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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;
247retry:
248 curr_cputime = atomic64_read(cputime);
249 if (sum_cputime > curr_cputime) {
250 if (atomic64_cmpxchg(cputime, curr_cputime, sum_cputime) != curr_cputime)
251 goto retry;
252 }
253}
254
255static void update_gt_cputime(struct task_cputime_atomic *cputime_atomic,
256 struct task_cputime *sum)
257{
258 __update_gt_cputime(&cputime_atomic->utime, sum->utime);
259 __update_gt_cputime(&cputime_atomic->stime, sum->stime);
260 __update_gt_cputime(&cputime_atomic->sum_exec_runtime, sum->sum_exec_runtime);
261}
262
263/**
264 * thread_group_sample_cputime - Sample cputime for a given task
265 * @tsk: Task for which cputime needs to be started
266 * @samples: Storage for time samples
267 *
268 * Called from sys_getitimer() to calculate the expiry time of an active
269 * timer. That means group cputime accounting is already active. Called
270 * with task sighand lock held.
271 *
272 * Updates @times with an uptodate sample of the thread group cputimes.
273 */
274void thread_group_sample_cputime(struct task_struct *tsk, u64 *samples)
275{
276 struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
277 struct posix_cputimers *pct = &tsk->signal->posix_cputimers;
278
279 WARN_ON_ONCE(!pct->timers_active);
280
281 proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
282}
283
284/**
285 * thread_group_start_cputime - Start cputime and return a sample
286 * @tsk: Task for which cputime needs to be started
287 * @samples: Storage for time samples
288 *
289 * The thread group cputime accounting is avoided when there are no posix
290 * CPU timers armed. Before starting a timer it's required to check whether
291 * the time accounting is active. If not, a full update of the atomic
292 * accounting store needs to be done and the accounting enabled.
293 *
294 * Updates @times with an uptodate sample of the thread group cputimes.
295 */
296static void thread_group_start_cputime(struct task_struct *tsk, u64 *samples)
297{
298 struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
299 struct posix_cputimers *pct = &tsk->signal->posix_cputimers;
300
301 lockdep_assert_task_sighand_held(tsk);
302
303 /* Check if cputimer isn't running. This is accessed without locking. */
304 if (!READ_ONCE(pct->timers_active)) {
305 struct task_cputime sum;
306
307 /*
308 * The POSIX timer interface allows for absolute time expiry
309 * values through the TIMER_ABSTIME flag, therefore we have
310 * to synchronize the timer to the clock every time we start it.
311 */
312 thread_group_cputime(tsk, &sum);
313 update_gt_cputime(&cputimer->cputime_atomic, &sum);
314
315 /*
316 * We're setting timers_active without a lock. Ensure this
317 * only gets written to in one operation. We set it after
318 * update_gt_cputime() as a small optimization, but
319 * barriers are not required because update_gt_cputime()
320 * can handle concurrent updates.
321 */
322 WRITE_ONCE(pct->timers_active, true);
323 }
324 proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
325}
326
327static void __thread_group_cputime(struct task_struct *tsk, u64 *samples)
328{
329 struct task_cputime ct;
330
331 thread_group_cputime(tsk, &ct);
332 store_samples(samples, ct.stime, ct.utime, ct.sum_exec_runtime);
333}
334
335/*
336 * Sample a process (thread group) clock for the given task clkid. If the
337 * group's cputime accounting is already enabled, read the atomic
338 * store. Otherwise a full update is required. clkid is already validated.
339 */
340static u64 cpu_clock_sample_group(const clockid_t clkid, struct task_struct *p,
341 bool start)
342{
343 struct thread_group_cputimer *cputimer = &p->signal->cputimer;
344 struct posix_cputimers *pct = &p->signal->posix_cputimers;
345 u64 samples[CPUCLOCK_MAX];
346
347 if (!READ_ONCE(pct->timers_active)) {
348 if (start)
349 thread_group_start_cputime(p, samples);
350 else
351 __thread_group_cputime(p, samples);
352 } else {
353 proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
354 }
355
356 return samples[clkid];
357}
358
359static int posix_cpu_clock_get(const clockid_t clock, struct timespec64 *tp)
360{
361 const clockid_t clkid = CPUCLOCK_WHICH(clock);
362 struct task_struct *tsk;
363 u64 t;
364
365 rcu_read_lock();
366 tsk = pid_task(pid_for_clock(clock, true), clock_pid_type(clock));
367 if (!tsk) {
368 rcu_read_unlock();
369 return -EINVAL;
370 }
371
372 if (CPUCLOCK_PERTHREAD(clock))
373 t = cpu_clock_sample(clkid, tsk);
374 else
375 t = cpu_clock_sample_group(clkid, tsk, false);
376 rcu_read_unlock();
377
378 *tp = ns_to_timespec64(t);
379 return 0;
380}
381
382/*
383 * Validate the clockid_t for a new CPU-clock timer, and initialize the timer.
384 * This is called from sys_timer_create() and do_cpu_nanosleep() with the
385 * new timer already all-zeros initialized.
386 */
387static int posix_cpu_timer_create(struct k_itimer *new_timer)
388{
389 static struct lock_class_key posix_cpu_timers_key;
390 struct pid *pid;
391
392 rcu_read_lock();
393 pid = pid_for_clock(new_timer->it_clock, false);
394 if (!pid) {
395 rcu_read_unlock();
396 return -EINVAL;
397 }
398
399 /*
400 * If posix timer expiry is handled in task work context then
401 * timer::it_lock can be taken without disabling interrupts as all
402 * other locking happens in task context. This requires a separate
403 * lock class key otherwise regular posix timer expiry would record
404 * the lock class being taken in interrupt context and generate a
405 * false positive warning.
406 */
407 if (IS_ENABLED(CONFIG_POSIX_CPU_TIMERS_TASK_WORK))
408 lockdep_set_class(&new_timer->it_lock, &posix_cpu_timers_key);
409
410 new_timer->kclock = &clock_posix_cpu;
411 timerqueue_init(&new_timer->it.cpu.node);
412 new_timer->it.cpu.pid = get_pid(pid);
413 rcu_read_unlock();
414 return 0;
415}
416
417static struct posix_cputimer_base *timer_base(struct k_itimer *timer,
418 struct task_struct *tsk)
419{
420 int clkidx = CPUCLOCK_WHICH(timer->it_clock);
421
422 if (CPUCLOCK_PERTHREAD(timer->it_clock))
423 return tsk->posix_cputimers.bases + clkidx;
424 else
425 return tsk->signal->posix_cputimers.bases + clkidx;
426}
427
428/*
429 * Force recalculating the base earliest expiration on the next tick.
430 * This will also re-evaluate the need to keep around the process wide
431 * cputime counter and tick dependency and eventually shut these down
432 * if necessary.
433 */
434static void trigger_base_recalc_expires(struct k_itimer *timer,
435 struct task_struct *tsk)
436{
437 struct posix_cputimer_base *base = timer_base(timer, tsk);
438
439 base->nextevt = 0;
440}
441
442/*
443 * Dequeue the timer and reset the base if it was its earliest expiration.
444 * It makes sure the next tick recalculates the base next expiration so we
445 * don't keep the costly process wide cputime counter around for a random
446 * amount of time, along with the tick dependency.
447 *
448 * If another timer gets queued between this and the next tick, its
449 * expiration will update the base next event if necessary on the next
450 * tick.
451 */
452static void disarm_timer(struct k_itimer *timer, struct task_struct *p)
453{
454 struct cpu_timer *ctmr = &timer->it.cpu;
455 struct posix_cputimer_base *base;
456
457 if (!cpu_timer_dequeue(ctmr))
458 return;
459
460 base = timer_base(timer, p);
461 if (cpu_timer_getexpires(ctmr) == base->nextevt)
462 trigger_base_recalc_expires(timer, p);
463}
464
465
466/*
467 * Clean up a CPU-clock timer that is about to be destroyed.
468 * This is called from timer deletion with the timer already locked.
469 * If we return TIMER_RETRY, it's necessary to release the timer's lock
470 * and try again. (This happens when the timer is in the middle of firing.)
471 */
472static int posix_cpu_timer_del(struct k_itimer *timer)
473{
474 struct cpu_timer *ctmr = &timer->it.cpu;
475 struct sighand_struct *sighand;
476 struct task_struct *p;
477 unsigned long flags;
478 int ret = 0;
479
480 rcu_read_lock();
481 p = cpu_timer_task_rcu(timer);
482 if (!p)
483 goto out;
484
485 /*
486 * Protect against sighand release/switch in exit/exec and process/
487 * thread timer list entry concurrent read/writes.
488 */
489 sighand = lock_task_sighand(p, &flags);
490 if (unlikely(sighand == NULL)) {
491 /*
492 * This raced with the reaping of the task. The exit cleanup
493 * should have removed this timer from the timer queue.
494 */
495 WARN_ON_ONCE(ctmr->head || timerqueue_node_queued(&ctmr->node));
496 } else {
497 if (timer->it.cpu.firing)
498 ret = TIMER_RETRY;
499 else
500 disarm_timer(timer, p);
501
502 unlock_task_sighand(p, &flags);
503 }
504
505out:
506 rcu_read_unlock();
507 if (!ret)
508 put_pid(ctmr->pid);
509
510 return ret;
511}
512
513static void cleanup_timerqueue(struct timerqueue_head *head)
514{
515 struct timerqueue_node *node;
516 struct cpu_timer *ctmr;
517
518 while ((node = timerqueue_getnext(head))) {
519 timerqueue_del(head, node);
520 ctmr = container_of(node, struct cpu_timer, node);
521 ctmr->head = NULL;
522 }
523}
524
525/*
526 * Clean out CPU timers which are still armed when a thread exits. The
527 * timers are only removed from the list. No other updates are done. The
528 * corresponding posix timers are still accessible, but cannot be rearmed.
529 *
530 * This must be called with the siglock held.
531 */
532static void cleanup_timers(struct posix_cputimers *pct)
533{
534 cleanup_timerqueue(&pct->bases[CPUCLOCK_PROF].tqhead);
535 cleanup_timerqueue(&pct->bases[CPUCLOCK_VIRT].tqhead);
536 cleanup_timerqueue(&pct->bases[CPUCLOCK_SCHED].tqhead);
537}
538
539/*
540 * These are both called with the siglock held, when the current thread
541 * is being reaped. When the final (leader) thread in the group is reaped,
542 * posix_cpu_timers_exit_group will be called after posix_cpu_timers_exit.
543 */
544void posix_cpu_timers_exit(struct task_struct *tsk)
545{
546 cleanup_timers(&tsk->posix_cputimers);
547}
548void posix_cpu_timers_exit_group(struct task_struct *tsk)
549{
550 cleanup_timers(&tsk->signal->posix_cputimers);
551}
552
553/*
554 * Insert the timer on the appropriate list before any timers that
555 * expire later. This must be called with the sighand lock held.
556 */
557static void arm_timer(struct k_itimer *timer, struct task_struct *p)
558{
559 struct posix_cputimer_base *base = timer_base(timer, p);
560 struct cpu_timer *ctmr = &timer->it.cpu;
561 u64 newexp = cpu_timer_getexpires(ctmr);
562
563 if (!cpu_timer_enqueue(&base->tqhead, ctmr))
564 return;
565
566 /*
567 * We are the new earliest-expiring POSIX 1.b timer, hence
568 * need to update expiration cache. Take into account that
569 * for process timers we share expiration cache with itimers
570 * and RLIMIT_CPU and for thread timers with RLIMIT_RTTIME.
571 */
572 if (newexp < base->nextevt)
573 base->nextevt = newexp;
574
575 if (CPUCLOCK_PERTHREAD(timer->it_clock))
576 tick_dep_set_task(p, TICK_DEP_BIT_POSIX_TIMER);
577 else
578 tick_dep_set_signal(p, TICK_DEP_BIT_POSIX_TIMER);
579}
580
581/*
582 * The timer is locked, fire it and arrange for its reload.
583 */
584static void cpu_timer_fire(struct k_itimer *timer)
585{
586 struct cpu_timer *ctmr = &timer->it.cpu;
587
588 if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
589 /*
590 * User don't want any signal.
591 */
592 cpu_timer_setexpires(ctmr, 0);
593 } else if (unlikely(timer->sigq == NULL)) {
594 /*
595 * This a special case for clock_nanosleep,
596 * not a normal timer from sys_timer_create.
597 */
598 wake_up_process(timer->it_process);
599 cpu_timer_setexpires(ctmr, 0);
600 } else if (!timer->it_interval) {
601 /*
602 * One-shot timer. Clear it as soon as it's fired.
603 */
604 posix_timer_event(timer, 0);
605 cpu_timer_setexpires(ctmr, 0);
606 } else if (posix_timer_event(timer, ++timer->it_requeue_pending)) {
607 /*
608 * The signal did not get queued because the signal
609 * was ignored, so we won't get any callback to
610 * reload the timer. But we need to keep it
611 * ticking in case the signal is deliverable next time.
612 */
613 posix_cpu_timer_rearm(timer);
614 ++timer->it_requeue_pending;
615 }
616}
617
618/*
619 * Guts of sys_timer_settime for CPU timers.
620 * This is called with the timer locked and interrupts disabled.
621 * If we return TIMER_RETRY, it's necessary to release the timer's lock
622 * and try again. (This happens when the timer is in the middle of firing.)
623 */
624static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
625 struct itimerspec64 *new, struct itimerspec64 *old)
626{
627 clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
628 u64 old_expires, new_expires, old_incr, val;
629 struct cpu_timer *ctmr = &timer->it.cpu;
630 struct sighand_struct *sighand;
631 struct task_struct *p;
632 unsigned long flags;
633 int ret = 0;
634
635 rcu_read_lock();
636 p = cpu_timer_task_rcu(timer);
637 if (!p) {
638 /*
639 * If p has just been reaped, we can no
640 * longer get any information about it at all.
641 */
642 rcu_read_unlock();
643 return -ESRCH;
644 }
645
646 /*
647 * Use the to_ktime conversion because that clamps the maximum
648 * value to KTIME_MAX and avoid multiplication overflows.
649 */
650 new_expires = ktime_to_ns(timespec64_to_ktime(new->it_value));
651
652 /*
653 * Protect against sighand release/switch in exit/exec and p->cpu_timers
654 * and p->signal->cpu_timers read/write in arm_timer()
655 */
656 sighand = lock_task_sighand(p, &flags);
657 /*
658 * If p has just been reaped, we can no
659 * longer get any information about it at all.
660 */
661 if (unlikely(sighand == NULL)) {
662 rcu_read_unlock();
663 return -ESRCH;
664 }
665
666 /*
667 * Disarm any old timer after extracting its expiry time.
668 */
669 old_incr = timer->it_interval;
670 old_expires = cpu_timer_getexpires(ctmr);
671
672 if (unlikely(timer->it.cpu.firing)) {
673 timer->it.cpu.firing = -1;
674 ret = TIMER_RETRY;
675 } else {
676 cpu_timer_dequeue(ctmr);
677 }
678
679 /*
680 * We need to sample the current value to convert the new
681 * value from to relative and absolute, and to convert the
682 * old value from absolute to relative. To set a process
683 * timer, we need a sample to balance the thread expiry
684 * times (in arm_timer). With an absolute time, we must
685 * check if it's already passed. In short, we need a sample.
686 */
687 if (CPUCLOCK_PERTHREAD(timer->it_clock))
688 val = cpu_clock_sample(clkid, p);
689 else
690 val = cpu_clock_sample_group(clkid, p, true);
691
692 if (old) {
693 if (old_expires == 0) {
694 old->it_value.tv_sec = 0;
695 old->it_value.tv_nsec = 0;
696 } else {
697 /*
698 * Update the timer in case it has overrun already.
699 * If it has, we'll report it as having overrun and
700 * with the next reloaded timer already ticking,
701 * though we are swallowing that pending
702 * notification here to install the new setting.
703 */
704 u64 exp = bump_cpu_timer(timer, val);
705
706 if (val < exp) {
707 old_expires = exp - val;
708 old->it_value = ns_to_timespec64(old_expires);
709 } else {
710 old->it_value.tv_nsec = 1;
711 old->it_value.tv_sec = 0;
712 }
713 }
714 }
715
716 if (unlikely(ret)) {
717 /*
718 * We are colliding with the timer actually firing.
719 * Punt after filling in the timer's old value, and
720 * disable this firing since we are already reporting
721 * it as an overrun (thanks to bump_cpu_timer above).
722 */
723 unlock_task_sighand(p, &flags);
724 goto out;
725 }
726
727 if (new_expires != 0 && !(timer_flags & TIMER_ABSTIME)) {
728 new_expires += val;
729 }
730
731 /*
732 * Install the new expiry time (or zero).
733 * For a timer with no notification action, we don't actually
734 * arm the timer (we'll just fake it for timer_gettime).
735 */
736 cpu_timer_setexpires(ctmr, new_expires);
737 if (new_expires != 0 && val < new_expires) {
738 arm_timer(timer, p);
739 }
740
741 unlock_task_sighand(p, &flags);
742 /*
743 * Install the new reload setting, and
744 * set up the signal and overrun bookkeeping.
745 */
746 timer->it_interval = timespec64_to_ktime(new->it_interval);
747
748 /*
749 * This acts as a modification timestamp for the timer,
750 * so any automatic reload attempt will punt on seeing
751 * that we have reset the timer manually.
752 */
753 timer->it_requeue_pending = (timer->it_requeue_pending + 2) &
754 ~REQUEUE_PENDING;
755 timer->it_overrun_last = 0;
756 timer->it_overrun = -1;
757
758 if (val >= new_expires) {
759 if (new_expires != 0) {
760 /*
761 * The designated time already passed, so we notify
762 * immediately, even if the thread never runs to
763 * accumulate more time on this clock.
764 */
765 cpu_timer_fire(timer);
766 }
767
768 /*
769 * Make sure we don't keep around the process wide cputime
770 * counter or the tick dependency if they are not necessary.
771 */
772 sighand = lock_task_sighand(p, &flags);
773 if (!sighand)
774 goto out;
775
776 if (!cpu_timer_queued(ctmr))
777 trigger_base_recalc_expires(timer, p);
778
779 unlock_task_sighand(p, &flags);
780 }
781 out:
782 rcu_read_unlock();
783 if (old)
784 old->it_interval = ns_to_timespec64(old_incr);
785
786 return ret;
787}
788
789static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp)
790{
791 clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
792 struct cpu_timer *ctmr = &timer->it.cpu;
793 u64 now, expires = cpu_timer_getexpires(ctmr);
794 struct task_struct *p;
795
796 rcu_read_lock();
797 p = cpu_timer_task_rcu(timer);
798 if (!p)
799 goto out;
800
801 /*
802 * Easy part: convert the reload time.
803 */
804 itp->it_interval = ktime_to_timespec64(timer->it_interval);
805
806 if (!expires)
807 goto out;
808
809 /*
810 * Sample the clock to take the difference with the expiry time.
811 */
812 if (CPUCLOCK_PERTHREAD(timer->it_clock))
813 now = cpu_clock_sample(clkid, p);
814 else
815 now = cpu_clock_sample_group(clkid, p, false);
816
817 if (now < expires) {
818 itp->it_value = ns_to_timespec64(expires - now);
819 } else {
820 /*
821 * The timer should have expired already, but the firing
822 * hasn't taken place yet. Say it's just about to expire.
823 */
824 itp->it_value.tv_nsec = 1;
825 itp->it_value.tv_sec = 0;
826 }
827out:
828 rcu_read_unlock();
829}
830
831#define MAX_COLLECTED 20
832
833static u64 collect_timerqueue(struct timerqueue_head *head,
834 struct list_head *firing, u64 now)
835{
836 struct timerqueue_node *next;
837 int i = 0;
838
839 while ((next = timerqueue_getnext(head))) {
840 struct cpu_timer *ctmr;
841 u64 expires;
842
843 ctmr = container_of(next, struct cpu_timer, node);
844 expires = cpu_timer_getexpires(ctmr);
845 /* Limit the number of timers to expire at once */
846 if (++i == MAX_COLLECTED || now < expires)
847 return expires;
848
849 ctmr->firing = 1;
850 cpu_timer_dequeue(ctmr);
851 list_add_tail(&ctmr->elist, firing);
852 }
853
854 return U64_MAX;
855}
856
857static void collect_posix_cputimers(struct posix_cputimers *pct, u64 *samples,
858 struct list_head *firing)
859{
860 struct posix_cputimer_base *base = pct->bases;
861 int i;
862
863 for (i = 0; i < CPUCLOCK_MAX; i++, base++) {
864 base->nextevt = collect_timerqueue(&base->tqhead, firing,
865 samples[i]);
866 }
867}
868
869static inline void check_dl_overrun(struct task_struct *tsk)
870{
871 if (tsk->dl.dl_overrun) {
872 tsk->dl.dl_overrun = 0;
873 send_signal_locked(SIGXCPU, SEND_SIG_PRIV, tsk, PIDTYPE_TGID);
874 }
875}
876
877static bool check_rlimit(u64 time, u64 limit, int signo, bool rt, bool hard)
878{
879 if (time < limit)
880 return false;
881
882 if (print_fatal_signals) {
883 pr_info("%s Watchdog Timeout (%s): %s[%d]\n",
884 rt ? "RT" : "CPU", hard ? "hard" : "soft",
885 current->comm, task_pid_nr(current));
886 }
887 send_signal_locked(signo, SEND_SIG_PRIV, current, PIDTYPE_TGID);
888 return true;
889}
890
891/*
892 * Check for any per-thread CPU timers that have fired and move them off
893 * the tsk->cpu_timers[N] list onto the firing list. Here we update the
894 * tsk->it_*_expires values to reflect the remaining thread CPU timers.
895 */
896static void check_thread_timers(struct task_struct *tsk,
897 struct list_head *firing)
898{
899 struct posix_cputimers *pct = &tsk->posix_cputimers;
900 u64 samples[CPUCLOCK_MAX];
901 unsigned long soft;
902
903 if (dl_task(tsk))
904 check_dl_overrun(tsk);
905
906 if (expiry_cache_is_inactive(pct))
907 return;
908
909 task_sample_cputime(tsk, samples);
910 collect_posix_cputimers(pct, samples, firing);
911
912 /*
913 * Check for the special case thread timers.
914 */
915 soft = task_rlimit(tsk, RLIMIT_RTTIME);
916 if (soft != RLIM_INFINITY) {
917 /* Task RT timeout is accounted in jiffies. RTTIME is usec */
918 unsigned long rttime = tsk->rt.timeout * (USEC_PER_SEC / HZ);
919 unsigned long hard = task_rlimit_max(tsk, RLIMIT_RTTIME);
920
921 /* At the hard limit, send SIGKILL. No further action. */
922 if (hard != RLIM_INFINITY &&
923 check_rlimit(rttime, hard, SIGKILL, true, true))
924 return;
925
926 /* At the soft limit, send a SIGXCPU every second */
927 if (check_rlimit(rttime, soft, SIGXCPU, true, false)) {
928 soft += USEC_PER_SEC;
929 tsk->signal->rlim[RLIMIT_RTTIME].rlim_cur = soft;
930 }
931 }
932
933 if (expiry_cache_is_inactive(pct))
934 tick_dep_clear_task(tsk, TICK_DEP_BIT_POSIX_TIMER);
935}
936
937static inline void stop_process_timers(struct signal_struct *sig)
938{
939 struct posix_cputimers *pct = &sig->posix_cputimers;
940
941 /* Turn off the active flag. This is done without locking. */
942 WRITE_ONCE(pct->timers_active, false);
943 tick_dep_clear_signal(sig, TICK_DEP_BIT_POSIX_TIMER);
944}
945
946static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
947 u64 *expires, u64 cur_time, int signo)
948{
949 if (!it->expires)
950 return;
951
952 if (cur_time >= it->expires) {
953 if (it->incr)
954 it->expires += it->incr;
955 else
956 it->expires = 0;
957
958 trace_itimer_expire(signo == SIGPROF ?
959 ITIMER_PROF : ITIMER_VIRTUAL,
960 task_tgid(tsk), cur_time);
961 send_signal_locked(signo, SEND_SIG_PRIV, tsk, PIDTYPE_TGID);
962 }
963
964 if (it->expires && it->expires < *expires)
965 *expires = it->expires;
966}
967
968/*
969 * Check for any per-thread CPU timers that have fired and move them
970 * off the tsk->*_timers list onto the firing list. Per-thread timers
971 * have already been taken off.
972 */
973static void check_process_timers(struct task_struct *tsk,
974 struct list_head *firing)
975{
976 struct signal_struct *const sig = tsk->signal;
977 struct posix_cputimers *pct = &sig->posix_cputimers;
978 u64 samples[CPUCLOCK_MAX];
979 unsigned long soft;
980
981 /*
982 * If there are no active process wide timers (POSIX 1.b, itimers,
983 * RLIMIT_CPU) nothing to check. Also skip the process wide timer
984 * processing when there is already another task handling them.
985 */
986 if (!READ_ONCE(pct->timers_active) || pct->expiry_active)
987 return;
988
989 /*
990 * Signify that a thread is checking for process timers.
991 * Write access to this field is protected by the sighand lock.
992 */
993 pct->expiry_active = true;
994
995 /*
996 * Collect the current process totals. Group accounting is active
997 * so the sample can be taken directly.
998 */
999 proc_sample_cputime_atomic(&sig->cputimer.cputime_atomic, samples);
1000 collect_posix_cputimers(pct, samples, firing);
1001
1002 /*
1003 * Check for the special case process timers.
1004 */
1005 check_cpu_itimer(tsk, &sig->it[CPUCLOCK_PROF],
1006 &pct->bases[CPUCLOCK_PROF].nextevt,
1007 samples[CPUCLOCK_PROF], SIGPROF);
1008 check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT],
1009 &pct->bases[CPUCLOCK_VIRT].nextevt,
1010 samples[CPUCLOCK_VIRT], SIGVTALRM);
1011
1012 soft = task_rlimit(tsk, RLIMIT_CPU);
1013 if (soft != RLIM_INFINITY) {
1014 /* RLIMIT_CPU is in seconds. Samples are nanoseconds */
1015 unsigned long hard = task_rlimit_max(tsk, RLIMIT_CPU);
1016 u64 ptime = samples[CPUCLOCK_PROF];
1017 u64 softns = (u64)soft * NSEC_PER_SEC;
1018 u64 hardns = (u64)hard * NSEC_PER_SEC;
1019
1020 /* At the hard limit, send SIGKILL. No further action. */
1021 if (hard != RLIM_INFINITY &&
1022 check_rlimit(ptime, hardns, SIGKILL, false, true))
1023 return;
1024
1025 /* At the soft limit, send a SIGXCPU every second */
1026 if (check_rlimit(ptime, softns, SIGXCPU, false, false)) {
1027 sig->rlim[RLIMIT_CPU].rlim_cur = soft + 1;
1028 softns += NSEC_PER_SEC;
1029 }
1030
1031 /* Update the expiry cache */
1032 if (softns < pct->bases[CPUCLOCK_PROF].nextevt)
1033 pct->bases[CPUCLOCK_PROF].nextevt = softns;
1034 }
1035
1036 if (expiry_cache_is_inactive(pct))
1037 stop_process_timers(sig);
1038
1039 pct->expiry_active = false;
1040}
1041
1042/*
1043 * This is called from the signal code (via posixtimer_rearm)
1044 * when the last timer signal was delivered and we have to reload the timer.
1045 */
1046static void posix_cpu_timer_rearm(struct k_itimer *timer)
1047{
1048 clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
1049 struct task_struct *p;
1050 struct sighand_struct *sighand;
1051 unsigned long flags;
1052 u64 now;
1053
1054 rcu_read_lock();
1055 p = cpu_timer_task_rcu(timer);
1056 if (!p)
1057 goto out;
1058
1059 /* Protect timer list r/w in arm_timer() */
1060 sighand = lock_task_sighand(p, &flags);
1061 if (unlikely(sighand == NULL))
1062 goto out;
1063
1064 /*
1065 * Fetch the current sample and update the timer's expiry time.
1066 */
1067 if (CPUCLOCK_PERTHREAD(timer->it_clock))
1068 now = cpu_clock_sample(clkid, p);
1069 else
1070 now = cpu_clock_sample_group(clkid, p, true);
1071
1072 bump_cpu_timer(timer, now);
1073
1074 /*
1075 * Now re-arm for the new expiry time.
1076 */
1077 arm_timer(timer, p);
1078 unlock_task_sighand(p, &flags);
1079out:
1080 rcu_read_unlock();
1081}
1082
1083/**
1084 * task_cputimers_expired - Check whether posix CPU timers are expired
1085 *
1086 * @samples: Array of current samples for the CPUCLOCK clocks
1087 * @pct: Pointer to a posix_cputimers container
1088 *
1089 * Returns true if any member of @samples is greater than the corresponding
1090 * member of @pct->bases[CLK].nextevt. False otherwise
1091 */
1092static inline bool
1093task_cputimers_expired(const u64 *samples, struct posix_cputimers *pct)
1094{
1095 int i;
1096
1097 for (i = 0; i < CPUCLOCK_MAX; i++) {
1098 if (samples[i] >= pct->bases[i].nextevt)
1099 return true;
1100 }
1101 return false;
1102}
1103
1104/**
1105 * fastpath_timer_check - POSIX CPU timers fast path.
1106 *
1107 * @tsk: The task (thread) being checked.
1108 *
1109 * Check the task and thread group timers. If both are zero (there are no
1110 * timers set) return false. Otherwise snapshot the task and thread group
1111 * timers and compare them with the corresponding expiration times. Return
1112 * true if a timer has expired, else return false.
1113 */
1114static inline bool fastpath_timer_check(struct task_struct *tsk)
1115{
1116 struct posix_cputimers *pct = &tsk->posix_cputimers;
1117 struct signal_struct *sig;
1118
1119 if (!expiry_cache_is_inactive(pct)) {
1120 u64 samples[CPUCLOCK_MAX];
1121
1122 task_sample_cputime(tsk, samples);
1123 if (task_cputimers_expired(samples, pct))
1124 return true;
1125 }
1126
1127 sig = tsk->signal;
1128 pct = &sig->posix_cputimers;
1129 /*
1130 * Check if thread group timers expired when timers are active and
1131 * no other thread in the group is already handling expiry for
1132 * thread group cputimers. These fields are read without the
1133 * sighand lock. However, this is fine because this is meant to be
1134 * a fastpath heuristic to determine whether we should try to
1135 * acquire the sighand lock to handle timer expiry.
1136 *
1137 * In the worst case scenario, if concurrently timers_active is set
1138 * or expiry_active is cleared, but the current thread doesn't see
1139 * the change yet, the timer checks are delayed until the next
1140 * thread in the group gets a scheduler interrupt to handle the
1141 * timer. This isn't an issue in practice because these types of
1142 * delays with signals actually getting sent are expected.
1143 */
1144 if (READ_ONCE(pct->timers_active) && !READ_ONCE(pct->expiry_active)) {
1145 u64 samples[CPUCLOCK_MAX];
1146
1147 proc_sample_cputime_atomic(&sig->cputimer.cputime_atomic,
1148 samples);
1149
1150 if (task_cputimers_expired(samples, pct))
1151 return true;
1152 }
1153
1154 if (dl_task(tsk) && tsk->dl.dl_overrun)
1155 return true;
1156
1157 return false;
1158}
1159
1160static void handle_posix_cpu_timers(struct task_struct *tsk);
1161
1162#ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK
1163static void posix_cpu_timers_work(struct callback_head *work)
1164{
1165 handle_posix_cpu_timers(current);
1166}
1167
1168/*
1169 * Clear existing posix CPU timers task work.
1170 */
1171void clear_posix_cputimers_work(struct task_struct *p)
1172{
1173 /*
1174 * A copied work entry from the old task is not meaningful, clear it.
1175 * N.B. init_task_work will not do this.
1176 */
1177 memset(&p->posix_cputimers_work.work, 0,
1178 sizeof(p->posix_cputimers_work.work));
1179 init_task_work(&p->posix_cputimers_work.work,
1180 posix_cpu_timers_work);
1181 p->posix_cputimers_work.scheduled = false;
1182}
1183
1184/*
1185 * Initialize posix CPU timers task work in init task. Out of line to
1186 * keep the callback static and to avoid header recursion hell.
1187 */
1188void __init posix_cputimers_init_work(void)
1189{
1190 clear_posix_cputimers_work(current);
1191}
1192
1193/*
1194 * Note: All operations on tsk->posix_cputimer_work.scheduled happen either
1195 * in hard interrupt context or in task context with interrupts
1196 * disabled. Aside of that the writer/reader interaction is always in the
1197 * context of the current task, which means they are strict per CPU.
1198 */
1199static inline bool posix_cpu_timers_work_scheduled(struct task_struct *tsk)
1200{
1201 return tsk->posix_cputimers_work.scheduled;
1202}
1203
1204static inline void __run_posix_cpu_timers(struct task_struct *tsk)
1205{
1206 if (WARN_ON_ONCE(tsk->posix_cputimers_work.scheduled))
1207 return;
1208
1209 /* Schedule task work to actually expire the timers */
1210 tsk->posix_cputimers_work.scheduled = true;
1211 task_work_add(tsk, &tsk->posix_cputimers_work.work, TWA_RESUME);
1212}
1213
1214static inline bool posix_cpu_timers_enable_work(struct task_struct *tsk,
1215 unsigned long start)
1216{
1217 bool ret = true;
1218
1219 /*
1220 * On !RT kernels interrupts are disabled while collecting expired
1221 * timers, so no tick can happen and the fast path check can be
1222 * reenabled without further checks.
1223 */
1224 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
1225 tsk->posix_cputimers_work.scheduled = false;
1226 return true;
1227 }
1228
1229 /*
1230 * On RT enabled kernels ticks can happen while the expired timers
1231 * are collected under sighand lock. But any tick which observes
1232 * the CPUTIMERS_WORK_SCHEDULED bit set, does not run the fastpath
1233 * checks. So reenabling the tick work has do be done carefully:
1234 *
1235 * Disable interrupts and run the fast path check if jiffies have
1236 * advanced since the collecting of expired timers started. If
1237 * jiffies have not advanced or the fast path check did not find
1238 * newly expired timers, reenable the fast path check in the timer
1239 * interrupt. If there are newly expired timers, return false and
1240 * let the collection loop repeat.
1241 */
1242 local_irq_disable();
1243 if (start != jiffies && fastpath_timer_check(tsk))
1244 ret = false;
1245 else
1246 tsk->posix_cputimers_work.scheduled = false;
1247 local_irq_enable();
1248
1249 return ret;
1250}
1251#else /* CONFIG_POSIX_CPU_TIMERS_TASK_WORK */
1252static inline void __run_posix_cpu_timers(struct task_struct *tsk)
1253{
1254 lockdep_posixtimer_enter();
1255 handle_posix_cpu_timers(tsk);
1256 lockdep_posixtimer_exit();
1257}
1258
1259static inline bool posix_cpu_timers_work_scheduled(struct task_struct *tsk)
1260{
1261 return false;
1262}
1263
1264static inline bool posix_cpu_timers_enable_work(struct task_struct *tsk,
1265 unsigned long start)
1266{
1267 return true;
1268}
1269#endif /* CONFIG_POSIX_CPU_TIMERS_TASK_WORK */
1270
1271static void handle_posix_cpu_timers(struct task_struct *tsk)
1272{
1273 struct k_itimer *timer, *next;
1274 unsigned long flags, start;
1275 LIST_HEAD(firing);
1276
1277 if (!lock_task_sighand(tsk, &flags))
1278 return;
1279
1280 do {
1281 /*
1282 * On RT locking sighand lock does not disable interrupts,
1283 * so this needs to be careful vs. ticks. Store the current
1284 * jiffies value.
1285 */
1286 start = READ_ONCE(jiffies);
1287 barrier();
1288
1289 /*
1290 * Here we take off tsk->signal->cpu_timers[N] and
1291 * tsk->cpu_timers[N] all the timers that are firing, and
1292 * put them on the firing list.
1293 */
1294 check_thread_timers(tsk, &firing);
1295
1296 check_process_timers(tsk, &firing);
1297
1298 /*
1299 * The above timer checks have updated the expiry cache and
1300 * because nothing can have queued or modified timers after
1301 * sighand lock was taken above it is guaranteed to be
1302 * consistent. So the next timer interrupt fastpath check
1303 * will find valid data.
1304 *
1305 * If timer expiry runs in the timer interrupt context then
1306 * the loop is not relevant as timers will be directly
1307 * expired in interrupt context. The stub function below
1308 * returns always true which allows the compiler to
1309 * optimize the loop out.
1310 *
1311 * If timer expiry is deferred to task work context then
1312 * the following rules apply:
1313 *
1314 * - On !RT kernels no tick can have happened on this CPU
1315 * after sighand lock was acquired because interrupts are
1316 * disabled. So reenabling task work before dropping
1317 * sighand lock and reenabling interrupts is race free.
1318 *
1319 * - On RT kernels ticks might have happened but the tick
1320 * work ignored posix CPU timer handling because the
1321 * CPUTIMERS_WORK_SCHEDULED bit is set. Reenabling work
1322 * must be done very carefully including a check whether
1323 * ticks have happened since the start of the timer
1324 * expiry checks. posix_cpu_timers_enable_work() takes
1325 * care of that and eventually lets the expiry checks
1326 * run again.
1327 */
1328 } while (!posix_cpu_timers_enable_work(tsk, start));
1329
1330 /*
1331 * We must release sighand lock before taking any timer's lock.
1332 * There is a potential race with timer deletion here, as the
1333 * siglock now protects our private firing list. We have set
1334 * the firing flag in each timer, so that a deletion attempt
1335 * that gets the timer lock before we do will give it up and
1336 * spin until we've taken care of that timer below.
1337 */
1338 unlock_task_sighand(tsk, &flags);
1339
1340 /*
1341 * Now that all the timers on our list have the firing flag,
1342 * no one will touch their list entries but us. We'll take
1343 * each timer's lock before clearing its firing flag, so no
1344 * timer call will interfere.
1345 */
1346 list_for_each_entry_safe(timer, next, &firing, it.cpu.elist) {
1347 int cpu_firing;
1348
1349 /*
1350 * spin_lock() is sufficient here even independent of the
1351 * expiry context. If expiry happens in hard interrupt
1352 * context it's obvious. For task work context it's safe
1353 * because all other operations on timer::it_lock happen in
1354 * task context (syscall or exit).
1355 */
1356 spin_lock(&timer->it_lock);
1357 list_del_init(&timer->it.cpu.elist);
1358 cpu_firing = timer->it.cpu.firing;
1359 timer->it.cpu.firing = 0;
1360 /*
1361 * The firing flag is -1 if we collided with a reset
1362 * of the timer, which already reported this
1363 * almost-firing as an overrun. So don't generate an event.
1364 */
1365 if (likely(cpu_firing >= 0))
1366 cpu_timer_fire(timer);
1367 spin_unlock(&timer->it_lock);
1368 }
1369}
1370
1371/*
1372 * This is called from the timer interrupt handler. The irq handler has
1373 * already updated our counts. We need to check if any timers fire now.
1374 * Interrupts are disabled.
1375 */
1376void run_posix_cpu_timers(void)
1377{
1378 struct task_struct *tsk = current;
1379
1380 lockdep_assert_irqs_disabled();
1381
1382 /*
1383 * If the actual expiry is deferred to task work context and the
1384 * work is already scheduled there is no point to do anything here.
1385 */
1386 if (posix_cpu_timers_work_scheduled(tsk))
1387 return;
1388
1389 /*
1390 * The fast path checks that there are no expired thread or thread
1391 * group timers. If that's so, just return.
1392 */
1393 if (!fastpath_timer_check(tsk))
1394 return;
1395
1396 __run_posix_cpu_timers(tsk);
1397}
1398
1399/*
1400 * Set one of the process-wide special case CPU timers or RLIMIT_CPU.
1401 * The tsk->sighand->siglock must be held by the caller.
1402 */
1403void set_process_cpu_timer(struct task_struct *tsk, unsigned int clkid,
1404 u64 *newval, u64 *oldval)
1405{
1406 u64 now, *nextevt;
1407
1408 if (WARN_ON_ONCE(clkid >= CPUCLOCK_SCHED))
1409 return;
1410
1411 nextevt = &tsk->signal->posix_cputimers.bases[clkid].nextevt;
1412 now = cpu_clock_sample_group(clkid, tsk, true);
1413
1414 if (oldval) {
1415 /*
1416 * We are setting itimer. The *oldval is absolute and we update
1417 * it to be relative, *newval argument is relative and we update
1418 * it to be absolute.
1419 */
1420 if (*oldval) {
1421 if (*oldval <= now) {
1422 /* Just about to fire. */
1423 *oldval = TICK_NSEC;
1424 } else {
1425 *oldval -= now;
1426 }
1427 }
1428
1429 if (*newval)
1430 *newval += now;
1431 }
1432
1433 /*
1434 * Update expiration cache if this is the earliest timer. CPUCLOCK_PROF
1435 * expiry cache is also used by RLIMIT_CPU!.
1436 */
1437 if (*newval < *nextevt)
1438 *nextevt = *newval;
1439
1440 tick_dep_set_signal(tsk, TICK_DEP_BIT_POSIX_TIMER);
1441}
1442
1443static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
1444 const struct timespec64 *rqtp)
1445{
1446 struct itimerspec64 it;
1447 struct k_itimer timer;
1448 u64 expires;
1449 int error;
1450
1451 /*
1452 * Set up a temporary timer and then wait for it to go off.
1453 */
1454 memset(&timer, 0, sizeof timer);
1455 spin_lock_init(&timer.it_lock);
1456 timer.it_clock = which_clock;
1457 timer.it_overrun = -1;
1458 error = posix_cpu_timer_create(&timer);
1459 timer.it_process = current;
1460
1461 if (!error) {
1462 static struct itimerspec64 zero_it;
1463 struct restart_block *restart;
1464
1465 memset(&it, 0, sizeof(it));
1466 it.it_value = *rqtp;
1467
1468 spin_lock_irq(&timer.it_lock);
1469 error = posix_cpu_timer_set(&timer, flags, &it, NULL);
1470 if (error) {
1471 spin_unlock_irq(&timer.it_lock);
1472 return error;
1473 }
1474
1475 while (!signal_pending(current)) {
1476 if (!cpu_timer_getexpires(&timer.it.cpu)) {
1477 /*
1478 * Our timer fired and was reset, below
1479 * deletion can not fail.
1480 */
1481 posix_cpu_timer_del(&timer);
1482 spin_unlock_irq(&timer.it_lock);
1483 return 0;
1484 }
1485
1486 /*
1487 * Block until cpu_timer_fire (or a signal) wakes us.
1488 */
1489 __set_current_state(TASK_INTERRUPTIBLE);
1490 spin_unlock_irq(&timer.it_lock);
1491 schedule();
1492 spin_lock_irq(&timer.it_lock);
1493 }
1494
1495 /*
1496 * We were interrupted by a signal.
1497 */
1498 expires = cpu_timer_getexpires(&timer.it.cpu);
1499 error = posix_cpu_timer_set(&timer, 0, &zero_it, &it);
1500 if (!error) {
1501 /*
1502 * Timer is now unarmed, deletion can not fail.
1503 */
1504 posix_cpu_timer_del(&timer);
1505 }
1506 spin_unlock_irq(&timer.it_lock);
1507
1508 while (error == TIMER_RETRY) {
1509 /*
1510 * We need to handle case when timer was or is in the
1511 * middle of firing. In other cases we already freed
1512 * resources.
1513 */
1514 spin_lock_irq(&timer.it_lock);
1515 error = posix_cpu_timer_del(&timer);
1516 spin_unlock_irq(&timer.it_lock);
1517 }
1518
1519 if ((it.it_value.tv_sec | it.it_value.tv_nsec) == 0) {
1520 /*
1521 * It actually did fire already.
1522 */
1523 return 0;
1524 }
1525
1526 error = -ERESTART_RESTARTBLOCK;
1527 /*
1528 * Report back to the user the time still remaining.
1529 */
1530 restart = ¤t->restart_block;
1531 restart->nanosleep.expires = expires;
1532 if (restart->nanosleep.type != TT_NONE)
1533 error = nanosleep_copyout(restart, &it.it_value);
1534 }
1535
1536 return error;
1537}
1538
1539static long posix_cpu_nsleep_restart(struct restart_block *restart_block);
1540
1541static int posix_cpu_nsleep(const clockid_t which_clock, int flags,
1542 const struct timespec64 *rqtp)
1543{
1544 struct restart_block *restart_block = ¤t->restart_block;
1545 int error;
1546
1547 /*
1548 * Diagnose required errors first.
1549 */
1550 if (CPUCLOCK_PERTHREAD(which_clock) &&
1551 (CPUCLOCK_PID(which_clock) == 0 ||
1552 CPUCLOCK_PID(which_clock) == task_pid_vnr(current)))
1553 return -EINVAL;
1554
1555 error = do_cpu_nanosleep(which_clock, flags, rqtp);
1556
1557 if (error == -ERESTART_RESTARTBLOCK) {
1558
1559 if (flags & TIMER_ABSTIME)
1560 return -ERESTARTNOHAND;
1561
1562 restart_block->nanosleep.clockid = which_clock;
1563 set_restart_fn(restart_block, posix_cpu_nsleep_restart);
1564 }
1565 return error;
1566}
1567
1568static long posix_cpu_nsleep_restart(struct restart_block *restart_block)
1569{
1570 clockid_t which_clock = restart_block->nanosleep.clockid;
1571 struct timespec64 t;
1572
1573 t = ns_to_timespec64(restart_block->nanosleep.expires);
1574
1575 return do_cpu_nanosleep(which_clock, TIMER_ABSTIME, &t);
1576}
1577
1578#define PROCESS_CLOCK make_process_cpuclock(0, CPUCLOCK_SCHED)
1579#define THREAD_CLOCK make_thread_cpuclock(0, CPUCLOCK_SCHED)
1580
1581static int process_cpu_clock_getres(const clockid_t which_clock,
1582 struct timespec64 *tp)
1583{
1584 return posix_cpu_clock_getres(PROCESS_CLOCK, tp);
1585}
1586static int process_cpu_clock_get(const clockid_t which_clock,
1587 struct timespec64 *tp)
1588{
1589 return posix_cpu_clock_get(PROCESS_CLOCK, tp);
1590}
1591static int process_cpu_timer_create(struct k_itimer *timer)
1592{
1593 timer->it_clock = PROCESS_CLOCK;
1594 return posix_cpu_timer_create(timer);
1595}
1596static int process_cpu_nsleep(const clockid_t which_clock, int flags,
1597 const struct timespec64 *rqtp)
1598{
1599 return posix_cpu_nsleep(PROCESS_CLOCK, flags, rqtp);
1600}
1601static int thread_cpu_clock_getres(const clockid_t which_clock,
1602 struct timespec64 *tp)
1603{
1604 return posix_cpu_clock_getres(THREAD_CLOCK, tp);
1605}
1606static int thread_cpu_clock_get(const clockid_t which_clock,
1607 struct timespec64 *tp)
1608{
1609 return posix_cpu_clock_get(THREAD_CLOCK, tp);
1610}
1611static int thread_cpu_timer_create(struct k_itimer *timer)
1612{
1613 timer->it_clock = THREAD_CLOCK;
1614 return posix_cpu_timer_create(timer);
1615}
1616
1617const struct k_clock clock_posix_cpu = {
1618 .clock_getres = posix_cpu_clock_getres,
1619 .clock_set = posix_cpu_clock_set,
1620 .clock_get_timespec = posix_cpu_clock_get,
1621 .timer_create = posix_cpu_timer_create,
1622 .nsleep = posix_cpu_nsleep,
1623 .timer_set = posix_cpu_timer_set,
1624 .timer_del = posix_cpu_timer_del,
1625 .timer_get = posix_cpu_timer_get,
1626 .timer_rearm = posix_cpu_timer_rearm,
1627};
1628
1629const struct k_clock clock_process = {
1630 .clock_getres = process_cpu_clock_getres,
1631 .clock_get_timespec = process_cpu_clock_get,
1632 .timer_create = process_cpu_timer_create,
1633 .nsleep = process_cpu_nsleep,
1634};
1635
1636const struct k_clock clock_thread = {
1637 .clock_getres = thread_cpu_clock_getres,
1638 .clock_get_timespec = thread_cpu_clock_get,
1639 .timer_create = thread_cpu_timer_create,
1640};
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 = ¤t->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 = ¤t->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};