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 // 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/random.h>
 #include <linux/sysctl.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. We start from the last possible delta of the previous level
  * so that we can later add an extra LVL_GRAN(n) to n (see calc_index()).
  */
 #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            next_expiry_recalc;
     bool            is_idle;
     bool            timers_pending;
     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
 static 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);
 }
 
 #ifdef CONFIG_SYSCTL
 static int timer_migration_handler(struct ctl_table *table, int write,
                 void *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 struct ctl_table timer_sysctl[] = {
     {
         .procname   = "timer_migration",
         .data       = &sysctl_timer_migration,
         .maxlen     = sizeof(unsigned int),
         .mode       = 0644,
         .proc_handler   = timer_migration_handler,
         .extra1     = SYSCTL_ZERO,
         .extra2     = SYSCTL_ONE,
     },
     {}
 };
 
 static int __init timer_sysctl_init(void)
 {
     register_sysctl("kernel", timer_sysctl);
     return 0;
 }
 device_initcall(timer_sysctl_init);
 #endif /* CONFIG_SYSCTL */
 #else /* CONFIG_SMP */
 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);
 }
 
 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 long expires, unsigned lvl,
                   unsigned long *bucket_expiry)
 {
 
     /*
      * The timer wheel has to guarantee that a timer does not fire
      * early. Early expiry can happen due to:
      * - Timer is armed at the edge of a tick
      * - Truncation of the expiry time in the outer wheel levels
      *
      * Round up with level granularity to prevent this.
      */
     expires = (expires >> LVL_SHIFT(lvl)) + 1;
     *bucket_expiry = expires << LVL_SHIFT(lvl);
     return LVL_OFFS(lvl) + (expires & LVL_MASK);
 }
 
 static int calc_wheel_index(unsigned long expires, unsigned long clk,
                 unsigned long *bucket_expiry)
 {
     unsigned long delta = expires - clk;
     unsigned int idx;
 
     if (delta < LVL_START(1)) {
         idx = calc_index(expires, 0, bucket_expiry);
     } else if (delta < LVL_START(2)) {
         idx = calc_index(expires, 1, bucket_expiry);
     } else if (delta < LVL_START(3)) {
         idx = calc_index(expires, 2, bucket_expiry);
     } else if (delta < LVL_START(4)) {
         idx = calc_index(expires, 3, bucket_expiry);
     } else if (delta < LVL_START(5)) {
         idx = calc_index(expires, 4, bucket_expiry);
     } else if (delta < LVL_START(6)) {
         idx = calc_index(expires, 5, bucket_expiry);
     } else if (delta < LVL_START(7)) {
         idx = calc_index(expires, 6, bucket_expiry);
     } else if (LVL_DEPTH > 8 && delta < LVL_START(8)) {
         idx = calc_index(expires, 7, bucket_expiry);
     } else if ((long) delta < 0) {
         idx = clk & LVL_MASK;
         *bucket_expiry = clk;
     } else {
         /*
          * Force expire obscene large timeouts to expire at the
          * capacity limit of the wheel.
          */
         if (delta >= WHEEL_TIMEOUT_CUTOFF)
             expires = clk + WHEEL_TIMEOUT_MAX;
 
         idx = calc_index(expires, LVL_DEPTH - 1, bucket_expiry);
     }
     return 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)
         wake_up_nohz_cpu(base->cpu);
 }
 
 /*
  * Enqueue the timer into the hash bucket, mark it pending in
  * the bitmap, store the index in the timer flags then wake up
  * the target CPU if needed.
  */
 static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
               unsigned int idx, unsigned long bucket_expiry)
 {
 
     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);
 
     /*
      * Check whether this is the new first expiring timer. The
      * effective expiry time of the timer is required here
      * (bucket_expiry) instead of timer->expires.
      */
     if (time_before(bucket_expiry, base->next_expiry)) {
         /*
          * Set the next expiry time and kick the CPU so it
          * can reevaluate the wheel:
          */
         base->next_expiry = bucket_expiry;
         base->timers_pending = true;
         base->next_expiry_recalc = false;
         trigger_dyntick_cpu(base, timer);
     }
 }
 
 static void internal_add_timer(struct timer_base *base, struct timer_list *timer)
 {
     unsigned long bucket_expiry;
     unsigned int idx;
 
     idx = calc_wheel_index(timer->expires, base->clk, &bucket_expiry);
     enqueue_timer(base, timer, idx, bucket_expiry);
 }
 
 #ifdef CONFIG_DEBUG_OBJECTS_TIMERS
 
 static const struct debug_obj_descr timer_debug_descr;
 
 struct timer_hint {
     void    (*function)(struct timer_list *t);
     long    offset;
 };
 
 #define TIMER_HINT(fn, container, timr, hintfn)         \
     {                           \
         .function = fn,                 \
         .offset   = offsetof(container, hintfn) -   \
                 offsetof(container, timr)       \
     }
 
 static const struct timer_hint timer_hints[] = {
     TIMER_HINT(delayed_work_timer_fn,
            struct delayed_work, timer, work.func),
     TIMER_HINT(kthread_delayed_work_timer_fn,
            struct kthread_delayed_work, timer, work.func),
 };
 
 static void *timer_debug_hint(void *addr)
 {
     struct timer_list *timer = addr;
     int i;
 
     for (i = 0; i < ARRAY_SIZE(timer_hints); i++) {
         if (timer_hints[i].function == timer->function) {
             void (**fn)(void) = addr + timer_hints[i].offset;
 
             return *fn;
         }
     }
 
     return timer->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);
         fallthrough;
     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 const 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_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;
     if (WARN_ON_ONCE(flags & ~TIMER_INIT_FLAGS))
         flags &= TIMER_INIT_FLAGS;
     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);
         base->next_expiry_recalc = true;
     }
 
     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)
 {
     unsigned long jnow = READ_ONCE(jiffies);
 
     /*
      * No need to forward if we are close enough below jiffies.
      * Also while executing timers, base->clk is 1 offset ahead
      * of jiffies to avoid endless requeuing to current jiffies.
      */
     if ((long)(jnow - base->clk) < 1)
         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 {
         if (WARN_ON_ONCE(time_before(base->next_expiry, base->clk)))
             return;
         base->clk = base->next_expiry;
     }
 }
 
 
 /*
  * 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
 #define MOD_TIMER_NOTPENDING        0x04
 
 static inline int
 __mod_timer(struct timer_list *timer, unsigned long expires, unsigned int options)
 {
     unsigned long clk = 0, flags, bucket_expiry;
     struct timer_base *base, *new_base;
     unsigned int idx = UINT_MAX;
     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 (!(options & MOD_TIMER_NOTPENDING) && 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, &bucket_expiry);
 
         /*
          * 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() 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, bucket_expiry);
     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, MOD_TIMER_NOTPENDING);
 }
 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 reacquire 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)) {
         raw_spin_unlock_irq(&base->lock);
         spin_unlock(&base->expiry_lock);
         spin_lock(&base->expiry_lock);
         raw_spin_lock_irq(&base->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 | TIMER_IRQSAFE))) {
         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));
 
     /*
      * Must be able to sleep on PREEMPT_RT because of the slowpath in
      * del_timer_wait_running().
      */
     if (IS_ENABLED(CONFIG_PREEMPT_RT) && !(timer->flags & TIMER_IRQSAFE))
         lockdep_assert_preemption_enabled();
 
     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);
             raw_spin_lock(&base->lock);
             base->running_timer = NULL;
         } else {
             raw_spin_unlock_irq(&base->lock);
             call_timer_fn(timer, fn, baseclk);
             raw_spin_lock_irq(&base->lock);
             base->running_timer = NULL;
             timer_sync_wait_running(base);
         }
     }
 }
 
 static int collect_expired_timers(struct timer_base *base,
                   struct hlist_head *heads)
 {
     unsigned long clk = base->clk = base->next_expiry;
     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;
 }
 
 /*
  * 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);
         unsigned long lvl_clk = clk & LVL_CLK_MASK;
 
         if (pos >= 0) {
             unsigned long tmp = clk + (unsigned long) pos;
 
             tmp <<= LVL_SHIFT(lvl);
             if (time_before(tmp, next))
                 next = tmp;
 
             /*
              * If the next expiration happens before we reach
              * the next level, no need to check further.
              */
             if (pos <= ((LVL_CLK_DIV - lvl_clk) & LVL_CLK_MASK))
                 break;
         }
         /*
          * 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 = lvl_clk ? 1 : 0;
         clk >>= LVL_CLK_SHIFT;
         clk += adj;
     }
 
     base->next_expiry_recalc = false;
     base->timers_pending = !(next == base->clk + NEXT_TIMER_MAX_DELTA);
 
     return next;
 }
 
 #ifdef CONFIG_NO_HZ_COMMON
 /*
  * 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;
 
     /*
      * 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);
     if (base->next_expiry_recalc)
         base->next_expiry = __next_timer_interrupt(base);
     nextevt = base->next_expiry;
 
     /*
      * 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 (base->timers_pending)
             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->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;
 }
 #endif
 
 /**
  * __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_before(jiffies, base->next_expiry))
         return;
 
     timer_base_lock_expiry(base);
     raw_spin_lock_irq(&base->lock);
 
     while (time_after_eq(jiffies, base->clk) &&
            time_after_eq(jiffies, base->next_expiry)) {
         levels = collect_expired_timers(base, heads);
         /*
          * The two possible reasons for not finding any expired
          * timer at this clk are that all matching timers have been
          * dequeued or no timer has been queued since
          * base::next_expiry was set to base::clk +
          * NEXT_TIMER_MAX_DELTA.
          */
         WARN_ON_ONCE(!levels && !base->next_expiry_recalc
                  && base->timers_pending);
         base->clk++;
         base->next_expiry = __next_timer_interrupt(base);
 
         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.
  */
 static 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->next_expiry)) {
         if (!IS_ENABLED(CONFIG_NO_HZ_COMMON))
             return;
         /* CPU is awake, so check the deferrable base. */
         base++;
         if (time_before(jiffies, base->next_expiry))
             return;
     }
     raise_softirq(TIMER_SOFTIRQ);
 }
 
 /*
  * 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();
 }
 
 /*
  * 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 function behavior depends on the current task state
  * (see also set_current_state() description):
  *
  * %TASK_RUNNING - the scheduler is called, but the task does not sleep
  * at all. That happens because sched_submit_work() does nothing for
  * tasks in %TASK_RUNNING state.
  *
  * %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();
             __set_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, MOD_TIMER_NOTPENDING);
     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->next_expiry_recalc = false;
         base->timers_pending = false;
         base->is_idle = false;
     }
     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;
         base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
         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();
     posix_cputimers_init_work();
     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_state - Sleep for an approximate time in a given state
  * @min:    Minimum time in usecs to sleep
  * @max:    Maximum time in usecs to sleep
  * @state:  State of the current task that will be while sleeping
  *
  * In non-atomic context where the exact wakeup time is flexible, use
  * usleep_range_state() 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_state(unsigned long min, unsigned long max,
                 unsigned int state)
 {
     ktime_t exp = ktime_add_us(ktime_get(), min);
     u64 delta = (u64)(max - min) * NSEC_PER_USEC;
 
     for (;;) {
         __set_current_state(state);
         /* Do not return before the requested sleep time has elapsed */
         if (!schedule_hrtimeout_range(&exp, delta, HRTIMER_MODE_ABS))
             break;
     }
 }
 EXPORT_SYMBOL(usleep_range_state);

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