Linux-2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 1559 insertions, 0 deletions

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
new file mode 100644
index 000000000000..ad85d3f0dcc4
--- /dev/null
+++ b/kernel/posix-cpu-timers.c
@@ -0,0 +1,1559 @@
+/*
+ * Implement CPU time clocks for the POSIX clock interface.
+ */
+
+#include <linux/sched.h>
+#include <linux/posix-timers.h>
+#include <asm/uaccess.h>
+#include <linux/errno.h>
+
+static int check_clock(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_pid(pid);
+	if (!p || (CPUCLOCK_PERTHREAD(which_clock) ?
+		   p->tgid != current->tgid : p->tgid != pid)) {
+		error = -EINVAL;
+	}
+	read_unlock(&tasklist_lock);
+
+	return error;
+}
+
+static inline union cpu_time_count
+timespec_to_sample(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 = tp->tv_sec * NSEC_PER_SEC + tp->tv_nsec;
+	} else {
+		ret.cpu = timespec_to_cputime(tp);
+	}
+	return ret;
+}
+
+static void sample_to_timespec(clockid_t which_clock,
+			       union cpu_time_count cpu,
+			       struct timespec *tp)
+{
+	if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
+		tp->tv_sec = div_long_long_rem(cpu.sched,
+					       NSEC_PER_SEC, &tp->tv_nsec);
+	} else {
+		cputime_to_timespec(cpu.cpu, tp);
+	}
+}
+
+static inline int cpu_time_before(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(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(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;
+}
+
+/*
+ * Update expiry time from increment, and increase overrun count,
+ * given the current clock sample.
+ */
+static inline 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_le(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;
+}
+static inline unsigned long long sched_ns(struct task_struct *p)
+{
+	return (p == current) ? current_sched_time(p) : p->sched_time;
+}
+
+int posix_cpu_clock_getres(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(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(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 = sched_ns(p);
+		break;
+	}
+	return 0;
+}
+
+/*
+ * Sample a process (thread group) clock for the given group_leader task.
+ * Must be called with tasklist_lock held for reading.
+ * Must be called with tasklist_lock held for reading, and p->sighand->siglock.
+ */
+static int cpu_clock_sample_group_locked(unsigned int clock_idx,
+					 struct task_struct *p,
+					 union cpu_time_count *cpu)
+{
+	struct task_struct *t = p;
+ 	switch (clock_idx) {
+	default:
+		return -EINVAL;
+	case CPUCLOCK_PROF:
+		cpu->cpu = cputime_add(p->signal->utime, p->signal->stime);
+		do {
+			cpu->cpu = cputime_add(cpu->cpu, prof_ticks(t));
+			t = next_thread(t);
+		} while (t != p);
+		break;
+	case CPUCLOCK_VIRT:
+		cpu->cpu = p->signal->utime;
+		do {
+			cpu->cpu = cputime_add(cpu->cpu, virt_ticks(t));
+			t = next_thread(t);
+		} while (t != p);
+		break;
+	case CPUCLOCK_SCHED:
+		cpu->sched = p->signal->sched_time;
+		/* Add in each other live thread.  */
+		while ((t = next_thread(t)) != p) {
+			cpu->sched += t->sched_time;
+		}
+		if (p->tgid == current->tgid) {
+			/*
+			 * We're sampling ourselves, so include the
+			 * cycles not yet banked.  We still omit
+			 * other threads running on other CPUs,
+			 * so the total can always be behind as
+			 * much as max(nthreads-1,ncpus) * (NSEC_PER_SEC/HZ).
+			 */
+			cpu->sched += current_sched_time(current);
+		} else {
+			cpu->sched += p->sched_time;
+		}
+		break;
+	}
+	return 0;
+}
+
+/*
+ * 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(clockid_t which_clock,
+				  struct task_struct *p,
+				  union cpu_time_count *cpu)
+{
+	int ret;
+	unsigned long flags;
+	spin_lock_irqsave(&p->sighand->siglock, flags);
+	ret = cpu_clock_sample_group_locked(CPUCLOCK_WHICH(which_clock), p,
+					    cpu);
+	spin_unlock_irqrestore(&p->sighand->siglock, flags);
+	return ret;
+}
+
+
+int posix_cpu_clock_get(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;
+		read_lock(&tasklist_lock);
+		p = find_task_by_pid(pid);
+		if (p) {
+			if (CPUCLOCK_PERTHREAD(which_clock)) {
+				if (p->tgid == current->tgid) {
+					error = cpu_clock_sample(which_clock,
+								 p, &rtn);
+				}
+			} else if (p->tgid == pid && p->signal) {
+				error = cpu_clock_sample_group(which_clock,
+							       p, &rtn);
+			}
+		}
+		read_unlock(&tasklist_lock);
+	}
+
+	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_pid(pid);
+			if (p && p->tgid != current->tgid)
+				p = NULL;
+		}
+	} else {
+		if (pid == 0) {
+			p = current->group_leader;
+		} else {
+			p = find_task_by_pid(pid);
+			if (p && p->tgid != pid)
+				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;
+
+	if (timer->it.cpu.firing)
+		return TIMER_RETRY;
+
+	if (unlikely(p == NULL))
+		return 0;
+
+	if (!list_empty(&timer->it.cpu.entry)) {
+		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 {
+			/*
+			 * Take us off the task's timer list.
+			 */
+			spin_lock(&p->sighand->siglock);
+			list_del(&timer->it.cpu.entry);
+			spin_unlock(&p->sighand->siglock);
+		}
+		read_unlock(&tasklist_lock);
+	}
+	put_task_struct(p);
+
+	return 0;
+}
+
+/*
+ * 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 sched_time)
+{
+	struct cpu_timer_list *timer, *next;
+	cputime_t ptime = cputime_add(utime, stime);
+
+	list_for_each_entry_safe(timer, next, head, entry) {
+		timer->task = NULL;
+		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) {
+		timer->task = NULL;
+		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) {
+		timer->task = NULL;
+		list_del_init(&timer->entry);
+		if (timer->expires.sched < sched_time) {
+			timer->expires.sched = 0;
+		} else {
+			timer->expires.sched -= sched_time;
+		}
+	}
+}
+
+/*
+ * 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->sched_time);
+
+}
+void posix_cpu_timers_exit_group(struct task_struct *tsk)
+{
+	cleanup_timers(tsk->signal->cpu_timers,
+		       cputime_add(tsk->utime, tsk->signal->utime),
+		       cputime_add(tsk->stime, tsk->signal->stime),
+		       tsk->sched_time + tsk->signal->sched_time);
+}
+
+
+/*
+ * Set the expiry times of all the threads in the process so one of them
+ * will go off before the process cumulative expiry total is reached.
+ */
+static void process_timer_rebalance(struct task_struct *p,
+				    unsigned int clock_idx,
+				    union cpu_time_count expires,
+				    union cpu_time_count val)
+{
+	cputime_t ticks, left;
+	unsigned long long ns, nsleft;
+ 	struct task_struct *t = p;
+	unsigned int nthreads = atomic_read(&p->signal->live);
+
+	switch (clock_idx) {
+	default:
+		BUG();
+		break;
+	case CPUCLOCK_PROF:
+		left = cputime_div(cputime_sub(expires.cpu, val.cpu),
+				   nthreads);
+		do {
+			if (!unlikely(t->exit_state)) {
+				ticks = cputime_add(prof_ticks(t), left);
+				if (cputime_eq(t->it_prof_expires,
+					       cputime_zero) ||
+				    cputime_gt(t->it_prof_expires, ticks)) {
+					t->it_prof_expires = ticks;
+				}
+			}
+			t = next_thread(t);
+		} while (t != p);
+		break;
+	case CPUCLOCK_VIRT:
+		left = cputime_div(cputime_sub(expires.cpu, val.cpu),
+				   nthreads);
+		do {
+			if (!unlikely(t->exit_state)) {
+				ticks = cputime_add(virt_ticks(t), left);
+				if (cputime_eq(t->it_virt_expires,
+					       cputime_zero) ||
+				    cputime_gt(t->it_virt_expires, ticks)) {
+					t->it_virt_expires = ticks;
+				}
+			}
+			t = next_thread(t);
+		} while (t != p);
+		break;
+	case CPUCLOCK_SCHED:
+		nsleft = expires.sched - val.sched;
+		do_div(nsleft, nthreads);
+		do {
+			if (!unlikely(t->exit_state)) {
+				ns = t->sched_time + nsleft;
+				if (t->it_sched_expires == 0 ||
+				    t->it_sched_expires > ns) {
+					t->it_sched_expires = ns;
+				}
+			}
+			t = next_thread(t);
+		} while (t != p);
+		break;
+	}
+}
+
+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) {
+				listpos = &next->entry;
+				break;
+			}
+		}
+	} else {
+		list_for_each_entry(next, head, entry) {
+			if (cputime_gt(next->expires.cpu, nt->expires.cpu)) {
+				listpos = &next->entry;
+				break;
+			}
+		}
+	}
+	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->it_prof_expires,
+					       cputime_zero) ||
+				    cputime_gt(p->it_prof_expires,
+					       nt->expires.cpu))
+					p->it_prof_expires = nt->expires.cpu;
+				break;
+			case CPUCLOCK_VIRT:
+				if (cputime_eq(p->it_virt_expires,
+					       cputime_zero) ||
+				    cputime_gt(p->it_virt_expires,
+					       nt->expires.cpu))
+					p->it_virt_expires = nt->expires.cpu;
+				break;
+			case CPUCLOCK_SCHED:
+				if (p->it_sched_expires == 0 ||
+				    p->it_sched_expires > nt->expires.sched)
+					p->it_sched_expires = nt->expires.sched;
+				break;
+			}
+		} else {
+			/*
+			 * For a process timer, we must balance
+			 * all the live threads' expirations.
+			 */
+			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;
+				goto rebalance;
+			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;
+				goto rebalance;
+			case CPUCLOCK_SCHED:
+			rebalance:
+				process_timer_rebalance(
+					timer->it.cpu.task,
+					CPUCLOCK_WHICH(timer->it_clock),
+					timer->it.cpu.expires, now);
+				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);
+	}
+}
+
+/*
+ * 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());
+	spin_lock(&p->sighand->siglock);
+	old_expires = timer->it.cpu.expires;
+	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_clock_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(timer->it.cpu.firing)) {
+		/*
+		 * 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);
+		timer->it.cpu.firing = -1;
+		ret = TIMER_RETRY;
+		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_clock_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)
+{
+	struct list_head *timers = tsk->cpu_timers;
+
+	tsk->it_prof_expires = cputime_zero;
+	while (!list_empty(timers)) {
+		struct cpu_timer_list *t = list_entry(timers->next,
+						      struct cpu_timer_list,
+						      entry);
+		if (cputime_lt(prof_ticks(tsk), t->expires.cpu)) {
+			tsk->it_prof_expires = t->expires.cpu;
+			break;
+		}
+		t->firing = 1;
+		list_move_tail(&t->entry, firing);
+	}
+
+	++timers;
+	tsk->it_virt_expires = cputime_zero;
+	while (!list_empty(timers)) {
+		struct cpu_timer_list *t = list_entry(timers->next,
+						      struct cpu_timer_list,
+						      entry);
+		if (cputime_lt(virt_ticks(tsk), t->expires.cpu)) {
+			tsk->it_virt_expires = t->expires.cpu;
+			break;
+		}
+		t->firing = 1;
+		list_move_tail(&t->entry, firing);
+	}
+
+	++timers;
+	tsk->it_sched_expires = 0;
+	while (!list_empty(timers)) {
+		struct cpu_timer_list *t = list_entry(timers->next,
+						      struct cpu_timer_list,
+						      entry);
+		if (tsk->sched_time < t->expires.sched) {
+			tsk->it_sched_expires = t->expires.sched;
+			break;
+		}
+		t->firing = 1;
+		list_move_tail(&t->entry, firing);
+	}
+}
+
+/*
+ * 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;
+	cputime_t utime, stime, ptime, virt_expires, prof_expires;
+	unsigned long long sched_time, sched_expires;
+	struct task_struct *t;
+	struct list_head *timers = sig->cpu_timers;
+
+	/*
+	 * 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]))
+		return;
+
+	/*
+	 * Collect the current process totals.
+	 */
+	utime = sig->utime;
+	stime = sig->stime;
+	sched_time = sig->sched_time;
+	t = tsk;
+	do {
+		utime = cputime_add(utime, t->utime);
+		stime = cputime_add(stime, t->stime);
+		sched_time += t->sched_time;
+		t = next_thread(t);
+	} while (t != tsk);
+	ptime = cputime_add(utime, stime);
+
+	prof_expires = cputime_zero;
+	while (!list_empty(timers)) {
+		struct cpu_timer_list *t = list_entry(timers->next,
+						      struct cpu_timer_list,
+						      entry);
+		if (cputime_lt(ptime, t->expires.cpu)) {
+			prof_expires = t->expires.cpu;
+			break;
+		}
+		t->firing = 1;
+		list_move_tail(&t->entry, firing);
+	}
+
+	++timers;
+	virt_expires = cputime_zero;
+	while (!list_empty(timers)) {
+		struct cpu_timer_list *t = list_entry(timers->next,
+						      struct cpu_timer_list,
+						      entry);
+		if (cputime_lt(utime, t->expires.cpu)) {
+			virt_expires = t->expires.cpu;
+			break;
+		}
+		t->firing = 1;
+		list_move_tail(&t->entry, firing);
+	}
+
+	++timers;
+	sched_expires = 0;
+	while (!list_empty(timers)) {
+		struct cpu_timer_list *t = list_entry(timers->next,
+						      struct cpu_timer_list,
+						      entry);
+		if (sched_time < t->expires.sched) {
+			sched_expires = t->expires.sched;
+			break;
+		}
+		t->firing = 1;
+		list_move_tail(&t->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(virt_expires, cputime_zero) ||
+	    sched_expires != 0) {
+		/*
+		 * Rebalance the threads' expiry times for the remaining
+		 * process CPU timers.
+		 */
+
+		cputime_t prof_left, virt_left, ticks;
+		unsigned long long sched_left, sched;
+		const unsigned int nthreads = atomic_read(&sig->live);
+
+		prof_left = cputime_sub(prof_expires, utime);
+		prof_left = cputime_sub(prof_left, stime);
+		prof_left = cputime_div(prof_left, nthreads);
+		virt_left = cputime_sub(virt_expires, utime);
+		virt_left = cputime_div(virt_left, nthreads);
+		if (sched_expires) {
+			sched_left = sched_expires - sched_time;
+			do_div(sched_left, nthreads);
+		} else {
+			sched_left = 0;
+		}
+		t = tsk;
+		do {
+			ticks = cputime_add(cputime_add(t->utime, t->stime),
+					    prof_left);
+			if (!cputime_eq(prof_expires, cputime_zero) &&
+			    (cputime_eq(t->it_prof_expires, cputime_zero) ||
+			     cputime_gt(t->it_prof_expires, ticks))) {
+				t->it_prof_expires = ticks;
+			}
+
+			ticks = cputime_add(t->utime, virt_left);
+			if (!cputime_eq(virt_expires, cputime_zero) &&
+			    (cputime_eq(t->it_virt_expires, cputime_zero) ||
+			     cputime_gt(t->it_virt_expires, ticks))) {
+				t->it_virt_expires = ticks;
+			}
+
+			sched = t->sched_time + sched_left;
+			if (sched_expires && (t->it_sched_expires == 0 ||
+					      t->it_sched_expires > sched)) {
+				t->it_sched_expires = sched;
+			}
+
+			do {
+				t = next_thread(t);
+			} while (unlikely(t->exit_state));
+		} while (t != tsk);
+	}
+}
+
+/*
+ * 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.
+		 */
+		return;
+
+	/*
+	 * 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);
+			return;
+		}
+		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;
+			read_unlock(&tasklist_lock);
+			return;
+		} 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);
+			read_unlock(&tasklist_lock);
+			return;
+		}
+		cpu_clock_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);
+
+	read_unlock(&tasklist_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(struct task_struct *tsk)
+{
+	LIST_HEAD(firing);
+	struct k_itimer *timer, *next;
+
+	BUG_ON(!irqs_disabled());
+
+#define UNEXPIRED(clock) \
+		(cputime_eq(tsk->it_##clock##_expires, cputime_zero) || \
+		 cputime_lt(clock##_ticks(tsk), tsk->it_##clock##_expires))
+
+	if (UNEXPIRED(prof) && UNEXPIRED(virt) &&
+	    (tsk->it_sched_expires == 0 ||
+	     tsk->sched_time < tsk->it_sched_expires))
+		return;
+
+#undef	UNEXPIRED
+
+	BUG_ON(tsk->exit_state);
+
+	/*
+	 * Double-check with locks held.
+	 */
+	read_lock(&tasklist_lock);
+	spin_lock(&tsk->sighand->siglock);
+
+	/*
+	 * Here we take off tsk->cpu_timers[N] and tsk->signal->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);
+	read_unlock(&tasklist_lock);
+
+	/*
+	 * 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 firing;
+		spin_lock(&timer->it_lock);
+		list_del_init(&timer->it.cpu.entry);
+		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(firing >= 0)) {
+			cpu_timer_fire(timer);
+		}
+		spin_unlock(&timer->it_lock);
+	}
+}
+
+/*
+ * Set one of the process-wide special case CPU timers.
+ * The tasklist_lock and tsk->sighand->siglock must be held by the caller.
+ * The oldval argument is null for the RLIMIT_CPU timer, where *newval is
+ * absolute; non-null for ITIMER_*, where *newval 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_clock_sample_group_locked(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_entry(head->next,
+				  struct cpu_timer_list, entry)->expires.cpu,
+		       *newval)) {
+		/*
+		 * Rejigger each thread's expiry time so that one will
+		 * notice before we hit the process-cumulative expiry time.
+		 */
+		union cpu_time_count expires = { .sched = 0 };
+		expires.cpu = *newval;
+		process_timer_rebalance(tsk, clock_idx, expires, now);
+	}
+}
+
+static long posix_cpu_clock_nanosleep_restart(struct restart_block *);
+
+int posix_cpu_nsleep(clockid_t which_clock, int flags,
+		     struct timespec *rqtp)
+{
+	struct restart_block *restart_block =
+	    &current_thread_info()->restart_block;
+	struct k_itimer timer;
+	int error;
+
+	/*
+	 * Diagnose required errors first.
+	 */
+	if (CPUCLOCK_PERTHREAD(which_clock) &&
+	    (CPUCLOCK_PID(which_clock) == 0 ||
+	     CPUCLOCK_PID(which_clock) == current->pid))
+		return -EINVAL;
+
+	/*
+	 * 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) {
+		struct timespec __user *rmtp;
+		static struct itimerspec zero_it;
+		struct itimerspec it = { .it_value = *rqtp,
+					 .it_interval = {} };
+
+		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;
+		}
+
+		/*
+		 * Report back to the user the time still remaining.
+		 */
+		rmtp = (struct timespec __user *) restart_block->arg1;
+		if (rmtp != NULL && !(flags & TIMER_ABSTIME) &&
+		    copy_to_user(rmtp, &it.it_value, sizeof *rmtp))
+			return -EFAULT;
+
+		restart_block->fn = posix_cpu_clock_nanosleep_restart;
+		/* Caller already set restart_block->arg1 */
+		restart_block->arg0 = which_clock;
+		restart_block->arg2 = rqtp->tv_sec;
+		restart_block->arg3 = rqtp->tv_nsec;
+
+		error = -ERESTART_RESTARTBLOCK;
+	}
+
+	return error;
+}
+
+static long
+posix_cpu_clock_nanosleep_restart(struct restart_block *restart_block)
+{
+	clockid_t which_clock = restart_block->arg0;
+	struct timespec t = { .tv_sec = restart_block->arg2,
+			      .tv_nsec = restart_block->arg3 };
+	restart_block->fn = do_no_restart_syscall;
+	return posix_cpu_nsleep(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(clockid_t which_clock, struct timespec *tp)
+{
+	return posix_cpu_clock_getres(PROCESS_CLOCK, tp);
+}
+static int process_cpu_clock_get(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(clockid_t which_clock, int flags,
+			      struct timespec *rqtp)
+{
+	return posix_cpu_nsleep(PROCESS_CLOCK, flags, rqtp);
+}
+static int thread_cpu_clock_getres(clockid_t which_clock, struct timespec *tp)
+{
+	return posix_cpu_clock_getres(THREAD_CLOCK, tp);
+}
+static int thread_cpu_clock_get(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(clockid_t which_clock, int flags,
+			      struct timespec *rqtp)
+{
+	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,
+	};
+	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,
+	};
+
+	register_posix_clock(CLOCK_PROCESS_CPUTIME_ID, &process);
+	register_posix_clock(CLOCK_THREAD_CPUTIME_ID, &thread);
+
+	return 0;
+}
+__initcall(init_posix_cpu_timers);