diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
new file mode 100644
index 0000000..ce32cf7
--- /dev/null
+++ b/kernel/time/posix-cpu-timers.c
@@ -0,0 +1,1445 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Implement CPU time clocks for the POSIX clock interface.
+ */
+
+#include <linux/sched/signal.h>
+#include <linux/sched/cputime.h>
+#include <linux/posix-timers.h>
+#include <linux/errno.h>
+#include <linux/math64.h>
+#include <linux/uaccess.h>
+#include <linux/kernel_stat.h>
+#include <trace/events/timer.h>
+#include <linux/tick.h>
+#include <linux/workqueue.h>
+#include <linux/compat.h>
+#include <linux/sched/deadline.h>
+
+#include "posix-timers.h"
+
+static void posix_cpu_timer_rearm(struct k_itimer *timer);
+
+/*
+ * Called after updating RLIMIT_CPU to run cpu timer and update
+ * tsk->signal->cputime_expires expiration cache if necessary. Needs
+ * siglock protection since other code may update expiration cache as
+ * well.
+ */
+void update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new)
+{
+	u64 nsecs = rlim_new * NSEC_PER_SEC;
+
+	spin_lock_irq(&task->sighand->siglock);
+	set_process_cpu_timer(task, CPUCLOCK_PROF, &nsecs, NULL);
+	spin_unlock_irq(&task->sighand->siglock);
+}
+
+static int check_clock(const clockid_t which_clock)
+{
+	int error = 0;
+	struct task_struct *p;
+	const pid_t pid = CPUCLOCK_PID(which_clock);
+
+	if (CPUCLOCK_WHICH(which_clock) >= CPUCLOCK_MAX)
+		return -EINVAL;
+
+	if (pid == 0)
+		return 0;
+
+	rcu_read_lock();
+	p = find_task_by_vpid(pid);
+	if (!p || !(CPUCLOCK_PERTHREAD(which_clock) ?
+		   same_thread_group(p, current) : has_group_leader_pid(p))) {
+		error = -EINVAL;
+	}
+	rcu_read_unlock();
+
+	return error;
+}
+
+/*
+ * Update expiry time from increment, and increase overrun count,
+ * given the current clock sample.
+ */
+static void bump_cpu_timer(struct k_itimer *timer, u64 now)
+{
+	int i;
+	u64 delta, incr;
+
+	if (timer->it.cpu.incr == 0)
+		return;
+
+	if (now < timer->it.cpu.expires)
+		return;
+
+	incr = timer->it.cpu.incr;
+	delta = now + incr - timer->it.cpu.expires;
+
+	/* Don't use (incr*2 < delta), incr*2 might overflow. */
+	for (i = 0; incr < delta - incr; i++)
+		incr = incr << 1;
+
+	for (; i >= 0; incr >>= 1, i--) {
+		if (delta < incr)
+			continue;
+
+		timer->it.cpu.expires += incr;
+		timer->it_overrun += 1LL << i;
+		delta -= incr;
+	}
+}
+
+/**
+ * task_cputime_zero - Check a task_cputime struct for all zero fields.
+ *
+ * @cputime:	The struct to compare.
+ *
+ * Checks @cputime to see if all fields are zero.  Returns true if all fields
+ * are zero, false if any field is nonzero.
+ */
+static inline int task_cputime_zero(const struct task_cputime *cputime)
+{
+	if (!cputime->utime && !cputime->stime && !cputime->sum_exec_runtime)
+		return 1;
+	return 0;
+}
+
+static inline u64 prof_ticks(struct task_struct *p)
+{
+	u64 utime, stime;
+
+	task_cputime(p, &utime, &stime);
+
+	return utime + stime;
+}
+static inline u64 virt_ticks(struct task_struct *p)
+{
+	u64 utime, stime;
+
+	task_cputime(p, &utime, &stime);
+
+	return utime;
+}
+
+static int
+posix_cpu_clock_getres(const clockid_t which_clock, struct timespec64 *tp)
+{
+	int error = check_clock(which_clock);
+	if (!error) {
+		tp->tv_sec = 0;
+		tp->tv_nsec = ((NSEC_PER_SEC + HZ - 1) / HZ);
+		if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
+			/*
+			 * If sched_clock is using a cycle counter, we
+			 * don't have any idea of its true resolution
+			 * exported, but it is much more than 1s/HZ.
+			 */
+			tp->tv_nsec = 1;
+		}
+	}
+	return error;
+}
+
+static int
+posix_cpu_clock_set(const clockid_t which_clock, const struct timespec64 *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, u64 *sample)
+{
+	switch (CPUCLOCK_WHICH(which_clock)) {
+	default:
+		return -EINVAL;
+	case CPUCLOCK_PROF:
+		*sample = prof_ticks(p);
+		break;
+	case CPUCLOCK_VIRT:
+		*sample = virt_ticks(p);
+		break;
+	case CPUCLOCK_SCHED:
+		*sample = task_sched_runtime(p);
+		break;
+	}
+	return 0;
+}
+
+/*
+ * Set cputime to sum_cputime if sum_cputime > cputime. Use cmpxchg
+ * to avoid race conditions with concurrent updates to cputime.
+ */
+static inline void __update_gt_cputime(atomic64_t *cputime, u64 sum_cputime)
+{
+	u64 curr_cputime;
+retry:
+	curr_cputime = atomic64_read(cputime);
+	if (sum_cputime > curr_cputime) {
+		if (atomic64_cmpxchg(cputime, curr_cputime, sum_cputime) != curr_cputime)
+			goto retry;
+	}
+}
+
+static void update_gt_cputime(struct task_cputime_atomic *cputime_atomic, struct task_cputime *sum)
+{
+	__update_gt_cputime(&cputime_atomic->utime, sum->utime);
+	__update_gt_cputime(&cputime_atomic->stime, sum->stime);
+	__update_gt_cputime(&cputime_atomic->sum_exec_runtime, sum->sum_exec_runtime);
+}
+
+/* Sample task_cputime_atomic values in "atomic_timers", store results in "times". */
+static inline void sample_cputime_atomic(struct task_cputime *times,
+					 struct task_cputime_atomic *atomic_times)
+{
+	times->utime = atomic64_read(&atomic_times->utime);
+	times->stime = atomic64_read(&atomic_times->stime);
+	times->sum_exec_runtime = atomic64_read(&atomic_times->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;
+
+	/* Check if cputimer isn't running. This is accessed without locking. */
+	if (!READ_ONCE(cputimer->running)) {
+		/*
+		 * The POSIX timer interface allows for absolute time expiry
+		 * values through the TIMER_ABSTIME flag, therefore we have
+		 * to synchronize the timer to the clock every time we start it.
+		 */
+		thread_group_cputime(tsk, &sum);
+		update_gt_cputime(&cputimer->cputime_atomic, &sum);
+
+		/*
+		 * We're setting cputimer->running without a lock. Ensure
+		 * this only gets written to in one operation. We set
+		 * running after update_gt_cputime() as a small optimization,
+		 * but barriers are not required because update_gt_cputime()
+		 * can handle concurrent updates.
+		 */
+		WRITE_ONCE(cputimer->running, true);
+	}
+	sample_cputime_atomic(times, &cputimer->cputime_atomic);
+}
+
+/*
+ * Sample a process (thread group) clock for the given group_leader task.
+ * Must be called with task sighand lock held for safe while_each_thread()
+ * traversal.
+ */
+static int cpu_clock_sample_group(const clockid_t which_clock,
+				  struct task_struct *p,
+				  u64 *sample)
+{
+	struct task_cputime cputime;
+
+	switch (CPUCLOCK_WHICH(which_clock)) {
+	default:
+		return -EINVAL;
+	case CPUCLOCK_PROF:
+		thread_group_cputime(p, &cputime);
+		*sample = cputime.utime + cputime.stime;
+		break;
+	case CPUCLOCK_VIRT:
+		thread_group_cputime(p, &cputime);
+		*sample = cputime.utime;
+		break;
+	case CPUCLOCK_SCHED:
+		thread_group_cputime(p, &cputime);
+		*sample = cputime.sum_exec_runtime;
+		break;
+	}
+	return 0;
+}
+
+static int posix_cpu_clock_get_task(struct task_struct *tsk,
+				    const clockid_t which_clock,
+				    struct timespec64 *tp)
+{
+	int err = -EINVAL;
+	u64 rtn;
+
+	if (CPUCLOCK_PERTHREAD(which_clock)) {
+		if (same_thread_group(tsk, current))
+			err = cpu_clock_sample(which_clock, tsk, &rtn);
+	} else {
+		if (tsk == current || thread_group_leader(tsk))
+			err = cpu_clock_sample_group(which_clock, tsk, &rtn);
+	}
+
+	if (!err)
+		*tp = ns_to_timespec64(rtn);
+
+	return err;
+}
+
+
+static int posix_cpu_clock_get(const clockid_t which_clock, struct timespec64 *tp)
+{
+	const pid_t pid = CPUCLOCK_PID(which_clock);
+	int err = -EINVAL;
+
+	if (pid == 0) {
+		/*
+		 * Special case constant value for our own clocks.
+		 * We don't have to do any lookup to find ourselves.
+		 */
+		err = posix_cpu_clock_get_task(current, which_clock, tp);
+	} 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)
+			err = posix_cpu_clock_get_task(p, which_clock, tp);
+		rcu_read_unlock();
+	}
+
+	return err;
+}
+
+/*
+ * Validate the clockid_t for a new CPU-clock timer, and initialize the timer.
+ * This is called from sys_timer_create() and do_cpu_nanosleep() with the
+ * new timer already all-zeros initialized.
+ */
+static int posix_cpu_timer_create(struct k_itimer *new_timer)
+{
+	int ret = 0;
+	const pid_t pid = CPUCLOCK_PID(new_timer->it_clock);
+	struct task_struct *p;
+
+	if (CPUCLOCK_WHICH(new_timer->it_clock) >= CPUCLOCK_MAX)
+		return -EINVAL;
+
+	new_timer->kclock = &clock_posix_cpu;
+
+	INIT_LIST_HEAD(&new_timer->it.cpu.entry);
+
+	rcu_read_lock();
+	if (CPUCLOCK_PERTHREAD(new_timer->it_clock)) {
+		if (pid == 0) {
+			p = current;
+		} else {
+			p = find_task_by_vpid(pid);
+			if (p && !same_thread_group(p, current))
+				p = NULL;
+		}
+	} else {
+		if (pid == 0) {
+			p = current->group_leader;
+		} else {
+			p = find_task_by_vpid(pid);
+			if (p && !has_group_leader_pid(p))
+				p = NULL;
+		}
+	}
+	new_timer->it.cpu.task = p;
+	if (p) {
+		get_task_struct(p);
+	} else {
+		ret = -EINVAL;
+	}
+	rcu_read_unlock();
+
+	return ret;
+}
+
+/*
+ * Clean up a CPU-clock timer that is about to be destroyed.
+ * This is called from timer deletion with the timer already locked.
+ * If we return TIMER_RETRY, it's necessary to release the timer's lock
+ * and try again.  (This happens when the timer is in the middle of firing.)
+ */
+static int posix_cpu_timer_del(struct k_itimer *timer)
+{
+	int ret = 0;
+	unsigned long flags;
+	struct sighand_struct *sighand;
+	struct task_struct *p = timer->it.cpu.task;
+
+	WARN_ON_ONCE(p == NULL);
+
+	/*
+	 * Protect against sighand release/switch in exit/exec and process/
+	 * thread timer list entry concurrent read/writes.
+	 */
+	sighand = lock_task_sighand(p, &flags);
+	if (unlikely(sighand == NULL)) {
+		/*
+		 * We raced with the reaping of the task.
+		 * The deletion should have cleared us off the list.
+		 */
+		WARN_ON_ONCE(!list_empty(&timer->it.cpu.entry));
+	} else {
+		if (timer->it.cpu.firing)
+			ret = TIMER_RETRY;
+		else
+			list_del(&timer->it.cpu.entry);
+
+		unlock_task_sighand(p, &flags);
+	}
+
+	if (!ret)
+		put_task_struct(p);
+
+	return ret;
+}
+
+static void cleanup_timers_list(struct list_head *head)
+{
+	struct cpu_timer_list *timer, *next;
+
+	list_for_each_entry_safe(timer, next, head, entry)
+		list_del_init(&timer->entry);
+}
+
+/*
+ * 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)
+{
+	cleanup_timers_list(head);
+	cleanup_timers_list(++head);
+	cleanup_timers_list(++head);
+}
+
+/*
+ * 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);
+}
+void posix_cpu_timers_exit_group(struct task_struct *tsk)
+{
+	cleanup_timers(tsk->signal->cpu_timers);
+}
+
+static inline int expires_gt(u64 expires, u64 new_exp)
+{
+	return expires == 0 || expires > new_exp;
+}
+
+/*
+ * Insert the timer on the appropriate list before any timers that
+ * expire later.  This must be called with the sighand lock held.
+ */
+static void arm_timer(struct k_itimer *timer)
+{
+	struct task_struct *p = timer->it.cpu.task;
+	struct list_head *head, *listpos;
+	struct task_cputime *cputime_expires;
+	struct cpu_timer_list *const nt = &timer->it.cpu;
+	struct cpu_timer_list *next;
+
+	if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
+		head = p->cpu_timers;
+		cputime_expires = &p->cputime_expires;
+	} else {
+		head = p->signal->cpu_timers;
+		cputime_expires = &p->signal->cputime_expires;
+	}
+	head += CPUCLOCK_WHICH(timer->it_clock);
+
+	listpos = head;
+	list_for_each_entry(next, head, entry) {
+		if (nt->expires < next->expires)
+			break;
+		listpos = &next->entry;
+	}
+	list_add(&nt->entry, listpos);
+
+	if (listpos == head) {
+		u64 exp = nt->expires;
+
+		/*
+		 * We are the new earliest-expiring POSIX 1.b timer, hence
+		 * need to update expiration cache. Take into account that
+		 * for process timers we share expiration cache with itimers
+		 * and RLIMIT_CPU and for thread timers with RLIMIT_RTTIME.
+		 */
+
+		switch (CPUCLOCK_WHICH(timer->it_clock)) {
+		case CPUCLOCK_PROF:
+			if (expires_gt(cputime_expires->prof_exp, exp))
+				cputime_expires->prof_exp = exp;
+			break;
+		case CPUCLOCK_VIRT:
+			if (expires_gt(cputime_expires->virt_exp, exp))
+				cputime_expires->virt_exp = exp;
+			break;
+		case CPUCLOCK_SCHED:
+			if (expires_gt(cputime_expires->sched_exp, exp))
+				cputime_expires->sched_exp = exp;
+			break;
+		}
+		if (CPUCLOCK_PERTHREAD(timer->it_clock))
+			tick_dep_set_task(p, TICK_DEP_BIT_POSIX_TIMER);
+		else
+			tick_dep_set_signal(p->signal, TICK_DEP_BIT_POSIX_TIMER);
+	}
+}
+
+/*
+ * The timer is locked, fire it and arrange for its reload.
+ */
+static void cpu_timer_fire(struct k_itimer *timer)
+{
+	if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
+		/*
+		 * User don't want any signal.
+		 */
+		timer->it.cpu.expires = 0;
+	} else if (unlikely(timer->sigq == NULL)) {
+		/*
+		 * This a special case for clock_nanosleep,
+		 * not a normal timer from sys_timer_create.
+		 */
+		wake_up_process(timer->it_process);
+		timer->it.cpu.expires = 0;
+	} else if (timer->it.cpu.incr == 0) {
+		/*
+		 * One-shot timer.  Clear it as soon as it's fired.
+		 */
+		posix_timer_event(timer, 0);
+		timer->it.cpu.expires = 0;
+	} else if (posix_timer_event(timer, ++timer->it_requeue_pending)) {
+		/*
+		 * The signal did not get queued because the signal
+		 * was ignored, so we won't get any callback to
+		 * reload the timer.  But we need to keep it
+		 * ticking in case the signal is deliverable next time.
+		 */
+		posix_cpu_timer_rearm(timer);
+		++timer->it_requeue_pending;
+	}
+}
+
+/*
+ * Sample a process (thread group) timer for the given group_leader task.
+ * Must be called with task sighand lock held for safe while_each_thread()
+ * traversal.
+ */
+static int cpu_timer_sample_group(const clockid_t which_clock,
+				  struct task_struct *p, u64 *sample)
+{
+	struct task_cputime cputime;
+
+	thread_group_cputimer(p, &cputime);
+	switch (CPUCLOCK_WHICH(which_clock)) {
+	default:
+		return -EINVAL;
+	case CPUCLOCK_PROF:
+		*sample = cputime.utime + cputime.stime;
+		break;
+	case CPUCLOCK_VIRT:
+		*sample = cputime.utime;
+		break;
+	case CPUCLOCK_SCHED:
+		*sample = cputime.sum_exec_runtime;
+		break;
+	}
+	return 0;
+}
+
+/*
+ * Guts of sys_timer_settime for CPU timers.
+ * This is called with the timer locked and interrupts disabled.
+ * If we return TIMER_RETRY, it's necessary to release the timer's lock
+ * and try again.  (This happens when the timer is in the middle of firing.)
+ */
+static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
+			       struct itimerspec64 *new, struct itimerspec64 *old)
+{
+	unsigned long flags;
+	struct sighand_struct *sighand;
+	struct task_struct *p = timer->it.cpu.task;
+	u64 old_expires, new_expires, old_incr, val;
+	int ret;
+
+	WARN_ON_ONCE(p == NULL);
+
+	/*
+	 * Use the to_ktime conversion because that clamps the maximum
+	 * value to KTIME_MAX and avoid multiplication overflows.
+	 */
+	new_expires = ktime_to_ns(timespec64_to_ktime(new->it_value));
+
+	/*
+	 * Protect against sighand release/switch in exit/exec and p->cpu_timers
+	 * and p->signal->cpu_timers read/write in arm_timer()
+	 */
+	sighand = lock_task_sighand(p, &flags);
+	/*
+	 * If p has just been reaped, we can no
+	 * longer get any information about it at all.
+	 */
+	if (unlikely(sighand == NULL)) {
+		return -ESRCH;
+	}
+
+	/*
+	 * Disarm any old timer after extracting its expiry time.
+	 */
+
+	ret = 0;
+	old_incr = timer->it.cpu.incr;
+	old_expires = timer->it.cpu.expires;
+	if (unlikely(timer->it.cpu.firing)) {
+		timer->it.cpu.firing = -1;
+		ret = TIMER_RETRY;
+	} else
+		list_del_init(&timer->it.cpu.entry);
+
+	/*
+	 * We need to sample the current value to convert the new
+	 * value from to relative and absolute, and to convert the
+	 * old value from absolute to relative.  To set a process
+	 * timer, we need a sample to balance the thread expiry
+	 * times (in arm_timer).  With an absolute time, we must
+	 * check if it's already passed.  In short, we need a sample.
+	 */
+	if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
+		cpu_clock_sample(timer->it_clock, p, &val);
+	} else {
+		cpu_timer_sample_group(timer->it_clock, p, &val);
+	}
+
+	if (old) {
+		if (old_expires == 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 (val < timer->it.cpu.expires) {
+				old_expires = timer->it.cpu.expires - val;
+				old->it_value = ns_to_timespec64(old_expires);
+			} else {
+				old->it_value.tv_nsec = 1;
+				old->it_value.tv_sec = 0;
+			}
+		}
+	}
+
+	if (unlikely(ret)) {
+		/*
+		 * We are colliding with the timer actually firing.
+		 * Punt after filling in the timer's old value, and
+		 * disable this firing since we are already reporting
+		 * it as an overrun (thanks to bump_cpu_timer above).
+		 */
+		unlock_task_sighand(p, &flags);
+		goto out;
+	}
+
+	if (new_expires != 0 && !(timer_flags & TIMER_ABSTIME)) {
+		new_expires += val;
+	}
+
+	/*
+	 * Install the new expiry time (or zero).
+	 * For a timer with no notification action, we don't actually
+	 * arm the timer (we'll just fake it for timer_gettime).
+	 */
+	timer->it.cpu.expires = new_expires;
+	if (new_expires != 0 && val < new_expires) {
+		arm_timer(timer);
+	}
+
+	unlock_task_sighand(p, &flags);
+	/*
+	 * Install the new reload setting, and
+	 * set up the signal and overrun bookkeeping.
+	 */
+	timer->it.cpu.incr = timespec64_to_ns(&new->it_interval);
+
+	/*
+	 * This acts as a modification timestamp for the timer,
+	 * so any automatic reload attempt will punt on seeing
+	 * that we have reset the timer manually.
+	 */
+	timer->it_requeue_pending = (timer->it_requeue_pending + 2) &
+		~REQUEUE_PENDING;
+	timer->it_overrun_last = 0;
+	timer->it_overrun = -1;
+
+	if (new_expires != 0 && !(val < new_expires)) {
+		/*
+		 * The designated time already passed, so we notify
+		 * immediately, even if the thread never runs to
+		 * accumulate more time on this clock.
+		 */
+		cpu_timer_fire(timer);
+	}
+
+	ret = 0;
+ out:
+	if (old)
+		old->it_interval = ns_to_timespec64(old_incr);
+
+	return ret;
+}
+
+static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp)
+{
+	u64 now;
+	struct task_struct *p = timer->it.cpu.task;
+
+	WARN_ON_ONCE(p == NULL);
+
+	/*
+	 * Easy part: convert the reload time.
+	 */
+	itp->it_interval = ns_to_timespec64(timer->it.cpu.incr);
+
+	if (!timer->it.cpu.expires)
+		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);
+	} else {
+		struct sighand_struct *sighand;
+		unsigned long flags;
+
+		/*
+		 * Protect against sighand release/switch in exit/exec and
+		 * also make timer sampling safe if it ends up calling
+		 * thread_group_cputime().
+		 */
+		sighand = lock_task_sighand(p, &flags);
+		if (unlikely(sighand == NULL)) {
+			/*
+			 * The process has been reaped.
+			 * We can't even collect a sample any more.
+			 * Call the timer disarmed, nothing else to do.
+			 */
+			timer->it.cpu.expires = 0;
+			return;
+		} else {
+			cpu_timer_sample_group(timer->it_clock, p, &now);
+			unlock_task_sighand(p, &flags);
+		}
+	}
+
+	if (now < timer->it.cpu.expires) {
+		itp->it_value = ns_to_timespec64(timer->it.cpu.expires - now);
+	} else {
+		/*
+		 * The timer should have expired already, but the firing
+		 * hasn't taken place yet.  Say it's just about to expire.
+		 */
+		itp->it_value.tv_nsec = 1;
+		itp->it_value.tv_sec = 0;
+	}
+}
+
+static unsigned long long
+check_timers_list(struct list_head *timers,
+		  struct list_head *firing,
+		  unsigned long long curr)
+{
+	int maxfire = 20;
+
+	while (!list_empty(timers)) {
+		struct cpu_timer_list *t;
+
+		t = list_first_entry(timers, struct cpu_timer_list, entry);
+
+		if (!--maxfire || curr < t->expires)
+			return t->expires;
+
+		t->firing = 1;
+		list_move_tail(&t->entry, firing);
+	}
+
+	return 0;
+}
+
+static inline void check_dl_overrun(struct task_struct *tsk)
+{
+	if (tsk->dl.dl_overrun) {
+		tsk->dl.dl_overrun = 0;
+		__group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
+	}
+}
+
+/*
+ * 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;
+	struct task_cputime *tsk_expires = &tsk->cputime_expires;
+	u64 expires;
+	unsigned long soft;
+
+	if (dl_task(tsk))
+		check_dl_overrun(tsk);
+
+	/*
+	 * If cputime_expires is zero, then there are no active
+	 * per thread CPU timers.
+	 */
+	if (task_cputime_zero(&tsk->cputime_expires))
+		return;
+
+	expires = check_timers_list(timers, firing, prof_ticks(tsk));
+	tsk_expires->prof_exp = expires;
+
+	expires = check_timers_list(++timers, firing, virt_ticks(tsk));
+	tsk_expires->virt_exp = expires;
+
+	tsk_expires->sched_exp = check_timers_list(++timers, firing,
+						   tsk->se.sum_exec_runtime);
+
+	/*
+	 * Check for the special case thread timers.
+	 */
+	soft = task_rlimit(tsk, RLIMIT_RTTIME);
+	if (soft != RLIM_INFINITY) {
+		unsigned long hard = task_rlimit_max(tsk, RLIMIT_RTTIME);
+
+		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.
+			 */
+			if (print_fatal_signals) {
+				pr_info("CPU Watchdog Timeout (hard): %s[%d]\n",
+					tsk->comm, task_pid_nr(tsk));
+			}
+			__group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
+			return;
+		}
+		if (tsk->rt.timeout > DIV_ROUND_UP(soft, USEC_PER_SEC/HZ)) {
+			/*
+			 * At the soft limit, send a SIGXCPU every second.
+			 */
+			if (soft < hard) {
+				soft += USEC_PER_SEC;
+				tsk->signal->rlim[RLIMIT_RTTIME].rlim_cur =
+					soft;
+			}
+			if (print_fatal_signals) {
+				pr_info("RT Watchdog Timeout (soft): %s[%d]\n",
+					tsk->comm, task_pid_nr(tsk));
+			}
+			__group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
+		}
+	}
+	if (task_cputime_zero(tsk_expires))
+		tick_dep_clear_task(tsk, TICK_DEP_BIT_POSIX_TIMER);
+}
+
+static inline void stop_process_timers(struct signal_struct *sig)
+{
+	struct thread_group_cputimer *cputimer = &sig->cputimer;
+
+	/* Turn off cputimer->running. This is done without locking. */
+	WRITE_ONCE(cputimer->running, false);
+	tick_dep_clear_signal(sig, TICK_DEP_BIT_POSIX_TIMER);
+}
+
+static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
+			     u64 *expires, u64 cur_time, int signo)
+{
+	if (!it->expires)
+		return;
+
+	if (cur_time >= it->expires) {
+		if (it->incr)
+			it->expires += it->incr;
+		else
+			it->expires = 0;
+
+		trace_itimer_expire(signo == SIGPROF ?
+				    ITIMER_PROF : ITIMER_VIRTUAL,
+				    task_tgid(tsk), cur_time);
+		__group_send_sig_info(signo, SEND_SIG_PRIV, tsk);
+	}
+
+	if (it->expires && (!*expires || it->expires < *expires))
+		*expires = it->expires;
+}
+
+/*
+ * Check for any per-thread CPU timers that have fired and move them
+ * off the tsk->*_timers list onto the firing list.  Per-thread timers
+ * have already been taken off.
+ */
+static void check_process_timers(struct task_struct *tsk,
+				 struct list_head *firing)
+{
+	struct signal_struct *const sig = tsk->signal;
+	u64 utime, ptime, virt_expires, prof_expires;
+	u64 sum_sched_runtime, sched_expires;
+	struct list_head *timers = sig->cpu_timers;
+	struct task_cputime cputime;
+	unsigned long soft;
+
+	if (dl_task(tsk))
+		check_dl_overrun(tsk);
+
+	/*
+	 * If cputimer is not running, then there are no active
+	 * process wide timers (POSIX 1.b, itimers, RLIMIT_CPU).
+	 */
+	if (!READ_ONCE(tsk->signal->cputimer.running))
+		return;
+
+        /*
+	 * Signify that a thread is checking for process timers.
+	 * Write access to this field is protected by the sighand lock.
+	 */
+	sig->cputimer.checking_timer = true;
+
+	/*
+	 * Collect the current process totals.
+	 */
+	thread_group_cputimer(tsk, &cputime);
+	utime = cputime.utime;
+	ptime = utime + cputime.stime;
+	sum_sched_runtime = cputime.sum_exec_runtime;
+
+	prof_expires = check_timers_list(timers, firing, ptime);
+	virt_expires = check_timers_list(++timers, firing, utime);
+	sched_expires = check_timers_list(++timers, firing, sum_sched_runtime);
+
+	/*
+	 * Check for the special case process timers.
+	 */
+	check_cpu_itimer(tsk, &sig->it[CPUCLOCK_PROF], &prof_expires, ptime,
+			 SIGPROF);
+	check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT], &virt_expires, utime,
+			 SIGVTALRM);
+	soft = task_rlimit(tsk, RLIMIT_CPU);
+	if (soft != RLIM_INFINITY) {
+		unsigned long psecs = div_u64(ptime, NSEC_PER_SEC);
+		unsigned long hard = task_rlimit_max(tsk, RLIMIT_CPU);
+		u64 x;
+		if (psecs >= hard) {
+			/*
+			 * At the hard limit, we just die.
+			 * No need to calculate anything else now.
+			 */
+			if (print_fatal_signals) {
+				pr_info("RT Watchdog Timeout (hard): %s[%d]\n",
+					tsk->comm, task_pid_nr(tsk));
+			}
+			__group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
+			return;
+		}
+		if (psecs >= soft) {
+			/*
+			 * At the soft limit, send a SIGXCPU every second.
+			 */
+			if (print_fatal_signals) {
+				pr_info("CPU Watchdog Timeout (soft): %s[%d]\n",
+					tsk->comm, task_pid_nr(tsk));
+			}
+			__group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
+			if (soft < hard) {
+				soft++;
+				sig->rlim[RLIMIT_CPU].rlim_cur = soft;
+			}
+		}
+		x = soft * NSEC_PER_SEC;
+		if (!prof_expires || x < prof_expires)
+			prof_expires = x;
+	}
+
+	sig->cputime_expires.prof_exp = prof_expires;
+	sig->cputime_expires.virt_exp = virt_expires;
+	sig->cputime_expires.sched_exp = sched_expires;
+	if (task_cputime_zero(&sig->cputime_expires))
+		stop_process_timers(sig);
+
+	sig->cputimer.checking_timer = false;
+}
+
+/*
+ * This is called from the signal code (via posixtimer_rearm)
+ * when the last timer signal was delivered and we have to reload the timer.
+ */
+static void posix_cpu_timer_rearm(struct k_itimer *timer)
+{
+	struct sighand_struct *sighand;
+	unsigned long flags;
+	struct task_struct *p = timer->it.cpu.task;
+	u64 now;
+
+	WARN_ON_ONCE(p == NULL);
+
+	/*
+	 * 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))
+			return;
+
+		/* Protect timer list r/w in arm_timer() */
+		sighand = lock_task_sighand(p, &flags);
+		if (!sighand)
+			return;
+	} else {
+		/*
+		 * Protect arm_timer() and timer sampling in case of call to
+		 * thread_group_cputime().
+		 */
+		sighand = lock_task_sighand(p, &flags);
+		if (unlikely(sighand == NULL)) {
+			/*
+			 * The process has been reaped.
+			 * We can't even collect a sample any more.
+			 */
+			timer->it.cpu.expires = 0;
+			return;
+		} else if (unlikely(p->exit_state) && thread_group_empty(p)) {
+			/* If the process is dying, no need to rearm */
+			goto unlock;
+		}
+		cpu_timer_sample_group(timer->it_clock, p, &now);
+		bump_cpu_timer(timer, now);
+		/* Leave the sighand locked for the call below.  */
+	}
+
+	/*
+	 * Now re-arm for the new expiry time.
+	 */
+	arm_timer(timer);
+unlock:
+	unlock_task_sighand(p, &flags);
+}
+
+/**
+ * task_cputime_expired - Compare two task_cputime entities.
+ *
+ * @sample:	The task_cputime structure to be checked for expiration.
+ * @expires:	Expiration times, against which @sample will be checked.
+ *
+ * Checks @sample against @expires to see if any field of @sample has expired.
+ * Returns true if any field of the former is greater than the corresponding
+ * field of the latter if the latter field is set.  Otherwise returns false.
+ */
+static inline int task_cputime_expired(const struct task_cputime *sample,
+					const struct task_cputime *expires)
+{
+	if (expires->utime && sample->utime >= expires->utime)
+		return 1;
+	if (expires->stime && sample->utime + sample->stime >= expires->stime)
+		return 1;
+	if (expires->sum_exec_runtime != 0 &&
+	    sample->sum_exec_runtime >= expires->sum_exec_runtime)
+		return 1;
+	return 0;
+}
+
+/**
+ * fastpath_timer_check - POSIX CPU timers fast path.
+ *
+ * @tsk:	The task (thread) being checked.
+ *
+ * Check the task and thread group timers.  If both are zero (there are no
+ * timers set) return false.  Otherwise snapshot the task and thread group
+ * timers and compare them with the corresponding expiration times.  Return
+ * true if a timer has expired, else return false.
+ */
+static inline int fastpath_timer_check(struct task_struct *tsk)
+{
+	struct signal_struct *sig;
+
+	if (!task_cputime_zero(&tsk->cputime_expires)) {
+		struct task_cputime task_sample;
+
+		task_cputime(tsk, &task_sample.utime, &task_sample.stime);
+		task_sample.sum_exec_runtime = tsk->se.sum_exec_runtime;
+		if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
+			return 1;
+	}
+
+	sig = tsk->signal;
+	/*
+	 * Check if thread group timers expired when the cputimer is
+	 * running and no other thread in the group is already checking
+	 * for thread group cputimers. These fields are read without the
+	 * sighand lock. However, this is fine because this is meant to
+	 * be a fastpath heuristic to determine whether we should try to
+	 * acquire the sighand lock to check/handle timers.
+	 *
+	 * In the worst case scenario, if 'running' or 'checking_timer' gets
+	 * set but the current thread doesn't see the change yet, we'll wait
+	 * until the next thread in the group gets a scheduler interrupt to
+	 * handle the timer. This isn't an issue in practice because these
+	 * types of delays with signals actually getting sent are expected.
+	 */
+	if (READ_ONCE(sig->cputimer.running) &&
+	    !READ_ONCE(sig->cputimer.checking_timer)) {
+		struct task_cputime group_sample;
+
+		sample_cputime_atomic(&group_sample, &sig->cputimer.cputime_atomic);
+
+		if (task_cputime_expired(&group_sample, &sig->cputime_expires))
+			return 1;
+	}
+
+	if (dl_task(tsk) && tsk->dl.dl_overrun)
+		return 1;
+
+	return 0;
+}
+
+/*
+ * This is called from the timer interrupt handler.  The irq handler has
+ * already updated our counts.  We need to check if any timers fire now.
+ * Interrupts are disabled.
+ */
+void run_posix_cpu_timers(struct task_struct *tsk)
+{
+	LIST_HEAD(firing);
+	struct k_itimer *timer, *next;
+	unsigned long flags;
+
+	lockdep_assert_irqs_disabled();
+
+	/*
+	 * The fast path checks that there are no expired thread or thread
+	 * group timers.  If that's so, just return.
+	 */
+	if (!fastpath_timer_check(tsk))
+		return;
+
+	if (!lock_task_sighand(tsk, &flags))
+		return;
+	/*
+	 * Here we take off tsk->signal->cpu_timers[N] and
+	 * tsk->cpu_timers[N] all the timers that are firing, and
+	 * put them on the firing list.
+	 */
+	check_thread_timers(tsk, &firing);
+
+	check_process_timers(tsk, &firing);
+
+	/*
+	 * We must release these locks before taking any timer's lock.
+	 * There is a potential race with timer deletion here, as the
+	 * siglock now protects our private firing list.  We have set
+	 * the firing flag in each timer, so that a deletion attempt
+	 * that gets the timer lock before we do will give it up and
+	 * spin until we've taken care of that timer below.
+	 */
+	unlock_task_sighand(tsk, &flags);
+
+	/*
+	 * Now that all the timers on our list have the firing flag,
+	 * no one will touch their list entries but us.  We'll take
+	 * each timer's lock before clearing its firing flag, so no
+	 * timer call will interfere.
+	 */
+	list_for_each_entry_safe(timer, next, &firing, it.cpu.entry) {
+		int cpu_firing;
+
+		spin_lock(&timer->it_lock);
+		list_del_init(&timer->it.cpu.entry);
+		cpu_firing = timer->it.cpu.firing;
+		timer->it.cpu.firing = 0;
+		/*
+		 * The firing flag is -1 if we collided with a reset
+		 * of the timer, which already reported this
+		 * almost-firing as an overrun.  So don't generate an event.
+		 */
+		if (likely(cpu_firing >= 0))
+			cpu_timer_fire(timer);
+		spin_unlock(&timer->it_lock);
+	}
+}
+
+/*
+ * Set one of the process-wide special case CPU timers or RLIMIT_CPU.
+ * The tsk->sighand->siglock must be held by the caller.
+ */
+void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
+			   u64 *newval, u64 *oldval)
+{
+	u64 now;
+	int ret;
+
+	WARN_ON_ONCE(clock_idx == CPUCLOCK_SCHED);
+	ret = cpu_timer_sample_group(clock_idx, tsk, &now);
+
+	if (oldval && ret != -EINVAL) {
+		/*
+		 * We are setting itimer. The *oldval is absolute and we update
+		 * it to be relative, *newval argument is relative and we update
+		 * it to be absolute.
+		 */
+		if (*oldval) {
+			if (*oldval <= now) {
+				/* Just about to fire. */
+				*oldval = TICK_NSEC;
+			} else {
+				*oldval -= now;
+			}
+		}
+
+		if (!*newval)
+			return;
+		*newval += now;
+	}
+
+	/*
+	 * Update expiration cache if we are the earliest timer, or eventually
+	 * RLIMIT_CPU limit is earlier than prof_exp cpu timer expire.
+	 */
+	switch (clock_idx) {
+	case CPUCLOCK_PROF:
+		if (expires_gt(tsk->signal->cputime_expires.prof_exp, *newval))
+			tsk->signal->cputime_expires.prof_exp = *newval;
+		break;
+	case CPUCLOCK_VIRT:
+		if (expires_gt(tsk->signal->cputime_expires.virt_exp, *newval))
+			tsk->signal->cputime_expires.virt_exp = *newval;
+		break;
+	}
+
+	tick_dep_set_signal(tsk->signal, TICK_DEP_BIT_POSIX_TIMER);
+}
+
+static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
+			    const struct timespec64 *rqtp)
+{
+	struct itimerspec64 it;
+	struct k_itimer timer;
+	u64 expires;
+	int error;
+
+	/*
+	 * Set up a temporary timer and then wait for it to go off.
+	 */
+	memset(&timer, 0, sizeof timer);
+	spin_lock_init(&timer.it_lock);
+	timer.it_clock = which_clock;
+	timer.it_overrun = -1;
+	error = posix_cpu_timer_create(&timer);
+	timer.it_process = current;
+	if (!error) {
+		static struct itimerspec64 zero_it;
+		struct restart_block *restart;
+
+		memset(&it, 0, sizeof(it));
+		it.it_value = *rqtp;
+
+		spin_lock_irq(&timer.it_lock);
+		error = posix_cpu_timer_set(&timer, flags, &it, NULL);
+		if (error) {
+			spin_unlock_irq(&timer.it_lock);
+			return error;
+		}
+
+		while (!signal_pending(current)) {
+			if (timer.it.cpu.expires == 0) {
+				/*
+				 * Our timer fired and was reset, below
+				 * deletion can not fail.
+				 */
+				posix_cpu_timer_del(&timer);
+				spin_unlock_irq(&timer.it_lock);
+				return 0;
+			}
+
+			/*
+			 * Block until cpu_timer_fire (or a signal) wakes us.
+			 */
+			__set_current_state(TASK_INTERRUPTIBLE);
+			spin_unlock_irq(&timer.it_lock);
+			schedule();
+			spin_lock_irq(&timer.it_lock);
+		}
+
+		/*
+		 * We were interrupted by a signal.
+		 */
+		expires = timer.it.cpu.expires;
+		error = posix_cpu_timer_set(&timer, 0, &zero_it, &it);
+		if (!error) {
+			/*
+			 * Timer is now unarmed, deletion can not fail.
+			 */
+			posix_cpu_timer_del(&timer);
+		}
+		spin_unlock_irq(&timer.it_lock);
+
+		while (error == TIMER_RETRY) {
+			/*
+			 * We need to handle case when timer was or is in the
+			 * middle of firing. In other cases we already freed
+			 * resources.
+			 */
+			spin_lock_irq(&timer.it_lock);
+			error = posix_cpu_timer_del(&timer);
+			spin_unlock_irq(&timer.it_lock);
+		}
+
+		if ((it.it_value.tv_sec | it.it_value.tv_nsec) == 0) {
+			/*
+			 * It actually did fire already.
+			 */
+			return 0;
+		}
+
+		error = -ERESTART_RESTARTBLOCK;
+		/*
+		 * Report back to the user the time still remaining.
+		 */
+		restart = &current->restart_block;
+		restart->nanosleep.expires = expires;
+		if (restart->nanosleep.type != TT_NONE)
+			error = nanosleep_copyout(restart, &it.it_value);
+	}
+
+	return error;
+}
+
+static long posix_cpu_nsleep_restart(struct restart_block *restart_block);
+
+static int posix_cpu_nsleep(const clockid_t which_clock, int flags,
+			    const struct timespec64 *rqtp)
+{
+	struct restart_block *restart_block = &current->restart_block;
+	int error;
+
+	/*
+	 * Diagnose required errors first.
+	 */
+	if (CPUCLOCK_PERTHREAD(which_clock) &&
+	    (CPUCLOCK_PID(which_clock) == 0 ||
+	     CPUCLOCK_PID(which_clock) == task_pid_vnr(current)))
+		return -EINVAL;
+
+	error = do_cpu_nanosleep(which_clock, flags, rqtp);
+
+	if (error == -ERESTART_RESTARTBLOCK) {
+
+		if (flags & TIMER_ABSTIME)
+			return -ERESTARTNOHAND;
+
+		restart_block->fn = posix_cpu_nsleep_restart;
+		restart_block->nanosleep.clockid = which_clock;
+	}
+	return error;
+}
+
+static long posix_cpu_nsleep_restart(struct restart_block *restart_block)
+{
+	clockid_t which_clock = restart_block->nanosleep.clockid;
+	struct timespec64 t;
+
+	t = ns_to_timespec64(restart_block->nanosleep.expires);
+
+	return do_cpu_nanosleep(which_clock, TIMER_ABSTIME, &t);
+}
+
+#define PROCESS_CLOCK	make_process_cpuclock(0, CPUCLOCK_SCHED)
+#define THREAD_CLOCK	make_thread_cpuclock(0, CPUCLOCK_SCHED)
+
+static int process_cpu_clock_getres(const clockid_t which_clock,
+				    struct timespec64 *tp)
+{
+	return posix_cpu_clock_getres(PROCESS_CLOCK, tp);
+}
+static int process_cpu_clock_get(const clockid_t which_clock,
+				 struct timespec64 *tp)
+{
+	return posix_cpu_clock_get(PROCESS_CLOCK, tp);
+}
+static int process_cpu_timer_create(struct k_itimer *timer)
+{
+	timer->it_clock = PROCESS_CLOCK;
+	return posix_cpu_timer_create(timer);
+}
+static int process_cpu_nsleep(const clockid_t which_clock, int flags,
+			      const struct timespec64 *rqtp)
+{
+	return posix_cpu_nsleep(PROCESS_CLOCK, flags, rqtp);
+}
+static int thread_cpu_clock_getres(const clockid_t which_clock,
+				   struct timespec64 *tp)
+{
+	return posix_cpu_clock_getres(THREAD_CLOCK, tp);
+}
+static int thread_cpu_clock_get(const clockid_t which_clock,
+				struct timespec64 *tp)
+{
+	return posix_cpu_clock_get(THREAD_CLOCK, tp);
+}
+static int thread_cpu_timer_create(struct k_itimer *timer)
+{
+	timer->it_clock = THREAD_CLOCK;
+	return posix_cpu_timer_create(timer);
+}
+
+const struct k_clock clock_posix_cpu = {
+	.clock_getres	= posix_cpu_clock_getres,
+	.clock_set	= posix_cpu_clock_set,
+	.clock_get	= posix_cpu_clock_get,
+	.timer_create	= posix_cpu_timer_create,
+	.nsleep		= posix_cpu_nsleep,
+	.timer_set	= posix_cpu_timer_set,
+	.timer_del	= posix_cpu_timer_del,
+	.timer_get	= posix_cpu_timer_get,
+	.timer_rearm	= posix_cpu_timer_rearm,
+};
+
+const struct k_clock clock_process = {
+	.clock_getres	= process_cpu_clock_getres,
+	.clock_get	= process_cpu_clock_get,
+	.timer_create	= process_cpu_timer_create,
+	.nsleep		= process_cpu_nsleep,
+};
+
+const struct k_clock clock_thread = {
+	.clock_getres	= thread_cpu_clock_getres,
+	.clock_get	= thread_cpu_clock_get,
+	.timer_create	= thread_cpu_timer_create,
+};