// SPDX-License-Identifier: GPL-2.0
/*
 *  Copyright(C) 2005-2006, Linutronix GmbH, Thomas Gleixner <tglx@kernel.org>
 *  Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
 *  Copyright(C) 2006-2007  Timesys Corp., Thomas Gleixner
 *
 *  High-resolution kernel timers
 *
 *  In contrast to the low-resolution timeout API, aka timer wheel,
 *  hrtimers provide finer resolution and accuracy depending on system
 *  configuration and capabilities.
 *
 *  Started by: Thomas Gleixner and Ingo Molnar
 *
 *  Credits:
 *      Based on the original timer wheel code
 *
 *      Help, testing, suggestions, bugfixes, improvements were
 *      provided by:
 *
 *      George Anzinger, Andrew Morton, Steven Rostedt, Roman Zippel
 *      et. al.
 */

#include <linux/cpu.h>
#include <linux/export.h>
#include <linux/percpu.h>
#include <linux/hrtimer.h>
#include <linux/notifier.h>
#include <linux/syscalls.h>
#include <linux/interrupt.h>
#include <linux/tick.h>
#include <linux/err.h>
#include <linux/debugobjects.h>
#include <linux/sched/signal.h>
#include <linux/sched/sysctl.h>
#include <linux/sched/rt.h>
#include <linux/sched/deadline.h>
#include <linux/sched/nohz.h>
#include <linux/sched/debug.h>
#include <linux/sched/isolation.h>
#include <linux/timer.h>
#include <linux/freezer.h>
#include <linux/compat.h>

#include <linux/uaccess.h>

#include <trace/events/timer.h>

#include "tick-internal.h"

/*
 * Constants to set the queued state of the timer (INACTIVE, ENQUEUED)
 *
 * The callback state is kept separate in the CPU base because having it in
 * the timer would required touching the timer after the callback, which
 * makes it impossible to free the timer from the callback function.
 *
 * Therefore we track the callback state in:
 *
 *      timer->base->cpu_base->running == timer
 *
 * On SMP it is possible to have a "callback function running and enqueued"
 * status. It happens for example when a posix timer expired and the callback
 * queued a signal. Between dropping the lock which protects the posix timer
 * and reacquiring the base lock of the hrtimer, another CPU can deliver the
 * signal and rearm the timer.
 *
 * All state transitions are protected by cpu_base->lock.
 */
#define HRTIMER_STATE_INACTIVE  false
#define HRTIMER_STATE_ENQUEUED  true

/*
 * The resolution of the clocks. The resolution value is returned in
 * the clock_getres() system call to give application programmers an
 * idea of the (in)accuracy of timers. Timer values are rounded up to
 * this resolution values.
 */
#define HIGH_RES_NSEC           1

/*
 * Masks for selecting the soft and hard context timers from
 * cpu_base->active
 */
#define MASK_SHIFT              (HRTIMER_BASE_MONOTONIC_SOFT)
#define HRTIMER_ACTIVE_HARD     ((1U << MASK_SHIFT) - 1)
#define HRTIMER_ACTIVE_SOFT     (HRTIMER_ACTIVE_HARD << MASK_SHIFT)
#define HRTIMER_ACTIVE_ALL      (HRTIMER_ACTIVE_SOFT | HRTIMER_ACTIVE_HARD)

static void retrigger_next_event(void *arg);
static ktime_t __hrtimer_cb_get_time(clockid_t clock_id);

/*
 * The timer bases:
 *
 * There are more clockids than hrtimer bases. Thus, we index
 * into the timer bases by the hrtimer_base_type enum. When trying
 * to reach a base using a clockid, hrtimer_clockid_to_base()
 * is used to convert from clockid to the proper hrtimer_base_type.
 */

#define BASE_INIT(idx, cid)                     \
        [idx] = { .index = idx, .clockid = cid }

DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
{
        .lock = __RAW_SPIN_LOCK_UNLOCKED(hrtimer_bases.lock),
        .clock_base = {
                BASE_INIT(HRTIMER_BASE_MONOTONIC,       CLOCK_MONOTONIC),
                BASE_INIT(HRTIMER_BASE_REALTIME,        CLOCK_REALTIME),
                BASE_INIT(HRTIMER_BASE_BOOTTIME,        CLOCK_BOOTTIME),
                BASE_INIT(HRTIMER_BASE_TAI,             CLOCK_TAI),
                BASE_INIT(HRTIMER_BASE_MONOTONIC_SOFT,  CLOCK_MONOTONIC),
                BASE_INIT(HRTIMER_BASE_REALTIME_SOFT,   CLOCK_REALTIME),
                BASE_INIT(HRTIMER_BASE_BOOTTIME_SOFT,   CLOCK_BOOTTIME),
                BASE_INIT(HRTIMER_BASE_TAI_SOFT,        CLOCK_TAI),
        },
        .csd = CSD_INIT(retrigger_next_event, NULL)
};

static inline bool hrtimer_base_is_online(struct hrtimer_cpu_base *base)
{
        if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
                return true;
        else
                return likely(base->online);
}

#ifdef CONFIG_HIGH_RES_TIMERS
DEFINE_STATIC_KEY_FALSE(hrtimer_highres_enabled_key);

static void hrtimer_hres_workfn(struct work_struct *work)
{
        static_branch_enable(&hrtimer_highres_enabled_key);
}

static DECLARE_WORK(hrtimer_hres_work, hrtimer_hres_workfn);

static inline void hrtimer_schedule_hres_work(void)
{
        if (!hrtimer_highres_enabled())
                schedule_work(&hrtimer_hres_work);
}
#else
static inline void hrtimer_schedule_hres_work(void) { }
#endif

/*
 * Functions and macros which are different for UP/SMP systems are kept in a
 * single place
 */
#ifdef CONFIG_SMP
/*
 * We require the migration_base for lock_hrtimer_base()/switch_hrtimer_base()
 * such that hrtimer_callback_running() can unconditionally dereference
 * timer->base->cpu_base
 */
static struct hrtimer_cpu_base migration_cpu_base = {
        .clock_base = {
                [0] = {
                        .cpu_base = &migration_cpu_base,
                        .seq      = SEQCNT_RAW_SPINLOCK_ZERO(migration_cpu_base.seq,
                                                             &migration_cpu_base.lock),
                },
        },
};

#define migration_base  migration_cpu_base.clock_base[0]

/*
 * We are using hashed locking: holding per_cpu(hrtimer_bases)[n].lock
 * means that all timers which are tied to this base via timer->base are
 * locked, and the base itself is locked too.
 *
 * So __run_timers/migrate_timers can safely modify all timers which could
 * be found on the lists/queues.
 *
 * When the timer's base is locked, and the timer removed from list, it is
 * possible to set timer->base = &migration_base and drop the lock: the timer
 * remains locked.
 */
static struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
                                                    unsigned long *flags)
        __acquires(&timer->base->lock)
{
        for (;;) {
                struct hrtimer_clock_base *base = READ_ONCE(timer->base);

                if (likely(base != &migration_base)) {
                        raw_spin_lock_irqsave(&base->cpu_base->lock, *flags);
                        if (likely(base == timer->base))
                                return base;
                        /* The timer has migrated to another CPU: */
                        raw_spin_unlock_irqrestore(&base->cpu_base->lock, *flags);
                }
                cpu_relax();
        }
}

/*
 * Check if the elected target is suitable considering its next
 * event and the hotplug state of the current CPU.
 *
 * If the elected target is remote and its next event is after the timer
 * to queue, then a remote reprogram is necessary. However there is no
 * guarantee the IPI handling the operation would arrive in time to meet
 * the high resolution deadline. In this case the local CPU becomes a
 * preferred target, unless it is offline.
 *
 * High and low resolution modes are handled the same way for simplicity.
 *
 * Called with cpu_base->lock of target cpu held.
 */
static bool hrtimer_suitable_target(struct hrtimer *timer, struct hrtimer_clock_base *new_base,
                                    struct hrtimer_cpu_base *new_cpu_base,
                                    struct hrtimer_cpu_base *this_cpu_base)
{
        ktime_t expires;

        /*
         * The local CPU clockevent can be reprogrammed. Also get_target_base()
         * guarantees it is online.
         */
        if (new_cpu_base == this_cpu_base)
                return true;

        /*
         * The offline local CPU can't be the default target if the
         * next remote target event is after this timer. Keep the
         * elected new base. An IPI will be issued to reprogram
         * it as a last resort.
         */
        if (!hrtimer_base_is_online(this_cpu_base))
                return true;

        expires = ktime_sub(hrtimer_get_expires(timer), new_base->offset);

        return expires >= new_base->cpu_base->expires_next;
}

static inline struct hrtimer_cpu_base *get_target_base(struct hrtimer_cpu_base *base, bool pinned)
{
        if (!hrtimer_base_is_online(base)) {
                int cpu = cpumask_any_and(cpu_online_mask, housekeeping_cpumask(HK_TYPE_TIMER));

                return &per_cpu(hrtimer_bases, cpu);
        }

#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
        if (static_branch_likely(&timers_migration_enabled) && !pinned)
                return &per_cpu(hrtimer_bases, get_nohz_timer_target());
#endif
        return base;
}

/*
 * We switch the timer base to a power-optimized selected CPU target,
 * if:
 *      - NO_HZ_COMMON is enabled
 *      - timer migration is enabled
 *      - the timer callback is not running
 *      - the timer is not the first expiring timer on the new target
 *
 * If one of the above requirements is not fulfilled we move the timer
 * to the current CPU or leave it on the previously assigned CPU if
 * the timer callback is currently running.
 */
static inline struct hrtimer_clock_base *
switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base, bool pinned)
{
        struct hrtimer_cpu_base *new_cpu_base, *this_cpu_base;
        struct hrtimer_clock_base *new_base;
        int basenum = base->index;

        this_cpu_base = this_cpu_ptr(&hrtimer_bases);
        new_cpu_base = get_target_base(this_cpu_base, pinned);
again:
        new_base = &new_cpu_base->clock_base[basenum];

        if (base != new_base) {
                /*
                 * We are trying to move timer to new_base. However we can't
                 * change timer's base while it is running, so we keep it on
                 * the same CPU. No hassle vs. reprogramming the event source
                 * in the high resolution case. The remote CPU will take care
                 * of this when the timer function has completed. There is no
                 * conflict as we hold the lock until the timer is enqueued.
                 */
                if (unlikely(hrtimer_callback_running(timer)))
                        return base;

                /* See the comment in lock_hrtimer_base() */
                WRITE_ONCE(timer->base, &migration_base);
                raw_spin_unlock(&base->cpu_base->lock);
                raw_spin_lock(&new_base->cpu_base->lock);

                if (!hrtimer_suitable_target(timer, new_base, new_cpu_base, this_cpu_base)) {
                        raw_spin_unlock(&new_base->cpu_base->lock);
                        raw_spin_lock(&base->cpu_base->lock);
                        new_cpu_base = this_cpu_base;
                        WRITE_ONCE(timer->base, base);
                        goto again;
                }
                WRITE_ONCE(timer->base, new_base);
        } else {
                if (!hrtimer_suitable_target(timer, new_base,  new_cpu_base, this_cpu_base)) {
                        new_cpu_base = this_cpu_base;
                        goto again;
                }
        }
        return new_base;
}

#else /* CONFIG_SMP */

static inline struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
                                                           unsigned long *flags)
        __acquires(&timer->base->cpu_base->lock)
{
        struct hrtimer_clock_base *base = timer->base;

        raw_spin_lock_irqsave(&base->cpu_base->lock, *flags);
        return base;
}

# define switch_hrtimer_base(t, b, p)   (b)

#endif  /* !CONFIG_SMP */

/*
 * Functions for the union type storage format of ktime_t which are
 * too large for inlining:
 */
#if BITS_PER_LONG < 64
/*
 * Divide a ktime value by a nanosecond value
 */
s64 __ktime_divns(const ktime_t kt, s64 div)
{
        int sft = 0;
        s64 dclc;
        u64 tmp;

        dclc = ktime_to_ns(kt);
        tmp = dclc < 0 ? -dclc : dclc;

        /* Make sure the divisor is less than 2^32: */
        while (div >> 32) {
                sft++;
                div >>= 1;
        }
        tmp >>= sft;
        do_div(tmp, (u32) div);
        return dclc < 0 ? -tmp : tmp;
}
EXPORT_SYMBOL_GPL(__ktime_divns);
#endif /* BITS_PER_LONG < 64 */

/*
 * Add two ktime values and do a safety check for overflow:
 */
ktime_t ktime_add_safe(const ktime_t lhs, const ktime_t rhs)
{
        ktime_t res = ktime_add_unsafe(lhs, rhs);

        /*
         * We use KTIME_SEC_MAX here, the maximum timeout which we can
         * return to user space in a timespec:
         */
        if (res < 0 || res < lhs || res < rhs)
                res = ktime_set(KTIME_SEC_MAX, 0);

        return res;
}

EXPORT_SYMBOL_GPL(ktime_add_safe);

#ifdef CONFIG_DEBUG_OBJECTS_TIMERS

static const struct debug_obj_descr hrtimer_debug_descr;

static void *hrtimer_debug_hint(void *addr)
{
        return ACCESS_PRIVATE((struct hrtimer *)addr, function);
}

/*
 * fixup_init is called when:
 * - an active object is initialized
 */
static bool hrtimer_fixup_init(void *addr, enum debug_obj_state state)
{
        struct hrtimer *timer = addr;

        switch (state) {
        case ODEBUG_STATE_ACTIVE:
                hrtimer_cancel(timer);
                debug_object_init(timer, &hrtimer_debug_descr);
                return true;
        default:
                return false;
        }
}

/*
 * fixup_activate is called when:
 * - an active object is activated
 * - an unknown non-static object is activated
 */
static bool hrtimer_fixup_activate(void *addr, enum debug_obj_state state)
{
        switch (state) {
        case ODEBUG_STATE_ACTIVE:
                WARN_ON(1);
                fallthrough;
        default:
                return false;
        }
}

/*
 * fixup_free is called when:
 * - an active object is freed
 */
static bool hrtimer_fixup_free(void *addr, enum debug_obj_state state)
{
        struct hrtimer *timer = addr;

        switch (state) {
        case ODEBUG_STATE_ACTIVE:
                hrtimer_cancel(timer);
                debug_object_free(timer, &hrtimer_debug_descr);
                return true;
        default:
                return false;
        }
}

/* Stub timer callback for improperly used timers. */
static enum hrtimer_restart stub_timer(struct hrtimer *unused)
{
        WARN_ON_ONCE(1);
        return HRTIMER_NORESTART;
}

/*
 * hrtimer_fixup_assert_init is called when:
 * - an untracked/uninit-ed object is found
 */
static bool hrtimer_fixup_assert_init(void *addr, enum debug_obj_state state)
{
        struct hrtimer *timer = addr;

        switch (state) {
        case ODEBUG_STATE_NOTAVAILABLE:
                hrtimer_setup(timer, stub_timer, CLOCK_MONOTONIC, 0);
                return true;
        default:
                return false;
        }
}

static const struct debug_obj_descr hrtimer_debug_descr = {
        .name                   = "hrtimer",
        .debug_hint             = hrtimer_debug_hint,
        .fixup_init             = hrtimer_fixup_init,
        .fixup_activate         = hrtimer_fixup_activate,
        .fixup_free             = hrtimer_fixup_free,
        .fixup_assert_init      = hrtimer_fixup_assert_init,
};

static inline void debug_hrtimer_init(struct hrtimer *timer)
{
        debug_object_init(timer, &hrtimer_debug_descr);
}

static inline void debug_hrtimer_init_on_stack(struct hrtimer *timer)
{
        debug_object_init_on_stack(timer, &hrtimer_debug_descr);
}

static inline void debug_hrtimer_activate(struct hrtimer *timer, enum hrtimer_mode mode)
{
        debug_object_activate(timer, &hrtimer_debug_descr);
}

static inline void debug_hrtimer_deactivate(struct hrtimer *timer)
{
        debug_object_deactivate(timer, &hrtimer_debug_descr);
}

static inline void debug_hrtimer_assert_init(struct hrtimer *timer)
{
        debug_object_assert_init(timer, &hrtimer_debug_descr);
}

void destroy_hrtimer_on_stack(struct hrtimer *timer)
{
        debug_object_free(timer, &hrtimer_debug_descr);
}
EXPORT_SYMBOL_GPL(destroy_hrtimer_on_stack);

#else

static inline void debug_hrtimer_init(struct hrtimer *timer) { }
static inline void debug_hrtimer_init_on_stack(struct hrtimer *timer) { }
static inline void debug_hrtimer_activate(struct hrtimer *timer, enum hrtimer_mode mode) { }
static inline void debug_hrtimer_deactivate(struct hrtimer *timer) { }
static inline void debug_hrtimer_assert_init(struct hrtimer *timer) { }
#endif

static inline void debug_setup(struct hrtimer *timer, clockid_t clockid, enum hrtimer_mode mode)
{
        debug_hrtimer_init(timer);
        trace_hrtimer_setup(timer, clockid, mode);
}

static inline void debug_setup_on_stack(struct hrtimer *timer, clockid_t clockid,
                                        enum hrtimer_mode mode)
{
        debug_hrtimer_init_on_stack(timer);
        trace_hrtimer_setup(timer, clockid, mode);
}

static inline void debug_activate(struct hrtimer *timer, enum hrtimer_mode mode, bool was_armed)
{
        debug_hrtimer_activate(timer, mode);
        trace_hrtimer_start(timer, mode, was_armed);
}

#define for_each_active_base(base, cpu_base, active)                                    \
        for (unsigned int idx = ffs(active); idx--; idx = ffs((active)))                \
                for (bool done = false; !done; active &= ~(1U << idx))                  \
                        for (base = &cpu_base->clock_base[idx]; !done; done = true)

#define hrtimer_from_timerqueue_node(_n) container_of_const(_n, struct hrtimer, node)

#if defined(CONFIG_NO_HZ_COMMON)
/*
 * Same as hrtimer_bases_next_event() below, but skips the excluded timer and
 * does not update cpu_base->next_timer/expires.
 */
static ktime_t hrtimer_bases_next_event_without(struct hrtimer_cpu_base *cpu_base,
                                                const struct hrtimer *exclude,
                                                unsigned int active, ktime_t expires_next)
{
        struct hrtimer_clock_base *base;
        ktime_t expires;

        lockdep_assert_held(&cpu_base->lock);

        for_each_active_base(base, cpu_base, active) {
                expires = ktime_sub(base->expires_next, base->offset);
                if (expires >= expires_next)
                        continue;

                /*
                 * If the excluded timer is the first on this base evaluate the
                 * next timer.
                 */
                struct timerqueue_linked_node *node = timerqueue_linked_first(&base->active);

                if (unlikely(&exclude->node == node)) {
                        node = timerqueue_linked_next(node);
                        if (!node)
                                continue;
                        expires = ktime_sub(node->expires, base->offset);
                        if (expires >= expires_next)
                                continue;
                }
                expires_next = expires;
        }
        /* If base->offset changed, the result might be negative */
        return max(expires_next, 0);
}
#endif

static __always_inline struct hrtimer *clock_base_next_timer(struct hrtimer_clock_base *base)
{
        struct timerqueue_linked_node *next = timerqueue_linked_first(&base->active);

        return hrtimer_from_timerqueue_node(next);
}

/* Find the base with the earliest expiry */
static void hrtimer_bases_first(struct hrtimer_cpu_base *cpu_base,unsigned int active,
                                ktime_t *expires_next, struct hrtimer **next_timer)
{
        struct hrtimer_clock_base *base;
        ktime_t expires;

        for_each_active_base(base, cpu_base, active) {
                expires = ktime_sub(base->expires_next, base->offset);
                if (expires < *expires_next) {
                        *expires_next = expires;
                        *next_timer = clock_base_next_timer(base);
                }
        }
}

/*
 * Recomputes cpu_base::*next_timer and returns the earliest expires_next
 * but does not set cpu_base::*expires_next, that is done by
 * hrtimer[_force]_reprogram and hrtimer_interrupt only. When updating
 * cpu_base::*expires_next right away, reprogramming logic would no longer
 * work.
 *
 * When a softirq is pending, we can ignore the HRTIMER_ACTIVE_SOFT bases,
 * those timers will get run whenever the softirq gets handled, at the end of
 * hrtimer_run_softirq(), hrtimer_update_softirq_timer() will re-add these bases.
 *
 * Therefore softirq values are those from the HRTIMER_ACTIVE_SOFT clock bases.
 * The !softirq values are the minima across HRTIMER_ACTIVE_ALL, unless an actual
 * softirq is pending, in which case they're the minima of HRTIMER_ACTIVE_HARD.
 *
 * @active_mask must be one of:
 *  - HRTIMER_ACTIVE_ALL,
 *  - HRTIMER_ACTIVE_SOFT, or
 *  - HRTIMER_ACTIVE_HARD.
 */
static ktime_t __hrtimer_get_next_event(struct hrtimer_cpu_base *cpu_base, unsigned int active_mask)
{
        struct hrtimer *next_timer = NULL;
        ktime_t expires_next = KTIME_MAX;
        unsigned int active;

        lockdep_assert_held(&cpu_base->lock);

        if (!cpu_base->softirq_activated && (active_mask & HRTIMER_ACTIVE_SOFT)) {
                active = cpu_base->active_bases & HRTIMER_ACTIVE_SOFT;
                if (active)
                        hrtimer_bases_first(cpu_base, active, &expires_next, &next_timer);
                cpu_base->softirq_next_timer = next_timer;
        }

        if (active_mask & HRTIMER_ACTIVE_HARD) {
                active = cpu_base->active_bases & HRTIMER_ACTIVE_HARD;
                if (active)
                        hrtimer_bases_first(cpu_base, active, &expires_next, &next_timer);
                cpu_base->next_timer = next_timer;
        }
        return max(expires_next, 0);
}

static ktime_t hrtimer_update_next_event(struct hrtimer_cpu_base *cpu_base)
{
        ktime_t expires_next, soft = KTIME_MAX;

        /*
         * If the soft interrupt has already been activated, ignore the
         * soft bases. They will be handled in the already raised soft
         * interrupt.
         */
        if (!cpu_base->softirq_activated) {
                soft = __hrtimer_get_next_event(cpu_base, HRTIMER_ACTIVE_SOFT);
                /*
                 * Update the soft expiry time. clock_settime() might have
                 * affected it.
                 */
                cpu_base->softirq_expires_next = soft;
        }

        expires_next = __hrtimer_get_next_event(cpu_base, HRTIMER_ACTIVE_HARD);
        /*
         * If a softirq timer is expiring first, update cpu_base->next_timer
         * and program the hardware with the soft expiry time.
         */
        if (expires_next > soft) {
                cpu_base->next_timer = cpu_base->softirq_next_timer;
                expires_next = soft;
        }

        return expires_next;
}

static inline ktime_t hrtimer_update_base(struct hrtimer_cpu_base *base)
{
        ktime_t *offs_real = &base->clock_base[HRTIMER_BASE_REALTIME].offset;
        ktime_t *offs_boot = &base->clock_base[HRTIMER_BASE_BOOTTIME].offset;
        ktime_t *offs_tai = &base->clock_base[HRTIMER_BASE_TAI].offset;

        ktime_t now = ktime_get_update_offsets_now(&base->clock_was_set_seq, offs_real,
                                                   offs_boot, offs_tai);

        base->clock_base[HRTIMER_BASE_REALTIME_SOFT].offset = *offs_real;
        base->clock_base[HRTIMER_BASE_BOOTTIME_SOFT].offset = *offs_boot;
        base->clock_base[HRTIMER_BASE_TAI_SOFT].offset = *offs_tai;

        return now;
}

/*
 * Is the high resolution mode active in the CPU base. This cannot use the
 * static key as the CPUs are switched to high resolution mode
 * asynchronously.
 */
static inline int hrtimer_hres_active(struct hrtimer_cpu_base *cpu_base)
{
        return IS_ENABLED(CONFIG_HIGH_RES_TIMERS) ?
                cpu_base->hres_active : 0;
}

static inline void hrtimer_rearm_event(ktime_t expires_next, bool deferred)
{
        trace_hrtimer_rearm(expires_next, deferred);
        tick_program_event(expires_next, 1);
}

static void __hrtimer_reprogram(struct hrtimer_cpu_base *cpu_base, struct hrtimer *next_timer,
                                ktime_t expires_next)
{
        cpu_base->expires_next = expires_next;

        /*
         * If hres is not active, hardware does not have to be
         * reprogrammed yet.
         *
         * If a hang was detected in the last timer interrupt then we
         * leave the hang delay active in the hardware. We want the
         * system to make progress. That also prevents the following
         * scenario:
         * T1 expires 50ms from now
         * T2 expires 5s from now
         *
         * T1 is removed, so this code is called and would reprogram
         * the hardware to 5s from now. Any hrtimer_start after that
         * will not reprogram the hardware due to hang_detected being
         * set. So we'd effectively block all timers until the T2 event
         * fires.
         */
        if (!hrtimer_hres_active(cpu_base) || cpu_base->hang_detected)
                return;

        hrtimer_rearm_event(expires_next, false);
}

/* Reprogram the event source with a evaluation of all clock bases */
static void hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, bool skip_equal)
{
        ktime_t expires_next = hrtimer_update_next_event(cpu_base);

        if (skip_equal && expires_next == cpu_base->expires_next)
                return;

        __hrtimer_reprogram(cpu_base, cpu_base->next_timer, expires_next);
}

/* High resolution timer related functions */
#ifdef CONFIG_HIGH_RES_TIMERS

/* High resolution timer enabled ? */
static bool hrtimer_hres_enabled __read_mostly  = true;
unsigned int hrtimer_resolution __read_mostly = LOW_RES_NSEC;
EXPORT_SYMBOL_GPL(hrtimer_resolution);

/* Enable / Disable high resolution mode */
static int __init setup_hrtimer_hres(char *str)
{
        return (kstrtobool(str, &hrtimer_hres_enabled) == 0);
}
__setup("highres=", setup_hrtimer_hres);

/* hrtimer_high_res_enabled - query, if the highres mode is enabled */
static inline bool hrtimer_is_hres_enabled(void)
{
        return hrtimer_hres_enabled;
}

/* Switch to high resolution mode */
static void hrtimer_switch_to_hres(void)
{
        struct hrtimer_cpu_base *base = this_cpu_ptr(&hrtimer_bases);

        if (tick_init_highres()) {
                pr_warn("Could not switch to high resolution mode on CPU %u\n", base->cpu);
                return;
        }
        base->hres_active = true;
        hrtimer_resolution = HIGH_RES_NSEC;

        tick_setup_sched_timer(true);
        /* "Retrigger" the interrupt to get things going */
        retrigger_next_event(NULL);
        hrtimer_schedule_hres_work();
}

#else

static inline bool hrtimer_is_hres_enabled(void) { return 0; }
static inline void hrtimer_switch_to_hres(void) { }

#endif /* CONFIG_HIGH_RES_TIMERS */

/*
 * Retrigger next event is called after clock was set with interrupts
 * disabled through an SMP function call or directly from low level
 * resume code.
 *
 * This is only invoked when:
 *      - CONFIG_HIGH_RES_TIMERS is enabled.
 *      - CONFIG_NO_HZ_COMMON is enabled
 *
 * For the other cases this function is empty and because the call sites
 * are optimized out it vanishes as well, i.e. no need for lots of
 * #ifdeffery.
 */
static void retrigger_next_event(void *arg)
{
        struct hrtimer_cpu_base *base = this_cpu_ptr(&hrtimer_bases);

        /*
         * When high resolution mode or nohz is active, then the offsets of
         * CLOCK_REALTIME/TAI/BOOTTIME have to be updated. Otherwise the
         * next tick will take care of that.
         *
         * If high resolution mode is active then the next expiring timer
         * must be reevaluated and the clock event device reprogrammed if
         * necessary.
         *
         * In the NOHZ case the update of the offset and the reevaluation
         * of the next expiring timer is enough. The return from the SMP
         * function call will take care of the reprogramming in case the
         * CPU was in a NOHZ idle sleep.
         *
         * In periodic low resolution mode, the next softirq expiration
         * must also be updated.
         */
        guard(raw_spinlock)(&base->lock);
        hrtimer_update_base(base);
        if (hrtimer_hres_active(base))
                hrtimer_force_reprogram(base, /* skip_equal */ false);
        else
                hrtimer_update_next_event(base);
}

/*
 * When a timer is enqueued and expires earlier than the already enqueued
 * timers, we have to check, whether it expires earlier than the timer for
 * which the clock event device was armed.
 *
 * Called with interrupts disabled and base->cpu_base.lock held
 */
static void hrtimer_reprogram(struct hrtimer *timer, bool reprogram)
{
        struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
        struct hrtimer_clock_base *base = timer->base;
        ktime_t expires = hrtimer_get_expires(timer);

        WARN_ON_ONCE(expires < 0);

        expires = ktime_sub(expires, base->offset);
        /*
         * CLOCK_REALTIME timer might be requested with an absolute
         * expiry time which is less than base->offset. Set it to 0.
         */
        if (expires < 0)
                expires = 0;

        if (timer->is_soft) {
                /*
                 * soft hrtimer could be started on a remote CPU. In this
                 * case softirq_expires_next needs to be updated on the
                 * remote CPU. The soft hrtimer will not expire before the
                 * first hard hrtimer on the remote CPU -
                 * hrtimer_check_target() prevents this case.
                 */
                struct hrtimer_cpu_base *timer_cpu_base = base->cpu_base;

                if (timer_cpu_base->softirq_activated)
                        return;

                if (!ktime_before(expires, timer_cpu_base->softirq_expires_next))
                        return;

                timer_cpu_base->softirq_next_timer = timer;
                timer_cpu_base->softirq_expires_next = expires;

                if (!ktime_before(expires, timer_cpu_base->expires_next) || !reprogram)
                        return;
        }

        /*
         * If the timer is not on the current cpu, we cannot reprogram
         * the other cpus clock event device.
         */
        if (base->cpu_base != cpu_base)
                return;

        if (expires >= cpu_base->expires_next)
                return;

        /* If a deferred rearm is pending skip reprogramming the device */
        if (cpu_base->deferred_rearm)
                return;

        cpu_base->next_timer = timer;

        __hrtimer_reprogram(cpu_base, timer, expires);
}

static bool update_needs_ipi(struct hrtimer_cpu_base *cpu_base, unsigned int active)
{
        struct hrtimer_clock_base *base;
        unsigned int seq;
        ktime_t expires;

        /*
         * Update the base offsets unconditionally so the following
         * checks whether the SMP function call is required works.
         *
         * The update is safe even when the remote CPU is in the hrtimer
         * interrupt or the hrtimer soft interrupt and expiring affected
         * bases. Either it will see the update before handling a base or
         * it will see it when it finishes the processing and reevaluates
         * the next expiring timer.
         */
        seq = cpu_base->clock_was_set_seq;
        hrtimer_update_base(cpu_base);

        /*
         * If the sequence did not change over the update then the
         * remote CPU already handled it.
         */
        if (seq == cpu_base->clock_was_set_seq)
                return false;

        /* If a deferred rearm is pending the remote CPU will take care of it */
        if (cpu_base->deferred_rearm) {
                cpu_base->deferred_needs_update = true;
                return false;
        }

        /*
         * Walk the affected clock bases and check whether the first expiring
         * timer in a clock base is moving ahead of the first expiring timer of
         * @cpu_base. If so, the IPI must be invoked because per CPU clock
         * event devices cannot be remotely reprogrammed.
         */
        active &= cpu_base->active_bases;

        for_each_active_base(base, cpu_base, active) {
                struct timerqueue_linked_node *next;

                next = timerqueue_linked_first(&base->active);
                expires = ktime_sub(next->expires, base->offset);
                if (expires < cpu_base->expires_next)
                        return true;

                /* Extra check for softirq clock bases */
                if (base->index < HRTIMER_BASE_MONOTONIC_SOFT)
                        continue;
                if (cpu_base->softirq_activated)
                        continue;
                if (expires < cpu_base->softirq_expires_next)
                        return true;
        }
        return false;
}

/*
 * Clock was set. This might affect CLOCK_REALTIME, CLOCK_TAI and
 * CLOCK_BOOTTIME (for late sleep time injection).
 *
 * This requires to update the offsets for these clocks
 * vs. CLOCK_MONOTONIC. When high resolution timers are enabled, then this
 * also requires to eventually reprogram the per CPU clock event devices
 * when the change moves an affected timer ahead of the first expiring
 * timer on that CPU. Obviously remote per CPU clock event devices cannot
 * be reprogrammed. The other reason why an IPI has to be sent is when the
 * system is in !HIGH_RES and NOHZ mode. The NOHZ mode updates the offsets
 * in the tick, which obviously might be stopped, so this has to bring out
 * the remote CPU which might sleep in idle to get this sorted.
 */
void clock_was_set(unsigned int bases)
{
        cpumask_var_t mask;

        if (!hrtimer_highres_enabled() && !tick_nohz_is_active())
                goto out_timerfd;

        if (!zalloc_cpumask_var(&mask, GFP_KERNEL)) {
                on_each_cpu(retrigger_next_event, NULL, 1);
                goto out_timerfd;
        }

        /* Avoid interrupting CPUs if possible */
        scoped_guard(cpus_read_lock) {
                int cpu;

                for_each_online_cpu(cpu) {
                        struct hrtimer_cpu_base *cpu_base = &per_cpu(hrtimer_bases, cpu);

                        guard(raw_spinlock_irqsave)(&cpu_base->lock);
                        if (update_needs_ipi(cpu_base, bases))
                                cpumask_set_cpu(cpu, mask);
                }
                scoped_guard(preempt)
                        smp_call_function_many(mask, retrigger_next_event, NULL, 1);
        }
        free_cpumask_var(mask);

out_timerfd:
        timerfd_clock_was_set();
}

static void clock_was_set_work(struct work_struct *work)
{
        clock_was_set(CLOCK_SET_WALL);
}

static DECLARE_WORK(hrtimer_work, clock_was_set_work);

/*
 * Called from timekeeping code to reprogram the hrtimer interrupt device
 * on all cpus and to notify timerfd.
 */
void clock_was_set_delayed(void)
{
        schedule_work(&hrtimer_work);
}

/*
 * Called during resume either directly from via timekeeping_resume()
 * or in the case of s2idle from tick_unfreeze() to ensure that the
 * hrtimers are up to date.
 */
void hrtimers_resume_local(void)
{
        lockdep_assert_irqs_disabled();
        /* Retrigger on the local CPU */
        retrigger_next_event(NULL);
}

/* Counterpart to lock_hrtimer_base above */
static inline void unlock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
        __releases(&timer->base->cpu_base->lock)
{
        raw_spin_unlock_irqrestore(&timer->base->cpu_base->lock, *flags);
}

/**
 * hrtimer_forward() - forward the timer expiry
 * @timer:      hrtimer to forward
 * @now:        forward past this time
 * @interval:   the interval to forward
 *
 * Forward the timer expiry so it will expire in the future.
 *
 * .. note::
 *  This only updates the timer expiry value and does not requeue the timer.
 *
 * There is also a variant of this function: hrtimer_forward_now().
 *
 * Context: Can be safely called from the callback function of @timer. If called
 *          from other contexts @timer must neither be enqueued nor running the
 *          callback and the caller needs to take care of serialization.
 *
 * Return: The number of overruns are returned.
 */
u64 hrtimer_forward(struct hrtimer *timer, ktime_t now, ktime_t interval)
{
        ktime_t delta;
        u64 orun = 1;

        delta = ktime_sub(now, hrtimer_get_expires(timer));

        if (delta < 0)
                return 0;

        if (WARN_ON(timer->is_queued))
                return 0;

        if (interval < hrtimer_resolution)
                interval = hrtimer_resolution;

        if (unlikely(delta >= interval)) {
                s64 incr = ktime_to_ns(interval);

                orun = ktime_divns(delta, incr);
                hrtimer_add_expires_ns(timer, incr * orun);
                if (hrtimer_get_expires(timer) > now)
                        return orun;
                /*
                 * This (and the ktime_add() below) is the
                 * correction for exact:
                 */
                orun++;
        }
        hrtimer_add_expires(timer, interval);

        return orun;
}
EXPORT_SYMBOL_GPL(hrtimer_forward);

/*
 * enqueue_hrtimer - internal function to (re)start a timer
 *
 * The timer is inserted in expiry order. Insertion into the
 * red black tree is O(log(n)).
 *
 * Returns true when the new timer is the leftmost timer in the tree.
 */
static bool enqueue_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base,
                            enum hrtimer_mode mode, bool was_armed)
{
        lockdep_assert_held(&base->cpu_base->lock);

        debug_activate(timer, mode, was_armed);
        WARN_ON_ONCE(!base->cpu_base->online);

        base->cpu_base->active_bases |= 1 << base->index;

        /* Pairs with the lockless read in hrtimer_is_queued() */
        WRITE_ONCE(timer->is_queued, HRTIMER_STATE_ENQUEUED);

        if (!timerqueue_linked_add(&base->active, &timer->node))
                return false;

        base->expires_next = hrtimer_get_expires(timer);
        return true;
}

static inline void base_update_next_timer(struct hrtimer_clock_base *base)
{
        struct timerqueue_linked_node *next = timerqueue_linked_first(&base->active);

        base->expires_next = next ? next->expires : KTIME_MAX;
}

/*
 * __remove_hrtimer - internal function to remove a timer
 *
 * High resolution timer mode reprograms the clock event device when the
 * timer is the one which expires next. The caller can disable this by setting
 * reprogram to zero. This is useful, when the context does a reprogramming
 * anyway (e.g. timer interrupt)
 */
static void __remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base,
                             bool newstate, bool reprogram)
{
        struct hrtimer_cpu_base *cpu_base = base->cpu_base;
        bool was_first;

        lockdep_assert_held(&cpu_base->lock);

        if (!timer->is_queued)
                return;

        /* Pairs with the lockless read in hrtimer_is_queued() */
        WRITE_ONCE(timer->is_queued, newstate);

        was_first = !timerqueue_linked_prev(&timer->node);

        if (!timerqueue_linked_del(&base->active, &timer->node))
                cpu_base->active_bases &= ~(1 << base->index);

        /* Nothing to update if this was not the first timer in the base */
        if (!was_first)
                return;

        base_update_next_timer(base);

        /*
         * If reprogram is false don't update cpu_base->next_timer and do not
         * touch the clock event device.
         *
         * This happens when removing the first timer on a remote CPU, which
         * will be handled by the remote CPU's interrupt. It also happens when
         * a local timer is removed to be immediately restarted. That's handled
         * at the call site.
         */
        if (!reprogram || timer != cpu_base->next_timer || timer->is_lazy)
                return;

        if (cpu_base->deferred_rearm)
                cpu_base->deferred_needs_update = true;
        else
                hrtimer_force_reprogram(cpu_base, /* skip_equal */ true);
}

static inline bool remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base,
                                  bool newstate)
{
        lockdep_assert_held(&base->cpu_base->lock);

        if (timer->is_queued) {
                bool reprogram;

                debug_hrtimer_deactivate(timer);

                /*
                 * Remove the timer and force reprogramming when high
                 * resolution mode is active and the timer is on the current
                 * CPU. If we remove a timer on another CPU, reprogramming is
                 * skipped. The interrupt event on this CPU is fired and
                 * reprogramming happens in the interrupt handler. This is a
                 * rare case and less expensive than a smp call.
                 */
                reprogram = base->cpu_base == this_cpu_ptr(&hrtimer_bases);

                __remove_hrtimer(timer, base, newstate, reprogram);
                return true;
        }
        return false;
}

/*
 * Update in place has to retrieve the expiry times of the neighbour nodes
 * if they exist. That is cache line neutral because the dequeue/enqueue
 * operation is going to need the same cache lines. But there is a big win
 * when the dequeue/enqueue can be avoided because the RB tree does not
 * have to be rebalanced twice.
 */
static inline bool
hrtimer_can_update_in_place(struct hrtimer *timer, struct hrtimer_clock_base *base, ktime_t expires)
{
        struct timerqueue_linked_node *next = timerqueue_linked_next(&timer->node);
        struct timerqueue_linked_node *prev = timerqueue_linked_prev(&timer->node);

        /* If the new expiry goes behind the next timer, requeue is required */
        if (next && expires > next->expires)
                return false;

        /* If this is the first timer, update in place */
        if (!prev)
                return true;

        /* Update in place when it does not go ahead of the previous one */
        return expires >= prev->expires;
}

static inline bool
remove_and_enqueue_same_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
                             const enum hrtimer_mode mode, ktime_t expires, u64 delta_ns)
{
        bool was_first = false;

        /* Remove it from the timer queue if active */
        if (timer->is_queued) {
                was_first = !timerqueue_linked_prev(&timer->node);

                /* Try to update in place to avoid the de/enqueue dance */
                if (hrtimer_can_update_in_place(timer, base, expires)) {
                        hrtimer_set_expires_range_ns(timer, expires, delta_ns);
                        trace_hrtimer_start(timer, mode, true);
                        if (was_first)
                                base->expires_next = expires;
                        return was_first;
                }

                debug_hrtimer_deactivate(timer);
                timerqueue_linked_del(&base->active, &timer->node);
        }

        /* Set the new expiry time */
        hrtimer_set_expires_range_ns(timer, expires, delta_ns);

        debug_activate(timer, mode, timer->is_queued);
        base->cpu_base->active_bases |= 1 << base->index;

        /* Pairs with the lockless read in hrtimer_is_queued() */
        WRITE_ONCE(timer->is_queued, HRTIMER_STATE_ENQUEUED);

        /* If it's the first expiring timer now or again, update base */
        if (timerqueue_linked_add(&base->active, &timer->node)) {
                base->expires_next = expires;
                return true;
        }

        if (was_first)
                base_update_next_timer(base);

        return false;
}

static inline ktime_t hrtimer_update_lowres(struct hrtimer *timer, ktime_t tim,
                                            const enum hrtimer_mode mode)
{
#ifdef CONFIG_TIME_LOW_RES
        /*
         * CONFIG_TIME_LOW_RES indicates that the system has no way to return
         * granular time values. For relative timers we add hrtimer_resolution
         * (i.e. one jiffy) to prevent short timeouts.
         */
        timer->is_rel = mode & HRTIMER_MODE_REL;
        if (timer->is_rel)
                tim = ktime_add_safe(tim, hrtimer_resolution);
#endif
        return tim;
}

static void hrtimer_update_softirq_timer(struct hrtimer_cpu_base *cpu_base, bool reprogram)
{
        ktime_t expires = __hrtimer_get_next_event(cpu_base, HRTIMER_ACTIVE_SOFT);

        /*
         * Reprogramming needs to be triggered, even if the next soft
         * hrtimer expires at the same time as the next hard
         * hrtimer. cpu_base->softirq_expires_next needs to be updated!
         */
        if (expires == KTIME_MAX)
                return;

        /*
         * cpu_base->next_timer is recomputed by __hrtimer_get_next_event()
         * cpu_base->expires_next is only set by hrtimer_reprogram()
         */
        hrtimer_reprogram(cpu_base->softirq_next_timer, reprogram);
}

#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
static __always_inline bool hrtimer_prefer_local(bool is_local, bool is_first, bool is_pinned)
{
        if (static_branch_likely(&timers_migration_enabled)) {
                /*
                 * If it is local and the first expiring timer keep it on the local
                 * CPU to optimize reprogramming of the clockevent device. Also
                 * avoid switch_hrtimer_base() overhead when local and pinned.
                 */
                if (!is_local)
                        return false;
                if (is_first || is_pinned)
                        return true;

                /* Honour the NOHZ full restrictions */
                if (!housekeeping_cpu(smp_processor_id(), HK_TYPE_KERNEL_NOISE))
                        return false;

                /*
                 * If the tick is not stopped or need_resched() is set, then
                 * there is no point in moving the timer somewhere else.
                 */
                return !tick_nohz_tick_stopped() || need_resched();
        }
        return is_local;
}
#else
static __always_inline bool hrtimer_prefer_local(bool is_local, bool is_first, bool is_pinned)
{
        return is_local;
}
#endif

static inline bool hrtimer_keep_base(struct hrtimer *timer, bool is_local, bool is_first,
                                     bool is_pinned)
{
        /* If the timer is running the callback it has to stay on its CPU base. */
        if (unlikely(timer->base->running == timer))
                return true;

        return hrtimer_prefer_local(is_local, is_first, is_pinned);
}

enum {
        HRTIMER_REPROGRAM_NONE,
        HRTIMER_REPROGRAM,
        HRTIMER_REPROGRAM_FORCE,
};

static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, u64 delta_ns,
                                    const enum hrtimer_mode mode, struct hrtimer_clock_base *base)
{
        struct hrtimer_cpu_base *this_cpu_base = this_cpu_ptr(&hrtimer_bases);
        bool is_pinned, first, was_first, keep_base = false;
        struct hrtimer_cpu_base *cpu_base = base->cpu_base;

        was_first = cpu_base->next_timer == timer;
        is_pinned = !!(mode & HRTIMER_MODE_PINNED);

        /*
         * Don't keep it local if this enqueue happens on a unplugged CPU
         * after hrtimer_cpu_dying() has been invoked.
         */
        if (likely(this_cpu_base->online)) {
                bool is_local = cpu_base == this_cpu_base;

                keep_base = hrtimer_keep_base(timer, is_local, was_first, is_pinned);
        }

        /* Calculate absolute expiry time for relative timers */
        if (mode & HRTIMER_MODE_REL)
                tim = ktime_add_safe(tim, __hrtimer_cb_get_time(base->clockid));
        /* Compensate for low resolution granularity */
        tim = hrtimer_update_lowres(timer, tim, mode);

        /*
         * Remove an active timer from the queue. In case it is not queued
         * on the current CPU, make sure that remove_hrtimer() updates the
         * remote data correctly.
         *
         * If it's on the current CPU and the first expiring timer, then
         * skip reprogramming, keep the timer local and enforce
         * reprogramming later if it was the first expiring timer.  This
         * avoids programming the underlying clock event twice (once at
         * removal and once after enqueue).
         *
         * @keep_base is also true if the timer callback is running on a
         * remote CPU and for local pinned timers.
         */
        if (likely(keep_base)) {
                first = remove_and_enqueue_same_base(timer, base, mode, tim, delta_ns);
        } else {
                /* Keep the ENQUEUED state in case it is queued */
                bool was_armed = remove_hrtimer(timer, base, HRTIMER_STATE_ENQUEUED);

                hrtimer_set_expires_range_ns(timer, tim, delta_ns);

                /* Switch the timer base, if necessary: */
                base = switch_hrtimer_base(timer, base, is_pinned);
                cpu_base = base->cpu_base;

                first = enqueue_hrtimer(timer, base, mode, was_armed);
        }

        /* If a deferred rearm is pending skip reprogramming the device */
        if (cpu_base->deferred_rearm) {
                cpu_base->deferred_needs_update = true;
                return HRTIMER_REPROGRAM_NONE;
        }

        if (!was_first || cpu_base != this_cpu_base) {
                /*
                 * If the current CPU base is online, then the timer is never
                 * queued on a remote CPU if it would be the first expiring
                 * timer there unless the timer callback is currently executed
                 * on the remote CPU. In the latter case the remote CPU will
                 * re-evaluate the first expiring timer after completing the
                 * callbacks.
                 */
                if (likely(hrtimer_base_is_online(this_cpu_base)))
                        return first ? HRTIMER_REPROGRAM : HRTIMER_REPROGRAM_NONE;

                /*
                 * Timer was enqueued remote because the current base is
                 * already offline. If the timer is the first to expire,
                 * kick the remote CPU to reprogram the clock event.
                 */
                if (first)
                        smp_call_function_single_async(cpu_base->cpu, &cpu_base->csd);
                return HRTIMER_REPROGRAM_NONE;
        }

        /*
         * Special case for the HRTICK timer. It is frequently rearmed and most
         * of the time moves the expiry into the future. That's expensive in
         * virtual machines and it's better to take the pointless already armed
         * interrupt than reprogramming the hardware on every context switch.
         *
         * If the new expiry is before the armed time, then reprogramming is
         * required.
         */
        if (timer->is_lazy) {
                if (cpu_base->expires_next <= hrtimer_get_expires(timer))
                        return HRTIMER_REPROGRAM_NONE;
        }

        /*
         * Timer was the first expiring timer and forced to stay on the
         * current CPU to avoid reprogramming on removal and enqueue. Force
         * reprogram the hardware by evaluating the new first expiring
         * timer.
         */
        return HRTIMER_REPROGRAM_FORCE;
}

static int hrtimer_start_range_ns_common(struct hrtimer *timer, ktime_t tim,
                                         u64 delta_ns, const enum hrtimer_mode mode,
                                         struct hrtimer_clock_base *base)
{
        /*
         * Check whether the HRTIMER_MODE_SOFT bit and hrtimer.is_soft
         * match on CONFIG_PREEMPT_RT = n. With PREEMPT_RT check the hard
         * expiry mode because unmarked timers are moved to softirq expiry.
         */
        if (!IS_ENABLED(CONFIG_PREEMPT_RT))
                WARN_ON_ONCE(!(mode & HRTIMER_MODE_SOFT) ^ !timer->is_soft);
        else
                WARN_ON_ONCE(!(mode & HRTIMER_MODE_HARD) ^ !timer->is_hard);

        return __hrtimer_start_range_ns(timer, tim, delta_ns, mode, base);
}

/**
 * hrtimer_start_range_ns - (re)start an hrtimer
 * @timer:      the timer to be added
 * @tim:        expiry time
 * @delta_ns:   "slack" range for the timer
 * @mode:       timer mode: absolute (HRTIMER_MODE_ABS) or
 *              relative (HRTIMER_MODE_REL), and pinned (HRTIMER_MODE_PINNED);
 *              softirq based mode is considered for debug purpose only!
 */
void hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, u64 delta_ns,
                            const enum hrtimer_mode mode)
{
        struct hrtimer_clock_base *base;
        unsigned long flags;

        debug_hrtimer_assert_init(timer);

        base = lock_hrtimer_base(timer, &flags);

        switch (hrtimer_start_range_ns_common(timer, tim, delta_ns, mode, base)) {
        case HRTIMER_REPROGRAM:
                hrtimer_reprogram(timer, true);
                break;
        case HRTIMER_REPROGRAM_FORCE:
                hrtimer_force_reprogram(timer->base->cpu_base, 1);
                break;
        case HRTIMER_REPROGRAM_NONE:
                break;
        }

        unlock_hrtimer_base(timer, &flags);
}
EXPORT_SYMBOL_GPL(hrtimer_start_range_ns);

static inline bool hrtimer_check_user_timer(struct hrtimer *timer)
{
        struct hrtimer_cpu_base *cpu_base = timer->base->cpu_base;
        ktime_t expires;

        /*
         * This uses soft expires because that's the user provided
         * expiry time, while expires can be further in the past
         * due to a slack value added to the user expiry time.
         */
        expires = hrtimer_get_softexpires(timer);

        /* Convert to monotonic */
        expires = ktime_sub(expires, timer->base->offset);

        /*
         * Check whether this timer will end up as the first expiring timer in
         * the CPU base. If not, no further checks required as it's then
         * guaranteed to expire in the future.
         */
        if (expires >= cpu_base->expires_next)
                return true;

        /* Validate that the expiry time is in the future. */
        if (expires > ktime_get())
                return true;

        debug_hrtimer_deactivate(timer);
        __remove_hrtimer(timer, timer->base, HRTIMER_STATE_INACTIVE, false);
        trace_hrtimer_start_expired(timer);
        return false;
}

/**
 * hrtimer_start_range_ns_user - (re)start an user controlled hrtimer
 * @timer:      the timer to be added
 * @tim:        expiry time
 * @delta_ns:   "slack" range for the timer
 * @mode:       timer mode: absolute (HRTIMER_MODE_ABS) or
 *              relative (HRTIMER_MODE_REL), and pinned (HRTIMER_MODE_PINNED);
 *              softirq based mode is considered for debug purpose only!
 *
 * Returns: True when the timer was queued, false if it was already expired
 *
 * This function cannot invoke the timer callback for expired timers as it might
 * be called under a lock which the timer callback needs to acquire. So the
 * caller has to handle that case.
 */
bool hrtimer_start_range_ns_user(struct hrtimer *timer, ktime_t tim,
                                 u64 delta_ns, const enum hrtimer_mode mode)
{
        struct hrtimer_clock_base *base;
        unsigned long flags;
        bool ret = true;

        debug_hrtimer_assert_init(timer);

        base = lock_hrtimer_base(timer, &flags);

        switch (hrtimer_start_range_ns_common(timer, tim, delta_ns, mode, base)) {
        case HRTIMER_REPROGRAM:
                ret = hrtimer_check_user_timer(timer);
                if (ret)
                        hrtimer_reprogram(timer, true);
                break;
        case HRTIMER_REPROGRAM_FORCE:
                ret = hrtimer_check_user_timer(timer);
                /*
                 * The base must always be reevaluated, independent of the
                 * result above because the timer was the first pending timer.
                 */
                hrtimer_force_reprogram(timer->base->cpu_base, 1);
                break;
        case HRTIMER_REPROGRAM_NONE:
                break;
        }

        unlock_hrtimer_base(timer, &flags);
        return ret;
}
EXPORT_SYMBOL_GPL(hrtimer_start_range_ns_user);

/**
 * hrtimer_try_to_cancel - try to deactivate a timer
 * @timer:      hrtimer to stop
 *
 * Returns:
 *
 *  *  0 when the timer was not active
 *  *  1 when the timer was active
 *  * -1 when the timer is currently executing the callback function and
 *    cannot be stopped
 */
int hrtimer_try_to_cancel(struct hrtimer *timer)
{
        struct hrtimer_clock_base *base;
        unsigned long flags;
        int ret = -1;

        /*
         * Check lockless first. If the timer is not active (neither
         * enqueued nor running the callback, nothing to do here.  The
         * base lock does not serialize against a concurrent enqueue,
         * so we can avoid taking it.
         */
        if (!hrtimer_active(timer))
                return 0;

        base = lock_hrtimer_base(timer, &flags);

        if (!hrtimer_callback_running(timer)) {
                ret = remove_hrtimer(timer, base, HRTIMER_STATE_INACTIVE);
                if (ret)
                        trace_hrtimer_cancel(timer);
        }

        unlock_hrtimer_base(timer, &flags);

        return ret;

}
EXPORT_SYMBOL_GPL(hrtimer_try_to_cancel);

#ifdef CONFIG_PREEMPT_RT
static void hrtimer_cpu_base_init_expiry_lock(struct hrtimer_cpu_base *base)
{
        spin_lock_init(&base->softirq_expiry_lock);
}

static void hrtimer_cpu_base_lock_expiry(struct hrtimer_cpu_base *base)
        __acquires(&base->softirq_expiry_lock)
{
        spin_lock(&base->softirq_expiry_lock);
}

static void hrtimer_cpu_base_unlock_expiry(struct hrtimer_cpu_base *base)
        __releases(&base->softirq_expiry_lock)
{
        spin_unlock(&base->softirq_expiry_lock);
}

/*
 * The counterpart to hrtimer_cancel_wait_running().
 *
 * If there is a waiter for cpu_base->expiry_lock, then it was waiting for
 * the timer callback to finish. Drop expiry_lock and reacquire it. That
 * allows the waiter to acquire the lock and make progress.
 */
static void hrtimer_sync_wait_running(struct hrtimer_cpu_base *cpu_base, unsigned long flags)
{
        if (atomic_read(&cpu_base->timer_waiters)) {
                raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
                spin_unlock(&cpu_base->softirq_expiry_lock);
                spin_lock(&cpu_base->softirq_expiry_lock);
                raw_spin_lock_irq(&cpu_base->lock);
        }
}

#ifdef CONFIG_SMP
static __always_inline bool is_migration_base(struct hrtimer_clock_base *base)
{
        return base == &migration_base;
}
#else
static __always_inline bool is_migration_base(struct hrtimer_clock_base *base)
{
        return false;
}
#endif

/*
 * This function is called on PREEMPT_RT kernels when the fast path
 * deletion of a timer failed because the timer callback function was
 * running.
 *
 * This prevents priority inversion: if the soft irq thread is preempted
 * in the middle of a timer callback, then calling hrtimer_cancel() can
 * lead to two issues:
 *
 *  - If the caller is on a remote CPU then it has to spin wait for the timer
 *    handler to complete. This can result in unbound priority inversion.
 *
 *  - If the caller originates from the task which preempted the timer
 *    handler on the same CPU, then spin waiting for the timer handler to
 *    complete is never going to end.
 */
void hrtimer_cancel_wait_running(const struct hrtimer *timer)
{
        /* Lockless read. Prevent the compiler from reloading it below */
        struct hrtimer_clock_base *base = READ_ONCE(timer->base);

        /*
         * Just relax if the timer expires in hard interrupt context or if
         * it is currently on the migration base.
         */
        if (!timer->is_soft || is_migration_base(base)) {
                cpu_relax();
                return;
        }

        /*
         * Mark the base as contended and grab the expiry lock, which is
         * held by the softirq across the timer callback. Drop the lock
         * immediately so the softirq can expire the next timer. In theory
         * the timer could already be running again, but that's more than
         * unlikely and just causes another wait loop.
         */
        atomic_inc(&base->cpu_base->timer_waiters);
        spin_lock_bh(&base->cpu_base->softirq_expiry_lock);
        atomic_dec(&base->cpu_base->timer_waiters);
        spin_unlock_bh(&base->cpu_base->softirq_expiry_lock);
}
#else
static inline void hrtimer_cpu_base_init_expiry_lock(struct hrtimer_cpu_base *base) { }
static inline void hrtimer_cpu_base_lock_expiry(struct hrtimer_cpu_base *base) { }
static inline void hrtimer_cpu_base_unlock_expiry(struct hrtimer_cpu_base *base) { }
static inline void hrtimer_sync_wait_running(struct hrtimer_cpu_base *base, unsigned long fl) { }
#endif

/**
 * hrtimer_cancel - cancel a timer and wait for the handler to finish.
 * @timer:      the timer to be cancelled
 *
 * Returns:
 *  0 when the timer was not active
 *  1 when the timer was active
 */
int hrtimer_cancel(struct hrtimer *timer)
{
        int ret;

        do {
                ret = hrtimer_try_to_cancel(timer);

                if (ret < 0)
                        hrtimer_cancel_wait_running(timer);
        } while (ret < 0);
        return ret;
}
EXPORT_SYMBOL_GPL(hrtimer_cancel);

/**
 * __hrtimer_get_remaining - get remaining time for the timer
 * @timer:      the timer to read
 * @adjust:     adjust relative timers when CONFIG_TIME_LOW_RES=y
 */
ktime_t __hrtimer_get_remaining(const struct hrtimer *timer, bool adjust)
{
        unsigned long flags;
        ktime_t rem;

        lock_hrtimer_base(timer, &flags);
        if (IS_ENABLED(CONFIG_TIME_LOW_RES) && adjust)
                rem = hrtimer_expires_remaining_adjusted(timer);
        else
                rem = hrtimer_expires_remaining(timer);
        unlock_hrtimer_base(timer, &flags);

        return rem;
}
EXPORT_SYMBOL_GPL(__hrtimer_get_remaining);

#ifdef CONFIG_NO_HZ_COMMON
/**
 * hrtimer_get_next_event - get the time until next expiry event
 *
 * Returns the next expiry time or KTIME_MAX if no timer is pending.
 */
ktime_t hrtimer_get_next_event(void)
{
        struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
        ktime_t expires = KTIME_MAX;

        guard(raw_spinlock_irqsave)(&cpu_base->lock);
        if (!hrtimer_hres_active(cpu_base))
                expires = __hrtimer_get_next_event(cpu_base, HRTIMER_ACTIVE_ALL);

        return expires;
}

/**
 * hrtimer_next_event_without - time until next expiry event w/o one timer
 * @exclude:    timer to exclude
 *
 * Returns the next expiry time over all timers except for the @exclude one or
 * KTIME_MAX if none of them is pending.
 */
ktime_t hrtimer_next_event_without(const struct hrtimer *exclude)
{
        struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
        ktime_t expires = KTIME_MAX;
        unsigned int active;

        guard(raw_spinlock_irqsave)(&cpu_base->lock);
        if (!hrtimer_hres_active(cpu_base))
                return expires;

        active = cpu_base->active_bases & HRTIMER_ACTIVE_SOFT;
        if (active && !cpu_base->softirq_activated)
                expires = hrtimer_bases_next_event_without(cpu_base, exclude, active, KTIME_MAX);

        active = cpu_base->active_bases & HRTIMER_ACTIVE_HARD;
        if (!active)
                return expires;
        return hrtimer_bases_next_event_without(cpu_base, exclude, active, expires);
}
#endif

static inline int hrtimer_clockid_to_base(clockid_t clock_id)
{
        switch (clock_id) {
        case CLOCK_MONOTONIC:
                return HRTIMER_BASE_MONOTONIC;
        case CLOCK_REALTIME:
                return HRTIMER_BASE_REALTIME;
        case CLOCK_BOOTTIME:
                return HRTIMER_BASE_BOOTTIME;
        case CLOCK_TAI:
                return HRTIMER_BASE_TAI;
        default:
                WARN(1, "Invalid clockid %d. Using MONOTONIC\n", clock_id);
                return HRTIMER_BASE_MONOTONIC;
        }
}

static ktime_t __hrtimer_cb_get_time(clockid_t clock_id)
{
        switch (clock_id) {
        case CLOCK_MONOTONIC:
                return ktime_get();
        case CLOCK_REALTIME:
                return ktime_get_real();
        case CLOCK_BOOTTIME:
                return ktime_get_boottime();
        case CLOCK_TAI:
                return ktime_get_clocktai();
        default:
                WARN(1, "Invalid clockid %d. Using MONOTONIC\n", clock_id);
                return ktime_get();
        }
}

ktime_t hrtimer_cb_get_time(const struct hrtimer *timer)
{
        return __hrtimer_cb_get_time(timer->base->clockid);
}
EXPORT_SYMBOL_GPL(hrtimer_cb_get_time);

static void __hrtimer_setup(struct hrtimer *timer, enum hrtimer_restart (*fn)(struct hrtimer *),
                            clockid_t clock_id, enum hrtimer_mode mode)
{
        bool softtimer = !!(mode & HRTIMER_MODE_SOFT);
        struct hrtimer_cpu_base *cpu_base;
        int base;

        /*
         * On PREEMPT_RT enabled kernels hrtimers which are not explicitly
         * marked for hard interrupt expiry mode are moved into soft
         * interrupt context for latency reasons and because the callbacks
         * can invoke functions which might sleep on RT, e.g. spin_lock().
         */
        if (IS_ENABLED(CONFIG_PREEMPT_RT) && !(mode & HRTIMER_MODE_HARD))
                softtimer = true;

        memset(timer, 0, sizeof(struct hrtimer));

        cpu_base = raw_cpu_ptr(&hrtimer_bases);

        /*
         * POSIX magic: Relative CLOCK_REALTIME timers are not affected by
         * clock modifications, so they needs to become CLOCK_MONOTONIC to
         * ensure POSIX compliance.
         */
        if (clock_id == CLOCK_REALTIME && mode & HRTIMER_MODE_REL)
                clock_id = CLOCK_MONOTONIC;

        base = softtimer ? HRTIMER_MAX_CLOCK_BASES / 2 : 0;
        base += hrtimer_clockid_to_base(clock_id);
        timer->is_soft = softtimer;
        timer->is_hard = !!(mode & HRTIMER_MODE_HARD);
        timer->is_lazy = !!(mode & HRTIMER_MODE_LAZY_REARM);
        timer->base = &cpu_base->clock_base[base];
        timerqueue_linked_init(&timer->node);

        if (WARN_ON_ONCE(!fn))
                ACCESS_PRIVATE(timer, function) = hrtimer_dummy_timeout;
        else
                ACCESS_PRIVATE(timer, function) = fn;
}

/**
 * hrtimer_setup - initialize a timer to the given clock
 * @timer:      the timer to be initialized
 * @function:   the callback function
 * @clock_id:   the clock to be used
 * @mode:       The modes which are relevant for initialization:
 *              HRTIMER_MODE_ABS, HRTIMER_MODE_REL, HRTIMER_MODE_ABS_SOFT,
 *              HRTIMER_MODE_REL_SOFT
 *
 *              The PINNED variants of the above can be handed in,
 *              but the PINNED bit is ignored as pinning happens
 *              when the hrtimer is started
 */
void hrtimer_setup(struct hrtimer *timer, enum hrtimer_restart (*function)(struct hrtimer *),
                   clockid_t clock_id, enum hrtimer_mode mode)
{
        debug_setup(timer, clock_id, mode);
        __hrtimer_setup(timer, function, clock_id, mode);
}
EXPORT_SYMBOL_GPL(hrtimer_setup);

/**
 * hrtimer_setup_on_stack - initialize a timer on stack memory
 * @timer:      The timer to be initialized
 * @function:   the callback function
 * @clock_id:   The clock to be used
 * @mode:       The timer mode
 *
 * Similar to hrtimer_setup(), except that this one must be used if struct hrtimer is in stack
 * memory.
 */
void hrtimer_setup_on_stack(struct hrtimer *timer,
                            enum hrtimer_restart (*function)(struct hrtimer *),
                            clockid_t clock_id, enum hrtimer_mode mode)
{
        debug_setup_on_stack(timer, clock_id, mode);
        __hrtimer_setup(timer, function, clock_id, mode);
}
EXPORT_SYMBOL_GPL(hrtimer_setup_on_stack);

/*
 * A timer is active, when it is enqueued into the rbtree or the
 * callback function is running or it's in the state of being migrated
 * to another cpu.
 *
 * It is important for this function to not return a false negative.
 */
bool hrtimer_active(const struct hrtimer *timer)
{
        struct hrtimer_clock_base *base;
        unsigned int seq;

        do {
                base = READ_ONCE(timer->base);
                seq = raw_read_seqcount_begin(&base->seq);

                if (timer->is_queued || base->running == timer)
                        return true;

        } while (read_seqcount_retry(&base->seq, seq) || base != READ_ONCE(timer->base));

        return false;
}
EXPORT_SYMBOL_GPL(hrtimer_active);

/*
 * The write_seqcount_barrier()s in __run_hrtimer() split the thing into 3
 * distinct sections:
 *
 *  - queued:   the timer is queued
 *  - callback: the timer is being ran
 *  - post:     the timer is inactive or (re)queued
 *
 * On the read side we ensure we observe timer->is_queued and cpu_base->running
 * from the same section, if anything changed while we looked at it, we retry.
 * This includes timer->base changing because sequence numbers alone are
 * insufficient for that.
 *
 * The sequence numbers are required because otherwise we could still observe
 * a false negative if the read side got smeared over multiple consecutive
 * __run_hrtimer() invocations.
 */
static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base, struct hrtimer_clock_base *base,
                          struct hrtimer *timer, ktime_t now, unsigned long flags)
        __must_hold(&cpu_base->lock)
{
        enum hrtimer_restart (*fn)(struct hrtimer *);
        bool expires_in_hardirq;
        int restart;

        lockdep_assert_held(&cpu_base->lock);

        debug_hrtimer_deactivate(timer);
        base->running = timer;

        /*
         * Separate the ->running assignment from the ->is_queued assignment.
         *
         * As with a regular write barrier, this ensures the read side in
         * hrtimer_active() cannot observe base->running == NULL &&
         * timer->is_queued == INACTIVE.
         */
        raw_write_seqcount_barrier(&base->seq);

        __remove_hrtimer(timer, base, HRTIMER_STATE_INACTIVE, false);
        fn = ACCESS_PRIVATE(timer, function);

        /*
         * Clear the 'is relative' flag for the TIME_LOW_RES case. If the
         * timer is restarted with a period then it becomes an absolute
         * timer. If its not restarted it does not matter.
         */
        if (IS_ENABLED(CONFIG_TIME_LOW_RES))
                timer->is_rel = false;

        /*
         * The timer is marked as running in the CPU base, so it is
         * protected against migration to a different CPU even if the lock
         * is dropped.
         */
        raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
        trace_hrtimer_expire_entry(timer, now);
        expires_in_hardirq = lockdep_hrtimer_enter(timer);

        restart = fn(timer);

        lockdep_hrtimer_exit(expires_in_hardirq);
        trace_hrtimer_expire_exit(timer);
        raw_spin_lock_irq(&cpu_base->lock);

        /*
         * Note: We clear the running state after enqueue_hrtimer and
         * we do not reprogram the event hardware. Happens either in
         * hrtimer_start_range_ns() or in hrtimer_interrupt()
         *
         * Note: Because we dropped the cpu_base->lock above,
         * hrtimer_start_range_ns() can have popped in and enqueued the timer
         * for us already.
         */
        if (restart == HRTIMER_RESTART && !timer->is_queued)
                enqueue_hrtimer(timer, base, HRTIMER_MODE_ABS, false);

        /*
         * Separate the ->running assignment from the ->is_queued assignment.
         *
         * As with a regular write barrier, this ensures the read side in
         * hrtimer_active() cannot observe base->running.timer == NULL &&
         * timer->is_queued == INACTIVE.
         */
        raw_write_seqcount_barrier(&base->seq);

        WARN_ON_ONCE(base->running != timer);
        base->running = NULL;
}

static __always_inline struct hrtimer *clock_base_next_timer_safe(struct hrtimer_clock_base *base)
{
        struct timerqueue_linked_node *next = timerqueue_linked_first(&base->active);

        return next ? hrtimer_from_timerqueue_node(next) : NULL;
}

static void __hrtimer_run_queues(struct hrtimer_cpu_base *cpu_base, ktime_t now,
                                 unsigned long flags, unsigned int active_mask)
{
        unsigned int active = cpu_base->active_bases & active_mask;
        struct hrtimer_clock_base *base;

        for_each_active_base(base, cpu_base, active) {
                ktime_t basenow = ktime_add(now, base->offset);
                struct hrtimer *timer;

                while ((timer = clock_base_next_timer(base))) {
                        /*
                         * The immediate goal for using the softexpires is
                         * minimizing wakeups, not running timers at the
                         * earliest interrupt after their soft expiration.
                         * This allows us to avoid using a Priority Search
                         * Tree, which can answer a stabbing query for
                         * overlapping intervals and instead use the simple
                         * BST we already have.
                         * We don't add extra wakeups by delaying timers that
                         * are right-of a not yet expired timer, because that
                         * timer will have to trigger a wakeup anyway.
                         */
                        if (basenow < hrtimer_get_softexpires(timer))
                                break;

                        __run_hrtimer(cpu_base, base, timer, basenow, flags);
                        if (active_mask == HRTIMER_ACTIVE_SOFT)
                                hrtimer_sync_wait_running(cpu_base, flags);
                }
        }
}

static __latent_entropy void hrtimer_run_softirq(void)
{
        struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
        unsigned long flags;
        ktime_t now;

        hrtimer_cpu_base_lock_expiry(cpu_base);
        raw_spin_lock_irqsave(&cpu_base->lock, flags);

        now = hrtimer_update_base(cpu_base);
        __hrtimer_run_queues(cpu_base, now, flags, HRTIMER_ACTIVE_SOFT);

        cpu_base->softirq_activated = false;
        hrtimer_update_softirq_timer(cpu_base, true);

        raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
        hrtimer_cpu_base_unlock_expiry(cpu_base);
}

#ifdef CONFIG_HIGH_RES_TIMERS

/*
 * Very similar to hrtimer_force_reprogram(), except it deals with
 * deferred_rearm and hang_detected.
 */
static void hrtimer_rearm(struct hrtimer_cpu_base *cpu_base, ktime_t expires_next, bool deferred)
{
        cpu_base->expires_next = expires_next;
        cpu_base->deferred_rearm = false;

        if (unlikely(cpu_base->hang_detected)) {
                /*
                 * Give the system a chance to do something else than looping
                 * on hrtimer interrupts.
                 */
                expires_next = ktime_add_ns(ktime_get(),
                                            min(100 * NSEC_PER_MSEC, cpu_base->max_hang_time));
        }
        hrtimer_rearm_event(expires_next, deferred);
}

#ifdef CONFIG_HRTIMER_REARM_DEFERRED
void __hrtimer_rearm_deferred(void)
{
        struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
        ktime_t expires_next;

        if (!cpu_base->deferred_rearm)
                return;

        guard(raw_spinlock)(&cpu_base->lock);
        if (cpu_base->deferred_needs_update) {
                hrtimer_update_base(cpu_base);
                expires_next = hrtimer_update_next_event(cpu_base);
        } else {
                /* No timer added/removed. Use the cached value */
                expires_next = cpu_base->deferred_expires_next;
        }
        hrtimer_rearm(cpu_base, expires_next, true);
}

static __always_inline void
hrtimer_interrupt_rearm(struct hrtimer_cpu_base *cpu_base, ktime_t expires_next)
{
        /* hrtimer_interrupt() just re-evaluated the first expiring timer */
        cpu_base->deferred_needs_update = false;
        /* Cache the expiry time */
        cpu_base->deferred_expires_next = expires_next;
        set_thread_flag(TIF_HRTIMER_REARM);
}
#else  /* CONFIG_HRTIMER_REARM_DEFERRED */
static __always_inline void
hrtimer_interrupt_rearm(struct hrtimer_cpu_base *cpu_base, ktime_t expires_next)
{
        hrtimer_rearm(cpu_base, expires_next, false);
}
#endif  /* !CONFIG_HRTIMER_REARM_DEFERRED */

/*
 * High resolution timer interrupt
 * Called with interrupts disabled
 */
void hrtimer_interrupt(struct clock_event_device *dev)
{
        struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
        ktime_t expires_next, now, entry_time, delta;
        unsigned long flags;
        int retries = 0;

        BUG_ON(!cpu_base->hres_active);
        cpu_base->nr_events++;
        dev->next_event = KTIME_MAX;
        dev->next_event_forced = 0;

        raw_spin_lock_irqsave(&cpu_base->lock, flags);
        entry_time = now = hrtimer_update_base(cpu_base);
retry:
        cpu_base->deferred_rearm = true;
        /*
         * Set expires_next to KTIME_MAX, which prevents that remote CPUs queue
         * timers while __hrtimer_run_queues() is expiring the clock bases.
         * Timers which are re/enqueued on the local CPU are not affected by
         * this.
         */
        cpu_base->expires_next = KTIME_MAX;

        if (!ktime_before(now, cpu_base->softirq_expires_next)) {
                cpu_base->softirq_expires_next = KTIME_MAX;
                cpu_base->softirq_activated = true;
                raise_timer_softirq(HRTIMER_SOFTIRQ);
        }

        __hrtimer_run_queues(cpu_base, now, flags, HRTIMER_ACTIVE_HARD);

        /*
         * The next timer was already expired due to:
         * - tracing
         * - long lasting callbacks
         * - being scheduled away when running in a VM
         *
         * We need to prevent that we loop forever in the hrtiner interrupt
         * routine. We give it 3 attempts to avoid overreacting on some
         * spurious event.
         */
        now = hrtimer_update_base(cpu_base);
        expires_next = hrtimer_update_next_event(cpu_base);
        cpu_base->hang_detected = false;
        if (expires_next < now) {
                if (++retries < 3)
                        goto retry;

                delta = ktime_sub(now, entry_time);
                cpu_base->max_hang_time = max_t(unsigned int, cpu_base->max_hang_time, delta);
                cpu_base->nr_hangs++;
                cpu_base->hang_detected = true;
        }

        hrtimer_interrupt_rearm(cpu_base, expires_next);
        raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
}

#endif /* !CONFIG_HIGH_RES_TIMERS */

/*
 * Called from run_local_timers in hardirq context every jiffy
 */
void hrtimer_run_queues(void)
{
        struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
        unsigned long flags;
        ktime_t now;

        if (hrtimer_hres_active(cpu_base))
                return;

        /*
         * This _is_ ugly: We have to check periodically, whether we
         * can switch to highres and / or nohz mode. The clocksource
         * switch happens with xtime_lock held. Notification from
         * there only sets the check bit in the tick_oneshot code,
         * otherwise we might deadlock vs. xtime_lock.
         */
        if (tick_check_oneshot_change(!hrtimer_is_hres_enabled())) {
                hrtimer_switch_to_hres();
                return;
        }

        raw_spin_lock_irqsave(&cpu_base->lock, flags);
        now = hrtimer_update_base(cpu_base);

        if (!ktime_before(now, cpu_base->softirq_expires_next)) {
                cpu_base->softirq_expires_next = KTIME_MAX;
                cpu_base->softirq_activated = true;
                raise_timer_softirq(HRTIMER_SOFTIRQ);
        }

        __hrtimer_run_queues(cpu_base, now, flags, HRTIMER_ACTIVE_HARD);
        raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
}

/*
 * Sleep related functions:
 */
static enum hrtimer_restart hrtimer_wakeup(struct hrtimer *timer)
{
        struct hrtimer_sleeper *t = container_of(timer, struct hrtimer_sleeper, timer);
        struct task_struct *task = t->task;

        t->task = NULL;
        if (task)
                wake_up_process(task);

        return HRTIMER_NORESTART;
}

/**
 * hrtimer_sleeper_start_expires - Start a hrtimer sleeper timer
 * @sl:         sleeper to be started
 * @mode:       timer mode abs/rel
 *
 * Wrapper around hrtimer_start_expires() for hrtimer_sleeper based timers
 * to allow PREEMPT_RT to tweak the delivery mode (soft/hardirq context)
 */
void hrtimer_sleeper_start_expires(struct hrtimer_sleeper *sl, enum hrtimer_mode mode)
{
        /*
         * Make the enqueue delivery mode check work on RT. If the sleeper
         * was initialized for hard interrupt delivery, force the mode bit.
         * This is a special case for hrtimer_sleepers because
         * __hrtimer_setup_sleeper() determines the delivery mode on RT so the
         * fiddling with this decision is avoided at the call sites.
         */
        if (IS_ENABLED(CONFIG_PREEMPT_RT) && sl->timer.is_hard)
                mode |= HRTIMER_MODE_HARD;

        /* If already expired, clear the task pointer and set current state to running */
        if (!hrtimer_start_expires_user(&sl->timer, mode)) {
                sl->task = NULL;
                __set_current_state(TASK_RUNNING);
        }
}
EXPORT_SYMBOL_GPL(hrtimer_sleeper_start_expires);

static void __hrtimer_setup_sleeper(struct hrtimer_sleeper *sl, clockid_t clock_id,
                                    enum hrtimer_mode mode)
{
        /*
         * On PREEMPT_RT enabled kernels hrtimers which are not explicitly
         * marked for hard interrupt expiry mode are moved into soft
         * interrupt context either for latency reasons or because the
         * hrtimer callback takes regular spinlocks or invokes other
         * functions which are not suitable for hard interrupt context on
         * PREEMPT_RT.
         *
         * The hrtimer_sleeper callback is RT compatible in hard interrupt
         * context, but there is a latency concern: Untrusted userspace can
         * spawn many threads which arm timers for the same expiry time on
         * the same CPU. That causes a latency spike due to the wakeup of
         * a gazillion threads.
         *
         * OTOH, privileged real-time user space applications rely on the
         * low latency of hard interrupt wakeups. If the current task is in
         * a real-time scheduling class, mark the mode for hard interrupt
         * expiry.
         */
        if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
                if (rt_or_dl_task_policy(current) && !(mode & HRTIMER_MODE_SOFT))
                        mode |= HRTIMER_MODE_HARD;
        }

        __hrtimer_setup(&sl->timer, hrtimer_wakeup, clock_id, mode);
        sl->task = current;
}

/**
 * hrtimer_setup_sleeper_on_stack - initialize a sleeper in stack memory
 * @sl:         sleeper to be initialized
 * @clock_id:   the clock to be used
 * @mode:       timer mode abs/rel
 */
void hrtimer_setup_sleeper_on_stack(struct hrtimer_sleeper *sl, clockid_t clock_id,
                                    enum hrtimer_mode mode)
{
        debug_setup_on_stack(&sl->timer, clock_id, mode);
        __hrtimer_setup_sleeper(sl, clock_id, mode);
}
EXPORT_SYMBOL_GPL(hrtimer_setup_sleeper_on_stack);

int nanosleep_copyout(struct restart_block *restart, struct timespec64 *ts)
{
        switch(restart->nanosleep.type) {
#ifdef CONFIG_COMPAT_32BIT_TIME
        case TT_COMPAT:
                if (put_old_timespec32(ts, restart->nanosleep.compat_rmtp))
                        return -EFAULT;
                break;
#endif
        case TT_NATIVE:
                if (put_timespec64(ts, restart->nanosleep.rmtp))
                        return -EFAULT;
                break;
        default:
                BUG();
        }
        return -ERESTART_RESTARTBLOCK;
}

static int __sched do_nanosleep(struct hrtimer_sleeper *t, enum hrtimer_mode mode)
{
        struct restart_block *restart;

        do {
                set_current_state(TASK_INTERRUPTIBLE|TASK_FREEZABLE);
                hrtimer_sleeper_start_expires(t, mode);

                if (likely(t->task))
                        schedule();

                hrtimer_cancel(&t->timer);
                mode = HRTIMER_MODE_ABS;

        } while (t->task && !signal_pending(current));

        __set_current_state(TASK_RUNNING);

        if (!t->task)
                return 0;

        restart = &current->restart_block;
        if (restart->nanosleep.type != TT_NONE) {
                ktime_t rem = hrtimer_expires_remaining(&t->timer);
                struct timespec64 rmt;

                if (rem <= 0)
                        return 0;
                rmt = ktime_to_timespec64(rem);

                return nanosleep_copyout(restart, &rmt);
        }
        return -ERESTART_RESTARTBLOCK;
}

static long __sched hrtimer_nanosleep_restart(struct restart_block *restart)
{
        struct hrtimer_sleeper t;
        int ret;

        hrtimer_setup_sleeper_on_stack(&t, restart->nanosleep.clockid, HRTIMER_MODE_ABS);
        hrtimer_set_expires(&t.timer, restart->nanosleep.expires);
        ret = do_nanosleep(&t, HRTIMER_MODE_ABS);
        destroy_hrtimer_on_stack(&t.timer);
        return ret;
}

long hrtimer_nanosleep(ktime_t rqtp, const enum hrtimer_mode mode, const clockid_t clockid)
{
        struct restart_block *restart;
        struct hrtimer_sleeper t;
        int ret;

        hrtimer_setup_sleeper_on_stack(&t, clockid, mode);
        hrtimer_set_expires_range_ns(&t.timer, rqtp, current->timer_slack_ns);
        ret = do_nanosleep(&t, mode);
        if (ret != -ERESTART_RESTARTBLOCK)
                goto out;

        /* Absolute timers do not update the rmtp value and restart: */
        if (mode == HRTIMER_MODE_ABS) {
                ret = -ERESTARTNOHAND;
                goto out;
        }

        restart = &current->restart_block;
        restart->nanosleep.clockid = t.timer.base->clockid;
        restart->nanosleep.expires = hrtimer_get_expires(&t.timer);
        set_restart_fn(restart, hrtimer_nanosleep_restart);
out:
        destroy_hrtimer_on_stack(&t.timer);
        return ret;
}

#ifdef CONFIG_64BIT

SYSCALL_DEFINE2(nanosleep, struct __kernel_timespec __user *, rqtp,
                struct __kernel_timespec __user *, rmtp)
{
        struct timespec64 tu;

        if (get_timespec64(&tu, rqtp))
                return -EFAULT;

        if (!timespec64_valid(&tu))
                return -EINVAL;

        current->restart_block.fn = do_no_restart_syscall;
        current->restart_block.nanosleep.type = rmtp ? TT_NATIVE : TT_NONE;
        current->restart_block.nanosleep.rmtp = rmtp;
        return hrtimer_nanosleep(timespec64_to_ktime(tu), HRTIMER_MODE_REL, CLOCK_MONOTONIC);
}

#endif

#ifdef CONFIG_COMPAT_32BIT_TIME

SYSCALL_DEFINE2(nanosleep_time32, struct old_timespec32 __user *, rqtp,
                struct old_timespec32 __user *, rmtp)
{
        struct timespec64 tu;

        if (get_old_timespec32(&tu, rqtp))
                return -EFAULT;

        if (!timespec64_valid(&tu))
                return -EINVAL;

        current->restart_block.fn = do_no_restart_syscall;
        current->restart_block.nanosleep.type = rmtp ? TT_COMPAT : TT_NONE;
        current->restart_block.nanosleep.compat_rmtp = rmtp;
        return hrtimer_nanosleep(timespec64_to_ktime(tu), HRTIMER_MODE_REL, CLOCK_MONOTONIC);
}
#endif

/*
 * Functions related to boot-time initialization:
 */
int hrtimers_prepare_cpu(unsigned int cpu)
{
        struct hrtimer_cpu_base *cpu_base = &per_cpu(hrtimer_bases, cpu);

        for (int i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
                struct hrtimer_clock_base *clock_b = &cpu_base->clock_base[i];

                clock_b->cpu_base = cpu_base;
                seqcount_raw_spinlock_init(&clock_b->seq, &cpu_base->lock);
                timerqueue_linked_init_head(&clock_b->active);
        }

        cpu_base->cpu = cpu;
        hrtimer_cpu_base_init_expiry_lock(cpu_base);
        return 0;
}

int hrtimers_cpu_starting(unsigned int cpu)
{
        struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);

        /* Clear out any left over state from a CPU down operation */
        cpu_base->active_bases = 0;
        cpu_base->hres_active = false;
        cpu_base->hang_detected = false;
        cpu_base->next_timer = NULL;
        cpu_base->softirq_next_timer = NULL;
        cpu_base->expires_next = KTIME_MAX;
        cpu_base->softirq_expires_next = KTIME_MAX;
        cpu_base->softirq_activated = false;
        cpu_base->online = true;
        return 0;
}

#ifdef CONFIG_HOTPLUG_CPU

static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
                                struct hrtimer_clock_base *new_base)
{
        struct timerqueue_linked_node *node;
        struct hrtimer *timer;

        while ((node = timerqueue_linked_first(&old_base->active))) {
                timer = hrtimer_from_timerqueue_node(node);
                BUG_ON(hrtimer_callback_running(timer));
                debug_hrtimer_deactivate(timer);

                /*
                 * Mark it as ENQUEUED not INACTIVE otherwise the
                 * timer could be seen as !active and just vanish away
                 * under us on another CPU
                 */
                __remove_hrtimer(timer, old_base, HRTIMER_STATE_ENQUEUED, false);
                timer->base = new_base;
                /*
                 * Enqueue the timers on the new cpu. This does not
                 * reprogram the event device in case the timer
                 * expires before the earliest on this CPU, but we run
                 * hrtimer_interrupt after we migrated everything to
                 * sort out already expired timers and reprogram the
                 * event device.
                 */
                enqueue_hrtimer(timer, new_base, HRTIMER_MODE_ABS, true);
        }
}

int hrtimers_cpu_dying(unsigned int dying_cpu)
{
        int ncpu = cpumask_any_and(cpu_active_mask, housekeeping_cpumask(HK_TYPE_TIMER));
        struct hrtimer_cpu_base *old_base, *new_base;

        old_base = this_cpu_ptr(&hrtimer_bases);
        new_base = &per_cpu(hrtimer_bases, ncpu);

        /*
         * The caller is globally serialized and nobody else
         * takes two locks at once, deadlock is not possible.
         */
        raw_spin_lock(&old_base->lock);
        raw_spin_lock_nested(&new_base->lock, SINGLE_DEPTH_NESTING);

        for (int i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++)
                migrate_hrtimer_list(&old_base->clock_base[i], &new_base->clock_base[i]);

        /* Tell the other CPU to retrigger the next event */
        smp_call_function_single(ncpu, retrigger_next_event, NULL, 0);

        raw_spin_unlock(&new_base->lock);
        old_base->online = false;
        raw_spin_unlock(&old_base->lock);

        return 0;
}

#endif /* CONFIG_HOTPLUG_CPU */

void __init hrtimers_init(void)
{
        hrtimers_prepare_cpu(smp_processor_id());
        hrtimers_cpu_starting(smp_processor_id());
        open_softirq(HRTIMER_SOFTIRQ, hrtimer_run_softirq);
}