Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1693 insertions, 0 deletions

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
new file mode 100644
index 000000000..44b25ff35
--- /dev/null
+++ b/kernel/time/posix-cpu-timers.c
@@ -0,0 +1,1693 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Implement CPU time clocks for the POSIX clock interface.
+ */
+
+#include <linux/sched/signal.h>
+#include <linux/sched/cputime.h>
+#include <linux/posix-timers.h>
+#include <linux/errno.h>
+#include <linux/math64.h>
+#include <linux/uaccess.h>
+#include <linux/kernel_stat.h>
+#include <trace/events/timer.h>
+#include <linux/tick.h>
+#include <linux/workqueue.h>
+#include <linux/compat.h>
+#include <linux/sched/deadline.h>
+#include <linux/task_work.h>
+
+#include "posix-timers.h"
+
+static void posix_cpu_timer_rearm(struct k_itimer *timer);
+
+void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit)
+{
+	posix_cputimers_init(pct);
+	if (cpu_limit != RLIM_INFINITY) {
+		pct->bases[CPUCLOCK_PROF].nextevt = cpu_limit * NSEC_PER_SEC;
+		pct->timers_active = true;
+	}
+}
+
+/*
+ * Called after updating RLIMIT_CPU to run cpu timer and update
+ * tsk->signal->posix_cputimers.bases[clock].nextevt expiration cache if
+ * necessary. Needs siglock protection since other code may update the
+ * expiration cache as well.
+ *
+ * Returns 0 on success, -ESRCH on failure.  Can fail if the task is exiting and
+ * we cannot lock_task_sighand.  Cannot fail if task is current.
+ */
+int update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new)
+{
+	u64 nsecs = rlim_new * NSEC_PER_SEC;
+	unsigned long irq_fl;
+
+	if (!lock_task_sighand(task, &irq_fl))
+		return -ESRCH;
+	set_process_cpu_timer(task, CPUCLOCK_PROF, &nsecs, NULL);
+	unlock_task_sighand(task, &irq_fl);
+	return 0;
+}
+
+/*
+ * Functions for validating access to tasks.
+ */
+static struct pid *pid_for_clock(const clockid_t clock, bool gettime)
+{
+	const bool thread = !!CPUCLOCK_PERTHREAD(clock);
+	const pid_t upid = CPUCLOCK_PID(clock);
+	struct pid *pid;
+
+	if (CPUCLOCK_WHICH(clock) >= CPUCLOCK_MAX)
+		return NULL;
+
+	/*
+	 * If the encoded PID is 0, then the timer is targeted at current
+	 * or the process to which current belongs.
+	 */
+	if (upid == 0)
+		return thread ? task_pid(current) : task_tgid(current);
+
+	pid = find_vpid(upid);
+	if (!pid)
+		return NULL;
+
+	if (thread) {
+		struct task_struct *tsk = pid_task(pid, PIDTYPE_PID);
+		return (tsk && same_thread_group(tsk, current)) ? pid : NULL;
+	}
+
+	/*
+	 * For clock_gettime(PROCESS) allow finding the process by
+	 * with the pid of the current task.  The code needs the tgid
+	 * of the process so that pid_task(pid, PIDTYPE_TGID) can be
+	 * used to find the process.
+	 */
+	if (gettime && (pid == task_pid(current)))
+		return task_tgid(current);
+
+	/*
+	 * For processes require that pid identifies a process.
+	 */
+	return pid_has_task(pid, PIDTYPE_TGID) ? pid : NULL;
+}
+
+static inline int validate_clock_permissions(const clockid_t clock)
+{
+	int ret;
+
+	rcu_read_lock();
+	ret = pid_for_clock(clock, false) ? 0 : -EINVAL;
+	rcu_read_unlock();
+
+	return ret;
+}
+
+static inline enum pid_type clock_pid_type(const clockid_t clock)
+{
+	return CPUCLOCK_PERTHREAD(clock) ? PIDTYPE_PID : PIDTYPE_TGID;
+}
+
+static inline struct task_struct *cpu_timer_task_rcu(struct k_itimer *timer)
+{
+	return pid_task(timer->it.cpu.pid, clock_pid_type(timer->it_clock));
+}
+
+/*
+ * Update expiry time from increment, and increase overrun count,
+ * given the current clock sample.
+ */
+static u64 bump_cpu_timer(struct k_itimer *timer, u64 now)
+{
+	u64 delta, incr, expires = timer->it.cpu.node.expires;
+	int i;
+
+	if (!timer->it_interval)
+		return expires;
+
+	if (now < expires)
+		return expires;
+
+	incr = timer->it_interval;
+	delta = now + incr - expires;
+
+	/* Don't use (incr*2 < delta), incr*2 might overflow. */
+	for (i = 0; incr < delta - incr; i++)
+		incr = incr << 1;
+
+	for (; i >= 0; incr >>= 1, i--) {
+		if (delta < incr)
+			continue;
+
+		timer->it.cpu.node.expires += incr;
+		timer->it_overrun += 1LL << i;
+		delta -= incr;
+	}
+	return timer->it.cpu.node.expires;
+}
+
+/* Check whether all cache entries contain U64_MAX, i.e. eternal expiry time */
+static inline bool expiry_cache_is_inactive(const struct posix_cputimers *pct)
+{
+	return !(~pct->bases[CPUCLOCK_PROF].nextevt |
+		 ~pct->bases[CPUCLOCK_VIRT].nextevt |
+		 ~pct->bases[CPUCLOCK_SCHED].nextevt);
+}
+
+static int
+posix_cpu_clock_getres(const clockid_t which_clock, struct timespec64 *tp)
+{
+	int error = validate_clock_permissions(which_clock);
+
+	if (!error) {
+		tp->tv_sec = 0;
+		tp->tv_nsec = ((NSEC_PER_SEC + HZ - 1) / HZ);
+		if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
+			/*
+			 * If sched_clock is using a cycle counter, we
+			 * don't have any idea of its true resolution
+			 * exported, but it is much more than 1s/HZ.
+			 */
+			tp->tv_nsec = 1;
+		}
+	}
+	return error;
+}
+
+static int
+posix_cpu_clock_set(const clockid_t clock, const struct timespec64 *tp)
+{
+	int error = validate_clock_permissions(clock);
+
+	/*
+	 * You can never reset a CPU clock, but we check for other errors
+	 * in the call before failing with EPERM.
+	 */
+	return error ? : -EPERM;
+}
+
+/*
+ * Sample a per-thread clock for the given task. clkid is validated.
+ */
+static u64 cpu_clock_sample(const clockid_t clkid, struct task_struct *p)
+{
+	u64 utime, stime;
+
+	if (clkid == CPUCLOCK_SCHED)
+		return task_sched_runtime(p);
+
+	task_cputime(p, &utime, &stime);
+
+	switch (clkid) {
+	case CPUCLOCK_PROF:
+		return utime + stime;
+	case CPUCLOCK_VIRT:
+		return utime;
+	default:
+		WARN_ON_ONCE(1);
+	}
+	return 0;
+}
+
+static inline void store_samples(u64 *samples, u64 stime, u64 utime, u64 rtime)
+{
+	samples[CPUCLOCK_PROF] = stime + utime;
+	samples[CPUCLOCK_VIRT] = utime;
+	samples[CPUCLOCK_SCHED] = rtime;
+}
+
+static void task_sample_cputime(struct task_struct *p, u64 *samples)
+{
+	u64 stime, utime;
+
+	task_cputime(p, &utime, &stime);
+	store_samples(samples, stime, utime, p->se.sum_exec_runtime);
+}
+
+static void proc_sample_cputime_atomic(struct task_cputime_atomic *at,
+				       u64 *samples)
+{
+	u64 stime, utime, rtime;
+
+	utime = atomic64_read(&at->utime);
+	stime = atomic64_read(&at->stime);
+	rtime = atomic64_read(&at->sum_exec_runtime);
+	store_samples(samples, stime, utime, rtime);
+}
+
+/*
+ * Set cputime to sum_cputime if sum_cputime > cputime. Use cmpxchg
+ * to avoid race conditions with concurrent updates to cputime.
+ */
+static inline void __update_gt_cputime(atomic64_t *cputime, u64 sum_cputime)
+{
+	u64 curr_cputime;
+retry:
+	curr_cputime = atomic64_read(cputime);
+	if (sum_cputime > curr_cputime) {
+		if (atomic64_cmpxchg(cputime, curr_cputime, sum_cputime) != curr_cputime)
+			goto retry;
+	}
+}
+
+static void update_gt_cputime(struct task_cputime_atomic *cputime_atomic,
+			      struct task_cputime *sum)
+{
+	__update_gt_cputime(&cputime_atomic->utime, sum->utime);
+	__update_gt_cputime(&cputime_atomic->stime, sum->stime);
+	__update_gt_cputime(&cputime_atomic->sum_exec_runtime, sum->sum_exec_runtime);
+}
+
+/**
+ * thread_group_sample_cputime - Sample cputime for a given task
+ * @tsk:	Task for which cputime needs to be started
+ * @samples:	Storage for time samples
+ *
+ * Called from sys_getitimer() to calculate the expiry time of an active
+ * timer. That means group cputime accounting is already active. Called
+ * with task sighand lock held.
+ *
+ * Updates @times with an uptodate sample of the thread group cputimes.
+ */
+void thread_group_sample_cputime(struct task_struct *tsk, u64 *samples)
+{
+	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
+	struct posix_cputimers *pct = &tsk->signal->posix_cputimers;
+
+	WARN_ON_ONCE(!pct->timers_active);
+
+	proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
+}
+
+/**
+ * thread_group_start_cputime - Start cputime and return a sample
+ * @tsk:	Task for which cputime needs to be started
+ * @samples:	Storage for time samples
+ *
+ * The thread group cputime accounting is avoided when there are no posix
+ * CPU timers armed. Before starting a timer it's required to check whether
+ * the time accounting is active. If not, a full update of the atomic
+ * accounting store needs to be done and the accounting enabled.
+ *
+ * Updates @times with an uptodate sample of the thread group cputimes.
+ */
+static void thread_group_start_cputime(struct task_struct *tsk, u64 *samples)
+{
+	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
+	struct posix_cputimers *pct = &tsk->signal->posix_cputimers;
+
+	lockdep_assert_task_sighand_held(tsk);
+
+	/* Check if cputimer isn't running. This is accessed without locking. */
+	if (!READ_ONCE(pct->timers_active)) {
+		struct task_cputime sum;
+
+		/*
+		 * The POSIX timer interface allows for absolute time expiry
+		 * values through the TIMER_ABSTIME flag, therefore we have
+		 * to synchronize the timer to the clock every time we start it.
+		 */
+		thread_group_cputime(tsk, &sum);
+		update_gt_cputime(&cputimer->cputime_atomic, &sum);
+
+		/*
+		 * We're setting timers_active without a lock. Ensure this
+		 * only gets written to in one operation. We set it after
+		 * update_gt_cputime() as a small optimization, but
+		 * barriers are not required because update_gt_cputime()
+		 * can handle concurrent updates.
+		 */
+		WRITE_ONCE(pct->timers_active, true);
+	}
+	proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
+}
+
+static void __thread_group_cputime(struct task_struct *tsk, u64 *samples)
+{
+	struct task_cputime ct;
+
+	thread_group_cputime(tsk, &ct);
+	store_samples(samples, ct.stime, ct.utime, ct.sum_exec_runtime);
+}
+
+/*
+ * Sample a process (thread group) clock for the given task clkid. If the
+ * group's cputime accounting is already enabled, read the atomic
+ * store. Otherwise a full update is required.  clkid is already validated.
+ */
+static u64 cpu_clock_sample_group(const clockid_t clkid, struct task_struct *p,
+				  bool start)
+{
+	struct thread_group_cputimer *cputimer = &p->signal->cputimer;
+	struct posix_cputimers *pct = &p->signal->posix_cputimers;
+	u64 samples[CPUCLOCK_MAX];
+
+	if (!READ_ONCE(pct->timers_active)) {
+		if (start)
+			thread_group_start_cputime(p, samples);
+		else
+			__thread_group_cputime(p, samples);
+	} else {
+		proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
+	}
+
+	return samples[clkid];
+}
+
+static int posix_cpu_clock_get(const clockid_t clock, struct timespec64 *tp)
+{
+	const clockid_t clkid = CPUCLOCK_WHICH(clock);
+	struct task_struct *tsk;
+	u64 t;
+
+	rcu_read_lock();
+	tsk = pid_task(pid_for_clock(clock, true), clock_pid_type(clock));
+	if (!tsk) {
+		rcu_read_unlock();
+		return -EINVAL;
+	}
+
+	if (CPUCLOCK_PERTHREAD(clock))
+		t = cpu_clock_sample(clkid, tsk);
+	else
+		t = cpu_clock_sample_group(clkid, tsk, false);
+	rcu_read_unlock();
+
+	*tp = ns_to_timespec64(t);
+	return 0;
+}
+
+/*
+ * Validate the clockid_t for a new CPU-clock timer, and initialize the timer.
+ * This is called from sys_timer_create() and do_cpu_nanosleep() with the
+ * new timer already all-zeros initialized.
+ */
+static int posix_cpu_timer_create(struct k_itimer *new_timer)
+{
+	static struct lock_class_key posix_cpu_timers_key;
+	struct pid *pid;
+
+	rcu_read_lock();
+	pid = pid_for_clock(new_timer->it_clock, false);
+	if (!pid) {
+		rcu_read_unlock();
+		return -EINVAL;
+	}
+
+	/*
+	 * If posix timer expiry is handled in task work context then
+	 * timer::it_lock can be taken without disabling interrupts as all
+	 * other locking happens in task context. This requires a separate
+	 * lock class key otherwise regular posix timer expiry would record
+	 * the lock class being taken in interrupt context and generate a
+	 * false positive warning.
+	 */
+	if (IS_ENABLED(CONFIG_POSIX_CPU_TIMERS_TASK_WORK))
+		lockdep_set_class(&new_timer->it_lock, &posix_cpu_timers_key);
+
+	new_timer->kclock = &clock_posix_cpu;
+	timerqueue_init(&new_timer->it.cpu.node);
+	new_timer->it.cpu.pid = get_pid(pid);
+	rcu_read_unlock();
+	return 0;
+}
+
+static struct posix_cputimer_base *timer_base(struct k_itimer *timer,
+					      struct task_struct *tsk)
+{
+	int clkidx = CPUCLOCK_WHICH(timer->it_clock);
+
+	if (CPUCLOCK_PERTHREAD(timer->it_clock))
+		return tsk->posix_cputimers.bases + clkidx;
+	else
+		return tsk->signal->posix_cputimers.bases + clkidx;
+}
+
+/*
+ * Force recalculating the base earliest expiration on the next tick.
+ * This will also re-evaluate the need to keep around the process wide
+ * cputime counter and tick dependency and eventually shut these down
+ * if necessary.
+ */
+static void trigger_base_recalc_expires(struct k_itimer *timer,
+					struct task_struct *tsk)
+{
+	struct posix_cputimer_base *base = timer_base(timer, tsk);
+
+	base->nextevt = 0;
+}
+
+/*
+ * Dequeue the timer and reset the base if it was its earliest expiration.
+ * It makes sure the next tick recalculates the base next expiration so we
+ * don't keep the costly process wide cputime counter around for a random
+ * amount of time, along with the tick dependency.
+ *
+ * If another timer gets queued between this and the next tick, its
+ * expiration will update the base next event if necessary on the next
+ * tick.
+ */
+static void disarm_timer(struct k_itimer *timer, struct task_struct *p)
+{
+	struct cpu_timer *ctmr = &timer->it.cpu;
+	struct posix_cputimer_base *base;
+
+	if (!cpu_timer_dequeue(ctmr))
+		return;
+
+	base = timer_base(timer, p);
+	if (cpu_timer_getexpires(ctmr) == base->nextevt)
+		trigger_base_recalc_expires(timer, p);
+}
+
+
+/*
+ * Clean up a CPU-clock timer that is about to be destroyed.
+ * This is called from timer deletion with the timer already locked.
+ * If we return TIMER_RETRY, it's necessary to release the timer's lock
+ * and try again.  (This happens when the timer is in the middle of firing.)
+ */
+static int posix_cpu_timer_del(struct k_itimer *timer)
+{
+	struct cpu_timer *ctmr = &timer->it.cpu;
+	struct sighand_struct *sighand;
+	struct task_struct *p;
+	unsigned long flags;
+	int ret = 0;
+
+	rcu_read_lock();
+	p = cpu_timer_task_rcu(timer);
+	if (!p)
+		goto out;
+
+	/*
+	 * Protect against sighand release/switch in exit/exec and process/
+	 * thread timer list entry concurrent read/writes.
+	 */
+	sighand = lock_task_sighand(p, &flags);
+	if (unlikely(sighand == NULL)) {
+		/*
+		 * This raced with the reaping of the task. The exit cleanup
+		 * should have removed this timer from the timer queue.
+		 */
+		WARN_ON_ONCE(ctmr->head || timerqueue_node_queued(&ctmr->node));
+	} else {
+		if (timer->it.cpu.firing)
+			ret = TIMER_RETRY;
+		else
+			disarm_timer(timer, p);
+
+		unlock_task_sighand(p, &flags);
+	}
+
+out:
+	rcu_read_unlock();
+	if (!ret)
+		put_pid(ctmr->pid);
+
+	return ret;
+}
+
+static void cleanup_timerqueue(struct timerqueue_head *head)
+{
+	struct timerqueue_node *node;
+	struct cpu_timer *ctmr;
+
+	while ((node = timerqueue_getnext(head))) {
+		timerqueue_del(head, node);
+		ctmr = container_of(node, struct cpu_timer, node);
+		ctmr->head = NULL;
+	}
+}
+
+/*
+ * Clean out CPU timers which are still armed when a thread exits. The
+ * timers are only removed from the list. No other updates are done. The
+ * corresponding posix timers are still accessible, but cannot be rearmed.
+ *
+ * This must be called with the siglock held.
+ */
+static void cleanup_timers(struct posix_cputimers *pct)
+{
+	cleanup_timerqueue(&pct->bases[CPUCLOCK_PROF].tqhead);
+	cleanup_timerqueue(&pct->bases[CPUCLOCK_VIRT].tqhead);
+	cleanup_timerqueue(&pct->bases[CPUCLOCK_SCHED].tqhead);
+}
+
+/*
+ * These are both called with the siglock held, when the current thread
+ * is being reaped.  When the final (leader) thread in the group is reaped,
+ * posix_cpu_timers_exit_group will be called after posix_cpu_timers_exit.
+ */
+void posix_cpu_timers_exit(struct task_struct *tsk)
+{
+	cleanup_timers(&tsk->posix_cputimers);
+}
+void posix_cpu_timers_exit_group(struct task_struct *tsk)
+{
+	cleanup_timers(&tsk->signal->posix_cputimers);
+}
+
+/*
+ * Insert the timer on the appropriate list before any timers that
+ * expire later.  This must be called with the sighand lock held.
+ */
+static void arm_timer(struct k_itimer *timer, struct task_struct *p)
+{
+	struct posix_cputimer_base *base = timer_base(timer, p);
+	struct cpu_timer *ctmr = &timer->it.cpu;
+	u64 newexp = cpu_timer_getexpires(ctmr);
+
+	if (!cpu_timer_enqueue(&base->tqhead, ctmr))
+		return;
+
+	/*
+	 * We are the new earliest-expiring POSIX 1.b timer, hence
+	 * need to update expiration cache. Take into account that
+	 * for process timers we share expiration cache with itimers
+	 * and RLIMIT_CPU and for thread timers with RLIMIT_RTTIME.
+	 */
+	if (newexp < base->nextevt)
+		base->nextevt = newexp;
+
+	if (CPUCLOCK_PERTHREAD(timer->it_clock))
+		tick_dep_set_task(p, TICK_DEP_BIT_POSIX_TIMER);
+	else
+		tick_dep_set_signal(p, TICK_DEP_BIT_POSIX_TIMER);
+}
+
+/*
+ * The timer is locked, fire it and arrange for its reload.
+ */
+static void cpu_timer_fire(struct k_itimer *timer)
+{
+	struct cpu_timer *ctmr = &timer->it.cpu;
+
+	if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
+		/*
+		 * User don't want any signal.
+		 */
+		cpu_timer_setexpires(ctmr, 0);
+	} else if (unlikely(timer->sigq == NULL)) {
+		/*
+		 * This a special case for clock_nanosleep,
+		 * not a normal timer from sys_timer_create.
+		 */
+		wake_up_process(timer->it_process);
+		cpu_timer_setexpires(ctmr, 0);
+	} else if (!timer->it_interval) {
+		/*
+		 * One-shot timer.  Clear it as soon as it's fired.
+		 */
+		posix_timer_event(timer, 0);
+		cpu_timer_setexpires(ctmr, 0);
+	} else if (posix_timer_event(timer, ++timer->it_requeue_pending)) {
+		/*
+		 * The signal did not get queued because the signal
+		 * was ignored, so we won't get any callback to
+		 * reload the timer.  But we need to keep it
+		 * ticking in case the signal is deliverable next time.
+		 */
+		posix_cpu_timer_rearm(timer);
+		++timer->it_requeue_pending;
+	}
+}
+
+/*
+ * Guts of sys_timer_settime for CPU timers.
+ * This is called with the timer locked and interrupts disabled.
+ * If we return TIMER_RETRY, it's necessary to release the timer's lock
+ * and try again.  (This happens when the timer is in the middle of firing.)
+ */
+static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
+			       struct itimerspec64 *new, struct itimerspec64 *old)
+{
+	clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
+	u64 old_expires, new_expires, old_incr, val;
+	struct cpu_timer *ctmr = &timer->it.cpu;
+	struct sighand_struct *sighand;
+	struct task_struct *p;
+	unsigned long flags;
+	int ret = 0;
+
+	rcu_read_lock();
+	p = cpu_timer_task_rcu(timer);
+	if (!p) {
+		/*
+		 * If p has just been reaped, we can no
+		 * longer get any information about it at all.
+		 */
+		rcu_read_unlock();
+		return -ESRCH;
+	}
+
+	/*
+	 * Use the to_ktime conversion because that clamps the maximum
+	 * value to KTIME_MAX and avoid multiplication overflows.
+	 */
+	new_expires = ktime_to_ns(timespec64_to_ktime(new->it_value));
+
+	/*
+	 * Protect against sighand release/switch in exit/exec and p->cpu_timers
+	 * and p->signal->cpu_timers read/write in arm_timer()
+	 */
+	sighand = lock_task_sighand(p, &flags);
+	/*
+	 * If p has just been reaped, we can no
+	 * longer get any information about it at all.
+	 */
+	if (unlikely(sighand == NULL)) {
+		rcu_read_unlock();
+		return -ESRCH;
+	}
+
+	/*
+	 * Disarm any old timer after extracting its expiry time.
+	 */
+	old_incr = timer->it_interval;
+	old_expires = cpu_timer_getexpires(ctmr);
+
+	if (unlikely(timer->it.cpu.firing)) {
+		timer->it.cpu.firing = -1;
+		ret = TIMER_RETRY;
+	} else {
+		cpu_timer_dequeue(ctmr);
+	}
+
+	/*
+	 * We need to sample the current value to convert the new
+	 * value from to relative and absolute, and to convert the
+	 * old value from absolute to relative.  To set a process
+	 * timer, we need a sample to balance the thread expiry
+	 * times (in arm_timer).  With an absolute time, we must
+	 * check if it's already passed.  In short, we need a sample.
+	 */
+	if (CPUCLOCK_PERTHREAD(timer->it_clock))
+		val = cpu_clock_sample(clkid, p);
+	else
+		val = cpu_clock_sample_group(clkid, p, true);
+
+	if (old) {
+		if (old_expires == 0) {
+			old->it_value.tv_sec = 0;
+			old->it_value.tv_nsec = 0;
+		} else {
+			/*
+			 * Update the timer in case it has overrun already.
+			 * If it has, we'll report it as having overrun and
+			 * with the next reloaded timer already ticking,
+			 * though we are swallowing that pending
+			 * notification here to install the new setting.
+			 */
+			u64 exp = bump_cpu_timer(timer, val);
+
+			if (val < exp) {
+				old_expires = exp - val;
+				old->it_value = ns_to_timespec64(old_expires);
+			} else {
+				old->it_value.tv_nsec = 1;
+				old->it_value.tv_sec = 0;
+			}
+		}
+	}
+
+	if (unlikely(ret)) {
+		/*
+		 * We are colliding with the timer actually firing.
+		 * Punt after filling in the timer's old value, and
+		 * disable this firing since we are already reporting
+		 * it as an overrun (thanks to bump_cpu_timer above).
+		 */
+		unlock_task_sighand(p, &flags);
+		goto out;
+	}
+
+	if (new_expires != 0 && !(timer_flags & TIMER_ABSTIME)) {
+		new_expires += val;
+	}
+
+	/*
+	 * Install the new expiry time (or zero).
+	 * For a timer with no notification action, we don't actually
+	 * arm the timer (we'll just fake it for timer_gettime).
+	 */
+	cpu_timer_setexpires(ctmr, new_expires);
+	if (new_expires != 0 && val < new_expires) {
+		arm_timer(timer, p);
+	}
+
+	unlock_task_sighand(p, &flags);
+	/*
+	 * Install the new reload setting, and
+	 * set up the signal and overrun bookkeeping.
+	 */
+	timer->it_interval = timespec64_to_ktime(new->it_interval);
+
+	/*
+	 * This acts as a modification timestamp for the timer,
+	 * so any automatic reload attempt will punt on seeing
+	 * that we have reset the timer manually.
+	 */
+	timer->it_requeue_pending = (timer->it_requeue_pending + 2) &
+		~REQUEUE_PENDING;
+	timer->it_overrun_last = 0;
+	timer->it_overrun = -1;
+
+	if (val >= new_expires) {
+		if (new_expires != 0) {
+			/*
+			 * The designated time already passed, so we notify
+			 * immediately, even if the thread never runs to
+			 * accumulate more time on this clock.
+			 */
+			cpu_timer_fire(timer);
+		}
+
+		/*
+		 * Make sure we don't keep around the process wide cputime
+		 * counter or the tick dependency if they are not necessary.
+		 */
+		sighand = lock_task_sighand(p, &flags);
+		if (!sighand)
+			goto out;
+
+		if (!cpu_timer_queued(ctmr))
+			trigger_base_recalc_expires(timer, p);
+
+		unlock_task_sighand(p, &flags);
+	}
+ out:
+	rcu_read_unlock();
+	if (old)
+		old->it_interval = ns_to_timespec64(old_incr);
+
+	return ret;
+}
+
+static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp)
+{
+	clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
+	struct cpu_timer *ctmr = &timer->it.cpu;
+	u64 now, expires = cpu_timer_getexpires(ctmr);
+	struct task_struct *p;
+
+	rcu_read_lock();
+	p = cpu_timer_task_rcu(timer);
+	if (!p)
+		goto out;
+
+	/*
+	 * Easy part: convert the reload time.
+	 */
+	itp->it_interval = ktime_to_timespec64(timer->it_interval);
+
+	if (!expires)
+		goto out;
+
+	/*
+	 * Sample the clock to take the difference with the expiry time.
+	 */
+	if (CPUCLOCK_PERTHREAD(timer->it_clock))
+		now = cpu_clock_sample(clkid, p);
+	else
+		now = cpu_clock_sample_group(clkid, p, false);
+
+	if (now < expires) {
+		itp->it_value = ns_to_timespec64(expires - now);
+	} else {
+		/*
+		 * The timer should have expired already, but the firing
+		 * hasn't taken place yet.  Say it's just about to expire.
+		 */
+		itp->it_value.tv_nsec = 1;
+		itp->it_value.tv_sec = 0;
+	}
+out:
+	rcu_read_unlock();
+}
+
+#define MAX_COLLECTED	20
+
+static u64 collect_timerqueue(struct timerqueue_head *head,
+			      struct list_head *firing, u64 now)
+{
+	struct timerqueue_node *next;
+	int i = 0;
+
+	while ((next = timerqueue_getnext(head))) {
+		struct cpu_timer *ctmr;
+		u64 expires;
+
+		ctmr = container_of(next, struct cpu_timer, node);
+		expires = cpu_timer_getexpires(ctmr);
+		/* Limit the number of timers to expire at once */
+		if (++i == MAX_COLLECTED || now < expires)
+			return expires;
+
+		ctmr->firing = 1;
+		/* See posix_cpu_timer_wait_running() */
+		rcu_assign_pointer(ctmr->handling, current);
+		cpu_timer_dequeue(ctmr);
+		list_add_tail(&ctmr->elist, firing);
+	}
+
+	return U64_MAX;
+}
+
+static void collect_posix_cputimers(struct posix_cputimers *pct, u64 *samples,
+				    struct list_head *firing)
+{
+	struct posix_cputimer_base *base = pct->bases;
+	int i;
+
+	for (i = 0; i < CPUCLOCK_MAX; i++, base++) {
+		base->nextevt = collect_timerqueue(&base->tqhead, firing,
+						    samples[i]);
+	}
+}
+
+static inline void check_dl_overrun(struct task_struct *tsk)
+{
+	if (tsk->dl.dl_overrun) {
+		tsk->dl.dl_overrun = 0;
+		send_signal_locked(SIGXCPU, SEND_SIG_PRIV, tsk, PIDTYPE_TGID);
+	}
+}
+
+static bool check_rlimit(u64 time, u64 limit, int signo, bool rt, bool hard)
+{
+	if (time < limit)
+		return false;
+
+	if (print_fatal_signals) {
+		pr_info("%s Watchdog Timeout (%s): %s[%d]\n",
+			rt ? "RT" : "CPU", hard ? "hard" : "soft",
+			current->comm, task_pid_nr(current));
+	}
+	send_signal_locked(signo, SEND_SIG_PRIV, current, PIDTYPE_TGID);
+	return true;
+}
+
+/*
+ * Check for any per-thread CPU timers that have fired and move them off
+ * the tsk->cpu_timers[N] list onto the firing list.  Here we update the
+ * tsk->it_*_expires values to reflect the remaining thread CPU timers.
+ */
+static void check_thread_timers(struct task_struct *tsk,
+				struct list_head *firing)
+{
+	struct posix_cputimers *pct = &tsk->posix_cputimers;
+	u64 samples[CPUCLOCK_MAX];
+	unsigned long soft;
+
+	if (dl_task(tsk))
+		check_dl_overrun(tsk);
+
+	if (expiry_cache_is_inactive(pct))
+		return;
+
+	task_sample_cputime(tsk, samples);
+	collect_posix_cputimers(pct, samples, firing);
+
+	/*
+	 * Check for the special case thread timers.
+	 */
+	soft = task_rlimit(tsk, RLIMIT_RTTIME);
+	if (soft != RLIM_INFINITY) {
+		/* Task RT timeout is accounted in jiffies. RTTIME is usec */
+		unsigned long rttime = tsk->rt.timeout * (USEC_PER_SEC / HZ);
+		unsigned long hard = task_rlimit_max(tsk, RLIMIT_RTTIME);
+
+		/* At the hard limit, send SIGKILL. No further action. */
+		if (hard != RLIM_INFINITY &&
+		    check_rlimit(rttime, hard, SIGKILL, true, true))
+			return;
+
+		/* At the soft limit, send a SIGXCPU every second */
+		if (check_rlimit(rttime, soft, SIGXCPU, true, false)) {
+			soft += USEC_PER_SEC;
+			tsk->signal->rlim[RLIMIT_RTTIME].rlim_cur = soft;
+		}
+	}
+
+	if (expiry_cache_is_inactive(pct))
+		tick_dep_clear_task(tsk, TICK_DEP_BIT_POSIX_TIMER);
+}
+
+static inline void stop_process_timers(struct signal_struct *sig)
+{
+	struct posix_cputimers *pct = &sig->posix_cputimers;
+
+	/* Turn off the active flag. This is done without locking. */
+	WRITE_ONCE(pct->timers_active, false);
+	tick_dep_clear_signal(sig, TICK_DEP_BIT_POSIX_TIMER);
+}
+
+static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
+			     u64 *expires, u64 cur_time, int signo)
+{
+	if (!it->expires)
+		return;
+
+	if (cur_time >= it->expires) {
+		if (it->incr)
+			it->expires += it->incr;
+		else
+			it->expires = 0;
+
+		trace_itimer_expire(signo == SIGPROF ?
+				    ITIMER_PROF : ITIMER_VIRTUAL,
+				    task_tgid(tsk), cur_time);
+		send_signal_locked(signo, SEND_SIG_PRIV, tsk, PIDTYPE_TGID);
+	}
+
+	if (it->expires && it->expires < *expires)
+		*expires = it->expires;
+}
+
+/*
+ * Check for any per-thread CPU timers that have fired and move them
+ * off the tsk->*_timers list onto the firing list.  Per-thread timers
+ * have already been taken off.
+ */
+static void check_process_timers(struct task_struct *tsk,
+				 struct list_head *firing)
+{
+	struct signal_struct *const sig = tsk->signal;
+	struct posix_cputimers *pct = &sig->posix_cputimers;
+	u64 samples[CPUCLOCK_MAX];
+	unsigned long soft;
+
+	/*
+	 * If there are no active process wide timers (POSIX 1.b, itimers,
+	 * RLIMIT_CPU) nothing to check. Also skip the process wide timer
+	 * processing when there is already another task handling them.
+	 */
+	if (!READ_ONCE(pct->timers_active) || pct->expiry_active)
+		return;
+
+	/*
+	 * Signify that a thread is checking for process timers.
+	 * Write access to this field is protected by the sighand lock.
+	 */
+	pct->expiry_active = true;
+
+	/*
+	 * Collect the current process totals. Group accounting is active
+	 * so the sample can be taken directly.
+	 */
+	proc_sample_cputime_atomic(&sig->cputimer.cputime_atomic, samples);
+	collect_posix_cputimers(pct, samples, firing);
+
+	/*
+	 * Check for the special case process timers.
+	 */
+	check_cpu_itimer(tsk, &sig->it[CPUCLOCK_PROF],
+			 &pct->bases[CPUCLOCK_PROF].nextevt,
+			 samples[CPUCLOCK_PROF], SIGPROF);
+	check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT],
+			 &pct->bases[CPUCLOCK_VIRT].nextevt,
+			 samples[CPUCLOCK_VIRT], SIGVTALRM);
+
+	soft = task_rlimit(tsk, RLIMIT_CPU);
+	if (soft != RLIM_INFINITY) {
+		/* RLIMIT_CPU is in seconds. Samples are nanoseconds */
+		unsigned long hard = task_rlimit_max(tsk, RLIMIT_CPU);
+		u64 ptime = samples[CPUCLOCK_PROF];
+		u64 softns = (u64)soft * NSEC_PER_SEC;
+		u64 hardns = (u64)hard * NSEC_PER_SEC;
+
+		/* At the hard limit, send SIGKILL. No further action. */
+		if (hard != RLIM_INFINITY &&
+		    check_rlimit(ptime, hardns, SIGKILL, false, true))
+			return;
+
+		/* At the soft limit, send a SIGXCPU every second */
+		if (check_rlimit(ptime, softns, SIGXCPU, false, false)) {
+			sig->rlim[RLIMIT_CPU].rlim_cur = soft + 1;
+			softns += NSEC_PER_SEC;
+		}
+
+		/* Update the expiry cache */
+		if (softns < pct->bases[CPUCLOCK_PROF].nextevt)
+			pct->bases[CPUCLOCK_PROF].nextevt = softns;
+	}
+
+	if (expiry_cache_is_inactive(pct))
+		stop_process_timers(sig);
+
+	pct->expiry_active = false;
+}
+
+/*
+ * This is called from the signal code (via posixtimer_rearm)
+ * when the last timer signal was delivered and we have to reload the timer.
+ */
+static void posix_cpu_timer_rearm(struct k_itimer *timer)
+{
+	clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
+	struct task_struct *p;
+	struct sighand_struct *sighand;
+	unsigned long flags;
+	u64 now;
+
+	rcu_read_lock();
+	p = cpu_timer_task_rcu(timer);
+	if (!p)
+		goto out;
+
+	/* Protect timer list r/w in arm_timer() */
+	sighand = lock_task_sighand(p, &flags);
+	if (unlikely(sighand == NULL))
+		goto out;
+
+	/*
+	 * Fetch the current sample and update the timer's expiry time.
+	 */
+	if (CPUCLOCK_PERTHREAD(timer->it_clock))
+		now = cpu_clock_sample(clkid, p);
+	else
+		now = cpu_clock_sample_group(clkid, p, true);
+
+	bump_cpu_timer(timer, now);
+
+	/*
+	 * Now re-arm for the new expiry time.
+	 */
+	arm_timer(timer, p);
+	unlock_task_sighand(p, &flags);
+out:
+	rcu_read_unlock();
+}
+
+/**
+ * task_cputimers_expired - Check whether posix CPU timers are expired
+ *
+ * @samples:	Array of current samples for the CPUCLOCK clocks
+ * @pct:	Pointer to a posix_cputimers container
+ *
+ * Returns true if any member of @samples is greater than the corresponding
+ * member of @pct->bases[CLK].nextevt. False otherwise
+ */
+static inline bool
+task_cputimers_expired(const u64 *samples, struct posix_cputimers *pct)
+{
+	int i;
+
+	for (i = 0; i < CPUCLOCK_MAX; i++) {
+		if (samples[i] >= pct->bases[i].nextevt)
+			return true;
+	}
+	return false;
+}
+
+/**
+ * fastpath_timer_check - POSIX CPU timers fast path.
+ *
+ * @tsk:	The task (thread) being checked.
+ *
+ * Check the task and thread group timers.  If both are zero (there are no
+ * timers set) return false.  Otherwise snapshot the task and thread group
+ * timers and compare them with the corresponding expiration times.  Return
+ * true if a timer has expired, else return false.
+ */
+static inline bool fastpath_timer_check(struct task_struct *tsk)
+{
+	struct posix_cputimers *pct = &tsk->posix_cputimers;
+	struct signal_struct *sig;
+
+	if (!expiry_cache_is_inactive(pct)) {
+		u64 samples[CPUCLOCK_MAX];
+
+		task_sample_cputime(tsk, samples);
+		if (task_cputimers_expired(samples, pct))
+			return true;
+	}
+
+	sig = tsk->signal;
+	pct = &sig->posix_cputimers;
+	/*
+	 * Check if thread group timers expired when timers are active and
+	 * no other thread in the group is already handling expiry for
+	 * thread group cputimers. These fields are read without the
+	 * sighand lock. However, this is fine because this is meant to be
+	 * a fastpath heuristic to determine whether we should try to
+	 * acquire the sighand lock to handle timer expiry.
+	 *
+	 * In the worst case scenario, if concurrently timers_active is set
+	 * or expiry_active is cleared, but the current thread doesn't see
+	 * the change yet, the timer checks are delayed until the next
+	 * thread in the group gets a scheduler interrupt to handle the
+	 * timer. This isn't an issue in practice because these types of
+	 * delays with signals actually getting sent are expected.
+	 */
+	if (READ_ONCE(pct->timers_active) && !READ_ONCE(pct->expiry_active)) {
+		u64 samples[CPUCLOCK_MAX];
+
+		proc_sample_cputime_atomic(&sig->cputimer.cputime_atomic,
+					   samples);
+
+		if (task_cputimers_expired(samples, pct))
+			return true;
+	}
+
+	if (dl_task(tsk) && tsk->dl.dl_overrun)
+		return true;
+
+	return false;
+}
+
+static void handle_posix_cpu_timers(struct task_struct *tsk);
+
+#ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK
+static void posix_cpu_timers_work(struct callback_head *work)
+{
+	struct posix_cputimers_work *cw = container_of(work, typeof(*cw), work);
+
+	mutex_lock(&cw->mutex);
+	handle_posix_cpu_timers(current);
+	mutex_unlock(&cw->mutex);
+}
+
+/*
+ * Invoked from the posix-timer core when a cancel operation failed because
+ * the timer is marked firing. The caller holds rcu_read_lock(), which
+ * protects the timer and the task which is expiring it from being freed.
+ */
+static void posix_cpu_timer_wait_running(struct k_itimer *timr)
+{
+	struct task_struct *tsk = rcu_dereference(timr->it.cpu.handling);
+
+	/* Has the handling task completed expiry already? */
+	if (!tsk)
+		return;
+
+	/* Ensure that the task cannot go away */
+	get_task_struct(tsk);
+	/* Now drop the RCU protection so the mutex can be locked */
+	rcu_read_unlock();
+	/* Wait on the expiry mutex */
+	mutex_lock(&tsk->posix_cputimers_work.mutex);
+	/* Release it immediately again. */
+	mutex_unlock(&tsk->posix_cputimers_work.mutex);
+	/* Drop the task reference. */
+	put_task_struct(tsk);
+	/* Relock RCU so the callsite is balanced */
+	rcu_read_lock();
+}
+
+static void posix_cpu_timer_wait_running_nsleep(struct k_itimer *timr)
+{
+	/* Ensure that timr->it.cpu.handling task cannot go away */
+	rcu_read_lock();
+	spin_unlock_irq(&timr->it_lock);
+	posix_cpu_timer_wait_running(timr);
+	rcu_read_unlock();
+	/* @timr is on stack and is valid */
+	spin_lock_irq(&timr->it_lock);
+}
+
+/*
+ * Clear existing posix CPU timers task work.
+ */
+void clear_posix_cputimers_work(struct task_struct *p)
+{
+	/*
+	 * A copied work entry from the old task is not meaningful, clear it.
+	 * N.B. init_task_work will not do this.
+	 */
+	memset(&p->posix_cputimers_work.work, 0,
+	       sizeof(p->posix_cputimers_work.work));
+	init_task_work(&p->posix_cputimers_work.work,
+		       posix_cpu_timers_work);
+	mutex_init(&p->posix_cputimers_work.mutex);
+	p->posix_cputimers_work.scheduled = false;
+}
+
+/*
+ * Initialize posix CPU timers task work in init task. Out of line to
+ * keep the callback static and to avoid header recursion hell.
+ */
+void __init posix_cputimers_init_work(void)
+{
+	clear_posix_cputimers_work(current);
+}
+
+/*
+ * Note: All operations on tsk->posix_cputimer_work.scheduled happen either
+ * in hard interrupt context or in task context with interrupts
+ * disabled. Aside of that the writer/reader interaction is always in the
+ * context of the current task, which means they are strict per CPU.
+ */
+static inline bool posix_cpu_timers_work_scheduled(struct task_struct *tsk)
+{
+	return tsk->posix_cputimers_work.scheduled;
+}
+
+static inline void __run_posix_cpu_timers(struct task_struct *tsk)
+{
+	if (WARN_ON_ONCE(tsk->posix_cputimers_work.scheduled))
+		return;
+
+	/* Schedule task work to actually expire the timers */
+	tsk->posix_cputimers_work.scheduled = true;
+	task_work_add(tsk, &tsk->posix_cputimers_work.work, TWA_RESUME);
+}
+
+static inline bool posix_cpu_timers_enable_work(struct task_struct *tsk,
+						unsigned long start)
+{
+	bool ret = true;
+
+	/*
+	 * On !RT kernels interrupts are disabled while collecting expired
+	 * timers, so no tick can happen and the fast path check can be
+	 * reenabled without further checks.
+	 */
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		tsk->posix_cputimers_work.scheduled = false;
+		return true;
+	}
+
+	/*
+	 * On RT enabled kernels ticks can happen while the expired timers
+	 * are collected under sighand lock. But any tick which observes
+	 * the CPUTIMERS_WORK_SCHEDULED bit set, does not run the fastpath
+	 * checks. So reenabling the tick work has do be done carefully:
+	 *
+	 * Disable interrupts and run the fast path check if jiffies have
+	 * advanced since the collecting of expired timers started. If
+	 * jiffies have not advanced or the fast path check did not find
+	 * newly expired timers, reenable the fast path check in the timer
+	 * interrupt. If there are newly expired timers, return false and
+	 * let the collection loop repeat.
+	 */
+	local_irq_disable();
+	if (start != jiffies && fastpath_timer_check(tsk))
+		ret = false;
+	else
+		tsk->posix_cputimers_work.scheduled = false;
+	local_irq_enable();
+
+	return ret;
+}
+#else /* CONFIG_POSIX_CPU_TIMERS_TASK_WORK */
+static inline void __run_posix_cpu_timers(struct task_struct *tsk)
+{
+	lockdep_posixtimer_enter();
+	handle_posix_cpu_timers(tsk);
+	lockdep_posixtimer_exit();
+}
+
+static void posix_cpu_timer_wait_running(struct k_itimer *timr)
+{
+	cpu_relax();
+}
+
+static void posix_cpu_timer_wait_running_nsleep(struct k_itimer *timr)
+{
+	spin_unlock_irq(&timr->it_lock);
+	cpu_relax();
+	spin_lock_irq(&timr->it_lock);
+}
+
+static inline bool posix_cpu_timers_work_scheduled(struct task_struct *tsk)
+{
+	return false;
+}
+
+static inline bool posix_cpu_timers_enable_work(struct task_struct *tsk,
+						unsigned long start)
+{
+	return true;
+}
+#endif /* CONFIG_POSIX_CPU_TIMERS_TASK_WORK */
+
+static void handle_posix_cpu_timers(struct task_struct *tsk)
+{
+	struct k_itimer *timer, *next;
+	unsigned long flags, start;
+	LIST_HEAD(firing);
+
+	if (!lock_task_sighand(tsk, &flags))
+		return;
+
+	do {
+		/*
+		 * On RT locking sighand lock does not disable interrupts,
+		 * so this needs to be careful vs. ticks. Store the current
+		 * jiffies value.
+		 */
+		start = READ_ONCE(jiffies);
+		barrier();
+
+		/*
+		 * Here we take off tsk->signal->cpu_timers[N] and
+		 * tsk->cpu_timers[N] all the timers that are firing, and
+		 * put them on the firing list.
+		 */
+		check_thread_timers(tsk, &firing);
+
+		check_process_timers(tsk, &firing);
+
+		/*
+		 * The above timer checks have updated the expiry cache and
+		 * because nothing can have queued or modified timers after
+		 * sighand lock was taken above it is guaranteed to be
+		 * consistent. So the next timer interrupt fastpath check
+		 * will find valid data.
+		 *
+		 * If timer expiry runs in the timer interrupt context then
+		 * the loop is not relevant as timers will be directly
+		 * expired in interrupt context. The stub function below
+		 * returns always true which allows the compiler to
+		 * optimize the loop out.
+		 *
+		 * If timer expiry is deferred to task work context then
+		 * the following rules apply:
+		 *
+		 * - On !RT kernels no tick can have happened on this CPU
+		 *   after sighand lock was acquired because interrupts are
+		 *   disabled. So reenabling task work before dropping
+		 *   sighand lock and reenabling interrupts is race free.
+		 *
+		 * - On RT kernels ticks might have happened but the tick
+		 *   work ignored posix CPU timer handling because the
+		 *   CPUTIMERS_WORK_SCHEDULED bit is set. Reenabling work
+		 *   must be done very carefully including a check whether
+		 *   ticks have happened since the start of the timer
+		 *   expiry checks. posix_cpu_timers_enable_work() takes
+		 *   care of that and eventually lets the expiry checks
+		 *   run again.
+		 */
+	} while (!posix_cpu_timers_enable_work(tsk, start));
+
+	/*
+	 * We must release sighand lock before taking any timer's lock.
+	 * There is a potential race with timer deletion here, as the
+	 * siglock now protects our private firing list.  We have set
+	 * the firing flag in each timer, so that a deletion attempt
+	 * that gets the timer lock before we do will give it up and
+	 * spin until we've taken care of that timer below.
+	 */
+	unlock_task_sighand(tsk, &flags);
+
+	/*
+	 * Now that all the timers on our list have the firing flag,
+	 * no one will touch their list entries but us.  We'll take
+	 * each timer's lock before clearing its firing flag, so no
+	 * timer call will interfere.
+	 */
+	list_for_each_entry_safe(timer, next, &firing, it.cpu.elist) {
+		int cpu_firing;
+
+		/*
+		 * spin_lock() is sufficient here even independent of the
+		 * expiry context. If expiry happens in hard interrupt
+		 * context it's obvious. For task work context it's safe
+		 * because all other operations on timer::it_lock happen in
+		 * task context (syscall or exit).
+		 */
+		spin_lock(&timer->it_lock);
+		list_del_init(&timer->it.cpu.elist);
+		cpu_firing = timer->it.cpu.firing;
+		timer->it.cpu.firing = 0;
+		/*
+		 * The firing flag is -1 if we collided with a reset
+		 * of the timer, which already reported this
+		 * almost-firing as an overrun.  So don't generate an event.
+		 */
+		if (likely(cpu_firing >= 0))
+			cpu_timer_fire(timer);
+		/* See posix_cpu_timer_wait_running() */
+		rcu_assign_pointer(timer->it.cpu.handling, NULL);
+		spin_unlock(&timer->it_lock);
+	}
+}
+
+/*
+ * This is called from the timer interrupt handler.  The irq handler has
+ * already updated our counts.  We need to check if any timers fire now.
+ * Interrupts are disabled.
+ */
+void run_posix_cpu_timers(void)
+{
+	struct task_struct *tsk = current;
+
+	lockdep_assert_irqs_disabled();
+
+	/*
+	 * If the actual expiry is deferred to task work context and the
+	 * work is already scheduled there is no point to do anything here.
+	 */
+	if (posix_cpu_timers_work_scheduled(tsk))
+		return;
+
+	/*
+	 * The fast path checks that there are no expired thread or thread
+	 * group timers.  If that's so, just return.
+	 */
+	if (!fastpath_timer_check(tsk))
+		return;
+
+	__run_posix_cpu_timers(tsk);
+}
+
+/*
+ * Set one of the process-wide special case CPU timers or RLIMIT_CPU.
+ * The tsk->sighand->siglock must be held by the caller.
+ */
+void set_process_cpu_timer(struct task_struct *tsk, unsigned int clkid,
+			   u64 *newval, u64 *oldval)
+{
+	u64 now, *nextevt;
+
+	if (WARN_ON_ONCE(clkid >= CPUCLOCK_SCHED))
+		return;
+
+	nextevt = &tsk->signal->posix_cputimers.bases[clkid].nextevt;
+	now = cpu_clock_sample_group(clkid, tsk, true);
+
+	if (oldval) {
+		/*
+		 * We are setting itimer. The *oldval is absolute and we update
+		 * it to be relative, *newval argument is relative and we update
+		 * it to be absolute.
+		 */
+		if (*oldval) {
+			if (*oldval <= now) {
+				/* Just about to fire. */
+				*oldval = TICK_NSEC;
+			} else {
+				*oldval -= now;
+			}
+		}
+
+		if (*newval)
+			*newval += now;
+	}
+
+	/*
+	 * Update expiration cache if this is the earliest timer. CPUCLOCK_PROF
+	 * expiry cache is also used by RLIMIT_CPU!.
+	 */
+	if (*newval < *nextevt)
+		*nextevt = *newval;
+
+	tick_dep_set_signal(tsk, TICK_DEP_BIT_POSIX_TIMER);
+}
+
+static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
+			    const struct timespec64 *rqtp)
+{
+	struct itimerspec64 it;
+	struct k_itimer timer;
+	u64 expires;
+	int error;
+
+	/*
+	 * Set up a temporary timer and then wait for it to go off.
+	 */
+	memset(&timer, 0, sizeof timer);
+	spin_lock_init(&timer.it_lock);
+	timer.it_clock = which_clock;
+	timer.it_overrun = -1;
+	error = posix_cpu_timer_create(&timer);
+	timer.it_process = current;
+
+	if (!error) {
+		static struct itimerspec64 zero_it;
+		struct restart_block *restart;
+
+		memset(&it, 0, sizeof(it));
+		it.it_value = *rqtp;
+
+		spin_lock_irq(&timer.it_lock);
+		error = posix_cpu_timer_set(&timer, flags, &it, NULL);
+		if (error) {
+			spin_unlock_irq(&timer.it_lock);
+			return error;
+		}
+
+		while (!signal_pending(current)) {
+			if (!cpu_timer_getexpires(&timer.it.cpu)) {
+				/*
+				 * Our timer fired and was reset, below
+				 * deletion can not fail.
+				 */
+				posix_cpu_timer_del(&timer);
+				spin_unlock_irq(&timer.it_lock);
+				return 0;
+			}
+
+			/*
+			 * Block until cpu_timer_fire (or a signal) wakes us.
+			 */
+			__set_current_state(TASK_INTERRUPTIBLE);
+			spin_unlock_irq(&timer.it_lock);
+			schedule();
+			spin_lock_irq(&timer.it_lock);
+		}
+
+		/*
+		 * We were interrupted by a signal.
+		 */
+		expires = cpu_timer_getexpires(&timer.it.cpu);
+		error = posix_cpu_timer_set(&timer, 0, &zero_it, &it);
+		if (!error) {
+			/* Timer is now unarmed, deletion can not fail. */
+			posix_cpu_timer_del(&timer);
+		} else {
+			while (error == TIMER_RETRY) {
+				posix_cpu_timer_wait_running_nsleep(&timer);
+				error = posix_cpu_timer_del(&timer);
+			}
+		}
+
+		spin_unlock_irq(&timer.it_lock);
+
+		if ((it.it_value.tv_sec | it.it_value.tv_nsec) == 0) {
+			/*
+			 * It actually did fire already.
+			 */
+			return 0;
+		}
+
+		error = -ERESTART_RESTARTBLOCK;
+		/*
+		 * Report back to the user the time still remaining.
+		 */
+		restart = &current->restart_block;
+		restart->nanosleep.expires = expires;
+		if (restart->nanosleep.type != TT_NONE)
+			error = nanosleep_copyout(restart, &it.it_value);
+	}
+
+	return error;
+}
+
+static long posix_cpu_nsleep_restart(struct restart_block *restart_block);
+
+static int posix_cpu_nsleep(const clockid_t which_clock, int flags,
+			    const struct timespec64 *rqtp)
+{
+	struct restart_block *restart_block = &current->restart_block;
+	int error;
+
+	/*
+	 * Diagnose required errors first.
+	 */
+	if (CPUCLOCK_PERTHREAD(which_clock) &&
+	    (CPUCLOCK_PID(which_clock) == 0 ||
+	     CPUCLOCK_PID(which_clock) == task_pid_vnr(current)))
+		return -EINVAL;
+
+	error = do_cpu_nanosleep(which_clock, flags, rqtp);
+
+	if (error == -ERESTART_RESTARTBLOCK) {
+
+		if (flags & TIMER_ABSTIME)
+			return -ERESTARTNOHAND;
+
+		restart_block->nanosleep.clockid = which_clock;
+		set_restart_fn(restart_block, posix_cpu_nsleep_restart);
+	}
+	return error;
+}
+
+static long posix_cpu_nsleep_restart(struct restart_block *restart_block)
+{
+	clockid_t which_clock = restart_block->nanosleep.clockid;
+	struct timespec64 t;
+
+	t = ns_to_timespec64(restart_block->nanosleep.expires);
+
+	return do_cpu_nanosleep(which_clock, TIMER_ABSTIME, &t);
+}
+
+#define PROCESS_CLOCK	make_process_cpuclock(0, CPUCLOCK_SCHED)
+#define THREAD_CLOCK	make_thread_cpuclock(0, CPUCLOCK_SCHED)
+
+static int process_cpu_clock_getres(const clockid_t which_clock,
+				    struct timespec64 *tp)
+{
+	return posix_cpu_clock_getres(PROCESS_CLOCK, tp);
+}
+static int process_cpu_clock_get(const clockid_t which_clock,
+				 struct timespec64 *tp)
+{
+	return posix_cpu_clock_get(PROCESS_CLOCK, tp);
+}
+static int process_cpu_timer_create(struct k_itimer *timer)
+{
+	timer->it_clock = PROCESS_CLOCK;
+	return posix_cpu_timer_create(timer);
+}
+static int process_cpu_nsleep(const clockid_t which_clock, int flags,
+			      const struct timespec64 *rqtp)
+{
+	return posix_cpu_nsleep(PROCESS_CLOCK, flags, rqtp);
+}
+static int thread_cpu_clock_getres(const clockid_t which_clock,
+				   struct timespec64 *tp)
+{
+	return posix_cpu_clock_getres(THREAD_CLOCK, tp);
+}
+static int thread_cpu_clock_get(const clockid_t which_clock,
+				struct timespec64 *tp)
+{
+	return posix_cpu_clock_get(THREAD_CLOCK, tp);
+}
+static int thread_cpu_timer_create(struct k_itimer *timer)
+{
+	timer->it_clock = THREAD_CLOCK;
+	return posix_cpu_timer_create(timer);
+}
+
+const struct k_clock clock_posix_cpu = {
+	.clock_getres		= posix_cpu_clock_getres,
+	.clock_set		= posix_cpu_clock_set,
+	.clock_get_timespec	= posix_cpu_clock_get,
+	.timer_create		= posix_cpu_timer_create,
+	.nsleep			= posix_cpu_nsleep,
+	.timer_set		= posix_cpu_timer_set,
+	.timer_del		= posix_cpu_timer_del,
+	.timer_get		= posix_cpu_timer_get,
+	.timer_rearm		= posix_cpu_timer_rearm,
+	.timer_wait_running	= posix_cpu_timer_wait_running,
+};
+
+const struct k_clock clock_process = {
+	.clock_getres		= process_cpu_clock_getres,
+	.clock_get_timespec	= process_cpu_clock_get,
+	.timer_create		= process_cpu_timer_create,
+	.nsleep			= process_cpu_nsleep,
+};
+
+const struct k_clock clock_thread = {
+	.clock_getres		= thread_cpu_clock_getres,
+	.clock_get_timespec	= thread_cpu_clock_get,
+	.timer_create		= thread_cpu_timer_create,
+};