timers: Plug locking race vs. timer migration

[cascardo/linux.git] / kernel / time / timer.c

/*
 *  linux/kernel/timer.c
 *
 *  Kernel internal timers
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  1997-01-28  Modified by Finn Arne Gangstad to make timers scale better.
 *
 *  1997-09-10  Updated NTP code according to technical memorandum Jan '96
 *              "A Kernel Model for Precision Timekeeping" by Dave Mills
 *  1998-12-24  Fixed a xtime SMP race (we need the xtime_lock rw spinlock to
 *              serialize accesses to xtime/lost_ticks).
 *                              Copyright (C) 1998  Andrea Arcangeli
 *  1999-03-10  Improved NTP compatibility by Ulrich Windl
 *  2002-05-31  Move sys_sysinfo here and make its locking sane, Robert Love
 *  2000-10-05  Implemented scalable SMP per-CPU timer handling.
 *                              Copyright (C) 2000, 2001, 2002  Ingo Molnar
 *              Designed by David S. Miller, Alexey Kuznetsov and Ingo Molnar
 */

#include <linux/kernel_stat.h>
#include <linux/export.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/pid_namespace.h>
#include <linux/notifier.h>
#include <linux/thread_info.h>
#include <linux/time.h>
#include <linux/jiffies.h>
#include <linux/posix-timers.h>
#include <linux/cpu.h>
#include <linux/syscalls.h>
#include <linux/delay.h>
#include <linux/tick.h>
#include <linux/kallsyms.h>
#include <linux/irq_work.h>
#include <linux/sched.h>
#include <linux/sched/sysctl.h>
#include <linux/slab.h>
#include <linux/compat.h>

#include <asm/uaccess.h>
#include <asm/unistd.h>
#include <asm/div64.h>
#include <asm/timex.h>
#include <asm/io.h>

#include "tick-internal.h"

#define CREATE_TRACE_POINTS
#include <trace/events/timer.h>

__visible u64 jiffies_64 __cacheline_aligned_in_smp = INITIAL_JIFFIES;

EXPORT_SYMBOL(jiffies_64);

/*
 * The timer wheel has LVL_DEPTH array levels. Each level provides an array of
 * LVL_SIZE buckets. Each level is driven by its own clock and therefor each
 * level has a different granularity.
 *
 * The level granularity is:            LVL_CLK_DIV ^ lvl
 * The level clock frequency is:        HZ / (LVL_CLK_DIV ^ level)
 *
 * The array level of a newly armed timer depends on the relative expiry
 * time. The farther the expiry time is away the higher the array level and
 * therefor the granularity becomes.
 *
 * Contrary to the original timer wheel implementation, which aims for 'exact'
 * expiry of the timers, this implementation removes the need for recascading
 * the timers into the lower array levels. The previous 'classic' timer wheel
 * implementation of the kernel already violated the 'exact' expiry by adding
 * slack to the expiry time to provide batched expiration. The granularity
 * levels provide implicit batching.
 *
 * This is an optimization of the original timer wheel implementation for the
 * majority of the timer wheel use cases: timeouts. The vast majority of
 * timeout timers (networking, disk I/O ...) are canceled before expiry. If
 * the timeout expires it indicates that normal operation is disturbed, so it
 * does not matter much whether the timeout comes with a slight delay.
 *
 * The only exception to this are networking timers with a small expiry
 * time. They rely on the granularity. Those fit into the first wheel level,
 * which has HZ granularity.
 *
 * We don't have cascading anymore. timers with a expiry time above the
 * capacity of the last wheel level are force expired at the maximum timeout
 * value of the last wheel level. From data sampling we know that the maximum
 * value observed is 5 days (network connection tracking), so this should not
 * be an issue.
 *
 * The currently chosen array constants values are a good compromise between
 * array size and granularity.
 *
 * This results in the following granularity and range levels:
 *
 * HZ 1000 steps
 * Level Offset  Granularity            Range
 *  0      0         1 ms                0 ms -         63 ms
 *  1     64         8 ms               64 ms -        511 ms
 *  2    128        64 ms              512 ms -       4095 ms (512ms - ~4s)
 *  3    192       512 ms             4096 ms -      32767 ms (~4s - ~32s)
 *  4    256      4096 ms (~4s)      32768 ms -     262143 ms (~32s - ~4m)
 *  5    320     32768 ms (~32s)    262144 ms -    2097151 ms (~4m - ~34m)
 *  6    384    262144 ms (~4m)    2097152 ms -   16777215 ms (~34m - ~4h)
 *  7    448   2097152 ms (~34m)  16777216 ms -  134217727 ms (~4h - ~1d)
 *  8    512  16777216 ms (~4h)  134217728 ms - 1073741822 ms (~1d - ~12d)
 *
 * HZ  300
 * Level Offset  Granularity            Range
 *  0      0         3 ms                0 ms -        210 ms
 *  1     64        26 ms              213 ms -       1703 ms (213ms - ~1s)
 *  2    128       213 ms             1706 ms -      13650 ms (~1s - ~13s)
 *  3    192      1706 ms (~1s)      13653 ms -     109223 ms (~13s - ~1m)
 *  4    256     13653 ms (~13s)    109226 ms -     873810 ms (~1m - ~14m)
 *  5    320    109226 ms (~1m)     873813 ms -    6990503 ms (~14m - ~1h)
 *  6    384    873813 ms (~14m)   6990506 ms -   55924050 ms (~1h - ~15h)
 *  7    448   6990506 ms (~1h)   55924053 ms -  447392423 ms (~15h - ~5d)
 *  8    512  55924053 ms (~15h) 447392426 ms - 3579139406 ms (~5d - ~41d)
 *
 * HZ  250
 * Level Offset  Granularity            Range
 *  0      0         4 ms                0 ms -        255 ms
 *  1     64        32 ms              256 ms -       2047 ms (256ms - ~2s)
 *  2    128       256 ms             2048 ms -      16383 ms (~2s - ~16s)
 *  3    192      2048 ms (~2s)      16384 ms -     131071 ms (~16s - ~2m)
 *  4    256     16384 ms (~16s)    131072 ms -    1048575 ms (~2m - ~17m)
 *  5    320    131072 ms (~2m)    1048576 ms -    8388607 ms (~17m - ~2h)
 *  6    384   1048576 ms (~17m)   8388608 ms -   67108863 ms (~2h - ~18h)
 *  7    448   8388608 ms (~2h)   67108864 ms -  536870911 ms (~18h - ~6d)
 *  8    512  67108864 ms (~18h) 536870912 ms - 4294967288 ms (~6d - ~49d)
 *
 * HZ  100
 * Level Offset  Granularity            Range
 *  0      0         10 ms               0 ms -        630 ms
 *  1     64         80 ms             640 ms -       5110 ms (640ms - ~5s)
 *  2    128        640 ms            5120 ms -      40950 ms (~5s - ~40s)
 *  3    192       5120 ms (~5s)     40960 ms -     327670 ms (~40s - ~5m)
 *  4    256      40960 ms (~40s)   327680 ms -    2621430 ms (~5m - ~43m)
 *  5    320     327680 ms (~5m)   2621440 ms -   20971510 ms (~43m - ~5h)
 *  6    384    2621440 ms (~43m) 20971520 ms -  167772150 ms (~5h - ~1d)
 *  7    448   20971520 ms (~5h) 167772160 ms - 1342177270 ms (~1d - ~15d)
 */

/* Clock divisor for the next level */
#define LVL_CLK_SHIFT   3
#define LVL_CLK_DIV     (1UL << LVL_CLK_SHIFT)
#define LVL_CLK_MASK    (LVL_CLK_DIV - 1)
#define LVL_SHIFT(n)    ((n) * LVL_CLK_SHIFT)
#define LVL_GRAN(n)     (1UL << LVL_SHIFT(n))

/*
 * The time start value for each level to select the bucket at enqueue
 * time.
 */
#define LVL_START(n)    ((LVL_SIZE - 1) << (((n) - 1) * LVL_CLK_SHIFT))

/* Size of each clock level */
#define LVL_BITS        6
#define LVL_SIZE        (1UL << LVL_BITS)
#define LVL_MASK        (LVL_SIZE - 1)
#define LVL_OFFS(n)     ((n) * LVL_SIZE)

/* Level depth */
#if HZ > 100
# define LVL_DEPTH      9
# else
# define LVL_DEPTH      8
#endif

/* The cutoff (max. capacity of the wheel) */
#define WHEEL_TIMEOUT_CUTOFF    (LVL_START(LVL_DEPTH))
#define WHEEL_TIMEOUT_MAX       (WHEEL_TIMEOUT_CUTOFF - LVL_GRAN(LVL_DEPTH - 1))

/*
 * The resulting wheel size. If NOHZ is configured we allocate two
 * wheels so we have a separate storage for the deferrable timers.
 */
#define WHEEL_SIZE      (LVL_SIZE * LVL_DEPTH)

#ifdef CONFIG_NO_HZ_COMMON
# define NR_BASES       2
# define BASE_STD       0
# define BASE_DEF       1
#else
# define NR_BASES       1
# define BASE_STD       0
# define BASE_DEF       0
#endif

struct timer_base {
        spinlock_t              lock;
        struct timer_list       *running_timer;
        unsigned long           clk;
        unsigned long           next_expiry;
        unsigned int            cpu;
        bool                    migration_enabled;
        bool                    nohz_active;
        bool                    is_idle;
        DECLARE_BITMAP(pending_map, WHEEL_SIZE);
        struct hlist_head       vectors[WHEEL_SIZE];
} ____cacheline_aligned;

static DEFINE_PER_CPU(struct timer_base, timer_bases[NR_BASES]);

#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
unsigned int sysctl_timer_migration = 1;

void timers_update_migration(bool update_nohz)
{
        bool on = sysctl_timer_migration && tick_nohz_active;
        unsigned int cpu;

        /* Avoid the loop, if nothing to update */
        if (this_cpu_read(timer_bases[BASE_STD].migration_enabled) == on)
                return;

        for_each_possible_cpu(cpu) {
                per_cpu(timer_bases[BASE_STD].migration_enabled, cpu) = on;
                per_cpu(timer_bases[BASE_DEF].migration_enabled, cpu) = on;
                per_cpu(hrtimer_bases.migration_enabled, cpu) = on;
                if (!update_nohz)
                        continue;
                per_cpu(timer_bases[BASE_STD].nohz_active, cpu) = true;
                per_cpu(timer_bases[BASE_DEF].nohz_active, cpu) = true;
                per_cpu(hrtimer_bases.nohz_active, cpu) = true;
        }
}

int timer_migration_handler(struct ctl_table *table, int write,
                            void __user *buffer, size_t *lenp,
                            loff_t *ppos)
{
        static DEFINE_MUTEX(mutex);
        int ret;

        mutex_lock(&mutex);
        ret = proc_dointvec(table, write, buffer, lenp, ppos);
        if (!ret && write)
                timers_update_migration(false);
        mutex_unlock(&mutex);
        return ret;
}
#endif

static unsigned long round_jiffies_common(unsigned long j, int cpu,
                bool force_up)
{
        int rem;
        unsigned long original = j;

        /*
         * We don't want all cpus firing their timers at once hitting the
         * same lock or cachelines, so we skew each extra cpu with an extra
         * 3 jiffies. This 3 jiffies came originally from the mm/ code which
         * already did this.
         * The skew is done by adding 3*cpunr, then round, then subtract this
         * extra offset again.
         */
        j += cpu * 3;

        rem = j % HZ;

        /*
         * If the target jiffie is just after a whole second (which can happen
         * due to delays of the timer irq, long irq off times etc etc) then
         * we should round down to the whole second, not up. Use 1/4th second
         * as cutoff for this rounding as an extreme upper bound for this.
         * But never round down if @force_up is set.
         */
        if (rem < HZ/4 && !force_up) /* round down */
                j = j - rem;
        else /* round up */
                j = j - rem + HZ;

        /* now that we have rounded, subtract the extra skew again */
        j -= cpu * 3;

        /*
         * Make sure j is still in the future. Otherwise return the
         * unmodified value.
         */
        return time_is_after_jiffies(j) ? j : original;
}

/**
 * __round_jiffies - function to round jiffies to a full second
 * @j: the time in (absolute) jiffies that should be rounded
 * @cpu: the processor number on which the timeout will happen
 *
 * __round_jiffies() rounds an absolute time in the future (in jiffies)
 * up or down to (approximately) full seconds. This is useful for timers
 * for which the exact time they fire does not matter too much, as long as
 * they fire approximately every X seconds.
 *
 * By rounding these timers to whole seconds, all such timers will fire
 * at the same time, rather than at various times spread out. The goal
 * of this is to have the CPU wake up less, which saves power.
 *
 * The exact rounding is skewed for each processor to avoid all
 * processors firing at the exact same time, which could lead
 * to lock contention or spurious cache line bouncing.
 *
 * The return value is the rounded version of the @j parameter.
 */
unsigned long __round_jiffies(unsigned long j, int cpu)
{
        return round_jiffies_common(j, cpu, false);
}
EXPORT_SYMBOL_GPL(__round_jiffies);

/**
 * __round_jiffies_relative - function to round jiffies to a full second
 * @j: the time in (relative) jiffies that should be rounded
 * @cpu: the processor number on which the timeout will happen
 *
 * __round_jiffies_relative() rounds a time delta  in the future (in jiffies)
 * up or down to (approximately) full seconds. This is useful for timers
 * for which the exact time they fire does not matter too much, as long as
 * they fire approximately every X seconds.
 *
 * By rounding these timers to whole seconds, all such timers will fire
 * at the same time, rather than at various times spread out. The goal
 * of this is to have the CPU wake up less, which saves power.
 *
 * The exact rounding is skewed for each processor to avoid all
 * processors firing at the exact same time, which could lead
 * to lock contention or spurious cache line bouncing.
 *
 * The return value is the rounded version of the @j parameter.
 */
unsigned long __round_jiffies_relative(unsigned long j, int cpu)
{
        unsigned long j0 = jiffies;

        /* Use j0 because jiffies might change while we run */
        return round_jiffies_common(j + j0, cpu, false) - j0;
}
EXPORT_SYMBOL_GPL(__round_jiffies_relative);

/**
 * round_jiffies - function to round jiffies to a full second
 * @j: the time in (absolute) jiffies that should be rounded
 *
 * round_jiffies() rounds an absolute time in the future (in jiffies)
 * up or down to (approximately) full seconds. This is useful for timers
 * for which the exact time they fire does not matter too much, as long as
 * they fire approximately every X seconds.
 *
 * By rounding these timers to whole seconds, all such timers will fire
 * at the same time, rather than at various times spread out. The goal
 * of this is to have the CPU wake up less, which saves power.
 *
 * The return value is the rounded version of the @j parameter.
 */
unsigned long round_jiffies(unsigned long j)
{
        return round_jiffies_common(j, raw_smp_processor_id(), false);
}
EXPORT_SYMBOL_GPL(round_jiffies);

/**
 * round_jiffies_relative - function to round jiffies to a full second
 * @j: the time in (relative) jiffies that should be rounded
 *
 * round_jiffies_relative() rounds a time delta  in the future (in jiffies)
 * up or down to (approximately) full seconds. This is useful for timers
 * for which the exact time they fire does not matter too much, as long as
 * they fire approximately every X seconds.
 *
 * By rounding these timers to whole seconds, all such timers will fire
 * at the same time, rather than at various times spread out. The goal
 * of this is to have the CPU wake up less, which saves power.
 *
 * The return value is the rounded version of the @j parameter.
 */
unsigned long round_jiffies_relative(unsigned long j)
{
        return __round_jiffies_relative(j, raw_smp_processor_id());
}
EXPORT_SYMBOL_GPL(round_jiffies_relative);

/**
 * __round_jiffies_up - function to round jiffies up to a full second
 * @j: the time in (absolute) jiffies that should be rounded
 * @cpu: the processor number on which the timeout will happen
 *
 * This is the same as __round_jiffies() except that it will never
 * round down.  This is useful for timeouts for which the exact time
 * of firing does not matter too much, as long as they don't fire too
 * early.
 */
unsigned long __round_jiffies_up(unsigned long j, int cpu)
{
        return round_jiffies_common(j, cpu, true);
}
EXPORT_SYMBOL_GPL(__round_jiffies_up);

/**
 * __round_jiffies_up_relative - function to round jiffies up to a full second
 * @j: the time in (relative) jiffies that should be rounded
 * @cpu: the processor number on which the timeout will happen
 *
 * This is the same as __round_jiffies_relative() except that it will never
 * round down.  This is useful for timeouts for which the exact time
 * of firing does not matter too much, as long as they don't fire too
 * early.
 */
unsigned long __round_jiffies_up_relative(unsigned long j, int cpu)
{
        unsigned long j0 = jiffies;

        /* Use j0 because jiffies might change while we run */
        return round_jiffies_common(j + j0, cpu, true) - j0;
}
EXPORT_SYMBOL_GPL(__round_jiffies_up_relative);

/**
 * round_jiffies_up - function to round jiffies up to a full second
 * @j: the time in (absolute) jiffies that should be rounded
 *
 * This is the same as round_jiffies() except that it will never
 * round down.  This is useful for timeouts for which the exact time
 * of firing does not matter too much, as long as they don't fire too
 * early.
 */
unsigned long round_jiffies_up(unsigned long j)
{
        return round_jiffies_common(j, raw_smp_processor_id(), true);
}
EXPORT_SYMBOL_GPL(round_jiffies_up);

/**
 * round_jiffies_up_relative - function to round jiffies up to a full second
 * @j: the time in (relative) jiffies that should be rounded
 *
 * This is the same as round_jiffies_relative() except that it will never
 * round down.  This is useful for timeouts for which the exact time
 * of firing does not matter too much, as long as they don't fire too
 * early.
 */
unsigned long round_jiffies_up_relative(unsigned long j)
{
        return __round_jiffies_up_relative(j, raw_smp_processor_id());
}
EXPORT_SYMBOL_GPL(round_jiffies_up_relative);


static inline unsigned int timer_get_idx(struct timer_list *timer)
{
        return (timer->flags & TIMER_ARRAYMASK) >> TIMER_ARRAYSHIFT;
}

static inline void timer_set_idx(struct timer_list *timer, unsigned int idx)
{
        timer->flags = (timer->flags & ~TIMER_ARRAYMASK) |
                        idx << TIMER_ARRAYSHIFT;
}

/*
 * Helper function to calculate the array index for a given expiry
 * time.
 */
static inline unsigned calc_index(unsigned expires, unsigned lvl)
{
        expires = (expires + LVL_GRAN(lvl)) >> LVL_SHIFT(lvl);
        return LVL_OFFS(lvl) + (expires & LVL_MASK);
}

static int calc_wheel_index(unsigned long expires, unsigned long clk)
{
        unsigned long delta = expires - clk;
        unsigned int idx;

        if (delta < LVL_START(1)) {
                idx = calc_index(expires, 0);
        } else if (delta < LVL_START(2)) {
                idx = calc_index(expires, 1);
        } else if (delta < LVL_START(3)) {
                idx = calc_index(expires, 2);
        } else if (delta < LVL_START(4)) {
                idx = calc_index(expires, 3);
        } else if (delta < LVL_START(5)) {
                idx = calc_index(expires, 4);
        } else if (delta < LVL_START(6)) {
                idx = calc_index(expires, 5);
        } else if (delta < LVL_START(7)) {
                idx = calc_index(expires, 6);
        } else if (LVL_DEPTH > 8 && delta < LVL_START(8)) {
                idx = calc_index(expires, 7);
        } else if ((long) delta < 0) {
                idx = clk & LVL_MASK;
        } else {
                /*
                 * Force expire obscene large timeouts to expire at the
                 * capacity limit of the wheel.
                 */
                if (expires >= WHEEL_TIMEOUT_CUTOFF)
                        expires = WHEEL_TIMEOUT_MAX;

                idx = calc_index(expires, LVL_DEPTH - 1);
        }
        return idx;
}

/*
 * Enqueue the timer into the hash bucket, mark it pending in
 * the bitmap and store the index in the timer flags.
 */
static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
                          unsigned int idx)
{
        hlist_add_head(&timer->entry, base->vectors + idx);
        __set_bit(idx, base->pending_map);
        timer_set_idx(timer, idx);
}

static void
__internal_add_timer(struct timer_base *base, struct timer_list *timer)
{
        unsigned int idx;

        idx = calc_wheel_index(timer->expires, base->clk);
        enqueue_timer(base, timer, idx);
}

static void
trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
{
        if (!IS_ENABLED(CONFIG_NO_HZ_COMMON) || !base->nohz_active)
                return;

        /*
         * TODO: This wants some optimizing similar to the code below, but we
         * will do that when we switch from push to pull for deferrable timers.
         */
        if (timer->flags & TIMER_DEFERRABLE) {
                if (tick_nohz_full_cpu(base->cpu))
                        wake_up_nohz_cpu(base->cpu);
                return;
        }

        /*
         * We might have to IPI the remote CPU if the base is idle and the
         * timer is not deferrable. If the other CPU is on the way to idle
         * then it can't set base->is_idle as we hold the base lock:
         */
        if (!base->is_idle)
                return;

        /* Check whether this is the new first expiring timer: */
        if (time_after_eq(timer->expires, base->next_expiry))
                return;

        /*
         * Set the next expiry time and kick the CPU so it can reevaluate the
         * wheel:
         */
        base->next_expiry = timer->expires;
                wake_up_nohz_cpu(base->cpu);
}

static void
internal_add_timer(struct timer_base *base, struct timer_list *timer)
{
        __internal_add_timer(base, timer);
        trigger_dyntick_cpu(base, timer);
}

#ifdef CONFIG_TIMER_STATS
void __timer_stats_timer_set_start_info(struct timer_list *timer, void *addr)
{
        if (timer->start_site)
                return;

        timer->start_site = addr;
        memcpy(timer->start_comm, current->comm, TASK_COMM_LEN);
        timer->start_pid = current->pid;
}

static void timer_stats_account_timer(struct timer_list *timer)
{
        void *site;

        /*
         * start_site can be concurrently reset by
         * timer_stats_timer_clear_start_info()
         */
        site = READ_ONCE(timer->start_site);
        if (likely(!site))
                return;

        timer_stats_update_stats(timer, timer->start_pid, site,
                                 timer->function, timer->start_comm,
                                 timer->flags);
}

#else
static void timer_stats_account_timer(struct timer_list *timer) {}
#endif

#ifdef CONFIG_DEBUG_OBJECTS_TIMERS

static struct debug_obj_descr timer_debug_descr;

static void *timer_debug_hint(void *addr)
{
        return ((struct timer_list *) addr)->function;
}

static bool timer_is_static_object(void *addr)
{
        struct timer_list *timer = addr;

        return (timer->entry.pprev == NULL &&
                timer->entry.next == TIMER_ENTRY_STATIC);
}

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

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

/* Stub timer callback for improperly used timers. */
static void stub_timer(unsigned long data)
{
        WARN_ON(1);
}

/*
 * fixup_activate is called when:
 * - an active object is activated
 * - an unknown non-static object is activated
 */
static bool timer_fixup_activate(void *addr, enum debug_obj_state state)
{
        struct timer_list *timer = addr;

        switch (state) {
        case ODEBUG_STATE_NOTAVAILABLE:
                setup_timer(timer, stub_timer, 0);
                return true;

        case ODEBUG_STATE_ACTIVE:
                WARN_ON(1);

        default:
                return false;
        }
}

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

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

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

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

static struct debug_obj_descr timer_debug_descr = {
        .name                   = "timer_list",
        .debug_hint             = timer_debug_hint,
        .is_static_object       = timer_is_static_object,
        .fixup_init             = timer_fixup_init,
        .fixup_activate         = timer_fixup_activate,
        .fixup_free             = timer_fixup_free,
        .fixup_assert_init      = timer_fixup_assert_init,
};

static inline void debug_timer_init(struct timer_list *timer)
{
        debug_object_init(timer, &timer_debug_descr);
}

static inline void debug_timer_activate(struct timer_list *timer)
{
        debug_object_activate(timer, &timer_debug_descr);
}

static inline void debug_timer_deactivate(struct timer_list *timer)
{
        debug_object_deactivate(timer, &timer_debug_descr);
}

static inline void debug_timer_free(struct timer_list *timer)
{
        debug_object_free(timer, &timer_debug_descr);
}

static inline void debug_timer_assert_init(struct timer_list *timer)
{
        debug_object_assert_init(timer, &timer_debug_descr);
}

static void do_init_timer(struct timer_list *timer, unsigned int flags,
                          const char *name, struct lock_class_key *key);

void init_timer_on_stack_key(struct timer_list *timer, unsigned int flags,
                             const char *name, struct lock_class_key *key)
{
        debug_object_init_on_stack(timer, &timer_debug_descr);
        do_init_timer(timer, flags, name, key);
}
EXPORT_SYMBOL_GPL(init_timer_on_stack_key);

void destroy_timer_on_stack(struct timer_list *timer)
{
        debug_object_free(timer, &timer_debug_descr);
}
EXPORT_SYMBOL_GPL(destroy_timer_on_stack);

#else
static inline void debug_timer_init(struct timer_list *timer) { }
static inline void debug_timer_activate(struct timer_list *timer) { }
static inline void debug_timer_deactivate(struct timer_list *timer) { }
static inline void debug_timer_assert_init(struct timer_list *timer) { }
#endif

static inline void debug_init(struct timer_list *timer)
{
        debug_timer_init(timer);
        trace_timer_init(timer);
}

static inline void
debug_activate(struct timer_list *timer, unsigned long expires)
{
        debug_timer_activate(timer);
        trace_timer_start(timer, expires, timer->flags);
}

static inline void debug_deactivate(struct timer_list *timer)
{
        debug_timer_deactivate(timer);
        trace_timer_cancel(timer);
}

static inline void debug_assert_init(struct timer_list *timer)
{
        debug_timer_assert_init(timer);
}

static void do_init_timer(struct timer_list *timer, unsigned int flags,
                          const char *name, struct lock_class_key *key)
{
        timer->entry.pprev = NULL;
        timer->flags = flags | raw_smp_processor_id();
#ifdef CONFIG_TIMER_STATS
        timer->start_site = NULL;
        timer->start_pid = -1;
        memset(timer->start_comm, 0, TASK_COMM_LEN);
#endif
        lockdep_init_map(&timer->lockdep_map, name, key, 0);
}

/**
 * init_timer_key - initialize a timer
 * @timer: the timer to be initialized
 * @flags: timer flags
 * @name: name of the timer
 * @key: lockdep class key of the fake lock used for tracking timer
 *       sync lock dependencies
 *
 * init_timer_key() must be done to a timer prior calling *any* of the
 * other timer functions.
 */
void init_timer_key(struct timer_list *timer, unsigned int flags,
                    const char *name, struct lock_class_key *key)
{
        debug_init(timer);
        do_init_timer(timer, flags, name, key);
}
EXPORT_SYMBOL(init_timer_key);

static inline void detach_timer(struct timer_list *timer, bool clear_pending)
{
        struct hlist_node *entry = &timer->entry;

        debug_deactivate(timer);

        __hlist_del(entry);
        if (clear_pending)
                entry->pprev = NULL;
        entry->next = LIST_POISON2;
}

static int detach_if_pending(struct timer_list *timer, struct timer_base *base,
                             bool clear_pending)
{
        unsigned idx = timer_get_idx(timer);

        if (!timer_pending(timer))
                return 0;

        if (hlist_is_singular_node(&timer->entry, base->vectors + idx))
                __clear_bit(idx, base->pending_map);

        detach_timer(timer, clear_pending);
        return 1;
}

static inline struct timer_base *get_timer_cpu_base(u32 tflags, u32 cpu)
{
        struct timer_base *base = per_cpu_ptr(&timer_bases[BASE_STD], cpu);

        /*
         * If the timer is deferrable and nohz is active then we need to use
         * the deferrable base.
         */
        if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active &&
            (tflags & TIMER_DEFERRABLE))
                base = per_cpu_ptr(&timer_bases[BASE_DEF], cpu);
        return base;
}

static inline struct timer_base *get_timer_this_cpu_base(u32 tflags)
{
        struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);

        /*
         * If the timer is deferrable and nohz is active then we need to use
         * the deferrable base.
         */
        if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active &&
            (tflags & TIMER_DEFERRABLE))
                base = this_cpu_ptr(&timer_bases[BASE_DEF]);
        return base;
}

static inline struct timer_base *get_timer_base(u32 tflags)
{
        return get_timer_cpu_base(tflags, tflags & TIMER_CPUMASK);
}

#ifdef CONFIG_NO_HZ_COMMON
static inline struct timer_base *
__get_target_base(struct timer_base *base, unsigned tflags)
{
#ifdef CONFIG_SMP
        if ((tflags & TIMER_PINNED) || !base->migration_enabled)
                return get_timer_this_cpu_base(tflags);
        return get_timer_cpu_base(tflags, get_nohz_timer_target());
#else
        return get_timer_this_cpu_base(tflags);
#endif
}

static inline void forward_timer_base(struct timer_base *base)
{
        /*
         * We only forward the base when it's idle and we have a delta between
         * base clock and jiffies.
         */
        if (!base->is_idle || (long) (jiffies - base->clk) < 2)
                return;

        /*
         * If the next expiry value is > jiffies, then we fast forward to
         * jiffies otherwise we forward to the next expiry value.
         */
        if (time_after(base->next_expiry, jiffies))
                base->clk = jiffies;
        else
                base->clk = base->next_expiry;
}
#else
static inline struct timer_base *
__get_target_base(struct timer_base *base, unsigned tflags)
{
        return get_timer_this_cpu_base(tflags);
}

static inline void forward_timer_base(struct timer_base *base) { }
#endif

static inline struct timer_base *
get_target_base(struct timer_base *base, unsigned tflags)
{
        struct timer_base *target = __get_target_base(base, tflags);

        forward_timer_base(target);
        return target;
}

/*
 * We are using hashed locking: Holding per_cpu(timer_bases[x]).lock means
 * that all timers which are tied to this base are locked, and the base itself
 * is locked too.
 *
 * So __run_timers/migrate_timers can safely modify all timers which could
 * be found in the base->vectors array.
 *
 * When a timer is migrating then the TIMER_MIGRATING flag is set and we need
 * to wait until the migration is done.
 */
static struct timer_base *lock_timer_base(struct timer_list *timer,
                                          unsigned long *flags)
        __acquires(timer->base->lock)
{
        for (;;) {
                struct timer_base *base;
                u32 tf;

                /*
                 * We need to use READ_ONCE() here, otherwise the compiler
                 * might re-read @tf between the check for TIMER_MIGRATING
                 * and spin_lock().
                 */
                tf = READ_ONCE(timer->flags);

                if (!(tf & TIMER_MIGRATING)) {
                        base = get_timer_base(tf);
                        spin_lock_irqsave(&base->lock, *flags);
                        if (timer->flags == tf)
                                return base;
                        spin_unlock_irqrestore(&base->lock, *flags);
                }
                cpu_relax();
        }
}

static inline int
__mod_timer(struct timer_list *timer, unsigned long expires, bool pending_only)
{
        struct timer_base *base, *new_base;
        unsigned int idx = UINT_MAX;
        unsigned long clk = 0, flags;
        int ret = 0;

        /*
         * This is a common optimization triggered by the networking code - if
         * the timer is re-modified to have the same timeout or ends up in the
         * same array bucket then just return:
         */
        if (timer_pending(timer)) {
                if (timer->expires == expires)
                        return 1;
                /*
                 * Take the current timer_jiffies of base, but without holding
                 * the lock!
                 */
                base = get_timer_base(timer->flags);
                clk = base->clk;

                idx = calc_wheel_index(expires, clk);

                /*
                 * Retrieve and compare the array index of the pending
                 * timer. If it matches set the expiry to the new value so a
                 * subsequent call will exit in the expires check above.
                 */
                if (idx == timer_get_idx(timer)) {
                        timer->expires = expires;
                        return 1;
                }
        }

        timer_stats_timer_set_start_info(timer);
        BUG_ON(!timer->function);

        base = lock_timer_base(timer, &flags);

        ret = detach_if_pending(timer, base, false);
        if (!ret && pending_only)
                goto out_unlock;

        debug_activate(timer, expires);

        new_base = get_target_base(base, timer->flags);

        if (base != new_base) {
                /*
                 * We are trying to schedule the timer on the new base.
                 * However we can't change timer's base while it is running,
                 * otherwise del_timer_sync() can't detect that the timer's
                 * handler yet has not finished. This also guarantees that the
                 * timer is serialized wrt itself.
                 */
                if (likely(base->running_timer != timer)) {
                        /* See the comment in lock_timer_base() */
                        timer->flags |= TIMER_MIGRATING;

                        spin_unlock(&base->lock);
                        base = new_base;
                        spin_lock(&base->lock);
                        WRITE_ONCE(timer->flags,
                                   (timer->flags & ~TIMER_BASEMASK) | base->cpu);
                }
        }

        timer->expires = expires;
        /*
         * If 'idx' was calculated above and the base time did not advance
         * between calculating 'idx' and taking the lock, only enqueue_timer()
         * and trigger_dyntick_cpu() is required. Otherwise we need to
         * (re)calculate the wheel index via internal_add_timer().
         */
        if (idx != UINT_MAX && clk == base->clk) {
                enqueue_timer(base, timer, idx);
                trigger_dyntick_cpu(base, timer);
        } else {
                internal_add_timer(base, timer);
        }

out_unlock:
        spin_unlock_irqrestore(&base->lock, flags);

        return ret;
}

/**
 * mod_timer_pending - modify a pending timer's timeout
 * @timer: the pending timer to be modified
 * @expires: new timeout in jiffies
 *
 * mod_timer_pending() is the same for pending timers as mod_timer(),
 * but will not re-activate and modify already deleted timers.
 *
 * It is useful for unserialized use of timers.
 */
int mod_timer_pending(struct timer_list *timer, unsigned long expires)
{
        return __mod_timer(timer, expires, true);
}
EXPORT_SYMBOL(mod_timer_pending);

/**
 * mod_timer - modify a timer's timeout
 * @timer: the timer to be modified
 * @expires: new timeout in jiffies
 *
 * mod_timer() is a more efficient way to update the expire field of an
 * active timer (if the timer is inactive it will be activated)
 *
 * mod_timer(timer, expires) is equivalent to:
 *
 *     del_timer(timer); timer->expires = expires; add_timer(timer);
 *
 * Note that if there are multiple unserialized concurrent users of the
 * same timer, then mod_timer() is the only safe way to modify the timeout,
 * since add_timer() cannot modify an already running timer.
 *
 * The function returns whether it has modified a pending timer or not.
 * (ie. mod_timer() of an inactive timer returns 0, mod_timer() of an
 * active timer returns 1.)
 */
int mod_timer(struct timer_list *timer, unsigned long expires)
{
        return __mod_timer(timer, expires, false);
}
EXPORT_SYMBOL(mod_timer);

/**
 * add_timer - start a timer
 * @timer: the timer to be added
 *
 * The kernel will do a ->function(->data) callback from the
 * timer interrupt at the ->expires point in the future. The
 * current time is 'jiffies'.
 *
 * The timer's ->expires, ->function (and if the handler uses it, ->data)
 * fields must be set prior calling this function.
 *
 * Timers with an ->expires field in the past will be executed in the next
 * timer tick.
 */
void add_timer(struct timer_list *timer)
{
        BUG_ON(timer_pending(timer));
        mod_timer(timer, timer->expires);
}
EXPORT_SYMBOL(add_timer);

/**
 * add_timer_on - start a timer on a particular CPU
 * @timer: the timer to be added
 * @cpu: the CPU to start it on
 *
 * This is not very scalable on SMP. Double adds are not possible.
 */
void add_timer_on(struct timer_list *timer, int cpu)
{
        struct timer_base *new_base, *base;
        unsigned long flags;

        timer_stats_timer_set_start_info(timer);
        BUG_ON(timer_pending(timer) || !timer->function);

        new_base = get_timer_cpu_base(timer->flags, cpu);

        /*
         * If @timer was on a different CPU, it should be migrated with the
         * old base locked to prevent other operations proceeding with the
         * wrong base locked.  See lock_timer_base().
         */
        base = lock_timer_base(timer, &flags);
        if (base != new_base) {
                timer->flags |= TIMER_MIGRATING;

                spin_unlock(&base->lock);
                base = new_base;
                spin_lock(&base->lock);
                WRITE_ONCE(timer->flags,
                           (timer->flags & ~TIMER_BASEMASK) | cpu);
        }

        debug_activate(timer, timer->expires);
        internal_add_timer(base, timer);
        spin_unlock_irqrestore(&base->lock, flags);
}
EXPORT_SYMBOL_GPL(add_timer_on);

/**
 * del_timer - deactive a timer.
 * @timer: the timer to be deactivated
 *
 * del_timer() deactivates a timer - this works on both active and inactive
 * timers.
 *
 * The function returns whether it has deactivated a pending timer or not.
 * (ie. del_timer() of an inactive timer returns 0, del_timer() of an
 * active timer returns 1.)
 */
int del_timer(struct timer_list *timer)
{
        struct timer_base *base;
        unsigned long flags;
        int ret = 0;

        debug_assert_init(timer);

        timer_stats_timer_clear_start_info(timer);
        if (timer_pending(timer)) {
                base = lock_timer_base(timer, &flags);
                ret = detach_if_pending(timer, base, true);
                spin_unlock_irqrestore(&base->lock, flags);
        }

        return ret;
}
EXPORT_SYMBOL(del_timer);

/**
 * try_to_del_timer_sync - Try to deactivate a timer
 * @timer: timer do del
 *
 * This function tries to deactivate a timer. Upon successful (ret >= 0)
 * exit the timer is not queued and the handler is not running on any CPU.
 */
int try_to_del_timer_sync(struct timer_list *timer)
{
        struct timer_base *base;
        unsigned long flags;
        int ret = -1;

        debug_assert_init(timer);

        base = lock_timer_base(timer, &flags);

        if (base->running_timer != timer) {
                timer_stats_timer_clear_start_info(timer);
                ret = detach_if_pending(timer, base, true);
        }
        spin_unlock_irqrestore(&base->lock, flags);

        return ret;
}
EXPORT_SYMBOL(try_to_del_timer_sync);

#ifdef CONFIG_SMP
/**
 * del_timer_sync - deactivate a timer and wait for the handler to finish.
 * @timer: the timer to be deactivated
 *
 * This function only differs from del_timer() on SMP: besides deactivating
 * the timer it also makes sure the handler has finished executing on other
 * CPUs.
 *
 * Synchronization rules: Callers must prevent restarting of the timer,
 * otherwise this function is meaningless. It must not be called from
 * interrupt contexts unless the timer is an irqsafe one. The caller must
 * not hold locks which would prevent completion of the timer's
 * handler. The timer's handler must not call add_timer_on(). Upon exit the
 * timer is not queued and the handler is not running on any CPU.
 *
 * Note: For !irqsafe timers, you must not hold locks that are held in
 *   interrupt context while calling this function. Even if the lock has
 *   nothing to do with the timer in question.  Here's why:
 *
 *    CPU0                             CPU1
 *    ----                             ----
 *                                   <SOFTIRQ>
 *                                   call_timer_fn();
 *                                     base->running_timer = mytimer;
 *  spin_lock_irq(somelock);
 *                                     <IRQ>
 *                                        spin_lock(somelock);
 *  del_timer_sync(mytimer);
 *   while (base->running_timer == mytimer);
 *
 * Now del_timer_sync() will never return and never release somelock.
 * The interrupt on the other CPU is waiting to grab somelock but
 * it has interrupted the softirq that CPU0 is waiting to finish.
 *
 * The function returns whether it has deactivated a pending timer or not.
 */
int del_timer_sync(struct timer_list *timer)
{
#ifdef CONFIG_LOCKDEP
        unsigned long flags;

        /*
         * If lockdep gives a backtrace here, please reference
         * the synchronization rules above.
         */
        local_irq_save(flags);
        lock_map_acquire(&timer->lockdep_map);
        lock_map_release(&timer->lockdep_map);
        local_irq_restore(flags);
#endif
        /*
         * don't use it in hardirq context, because it
         * could lead to deadlock.
         */
        WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE));
        for (;;) {
                int ret = try_to_del_timer_sync(timer);
                if (ret >= 0)
                        return ret;
                cpu_relax();
        }
}
EXPORT_SYMBOL(del_timer_sync);
#endif

static void call_timer_fn(struct timer_list *timer, void (*fn)(unsigned long),
                          unsigned long data)
{
        int count = preempt_count();

#ifdef CONFIG_LOCKDEP
        /*
         * It is permissible to free the timer from inside the
         * function that is called from it, this we need to take into
         * account for lockdep too. To avoid bogus "held lock freed"
         * warnings as well as problems when looking into
         * timer->lockdep_map, make a copy and use that here.
         */
        struct lockdep_map lockdep_map;

        lockdep_copy_map(&lockdep_map, &timer->lockdep_map);
#endif
        /*
         * Couple the lock chain with the lock chain at
         * del_timer_sync() by acquiring the lock_map around the fn()
         * call here and in del_timer_sync().
         */
        lock_map_acquire(&lockdep_map);

        trace_timer_expire_entry(timer);
        fn(data);
        trace_timer_expire_exit(timer);

        lock_map_release(&lockdep_map);

        if (count != preempt_count()) {
                WARN_ONCE(1, "timer: %pF preempt leak: %08x -> %08x\n",
                          fn, count, preempt_count());
                /*
                 * Restore the preempt count. That gives us a decent
                 * chance to survive and extract information. If the
                 * callback kept a lock held, bad luck, but not worse
                 * than the BUG() we had.
                 */
                preempt_count_set(count);
        }
}

static void expire_timers(struct timer_base *base, struct hlist_head *head)
{
        while (!hlist_empty(head)) {
                struct timer_list *timer;
                void (*fn)(unsigned long);
                unsigned long data;

                timer = hlist_entry(head->first, struct timer_list, entry);
                timer_stats_account_timer(timer);

                base->running_timer = timer;
                detach_timer(timer, true);

                fn = timer->function;
                data = timer->data;

                if (timer->flags & TIMER_IRQSAFE) {
                        spin_unlock(&base->lock);
                        call_timer_fn(timer, fn, data);
                        spin_lock(&base->lock);
                } else {
                        spin_unlock_irq(&base->lock);
                        call_timer_fn(timer, fn, data);
                        spin_lock_irq(&base->lock);
                }
        }
}

static int __collect_expired_timers(struct timer_base *base,
                                    struct hlist_head *heads)
{
        unsigned long clk = base->clk;
        struct hlist_head *vec;
        int i, levels = 0;
        unsigned int idx;

        for (i = 0; i < LVL_DEPTH; i++) {
                idx = (clk & LVL_MASK) + i * LVL_SIZE;

                if (__test_and_clear_bit(idx, base->pending_map)) {
                        vec = base->vectors + idx;
                        hlist_move_list(vec, heads++);
                        levels++;
                }
                /* Is it time to look at the next level? */
                if (clk & LVL_CLK_MASK)
                        break;
                /* Shift clock for the next level granularity */
                clk >>= LVL_CLK_SHIFT;
        }
        return levels;
}

#ifdef CONFIG_NO_HZ_COMMON
/*
 * Find the next pending bucket of a level. Search from level start (@offset)
 * + @clk upwards and if nothing there, search from start of the level
 * (@offset) up to @offset + clk.
 */
static int next_pending_bucket(struct timer_base *base, unsigned offset,
                               unsigned clk)
{
        unsigned pos, start = offset + clk;
        unsigned end = offset + LVL_SIZE;

        pos = find_next_bit(base->pending_map, end, start);
        if (pos < end)
                return pos - start;

        pos = find_next_bit(base->pending_map, start, offset);
        return pos < start ? pos + LVL_SIZE - start : -1;
}

/*
 * Search the first expiring timer in the various clock levels. Caller must
 * hold base->lock.
 */
static unsigned long __next_timer_interrupt(struct timer_base *base)
{
        unsigned long clk, next, adj;
        unsigned lvl, offset = 0;

        next = base->clk + NEXT_TIMER_MAX_DELTA;
        clk = base->clk;
        for (lvl = 0; lvl < LVL_DEPTH; lvl++, offset += LVL_SIZE) {
                int pos = next_pending_bucket(base, offset, clk & LVL_MASK);

                if (pos >= 0) {
                        unsigned long tmp = clk + (unsigned long) pos;

                        tmp <<= LVL_SHIFT(lvl);
                        if (time_before(tmp, next))
                                next = tmp;
                }
                /*
                 * Clock for the next level. If the current level clock lower
                 * bits are zero, we look at the next level as is. If not we
                 * need to advance it by one because that's going to be the
                 * next expiring bucket in that level. base->clk is the next
                 * expiring jiffie. So in case of:
                 *
                 * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0
                 *  0    0    0    0    0    0
                 *
                 * we have to look at all levels @index 0. With
                 *
                 * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0
                 *  0    0    0    0    0    2
                 *
                 * LVL0 has the next expiring bucket @index 2. The upper
                 * levels have the next expiring bucket @index 1.
                 *
                 * In case that the propagation wraps the next level the same
                 * rules apply:
                 *
                 * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0
                 *  0    0    0    0    F    2
                 *
                 * So after looking at LVL0 we get:
                 *
                 * LVL5 LVL4 LVL3 LVL2 LVL1
                 *  0    0    0    1    0
                 *
                 * So no propagation from LVL1 to LVL2 because that happened
                 * with the add already, but then we need to propagate further
                 * from LVL2 to LVL3.
                 *
                 * So the simple check whether the lower bits of the current
                 * level are 0 or not is sufficient for all cases.
                 */
                adj = clk & LVL_CLK_MASK ? 1 : 0;
                clk >>= LVL_CLK_SHIFT;
                clk += adj;
        }
        return next;
}

/*
 * Check, if the next hrtimer event is before the next timer wheel
 * event:
 */
static u64 cmp_next_hrtimer_event(u64 basem, u64 expires)
{
        u64 nextevt = hrtimer_get_next_event();

        /*
         * If high resolution timers are enabled
         * hrtimer_get_next_event() returns KTIME_MAX.
         */
        if (expires <= nextevt)
                return expires;

        /*
         * If the next timer is already expired, return the tick base
         * time so the tick is fired immediately.
         */
        if (nextevt <= basem)
                return basem;

        /*
         * Round up to the next jiffie. High resolution timers are
         * off, so the hrtimers are expired in the tick and we need to
         * make sure that this tick really expires the timer to avoid
         * a ping pong of the nohz stop code.
         *
         * Use DIV_ROUND_UP_ULL to prevent gcc calling __divdi3
         */
        return DIV_ROUND_UP_ULL(nextevt, TICK_NSEC) * TICK_NSEC;
}

/**
 * get_next_timer_interrupt - return the time (clock mono) of the next timer
 * @basej:      base time jiffies
 * @basem:      base time clock monotonic
 *
 * Returns the tick aligned clock monotonic time of the next pending
 * timer or KTIME_MAX if no timer is pending.
 */
u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
{
        struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
        u64 expires = KTIME_MAX;
        unsigned long nextevt;
        bool is_max_delta;

        /*
         * Pretend that there is no timer pending if the cpu is offline.
         * Possible pending timers will be migrated later to an active cpu.
         */
        if (cpu_is_offline(smp_processor_id()))
                return expires;

        spin_lock(&base->lock);
        nextevt = __next_timer_interrupt(base);
        is_max_delta = (nextevt == base->clk + NEXT_TIMER_MAX_DELTA);
        base->next_expiry = nextevt;
        /*
         * We have a fresh next event. Check whether we can forward the base:
         */
        if (time_after(nextevt, jiffies))
                base->clk = jiffies;
        else if (time_after(nextevt, base->clk))
                base->clk = nextevt;

        if (time_before_eq(nextevt, basej)) {
                expires = basem;
                base->is_idle = false;
        } else {
                if (!is_max_delta)
                        expires = basem + (nextevt - basej) * TICK_NSEC;
                /*
                 * If we expect to sleep more than a tick, mark the base idle:
                 */
                if ((expires - basem) > TICK_NSEC)
                        base->is_idle = true;
        }
        spin_unlock(&base->lock);

        return cmp_next_hrtimer_event(basem, expires);
}

/**
 * timer_clear_idle - Clear the idle state of the timer base
 *
 * Called with interrupts disabled
 */
void timer_clear_idle(void)
{
        struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);

        /*
         * We do this unlocked. The worst outcome is a remote enqueue sending
         * a pointless IPI, but taking the lock would just make the window for
         * sending the IPI a few instructions smaller for the cost of taking
         * the lock in the exit from idle path.
         */
        base->is_idle = false;
}

static int collect_expired_timers(struct timer_base *base,
                                  struct hlist_head *heads)
{
        /*
         * NOHZ optimization. After a long idle sleep we need to forward the
         * base to current jiffies. Avoid a loop by searching the bitfield for
         * the next expiring timer.
         */
        if ((long)(jiffies - base->clk) > 2) {
                unsigned long next = __next_timer_interrupt(base);

                /*
                 * If the next timer is ahead of time forward to current
                 * jiffies, otherwise forward to the next expiry time:
                 */
                if (time_after(next, jiffies)) {
                        /* The call site will increment clock! */
                        base->clk = jiffies - 1;
                        return 0;
                }
                base->clk = next;
        }
        return __collect_expired_timers(base, heads);
}
#else
static inline int collect_expired_timers(struct timer_base *base,
                                         struct hlist_head *heads)
{
        return __collect_expired_timers(base, heads);
}
#endif

/*
 * Called from the timer interrupt handler to charge one tick to the current
 * process.  user_tick is 1 if the tick is user time, 0 for system.
 */
void update_process_times(int user_tick)
{
        struct task_struct *p = current;

        /* Note: this timer irq context must be accounted for as well. */
        account_process_tick(p, user_tick);
        run_local_timers();
        rcu_check_callbacks(user_tick);
#ifdef CONFIG_IRQ_WORK
        if (in_irq())
                irq_work_tick();
#endif
        scheduler_tick();
        run_posix_cpu_timers(p);
}

/**
 * __run_timers - run all expired timers (if any) on this CPU.
 * @base: the timer vector to be processed.
 */
static inline void __run_timers(struct timer_base *base)
{
        struct hlist_head heads[LVL_DEPTH];
        int levels;

        if (!time_after_eq(jiffies, base->clk))
                return;

        spin_lock_irq(&base->lock);

        while (time_after_eq(jiffies, base->clk)) {

                levels = collect_expired_timers(base, heads);
                base->clk++;

                while (levels--)
                        expire_timers(base, heads + levels);
        }
        base->running_timer = NULL;
        spin_unlock_irq(&base->lock);
}

/*
 * This function runs timers and the timer-tq in bottom half context.
 */
static __latent_entropy void run_timer_softirq(struct softirq_action *h)
{
        struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);

        __run_timers(base);
        if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active)
                __run_timers(this_cpu_ptr(&timer_bases[BASE_DEF]));
}

/*
 * Called by the local, per-CPU timer interrupt on SMP.
 */
void run_local_timers(void)
{
        struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);

        hrtimer_run_queues();
        /* Raise the softirq only if required. */
        if (time_before(jiffies, base->clk)) {
                if (!IS_ENABLED(CONFIG_NO_HZ_COMMON) || !base->nohz_active)
                        return;
                /* CPU is awake, so check the deferrable base. */
                base++;
                if (time_before(jiffies, base->clk))
                        return;
        }
        raise_softirq(TIMER_SOFTIRQ);
}

#ifdef __ARCH_WANT_SYS_ALARM

/*
 * For backwards compatibility?  This can be done in libc so Alpha
 * and all newer ports shouldn't need it.
 */
SYSCALL_DEFINE1(alarm, unsigned int, seconds)
{
        return alarm_setitimer(seconds);
}

#endif

static void process_timeout(unsigned long __data)
{
        wake_up_process((struct task_struct *)__data);
}

/**
 * schedule_timeout - sleep until timeout
 * @timeout: timeout value in jiffies
 *
 * Make the current task sleep until @timeout jiffies have
 * elapsed. The routine will return immediately unless
 * the current task state has been set (see set_current_state()).
 *
 * You can set the task state as follows -
 *
 * %TASK_UNINTERRUPTIBLE - at least @timeout jiffies are guaranteed to
 * pass before the routine returns. The routine will return 0
 *
 * %TASK_INTERRUPTIBLE - the routine may return early if a signal is
 * delivered to the current task. In this case the remaining time
 * in jiffies will be returned, or 0 if the timer expired in time
 *
 * The current task state is guaranteed to be TASK_RUNNING when this
 * routine returns.
 *
 * Specifying a @timeout value of %MAX_SCHEDULE_TIMEOUT will schedule
 * the CPU away without a bound on the timeout. In this case the return
 * value will be %MAX_SCHEDULE_TIMEOUT.
 *
 * In all cases the return value is guaranteed to be non-negative.
 */
signed long __sched schedule_timeout(signed long timeout)
{
        struct timer_list timer;
        unsigned long expire;

        switch (timeout)
        {
        case MAX_SCHEDULE_TIMEOUT:
                /*
                 * These two special cases are useful to be comfortable
                 * in the caller. Nothing more. We could take
                 * MAX_SCHEDULE_TIMEOUT from one of the negative value
                 * but I' d like to return a valid offset (>=0) to allow
                 * the caller to do everything it want with the retval.
                 */
                schedule();
                goto out;
        default:
                /*
                 * Another bit of PARANOID. Note that the retval will be
                 * 0 since no piece of kernel is supposed to do a check
                 * for a negative retval of schedule_timeout() (since it
                 * should never happens anyway). You just have the printk()
                 * that will tell you if something is gone wrong and where.
                 */
                if (timeout < 0) {
                        printk(KERN_ERR "schedule_timeout: wrong timeout "
                                "value %lx\n", timeout);
                        dump_stack();
                        current->state = TASK_RUNNING;
                        goto out;
                }
        }

        expire = timeout + jiffies;

        setup_timer_on_stack(&timer, process_timeout, (unsigned long)current);
        __mod_timer(&timer, expire, false);
        schedule();
        del_singleshot_timer_sync(&timer);

        /* Remove the timer from the object tracker */
        destroy_timer_on_stack(&timer);

        timeout = expire - jiffies;

 out:
        return timeout < 0 ? 0 : timeout;
}
EXPORT_SYMBOL(schedule_timeout);

/*
 * We can use __set_current_state() here because schedule_timeout() calls
 * schedule() unconditionally.
 */
signed long __sched schedule_timeout_interruptible(signed long timeout)
{
        __set_current_state(TASK_INTERRUPTIBLE);
        return schedule_timeout(timeout);
}
EXPORT_SYMBOL(schedule_timeout_interruptible);

signed long __sched schedule_timeout_killable(signed long timeout)
{
        __set_current_state(TASK_KILLABLE);
        return schedule_timeout(timeout);
}
EXPORT_SYMBOL(schedule_timeout_killable);

signed long __sched schedule_timeout_uninterruptible(signed long timeout)
{
        __set_current_state(TASK_UNINTERRUPTIBLE);
        return schedule_timeout(timeout);
}
EXPORT_SYMBOL(schedule_timeout_uninterruptible);

/*
 * Like schedule_timeout_uninterruptible(), except this task will not contribute
 * to load average.
 */
signed long __sched schedule_timeout_idle(signed long timeout)
{
        __set_current_state(TASK_IDLE);
        return schedule_timeout(timeout);
}
EXPORT_SYMBOL(schedule_timeout_idle);

#ifdef CONFIG_HOTPLUG_CPU
static void migrate_timer_list(struct timer_base *new_base, struct hlist_head *head)
{
        struct timer_list *timer;
        int cpu = new_base->cpu;

        while (!hlist_empty(head)) {
                timer = hlist_entry(head->first, struct timer_list, entry);
                detach_timer(timer, false);
                timer->flags = (timer->flags & ~TIMER_BASEMASK) | cpu;
                internal_add_timer(new_base, timer);
        }
}

int timers_dead_cpu(unsigned int cpu)
{
        struct timer_base *old_base;
        struct timer_base *new_base;
        int b, i;

        BUG_ON(cpu_online(cpu));

        for (b = 0; b < NR_BASES; b++) {
                old_base = per_cpu_ptr(&timer_bases[b], cpu);
                new_base = get_cpu_ptr(&timer_bases[b]);
                /*
                 * The caller is globally serialized and nobody else
                 * takes two locks at once, deadlock is not possible.
                 */
                spin_lock_irq(&new_base->lock);
                spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);

                BUG_ON(old_base->running_timer);

                for (i = 0; i < WHEEL_SIZE; i++)
                        migrate_timer_list(new_base, old_base->vectors + i);

                spin_unlock(&old_base->lock);
                spin_unlock_irq(&new_base->lock);
                put_cpu_ptr(&timer_bases);
        }
        return 0;
}

#endif /* CONFIG_HOTPLUG_CPU */

static void __init init_timer_cpu(int cpu)
{
        struct timer_base *base;
        int i;

        for (i = 0; i < NR_BASES; i++) {
                base = per_cpu_ptr(&timer_bases[i], cpu);
                base->cpu = cpu;
                spin_lock_init(&base->lock);
                base->clk = jiffies;
        }
}

static void __init init_timer_cpus(void)
{
        int cpu;

        for_each_possible_cpu(cpu)
                init_timer_cpu(cpu);
}

void __init init_timers(void)
{
        init_timer_cpus();
        init_timer_stats();
        open_softirq(TIMER_SOFTIRQ, run_timer_softirq);
}

/**
 * msleep - sleep safely even with waitqueue interruptions
 * @msecs: Time in milliseconds to sleep for
 */
void msleep(unsigned int msecs)
{
        unsigned long timeout = msecs_to_jiffies(msecs) + 1;

        while (timeout)
                timeout = schedule_timeout_uninterruptible(timeout);
}

EXPORT_SYMBOL(msleep);

/**
 * msleep_interruptible - sleep waiting for signals
 * @msecs: Time in milliseconds to sleep for
 */
unsigned long msleep_interruptible(unsigned int msecs)
{
        unsigned long timeout = msecs_to_jiffies(msecs) + 1;

        while (timeout && !signal_pending(current))
                timeout = schedule_timeout_interruptible(timeout);
        return jiffies_to_msecs(timeout);
}

EXPORT_SYMBOL(msleep_interruptible);

static void __sched do_usleep_range(unsigned long min, unsigned long max)
{
        ktime_t kmin;
        u64 delta;

        kmin = ktime_set(0, min * NSEC_PER_USEC);
        delta = (u64)(max - min) * NSEC_PER_USEC;
        schedule_hrtimeout_range(&kmin, delta, HRTIMER_MODE_REL);
}

/**
 * usleep_range - Sleep for an approximate time
 * @min: Minimum time in usecs to sleep
 * @max: Maximum time in usecs to sleep
 *
 * In non-atomic context where the exact wakeup time is flexible, use
 * usleep_range() instead of udelay().  The sleep improves responsiveness
 * by avoiding the CPU-hogging busy-wait of udelay(), and the range reduces
 * power usage by allowing hrtimers to take advantage of an already-
 * scheduled interrupt instead of scheduling a new one just for this sleep.
 */
void __sched usleep_range(unsigned long min, unsigned long max)
{
        __set_current_state(TASK_UNINTERRUPTIBLE);
        do_usleep_range(min, max);
}
EXPORT_SYMBOL(usleep_range);