cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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posix-cpu-timers.c (45685B)


      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 = &current->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 = &current->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};