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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // 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 <linux/task_work.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.
  *
  * Returns 0 on success, -ESRCH on failure.  Can fail if the task is exiting and
  * we cannot lock_task_sighand.  Cannot fail if task is current.
  */
 int update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new)
 {
     u64 nsecs = rlim_new * NSEC_PER_SEC;
     unsigned long irq_fl;
 
     if (!lock_task_sighand(task, &irq_fl))
         return -ESRCH;
     set_process_cpu_timer(task, CPUCLOCK_PROF, &nsecs, NULL);
     unlock_task_sighand(task, &irq_fl);
     return 0;
 }
 
 /*
  * 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 accounting 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;
 
     lockdep_assert_task_sighand_held(tsk);
 
     /* 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 separate
      * 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;
 }
 
 static struct posix_cputimer_base *timer_base(struct k_itimer *timer,
                           struct task_struct *tsk)
 {
     int clkidx = CPUCLOCK_WHICH(timer->it_clock);
 
     if (CPUCLOCK_PERTHREAD(timer->it_clock))
         return tsk->posix_cputimers.bases + clkidx;
     else
         return tsk->signal->posix_cputimers.bases + clkidx;
 }
 
 /*
  * Force recalculating the base earliest expiration on the next tick.
  * This will also re-evaluate the need to keep around the process wide
  * cputime counter and tick dependency and eventually shut these down
  * if necessary.
  */
 static void trigger_base_recalc_expires(struct k_itimer *timer,
                     struct task_struct *tsk)
 {
     struct posix_cputimer_base *base = timer_base(timer, tsk);
 
     base->nextevt = 0;
 }
 
 /*
  * Dequeue the timer and reset the base if it was its earliest expiration.
  * It makes sure the next tick recalculates the base next expiration so we
  * don't keep the costly process wide cputime counter around for a random
  * amount of time, along with the tick dependency.
  *
  * If another timer gets queued between this and the next tick, its
  * expiration will update the base next event if necessary on the next
  * tick.
  */
 static void disarm_timer(struct k_itimer *timer, struct task_struct *p)
 {
     struct cpu_timer *ctmr = &timer->it.cpu;
     struct posix_cputimer_base *base;
 
     if (!cpu_timer_dequeue(ctmr))
         return;
 
     base = timer_base(timer, p);
     if (cpu_timer_getexpires(ctmr) == base->nextevt)
         trigger_base_recalc_expires(timer, p);
 }
 
 
 /*
  * 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
             disarm_timer(timer, p);
 
         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)
 {
     struct posix_cputimer_base *base = timer_base(timer, p);
     struct cpu_timer *ctmr = &timer->it.cpu;
     u64 newexp = cpu_timer_getexpires(ctmr);
 
     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, 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 (val >= new_expires) {
         if (new_expires != 0) {
             /*
              * 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);
         }
 
         /*
          * Make sure we don't keep around the process wide cputime
          * counter or the tick dependency if they are not necessary.
          */
         sighand = lock_task_sighand(p, &flags);
         if (!sighand)
             goto out;
 
         if (!cpu_timer_queued(ctmr))
             trigger_base_recalc_expires(timer, p);
 
         unlock_task_sighand(p, &flags);
     }
  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;
         send_signal_locked(SIGXCPU, SEND_SIG_PRIV, tsk, PIDTYPE_TGID);
     }
 }
 
 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]\n",
             rt ? "RT" : "CPU", hard ? "hard" : "soft",
             current->comm, task_pid_nr(current));
     }
     send_signal_locked(signo, SEND_SIG_PRIV, current, PIDTYPE_TGID);
     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);
         send_signal_locked(signo, SEND_SIG_PRIV, tsk, PIDTYPE_TGID);
     }
 
     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;
 
     /* Protect timer list r/w in arm_timer() */
     sighand = lock_task_sighand(p, &flags);
     if (unlikely(sighand == NULL))
         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);
 
     /*
      * 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);
 }
 
 /*
  * Clear existing posix CPU timers task work.
  */
 void clear_posix_cputimers_work(struct task_struct *p)
 {
     /*
      * A copied work entry from the old task is not meaningful, clear it.
      * N.B. init_task_work will not do this.
      */
     memset(&p->posix_cputimers_work.work, 0,
            sizeof(p->posix_cputimers_work.work));
     init_task_work(&p->posix_cputimers_work.work,
                posix_cpu_timers_work);
     p->posix_cputimers_work.scheduled = false;
 }
 
 /*
  * 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)
 {
     clear_posix_cputimers_work(current);
 }
 
 /*
  * 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 expiry 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)
             *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, 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) {
 
         if (flags & TIMER_ABSTIME)
             return -ERESTARTNOHAND;
 
         restart_block->nanosleep.clockid = which_clock;
         set_restart_fn(restart_block, posix_cpu_nsleep_restart);
     }
     return error;
 }
 
 static long posix_cpu_nsleep_restart(struct restart_block *restart_block)
 {
     clockid_t which_clock = restart_block->nanosleep.clockid;
     struct timespec64 t;
 
     t = ns_to_timespec64(restart_block->nanosleep.expires);
 
     return do_cpu_nanosleep(which_clock, TIMER_ABSTIME, &t);
 }
 
 #define PROCESS_CLOCK   make_process_cpuclock(0, CPUCLOCK_SCHED)
 #define THREAD_CLOCK    make_thread_cpuclock(0, CPUCLOCK_SCHED)
 
 static int process_cpu_clock_getres(const clockid_t which_clock,
                     struct timespec64 *tp)
 {
     return posix_cpu_clock_getres(PROCESS_CLOCK, tp);
 }
 static int process_cpu_clock_get(const clockid_t which_clock,
                  struct timespec64 *tp)
 {
     return posix_cpu_clock_get(PROCESS_CLOCK, tp);
 }
 static int process_cpu_timer_create(struct k_itimer *timer)
 {
     timer->it_clock = PROCESS_CLOCK;
     return posix_cpu_timer_create(timer);
 }
 static int process_cpu_nsleep(const clockid_t which_clock, int flags,
                   const struct timespec64 *rqtp)
 {
     return posix_cpu_nsleep(PROCESS_CLOCK, flags, rqtp);
 }
 static int thread_cpu_clock_getres(const clockid_t which_clock,
                    struct timespec64 *tp)
 {
     return posix_cpu_clock_getres(THREAD_CLOCK, tp);
 }
 static int thread_cpu_clock_get(const clockid_t which_clock,
                 struct timespec64 *tp)
 {
     return posix_cpu_clock_get(THREAD_CLOCK, tp);
 }
 static int thread_cpu_timer_create(struct k_itimer *timer)
 {
     timer->it_clock = THREAD_CLOCK;
     return posix_cpu_timer_create(timer);
 }
 
 const struct k_clock clock_posix_cpu = {
     .clock_getres       = posix_cpu_clock_getres,
     .clock_set      = posix_cpu_clock_set,
     .clock_get_timespec = posix_cpu_clock_get,
     .timer_create       = posix_cpu_timer_create,
     .nsleep         = posix_cpu_nsleep,
     .timer_set      = posix_cpu_timer_set,
     .timer_del      = posix_cpu_timer_del,
     .timer_get      = posix_cpu_timer_get,
     .timer_rearm        = posix_cpu_timer_rearm,
 };
 
 const struct k_clock clock_process = {
     .clock_getres       = process_cpu_clock_getres,
     .clock_get_timespec = process_cpu_clock_get,
     .timer_create       = process_cpu_timer_create,
     .nsleep         = process_cpu_nsleep,
 };
 
 const struct k_clock clock_thread = {
     .clock_getres       = thread_cpu_clock_getres,
     .clock_get_timespec = thread_cpu_clock_get,
     .timer_create       = thread_cpu_timer_create,
 };

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