// SPDX-License-Identifier: GPL-2.0

  /*
   * Implement CPU time clocks for the POSIX clock interface.
   */

  #include <linux/sched/signal.h>

  #include <linux/sched/cputime.h>

  #include <linux/posix-timers.h>

  #include <linux/errno.h>

  #include <linux/math64.h>

  #include <linux/uaccess.h>

  #include <linux/kernel_stat.h>

  #include <trace/events/timer.h>

  #include <linux/tick.h>
  #include <linux/workqueue.h>

  #include <linux/compat.h>

  #include <linux/sched/deadline.h>

  #include "posix-timers.h"

  static void posix_cpu_timer_rearm(struct k_itimer *timer);

  /*

   * Called after updating RLIMIT_CPU to run cpu timer and update
   * tsk->signal->cputime_expires expiration cache if necessary. Needs
   * siglock protection since other code may update expiration cache as
   * well.

   */

  void update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new)

  {

  	u64 nsecs = rlim_new * NSEC_PER_SEC;

  	spin_lock_irq(&task->sighand->siglock);

  	set_process_cpu_timer(task, CPUCLOCK_PROF, &nsecs, NULL);

  	spin_unlock_irq(&task->sighand->siglock);

  }

  static int check_clock(const clockid_t which_clock)

  {
  	int error = 0;
  	struct task_struct *p;
  	const pid_t pid = CPUCLOCK_PID(which_clock);
  
  	if (CPUCLOCK_WHICH(which_clock) >= CPUCLOCK_MAX)
  		return -EINVAL;
  
  	if (pid == 0)
  		return 0;

  	rcu_read_lock();

  	p = find_task_by_vpid(pid);

  	if (!p || !(CPUCLOCK_PERTHREAD(which_clock) ?

  		   same_thread_group(p, current) : has_group_leader_pid(p))) {

  		error = -EINVAL;
  	}

  	rcu_read_unlock();

  
  	return error;
  }

  /*
   * Update expiry time from increment, and increase overrun count,
   * given the current clock sample.
   */

  static void bump_cpu_timer(struct k_itimer *timer, u64 now)

  {
  	int i;

  	u64 delta, incr;

  	if (timer->it.cpu.incr == 0)

  		return;

  	if (now < timer->it.cpu.expires)
  		return;

  	incr = timer->it.cpu.incr;
  	delta = now + incr - timer->it.cpu.expires;

  	/* Don't use (incr*2 < delta), incr*2 might overflow. */
  	for (i = 0; incr < delta - incr; i++)
  		incr = incr << 1;
  
  	for (; i >= 0; incr >>= 1, i--) {
  		if (delta < incr)
  			continue;
  
  		timer->it.cpu.expires += incr;

  		timer->it_overrun += 1LL << i;

  		delta -= incr;

  	}
  }

  /**
   * task_cputime_zero - Check a task_cputime struct for all zero fields.
   *
   * @cputime:	The struct to compare.
   *
   * Checks @cputime to see if all fields are zero.  Returns true if all fields
   * are zero, false if any field is nonzero.
   */

  static inline int task_cputime_zero(const struct task_cputime *cputime)

  {
  	if (!cputime->utime && !cputime->stime && !cputime->sum_exec_runtime)
  		return 1;
  	return 0;
  }

  static inline u64 prof_ticks(struct task_struct *p)

  {

  	u64 utime, stime;

  	task_cputime(p, &utime, &stime);

  	return utime + stime;

  }

  static inline u64 virt_ticks(struct task_struct *p)

  {

  	u64 utime, stime;

  	task_cputime(p, &utime, &stime);

  	return utime;

  }

  static int

  posix_cpu_clock_getres(const clockid_t which_clock, struct timespec64 *tp)

  {
  	int error = check_clock(which_clock);
  	if (!error) {
  		tp->tv_sec = 0;
  		tp->tv_nsec = ((NSEC_PER_SEC + HZ - 1) / HZ);
  		if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
  			/*
  			 * If sched_clock is using a cycle counter, we
  			 * don't have any idea of its true resolution
  			 * exported, but it is much more than 1s/HZ.
  			 */
  			tp->tv_nsec = 1;
  		}
  	}
  	return error;
  }

  static int

  posix_cpu_clock_set(const clockid_t which_clock, const struct timespec64 *tp)

  {
  	/*
  	 * You can never reset a CPU clock, but we check for other errors
  	 * in the call before failing with EPERM.
  	 */
  	int error = check_clock(which_clock);
  	if (error == 0) {
  		error = -EPERM;
  	}
  	return error;
  }
  
  
  /*
   * Sample a per-thread clock for the given task.
   */

  static int cpu_clock_sample(const clockid_t which_clock,
  			    struct task_struct *p, u64 *sample)

  {
  	switch (CPUCLOCK_WHICH(which_clock)) {
  	default:
  		return -EINVAL;
  	case CPUCLOCK_PROF:

  		*sample = prof_ticks(p);

  		break;
  	case CPUCLOCK_VIRT:

  		*sample = virt_ticks(p);

  		break;
  	case CPUCLOCK_SCHED:

  		*sample = task_sched_runtime(p);

  		break;
  	}
  	return 0;
  }

  /*
   * Set cputime to sum_cputime if sum_cputime > cputime. Use cmpxchg
   * to avoid race conditions with concurrent updates to cputime.
   */
  static inline void __update_gt_cputime(atomic64_t *cputime, u64 sum_cputime)

  {

  	u64 curr_cputime;
  retry:
  	curr_cputime = atomic64_read(cputime);
  	if (sum_cputime > curr_cputime) {
  		if (atomic64_cmpxchg(cputime, curr_cputime, sum_cputime) != curr_cputime)
  			goto retry;
  	}
  }

  static void update_gt_cputime(struct task_cputime_atomic *cputime_atomic, struct task_cputime *sum)

  {

  	__update_gt_cputime(&cputime_atomic->utime, sum->utime);
  	__update_gt_cputime(&cputime_atomic->stime, sum->stime);
  	__update_gt_cputime(&cputime_atomic->sum_exec_runtime, sum->sum_exec_runtime);

  }

  /* Sample task_cputime_atomic values in "atomic_timers", store results in "times". */

  static inline void sample_cputime_atomic(struct task_cputime *times,

  					 struct task_cputime_atomic *atomic_times)

  {

  	times->utime = atomic64_read(&atomic_times->utime);
  	times->stime = atomic64_read(&atomic_times->stime);
  	times->sum_exec_runtime = atomic64_read(&atomic_times->sum_exec_runtime);

  }

  void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)

  {
  	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;

  	struct task_cputime sum;

  	/* Check if cputimer isn't running. This is accessed without locking. */
  	if (!READ_ONCE(cputimer->running)) {

  		/*
  		 * The POSIX timer interface allows for absolute time expiry
  		 * values through the TIMER_ABSTIME flag, therefore we have

  		 * to synchronize the timer to the clock every time we start it.

  		 */

  		thread_group_cputime(tsk, &sum);

  		update_gt_cputime(&cputimer->cputime_atomic, &sum);

  
  		/*
  		 * We're setting cputimer->running without a lock. Ensure
  		 * this only gets written to in one operation. We set
  		 * running after update_gt_cputime() as a small optimization,
  		 * but barriers are not required because update_gt_cputime()
  		 * can handle concurrent updates.
  		 */

  		WRITE_ONCE(cputimer->running, true);

  	}

  	sample_cputime_atomic(times, &cputimer->cputime_atomic);

  }

  /*
   * Sample a process (thread group) clock for the given group_leader task.

   * Must be called with task sighand lock held for safe while_each_thread()
   * traversal.

   */

  static int cpu_clock_sample_group(const clockid_t which_clock,
  				  struct task_struct *p,

  				  u64 *sample)

  {

  	struct task_cputime cputime;

  	switch (CPUCLOCK_WHICH(which_clock)) {

  	default:
  		return -EINVAL;
  	case CPUCLOCK_PROF:

  		thread_group_cputime(p, &cputime);
  		*sample = cputime.utime + cputime.stime;

  		break;
  	case CPUCLOCK_VIRT:

  		thread_group_cputime(p, &cputime);
  		*sample = cputime.utime;

  		break;
  	case CPUCLOCK_SCHED:

  		thread_group_cputime(p, &cputime);

  		*sample = cputime.sum_exec_runtime;

  		break;
  	}
  	return 0;
  }

  static int posix_cpu_clock_get_task(struct task_struct *tsk,
  				    const clockid_t which_clock,

  				    struct timespec64 *tp)

  {
  	int err = -EINVAL;

  	u64 rtn;

  
  	if (CPUCLOCK_PERTHREAD(which_clock)) {
  		if (same_thread_group(tsk, current))
  			err = cpu_clock_sample(which_clock, tsk, &rtn);
  	} else {

  		if (tsk == current || thread_group_leader(tsk))

  			err = cpu_clock_sample_group(which_clock, tsk, &rtn);

  	}
  
  	if (!err)

  		*tp = ns_to_timespec64(rtn);

  
  	return err;
  }

  static int posix_cpu_clock_get(const clockid_t which_clock, struct timespec64 *tp)

  {
  	const pid_t pid = CPUCLOCK_PID(which_clock);

  	int err = -EINVAL;

  
  	if (pid == 0) {
  		/*
  		 * Special case constant value for our own clocks.
  		 * We don't have to do any lookup to find ourselves.
  		 */

  		err = posix_cpu_clock_get_task(current, which_clock, tp);

  	} else {
  		/*
  		 * Find the given PID, and validate that the caller
  		 * should be able to see it.
  		 */
  		struct task_struct *p;

  		rcu_read_lock();

  		p = find_task_by_vpid(pid);

  		if (p)
  			err = posix_cpu_clock_get_task(p, which_clock, tp);

  		rcu_read_unlock();

  	}

  	return err;

  }

  /*
   * Validate the clockid_t for a new CPU-clock timer, and initialize the timer.

   * This is called from sys_timer_create() and do_cpu_nanosleep() with the
   * new timer already all-zeros initialized.

   */

  static int posix_cpu_timer_create(struct k_itimer *new_timer)

  {
  	int ret = 0;
  	const pid_t pid = CPUCLOCK_PID(new_timer->it_clock);
  	struct task_struct *p;
  
  	if (CPUCLOCK_WHICH(new_timer->it_clock) >= CPUCLOCK_MAX)
  		return -EINVAL;

  	new_timer->kclock = &clock_posix_cpu;

  	INIT_LIST_HEAD(&new_timer->it.cpu.entry);

  	rcu_read_lock();

  	if (CPUCLOCK_PERTHREAD(new_timer->it_clock)) {
  		if (pid == 0) {
  			p = current;
  		} else {

  			p = find_task_by_vpid(pid);

  			if (p && !same_thread_group(p, current))

  				p = NULL;
  		}
  	} else {
  		if (pid == 0) {
  			p = current->group_leader;
  		} else {

  			p = find_task_by_vpid(pid);

  			if (p && !has_group_leader_pid(p))

  				p = NULL;
  		}
  	}
  	new_timer->it.cpu.task = p;
  	if (p) {
  		get_task_struct(p);
  	} else {
  		ret = -EINVAL;
  	}

  	rcu_read_unlock();

  
  	return ret;
  }
  
  /*
   * Clean up a CPU-clock timer that is about to be destroyed.
   * This is called from timer deletion with the timer already locked.
   * If we return TIMER_RETRY, it's necessary to release the timer's lock
   * and try again.  (This happens when the timer is in the middle of firing.)
   */

  static int posix_cpu_timer_del(struct k_itimer *timer)

  {

  	int ret = 0;

  	unsigned long flags;
  	struct sighand_struct *sighand;
  	struct task_struct *p = timer->it.cpu.task;

  	WARN_ON_ONCE(p == NULL);

  	/*
  	 * Protect against sighand release/switch in exit/exec and process/
  	 * thread timer list entry concurrent read/writes.
  	 */
  	sighand = lock_task_sighand(p, &flags);
  	if (unlikely(sighand == NULL)) {

  		/*
  		 * We raced with the reaping of the task.
  		 * The deletion should have cleared us off the list.
  		 */

  		WARN_ON_ONCE(!list_empty(&timer->it.cpu.entry));

  	} else {

  		if (timer->it.cpu.firing)
  			ret = TIMER_RETRY;
  		else
  			list_del(&timer->it.cpu.entry);

  
  		unlock_task_sighand(p, &flags);

  	}

  
  	if (!ret)
  		put_task_struct(p);

  	return ret;

  }

  static void cleanup_timers_list(struct list_head *head)

  {
  	struct cpu_timer_list *timer, *next;

  	list_for_each_entry_safe(timer, next, head, entry)

  		list_del_init(&timer->entry);

  }

  /*
   * Clean out CPU timers still ticking when a thread exited.  The task
   * pointer is cleared, and the expiry time is replaced with the residual
   * time for later timer_gettime calls to return.
   * This must be called with the siglock held.
   */

  static void cleanup_timers(struct list_head *head)

  {

  	cleanup_timers_list(head);
  	cleanup_timers_list(++head);
  	cleanup_timers_list(++head);

  }
  
  /*
   * These are both called with the siglock held, when the current thread
   * is being reaped.  When the final (leader) thread in the group is reaped,
   * posix_cpu_timers_exit_group will be called after posix_cpu_timers_exit.
   */
  void posix_cpu_timers_exit(struct task_struct *tsk)
  {

  	cleanup_timers(tsk->cpu_timers);

  }
  void posix_cpu_timers_exit_group(struct task_struct *tsk)
  {

  	cleanup_timers(tsk->signal->cpu_timers);

  }

  static inline int expires_gt(u64 expires, u64 new_exp)

  {

  	return expires == 0 || expires > new_exp;

  }

  /*
   * Insert the timer on the appropriate list before any timers that

   * expire later.  This must be called with the sighand lock held.

   */

  static void arm_timer(struct k_itimer *timer)

  {
  	struct task_struct *p = timer->it.cpu.task;
  	struct list_head *head, *listpos;

  	struct task_cputime *cputime_expires;

  	struct cpu_timer_list *const nt = &timer->it.cpu;
  	struct cpu_timer_list *next;

  	if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
  		head = p->cpu_timers;
  		cputime_expires = &p->cputime_expires;
  	} else {
  		head = p->signal->cpu_timers;
  		cputime_expires = &p->signal->cputime_expires;
  	}

  	head += CPUCLOCK_WHICH(timer->it_clock);

  	listpos = head;

  	list_for_each_entry(next, head, entry) {

  		if (nt->expires < next->expires)

  			break;
  		listpos = &next->entry;

  	}
  	list_add(&nt->entry, listpos);
  
  	if (listpos == head) {

  		u64 exp = nt->expires;

  		/*

  		 * We are the new earliest-expiring POSIX 1.b timer, hence
  		 * need to update expiration cache. Take into account that
  		 * for process timers we share expiration cache with itimers
  		 * and RLIMIT_CPU and for thread timers with RLIMIT_RTTIME.

  		 */

  		switch (CPUCLOCK_WHICH(timer->it_clock)) {
  		case CPUCLOCK_PROF:

  			if (expires_gt(cputime_expires->prof_exp, exp))
  				cputime_expires->prof_exp = exp;

  			break;
  		case CPUCLOCK_VIRT:

  			if (expires_gt(cputime_expires->virt_exp, exp))
  				cputime_expires->virt_exp = exp;

  			break;
  		case CPUCLOCK_SCHED:

  			if (expires_gt(cputime_expires->sched_exp, exp))

  				cputime_expires->sched_exp = exp;

  			break;

  		}

  		if (CPUCLOCK_PERTHREAD(timer->it_clock))
  			tick_dep_set_task(p, TICK_DEP_BIT_POSIX_TIMER);
  		else
  			tick_dep_set_signal(p->signal, TICK_DEP_BIT_POSIX_TIMER);

  	}

  }
  
  /*
   * The timer is locked, fire it and arrange for its reload.
   */
  static void cpu_timer_fire(struct k_itimer *timer)
  {

  	if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
  		/*
  		 * User don't want any signal.
  		 */

  		timer->it.cpu.expires = 0;

  	} else if (unlikely(timer->sigq == NULL)) {

  		/*
  		 * This a special case for clock_nanosleep,
  		 * not a normal timer from sys_timer_create.
  		 */
  		wake_up_process(timer->it_process);

  		timer->it.cpu.expires = 0;
  	} else if (timer->it.cpu.incr == 0) {

  		/*
  		 * One-shot timer.  Clear it as soon as it's fired.
  		 */
  		posix_timer_event(timer, 0);

  		timer->it.cpu.expires = 0;

  	} else if (posix_timer_event(timer, ++timer->it_requeue_pending)) {
  		/*
  		 * The signal did not get queued because the signal
  		 * was ignored, so we won't get any callback to
  		 * reload the timer.  But we need to keep it
  		 * ticking in case the signal is deliverable next time.
  		 */

  		posix_cpu_timer_rearm(timer);

  		++timer->it_requeue_pending;

  	}
  }
  
  /*

   * Sample a process (thread group) timer for the given group_leader task.

   * Must be called with task sighand lock held for safe while_each_thread()
   * traversal.

   */
  static int cpu_timer_sample_group(const clockid_t which_clock,

  				  struct task_struct *p, u64 *sample)

  {

  	struct task_cputime cputime;

  
  	thread_group_cputimer(p, &cputime);
  	switch (CPUCLOCK_WHICH(which_clock)) {
  	default:
  		return -EINVAL;
  	case CPUCLOCK_PROF:

  		*sample = cputime.utime + cputime.stime;

  		break;
  	case CPUCLOCK_VIRT:

  		*sample = cputime.utime;

  		break;
  	case CPUCLOCK_SCHED:

  		*sample = cputime.sum_exec_runtime;

  		break;
  	}
  	return 0;
  }
  
  /*

   * Guts of sys_timer_settime for CPU timers.
   * This is called with the timer locked and interrupts disabled.
   * If we return TIMER_RETRY, it's necessary to release the timer's lock
   * and try again.  (This happens when the timer is in the middle of firing.)
   */

  static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,

  			       struct itimerspec64 *new, struct itimerspec64 *old)

  {

  	unsigned long flags;
  	struct sighand_struct *sighand;

  	struct task_struct *p = timer->it.cpu.task;

  	u64 old_expires, new_expires, old_incr, val;

  	int ret;

  	WARN_ON_ONCE(p == NULL);

  	/*
  	 * Use the to_ktime conversion because that clamps the maximum
  	 * value to KTIME_MAX and avoid multiplication overflows.
  	 */
  	new_expires = ktime_to_ns(timespec64_to_ktime(new->it_value));

  	/*

  	 * Protect against sighand release/switch in exit/exec and p->cpu_timers
  	 * and p->signal->cpu_timers read/write in arm_timer()
  	 */
  	sighand = lock_task_sighand(p, &flags);
  	/*
  	 * If p has just been reaped, we can no

  	 * longer get any information about it at all.
  	 */

  	if (unlikely(sighand == NULL)) {

  		return -ESRCH;
  	}
  
  	/*
  	 * Disarm any old timer after extracting its expiry time.
  	 */

  
  	ret = 0;

  	old_incr = timer->it.cpu.incr;

  	old_expires = timer->it.cpu.expires;

  	if (unlikely(timer->it.cpu.firing)) {
  		timer->it.cpu.firing = -1;
  		ret = TIMER_RETRY;
  	} else
  		list_del_init(&timer->it.cpu.entry);

  
  	/*
  	 * We need to sample the current value to convert the new
  	 * value from to relative and absolute, and to convert the
  	 * old value from absolute to relative.  To set a process
  	 * timer, we need a sample to balance the thread expiry
  	 * times (in arm_timer).  With an absolute time, we must
  	 * check if it's already passed.  In short, we need a sample.
  	 */
  	if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
  		cpu_clock_sample(timer->it_clock, p, &val);
  	} else {

  		cpu_timer_sample_group(timer->it_clock, p, &val);

  	}
  
  	if (old) {

  		if (old_expires == 0) {

  			old->it_value.tv_sec = 0;
  			old->it_value.tv_nsec = 0;
  		} else {
  			/*
  			 * Update the timer in case it has
  			 * overrun already.  If it has,
  			 * we'll report it as having overrun
  			 * and with the next reloaded timer
  			 * already ticking, though we are
  			 * swallowing that pending
  			 * notification here to install the
  			 * new setting.
  			 */
  			bump_cpu_timer(timer, val);

  			if (val < timer->it.cpu.expires) {
  				old_expires = timer->it.cpu.expires - val;

  				old->it_value = ns_to_timespec64(old_expires);

  			} else {
  				old->it_value.tv_nsec = 1;
  				old->it_value.tv_sec = 0;
  			}
  		}
  	}

  	if (unlikely(ret)) {

  		/*
  		 * We are colliding with the timer actually firing.
  		 * Punt after filling in the timer's old value, and
  		 * disable this firing since we are already reporting
  		 * it as an overrun (thanks to bump_cpu_timer above).
  		 */

  		unlock_task_sighand(p, &flags);

  		goto out;
  	}

  	if (new_expires != 0 && !(timer_flags & TIMER_ABSTIME)) {

  		new_expires += val;

  	}
  
  	/*
  	 * Install the new expiry time (or zero).
  	 * For a timer with no notification action, we don't actually
  	 * arm the timer (we'll just fake it for timer_gettime).
  	 */
  	timer->it.cpu.expires = new_expires;

  	if (new_expires != 0 && val < new_expires) {

  		arm_timer(timer);

  	}

  	unlock_task_sighand(p, &flags);

  	/*
  	 * Install the new reload setting, and
  	 * set up the signal and overrun bookkeeping.
  	 */

  	timer->it.cpu.incr = timespec64_to_ns(&new->it_interval);

  	timer->it_interval = ns_to_ktime(timer->it.cpu.incr);

  
  	/*
  	 * This acts as a modification timestamp for the timer,
  	 * so any automatic reload attempt will punt on seeing
  	 * that we have reset the timer manually.
  	 */
  	timer->it_requeue_pending = (timer->it_requeue_pending + 2) &
  		~REQUEUE_PENDING;
  	timer->it_overrun_last = 0;
  	timer->it_overrun = -1;

  	if (new_expires != 0 && !(val < new_expires)) {

  		/*
  		 * The designated time already passed, so we notify
  		 * immediately, even if the thread never runs to
  		 * accumulate more time on this clock.
  		 */
  		cpu_timer_fire(timer);
  	}
  
  	ret = 0;
   out:

  	if (old)

  		old->it_interval = ns_to_timespec64(old_incr);

  	return ret;
  }

  static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp)

  {

  	u64 now;

  	struct task_struct *p = timer->it.cpu.task;

  	WARN_ON_ONCE(p == NULL);

  	/*
  	 * Easy part: convert the reload time.
  	 */

  	itp->it_interval = ns_to_timespec64(timer->it.cpu.incr);

  	if (!timer->it.cpu.expires)

  		return;

  	/*
  	 * Sample the clock to take the difference with the expiry time.
  	 */
  	if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
  		cpu_clock_sample(timer->it_clock, p, &now);

  	} else {

  		struct sighand_struct *sighand;
  		unsigned long flags;
  
  		/*
  		 * Protect against sighand release/switch in exit/exec and
  		 * also make timer sampling safe if it ends up calling

  		 * thread_group_cputime().

  		 */
  		sighand = lock_task_sighand(p, &flags);
  		if (unlikely(sighand == NULL)) {

  			/*
  			 * The process has been reaped.
  			 * We can't even collect a sample any more.
  			 * Call the timer disarmed, nothing else to do.
  			 */

  			timer->it.cpu.expires = 0;

  			return;

  		} else {

  			cpu_timer_sample_group(timer->it_clock, p, &now);

  			unlock_task_sighand(p, &flags);

  		}

  	}

  	if (now < timer->it.cpu.expires) {

  		itp->it_value = ns_to_timespec64(timer->it.cpu.expires - now);

  	} else {
  		/*
  		 * The timer should have expired already, but the firing
  		 * hasn't taken place yet.  Say it's just about to expire.
  		 */
  		itp->it_value.tv_nsec = 1;
  		itp->it_value.tv_sec = 0;
  	}
  }

  static unsigned long long
  check_timers_list(struct list_head *timers,
  		  struct list_head *firing,
  		  unsigned long long curr)
  {
  	int maxfire = 20;
  
  	while (!list_empty(timers)) {
  		struct cpu_timer_list *t;
  
  		t = list_first_entry(timers, struct cpu_timer_list, entry);
  
  		if (!--maxfire || curr < t->expires)
  			return t->expires;
  
  		t->firing = 1;
  		list_move_tail(&t->entry, firing);
  	}
  
  	return 0;
  }

  static inline void check_dl_overrun(struct task_struct *tsk)
  {
  	if (tsk->dl.dl_overrun) {
  		tsk->dl.dl_overrun = 0;
  		__group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
  	}
  }

  /*
   * Check for any per-thread CPU timers that have fired and move them off
   * the tsk->cpu_timers[N] list onto the firing list.  Here we update the
   * tsk->it_*_expires values to reflect the remaining thread CPU timers.
   */
  static void check_thread_timers(struct task_struct *tsk,
  				struct list_head *firing)
  {
  	struct list_head *timers = tsk->cpu_timers;

  	struct task_cputime *tsk_expires = &tsk->cputime_expires;
  	u64 expires;

  	unsigned long soft;

  	if (dl_task(tsk))
  		check_dl_overrun(tsk);

  	/*
  	 * If cputime_expires is zero, then there are no active
  	 * per thread CPU timers.
  	 */
  	if (task_cputime_zero(&tsk->cputime_expires))
  		return;

  	expires = check_timers_list(timers, firing, prof_ticks(tsk));

  	tsk_expires->prof_exp = expires;

  	expires = check_timers_list(++timers, firing, virt_ticks(tsk));

  	tsk_expires->virt_exp = expires;

  	tsk_expires->sched_exp = check_timers_list(++timers, firing,
  						   tsk->se.sum_exec_runtime);

  
  	/*
  	 * Check for the special case thread timers.
  	 */

  	soft = task_rlimit(tsk, RLIMIT_RTTIME);

  	if (soft != RLIM_INFINITY) {

  		unsigned long hard = task_rlimit_max(tsk, RLIMIT_RTTIME);

  		if (hard != RLIM_INFINITY &&
  		    tsk->rt.timeout > DIV_ROUND_UP(hard, USEC_PER_SEC/HZ)) {

  			/*
  			 * At the hard limit, we just die.
  			 * No need to calculate anything else now.
  			 */

  			if (print_fatal_signals) {
  				pr_info("CPU Watchdog Timeout (hard): %s[%d]
  ",
  					tsk->comm, task_pid_nr(tsk));
  			}

  			__group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
  			return;
  		}

  		if (tsk->rt.timeout > DIV_ROUND_UP(soft, USEC_PER_SEC/HZ)) {

  			/*
  			 * At the soft limit, send a SIGXCPU every second.
  			 */

  			if (soft < hard) {
  				soft += USEC_PER_SEC;

  				tsk->signal->rlim[RLIMIT_RTTIME].rlim_cur =
  					soft;

  			}

  			if (print_fatal_signals) {
  				pr_info("RT Watchdog Timeout (soft): %s[%d]
  ",
  					tsk->comm, task_pid_nr(tsk));
  			}

  			__group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
  		}
  	}

  	if (task_cputime_zero(tsk_expires))
  		tick_dep_clear_task(tsk, TICK_DEP_BIT_POSIX_TIMER);

  }

  static inline void stop_process_timers(struct signal_struct *sig)

  {

  	struct thread_group_cputimer *cputimer = &sig->cputimer;

  	/* Turn off cputimer->running. This is done without locking. */

  	WRITE_ONCE(cputimer->running, false);

  	tick_dep_clear_signal(sig, TICK_DEP_BIT_POSIX_TIMER);

  }

  static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,

  			     u64 *expires, u64 cur_time, int signo)

  {

  	if (!it->expires)

  		return;

  	if (cur_time >= it->expires) {
  		if (it->incr)

  			it->expires += it->incr;

  		else

  			it->expires = 0;

  		trace_itimer_expire(signo == SIGPROF ?
  				    ITIMER_PROF : ITIMER_VIRTUAL,

  				    task_tgid(tsk), cur_time);

  		__group_send_sig_info(signo, SEND_SIG_PRIV, tsk);
  	}

  	if (it->expires && (!*expires || it->expires < *expires))
  		*expires = it->expires;

  }

  /*
   * Check for any per-thread CPU timers that have fired and move them
   * off the tsk->*_timers list onto the firing list.  Per-thread timers
   * have already been taken off.
   */
  static void check_process_timers(struct task_struct *tsk,
  				 struct list_head *firing)
  {
  	struct signal_struct *const sig = tsk->signal;

  	u64 utime, ptime, virt_expires, prof_expires;
  	u64 sum_sched_runtime, sched_expires;

  	struct list_head *timers = sig->cpu_timers;

  	struct task_cputime cputime;

  	unsigned long soft;

  	if (dl_task(tsk))
  		check_dl_overrun(tsk);

  	/*

  	 * If cputimer is not running, then there are no active
  	 * process wide timers (POSIX 1.b, itimers, RLIMIT_CPU).
  	 */
  	if (!READ_ONCE(tsk->signal->cputimer.running))
  		return;

          /*
  	 * Signify that a thread is checking for process timers.
  	 * Write access to this field is protected by the sighand lock.
  	 */
  	sig->cputimer.checking_timer = true;

  	/*

  	 * Collect the current process totals.
  	 */

  	thread_group_cputimer(tsk, &cputime);

  	utime = cputime.utime;
  	ptime = utime + cputime.stime;

  	sum_sched_runtime = cputime.sum_exec_runtime;

  	prof_expires = check_timers_list(timers, firing, ptime);
  	virt_expires = check_timers_list(++timers, firing, utime);
  	sched_expires = check_timers_list(++timers, firing, sum_sched_runtime);

  
  	/*
  	 * Check for the special case process timers.
  	 */

  	check_cpu_itimer(tsk, &sig->it[CPUCLOCK_PROF], &prof_expires, ptime,
  			 SIGPROF);
  	check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT], &virt_expires, utime,
  			 SIGVTALRM);

  	soft = task_rlimit(tsk, RLIMIT_CPU);

  	if (soft != RLIM_INFINITY) {

  		unsigned long psecs = div_u64(ptime, NSEC_PER_SEC);

  		unsigned long hard = task_rlimit_max(tsk, RLIMIT_CPU);

  		u64 x;

  		if (psecs >= hard) {

  			/*
  			 * At the hard limit, we just die.
  			 * No need to calculate anything else now.
  			 */

  			if (print_fatal_signals) {
  				pr_info("RT Watchdog Timeout (hard): %s[%d]
  ",
  					tsk->comm, task_pid_nr(tsk));
  			}

  			__group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
  			return;
  		}

  		if (psecs >= soft) {

  			/*
  			 * At the soft limit, send a SIGXCPU every second.
  			 */

  			if (print_fatal_signals) {
  				pr_info("CPU Watchdog Timeout (soft): %s[%d]
  ",
  					tsk->comm, task_pid_nr(tsk));
  			}

  			__group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);

  			if (soft < hard) {
  				soft++;
  				sig->rlim[RLIMIT_CPU].rlim_cur = soft;

  			}
  		}

  		x = soft * NSEC_PER_SEC;
  		if (!prof_expires || x < prof_expires)

  			prof_expires = x;

  	}

  	sig->cputime_expires.prof_exp = prof_expires;
  	sig->cputime_expires.virt_exp = virt_expires;

  	sig->cputime_expires.sched_exp = sched_expires;
  	if (task_cputime_zero(&sig->cputime_expires))
  		stop_process_timers(sig);

  
  	sig->cputimer.checking_timer = false;

  }
  
  /*

   * This is called from the signal code (via posixtimer_rearm)

   * when the last timer signal was delivered and we have to reload the timer.
   */

  static void posix_cpu_timer_rearm(struct k_itimer *timer)

  {

  	struct sighand_struct *sighand;
  	unsigned long flags;

  	struct task_struct *p = timer->it.cpu.task;

  	u64 now;

  	WARN_ON_ONCE(p == NULL);

  
  	/*
  	 * Fetch the current sample and update the timer's expiry time.
  	 */
  	if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
  		cpu_clock_sample(timer->it_clock, p, &now);
  		bump_cpu_timer(timer, now);

  		if (unlikely(p->exit_state))

  			return;

  		/* Protect timer list r/w in arm_timer() */
  		sighand = lock_task_sighand(p, &flags);
  		if (!sighand)

  			return;

  	} else {

  		/*
  		 * Protect arm_timer() and timer sampling in case of call to

  		 * thread_group_cputime().

  		 */
  		sighand = lock_task_sighand(p, &flags);
  		if (unlikely(sighand == NULL)) {

  			/*
  			 * The process has been reaped.
  			 * We can't even collect a sample any more.
  			 */

  			timer->it.cpu.expires = 0;

  			return;

  		} else if (unlikely(p->exit_state) && thread_group_empty(p)) {

  			/* If the process is dying, no need to rearm */
  			goto unlock;

  		}

  		cpu_timer_sample_group(timer->it_clock, p, &now);

  		bump_cpu_timer(timer, now);

  		/* Leave the sighand locked for the call below.  */

  	}
  
  	/*
  	 * Now re-arm for the new expiry time.
  	 */

  	arm_timer(timer);

  unlock:

  	unlock_task_sighand(p, &flags);

  }

  /**

   * task_cputime_expired - Compare two task_cputime entities.
   *
   * @sample:	The task_cputime structure to be checked for expiration.
   * @expires:	Expiration times, against which @sample will be checked.
   *
   * Checks @sample against @expires to see if any field of @sample has expired.
   * Returns true if any field of the former is greater than the corresponding
   * field of the latter if the latter field is set.  Otherwise returns false.
   */

  static inline int task_cputime_expired(const struct task_cputime *sample,
  					const struct task_cputime *expires)

  {

  	if (expires->utime && sample->utime >= expires->utime)

  		return 1;

  	if (expires->stime && sample->utime + sample->stime >= expires->stime)

  		return 1;
  	if (expires->sum_exec_runtime != 0 &&
  	    sample->sum_exec_runtime >= expires->sum_exec_runtime)
  		return 1;
  	return 0;
  }
  
  /**
   * fastpath_timer_check - POSIX CPU timers fast path.
   *
   * @tsk:	The task (thread) being checked.

   *

   * Check the task and thread group timers.  If both are zero (there are no
   * timers set) return false.  Otherwise snapshot the task and thread group
   * timers and compare them with the corresponding expiration times.  Return
   * true if a timer has expired, else return false.

   */

  static inline int fastpath_timer_check(struct task_struct *tsk)

  {

  	struct signal_struct *sig;

  	if (!task_cputime_zero(&tsk->cputime_expires)) {

  		struct task_cputime task_sample;

  		task_cputime(tsk, &task_sample.utime, &task_sample.stime);

  		task_sample.sum_exec_runtime = tsk->se.sum_exec_runtime;

  		if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
  			return 1;
  	}

  
  	sig = tsk->signal;

  	/*
  	 * Check if thread group timers expired when the cputimer is
  	 * running and no other thread in the group is already checking
  	 * for thread group cputimers. These fields are read without the
  	 * sighand lock. However, this is fine because this is meant to
  	 * be a fastpath heuristic to determine whether we should try to
  	 * acquire the sighand lock to check/handle timers.
  	 *
  	 * In the worst case scenario, if 'running' or 'checking_timer' gets
  	 * set but the current thread doesn't see the change yet, we'll wait
  	 * until the next thread in the group gets a scheduler interrupt to
  	 * handle the timer. This isn't an issue in practice because these
  	 * types of delays with signals actually getting sent are expected.
  	 */
  	if (READ_ONCE(sig->cputimer.running) &&
  	    !READ_ONCE(sig->cputimer.checking_timer)) {

  		struct task_cputime group_sample;

  		sample_cputime_atomic(&group_sample, &sig->cputimer.cputime_atomic);

  		if (task_cputime_expired(&group_sample, &sig->cputime_expires))
  			return 1;
  	}

  	if (dl_task(tsk) && tsk->dl.dl_overrun)
  		return 1;

  	return 0;

  }

  /*
   * This is called from the timer interrupt handler.  The irq handler has
   * already updated our counts.  We need to check if any timers fire now.
   * Interrupts are disabled.
   */
  void run_posix_cpu_timers(struct task_struct *tsk)
  {
  	LIST_HEAD(firing);
  	struct k_itimer *timer, *next;

  	unsigned long flags;

  	lockdep_assert_irqs_disabled();

  	/*

  	 * The fast path checks that there are no expired thread or thread

  	 * group timers.  If that's so, just return.

  	 */

  	if (!fastpath_timer_check(tsk))

  		return;

  	if (!lock_task_sighand(tsk, &flags))
  		return;

  	/*
  	 * Here we take off tsk->signal->cpu_timers[N] and
  	 * tsk->cpu_timers[N] all the timers that are firing, and
  	 * put them on the firing list.
  	 */
  	check_thread_timers(tsk, &firing);

  
  	check_process_timers(tsk, &firing);

  	/*
  	 * We must release these locks before taking any timer's lock.
  	 * There is a potential race with timer deletion here, as the
  	 * siglock now protects our private firing list.  We have set
  	 * the firing flag in each timer, so that a deletion attempt
  	 * that gets the timer lock before we do will give it up and
  	 * spin until we've taken care of that timer below.
  	 */

  	unlock_task_sighand(tsk, &flags);

  
  	/*
  	 * Now that all the timers on our list have the firing flag,

  	 * no one will touch their list entries but us.  We'll take

  	 * each timer's lock before clearing its firing flag, so no
  	 * timer call will interfere.
  	 */
  	list_for_each_entry_safe(timer, next, &firing, it.cpu.entry) {

  		int cpu_firing;

  		spin_lock(&timer->it_lock);
  		list_del_init(&timer->it.cpu.entry);

  		cpu_firing = timer->it.cpu.firing;

  		timer->it.cpu.firing = 0;
  		/*
  		 * The firing flag is -1 if we collided with a reset
  		 * of the timer, which already reported this
  		 * almost-firing as an overrun.  So don't generate an event.
  		 */

  		if (likely(cpu_firing >= 0))

  			cpu_timer_fire(timer);

  		spin_unlock(&timer->it_lock);
  	}
  }
  
  /*

   * Set one of the process-wide special case CPU timers or RLIMIT_CPU.

   * The tsk->sighand->siglock must be held by the caller.

   */
  void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,

  			   u64 *newval, u64 *oldval)

  {

  	u64 now;

  	int ret;

  	WARN_ON_ONCE(clock_idx == CPUCLOCK_SCHED);

  	ret = cpu_timer_sample_group(clock_idx, tsk, &now);

  	if (oldval && ret != -EINVAL) {

  		/*
  		 * We are setting itimer. The *oldval is absolute and we update
  		 * it to be relative, *newval argument is relative and we update
  		 * it to be absolute.
  		 */

  		if (*oldval) {

  			if (*oldval <= now) {

  				/* Just about to fire. */

  				*oldval = TICK_NSEC;

  			} else {

  				*oldval -= now;

  			}
  		}

  		if (!*newval)

  			return;

  		*newval += now;

  	}
  
  	/*

  	 * Update expiration cache if we are the earliest timer, or eventually
  	 * RLIMIT_CPU limit is earlier than prof_exp cpu timer expire.

  	 */

  	switch (clock_idx) {
  	case CPUCLOCK_PROF:

  		if (expires_gt(tsk->signal->cputime_expires.prof_exp, *newval))
  			tsk->signal->cputime_expires.prof_exp = *newval;

  		break;
  	case CPUCLOCK_VIRT:

  		if (expires_gt(tsk->signal->cputime_expires.virt_exp, *newval))
  			tsk->signal->cputime_expires.virt_exp = *newval;

  		break;

  	}

  
  	tick_dep_set_signal(tsk->signal, TICK_DEP_BIT_POSIX_TIMER);

  }

  static int do_cpu_nanosleep(const clockid_t which_clock, int flags,

  			    const struct timespec64 *rqtp)

  {

  	struct itimerspec64 it;

  	struct k_itimer timer;
  	u64 expires;

  	int error;
  
  	/*

  	 * Set up a temporary timer and then wait for it to go off.
  	 */
  	memset(&timer, 0, sizeof timer);
  	spin_lock_init(&timer.it_lock);
  	timer.it_clock = which_clock;
  	timer.it_overrun = -1;
  	error = posix_cpu_timer_create(&timer);
  	timer.it_process = current;
  	if (!error) {

  		static struct itimerspec64 zero_it;

  		struct restart_block *restart;

  		memset(&it, 0, sizeof(it));

  		it.it_value = *rqtp;

  
  		spin_lock_irq(&timer.it_lock);

  		error = posix_cpu_timer_set(&timer, flags, &it, NULL);

  		if (error) {
  			spin_unlock_irq(&timer.it_lock);
  			return error;
  		}
  
  		while (!signal_pending(current)) {

  			if (timer.it.cpu.expires == 0) {

  				/*

  				 * Our timer fired and was reset, below
  				 * deletion can not fail.

  				 */

  				posix_cpu_timer_del(&timer);

  				spin_unlock_irq(&timer.it_lock);
  				return 0;
  			}
  
  			/*
  			 * Block until cpu_timer_fire (or a signal) wakes us.
  			 */
  			__set_current_state(TASK_INTERRUPTIBLE);
  			spin_unlock_irq(&timer.it_lock);
  			schedule();
  			spin_lock_irq(&timer.it_lock);
  		}
  
  		/*
  		 * We were interrupted by a signal.
  		 */

  		expires = timer.it.cpu.expires;

  		error = posix_cpu_timer_set(&timer, 0, &zero_it, &it);

  		if (!error) {
  			/*
  			 * Timer is now unarmed, deletion can not fail.
  			 */
  			posix_cpu_timer_del(&timer);
  		}

  		spin_unlock_irq(&timer.it_lock);

  		while (error == TIMER_RETRY) {
  			/*
  			 * We need to handle case when timer was or is in the
  			 * middle of firing. In other cases we already freed
  			 * resources.
  			 */
  			spin_lock_irq(&timer.it_lock);
  			error = posix_cpu_timer_del(&timer);
  			spin_unlock_irq(&timer.it_lock);
  		}

  		if ((it.it_value.tv_sec | it.it_value.tv_nsec) == 0) {

  			/*
  			 * It actually did fire already.
  			 */
  			return 0;
  		}

  		error = -ERESTART_RESTARTBLOCK;

  		/*
  		 * Report back to the user the time still remaining.
  		 */

  		restart = &current->restart_block;

  		restart->nanosleep.expires = expires;

  		if (restart->nanosleep.type != TT_NONE)
  			error = nanosleep_copyout(restart, &it.it_value);

  	}
  
  	return error;
  }

  static long posix_cpu_nsleep_restart(struct restart_block *restart_block);
  
  static int posix_cpu_nsleep(const clockid_t which_clock, int flags,

  			    const struct timespec64 *rqtp)

  {

  	struct restart_block *restart_block = &current->restart_block;

  	int error;
  
  	/*
  	 * Diagnose required errors first.
  	 */
  	if (CPUCLOCK_PERTHREAD(which_clock) &&
  	    (CPUCLOCK_PID(which_clock) == 0 ||

  	     CPUCLOCK_PID(which_clock) == task_pid_vnr(current)))

  		return -EINVAL;

  	error = do_cpu_nanosleep(which_clock, flags, rqtp);

  
  	if (error == -ERESTART_RESTARTBLOCK) {

  		if (flags & TIMER_ABSTIME)

  			return -ERESTARTNOHAND;

  		restart_block->fn = posix_cpu_nsleep_restart;

  		restart_block->nanosleep.clockid = which_clock;

  	}

  	return error;
  }

  static long posix_cpu_nsleep_restart(struct restart_block *restart_block)

  {

  	clockid_t which_clock = restart_block->nanosleep.clockid;

  	struct timespec64 t;

  	t = ns_to_timespec64(restart_block->nanosleep.expires);

  	return do_cpu_nanosleep(which_clock, TIMER_ABSTIME, &t);

  }

  #define PROCESS_CLOCK	make_process_cpuclock(0, CPUCLOCK_SCHED)
  #define THREAD_CLOCK	make_thread_cpuclock(0, CPUCLOCK_SCHED)

  static int process_cpu_clock_getres(const clockid_t which_clock,

  				    struct timespec64 *tp)

  {
  	return posix_cpu_clock_getres(PROCESS_CLOCK, tp);
  }

  static int process_cpu_clock_get(const clockid_t which_clock,

  				 struct timespec64 *tp)

  {
  	return posix_cpu_clock_get(PROCESS_CLOCK, tp);
  }
  static int process_cpu_timer_create(struct k_itimer *timer)
  {
  	timer->it_clock = PROCESS_CLOCK;
  	return posix_cpu_timer_create(timer);
  }

  static int process_cpu_nsleep(const clockid_t which_clock, int flags,

  			      const struct timespec64 *rqtp)

  {

  	return posix_cpu_nsleep(PROCESS_CLOCK, flags, rqtp);

  }

  static int thread_cpu_clock_getres(const clockid_t which_clock,

  				   struct timespec64 *tp)

  {
  	return posix_cpu_clock_getres(THREAD_CLOCK, tp);
  }

  static int thread_cpu_clock_get(const clockid_t which_clock,

  				struct timespec64 *tp)

  {
  	return posix_cpu_clock_get(THREAD_CLOCK, tp);
  }
  static int thread_cpu_timer_create(struct k_itimer *timer)
  {
  	timer->it_clock = THREAD_CLOCK;
  	return posix_cpu_timer_create(timer);
  }

  const struct k_clock clock_posix_cpu = {

  	.clock_getres	= posix_cpu_clock_getres,
  	.clock_set	= posix_cpu_clock_set,
  	.clock_get	= posix_cpu_clock_get,
  	.timer_create	= posix_cpu_timer_create,
  	.nsleep		= posix_cpu_nsleep,

  	.timer_set	= posix_cpu_timer_set,
  	.timer_del	= posix_cpu_timer_del,
  	.timer_get	= posix_cpu_timer_get,

  	.timer_rearm	= posix_cpu_timer_rearm,

  };

  const struct k_clock clock_process = {
  	.clock_getres	= process_cpu_clock_getres,
  	.clock_get	= process_cpu_clock_get,
  	.timer_create	= process_cpu_timer_create,
  	.nsleep		= process_cpu_nsleep,

  };

  const struct k_clock clock_thread = {
  	.clock_getres	= thread_cpu_clock_getres,
  	.clock_get	= thread_cpu_clock_get,
  	.timer_create	= thread_cpu_timer_create,
  };