xref: /kernel/time/timer.c

// SPDX-License-Identifier: GPL-2.0
/*
 *  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/signal.h>
#include <linux/sched/sysctl.h>
#include <linux/sched/nohz.h>
#include <linux/sched/debug.h>
#include <linux/slab.h>
#include <linux/compat.h>

#include <linux/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 {
	raw_spinlock_t		lock;
	struct timer_list	*running_timer;
#ifdef CONFIG_PREEMPT_RT
	spinlock_t		expiry_lock;
	atomic_t		timer_waiters;
#endif
	unsigned long		clk;
	unsigned long		next_expiry;
	unsigned int		cpu;
	bool			is_idle;
	bool			must_forward_clk;
	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]);

#ifdef CONFIG_NO_HZ_COMMON

static DEFINE_STATIC_KEY_FALSE(timers_nohz_active);
static DEFINE_MUTEX(timer_keys_mutex);

static void timer_update_keys(struct work_struct *work);
static DECLARE_WORK(timer_update_work, timer_update_keys);

#ifdef CONFIG_SMP
unsigned int sysctl_timer_migration = 1;

DEFINE_STATIC_KEY_FALSE(timers_migration_enabled);

static void timers_update_migration(void)
{
	if (sysctl_timer_migration && tick_nohz_active)
		static_branch_enable(&timers_migration_enabled);
	else
		static_branch_disable(&timers_migration_enabled);
}
#else
static inline void timers_update_migration(void) { }
#endif /* !CONFIG_SMP */

static void timer_update_keys(struct work_struct *work)
{
	mutex_lock(&timer_keys_mutex);
	timers_update_migration();
	static_branch_enable(&timers_nohz_active);
	mutex_unlock(&timer_keys_mutex);
}

void timers_update_nohz(void)
{
	schedule_work(&timer_update_work);
}

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

	mutex_lock(&timer_keys_mutex);
	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
	if (!ret && write)
		timers_update_migration();
	mutex_unlock(&timer_keys_mutex);
	return ret;
}

static inline bool is_timers_nohz_active(void)
{
	return static_branch_unlikely(&timers_nohz_active);
}
#else
static inline bool is_timers_nohz_active(void) { return false; }
#endif /* NO_HZ_COMMON */

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);

	trace_timer_start(timer, timer->expires, timer->flags);
}

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_timers_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_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(struct timer_list *unused)
{
	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:
		timer_setup(timer, stub_timer, 0);
		return true;

	case ODEBUG_STATE_ACTIVE:
		WARN_ON(1);
		/* fall through */
	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:
		timer_setup(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,
			  void (*func)(struct timer_list *),
			  unsigned int flags,
			  const char *name, struct lock_class_key *key);

void init_timer_on_stack_key(struct timer_list *timer,
			     void (*func)(struct timer_list *),
			     unsigned int flags,
			     const char *name, struct lock_class_key *key)
{
	debug_object_init_on_stack(timer, &timer_debug_descr);
	do_init_timer(timer, func, 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_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,
			  void (*func)(struct timer_list *),
			  unsigned int flags,
			  const char *name, struct lock_class_key *key)
{
	timer->entry.pprev = NULL;
	timer->function = func;
	timer->flags = flags | raw_smp_processor_id();
	lockdep_init_map(&timer->lockdep_map, name, key, 0);
}

/**
 * init_timer_key - initialize a timer
 * @timer: the timer to be initialized
 * @func: timer callback function
 * @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,
		    void (*func)(struct timer_list *), unsigned int flags,
		    const char *name, struct lock_class_key *key)
{
	debug_init(timer);
	do_init_timer(timer, func, 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 NO_HZ_COMMON is set then we need
	 * to use the deferrable base.
	 */
	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (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 NO_HZ_COMMON is set then we need
	 * to use the deferrable base.
	 */
	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (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);
}

static inline struct timer_base *
get_target_base(struct timer_base *base, unsigned tflags)
{
#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
	if (static_branch_likely(&timers_migration_enabled) &&
	    !(tflags & TIMER_PINNED))
		return get_timer_cpu_base(tflags, get_nohz_timer_target());
#endif
	return get_timer_this_cpu_base(tflags);
}

static inline void forward_timer_base(struct timer_base *base)
{
#ifdef CONFIG_NO_HZ_COMMON
	unsigned long jnow;

	/*
	 * We only forward the base when we are idle or have just come out of
	 * idle (must_forward_clk logic), and have a delta between base clock
	 * and jiffies. In the common case, run_timers will take care of it.
	 */
	if (likely(!base->must_forward_clk))
		return;

	jnow = READ_ONCE(jiffies);
	base->must_forward_clk = base->is_idle;
	if ((long)(jnow - 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, jnow))
		base->clk = jnow;
	else
		base->clk = base->next_expiry;
#endif
}


/*
 * 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);
			raw_spin_lock_irqsave(&base->lock, *flags);
			if (timer->flags == tf)
				return base;
			raw_spin_unlock_irqrestore(&base->lock, *flags);
		}
		cpu_relax();
	}
}

#define MOD_TIMER_PENDING_ONLY		0x01
#define MOD_TIMER_REDUCE		0x02

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

	BUG_ON(!timer->function);

	/*
	 * 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)) {
		/*
		 * The downside of this optimization is that it can result in
		 * larger granularity than you would get from adding a new
		 * timer with this expiry.
		 */
		long diff = timer->expires - expires;

		if (!diff)
			return 1;
		if (options & MOD_TIMER_REDUCE && diff <= 0)
			return 1;

		/*
		 * We lock timer base and calculate the bucket index right
		 * here. If the timer ends up in the same bucket, then we
		 * just update the expiry time and avoid the whole
		 * dequeue/enqueue dance.
		 */
		base = lock_timer_base(timer, &flags);
		forward_timer_base(base);

		if (timer_pending(timer) && (options & MOD_TIMER_REDUCE) &&
		    time_before_eq(timer->expires, expires)) {
			ret = 1;
			goto out_unlock;
		}

		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)) {
			if (!(options & MOD_TIMER_REDUCE))
				timer->expires = expires;
			else if (time_after(timer->expires, expires))
				timer->expires = expires;
			ret = 1;
			goto out_unlock;
		}
	} else {
		base = lock_timer_base(timer, &flags);
		forward_timer_base(base);
	}

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

	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;

			raw_spin_unlock(&base->lock);
			base = new_base;
			raw_spin_lock(&base->lock);
			WRITE_ONCE(timer->flags,
				   (timer->flags & ~TIMER_BASEMASK) | base->cpu);
			forward_timer_base(base);
		}
	}

	debug_timer_activate(timer);

	timer->expires = expires;
	/*
	 * If 'idx' was calculated above and the base time did not advance
	 * between calculating 'idx' and possibly switching the base, 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:
	raw_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, MOD_TIMER_PENDING_ONLY);
}
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, 0);
}
EXPORT_SYMBOL(mod_timer);

/**
 * timer_reduce - Modify a timer's timeout if it would reduce the timeout
 * @timer:	The timer to be modified
 * @expires:	New timeout in jiffies
 *
 * timer_reduce() is very similar to mod_timer(), except that it will only
 * modify a running timer if that would reduce the expiration time (it will
 * start a timer that isn't running).
 */
int timer_reduce(struct timer_list *timer, unsigned long expires)
{
	return __mod_timer(timer, expires, MOD_TIMER_REDUCE);
}
EXPORT_SYMBOL(timer_reduce);

/**
 * add_timer - start a timer
 * @timer: the timer to be added
 *
 * The kernel will do a ->function(@timer) callback from the
 * timer interrupt at the ->expires point in the future. The
 * current time is 'jiffies'.
 *
 * The timer's ->expires, ->function 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;

	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;

		raw_spin_unlock(&base->lock);
		base = new_base;
		raw_spin_lock(&base->lock);
		WRITE_ONCE(timer->flags,
			   (timer->flags & ~TIMER_BASEMASK) | cpu);
	}
	forward_timer_base(base);

	debug_timer_activate(timer);
	internal_add_timer(base, timer);
	raw_spin_unlock_irqrestore(&base->lock, flags);
}
EXPORT_SYMBOL_GPL(add_timer_on);

/**
 * del_timer - deactivate 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);

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

	return ret;
}
EXPORT_SYMBOL(del_timer);

/**
 * try_to_del_timer_sync - Try to deactivate a timer
 * @timer: timer to delete
 *
 * 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)
		ret = detach_if_pending(timer, base, true);

	raw_spin_unlock_irqrestore(&base->lock, flags);

	return ret;
}
EXPORT_SYMBOL(try_to_del_timer_sync);

#ifdef CONFIG_PREEMPT_RT
static __init void timer_base_init_expiry_lock(struct timer_base *base)
{
	spin_lock_init(&base->expiry_lock);
}

static inline void timer_base_lock_expiry(struct timer_base *base)
{
	spin_lock(&base->expiry_lock);
}

static inline void timer_base_unlock_expiry(struct timer_base *base)
{
	spin_unlock(&base->expiry_lock);
}

/*
 * The counterpart to del_timer_wait_running().
 *
 * If there is a waiter for base->expiry_lock, then it was waiting for the
 * timer callback to finish. Drop expiry_lock and reaquire it. That allows
 * the waiter to acquire the lock and make progress.
 */
static void timer_sync_wait_running(struct timer_base *base)
{
	if (atomic_read(&base->timer_waiters)) {
		spin_unlock(&base->expiry_lock);
		spin_lock(&base->expiry_lock);
	}
}

/*
 * 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 softirq thread on a remote CPU
 * got preempted, and it prevents a life lock when the task which tries to
 * delete a timer preempted the softirq thread running the timer callback
 * function.
 */
static void del_timer_wait_running(struct timer_list *timer)
{
	u32 tf;

	tf = READ_ONCE(timer->flags);
	if (!(tf & TIMER_MIGRATING)) {
		struct timer_base *base = get_timer_base(tf);

		/*
		 * 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->timer_waiters);
		spin_lock_bh(&base->expiry_lock);
		atomic_dec(&base->timer_waiters);
		spin_unlock_bh(&base->expiry_lock);
	}
}
#else
static inline void timer_base_init_expiry_lock(struct timer_base *base) { }
static inline void timer_base_lock_expiry(struct timer_base *base) { }
static inline void timer_base_unlock_expiry(struct timer_base *base) { }
static inline void timer_sync_wait_running(struct timer_base *base) { }
static inline void del_timer_wait_running(struct timer_list *timer) { }
#endif

#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
/**
 * 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)
{
	int ret;

#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));

	do {
		ret = try_to_del_timer_sync(timer);

		if (unlikely(ret < 0)) {
			del_timer_wait_running(timer);
			cpu_relax();
		}
	} while (ret < 0);

	return ret;
}
EXPORT_SYMBOL(del_timer_sync);
#endif

static void call_timer_fn(struct timer_list *timer,
			  void (*fn)(struct timer_list *),
			  unsigned long baseclk)
{
	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, baseclk);
	fn(timer);
	trace_timer_expire_exit(timer);

	lock_map_release(&lockdep_map);

	if (count != preempt_count()) {
		WARN_ONCE(1, "timer: %pS 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)
{
	/*
	 * This value is required only for tracing. base->clk was
	 * incremented directly before expire_timers was called. But expiry
	 * is related to the old base->clk value.
	 */
	unsigned long baseclk = base->clk - 1;

	while (!hlist_empty(head)) {
		struct timer_list *timer;
		void (*fn)(struct timer_list *);

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

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

		fn = timer->function;

		if (timer->flags & TIMER_IRQSAFE) {
			raw_spin_unlock(&base->lock);
			call_timer_fn(timer, fn, baseclk);
			base->running_timer = NULL;
			raw_spin_lock(&base->lock);
		} else {
			raw_spin_unlock_irq(&base->lock);
			call_timer_fn(timer, fn, baseclk);
			base->running_timer = NULL;
			timer_sync_wait_running(base);
			raw_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;

	raw_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. We can only do that when @basej is past base->clk
	 * otherwise we might rewind base->clk.
	 */
	if (time_after(basej, base->clk)) {
		if (time_after(nextevt, basej))
			base->clk = basej;
		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 + (u64)(nextevt - basej) * TICK_NSEC;
		/*
		 * If we expect to sleep more than a tick, mark the base idle.
		 * Also the tick is stopped so any added timer must forward
		 * the base clk itself to keep granularity small. This idle
		 * logic is only maintained for the BASE_STD base, deferrable
		 * timers may still see large granularity skew (by design).
		 */
		if ((expires - basem) > TICK_NSEC) {
			base->must_forward_clk = true;
			base->is_idle = true;
		}
	}
	raw_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)
{
	unsigned long now = READ_ONCE(jiffies);

	/*
	 * 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)(now - 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, now)) {
			/*
			 * The call site will increment base->clk and then
			 * terminate the expiry loop immediately.
			 */
			base->clk = now;
			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_sched_clock_irq(user_tick);
#ifdef CONFIG_IRQ_WORK
	if (in_irq())
		irq_work_tick();
#endif
	scheduler_tick();
	if (IS_ENABLED(CONFIG_POSIX_TIMERS))
		run_posix_cpu_timers();
}

/**
 * __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;

	timer_base_lock_expiry(base);
	raw_spin_lock_irq(&base->lock);

	/*
	 * timer_base::must_forward_clk must be cleared before running
	 * timers so that any timer functions that call mod_timer() will
	 * not try to forward the base. Idle tracking / clock forwarding
	 * logic is only used with BASE_STD timers.
	 *
	 * The must_forward_clk flag is cleared unconditionally also for
	 * the deferrable base. The deferrable base is not affected by idle
	 * tracking and never forwarded, so clearing the flag is a NOOP.
	 *
	 * The fact that the deferrable base is never forwarded can cause
	 * large variations in granularity for deferrable timers, but they
	 * can be deferred for long periods due to idle anyway.
	 */
	base->must_forward_clk = false;

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

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

		while (levels--)
			expire_timers(base, heads + levels);
	}
	raw_spin_unlock_irq(&base->lock);
	timer_base_unlock_expiry(base);
}

/*
 * 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))
		__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))
			return;
		/* CPU is awake, so check the deferrable base. */
		base++;
		if (time_before(jiffies, base->clk))
			return;
	}
	raise_softirq(TIMER_SOFTIRQ);
}

/*
 * Since schedule_timeout()'s timer is defined on the stack, it must store
 * the target task on the stack as well.
 */
struct process_timer {
	struct timer_list timer;
	struct task_struct *task;
};

static void process_timeout(struct timer_list *t)
{
	struct process_timer *timeout = from_timer(timeout, t, timer);

	wake_up_process(timeout->task);
}

/**
 * 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 unless the current task is explicitly
 * woken up, (e.g. by wake_up_process())".
 *
 * %TASK_INTERRUPTIBLE - the routine may return early if a signal is
 * delivered to the current task or the current task is explicitly woken
 * up.
 *
 * 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.
 *
 * Returns 0 when the timer has expired otherwise the remaining time in
 * jiffies will be returned.  In all cases the return value is guaranteed
 * to be non-negative.
 */
signed long __sched schedule_timeout(signed long timeout)
{
	struct process_timer 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;

	timer.task = current;
	timer_setup_on_stack(&timer.timer, process_timeout, 0);
	__mod_timer(&timer.timer, expire, 0);
	schedule();
	del_singleshot_timer_sync(&timer.timer);

	/* Remove the timer from the object tracker */
	destroy_timer_on_stack(&timer.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_prepare_cpu(unsigned int cpu)
{
	struct timer_base *base;
	int b;

	for (b = 0; b < NR_BASES; b++) {
		base = per_cpu_ptr(&timer_bases[b], cpu);
		base->clk = jiffies;
		base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
		base->is_idle = false;
		base->must_forward_clk = true;
	}
	return 0;
}

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.
		 */
		raw_spin_lock_irq(&new_base->lock);
		raw_spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);

		/*
		 * The current CPUs base clock might be stale. Update it
		 * before moving the timers over.
		 */
		forward_timer_base(new_base);

		BUG_ON(old_base->running_timer);

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

		raw_spin_unlock(&old_base->lock);
		raw_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;
		raw_spin_lock_init(&base->lock);
		base->clk = jiffies;
		timer_base_init_expiry_lock(base);
	}
}

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();
	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);

/**
 * 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)
{
	ktime_t exp = ktime_add_us(ktime_get(), min);
	u64 delta = (u64)(max - min) * NSEC_PER_USEC;

	for (;;) {
		__set_current_state(TASK_UNINTERRUPTIBLE);
		/* Do not return before the requested sleep time has elapsed */
		if (!schedule_hrtimeout_range(&exp, delta, HRTIMER_MODE_ABS))
			break;
	}
}
EXPORT_SYMBOL(usleep_range);