;
1522
1523		memset(&it, 0, sizeof(it));
1524		it.it_value = *rqtp;
1525
1526		spin_lock_irq(&timer.it_lock);
1527		error = posix_cpu_timer_set(&timer, flags, &it, NULL);
1528		if (error) {
1529			spin_unlock_irq(&timer.it_lock);
1530			return error;
1531		}
1532
1533		while (!signal_pending(current)) {
1534			if (!cpu_timer_getexpires(&timer.it.cpu)) {
1535				/*
1536				 * Our timer fired and was reset, below
1537				 * deletion can not fail.
1538				 */
1539				posix_cpu_timer_del(&timer);
1540				spin_unlock_irq(&timer.it_lock);
1541				return 0;
1542			}
1543
1544			/*
1545			 * Block until cpu_timer_fire (or a signal) wakes us.
1546			 */
1547			__set_current_state(TASK_INTERRUPTIBLE);
1548			spin_unlock_irq(&timer.it_lock);
1549			schedule();
1550			spin_lock_irq(&timer.it_lock);
1551		}
1552
1553		/*
1554		 * We were interrupted by a signal.
1555		 */
1556		expires = cpu_timer_getexpires(&timer.it.cpu);
1557		error = posix_cpu_timer_set(&timer, 0, &zero_it, &it);
1558		if (!error) {
1559			/* Timer is now unarmed, deletion can not fail. */
 
 
1560			posix_cpu_timer_del(&timer);
1561		} else {
1562			while (error == TIMER_RETRY) {
1563				posix_cpu_timer_wait_running_nsleep(&timer);
1564				error = posix_cpu_timer_del(&timer);
1565			}
1566		}
1567
1568		spin_unlock_irq(&timer.it_lock);
1569
 
 
 
 
 
 
 
 
 
 
 
1570		if ((it.it_value.tv_sec | it.it_value.tv_nsec) == 0) {
1571			/*
1572			 * It actually did fire already.
1573			 */
1574			return 0;
1575		}
1576
1577		error = -ERESTART_RESTARTBLOCK;
1578		/*
1579		 * Report back to the user the time still remaining.
1580		 */
1581		restart = &current->restart_block;
1582		restart->nanosleep.expires = expires;
1583		if (restart->nanosleep.type != TT_NONE)
1584			error = nanosleep_copyout(restart, &it.it_value);
1585	}
1586
1587	return error;
1588}
1589
1590static long posix_cpu_nsleep_restart(struct restart_block *restart_block);
1591
1592static int posix_cpu_nsleep(const clockid_t which_clock, int flags,
1593			    const struct timespec64 *rqtp)
1594{
1595	struct restart_block *restart_block = &current->restart_block;
1596	int error;
1597
1598	/*
1599	 * Diagnose required errors first.
1600	 */
1601	if (CPUCLOCK_PERTHREAD(which_clock) &&
1602	    (CPUCLOCK_PID(which_clock) == 0 ||
1603	     CPUCLOCK_PID(which_clock) == task_pid_vnr(current)))
1604		return -EINVAL;
1605
1606	error = do_cpu_nanosleep(which_clock, flags, rqtp);
1607
1608	if (error == -ERESTART_RESTARTBLOCK) {
1609
1610		if (flags & TIMER_ABSTIME)
1611			return -ERESTARTNOHAND;
1612
1613		restart_block->nanosleep.clockid = which_clock;
1614		set_restart_fn(restart_block, posix_cpu_nsleep_restart);
1615	}
1616	return error;
1617}
1618
1619static long posix_cpu_nsleep_restart(struct restart_block *restart_block)
1620{
1621	clockid_t which_clock = restart_block->nanosleep.clockid;
1622	struct timespec64 t;
1623
1624	t = ns_to_timespec64(restart_block->nanosleep.expires);
1625
1626	return do_cpu_nanosleep(which_clock, TIMER_ABSTIME, &t);
1627}
1628
1629#define PROCESS_CLOCK	make_process_cpuclock(0, CPUCLOCK_SCHED)
1630#define THREAD_CLOCK	make_thread_cpuclock(0, CPUCLOCK_SCHED)
1631
1632static int process_cpu_clock_getres(const clockid_t which_clock,
1633				    struct timespec64 *tp)
1634{
1635	return posix_cpu_clock_getres(PROCESS_CLOCK, tp);
1636}
1637static int process_cpu_clock_get(const clockid_t which_clock,
1638				 struct timespec64 *tp)
1639{
1640	return posix_cpu_clock_get(PROCESS_CLOCK, tp);
1641}
1642static int process_cpu_timer_create(struct k_itimer *timer)
1643{
1644	timer->it_clock = PROCESS_CLOCK;
1645	return posix_cpu_timer_create(timer);
1646}
1647static int process_cpu_nsleep(const clockid_t which_clock, int flags,
1648			      const struct timespec64 *rqtp)
1649{
1650	return posix_cpu_nsleep(PROCESS_CLOCK, flags, rqtp);
1651}
1652static int thread_cpu_clock_getres(const clockid_t which_clock,
1653				   struct timespec64 *tp)
1654{
1655	return posix_cpu_clock_getres(THREAD_CLOCK, tp);
1656}
1657static int thread_cpu_clock_get(const clockid_t which_clock,
1658				struct timespec64 *tp)
1659{
1660	return posix_cpu_clock_get(THREAD_CLOCK, tp);
1661}
1662static int thread_cpu_timer_create(struct k_itimer *timer)
1663{
1664	timer->it_clock = THREAD_CLOCK;
1665	return posix_cpu_timer_create(timer);
1666}
1667
1668const struct k_clock clock_posix_cpu = {
1669	.clock_getres		= posix_cpu_clock_getres,
1670	.clock_set		= posix_cpu_clock_set,
1671	.clock_get_timespec	= posix_cpu_clock_get,
1672	.timer_create		= posix_cpu_timer_create,
1673	.nsleep			= posix_cpu_nsleep,
1674	.timer_set		= posix_cpu_timer_set,
1675	.timer_del		= posix_cpu_timer_del,
1676	.timer_get		= posix_cpu_timer_get,
1677	.timer_rearm		= posix_cpu_timer_rearm,
1678	.timer_wait_running	= posix_cpu_timer_wait_running,
1679};
1680
1681const struct k_clock clock_process = {
1682	.clock_getres		= process_cpu_clock_getres,
1683	.clock_get_timespec	= process_cpu_clock_get,
1684	.timer_create		= process_cpu_timer_create,
1685	.nsleep			= process_cpu_nsleep,
1686};
1687
1688const struct k_clock clock_thread = {
1689	.clock_getres		= thread_cpu_clock_getres,
1690	.clock_get_timespec	= thread_cpu_clock_get,
1691	.timer_create		= thread_cpu_timer_create,
1692};