// 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);

  void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit)
  {
  	posix_cputimers_init(pct);

  	if (cpu_limit != RLIM_INFINITY) {

  		pct->bases[CPUCLOCK_PROF].nextevt = cpu_limit * NSEC_PER_SEC;

  		pct->timers_active = true;
  	}

  }

  /*

   * Called after updating RLIMIT_CPU to run cpu timer and update

   * tsk->signal->posix_cputimers.bases[clock].nextevt expiration cache if
   * necessary. Needs siglock protection since other code may update the

   * 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);

  }

  /*
   * Functions for validating access to tasks.
   */

  static struct pid *pid_for_clock(const clockid_t clock, bool gettime)

  {

  	const bool thread = !!CPUCLOCK_PERTHREAD(clock);
  	const pid_t upid = CPUCLOCK_PID(clock);
  	struct pid *pid;
  
  	if (CPUCLOCK_WHICH(clock) >= CPUCLOCK_MAX)
  		return NULL;

  	/*
  	 * If the encoded PID is 0, then the timer is targeted at current
  	 * or the process to which current belongs.
  	 */

  	if (upid == 0)
  		return thread ? task_pid(current) : task_tgid(current);

  	pid = find_vpid(upid);
  	if (!pid)
  		return NULL;

  	if (thread) {
  		struct task_struct *tsk = pid_task(pid, PIDTYPE_PID);
  		return (tsk && same_thread_group(tsk, current)) ? pid : NULL;
  	}

  	/*

  	 * For clock_gettime(PROCESS) allow finding the process by
  	 * with the pid of the current task.  The code needs the tgid
  	 * of the process so that pid_task(pid, PIDTYPE_TGID) can be
  	 * used to find the process.

  	 */

  	if (gettime && (pid == task_pid(current)))
  		return task_tgid(current);

  
  	/*

  	 * For processes require that pid identifies a process.

  	 */

  	return pid_has_task(pid, PIDTYPE_TGID) ? pid : NULL;

  }
  
  static inline int validate_clock_permissions(const clockid_t clock)
  {

  	int ret;
  
  	rcu_read_lock();

  	ret = pid_for_clock(clock, false) ? 0 : -EINVAL;

  	rcu_read_unlock();
  
  	return ret;

  }

  static inline enum pid_type clock_pid_type(const clockid_t clock)

  {

  	return CPUCLOCK_PERTHREAD(clock) ? PIDTYPE_PID : PIDTYPE_TGID;

  }
  
  static inline struct task_struct *cpu_timer_task_rcu(struct k_itimer *timer)
  {

  	return pid_task(timer->it.cpu.pid, clock_pid_type(timer->it_clock));

  }

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

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

  {

  	u64 delta, incr, expires = timer->it.cpu.node.expires;

  	int i;

  	if (!timer->it_interval)

  		return expires;

  	if (now < expires)
  		return expires;

  	incr = timer->it_interval;

  	delta = now + incr - 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.node.expires += incr;

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

  		delta -= incr;

  	}

  	return timer->it.cpu.node.expires;

  }

  /* Check whether all cache entries contain U64_MAX, i.e. eternal expiry time */
  static inline bool expiry_cache_is_inactive(const struct posix_cputimers *pct)

  {

  	return !(~pct->bases[CPUCLOCK_PROF].nextevt |
  		 ~pct->bases[CPUCLOCK_VIRT].nextevt |
  		 ~pct->bases[CPUCLOCK_SCHED].nextevt);

  }

  static int

  posix_cpu_clock_getres(const clockid_t which_clock, struct timespec64 *tp)

  {

  	int error = validate_clock_permissions(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 clock, const struct timespec64 *tp)

  {

  	int error = validate_clock_permissions(clock);

  	/*
  	 * You can never reset a CPU clock, but we check for other errors
  	 * in the call before failing with EPERM.
  	 */

  	return error ? : -EPERM;

  }

  /*

   * Sample a per-thread clock for the given task. clkid is validated.

   */

  static u64 cpu_clock_sample(const clockid_t clkid, struct task_struct *p)

  {

  	u64 utime, stime;
  
  	if (clkid == CPUCLOCK_SCHED)
  		return task_sched_runtime(p);
  
  	task_cputime(p, &utime, &stime);

  	switch (clkid) {

  	case CPUCLOCK_PROF:

  		return utime + stime;

  	case CPUCLOCK_VIRT:

  		return utime;

  	default:
  		WARN_ON_ONCE(1);

  	}

  	return 0;

  }

  static inline void store_samples(u64 *samples, u64 stime, u64 utime, u64 rtime)
  {
  	samples[CPUCLOCK_PROF] = stime + utime;
  	samples[CPUCLOCK_VIRT] = utime;
  	samples[CPUCLOCK_SCHED] = rtime;
  }
  
  static void task_sample_cputime(struct task_struct *p, u64 *samples)
  {
  	u64 stime, utime;
  
  	task_cputime(p, &utime, &stime);
  	store_samples(samples, stime, utime, p->se.sum_exec_runtime);
  }
  
  static void proc_sample_cputime_atomic(struct task_cputime_atomic *at,
  				       u64 *samples)
  {
  	u64 stime, utime, rtime;
  
  	utime = atomic64_read(&at->utime);
  	stime = atomic64_read(&at->stime);
  	rtime = atomic64_read(&at->sum_exec_runtime);
  	store_samples(samples, stime, utime, rtime);
  }

  /*
   * 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);

  }

  /**
   * thread_group_sample_cputime - Sample cputime for a given task
   * @tsk:	Task for which cputime needs to be started

   * @samples:	Storage for time samples

   *
   * Called from sys_getitimer() to calculate the expiry time of an active
   * timer. That means group cputime accounting is already active. Called
   * with task sighand lock held.
   *
   * Updates @times with an uptodate sample of the thread group cputimes.
   */

  void thread_group_sample_cputime(struct task_struct *tsk, u64 *samples)

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

  	struct posix_cputimers *pct = &tsk->signal->posix_cputimers;

  	WARN_ON_ONCE(!pct->timers_active);

  	proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);

  }

  /**
   * thread_group_start_cputime - Start cputime and return a sample
   * @tsk:	Task for which cputime needs to be started

   * @samples:	Storage for time samples

   *
   * The thread group cputime accouting is avoided when there are no posix
   * CPU timers armed. Before starting a timer it's required to check whether
   * the time accounting is active. If not, a full update of the atomic
   * accounting store needs to be done and the accounting enabled.
   *
   * Updates @times with an uptodate sample of the thread group cputimes.
   */

  static void thread_group_start_cputime(struct task_struct *tsk, u64 *samples)

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

  	struct posix_cputimers *pct = &tsk->signal->posix_cputimers;

  	/* Check if cputimer isn't running. This is accessed without locking. */

  	if (!READ_ONCE(pct->timers_active)) {

  		struct task_cputime sum;

  		/*
  		 * 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 timers_active without a lock. Ensure this
  		 * only gets written to in one operation. We set it after
  		 * update_gt_cputime() as a small optimization, but
  		 * barriers are not required because update_gt_cputime()

  		 * can handle concurrent updates.
  		 */

  		WRITE_ONCE(pct->timers_active, true);

  	}

  	proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
  }
  
  static void __thread_group_cputime(struct task_struct *tsk, u64 *samples)
  {
  	struct task_cputime ct;
  
  	thread_group_cputime(tsk, &ct);
  	store_samples(samples, ct.stime, ct.utime, ct.sum_exec_runtime);

  }

  /*

   * Sample a process (thread group) clock for the given task clkid. If the
   * group's cputime accounting is already enabled, read the atomic

   * store. Otherwise a full update is required.  clkid is already validated.

   */

  static u64 cpu_clock_sample_group(const clockid_t clkid, struct task_struct *p,
  				  bool start)

  {

  	struct thread_group_cputimer *cputimer = &p->signal->cputimer;

  	struct posix_cputimers *pct = &p->signal->posix_cputimers;

  	u64 samples[CPUCLOCK_MAX];

  	if (!READ_ONCE(pct->timers_active)) {

  		if (start)

  			thread_group_start_cputime(p, samples);

  		else

  			__thread_group_cputime(p, samples);

  	} else {

  		proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);

  	}

  	return samples[clkid];

  }

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

  {

  	const clockid_t clkid = CPUCLOCK_WHICH(clock);
  	struct task_struct *tsk;
  	u64 t;

  	rcu_read_lock();

  	tsk = pid_task(pid_for_clock(clock, true), clock_pid_type(clock));

  	if (!tsk) {
  		rcu_read_unlock();

  		return -EINVAL;

  	}

  	if (CPUCLOCK_PERTHREAD(clock))

  		t = cpu_clock_sample(clkid, tsk);

  	else

  		t = cpu_clock_sample_group(clkid, tsk, false);

  	rcu_read_unlock();

  	*tp = ns_to_timespec64(t);
  	return 0;

  }

  /*
   * 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)

  {

  	static struct lock_class_key posix_cpu_timers_key;

  	struct pid *pid;

  	rcu_read_lock();

  	pid = pid_for_clock(new_timer->it_clock, false);
  	if (!pid) {

  		rcu_read_unlock();

  		return -EINVAL;

  	}

  	/*
  	 * If posix timer expiry is handled in task work context then
  	 * timer::it_lock can be taken without disabling interrupts as all
  	 * other locking happens in task context. This requires a seperate
  	 * lock class key otherwise regular posix timer expiry would record
  	 * the lock class being taken in interrupt context and generate a
  	 * false positive warning.
  	 */
  	if (IS_ENABLED(CONFIG_POSIX_CPU_TIMERS_TASK_WORK))
  		lockdep_set_class(&new_timer->it_lock, &posix_cpu_timers_key);

  	new_timer->kclock = &clock_posix_cpu;

  	timerqueue_init(&new_timer->it.cpu.node);

  	new_timer->it.cpu.pid = get_pid(pid);

  	rcu_read_unlock();

  	return 0;

  }
  
  /*
   * 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)

  {

  	struct cpu_timer *ctmr = &timer->it.cpu;

  	struct sighand_struct *sighand;

  	struct task_struct *p;

  	unsigned long flags;
  	int ret = 0;

  	rcu_read_lock();
  	p = cpu_timer_task_rcu(timer);
  	if (!p)
  		goto out;

  	/*
  	 * 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)) {

  		/*

  		 * This raced with the reaping of the task. The exit cleanup
  		 * should have removed this timer from the timer queue.

  		 */

  		WARN_ON_ONCE(ctmr->head || timerqueue_node_queued(&ctmr->node));

  	} else {

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

  			cpu_timer_dequeue(ctmr);

  
  		unlock_task_sighand(p, &flags);

  	}

  out:
  	rcu_read_unlock();

  	if (!ret)

  		put_pid(ctmr->pid);

  	return ret;

  }

  static void cleanup_timerqueue(struct timerqueue_head *head)

  {

  	struct timerqueue_node *node;
  	struct cpu_timer *ctmr;

  	while ((node = timerqueue_getnext(head))) {
  		timerqueue_del(head, node);
  		ctmr = container_of(node, struct cpu_timer, node);
  		ctmr->head = NULL;
  	}

  }

  /*

   * Clean out CPU timers which are still armed when a thread exits. The
   * timers are only removed from the list. No other updates are done. The
   * corresponding posix timers are still accessible, but cannot be rearmed.
   *

   * This must be called with the siglock held.
   */

  static void cleanup_timers(struct posix_cputimers *pct)

  {

  	cleanup_timerqueue(&pct->bases[CPUCLOCK_PROF].tqhead);
  	cleanup_timerqueue(&pct->bases[CPUCLOCK_VIRT].tqhead);
  	cleanup_timerqueue(&pct->bases[CPUCLOCK_SCHED].tqhead);

  }
  
  /*
   * 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->posix_cputimers);

  }
  void posix_cpu_timers_exit_group(struct task_struct *tsk)
  {

  	cleanup_timers(&tsk->signal->posix_cputimers);

  }

  /*
   * 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)

  {

  	int clkidx = CPUCLOCK_WHICH(timer->it_clock);

  	struct cpu_timer *ctmr = &timer->it.cpu;
  	u64 newexp = cpu_timer_getexpires(ctmr);

  	struct posix_cputimer_base *base;

  	if (CPUCLOCK_PERTHREAD(timer->it_clock))
  		base = p->posix_cputimers.bases + clkidx;
  	else
  		base = p->signal->posix_cputimers.bases + clkidx;

  	if (!cpu_timer_enqueue(&base->tqhead, ctmr))

  		return;

  	/*
  	 * 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.
  	 */

  	if (newexp < base->nextevt)

  		base->nextevt = newexp;

  	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)
  {

  	struct cpu_timer *ctmr = &timer->it.cpu;

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

  		cpu_timer_setexpires(ctmr, 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);

  		cpu_timer_setexpires(ctmr, 0);

  	} else if (!timer->it_interval) {

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

  		cpu_timer_setexpires(ctmr, 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;

  	}
  }
  
  /*
   * 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)

  {

  	clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);

  	u64 old_expires, new_expires, old_incr, val;

  	struct cpu_timer *ctmr = &timer->it.cpu;

  	struct sighand_struct *sighand;

  	struct task_struct *p;

  	unsigned long flags;

  	int ret = 0;

  	rcu_read_lock();
  	p = cpu_timer_task_rcu(timer);
  	if (!p) {
  		/*
  		 * If p has just been reaped, we can no
  		 * longer get any information about it at all.
  		 */
  		rcu_read_unlock();
  		return -ESRCH;
  	}

  	/*
  	 * 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)) {
  		rcu_read_unlock();

  		return -ESRCH;

  	}

  
  	/*
  	 * Disarm any old timer after extracting its expiry time.
  	 */

  	old_incr = timer->it_interval;

  	old_expires = cpu_timer_getexpires(ctmr);

  	if (unlikely(timer->it.cpu.firing)) {
  		timer->it.cpu.firing = -1;
  		ret = TIMER_RETRY;

  	} else {
  		cpu_timer_dequeue(ctmr);
  	}

  
  	/*
  	 * 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))
  		val = cpu_clock_sample(clkid, p);
  	else
  		val = cpu_clock_sample_group(clkid, p, true);

  
  	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.

  			 */

  			u64 exp = bump_cpu_timer(timer, val);
  
  			if (val < exp) {
  				old_expires = exp - 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).
  	 */

  	cpu_timer_setexpires(ctmr, new_expires);

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

  		arm_timer(timer, p);

  	}

  	unlock_task_sighand(p, &flags);

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

  	timer->it_interval = timespec64_to_ktime(new->it_interval);

  
  	/*
  	 * 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:

  	rcu_read_unlock();

  	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)

  {

  	clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);

  	struct cpu_timer *ctmr = &timer->it.cpu;
  	u64 now, expires = cpu_timer_getexpires(ctmr);

  	struct task_struct *p;

  	rcu_read_lock();
  	p = cpu_timer_task_rcu(timer);
  	if (!p)
  		goto out;

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

  	itp->it_interval = ktime_to_timespec64(timer->it_interval);

  	if (!expires)

  		goto out;

  	/*
  	 * Sample the clock to take the difference with the expiry time.
  	 */

  	if (CPUCLOCK_PERTHREAD(timer->it_clock))

  		now = cpu_clock_sample(clkid, p);

  	else
  		now = cpu_clock_sample_group(clkid, p, false);

  	if (now < expires) {
  		itp->it_value = ns_to_timespec64(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;
  	}

  out:
  	rcu_read_unlock();

  }

  #define MAX_COLLECTED	20

  static u64 collect_timerqueue(struct timerqueue_head *head,
  			      struct list_head *firing, u64 now)
  {
  	struct timerqueue_node *next;
  	int i = 0;
  
  	while ((next = timerqueue_getnext(head))) {
  		struct cpu_timer *ctmr;
  		u64 expires;
  
  		ctmr = container_of(next, struct cpu_timer, node);
  		expires = cpu_timer_getexpires(ctmr);
  		/* Limit the number of timers to expire at once */
  		if (++i == MAX_COLLECTED || now < expires)
  			return expires;
  
  		ctmr->firing = 1;
  		cpu_timer_dequeue(ctmr);
  		list_add_tail(&ctmr->elist, firing);

  	}

  	return U64_MAX;

  }

  static void collect_posix_cputimers(struct posix_cputimers *pct, u64 *samples,
  				    struct list_head *firing)

  {
  	struct posix_cputimer_base *base = pct->bases;
  	int i;
  
  	for (i = 0; i < CPUCLOCK_MAX; i++, base++) {

  		base->nextevt = collect_timerqueue(&base->tqhead, firing,
  						    samples[i]);

  	}
  }

  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);
  	}
  }

  static bool check_rlimit(u64 time, u64 limit, int signo, bool rt, bool hard)
  {
  	if (time < limit)
  		return false;
  
  	if (print_fatal_signals) {
  		pr_info("%s Watchdog Timeout (%s): %s[%d]
  ",
  			rt ? "RT" : "CPU", hard ? "hard" : "soft",
  			current->comm, task_pid_nr(current));
  	}
  	__group_send_sig_info(signo, SEND_SIG_PRIV, current);
  	return true;
  }

  /*
   * 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 posix_cputimers *pct = &tsk->posix_cputimers;
  	u64 samples[CPUCLOCK_MAX];

  	unsigned long soft;

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

  	if (expiry_cache_is_inactive(pct))

  		return;

  	task_sample_cputime(tsk, samples);
  	collect_posix_cputimers(pct, samples, firing);

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

  	soft = task_rlimit(tsk, RLIMIT_RTTIME);

  	if (soft != RLIM_INFINITY) {

  		/* Task RT timeout is accounted in jiffies. RTTIME is usec */

  		unsigned long rttime = tsk->rt.timeout * (USEC_PER_SEC / HZ);

  		unsigned long hard = task_rlimit_max(tsk, RLIMIT_RTTIME);

  		/* At the hard limit, send SIGKILL. No further action. */
  		if (hard != RLIM_INFINITY &&
  		    check_rlimit(rttime, hard, SIGKILL, true, true))

  			return;

  		/* At the soft limit, send a SIGXCPU every second */
  		if (check_rlimit(rttime, soft, SIGXCPU, true, false)) {

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

  		}
  	}

  	if (expiry_cache_is_inactive(pct))

  		tick_dep_clear_task(tsk, TICK_DEP_BIT_POSIX_TIMER);

  }

  static inline void stop_process_timers(struct signal_struct *sig)

  {

  	struct posix_cputimers *pct = &sig->posix_cputimers;

  	/* Turn off the active flag. This is done without locking. */
  	WRITE_ONCE(pct->timers_active, 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 && 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;

  	struct posix_cputimers *pct = &sig->posix_cputimers;
  	u64 samples[CPUCLOCK_MAX];

  	unsigned long soft;

  
  	/*

  	 * If there are no active process wide timers (POSIX 1.b, itimers,

  	 * RLIMIT_CPU) nothing to check. Also skip the process wide timer
  	 * processing when there is already another task handling them.

  	 */

  	if (!READ_ONCE(pct->timers_active) || pct->expiry_active)

  		return;

  	/*

  	 * Signify that a thread is checking for process timers.
  	 * Write access to this field is protected by the sighand lock.
  	 */

  	pct->expiry_active = true;

  	/*

  	 * Collect the current process totals. Group accounting is active
  	 * so the sample can be taken directly.

  	 */

  	proc_sample_cputime_atomic(&sig->cputimer.cputime_atomic, samples);

  	collect_posix_cputimers(pct, samples, firing);

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

  	check_cpu_itimer(tsk, &sig->it[CPUCLOCK_PROF],
  			 &pct->bases[CPUCLOCK_PROF].nextevt,

  			 samples[CPUCLOCK_PROF], SIGPROF);

  	check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT],
  			 &pct->bases[CPUCLOCK_VIRT].nextevt,
  			 samples[CPUCLOCK_VIRT], SIGVTALRM);

  	soft = task_rlimit(tsk, RLIMIT_CPU);

  	if (soft != RLIM_INFINITY) {

  		/* RLIMIT_CPU is in seconds. Samples are nanoseconds */

  		unsigned long hard = task_rlimit_max(tsk, RLIMIT_CPU);

  		u64 ptime = samples[CPUCLOCK_PROF];
  		u64 softns = (u64)soft * NSEC_PER_SEC;
  		u64 hardns = (u64)hard * NSEC_PER_SEC;

  		/* At the hard limit, send SIGKILL. No further action. */
  		if (hard != RLIM_INFINITY &&
  		    check_rlimit(ptime, hardns, SIGKILL, false, true))

  			return;

  		/* At the soft limit, send a SIGXCPU every second */
  		if (check_rlimit(ptime, softns, SIGXCPU, false, false)) {

  			sig->rlim[RLIMIT_CPU].rlim_cur = soft + 1;
  			softns += NSEC_PER_SEC;

  		}

  
  		/* Update the expiry cache */

  		if (softns < pct->bases[CPUCLOCK_PROF].nextevt)
  			pct->bases[CPUCLOCK_PROF].nextevt = softns;

  	}

  	if (expiry_cache_is_inactive(pct))

  		stop_process_timers(sig);

  	pct->expiry_active = 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)

  {

  	clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);

  	struct task_struct *p;

  	struct sighand_struct *sighand;
  	unsigned long flags;

  	u64 now;

  	rcu_read_lock();
  	p = cpu_timer_task_rcu(timer);
  	if (!p)
  		goto out;

  
  	/*
  	 * Fetch the current sample and update the timer's expiry time.
  	 */

  	if (CPUCLOCK_PERTHREAD(timer->it_clock))

  		now = cpu_clock_sample(clkid, p);

  	else

  		now = cpu_clock_sample_group(clkid, p, true);

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

  		goto out;

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

  	arm_timer(timer, p);

  	unlock_task_sighand(p, &flags);

  out:
  	rcu_read_unlock();

  }

  /**

   * task_cputimers_expired - Check whether posix CPU timers are expired

   *

   * @samples:	Array of current samples for the CPUCLOCK clocks

   * @pct:	Pointer to a posix_cputimers container

   *

   * Returns true if any member of @samples is greater than the corresponding
   * member of @pct->bases[CLK].nextevt. False otherwise

   */

  static inline bool

  task_cputimers_expired(const u64 *samples, struct posix_cputimers *pct)

  {

  	int i;
  
  	for (i = 0; i < CPUCLOCK_MAX; i++) {

  		if (samples[i] >= pct->bases[i].nextevt)

  			return true;
  	}
  	return false;

  }
  
  /**
   * 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 bool fastpath_timer_check(struct task_struct *tsk)

  {

  	struct posix_cputimers *pct = &tsk->posix_cputimers;

  	struct signal_struct *sig;

  	if (!expiry_cache_is_inactive(pct)) {

  		u64 samples[CPUCLOCK_MAX];

  		task_sample_cputime(tsk, samples);

  		if (task_cputimers_expired(samples, pct))

  			return true;

  	}

  
  	sig = tsk->signal;

  	pct = &sig->posix_cputimers;

  	/*

  	 * Check if thread group timers expired when timers are active and
  	 * no other thread in the group is already handling expiry 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 handle timer expiry.

  	 *

  	 * In the worst case scenario, if concurrently timers_active is set
  	 * or expiry_active is cleared, but the current thread doesn't see
  	 * the change yet, the timer checks are delayed 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(pct->timers_active) && !READ_ONCE(pct->expiry_active)) {

  		u64 samples[CPUCLOCK_MAX];

  		proc_sample_cputime_atomic(&sig->cputimer.cputime_atomic,
  					   samples);

  		if (task_cputimers_expired(samples, pct))

  			return true;

  	}

  	if (dl_task(tsk) && tsk->dl.dl_overrun)

  		return true;

  	return false;

  }

  static void handle_posix_cpu_timers(struct task_struct *tsk);
  
  #ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK
  static void posix_cpu_timers_work(struct callback_head *work)
  {
  	handle_posix_cpu_timers(current);
  }
  
  /*
   * Initialize posix CPU timers task work in init task. Out of line to
   * keep the callback static and to avoid header recursion hell.
   */
  void __init posix_cputimers_init_work(void)
  {
  	init_task_work(&current->posix_cputimers_work.work,
  		       posix_cpu_timers_work);
  }
  
  /*
   * Note: All operations on tsk->posix_cputimer_work.scheduled happen either
   * in hard interrupt context or in task context with interrupts
   * disabled. Aside of that the writer/reader interaction is always in the
   * context of the current task, which means they are strict per CPU.
   */
  static inline bool posix_cpu_timers_work_scheduled(struct task_struct *tsk)
  {
  	return tsk->posix_cputimers_work.scheduled;
  }
  
  static inline void __run_posix_cpu_timers(struct task_struct *tsk)
  {
  	if (WARN_ON_ONCE(tsk->posix_cputimers_work.scheduled))
  		return;
  
  	/* Schedule task work to actually expire the timers */
  	tsk->posix_cputimers_work.scheduled = true;
  	task_work_add(tsk, &tsk->posix_cputimers_work.work, TWA_RESUME);
  }
  
  static inline bool posix_cpu_timers_enable_work(struct task_struct *tsk,
  						unsigned long start)
  {
  	bool ret = true;
  
  	/*
  	 * On !RT kernels interrupts are disabled while collecting expired
  	 * timers, so no tick can happen and the fast path check can be
  	 * reenabled without further checks.
  	 */
  	if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
  		tsk->posix_cputimers_work.scheduled = false;
  		return true;
  	}
  
  	/*
  	 * On RT enabled kernels ticks can happen while the expired timers
  	 * are collected under sighand lock. But any tick which observes
  	 * the CPUTIMERS_WORK_SCHEDULED bit set, does not run the fastpath
  	 * checks. So reenabling the tick work has do be done carefully:
  	 *
  	 * Disable interrupts and run the fast path check if jiffies have
  	 * advanced since the collecting of expired timers started. If
  	 * jiffies have not advanced or the fast path check did not find
  	 * newly expired timers, reenable the fast path check in the timer
  	 * interrupt. If there are newly expired timers, return false and
  	 * let the collection loop repeat.
  	 */
  	local_irq_disable();
  	if (start != jiffies && fastpath_timer_check(tsk))
  		ret = false;
  	else
  		tsk->posix_cputimers_work.scheduled = false;
  	local_irq_enable();
  
  	return ret;
  }
  #else /* CONFIG_POSIX_CPU_TIMERS_TASK_WORK */
  static inline void __run_posix_cpu_timers(struct task_struct *tsk)
  {
  	lockdep_posixtimer_enter();
  	handle_posix_cpu_timers(tsk);
  	lockdep_posixtimer_exit();
  }
  
  static inline bool posix_cpu_timers_work_scheduled(struct task_struct *tsk)
  {
  	return false;
  }
  
  static inline bool posix_cpu_timers_enable_work(struct task_struct *tsk,
  						unsigned long start)
  {
  	return true;
  }
  #endif /* CONFIG_POSIX_CPU_TIMERS_TASK_WORK */
  
  static void handle_posix_cpu_timers(struct task_struct *tsk)

  {

  	struct k_itimer *timer, *next;

  	unsigned long flags, start;

  	LIST_HEAD(firing);

  	if (!lock_task_sighand(tsk, &flags))

  		return;

  	do {
  		/*
  		 * On RT locking sighand lock does not disable interrupts,
  		 * so this needs to be careful vs. ticks. Store the current
  		 * jiffies value.
  		 */
  		start = READ_ONCE(jiffies);
  		barrier();

  		/*
  		 * 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);
  
  		/*
  		 * The above timer checks have updated the exipry cache and
  		 * because nothing can have queued or modified timers after
  		 * sighand lock was taken above it is guaranteed to be
  		 * consistent. So the next timer interrupt fastpath check
  		 * will find valid data.
  		 *
  		 * If timer expiry runs in the timer interrupt context then
  		 * the loop is not relevant as timers will be directly
  		 * expired in interrupt context. The stub function below
  		 * returns always true which allows the compiler to
  		 * optimize the loop out.
  		 *
  		 * If timer expiry is deferred to task work context then
  		 * the following rules apply:
  		 *
  		 * - On !RT kernels no tick can have happened on this CPU
  		 *   after sighand lock was acquired because interrupts are
  		 *   disabled. So reenabling task work before dropping
  		 *   sighand lock and reenabling interrupts is race free.
  		 *
  		 * - On RT kernels ticks might have happened but the tick
  		 *   work ignored posix CPU timer handling because the
  		 *   CPUTIMERS_WORK_SCHEDULED bit is set. Reenabling work
  		 *   must be done very carefully including a check whether
  		 *   ticks have happened since the start of the timer
  		 *   expiry checks. posix_cpu_timers_enable_work() takes
  		 *   care of that and eventually lets the expiry checks
  		 *   run again.
  		 */
  	} while (!posix_cpu_timers_enable_work(tsk, start));

  	/*

  	 * We must release sighand lock 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.elist) {

  		int cpu_firing;

  		/*
  		 * spin_lock() is sufficient here even independent of the
  		 * expiry context. If expiry happens in hard interrupt
  		 * context it's obvious. For task work context it's safe
  		 * because all other operations on timer::it_lock happen in
  		 * task context (syscall or exit).
  		 */

  		spin_lock(&timer->it_lock);

  		list_del_init(&timer->it.cpu.elist);

  		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);
  	}

  }
  
  /*
   * 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(void)
  {
  	struct task_struct *tsk = current;
  
  	lockdep_assert_irqs_disabled();
  
  	/*

  	 * If the actual expiry is deferred to task work context and the
  	 * work is already scheduled there is no point to do anything here.
  	 */
  	if (posix_cpu_timers_work_scheduled(tsk))
  		return;
  
  	/*

  	 * 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;

  	__run_posix_cpu_timers(tsk);

  }
  
  /*

   * 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 clkid,

  			   u64 *newval, u64 *oldval)

  {

  	u64 now, *nextevt;

  	if (WARN_ON_ONCE(clkid >= CPUCLOCK_SCHED))

  		return;

  	nextevt = &tsk->signal->posix_cputimers.bases[clkid].nextevt;

  	now = cpu_clock_sample_group(clkid, tsk, true);

  	if (oldval) {

  		/*
  		 * 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 this is the earliest timer. CPUCLOCK_PROF
  	 * expiry cache is also used by RLIMIT_CPU!.

  	 */

  	if (*newval < *nextevt)

  		*nextevt = *newval;

  
  	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 (!cpu_timer_getexpires(&timer.it.cpu)) {

  				/*

  				 * 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 = cpu_timer_getexpires(&timer.it.cpu);

  		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) {