/*
   * 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>

  /*

   * Called after updating RLIMIT_CPU to set timer expiration if necessary.
   */
  void update_rlimit_cpu(unsigned long rlim_new)
  {
  	cputime_t cputime;
  
  	cputime = secs_to_cputime(rlim_new);
  	if (cputime_eq(current->signal->it_prof_expires, cputime_zero) ||

  	    cputime_gt(current->signal->it_prof_expires, cputime)) {

  		spin_lock_irq(&current->sighand->siglock);
  		set_process_cpu_timer(current, CPUCLOCK_PROF, &cputime, NULL);
  		spin_unlock_irq(&current->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;
  
  	read_lock(&tasklist_lock);

  	p = find_task_by_vpid(pid);

  	if (!p || !(CPUCLOCK_PERTHREAD(which_clock) ?
  		   same_thread_group(p, current) : thread_group_leader(p))) {

  		error = -EINVAL;
  	}
  	read_unlock(&tasklist_lock);
  
  	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 cputime_lt(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 = cputime_add(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 = cputime_sub(a.cpu, b.cpu);
  	}
  	return a;
  }
  
  /*

   * Divide and limit the result to res >= 1
   *
   * This is necessary to prevent signal delivery starvation, when the result of
   * the division would be rounded down to 0.
   */
  static inline cputime_t cputime_div_non_zero(cputime_t time, unsigned long div)
  {
  	cputime_t res = cputime_div(time, div);
  
  	return max_t(cputime_t, res, 1);
  }
  
  /*

   * 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 (cputime_lt(now.cpu, timer->it.cpu.expires.cpu))
  			return;
  		incr = timer->it.cpu.incr.cpu;
  		delta = cputime_sub(cputime_add(now.cpu, incr),
  				    timer->it.cpu.expires.cpu);
  		/* Don't use (incr*2 < delta), incr*2 might overflow. */
  		for (i = 0; cputime_lt(incr, cputime_sub(delta, incr)); i++)
  			     incr = cputime_add(incr, incr);
  		for (; i >= 0; incr = cputime_halve(incr), i--) {

  			if (cputime_lt(delta, incr))

  				continue;
  			timer->it.cpu.expires.cpu =
  				cputime_add(timer->it.cpu.expires.cpu, incr);
  			timer->it_overrun += 1 << i;
  			delta = cputime_sub(delta, incr);
  		}
  	}
  }
  
  static inline cputime_t prof_ticks(struct task_struct *p)
  {
  	return cputime_add(p->utime, p->stime);
  }
  static inline cputime_t virt_ticks(struct task_struct *p)
  {
  	return p->utime;
  }

  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;
  }

  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;
  }

  void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
  {
  	struct sighand_struct *sighand;
  	struct signal_struct *sig;
  	struct task_struct *t;
  
  	*times = INIT_CPUTIME;
  
  	rcu_read_lock();
  	sighand = rcu_dereference(tsk->sighand);
  	if (!sighand)
  		goto out;
  
  	sig = tsk->signal;
  
  	t = tsk;
  	do {
  		times->utime = cputime_add(times->utime, t->utime);
  		times->stime = cputime_add(times->stime, t->stime);
  		times->sum_exec_runtime += t->se.sum_exec_runtime;
  
  		t = next_thread(t);
  	} while (t != tsk);
  
  	times->utime = cputime_add(times->utime, sig->utime);
  	times->stime = cputime_add(times->stime, sig->stime);
  	times->sum_exec_runtime += sig->sum_sched_runtime;
  out:
  	rcu_read_unlock();
  }

  static void update_gt_cputime(struct task_cputime *a, struct task_cputime *b)
  {
  	if (cputime_gt(b->utime, a->utime))
  		a->utime = b->utime;
  
  	if (cputime_gt(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;
  
  	spin_lock_irqsave(&cputimer->lock, flags);
  	if (!cputimer->running) {
  		cputimer->running = 1;
  		/*
  		 * 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, &sum);
  	}
  	*times = cputimer->cputime;
  	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_add(cputime.utime, cputime.stime);

  		break;
  	case CPUCLOCK_VIRT:

  		thread_group_cputime(p, &cputime);

  		cpu->cpu = cputime.utime;

  		break;
  	case CPUCLOCK_SCHED:

  		cpu->sched = thread_group_sched_runtime(p);

  		break;
  	}
  	return 0;
  }

  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->signal) {

  					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 with the new timer already locked.
   */
  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);
  	new_timer->it.cpu.incr.sched = 0;
  	new_timer->it.cpu.expires.sched = 0;
  
  	read_lock(&tasklist_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 && !thread_group_leader(p))

  				p = NULL;
  		}
  	}
  	new_timer->it.cpu.task = p;
  	if (p) {
  		get_task_struct(p);
  	} else {
  		ret = -EINVAL;
  	}
  	read_unlock(&tasklist_lock);
  
  	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.)
   */
  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->signal == 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 = cputime_add(utime, stime);
  
  	list_for_each_entry_safe(timer, next, head, entry) {

  		list_del_init(&timer->entry);
  		if (cputime_lt(timer->expires.cpu, ptime)) {
  			timer->expires.cpu = cputime_zero;
  		} else {
  			timer->expires.cpu = cputime_sub(timer->expires.cpu,
  							 ptime);
  		}
  	}
  
  	++head;
  	list_for_each_entry_safe(timer, next, head, entry) {

  		list_del_init(&timer->entry);
  		if (cputime_lt(timer->expires.cpu, utime)) {
  			timer->expires.cpu = cputime_zero;
  		} else {
  			timer->expires.cpu = cputime_sub(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)
  {
  	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 task_cputime cputime;

  	thread_group_cputimer(tsk, &cputime);

  	cleanup_timers(tsk->signal->cpu_timers,
  		       cputime.utime, cputime.stime, cputime.sum_exec_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);
  }
  
  /*
   * Insert the timer on the appropriate list before any timers that
   * expire later.  This must be called with the tasklist_lock held
   * for reading, and interrupts disabled.
   */
  static void arm_timer(struct k_itimer *timer, union cpu_time_count now)
  {
  	struct task_struct *p = timer->it.cpu.task;
  	struct list_head *head, *listpos;
  	struct cpu_timer_list *const nt = &timer->it.cpu;
  	struct cpu_timer_list *next;
  	unsigned long i;
  
  	head = (CPUCLOCK_PERTHREAD(timer->it_clock) ?
  		p->cpu_timers : p->signal->cpu_timers);
  	head += CPUCLOCK_WHICH(timer->it_clock);
  
  	BUG_ON(!irqs_disabled());
  	spin_lock(&p->sighand->siglock);
  
  	listpos = head;
  	if (CPUCLOCK_WHICH(timer->it_clock) == CPUCLOCK_SCHED) {
  		list_for_each_entry(next, head, entry) {

  			if (next->expires.sched > nt->expires.sched)

  				break;

  			listpos = &next->entry;

  		}
  	} else {
  		list_for_each_entry(next, head, entry) {

  			if (cputime_gt(next->expires.cpu, nt->expires.cpu))

  				break;

  			listpos = &next->entry;

  		}
  	}
  	list_add(&nt->entry, listpos);
  
  	if (listpos == head) {
  		/*
  		 * We are the new earliest-expiring timer.
  		 * If we are a thread timer, there can always
  		 * be a process timer telling us to stop earlier.
  		 */
  
  		if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
  			switch (CPUCLOCK_WHICH(timer->it_clock)) {
  			default:
  				BUG();
  			case CPUCLOCK_PROF:

  				if (cputime_eq(p->cputime_expires.prof_exp,

  					       cputime_zero) ||

  				    cputime_gt(p->cputime_expires.prof_exp,

  					       nt->expires.cpu))

  					p->cputime_expires.prof_exp =
  						nt->expires.cpu;

  				break;
  			case CPUCLOCK_VIRT:

  				if (cputime_eq(p->cputime_expires.virt_exp,

  					       cputime_zero) ||

  				    cputime_gt(p->cputime_expires.virt_exp,

  					       nt->expires.cpu))

  					p->cputime_expires.virt_exp =
  						nt->expires.cpu;

  				break;
  			case CPUCLOCK_SCHED:

  				if (p->cputime_expires.sched_exp == 0 ||
  				    p->cputime_expires.sched_exp >
  							nt->expires.sched)
  					p->cputime_expires.sched_exp =
  						nt->expires.sched;

  				break;
  			}
  		} else {
  			/*

  			 * For a process timer, set the cached expiration time.

  			 */
  			switch (CPUCLOCK_WHICH(timer->it_clock)) {
  			default:
  				BUG();
  			case CPUCLOCK_VIRT:
  				if (!cputime_eq(p->signal->it_virt_expires,
  						cputime_zero) &&
  				    cputime_lt(p->signal->it_virt_expires,
  					       timer->it.cpu.expires.cpu))
  					break;

  				p->signal->cputime_expires.virt_exp =
  					timer->it.cpu.expires.cpu;
  				break;

  			case CPUCLOCK_PROF:
  				if (!cputime_eq(p->signal->it_prof_expires,
  						cputime_zero) &&
  				    cputime_lt(p->signal->it_prof_expires,
  					       timer->it.cpu.expires.cpu))
  					break;
  				i = p->signal->rlim[RLIMIT_CPU].rlim_cur;
  				if (i != RLIM_INFINITY &&
  				    i <= cputime_to_secs(timer->it.cpu.expires.cpu))
  					break;

  				p->signal->cputime_expires.prof_exp =
  					timer->it.cpu.expires.cpu;
  				break;

  			case CPUCLOCK_SCHED:

  				p->signal->cputime_expires.sched_exp =
  					timer->it.cpu.expires.sched;

  				break;
  			}
  		}
  	}
  
  	spin_unlock(&p->sighand->siglock);
  }
  
  /*
   * The timer is locked, fire it and arrange for its reload.
   */
  static void cpu_timer_fire(struct k_itimer *timer)
  {
  	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_add(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.)
   */
  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, 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->signal.  If p has just been reaped, we can no
  	 * longer get any information about it at all.
  	 */
  	if (unlikely(p->signal == 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;

  	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);

  	spin_unlock(&p->sighand->siglock);
  
  	/*
  	 * 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).
  		 */
  		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 &&
  	    (timer->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE &&
  	    cpu_time_before(timer->it_clock, val, new_expires)) {
  		arm_timer(timer, val);
  	}
  
  	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 &&
  	    (timer->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE &&
  	    !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,
  				   timer->it.cpu.incr, &old->it_interval);
  	}
  	return ret;
  }
  
  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->signal == 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 ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
  		if (timer->it.cpu.incr.sched == 0 &&
  		    cpu_time_before(timer->it_clock,
  				    timer->it.cpu.expires, now)) {
  			/*
  			 * Do-nothing timer expired and has no reload,
  			 * so it's as if it was never set.
  			 */
  			timer->it.cpu.expires.sched = 0;
  			itp->it_value.tv_sec = itp->it_value.tv_nsec = 0;
  			return;
  		}
  		/*
  		 * Account for any expirations and reloads that should
  		 * have happened.
  		 */
  		bump_cpu_timer(timer, now);
  	}
  
  	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;

  	maxfire = 20;

  	tsk->cputime_expires.prof_exp = cputime_zero;

  	while (!list_empty(timers)) {

  		struct cpu_timer_list *t = list_first_entry(timers,

  						      struct cpu_timer_list,
  						      entry);

  		if (!--maxfire || cputime_lt(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 = cputime_zero;

  	while (!list_empty(timers)) {

  		struct cpu_timer_list *t = list_first_entry(timers,

  						      struct cpu_timer_list,
  						      entry);

  		if (!--maxfire || cputime_lt(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.
  	 */
  	if (sig->rlim[RLIMIT_RTTIME].rlim_cur != RLIM_INFINITY) {
  		unsigned long hard = sig->rlim[RLIMIT_RTTIME].rlim_max;
  		unsigned long *soft = &sig->rlim[RLIMIT_RTTIME].rlim_cur;

  		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 (sig->rlim[RLIMIT_RTTIME].rlim_cur
  			    < sig->rlim[RLIMIT_RTTIME].rlim_max) {
  				sig->rlim[RLIMIT_RTTIME].rlim_cur +=
  								USEC_PER_SEC;
  			}

  			printk(KERN_INFO
  				"RT Watchdog Timeout: %s[%d]
  ",
  				tsk->comm, task_pid_nr(tsk));

  			__group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
  		}
  	}

  }

  static void stop_process_timers(struct task_struct *tsk)
  {
  	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
  	unsigned long flags;
  
  	if (!cputimer->running)
  		return;
  
  	spin_lock_irqsave(&cputimer->lock, flags);
  	cputimer->running = 0;
  	spin_unlock_irqrestore(&cputimer->lock, flags);
  }

  /*
   * 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;

  
  	/*
  	 * Don't sample the current process CPU clocks if there are no timers.
  	 */
  	if (list_empty(&timers[CPUCLOCK_PROF]) &&
  	    cputime_eq(sig->it_prof_expires, cputime_zero) &&
  	    sig->rlim[RLIMIT_CPU].rlim_cur == RLIM_INFINITY &&
  	    list_empty(&timers[CPUCLOCK_VIRT]) &&
  	    cputime_eq(sig->it_virt_expires, cputime_zero) &&

  	    list_empty(&timers[CPUCLOCK_SCHED])) {
  		stop_process_timers(tsk);

  		return;

  	}

  
  	/*
  	 * Collect the current process totals.
  	 */

  	thread_group_cputimer(tsk, &cputime);

  	utime = cputime.utime;
  	ptime = cputime_add(utime, cputime.stime);
  	sum_sched_runtime = cputime.sum_exec_runtime;

  	maxfire = 20;

  	prof_expires = cputime_zero;
  	while (!list_empty(timers)) {

  		struct cpu_timer_list *tl = list_first_entry(timers,

  						      struct cpu_timer_list,
  						      entry);

  		if (!--maxfire || cputime_lt(ptime, tl->expires.cpu)) {
  			prof_expires = tl->expires.cpu;

  			break;
  		}

  		tl->firing = 1;
  		list_move_tail(&tl->entry, firing);

  	}
  
  	++timers;

  	maxfire = 20;

  	virt_expires = cputime_zero;
  	while (!list_empty(timers)) {

  		struct cpu_timer_list *tl = list_first_entry(timers,

  						      struct cpu_timer_list,
  						      entry);

  		if (!--maxfire || cputime_lt(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.
  	 */
  	if (!cputime_eq(sig->it_prof_expires, cputime_zero)) {
  		if (cputime_ge(ptime, sig->it_prof_expires)) {
  			/* ITIMER_PROF fires and reloads.  */
  			sig->it_prof_expires = sig->it_prof_incr;
  			if (!cputime_eq(sig->it_prof_expires, cputime_zero)) {
  				sig->it_prof_expires = cputime_add(
  					sig->it_prof_expires, ptime);
  			}
  			__group_send_sig_info(SIGPROF, SEND_SIG_PRIV, tsk);
  		}
  		if (!cputime_eq(sig->it_prof_expires, cputime_zero) &&
  		    (cputime_eq(prof_expires, cputime_zero) ||
  		     cputime_lt(sig->it_prof_expires, prof_expires))) {
  			prof_expires = sig->it_prof_expires;
  		}
  	}
  	if (!cputime_eq(sig->it_virt_expires, cputime_zero)) {
  		if (cputime_ge(utime, sig->it_virt_expires)) {
  			/* ITIMER_VIRTUAL fires and reloads.  */
  			sig->it_virt_expires = sig->it_virt_incr;
  			if (!cputime_eq(sig->it_virt_expires, cputime_zero)) {
  				sig->it_virt_expires = cputime_add(
  					sig->it_virt_expires, utime);
  			}
  			__group_send_sig_info(SIGVTALRM, SEND_SIG_PRIV, tsk);
  		}
  		if (!cputime_eq(sig->it_virt_expires, cputime_zero) &&
  		    (cputime_eq(virt_expires, cputime_zero) ||
  		     cputime_lt(sig->it_virt_expires, virt_expires))) {
  			virt_expires = sig->it_virt_expires;
  		}
  	}
  	if (sig->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY) {
  		unsigned long psecs = cputime_to_secs(ptime);
  		cputime_t x;
  		if (psecs >= sig->rlim[RLIMIT_CPU].rlim_max) {
  			/*
  			 * 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 >= sig->rlim[RLIMIT_CPU].rlim_cur) {
  			/*
  			 * At the soft limit, send a SIGXCPU every second.
  			 */
  			__group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
  			if (sig->rlim[RLIMIT_CPU].rlim_cur
  			    < sig->rlim[RLIMIT_CPU].rlim_max) {
  				sig->rlim[RLIMIT_CPU].rlim_cur++;
  			}
  		}
  		x = secs_to_cputime(sig->rlim[RLIMIT_CPU].rlim_cur);
  		if (cputime_eq(prof_expires, cputime_zero) ||
  		    cputime_lt(x, prof_expires)) {
  			prof_expires = x;
  		}
  	}

  	if (!cputime_eq(prof_expires, cputime_zero) &&
  	    (cputime_eq(sig->cputime_expires.prof_exp, cputime_zero) ||
  	     cputime_gt(sig->cputime_expires.prof_exp, prof_expires)))
  		sig->cputime_expires.prof_exp = prof_expires;
  	if (!cputime_eq(virt_expires, cputime_zero) &&
  	    (cputime_eq(sig->cputime_expires.virt_exp, cputime_zero) ||
  	     cputime_gt(sig->cputime_expires.virt_exp, virt_expires)))
  		sig->cputime_expires.virt_exp = virt_expires;
  	if (sched_expires != 0 &&
  	    (sig->cputime_expires.sched_exp == 0 ||
  	     sig->cputime_expires.sched_exp > sched_expires))
  		sig->cputime_expires.sched_exp = sched_expires;

  }
  
  /*
   * 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.  */
  	} else {
  		read_lock(&tasklist_lock);
  		if (unlikely(p->signal == 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;

  		}

  		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.
  	 */
  	arm_timer(timer, now);

  out_unlock:

  	read_unlock(&tasklist_lock);

  
  out:
  	timer->it_overrun_last = timer->it_overrun;
  	timer->it_overrun = -1;
  	++timer->it_requeue_pending;

  }

  /**
   * 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_eq(cputime->utime, cputime_zero) &&
  	    cputime_eq(cputime->stime, cputime_zero) &&
  	    cputime->sum_exec_runtime == 0)
  		return 1;
  	return 0;
  }
  
  /**
   * 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 (!cputime_eq(expires->utime, cputime_zero) &&
  	    cputime_ge(sample->utime, expires->utime))
  		return 1;
  	if (!cputime_eq(expires->stime, cputime_zero) &&
  	    cputime_ge(cputime_add(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;

  	/* tsk == current, ensure it is safe to use ->signal/sighand */
  	if (unlikely(tsk->exit_state))

  		return 0;

  
  	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 (!task_cputime_zero(&sig->cputime_expires)) {
  		struct task_cputime group_sample;

  		thread_group_cputimer(tsk, &group_sample);

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

  
  	return sig->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY;

  }

  /*
   * 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;
  
  	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;

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

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

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

   * The tsk->sighand->siglock must be held by the caller.
   * The *newval argument is relative and we update it to be absolute, *oldval
   * is absolute and we update it to be relative.

   */
  void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
  			   cputime_t *newval, cputime_t *oldval)
  {
  	union cpu_time_count now;
  	struct list_head *head;
  
  	BUG_ON(clock_idx == CPUCLOCK_SCHED);

  	cpu_timer_sample_group(clock_idx, tsk, &now);

  
  	if (oldval) {
  		if (!cputime_eq(*oldval, cputime_zero)) {
  			if (cputime_le(*oldval, now.cpu)) {
  				/* Just about to fire. */
  				*oldval = jiffies_to_cputime(1);
  			} else {
  				*oldval = cputime_sub(*oldval, now.cpu);
  			}
  		}
  
  		if (cputime_eq(*newval, cputime_zero))
  			return;
  		*newval = cputime_add(*newval, now.cpu);
  
  		/*
  		 * If the RLIMIT_CPU timer will expire before the
  		 * ITIMER_PROF timer, we have nothing else to do.
  		 */
  		if (tsk->signal->rlim[RLIMIT_CPU].rlim_cur
  		    < cputime_to_secs(*newval))
  			return;
  	}
  
  	/*
  	 * Check whether there are any process timers already set to fire
  	 * before this one.  If so, we don't have anything more to do.
  	 */
  	head = &tsk->signal->cpu_timers[clock_idx];
  	if (list_empty(head) ||

  	    cputime_ge(list_first_entry(head,

  				  struct cpu_timer_list, entry)->expires.cpu,
  		       *newval)) {

  		switch (clock_idx) {
  		case CPUCLOCK_PROF:
  			tsk->signal->cputime_expires.prof_exp = *newval;
  			break;
  		case CPUCLOCK_VIRT:
  			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;
  }
  
  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 != NULL && copy_to_user(rmtp, &it.it_value, sizeof *rmtp))

  			return -EFAULT;

  		restart_block->fn = posix_cpu_nsleep_restart;

  		restart_block->arg0 = which_clock;

  		restart_block->arg1 = (unsigned long) rmtp;

  		restart_block->arg2 = rqtp->tv_sec;
  		restart_block->arg3 = rqtp->tv_nsec;

  	}

  	return error;
  }

  long posix_cpu_nsleep_restart(struct restart_block *restart_block)

  {
  	clockid_t which_clock = restart_block->arg0;

  	struct timespec __user *rmtp;
  	struct timespec t;

  	struct itimerspec it;
  	int error;

  
  	rmtp = (struct timespec __user *) restart_block->arg1;
  	t.tv_sec = restart_block->arg2;
  	t.tv_nsec = restart_block->arg3;

  	restart_block->fn = do_no_restart_syscall;

  	error = do_cpu_nanosleep(which_clock, TIMER_ABSTIME, &t, &it);
  
  	if (error == -ERESTART_RESTARTBLOCK) {
  		/*
  	 	 * Report back to the user the time still remaining.
  	 	 */
  		if (rmtp != NULL && copy_to_user(rmtp, &it.it_value, sizeof *rmtp))
  			return -EFAULT;
  
  		restart_block->fn = posix_cpu_nsleep_restart;
  		restart_block->arg0 = which_clock;
  		restart_block->arg1 = (unsigned long) rmtp;
  		restart_block->arg2 = t.tv_sec;
  		restart_block->arg3 = t.tv_nsec;
  	}
  	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);
  }

  static int thread_cpu_nsleep(const clockid_t which_clock, int flags,

  			      struct timespec *rqtp, struct timespec __user *rmtp)

  {
  	return -EINVAL;
  }

  static long thread_cpu_nsleep_restart(struct restart_block *restart_block)
  {
  	return -EINVAL;
  }

  
  static __init int init_posix_cpu_timers(void)
  {
  	struct k_clock process = {
  		.clock_getres = process_cpu_clock_getres,
  		.clock_get = process_cpu_clock_get,
  		.clock_set = do_posix_clock_nosettime,
  		.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,
  		.clock_set = do_posix_clock_nosettime,
  		.timer_create = thread_cpu_timer_create,
  		.nsleep = thread_cpu_nsleep,

  		.nsleep_restart = thread_cpu_nsleep_restart,

  	};
  
  	register_posix_clock(CLOCK_PROCESS_CPUTIME_ID, &process);
  	register_posix_clock(CLOCK_THREAD_CPUTIME_ID, &thread);
  
  	return 0;
  }
  __initcall(init_posix_cpu_timers);