FreeBSD/Linux Kernel Cross Reference
sys/kernel/posix-cpu-timers.c

     /*
      * Implement CPU time clocks for the POSIX clock interface.
      */
     
     #include <linux/sched.h>
     #include <linux/posix-timers.h>
     #include <linux/errno.h>
     #include <linux/math64.h>
     #include <asm/uaccess.h>
    #include <linux/kernel_stat.h>
    #include <trace/events/timer.h>
    #include <linux/random.h>
    
    /*
     * 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)
    {
            cputime_t cputime = secs_to_cputime(rlim_new);
    
            spin_lock_irq(&task->sighand->siglock);
            set_process_cpu_timer(task, CPUCLOCK_PROF, &cputime, 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;
    }
    
    static inline union cpu_time_count
    timespec_to_sample(const clockid_t which_clock, const struct timespec *tp)
    {
            union cpu_time_count ret;
            ret.sched = 0;          /* high half always zero when .cpu used */
            if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
                    ret.sched = (unsigned long long)tp->tv_sec * NSEC_PER_SEC + tp->tv_nsec;
            } else {
                    ret.cpu = timespec_to_cputime(tp);
            }
            return ret;
    }
    
    static void sample_to_timespec(const clockid_t which_clock,
                                   union cpu_time_count cpu,
                                   struct timespec *tp)
    {
            if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED)
                    *tp = ns_to_timespec(cpu.sched);
            else
                    cputime_to_timespec(cpu.cpu, tp);
    }
    
    static inline int cpu_time_before(const clockid_t which_clock,
                                      union cpu_time_count now,
                                      union cpu_time_count then)
    {
            if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
                    return now.sched < then.sched;
            }  else {
                    return now.cpu < then.cpu;
            }
    }
    static inline void cpu_time_add(const clockid_t which_clock,
                                    union cpu_time_count *acc,
                                    union cpu_time_count val)
    {
            if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
                    acc->sched += val.sched;
            }  else {
                    acc->cpu += val.cpu;
            }
    }
    static inline union cpu_time_count cpu_time_sub(const clockid_t which_clock,
                                                    union cpu_time_count a,
                                                    union cpu_time_count b)
    {
            if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
                   a.sched -= b.sched;
           }  else {
                   a.cpu -= b.cpu;
           }
           return a;
   }
   
   /*
    * Update expiry time from increment, and increase overrun count,
    * given the current clock sample.
    */
   static void bump_cpu_timer(struct k_itimer *timer,
                                     union cpu_time_count now)
   {
           int i;
   
           if (timer->it.cpu.incr.sched == 0)
                   return;
   
           if (CPUCLOCK_WHICH(timer->it_clock) == CPUCLOCK_SCHED) {
                   unsigned long long delta, incr;
   
                   if (now.sched < timer->it.cpu.expires.sched)
                           return;
                   incr = timer->it.cpu.incr.sched;
                   delta = now.sched + incr - timer->it.cpu.expires.sched;
                   /* 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.sched += incr;
                           timer->it_overrun += 1 << i;
                           delta -= incr;
                   }
           } else {
                   cputime_t delta, incr;
   
                   if (now.cpu < timer->it.cpu.expires.cpu)
                           return;
                   incr = timer->it.cpu.incr.cpu;
                   delta = now.cpu + incr - timer->it.cpu.expires.cpu;
                   /* Don't use (incr*2 < delta), incr*2 might overflow. */
                   for (i = 0; incr < delta - incr; i++)
                                incr += incr;
                   for (; i >= 0; incr = incr >> 1, i--) {
                           if (delta < incr)
                                   continue;
                           timer->it.cpu.expires.cpu += incr;
                           timer->it_overrun += 1 << i;
                           delta -= incr;
                   }
           }
   }
   
   static inline cputime_t prof_ticks(struct task_struct *p)
   {
           return p->utime + p->stime;
   }
   static inline cputime_t virt_ticks(struct task_struct *p)
   {
           return p->utime;
   }
   
   static int
   posix_cpu_clock_getres(const clockid_t which_clock, struct timespec *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 timespec *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,
                               union cpu_time_count *cpu)
   {
           switch (CPUCLOCK_WHICH(which_clock)) {
           default:
                   return -EINVAL;
           case CPUCLOCK_PROF:
                   cpu->cpu = prof_ticks(p);
                   break;
           case CPUCLOCK_VIRT:
                   cpu->cpu = virt_ticks(p);
                   break;
           case CPUCLOCK_SCHED:
                   cpu->sched = task_sched_runtime(p);
                   break;
           }
           return 0;
   }
   
   static void update_gt_cputime(struct task_cputime *a, struct task_cputime *b)
   {
           if (b->utime > a->utime)
                   a->utime = b->utime;
   
           if (b->stime > a->stime)
                   a->stime = b->stime;
   
           if (b->sum_exec_runtime > a->sum_exec_runtime)
                   a->sum_exec_runtime = b->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;
           unsigned long flags;
   
           if (!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);
                   raw_spin_lock_irqsave(&cputimer->lock, flags);
                   cputimer->running = 1;
                   update_gt_cputime(&cputimer->cputime, &sum);
           } else
                   raw_spin_lock_irqsave(&cputimer->lock, flags);
           *times = cputimer->cputime;
           raw_spin_unlock_irqrestore(&cputimer->lock, flags);
   }
   
   /*
    * Sample a process (thread group) clock for the given group_leader task.
    * Must be called with tasklist_lock held for reading.
    */
   static int cpu_clock_sample_group(const clockid_t which_clock,
                                     struct task_struct *p,
                                     union cpu_time_count *cpu)
   {
           struct task_cputime cputime;
   
           switch (CPUCLOCK_WHICH(which_clock)) {
           default:
                   return -EINVAL;
           case CPUCLOCK_PROF:
                   thread_group_cputime(p, &cputime);
                   cpu->cpu = cputime.utime + cputime.stime;
                   break;
           case CPUCLOCK_VIRT:
                   thread_group_cputime(p, &cputime);
                   cpu->cpu = cputime.utime;
                   break;
           case CPUCLOCK_SCHED:
                   thread_group_cputime(p, &cputime);
                   cpu->sched = cputime.sum_exec_runtime;
                   break;
           }
           return 0;
   }
   
   
   static int posix_cpu_clock_get(const clockid_t which_clock, struct timespec *tp)
   {
           const pid_t pid = CPUCLOCK_PID(which_clock);
           int error = -EINVAL;
           union cpu_time_count rtn;
   
           if (pid == 0) {
                   /*
                    * Special case constant value for our own clocks.
                    * We don't have to do any lookup to find ourselves.
                    */
                   if (CPUCLOCK_PERTHREAD(which_clock)) {
                           /*
                            * Sampling just ourselves we can do with no locking.
                            */
                           error = cpu_clock_sample(which_clock,
                                                    current, &rtn);
                   } else {
                           read_lock(&tasklist_lock);
                           error = cpu_clock_sample_group(which_clock,
                                                          current, &rtn);
                           read_unlock(&tasklist_lock);
                   }
           } 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) {
                           if (CPUCLOCK_PERTHREAD(which_clock)) {
                                   if (same_thread_group(p, current)) {
                                           error = cpu_clock_sample(which_clock,
                                                                    p, &rtn);
                                   }
                           } else {
                                   read_lock(&tasklist_lock);
                                   if (thread_group_leader(p) && p->sighand) {
                                           error =
                                               cpu_clock_sample_group(which_clock,
                                                                      p, &rtn);
                                   }
                                   read_unlock(&tasklist_lock);
                           }
                   }
                   rcu_read_unlock();
           }
   
           if (error)
                   return error;
           sample_to_timespec(which_clock, rtn, tp);
           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)
   {
           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;
   
           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)
   {
           struct task_struct *p = timer->it.cpu.task;
           int ret = 0;
   
           if (likely(p != NULL)) {
                   read_lock(&tasklist_lock);
                   if (unlikely(p->sighand == NULL)) {
                           /*
                            * We raced with the reaping of the task.
                            * The deletion should have cleared us off the list.
                            */
                           BUG_ON(!list_empty(&timer->it.cpu.entry));
                   } else {
                           spin_lock(&p->sighand->siglock);
                           if (timer->it.cpu.firing)
                                   ret = TIMER_RETRY;
                           else
                                   list_del(&timer->it.cpu.entry);
                           spin_unlock(&p->sighand->siglock);
                   }
                   read_unlock(&tasklist_lock);
   
                   if (!ret)
                           put_task_struct(p);
           }
   
           return ret;
   }
   
   /*
    * 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,
                              cputime_t utime, cputime_t stime,
                              unsigned long long sum_exec_runtime)
   {
           struct cpu_timer_list *timer, *next;
           cputime_t ptime = utime + stime;
   
           list_for_each_entry_safe(timer, next, head, entry) {
                   list_del_init(&timer->entry);
                   if (timer->expires.cpu < ptime) {
                           timer->expires.cpu = 0;
                   } else {
                           timer->expires.cpu -= ptime;
                   }
           }
   
           ++head;
           list_for_each_entry_safe(timer, next, head, entry) {
                   list_del_init(&timer->entry);
                   if (timer->expires.cpu < utime) {
                           timer->expires.cpu = 0;
                   } else {
                           timer->expires.cpu -= utime;
                   }
           }
   
           ++head;
           list_for_each_entry_safe(timer, next, head, entry) {
                   list_del_init(&timer->entry);
                   if (timer->expires.sched < sum_exec_runtime) {
                           timer->expires.sched = 0;
                   } else {
                           timer->expires.sched -= sum_exec_runtime;
                   }
           }
   }
   
   /*
    * 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)
   {
           add_device_randomness((const void*) &tsk->se.sum_exec_runtime,
                                                   sizeof(unsigned long long));
           cleanup_timers(tsk->cpu_timers,
                          tsk->utime, tsk->stime, tsk->se.sum_exec_runtime);
   
   }
   void posix_cpu_timers_exit_group(struct task_struct *tsk)
   {
           struct signal_struct *const sig = tsk->signal;
   
           cleanup_timers(tsk->signal->cpu_timers,
                          tsk->utime + sig->utime, tsk->stime + sig->stime,
                          tsk->se.sum_exec_runtime + sig->sum_sched_runtime);
   }
   
   static void clear_dead_task(struct k_itimer *timer, union cpu_time_count now)
   {
           /*
            * That's all for this thread or process.
            * We leave our residual in expires to be reported.
            */
           put_task_struct(timer->it.cpu.task);
           timer->it.cpu.task = NULL;
           timer->it.cpu.expires = cpu_time_sub(timer->it_clock,
                                                timer->it.cpu.expires,
                                                now);
   }
   
   static inline int expires_gt(cputime_t expires, cputime_t 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 tasklist_lock held
    * for reading, interrupts disabled and p->sighand->siglock taken.
    */
   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 (cpu_time_before(timer->it_clock, nt->expires, next->expires))
                           break;
                   listpos = &next->entry;
           }
           list_add(&nt->entry, listpos);
   
           if (listpos == head) {
                   union cpu_time_count *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->cpu))
                                   cputime_expires->prof_exp = exp->cpu;
                           break;
                   case CPUCLOCK_VIRT:
                           if (expires_gt(cputime_expires->virt_exp, exp->cpu))
                                   cputime_expires->virt_exp = exp->cpu;
                           break;
                   case CPUCLOCK_SCHED:
                           if (cputime_expires->sched_exp == 0 ||
                               cputime_expires->sched_exp > exp->sched)
                                   cputime_expires->sched_exp = exp->sched;
                           break;
                   }
           }
   }
   
   /*
    * 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.sched = 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.sched = 0;
           } else if (timer->it.cpu.incr.sched == 0) {
                   /*
                    * One-shot timer.  Clear it as soon as it's fired.
                    */
                   posix_timer_event(timer, 0);
                   timer->it.cpu.expires.sched = 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_schedule(timer);
           }
   }
   
   /*
    * Sample a process (thread group) timer for the given group_leader task.
    * Must be called with tasklist_lock held for reading.
    */
   static int cpu_timer_sample_group(const clockid_t which_clock,
                                     struct task_struct *p,
                                     union cpu_time_count *cpu)
   {
           struct task_cputime cputime;
   
           thread_group_cputimer(p, &cputime);
           switch (CPUCLOCK_WHICH(which_clock)) {
           default:
                   return -EINVAL;
           case CPUCLOCK_PROF:
                   cpu->cpu = cputime.utime + cputime.stime;
                   break;
           case CPUCLOCK_VIRT:
                   cpu->cpu = cputime.utime;
                   break;
           case CPUCLOCK_SCHED:
                   cpu->sched = cputime.sum_exec_runtime + task_delta_exec(p);
                   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 flags,
                                  struct itimerspec *new, struct itimerspec *old)
   {
           struct task_struct *p = timer->it.cpu.task;
           union cpu_time_count old_expires, new_expires, old_incr, val;
           int ret;
   
           if (unlikely(p == NULL)) {
                   /*
                    * Timer refers to a dead task's clock.
                    */
                   return -ESRCH;
           }
   
           new_expires = timespec_to_sample(timer->it_clock, &new->it_value);
   
           read_lock(&tasklist_lock);
           /*
            * We need the tasklist_lock to protect against reaping that
            * clears p->sighand.  If p has just been reaped, we can no
            * longer get any information about it at all.
            */
           if (unlikely(p->sighand == NULL)) {
                   read_unlock(&tasklist_lock);
                   put_task_struct(p);
                   timer->it.cpu.task = NULL;
                   return -ESRCH;
           }
   
           /*
            * Disarm any old timer after extracting its expiry time.
            */
           BUG_ON(!irqs_disabled());
   
           ret = 0;
           old_incr = timer->it.cpu.incr;
           spin_lock(&p->sighand->siglock);
           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.sched == 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 (cpu_time_before(timer->it_clock, val,
                                               timer->it.cpu.expires)) {
                                   old_expires = cpu_time_sub(
                                           timer->it_clock,
                                           timer->it.cpu.expires, val);
                                   sample_to_timespec(timer->it_clock,
                                                      old_expires,
                                                      &old->it_value);
                           } 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).
                    */
                   spin_unlock(&p->sighand->siglock);
                   read_unlock(&tasklist_lock);
                   goto out;
           }
   
           if (new_expires.sched != 0 && !(flags & TIMER_ABSTIME)) {
                   cpu_time_add(timer->it_clock, &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.sched != 0 &&
               cpu_time_before(timer->it_clock, val, new_expires)) {
                   arm_timer(timer);
           }
   
           spin_unlock(&p->sighand->siglock);
           read_unlock(&tasklist_lock);
   
           /*
            * Install the new reload setting, and
            * set up the signal and overrun bookkeeping.
            */
           timer->it.cpu.incr = timespec_to_sample(timer->it_clock,
                                                   &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.sched != 0 &&
               !cpu_time_before(timer->it_clock, 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) {
                   sample_to_timespec(timer->it_clock,
                                      old_incr, &old->it_interval);
           }
           return ret;
   }
   
   static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec *itp)
   {
           union cpu_time_count now;
           struct task_struct *p = timer->it.cpu.task;
           int clear_dead;
   
           /*
            * Easy part: convert the reload time.
            */
           sample_to_timespec(timer->it_clock,
                              timer->it.cpu.incr, &itp->it_interval);
   
           if (timer->it.cpu.expires.sched == 0) { /* Timer not armed at all.  */
                   itp->it_value.tv_sec = itp->it_value.tv_nsec = 0;
                   return;
           }
   
           if (unlikely(p == NULL)) {
                   /*
                    * This task already died and the timer will never fire.
                    * In this case, expires is actually the dead value.
                    */
           dead:
                   sample_to_timespec(timer->it_clock, timer->it.cpu.expires,
                                      &itp->it_value);
                   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);
                   clear_dead = p->exit_state;
           } else {
                   read_lock(&tasklist_lock);
                   if (unlikely(p->sighand == NULL)) {
                           /*
                            * The process has been reaped.
                            * We can't even collect a sample any more.
                            * Call the timer disarmed, nothing else to do.
                            */
                           put_task_struct(p);
                           timer->it.cpu.task = NULL;
                           timer->it.cpu.expires.sched = 0;
                           read_unlock(&tasklist_lock);
                           goto dead;
                   } else {
                           cpu_timer_sample_group(timer->it_clock, p, &now);
                           clear_dead = (unlikely(p->exit_state) &&
                                         thread_group_empty(p));
                   }
                   read_unlock(&tasklist_lock);
           }
   
           if (unlikely(clear_dead)) {
                   /*
                    * We've noticed that the thread is dead, but
                    * not yet reaped.  Take this opportunity to
                    * drop our task ref.
                    */
                   clear_dead_task(timer, now);
                   goto dead;
           }
   
           if (cpu_time_before(timer->it_clock, now, timer->it.cpu.expires)) {
                   sample_to_timespec(timer->it_clock,
                                      cpu_time_sub(timer->it_clock,
                                                   timer->it.cpu.expires, now),
                                      &itp->it_value);
           } 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;
           }
   }
   
   /*
    * 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)
   {
           int maxfire;
           struct list_head *timers = tsk->cpu_timers;
           struct signal_struct *const sig = tsk->signal;
           unsigned long soft;
   
           maxfire = 20;
           tsk->cputime_expires.prof_exp = 0;
           while (!list_empty(timers)) {
                   struct cpu_timer_list *t = list_first_entry(timers,
                                                         struct cpu_timer_list,
                                                         entry);
                   if (!--maxfire || prof_ticks(tsk) < t->expires.cpu) {
                           tsk->cputime_expires.prof_exp = t->expires.cpu;
                           break;
                   }
                   t->firing = 1;
                   list_move_tail(&t->entry, firing);
           }
   
           ++timers;
           maxfire = 20;
           tsk->cputime_expires.virt_exp = 0;
           while (!list_empty(timers)) {
                   struct cpu_timer_list *t = list_first_entry(timers,
                                                         struct cpu_timer_list,
                                                         entry);
                   if (!--maxfire || virt_ticks(tsk) < t->expires.cpu) {
                           tsk->cputime_expires.virt_exp = t->expires.cpu;
                           break;
                   }
                   t->firing = 1;
                   list_move_tail(&t->entry, firing);
           }
   
           ++timers;
           maxfire = 20;
           tsk->cputime_expires.sched_exp = 0;
           while (!list_empty(timers)) {
                   struct cpu_timer_list *t = list_first_entry(timers,
                                                         struct cpu_timer_list,
                                                         entry);
                   if (!--maxfire || tsk->se.sum_exec_runtime < t->expires.sched) {
                           tsk->cputime_expires.sched_exp = t->expires.sched;
                           break;
                   }
                   t->firing = 1;
                   list_move_tail(&t->entry, firing);
           }
   
           /*
            * Check for the special case thread timers.
            */
           soft = ACCESS_ONCE(sig->rlim[RLIMIT_RTTIME].rlim_cur);
           if (soft != RLIM_INFINITY) {
                   unsigned long hard =
                           ACCESS_ONCE(sig->rlim[RLIMIT_RTTIME].rlim_max);
   
                   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.
                            */
                           __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;
                                   sig->rlim[RLIMIT_RTTIME].rlim_cur = soft;
                           }
                           printk(KERN_INFO
                                   "RT Watchdog Timeout: %s[%d]\n",
                                   tsk->comm, task_pid_nr(tsk));
                           __group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
                   }
           }
   }
   
   static void stop_process_timers(struct signal_struct *sig)
   {
           struct thread_group_cputimer *cputimer = &sig->cputimer;
           unsigned long flags;
   
           raw_spin_lock_irqsave(&cputimer->lock, flags);
           cputimer->running = 0;
           raw_spin_unlock_irqrestore(&cputimer->lock, flags);
   }
   
   static u32 onecputick;
   
   static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
                                cputime_t *expires, cputime_t cur_time, int signo)
   {
           if (!it->expires)
                   return;
   
           if (cur_time >= it->expires) {
                   if (it->incr) {
                           it->expires += it->incr;
                           it->error += it->incr_error;
                           if (it->error >= onecputick) {
                                   it->expires -= cputime_one_jiffy;
                                   it->error -= onecputick;
                           }
                   } else {
                           it->expires = 0;
                   }
   
                   trace_itimer_expire(signo == SIGPROF ?
                                       ITIMER_PROF : ITIMER_VIRTUAL,
                                       tsk->signal->leader_pid, cur_time);
                   __group_send_sig_info(signo, SEND_SIG_PRIV, tsk);
           }
   
           if (it->expires && (!*expires || it->expires < *expires)) {
                   *expires = it->expires;
           }
   }
   
   /**
    * 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;
  }
  
  /*
   * 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)
  {
          int maxfire;
          struct signal_struct *const sig = tsk->signal;
          cputime_t utime, ptime, virt_expires, prof_expires;
          unsigned long long sum_sched_runtime, sched_expires;
          struct list_head *timers = sig->cpu_timers;
          struct task_cputime cputime;
          unsigned long soft;
  
          /*
           * Collect the current process totals.
           */
          thread_group_cputimer(tsk, &cputime);
          utime = cputime.utime;
          ptime = utime + cputime.stime;
          sum_sched_runtime = cputime.sum_exec_runtime;
          maxfire = 20;
          prof_expires = 0;
          while (!list_empty(timers)) {
                  struct cpu_timer_list *tl = list_first_entry(timers,
                                                        struct cpu_timer_list,
                                                        entry);
                  if (!--maxfire || ptime < tl->expires.cpu) {
                          prof_expires = tl->expires.cpu;
                          break;
                  }
                  tl->firing = 1;
                  list_move_tail(&tl->entry, firing);
          }
  
          ++timers;
          maxfire = 20;
          virt_expires = 0;
          while (!list_empty(timers)) {
                  struct cpu_timer_list *tl = list_first_entry(timers,
                                                        struct cpu_timer_list,
                                                        entry);
                  if (!--maxfire || utime < tl->expires.cpu) {
                          virt_expires = tl->expires.cpu;
                          break;
                  }
                  tl->firing = 1;
                  list_move_tail(&tl->entry, firing);
          }
  
          ++timers;
          maxfire = 20;
          sched_expires = 0;
          while (!list_empty(timers)) {
                  struct cpu_timer_list *tl = list_first_entry(timers,
                                                        struct cpu_timer_list,
                                                        entry);
                  if (!--maxfire || sum_sched_runtime < tl->expires.sched) {
                          sched_expires = tl->expires.sched;
                          break;
                  }
                  tl->firing = 1;
                  list_move_tail(&tl->entry, firing);
          }
  
          /*
           * 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 = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
          if (soft != RLIM_INFINITY) {
                  unsigned long psecs = cputime_to_secs(ptime);
                  unsigned long hard =
                          ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_max);
                  cputime_t x;
                  if (psecs >= hard) {
                          /*
                           * At the hard limit, we just die.
                           * No need to calculate anything else now.
                           */
                          __group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
                          return;
                  }
                  if (psecs >= soft) {
                          /*
                           * At the soft limit, send a SIGXCPU every second.
                           */
                          __group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
                          if (soft < hard) {
                                  soft++;
                                  sig->rlim[RLIMIT_CPU].rlim_cur = soft;
                          }
                  }
                  x = secs_to_cputime(soft);
                  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);
  }
  
  /*
   * This is called from the signal code (via do_schedule_next_timer)
   * when the last timer signal was delivered and we have to reload the timer.
   */
  void posix_cpu_timer_schedule(struct k_itimer *timer)
  {
          struct task_struct *p = timer->it.cpu.task;
          union cpu_time_count now;
  
          if (unlikely(p == NULL))
                  /*
                   * The task was cleaned up already, no future firings.
                   */
                  goto out;
  
          /*
           * 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)) {
                          clear_dead_task(timer, now);
                          goto out;
                  }
                  read_lock(&tasklist_lock); /* arm_timer needs it.  */
                  spin_lock(&p->sighand->siglock);
          } else {
                  read_lock(&tasklist_lock);
                  if (unlikely(p->sighand == NULL)) {
                          /*
                           * The process has been reaped.
                           * We can't even collect a sample any more.
                           */
                          put_task_struct(p);
                          timer->it.cpu.task = p = NULL;
                          timer->it.cpu.expires.sched = 0;
                          goto out_unlock;
                  } else if (unlikely(p->exit_state) && thread_group_empty(p)) {
                          /*
                           * We've noticed that the thread is dead, but
                           * not yet reaped.  Take this opportunity to
                           * drop our task ref.
                           */
                          clear_dead_task(timer, now);
                          goto out_unlock;
                  }
                  spin_lock(&p->sighand->siglock);
                  cpu_timer_sample_group(timer->it_clock, p, &now);
                  bump_cpu_timer(timer, now);
                  /* Leave the tasklist_lock locked for the call below.  */
          }
  
          /*
           * Now re-arm for the new expiry time.
           */
          BUG_ON(!irqs_disabled());
          arm_timer(timer);
          spin_unlock(&p->sighand->siglock);
  
  out_unlock:
          read_unlock(&tasklist_lock);
  
  out:
          timer->it_overrun_last = timer->it_overrun;
          timer->it_overrun = -1;
          ++timer->it_requeue_pending;
  }
  
  /**
   * 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 = {
                          .utime = tsk->utime,
                          .stime = tsk->stime,
                          .sum_exec_runtime = tsk->se.sum_exec_runtime
                  };
  
                  if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
                          return 1;
          }
  
          sig = tsk->signal;
          if (sig->cputimer.running) {
                  struct task_cputime group_sample;
  
                  raw_spin_lock(&sig->cputimer.lock);
                  group_sample = sig->cputimer.cputime;
                  raw_spin_unlock(&sig->cputimer.lock);
  
                  if (task_cputime_expired(&group_sample, &sig->cputime_expires))
                          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;
  
          BUG_ON(!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);
          /*
           * If there are any active process wide timers (POSIX 1.b, itimers,
           * RLIMIT_CPU) cputimer must be running.
           */
          if (tsk->signal->cputimer.running)
                  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,
                             cputime_t *newval, cputime_t *oldval)
  {
          union cpu_time_count now;
  
          BUG_ON(clock_idx == CPUCLOCK_SCHED);
          cpu_timer_sample_group(clock_idx, tsk, &now);
  
          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.cpu) {
                                  /* Just about to fire. */
                                  *oldval = cputime_one_jiffy;
                          } else {
                                  *oldval -= now.cpu;
                          }
                  }
  
                  if (!*newval)
                          return;
                  *newval += now.cpu;
          }
  
          /*
           * 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;
          }
  }
  
  static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
                              struct timespec *rqtp, struct itimerspec *it)
  {
          struct k_itimer timer;
          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 itimerspec zero_it;
  
                  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.sched == 0) {
                                  /*
                                   * Our timer fired and was reset.
                                   */
                                  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.
                   */
                  sample_to_timespec(which_clock, timer.it.cpu.expires, rqtp);
                  posix_cpu_timer_set(&timer, 0, &zero_it, it);
                  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;
          }
  
          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,
                              struct timespec *rqtp, struct timespec __user *rmtp)
  {
          struct restart_block *restart_block =
                  &current_thread_info()->restart_block;
          struct itimerspec it;
          int error;
  
          /*
           * Diagnose required errors first.
           */
          if (CPUCLOCK_PERTHREAD(which_clock) &&
              (CPUCLOCK_PID(which_clock) == 0 ||
               CPUCLOCK_PID(which_clock) == current->pid))
                  return -EINVAL;
  
          error = do_cpu_nanosleep(which_clock, flags, rqtp, &it);
  
          if (error == -ERESTART_RESTARTBLOCK) {
  
                  if (flags & TIMER_ABSTIME)
                          return -ERESTARTNOHAND;
                  /*
                   * Report back to the user the time still remaining.
                   */
                  if (rmtp && copy_to_user(rmtp, &it.it_value, sizeof *rmtp))
                          return -EFAULT;
  
                  restart_block->fn = posix_cpu_nsleep_restart;
                  restart_block->nanosleep.clockid = which_clock;
                  restart_block->nanosleep.rmtp = rmtp;
                  restart_block->nanosleep.expires = timespec_to_ns(rqtp);
          }
          return error;
  }
  
  static long posix_cpu_nsleep_restart(struct restart_block *restart_block)
  {
          clockid_t which_clock = restart_block->nanosleep.clockid;
          struct timespec t;
          struct itimerspec it;
          int error;
  
          t = ns_to_timespec(restart_block->nanosleep.expires);
  
          error = do_cpu_nanosleep(which_clock, TIMER_ABSTIME, &t, &it);
  
          if (error == -ERESTART_RESTARTBLOCK) {
                  struct timespec __user *rmtp = restart_block->nanosleep.rmtp;
                  /*
                   * Report back to the user the time still remaining.
                   */
                  if (rmtp && copy_to_user(rmtp, &it.it_value, sizeof *rmtp))
                          return -EFAULT;
  
                  restart_block->nanosleep.expires = timespec_to_ns(&t);
          }
          return error;
  
  }
  
  #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 timespec *tp)
  {
          return posix_cpu_clock_getres(PROCESS_CLOCK, tp);
  }
  static int process_cpu_clock_get(const clockid_t which_clock,
                                   struct timespec *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,
                                struct timespec *rqtp,
                                struct timespec __user *rmtp)
  {
          return posix_cpu_nsleep(PROCESS_CLOCK, flags, rqtp, rmtp);
  }
  static long process_cpu_nsleep_restart(struct restart_block *restart_block)
  {
          return -EINVAL;
  }
  static int thread_cpu_clock_getres(const clockid_t which_clock,
                                     struct timespec *tp)
  {
          return posix_cpu_clock_getres(THREAD_CLOCK, tp);
  }
  static int thread_cpu_clock_get(const clockid_t which_clock,
                                  struct timespec *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);
  }
  
  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,
          .nsleep_restart = posix_cpu_nsleep_restart,
          .timer_set      = posix_cpu_timer_set,
          .timer_del      = posix_cpu_timer_del,
          .timer_get      = posix_cpu_timer_get,
  };
  
  static __init int init_posix_cpu_timers(void)
  {
          struct k_clock process = {
                  .clock_getres   = process_cpu_clock_getres,
                  .clock_get      = process_cpu_clock_get,
                  .timer_create   = process_cpu_timer_create,
                  .nsleep         = process_cpu_nsleep,
                  .nsleep_restart = process_cpu_nsleep_restart,
          };
          struct k_clock thread = {
                  .clock_getres   = thread_cpu_clock_getres,
                  .clock_get      = thread_cpu_clock_get,
                  .timer_create   = thread_cpu_timer_create,
          };
          struct timespec ts;
  
          posix_timers_register_clock(CLOCK_PROCESS_CPUTIME_ID, &process);
          posix_timers_register_clock(CLOCK_THREAD_CPUTIME_ID, &thread);
  
          cputime_to_timespec(cputime_one_jiffy, &ts);
          onecputick = ts.tv_nsec;
          WARN_ON(ts.tv_sec != 0);
  
          return 0;
  }
  __initcall(init_posix_cpu_timers);

Cache object: 59a2229b076ff6e6b042759a7e672435