1/*
   2 *  linux/kernel/timer.c
   3 *
   4 *  Kernel internal timers
   5 *
   6 *  Copyright (C) 1991, 1992  Linus Torvalds
   7 *
   8 *  1997-01-28  Modified by Finn Arne Gangstad to make timers scale better.
   9 *
  10 *  1997-09-10  Updated NTP code according to technical memorandum Jan '96
  11 *              "A Kernel Model for Precision Timekeeping" by Dave Mills
  12 *  1998-12-24  Fixed a xtime SMP race (we need the xtime_lock rw spinlock to
  13 *              serialize accesses to xtime/lost_ticks).
  14 *                              Copyright (C) 1998  Andrea Arcangeli
  15 *  1999-03-10  Improved NTP compatibility by Ulrich Windl
  16 *  2002-05-31	Move sys_sysinfo here and make its locking sane, Robert Love
  17 *  2000-10-05  Implemented scalable SMP per-CPU timer handling.
  18 *                              Copyright (C) 2000, 2001, 2002  Ingo Molnar
  19 *              Designed by David S. Miller, Alexey Kuznetsov and Ingo Molnar
  20 */
  21
  22#include <linux/kernel_stat.h>
  23#include <linux/export.h>
  24#include <linux/interrupt.h>
  25#include <linux/percpu.h>
  26#include <linux/init.h>
  27#include <linux/mm.h>
  28#include <linux/swap.h>
  29#include <linux/pid_namespace.h>
  30#include <linux/notifier.h>
  31#include <linux/thread_info.h>
  32#include <linux/time.h>
  33#include <linux/jiffies.h>
  34#include <linux/posix-timers.h>
  35#include <linux/cpu.h>
  36#include <linux/syscalls.h>
  37#include <linux/delay.h>
  38#include <linux/tick.h>
  39#include <linux/kallsyms.h>
  40#include <linux/irq_work.h>
  41#include <linux/sched/signal.h>
  42#include <linux/sched/sysctl.h>
  43#include <linux/sched/nohz.h>
  44#include <linux/sched/debug.h>
  45#include <linux/slab.h>
  46#include <linux/compat.h>
 
  47
  48#include <linux/uaccess.h>
  49#include <asm/unistd.h>
  50#include <asm/div64.h>
  51#include <asm/timex.h>
  52#include <asm/io.h>
  53
  54#include "tick-internal.h"
  55
  56#define CREATE_TRACE_POINTS
  57#include <trace/events/timer.h>
  58
  59__visible u64 jiffies_64 __cacheline_aligned_in_smp = INITIAL_JIFFIES;
  60
  61EXPORT_SYMBOL(jiffies_64);
  62
  63/*
  64 * The timer wheel has LVL_DEPTH array levels. Each level provides an array of
  65 * LVL_SIZE buckets. Each level is driven by its own clock and therefor each
  66 * level has a different granularity.
  67 *
  68 * The level granularity is:		LVL_CLK_DIV ^ lvl
  69 * The level clock frequency is:	HZ / (LVL_CLK_DIV ^ level)
  70 *
  71 * The array level of a newly armed timer depends on the relative expiry
  72 * time. The farther the expiry time is away the higher the array level and
  73 * therefor the granularity becomes.
  74 *
  75 * Contrary to the original timer wheel implementation, which aims for 'exact'
  76 * expiry of the timers, this implementation removes the need for recascading
  77 * the timers into the lower array levels. The previous 'classic' timer wheel
  78 * implementation of the kernel already violated the 'exact' expiry by adding
  79 * slack to the expiry time to provide batched expiration. The granularity
  80 * levels provide implicit batching.
  81 *
  82 * This is an optimization of the original timer wheel implementation for the
  83 * majority of the timer wheel use cases: timeouts. The vast majority of
  84 * timeout timers (networking, disk I/O ...) are canceled before expiry. If
  85 * the timeout expires it indicates that normal operation is disturbed, so it
  86 * does not matter much whether the timeout comes with a slight delay.
  87 *
  88 * The only exception to this are networking timers with a small expiry
  89 * time. They rely on the granularity. Those fit into the first wheel level,
  90 * which has HZ granularity.
  91 *
  92 * We don't have cascading anymore. timers with a expiry time above the
  93 * capacity of the last wheel level are force expired at the maximum timeout
  94 * value of the last wheel level. From data sampling we know that the maximum
  95 * value observed is 5 days (network connection tracking), so this should not
  96 * be an issue.
  97 *
  98 * The currently chosen array constants values are a good compromise between
  99 * array size and granularity.
 100 *
 101 * This results in the following granularity and range levels:
 102 *
 103 * HZ 1000 steps
 104 * Level Offset  Granularity            Range
 105 *  0      0         1 ms                0 ms -         63 ms
 106 *  1     64         8 ms               64 ms -        511 ms
 107 *  2    128        64 ms              512 ms -       4095 ms (512ms - ~4s)
 108 *  3    192       512 ms             4096 ms -      32767 ms (~4s - ~32s)
 109 *  4    256      4096 ms (~4s)      32768 ms -     262143 ms (~32s - ~4m)
 110 *  5    320     32768 ms (~32s)    262144 ms -    2097151 ms (~4m - ~34m)
 111 *  6    384    262144 ms (~4m)    2097152 ms -   16777215 ms (~34m - ~4h)
 112 *  7    448   2097152 ms (~34m)  16777216 ms -  134217727 ms (~4h - ~1d)
 113 *  8    512  16777216 ms (~4h)  134217728 ms - 1073741822 ms (~1d - ~12d)
 114 *
 115 * HZ  300
 116 * Level Offset  Granularity            Range
 117 *  0	   0         3 ms                0 ms -        210 ms
 118 *  1	  64        26 ms              213 ms -       1703 ms (213ms - ~1s)
 119 *  2	 128       213 ms             1706 ms -      13650 ms (~1s - ~13s)
 120 *  3	 192      1706 ms (~1s)      13653 ms -     109223 ms (~13s - ~1m)
 121 *  4	 256     13653 ms (~13s)    109226 ms -     873810 ms (~1m - ~14m)
 122 *  5	 320    109226 ms (~1m)     873813 ms -    6990503 ms (~14m - ~1h)
 123 *  6	 384    873813 ms (~14m)   6990506 ms -   55924050 ms (~1h - ~15h)
 124 *  7	 448   6990506 ms (~1h)   55924053 ms -  447392423 ms (~15h - ~5d)
 125 *  8    512  55924053 ms (~15h) 447392426 ms - 3579139406 ms (~5d - ~41d)
 126 *
 127 * HZ  250
 128 * Level Offset  Granularity            Range
 129 *  0	   0         4 ms                0 ms -        255 ms
 130 *  1	  64        32 ms              256 ms -       2047 ms (256ms - ~2s)
 131 *  2	 128       256 ms             2048 ms -      16383 ms (~2s - ~16s)
 132 *  3	 192      2048 ms (~2s)      16384 ms -     131071 ms (~16s - ~2m)
 133 *  4	 256     16384 ms (~16s)    131072 ms -    1048575 ms (~2m - ~17m)
 134 *  5	 320    131072 ms (~2m)    1048576 ms -    8388607 ms (~17m - ~2h)
 135 *  6	 384   1048576 ms (~17m)   8388608 ms -   67108863 ms (~2h - ~18h)
 136 *  7	 448   8388608 ms (~2h)   67108864 ms -  536870911 ms (~18h - ~6d)
 137 *  8    512  67108864 ms (~18h) 536870912 ms - 4294967288 ms (~6d - ~49d)
 138 *
 139 * HZ  100
 140 * Level Offset  Granularity            Range
 141 *  0	   0         10 ms               0 ms -        630 ms
 142 *  1	  64         80 ms             640 ms -       5110 ms (640ms - ~5s)
 143 *  2	 128        640 ms            5120 ms -      40950 ms (~5s - ~40s)
 144 *  3	 192       5120 ms (~5s)     40960 ms -     327670 ms (~40s - ~5m)
 145 *  4	 256      40960 ms (~40s)   327680 ms -    2621430 ms (~5m - ~43m)
 146 *  5	 320     327680 ms (~5m)   2621440 ms -   20971510 ms (~43m - ~5h)
 147 *  6	 384    2621440 ms (~43m) 20971520 ms -  167772150 ms (~5h - ~1d)
 148 *  7	 448   20971520 ms (~5h) 167772160 ms - 1342177270 ms (~1d - ~15d)
 149 */
 150
 151/* Clock divisor for the next level */
 152#define LVL_CLK_SHIFT	3
 153#define LVL_CLK_DIV	(1UL << LVL_CLK_SHIFT)
 154#define LVL_CLK_MASK	(LVL_CLK_DIV - 1)
 155#define LVL_SHIFT(n)	((n) * LVL_CLK_SHIFT)
 156#define LVL_GRAN(n)	(1UL << LVL_SHIFT(n))
 157
 158/*
 159 * The time start value for each level to select the bucket at enqueue
 160 * time.
 
 161 */
 162#define LVL_START(n)	((LVL_SIZE - 1) << (((n) - 1) * LVL_CLK_SHIFT))
 163
 164/* Size of each clock level */
 165#define LVL_BITS	6
 166#define LVL_SIZE	(1UL << LVL_BITS)
 167#define LVL_MASK	(LVL_SIZE - 1)
 168#define LVL_OFFS(n)	((n) * LVL_SIZE)
 169
 170/* Level depth */
 171#if HZ > 100
 172# define LVL_DEPTH	9
 173# else
 174# define LVL_DEPTH	8
 175#endif
 176
 177/* The cutoff (max. capacity of the wheel) */
 178#define WHEEL_TIMEOUT_CUTOFF	(LVL_START(LVL_DEPTH))
 179#define WHEEL_TIMEOUT_MAX	(WHEEL_TIMEOUT_CUTOFF - LVL_GRAN(LVL_DEPTH - 1))
 180
 181/*
 182 * The resulting wheel size. If NOHZ is configured we allocate two
 183 * wheels so we have a separate storage for the deferrable timers.
 184 */
 185#define WHEEL_SIZE	(LVL_SIZE * LVL_DEPTH)
 186
 187#ifdef CONFIG_NO_HZ_COMMON
 188# define NR_BASES	2
 189# define BASE_STD	0
 190# define BASE_DEF	1
 191#else
 192# define NR_BASES	1
 193# define BASE_STD	0
 194# define BASE_DEF	0
 195#endif
 196
 197struct timer_base {
 198	raw_spinlock_t		lock;
 199	struct timer_list	*running_timer;
 
 
 
 
 200	unsigned long		clk;
 201	unsigned long		next_expiry;
 202	unsigned int		cpu;
 
 203	bool			is_idle;
 204	bool			must_forward_clk;
 205	DECLARE_BITMAP(pending_map, WHEEL_SIZE);
 206	struct hlist_head	vectors[WHEEL_SIZE];
 207} ____cacheline_aligned;
 208
 209static DEFINE_PER_CPU(struct timer_base, timer_bases[NR_BASES]);
 210
 211#ifdef CONFIG_NO_HZ_COMMON
 212
 213static DEFINE_STATIC_KEY_FALSE(timers_nohz_active);
 214static DEFINE_MUTEX(timer_keys_mutex);
 215
 216static void timer_update_keys(struct work_struct *work);
 217static DECLARE_WORK(timer_update_work, timer_update_keys);
 218
 219#ifdef CONFIG_SMP
 220unsigned int sysctl_timer_migration = 1;
 221
 222DEFINE_STATIC_KEY_FALSE(timers_migration_enabled);
 223
 224static void timers_update_migration(void)
 225{
 226	if (sysctl_timer_migration && tick_nohz_active)
 227		static_branch_enable(&timers_migration_enabled);
 228	else
 229		static_branch_disable(&timers_migration_enabled);
 230}
 231#else
 232static inline void timers_update_migration(void) { }
 233#endif /* !CONFIG_SMP */
 234
 235static void timer_update_keys(struct work_struct *work)
 236{
 237	mutex_lock(&timer_keys_mutex);
 238	timers_update_migration();
 239	static_branch_enable(&timers_nohz_active);
 240	mutex_unlock(&timer_keys_mutex);
 241}
 242
 243void timers_update_nohz(void)
 244{
 245	schedule_work(&timer_update_work);
 246}
 247
 248int timer_migration_handler(struct ctl_table *table, int write,
 249			    void __user *buffer, size_t *lenp,
 250			    loff_t *ppos)
 251{
 252	int ret;
 253
 254	mutex_lock(&timer_keys_mutex);
 255	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 256	if (!ret && write)
 257		timers_update_migration();
 258	mutex_unlock(&timer_keys_mutex);
 259	return ret;
 260}
 261
 262static inline bool is_timers_nohz_active(void)
 263{
 264	return static_branch_unlikely(&timers_nohz_active);
 265}
 266#else
 267static inline bool is_timers_nohz_active(void) { return false; }
 268#endif /* NO_HZ_COMMON */
 269
 270static unsigned long round_jiffies_common(unsigned long j, int cpu,
 271		bool force_up)
 272{
 273	int rem;
 274	unsigned long original = j;
 275
 276	/*
 277	 * We don't want all cpus firing their timers at once hitting the
 278	 * same lock or cachelines, so we skew each extra cpu with an extra
 279	 * 3 jiffies. This 3 jiffies came originally from the mm/ code which
 280	 * already did this.
 281	 * The skew is done by adding 3*cpunr, then round, then subtract this
 282	 * extra offset again.
 283	 */
 284	j += cpu * 3;
 285
 286	rem = j % HZ;
 287
 288	/*
 289	 * If the target jiffie is just after a whole second (which can happen
 290	 * due to delays of the timer irq, long irq off times etc etc) then
 291	 * we should round down to the whole second, not up. Use 1/4th second
 292	 * as cutoff for this rounding as an extreme upper bound for this.
 293	 * But never round down if @force_up is set.
 294	 */
 295	if (rem < HZ/4 && !force_up) /* round down */
 296		j = j - rem;
 297	else /* round up */
 298		j = j - rem + HZ;
 299
 300	/* now that we have rounded, subtract the extra skew again */
 301	j -= cpu * 3;
 302
 303	/*
 304	 * Make sure j is still in the future. Otherwise return the
 305	 * unmodified value.
 306	 */
 307	return time_is_after_jiffies(j) ? j : original;
 308}
 309
 310/**
 311 * __round_jiffies - function to round jiffies to a full second
 312 * @j: the time in (absolute) jiffies that should be rounded
 313 * @cpu: the processor number on which the timeout will happen
 314 *
 315 * __round_jiffies() rounds an absolute time in the future (in jiffies)
 316 * up or down to (approximately) full seconds. This is useful for timers
 317 * for which the exact time they fire does not matter too much, as long as
 318 * they fire approximately every X seconds.
 319 *
 320 * By rounding these timers to whole seconds, all such timers will fire
 321 * at the same time, rather than at various times spread out. The goal
 322 * of this is to have the CPU wake up less, which saves power.
 323 *
 324 * The exact rounding is skewed for each processor to avoid all
 325 * processors firing at the exact same time, which could lead
 326 * to lock contention or spurious cache line bouncing.
 327 *
 328 * The return value is the rounded version of the @j parameter.
 329 */
 330unsigned long __round_jiffies(unsigned long j, int cpu)
 331{
 332	return round_jiffies_common(j, cpu, false);
 333}
 334EXPORT_SYMBOL_GPL(__round_jiffies);
 335
 336/**
 337 * __round_jiffies_relative - function to round jiffies to a full second
 338 * @j: the time in (relative) jiffies that should be rounded
 339 * @cpu: the processor number on which the timeout will happen
 340 *
 341 * __round_jiffies_relative() rounds a time delta  in the future (in jiffies)
 342 * up or down to (approximately) full seconds. This is useful for timers
 343 * for which the exact time they fire does not matter too much, as long as
 344 * they fire approximately every X seconds.
 345 *
 346 * By rounding these timers to whole seconds, all such timers will fire
 347 * at the same time, rather than at various times spread out. The goal
 348 * of this is to have the CPU wake up less, which saves power.
 349 *
 350 * The exact rounding is skewed for each processor to avoid all
 351 * processors firing at the exact same time, which could lead
 352 * to lock contention or spurious cache line bouncing.
 353 *
 354 * The return value is the rounded version of the @j parameter.
 355 */
 356unsigned long __round_jiffies_relative(unsigned long j, int cpu)
 357{
 358	unsigned long j0 = jiffies;
 359
 360	/* Use j0 because jiffies might change while we run */
 361	return round_jiffies_common(j + j0, cpu, false) - j0;
 362}
 363EXPORT_SYMBOL_GPL(__round_jiffies_relative);
 364
 365/**
 366 * round_jiffies - function to round jiffies to a full second
 367 * @j: the time in (absolute) jiffies that should be rounded
 368 *
 369 * round_jiffies() rounds an absolute time in the future (in jiffies)
 370 * up or down to (approximately) full seconds. This is useful for timers
 371 * for which the exact time they fire does not matter too much, as long as
 372 * they fire approximately every X seconds.
 373 *
 374 * By rounding these timers to whole seconds, all such timers will fire
 375 * at the same time, rather than at various times spread out. The goal
 376 * of this is to have the CPU wake up less, which saves power.
 377 *
 378 * The return value is the rounded version of the @j parameter.
 379 */
 380unsigned long round_jiffies(unsigned long j)
 381{
 382	return round_jiffies_common(j, raw_smp_processor_id(), false);
 383}
 384EXPORT_SYMBOL_GPL(round_jiffies);
 385
 386/**
 387 * round_jiffies_relative - function to round jiffies to a full second
 388 * @j: the time in (relative) jiffies that should be rounded
 389 *
 390 * round_jiffies_relative() rounds a time delta  in the future (in jiffies)
 391 * up or down to (approximately) full seconds. This is useful for timers
 392 * for which the exact time they fire does not matter too much, as long as
 393 * they fire approximately every X seconds.
 394 *
 395 * By rounding these timers to whole seconds, all such timers will fire
 396 * at the same time, rather than at various times spread out. The goal
 397 * of this is to have the CPU wake up less, which saves power.
 398 *
 399 * The return value is the rounded version of the @j parameter.
 400 */
 401unsigned long round_jiffies_relative(unsigned long j)
 402{
 403	return __round_jiffies_relative(j, raw_smp_processor_id());
 404}
 405EXPORT_SYMBOL_GPL(round_jiffies_relative);
 406
 407/**
 408 * __round_jiffies_up - function to round jiffies up to a full second
 409 * @j: the time in (absolute) jiffies that should be rounded
 410 * @cpu: the processor number on which the timeout will happen
 411 *
 412 * This is the same as __round_jiffies() except that it will never
 413 * round down.  This is useful for timeouts for which the exact time
 414 * of firing does not matter too much, as long as they don't fire too
 415 * early.
 416 */
 417unsigned long __round_jiffies_up(unsigned long j, int cpu)
 418{
 419	return round_jiffies_common(j, cpu, true);
 420}
 421EXPORT_SYMBOL_GPL(__round_jiffies_up);
 422
 423/**
 424 * __round_jiffies_up_relative - function to round jiffies up to a full second
 425 * @j: the time in (relative) jiffies that should be rounded
 426 * @cpu: the processor number on which the timeout will happen
 427 *
 428 * This is the same as __round_jiffies_relative() except that it will never
 429 * round down.  This is useful for timeouts for which the exact time
 430 * of firing does not matter too much, as long as they don't fire too
 431 * early.
 432 */
 433unsigned long __round_jiffies_up_relative(unsigned long j, int cpu)
 434{
 435	unsigned long j0 = jiffies;
 436
 437	/* Use j0 because jiffies might change while we run */
 438	return round_jiffies_common(j + j0, cpu, true) - j0;
 439}
 440EXPORT_SYMBOL_GPL(__round_jiffies_up_relative);
 441
 442/**
 443 * round_jiffies_up - function to round jiffies up to a full second
 444 * @j: the time in (absolute) jiffies that should be rounded
 445 *
 446 * This is the same as round_jiffies() except that it will never
 447 * round down.  This is useful for timeouts for which the exact time
 448 * of firing does not matter too much, as long as they don't fire too
 449 * early.
 450 */
 451unsigned long round_jiffies_up(unsigned long j)
 452{
 453	return round_jiffies_common(j, raw_smp_processor_id(), true);
 454}
 455EXPORT_SYMBOL_GPL(round_jiffies_up);
 456
 457/**
 458 * round_jiffies_up_relative - function to round jiffies up to a full second
 459 * @j: the time in (relative) jiffies that should be rounded
 460 *
 461 * This is the same as round_jiffies_relative() except that it will never
 462 * round down.  This is useful for timeouts for which the exact time
 463 * of firing does not matter too much, as long as they don't fire too
 464 * early.
 465 */
 466unsigned long round_jiffies_up_relative(unsigned long j)
 467{
 468	return __round_jiffies_up_relative(j, raw_smp_processor_id());
 469}
 470EXPORT_SYMBOL_GPL(round_jiffies_up_relative);
 471
 472
 473static inline unsigned int timer_get_idx(struct timer_list *timer)
 474{
 475	return (timer->flags & TIMER_ARRAYMASK) >> TIMER_ARRAYSHIFT;
 476}
 477
 478static inline void timer_set_idx(struct timer_list *timer, unsigned int idx)
 479{
 480	timer->flags = (timer->flags & ~TIMER_ARRAYMASK) |
 481			idx << TIMER_ARRAYSHIFT;
 482}
 483
 484/*
 485 * Helper function to calculate the array index for a given expiry
 486 * time.
 487 */
 488static inline unsigned calc_index(unsigned expires, unsigned lvl)
 
 489{
 
 
 
 
 
 
 
 
 
 490	expires = (expires + LVL_GRAN(lvl)) >> LVL_SHIFT(lvl);
 
 491	return LVL_OFFS(lvl) + (expires & LVL_MASK);
 492}
 493
 494static int calc_wheel_index(unsigned long expires, unsigned long clk)
 
 495{
 496	unsigned long delta = expires - clk;
 497	unsigned int idx;
 498
 499	if (delta < LVL_START(1)) {
 500		idx = calc_index(expires, 0);
 501	} else if (delta < LVL_START(2)) {
 502		idx = calc_index(expires, 1);
 503	} else if (delta < LVL_START(3)) {
 504		idx = calc_index(expires, 2);
 505	} else if (delta < LVL_START(4)) {
 506		idx = calc_index(expires, 3);
 507	} else if (delta < LVL_START(5)) {
 508		idx = calc_index(expires, 4);
 509	} else if (delta < LVL_START(6)) {
 510		idx = calc_index(expires, 5);
 511	} else if (delta < LVL_START(7)) {
 512		idx = calc_index(expires, 6);
 513	} else if (LVL_DEPTH > 8 && delta < LVL_START(8)) {
 514		idx = calc_index(expires, 7);
 515	} else if ((long) delta < 0) {
 516		idx = clk & LVL_MASK;
 
 517	} else {
 518		/*
 519		 * Force expire obscene large timeouts to expire at the
 520		 * capacity limit of the wheel.
 521		 */
 522		if (expires >= WHEEL_TIMEOUT_CUTOFF)
 523			expires = WHEEL_TIMEOUT_MAX;
 524
 525		idx = calc_index(expires, LVL_DEPTH - 1);
 526	}
 527	return idx;
 528}
 529
 530/*
 531 * Enqueue the timer into the hash bucket, mark it pending in
 532 * the bitmap and store the index in the timer flags.
 533 */
 534static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
 535			  unsigned int idx)
 536{
 537	hlist_add_head(&timer->entry, base->vectors + idx);
 538	__set_bit(idx, base->pending_map);
 539	timer_set_idx(timer, idx);
 540}
 541
 542static void
 543__internal_add_timer(struct timer_base *base, struct timer_list *timer)
 544{
 545	unsigned int idx;
 546
 547	idx = calc_wheel_index(timer->expires, base->clk);
 548	enqueue_timer(base, timer, idx);
 549}
 550
 551static void
 552trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
 553{
 554	if (!is_timers_nohz_active())
 555		return;
 556
 557	/*
 558	 * TODO: This wants some optimizing similar to the code below, but we
 559	 * will do that when we switch from push to pull for deferrable timers.
 560	 */
 561	if (timer->flags & TIMER_DEFERRABLE) {
 562		if (tick_nohz_full_cpu(base->cpu))
 563			wake_up_nohz_cpu(base->cpu);
 564		return;
 565	}
 566
 567	/*
 568	 * We might have to IPI the remote CPU if the base is idle and the
 569	 * timer is not deferrable. If the other CPU is on the way to idle
 570	 * then it can't set base->is_idle as we hold the base lock:
 571	 */
 572	if (!base->is_idle)
 573		return;
 
 574
 575	/* Check whether this is the new first expiring timer: */
 576	if (time_after_eq(timer->expires, base->next_expiry))
 577		return;
 
 
 
 
 
 
 
 
 
 
 
 578
 579	/*
 580	 * Set the next expiry time and kick the CPU so it can reevaluate the
 581	 * wheel:
 
 582	 */
 583	base->next_expiry = timer->expires;
 584		wake_up_nohz_cpu(base->cpu);
 
 
 
 
 
 
 
 585}
 586
 587static void
 588internal_add_timer(struct timer_base *base, struct timer_list *timer)
 589{
 590	__internal_add_timer(base, timer);
 591	trigger_dyntick_cpu(base, timer);
 
 
 
 592}
 593
 594#ifdef CONFIG_DEBUG_OBJECTS_TIMERS
 595
 596static struct debug_obj_descr timer_debug_descr;
 597
 598static void *timer_debug_hint(void *addr)
 599{
 600	return ((struct timer_list *) addr)->function;
 601}
 602
 603static bool timer_is_static_object(void *addr)
 604{
 605	struct timer_list *timer = addr;
 606
 607	return (timer->entry.pprev == NULL &&
 608		timer->entry.next == TIMER_ENTRY_STATIC);
 609}
 610
 611/*
 612 * fixup_init is called when:
 613 * - an active object is initialized
 614 */
 615static bool timer_fixup_init(void *addr, enum debug_obj_state state)
 616{
 617	struct timer_list *timer = addr;
 618
 619	switch (state) {
 620	case ODEBUG_STATE_ACTIVE:
 621		del_timer_sync(timer);
 622		debug_object_init(timer, &timer_debug_descr);
 623		return true;
 624	default:
 625		return false;
 626	}
 627}
 628
 629/* Stub timer callback for improperly used timers. */
 630static void stub_timer(struct timer_list *unused)
 631{
 632	WARN_ON(1);
 633}
 634
 635/*
 636 * fixup_activate is called when:
 637 * - an active object is activated
 638 * - an unknown non-static object is activated
 639 */
 640static bool timer_fixup_activate(void *addr, enum debug_obj_state state)
 641{
 642	struct timer_list *timer = addr;
 643
 644	switch (state) {
 645	case ODEBUG_STATE_NOTAVAILABLE:
 646		timer_setup(timer, stub_timer, 0);
 647		return true;
 648
 649	case ODEBUG_STATE_ACTIVE:
 650		WARN_ON(1);
 651
 652	default:
 653		return false;
 654	}
 655}
 656
 657/*
 658 * fixup_free is called when:
 659 * - an active object is freed
 660 */
 661static bool timer_fixup_free(void *addr, enum debug_obj_state state)
 662{
 663	struct timer_list *timer = addr;
 664
 665	switch (state) {
 666	case ODEBUG_STATE_ACTIVE:
 667		del_timer_sync(timer);
 668		debug_object_free(timer, &timer_debug_descr);
 669		return true;
 670	default:
 671		return false;
 672	}
 673}
 674
 675/*
 676 * fixup_assert_init is called when:
 677 * - an untracked/uninit-ed object is found
 678 */
 679static bool timer_fixup_assert_init(void *addr, enum debug_obj_state state)
 680{
 681	struct timer_list *timer = addr;
 682
 683	switch (state) {
 684	case ODEBUG_STATE_NOTAVAILABLE:
 685		timer_setup(timer, stub_timer, 0);
 686		return true;
 687	default:
 688		return false;
 689	}
 690}
 691
 692static struct debug_obj_descr timer_debug_descr = {
 693	.name			= "timer_list",
 694	.debug_hint		= timer_debug_hint,
 695	.is_static_object	= timer_is_static_object,
 696	.fixup_init		= timer_fixup_init,
 697	.fixup_activate		= timer_fixup_activate,
 698	.fixup_free		= timer_fixup_free,
 699	.fixup_assert_init	= timer_fixup_assert_init,
 700};
 701
 702static inline void debug_timer_init(struct timer_list *timer)
 703{
 704	debug_object_init(timer, &timer_debug_descr);
 705}
 706
 707static inline void debug_timer_activate(struct timer_list *timer)
 708{
 709	debug_object_activate(timer, &timer_debug_descr);
 710}
 711
 712static inline void debug_timer_deactivate(struct timer_list *timer)
 713{
 714	debug_object_deactivate(timer, &timer_debug_descr);
 715}
 716
 717static inline void debug_timer_free(struct timer_list *timer)
 718{
 719	debug_object_free(timer, &timer_debug_descr);
 720}
 721
 722static inline void debug_timer_assert_init(struct timer_list *timer)
 723{
 724	debug_object_assert_init(timer, &timer_debug_descr);
 725}
 726
 727static void do_init_timer(struct timer_list *timer,
 728			  void (*func)(struct timer_list *),
 729			  unsigned int flags,
 730			  const char *name, struct lock_class_key *key);
 731
 732void init_timer_on_stack_key(struct timer_list *timer,
 733			     void (*func)(struct timer_list *),
 734			     unsigned int flags,
 735			     const char *name, struct lock_class_key *key)
 736{
 737	debug_object_init_on_stack(timer, &timer_debug_descr);
 738	do_init_timer(timer, func, flags, name, key);
 739}
 740EXPORT_SYMBOL_GPL(init_timer_on_stack_key);
 741
 742void destroy_timer_on_stack(struct timer_list *timer)
 743{
 744	debug_object_free(timer, &timer_debug_descr);
 745}
 746EXPORT_SYMBOL_GPL(destroy_timer_on_stack);
 747
 748#else
 749static inline void debug_timer_init(struct timer_list *timer) { }
 750static inline void debug_timer_activate(struct timer_list *timer) { }
 751static inline void debug_timer_deactivate(struct timer_list *timer) { }
 752static inline void debug_timer_assert_init(struct timer_list *timer) { }
 753#endif
 754
 755static inline void debug_init(struct timer_list *timer)
 756{
 757	debug_timer_init(timer);
 758	trace_timer_init(timer);
 759}
 760
 761static inline void
 762debug_activate(struct timer_list *timer, unsigned long expires)
 763{
 764	debug_timer_activate(timer);
 765	trace_timer_start(timer, expires, timer->flags);
 766}
 767
 768static inline void debug_deactivate(struct timer_list *timer)
 769{
 770	debug_timer_deactivate(timer);
 771	trace_timer_cancel(timer);
 772}
 773
 774static inline void debug_assert_init(struct timer_list *timer)
 775{
 776	debug_timer_assert_init(timer);
 777}
 778
 779static void do_init_timer(struct timer_list *timer,
 780			  void (*func)(struct timer_list *),
 781			  unsigned int flags,
 782			  const char *name, struct lock_class_key *key)
 783{
 784	timer->entry.pprev = NULL;
 785	timer->function = func;
 786	timer->flags = flags | raw_smp_processor_id();
 787	lockdep_init_map(&timer->lockdep_map, name, key, 0);
 788}
 789
 790/**
 791 * init_timer_key - initialize a timer
 792 * @timer: the timer to be initialized
 793 * @func: timer callback function
 794 * @flags: timer flags
 795 * @name: name of the timer
 796 * @key: lockdep class key of the fake lock used for tracking timer
 797 *       sync lock dependencies
 798 *
 799 * init_timer_key() must be done to a timer prior calling *any* of the
 800 * other timer functions.
 801 */
 802void init_timer_key(struct timer_list *timer,
 803		    void (*func)(struct timer_list *), unsigned int flags,
 804		    const char *name, struct lock_class_key *key)
 805{
 806	debug_init(timer);
 807	do_init_timer(timer, func, flags, name, key);
 808}
 809EXPORT_SYMBOL(init_timer_key);
 810
 811static inline void detach_timer(struct timer_list *timer, bool clear_pending)
 812{
 813	struct hlist_node *entry = &timer->entry;
 814
 815	debug_deactivate(timer);
 816
 817	__hlist_del(entry);
 818	if (clear_pending)
 819		entry->pprev = NULL;
 820	entry->next = LIST_POISON2;
 821}
 822
 823static int detach_if_pending(struct timer_list *timer, struct timer_base *base,
 824			     bool clear_pending)
 825{
 826	unsigned idx = timer_get_idx(timer);
 827
 828	if (!timer_pending(timer))
 829		return 0;
 830
 831	if (hlist_is_singular_node(&timer->entry, base->vectors + idx))
 832		__clear_bit(idx, base->pending_map);
 
 
 833
 834	detach_timer(timer, clear_pending);
 835	return 1;
 836}
 837
 838static inline struct timer_base *get_timer_cpu_base(u32 tflags, u32 cpu)
 839{
 840	struct timer_base *base = per_cpu_ptr(&timer_bases[BASE_STD], cpu);
 841
 842	/*
 843	 * If the timer is deferrable and NO_HZ_COMMON is set then we need
 844	 * to use the deferrable base.
 845	 */
 846	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (tflags & TIMER_DEFERRABLE))
 847		base = per_cpu_ptr(&timer_bases[BASE_DEF], cpu);
 848	return base;
 849}
 850
 851static inline struct timer_base *get_timer_this_cpu_base(u32 tflags)
 852{
 853	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
 854
 855	/*
 856	 * If the timer is deferrable and NO_HZ_COMMON is set then we need
 857	 * to use the deferrable base.
 858	 */
 859	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (tflags & TIMER_DEFERRABLE))
 860		base = this_cpu_ptr(&timer_bases[BASE_DEF]);
 861	return base;
 862}
 863
 864static inline struct timer_base *get_timer_base(u32 tflags)
 865{
 866	return get_timer_cpu_base(tflags, tflags & TIMER_CPUMASK);
 867}
 868
 869static inline struct timer_base *
 870get_target_base(struct timer_base *base, unsigned tflags)
 871{
 872#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
 873	if (static_branch_likely(&timers_migration_enabled) &&
 874	    !(tflags & TIMER_PINNED))
 875		return get_timer_cpu_base(tflags, get_nohz_timer_target());
 876#endif
 877	return get_timer_this_cpu_base(tflags);
 878}
 879
 880static inline void forward_timer_base(struct timer_base *base)
 881{
 882#ifdef CONFIG_NO_HZ_COMMON
 883	unsigned long jnow;
 884
 885	/*
 886	 * We only forward the base when we are idle or have just come out of
 887	 * idle (must_forward_clk logic), and have a delta between base clock
 888	 * and jiffies. In the common case, run_timers will take care of it.
 889	 */
 890	if (likely(!base->must_forward_clk))
 891		return;
 892
 893	jnow = READ_ONCE(jiffies);
 894	base->must_forward_clk = base->is_idle;
 895	if ((long)(jnow - base->clk) < 2)
 896		return;
 897
 898	/*
 899	 * If the next expiry value is > jiffies, then we fast forward to
 900	 * jiffies otherwise we forward to the next expiry value.
 901	 */
 902	if (time_after(base->next_expiry, jnow))
 903		base->clk = jnow;
 904	else
 
 
 905		base->clk = base->next_expiry;
 906#endif
 907}
 908
 909
 910/*
 911 * We are using hashed locking: Holding per_cpu(timer_bases[x]).lock means
 912 * that all timers which are tied to this base are locked, and the base itself
 913 * is locked too.
 914 *
 915 * So __run_timers/migrate_timers can safely modify all timers which could
 916 * be found in the base->vectors array.
 917 *
 918 * When a timer is migrating then the TIMER_MIGRATING flag is set and we need
 919 * to wait until the migration is done.
 920 */
 921static struct timer_base *lock_timer_base(struct timer_list *timer,
 922					  unsigned long *flags)
 923	__acquires(timer->base->lock)
 924{
 925	for (;;) {
 926		struct timer_base *base;
 927		u32 tf;
 928
 929		/*
 930		 * We need to use READ_ONCE() here, otherwise the compiler
 931		 * might re-read @tf between the check for TIMER_MIGRATING
 932		 * and spin_lock().
 933		 */
 934		tf = READ_ONCE(timer->flags);
 935
 936		if (!(tf & TIMER_MIGRATING)) {
 937			base = get_timer_base(tf);
 938			raw_spin_lock_irqsave(&base->lock, *flags);
 939			if (timer->flags == tf)
 940				return base;
 941			raw_spin_unlock_irqrestore(&base->lock, *flags);
 942		}
 943		cpu_relax();
 944	}
 945}
 946
 947#define MOD_TIMER_PENDING_ONLY		0x01
 948#define MOD_TIMER_REDUCE		0x02
 
 949
 950static inline int
 951__mod_timer(struct timer_list *timer, unsigned long expires, unsigned int options)
 952{
 
 953	struct timer_base *base, *new_base;
 954	unsigned int idx = UINT_MAX;
 955	unsigned long clk = 0, flags;
 956	int ret = 0;
 957
 958	BUG_ON(!timer->function);
 959
 960	/*
 961	 * This is a common optimization triggered by the networking code - if
 962	 * the timer is re-modified to have the same timeout or ends up in the
 963	 * same array bucket then just return:
 964	 */
 965	if (timer_pending(timer)) {
 966		/*
 967		 * The downside of this optimization is that it can result in
 968		 * larger granularity than you would get from adding a new
 969		 * timer with this expiry.
 970		 */
 971		long diff = timer->expires - expires;
 972
 973		if (!diff)
 974			return 1;
 975		if (options & MOD_TIMER_REDUCE && diff <= 0)
 976			return 1;
 977
 978		/*
 979		 * We lock timer base and calculate the bucket index right
 980		 * here. If the timer ends up in the same bucket, then we
 981		 * just update the expiry time and avoid the whole
 982		 * dequeue/enqueue dance.
 983		 */
 984		base = lock_timer_base(timer, &flags);
 985		forward_timer_base(base);
 986
 987		if (timer_pending(timer) && (options & MOD_TIMER_REDUCE) &&
 988		    time_before_eq(timer->expires, expires)) {
 989			ret = 1;
 990			goto out_unlock;
 991		}
 992
 993		clk = base->clk;
 994		idx = calc_wheel_index(expires, clk);
 995
 996		/*
 997		 * Retrieve and compare the array index of the pending
 998		 * timer. If it matches set the expiry to the new value so a
 999		 * subsequent call will exit in the expires check above.
1000		 */
1001		if (idx == timer_get_idx(timer)) {
1002			if (!(options & MOD_TIMER_REDUCE))
1003				timer->expires = expires;
1004			else if (time_after(timer->expires, expires))
1005				timer->expires = expires;
1006			ret = 1;
1007			goto out_unlock;
1008		}
1009	} else {
1010		base = lock_timer_base(timer, &flags);
1011		forward_timer_base(base);
1012	}
1013
1014	ret = detach_if_pending(timer, base, false);
1015	if (!ret && (options & MOD_TIMER_PENDING_ONLY))
1016		goto out_unlock;
1017
1018	new_base = get_target_base(base, timer->flags);
1019
1020	if (base != new_base) {
1021		/*
1022		 * We are trying to schedule the timer on the new base.
1023		 * However we can't change timer's base while it is running,
1024		 * otherwise del_timer_sync() can't detect that the timer's
1025		 * handler yet has not finished. This also guarantees that the
1026		 * timer is serialized wrt itself.
1027		 */
1028		if (likely(base->running_timer != timer)) {
1029			/* See the comment in lock_timer_base() */
1030			timer->flags |= TIMER_MIGRATING;
1031
1032			raw_spin_unlock(&base->lock);
1033			base = new_base;
1034			raw_spin_lock(&base->lock);
1035			WRITE_ONCE(timer->flags,
1036				   (timer->flags & ~TIMER_BASEMASK) | base->cpu);
1037			forward_timer_base(base);
1038		}
1039	}
1040
1041	debug_activate(timer, expires);
1042
1043	timer->expires = expires;
1044	/*
1045	 * If 'idx' was calculated above and the base time did not advance
1046	 * between calculating 'idx' and possibly switching the base, only
1047	 * enqueue_timer() and trigger_dyntick_cpu() is required. Otherwise
1048	 * we need to (re)calculate the wheel index via
1049	 * internal_add_timer().
1050	 */
1051	if (idx != UINT_MAX && clk == base->clk) {
1052		enqueue_timer(base, timer, idx);
1053		trigger_dyntick_cpu(base, timer);
1054	} else {
1055		internal_add_timer(base, timer);
1056	}
1057
1058out_unlock:
1059	raw_spin_unlock_irqrestore(&base->lock, flags);
1060
1061	return ret;
1062}
1063
1064/**
1065 * mod_timer_pending - modify a pending timer's timeout
1066 * @timer: the pending timer to be modified
1067 * @expires: new timeout in jiffies
1068 *
1069 * mod_timer_pending() is the same for pending timers as mod_timer(),
1070 * but will not re-activate and modify already deleted timers.
1071 *
1072 * It is useful for unserialized use of timers.
1073 */
1074int mod_timer_pending(struct timer_list *timer, unsigned long expires)
1075{
1076	return __mod_timer(timer, expires, MOD_TIMER_PENDING_ONLY);
1077}
1078EXPORT_SYMBOL(mod_timer_pending);
1079
1080/**
1081 * mod_timer - modify a timer's timeout
1082 * @timer: the timer to be modified
1083 * @expires: new timeout in jiffies
1084 *
1085 * mod_timer() is a more efficient way to update the expire field of an
1086 * active timer (if the timer is inactive it will be activated)
1087 *
1088 * mod_timer(timer, expires) is equivalent to:
1089 *
1090 *     del_timer(timer); timer->expires = expires; add_timer(timer);
1091 *
1092 * Note that if there are multiple unserialized concurrent users of the
1093 * same timer, then mod_timer() is the only safe way to modify the timeout,
1094 * since add_timer() cannot modify an already running timer.
1095 *
1096 * The function returns whether it has modified a pending timer or not.
1097 * (ie. mod_timer() of an inactive timer returns 0, mod_timer() of an
1098 * active timer returns 1.)
1099 */
1100int mod_timer(struct timer_list *timer, unsigned long expires)
1101{
1102	return __mod_timer(timer, expires, 0);
1103}
1104EXPORT_SYMBOL(mod_timer);
1105
1106/**
1107 * timer_reduce - Modify a timer's timeout if it would reduce the timeout
1108 * @timer:	The timer to be modified
1109 * @expires:	New timeout in jiffies
1110 *
1111 * timer_reduce() is very similar to mod_timer(), except that it will only
1112 * modify a running timer if that would reduce the expiration time (it will
1113 * start a timer that isn't running).
1114 */
1115int timer_reduce(struct timer_list *timer, unsigned long expires)
1116{
1117	return __mod_timer(timer, expires, MOD_TIMER_REDUCE);
1118}
1119EXPORT_SYMBOL(timer_reduce);
1120
1121/**
1122 * add_timer - start a timer
1123 * @timer: the timer to be added
1124 *
1125 * The kernel will do a ->function(@timer) callback from the
1126 * timer interrupt at the ->expires point in the future. The
1127 * current time is 'jiffies'.
1128 *
1129 * The timer's ->expires, ->function fields must be set prior calling this
1130 * function.
1131 *
1132 * Timers with an ->expires field in the past will be executed in the next
1133 * timer tick.
1134 */
1135void add_timer(struct timer_list *timer)
1136{
1137	BUG_ON(timer_pending(timer));
1138	mod_timer(timer, timer->expires);
1139}
1140EXPORT_SYMBOL(add_timer);
1141
1142/**
1143 * add_timer_on - start a timer on a particular CPU
1144 * @timer: the timer to be added
1145 * @cpu: the CPU to start it on
1146 *
1147 * This is not very scalable on SMP. Double adds are not possible.
1148 */
1149void add_timer_on(struct timer_list *timer, int cpu)
1150{
1151	struct timer_base *new_base, *base;
1152	unsigned long flags;
1153
1154	BUG_ON(timer_pending(timer) || !timer->function);
1155
1156	new_base = get_timer_cpu_base(timer->flags, cpu);
1157
1158	/*
1159	 * If @timer was on a different CPU, it should be migrated with the
1160	 * old base locked to prevent other operations proceeding with the
1161	 * wrong base locked.  See lock_timer_base().
1162	 */
1163	base = lock_timer_base(timer, &flags);
1164	if (base != new_base) {
1165		timer->flags |= TIMER_MIGRATING;
1166
1167		raw_spin_unlock(&base->lock);
1168		base = new_base;
1169		raw_spin_lock(&base->lock);
1170		WRITE_ONCE(timer->flags,
1171			   (timer->flags & ~TIMER_BASEMASK) | cpu);
1172	}
1173	forward_timer_base(base);
1174
1175	debug_activate(timer, timer->expires);
1176	internal_add_timer(base, timer);
1177	raw_spin_unlock_irqrestore(&base->lock, flags);
1178}
1179EXPORT_SYMBOL_GPL(add_timer_on);
1180
1181/**
1182 * del_timer - deactivate a timer.
1183 * @timer: the timer to be deactivated
1184 *
1185 * del_timer() deactivates a timer - this works on both active and inactive
1186 * timers.
1187 *
1188 * The function returns whether it has deactivated a pending timer or not.
1189 * (ie. del_timer() of an inactive timer returns 0, del_timer() of an
1190 * active timer returns 1.)
1191 */
1192int del_timer(struct timer_list *timer)
1193{
1194	struct timer_base *base;
1195	unsigned long flags;
1196	int ret = 0;
1197
1198	debug_assert_init(timer);
1199
1200	if (timer_pending(timer)) {
1201		base = lock_timer_base(timer, &flags);
1202		ret = detach_if_pending(timer, base, true);
1203		raw_spin_unlock_irqrestore(&base->lock, flags);
1204	}
1205
1206	return ret;
1207}
1208EXPORT_SYMBOL(del_timer);
1209
1210/**
1211 * try_to_del_timer_sync - Try to deactivate a timer
1212 * @timer: timer to delete
1213 *
1214 * This function tries to deactivate a timer. Upon successful (ret >= 0)
1215 * exit the timer is not queued and the handler is not running on any CPU.
1216 */
1217int try_to_del_timer_sync(struct timer_list *timer)
1218{
1219	struct timer_base *base;
1220	unsigned long flags;
1221	int ret = -1;
1222
1223	debug_assert_init(timer);
1224
1225	base = lock_timer_base(timer, &flags);
1226
1227	if (base->running_timer != timer)
1228		ret = detach_if_pending(timer, base, true);
1229
1230	raw_spin_unlock_irqrestore(&base->lock, flags);
1231
1232	return ret;
1233}
1234EXPORT_SYMBOL(try_to_del_timer_sync);
1235
1236#ifdef CONFIG_SMP
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1237/**
1238 * del_timer_sync - deactivate a timer and wait for the handler to finish.
1239 * @timer: the timer to be deactivated
1240 *
1241 * This function only differs from del_timer() on SMP: besides deactivating
1242 * the timer it also makes sure the handler has finished executing on other
1243 * CPUs.
1244 *
1245 * Synchronization rules: Callers must prevent restarting of the timer,
1246 * otherwise this function is meaningless. It must not be called from
1247 * interrupt contexts unless the timer is an irqsafe one. The caller must
1248 * not hold locks which would prevent completion of the timer's
1249 * handler. The timer's handler must not call add_timer_on(). Upon exit the
1250 * timer is not queued and the handler is not running on any CPU.
1251 *
1252 * Note: For !irqsafe timers, you must not hold locks that are held in
1253 *   interrupt context while calling this function. Even if the lock has
1254 *   nothing to do with the timer in question.  Here's why:
1255 *
1256 *    CPU0                             CPU1
1257 *    ----                             ----
1258 *                                   <SOFTIRQ>
1259 *                                   call_timer_fn();
1260 *                                     base->running_timer = mytimer;
1261 *  spin_lock_irq(somelock);
1262 *                                     <IRQ>
1263 *                                        spin_lock(somelock);
1264 *  del_timer_sync(mytimer);
1265 *   while (base->running_timer == mytimer);
1266 *
1267 * Now del_timer_sync() will never return and never release somelock.
1268 * The interrupt on the other CPU is waiting to grab somelock but
1269 * it has interrupted the softirq that CPU0 is waiting to finish.
1270 *
1271 * The function returns whether it has deactivated a pending timer or not.
1272 */
1273int del_timer_sync(struct timer_list *timer)
1274{
 
 
1275#ifdef CONFIG_LOCKDEP
1276	unsigned long flags;
1277
1278	/*
1279	 * If lockdep gives a backtrace here, please reference
1280	 * the synchronization rules above.
1281	 */
1282	local_irq_save(flags);
1283	lock_map_acquire(&timer->lockdep_map);
1284	lock_map_release(&timer->lockdep_map);
1285	local_irq_restore(flags);
1286#endif
1287	/*
1288	 * don't use it in hardirq context, because it
1289	 * could lead to deadlock.
1290	 */
1291	WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE));
1292	for (;;) {
1293		int ret = try_to_del_timer_sync(timer);
1294		if (ret >= 0)
1295			return ret;
1296		cpu_relax();
1297	}
 
 
 
 
 
1298}
1299EXPORT_SYMBOL(del_timer_sync);
1300#endif
1301
1302static void call_timer_fn(struct timer_list *timer, void (*fn)(struct timer_list *))
 
 
1303{
1304	int count = preempt_count();
1305
1306#ifdef CONFIG_LOCKDEP
1307	/*
1308	 * It is permissible to free the timer from inside the
1309	 * function that is called from it, this we need to take into
1310	 * account for lockdep too. To avoid bogus "held lock freed"
1311	 * warnings as well as problems when looking into
1312	 * timer->lockdep_map, make a copy and use that here.
1313	 */
1314	struct lockdep_map lockdep_map;
1315
1316	lockdep_copy_map(&lockdep_map, &timer->lockdep_map);
1317#endif
1318	/*
1319	 * Couple the lock chain with the lock chain at
1320	 * del_timer_sync() by acquiring the lock_map around the fn()
1321	 * call here and in del_timer_sync().
1322	 */
1323	lock_map_acquire(&lockdep_map);
1324
1325	trace_timer_expire_entry(timer);
1326	fn(timer);
1327	trace_timer_expire_exit(timer);
1328
1329	lock_map_release(&lockdep_map);
1330
1331	if (count != preempt_count()) {
1332		WARN_ONCE(1, "timer: %pF preempt leak: %08x -> %08x\n",
1333			  fn, count, preempt_count());
1334		/*
1335		 * Restore the preempt count. That gives us a decent
1336		 * chance to survive and extract information. If the
1337		 * callback kept a lock held, bad luck, but not worse
1338		 * than the BUG() we had.
1339		 */
1340		preempt_count_set(count);
1341	}
1342}
1343
1344static void expire_timers(struct timer_base *base, struct hlist_head *head)
1345{
 
 
 
 
 
 
 
1346	while (!hlist_empty(head)) {
1347		struct timer_list *timer;
1348		void (*fn)(struct timer_list *);
1349
1350		timer = hlist_entry(head->first, struct timer_list, entry);
1351
1352		base->running_timer = timer;
1353		detach_timer(timer, true);
1354
1355		fn = timer->function;
1356
1357		if (timer->flags & TIMER_IRQSAFE) {
1358			raw_spin_unlock(&base->lock);
1359			call_timer_fn(timer, fn);
 
1360			raw_spin_lock(&base->lock);
1361		} else {
1362			raw_spin_unlock_irq(&base->lock);
1363			call_timer_fn(timer, fn);
 
 
1364			raw_spin_lock_irq(&base->lock);
1365		}
1366	}
1367}
1368
1369static int __collect_expired_timers(struct timer_base *base,
1370				    struct hlist_head *heads)
1371{
1372	unsigned long clk = base->clk;
1373	struct hlist_head *vec;
1374	int i, levels = 0;
1375	unsigned int idx;
1376
1377	for (i = 0; i < LVL_DEPTH; i++) {
1378		idx = (clk & LVL_MASK) + i * LVL_SIZE;
1379
1380		if (__test_and_clear_bit(idx, base->pending_map)) {
1381			vec = base->vectors + idx;
1382			hlist_move_list(vec, heads++);
1383			levels++;
1384		}
1385		/* Is it time to look at the next level? */
1386		if (clk & LVL_CLK_MASK)
1387			break;
1388		/* Shift clock for the next level granularity */
1389		clk >>= LVL_CLK_SHIFT;
1390	}
1391	return levels;
1392}
1393
1394#ifdef CONFIG_NO_HZ_COMMON
1395/*
1396 * Find the next pending bucket of a level. Search from level start (@offset)
1397 * + @clk upwards and if nothing there, search from start of the level
1398 * (@offset) up to @offset + clk.
1399 */
1400static int next_pending_bucket(struct timer_base *base, unsigned offset,
1401			       unsigned clk)
1402{
1403	unsigned pos, start = offset + clk;
1404	unsigned end = offset + LVL_SIZE;
1405
1406	pos = find_next_bit(base->pending_map, end, start);
1407	if (pos < end)
1408		return pos - start;
1409
1410	pos = find_next_bit(base->pending_map, start, offset);
1411	return pos < start ? pos + LVL_SIZE - start : -1;
1412}
1413
1414/*
1415 * Search the first expiring timer in the various clock levels. Caller must
1416 * hold base->lock.
1417 */
1418static unsigned long __next_timer_interrupt(struct timer_base *base)
1419{
1420	unsigned long clk, next, adj;
1421	unsigned lvl, offset = 0;
1422
1423	next = base->clk + NEXT_TIMER_MAX_DELTA;
1424	clk = base->clk;
1425	for (lvl = 0; lvl < LVL_DEPTH; lvl++, offset += LVL_SIZE) {
1426		int pos = next_pending_bucket(base, offset, clk & LVL_MASK);
 
1427
1428		if (pos >= 0) {
1429			unsigned long tmp = clk + (unsigned long) pos;
1430
1431			tmp <<= LVL_SHIFT(lvl);
1432			if (time_before(tmp, next))
1433				next = tmp;
 
 
 
 
 
 
 
1434		}
1435		/*
1436		 * Clock for the next level. If the current level clock lower
1437		 * bits are zero, we look at the next level as is. If not we
1438		 * need to advance it by one because that's going to be the
1439		 * next expiring bucket in that level. base->clk is the next
1440		 * expiring jiffie. So in case of:
1441		 *
1442		 * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0
1443		 *  0    0    0    0    0    0
1444		 *
1445		 * we have to look at all levels @index 0. With
1446		 *
1447		 * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0
1448		 *  0    0    0    0    0    2
1449		 *
1450		 * LVL0 has the next expiring bucket @index 2. The upper
1451		 * levels have the next expiring bucket @index 1.
1452		 *
1453		 * In case that the propagation wraps the next level the same
1454		 * rules apply:
1455		 *
1456		 * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0
1457		 *  0    0    0    0    F    2
1458		 *
1459		 * So after looking at LVL0 we get:
1460		 *
1461		 * LVL5 LVL4 LVL3 LVL2 LVL1
1462		 *  0    0    0    1    0
1463		 *
1464		 * So no propagation from LVL1 to LVL2 because that happened
1465		 * with the add already, but then we need to propagate further
1466		 * from LVL2 to LVL3.
1467		 *
1468		 * So the simple check whether the lower bits of the current
1469		 * level are 0 or not is sufficient for all cases.
1470		 */
1471		adj = clk & LVL_CLK_MASK ? 1 : 0;
1472		clk >>= LVL_CLK_SHIFT;
1473		clk += adj;
1474	}
 
 
 
1475	return next;
1476}
1477
 
1478/*
1479 * Check, if the next hrtimer event is before the next timer wheel
1480 * event:
1481 */
1482static u64 cmp_next_hrtimer_event(u64 basem, u64 expires)
1483{
1484	u64 nextevt = hrtimer_get_next_event();
1485
1486	/*
1487	 * If high resolution timers are enabled
1488	 * hrtimer_get_next_event() returns KTIME_MAX.
1489	 */
1490	if (expires <= nextevt)
1491		return expires;
1492
1493	/*
1494	 * If the next timer is already expired, return the tick base
1495	 * time so the tick is fired immediately.
1496	 */
1497	if (nextevt <= basem)
1498		return basem;
1499
1500	/*
1501	 * Round up to the next jiffie. High resolution timers are
1502	 * off, so the hrtimers are expired in the tick and we need to
1503	 * make sure that this tick really expires the timer to avoid
1504	 * a ping pong of the nohz stop code.
1505	 *
1506	 * Use DIV_ROUND_UP_ULL to prevent gcc calling __divdi3
1507	 */
1508	return DIV_ROUND_UP_ULL(nextevt, TICK_NSEC) * TICK_NSEC;
1509}
1510
1511/**
1512 * get_next_timer_interrupt - return the time (clock mono) of the next timer
1513 * @basej:	base time jiffies
1514 * @basem:	base time clock monotonic
1515 *
1516 * Returns the tick aligned clock monotonic time of the next pending
1517 * timer or KTIME_MAX if no timer is pending.
1518 */
1519u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
1520{
1521	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
1522	u64 expires = KTIME_MAX;
1523	unsigned long nextevt;
1524	bool is_max_delta;
1525
1526	/*
1527	 * Pretend that there is no timer pending if the cpu is offline.
1528	 * Possible pending timers will be migrated later to an active cpu.
1529	 */
1530	if (cpu_is_offline(smp_processor_id()))
1531		return expires;
1532
1533	raw_spin_lock(&base->lock);
1534	nextevt = __next_timer_interrupt(base);
 
 
1535	is_max_delta = (nextevt == base->clk + NEXT_TIMER_MAX_DELTA);
1536	base->next_expiry = nextevt;
1537	/*
1538	 * We have a fresh next event. Check whether we can forward the
1539	 * base. We can only do that when @basej is past base->clk
1540	 * otherwise we might rewind base->clk.
1541	 */
1542	if (time_after(basej, base->clk)) {
1543		if (time_after(nextevt, basej))
1544			base->clk = basej;
1545		else if (time_after(nextevt, base->clk))
1546			base->clk = nextevt;
1547	}
1548
1549	if (time_before_eq(nextevt, basej)) {
1550		expires = basem;
1551		base->is_idle = false;
1552	} else {
1553		if (!is_max_delta)
1554			expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
1555		/*
1556		 * If we expect to sleep more than a tick, mark the base idle.
1557		 * Also the tick is stopped so any added timer must forward
1558		 * the base clk itself to keep granularity small. This idle
1559		 * logic is only maintained for the BASE_STD base, deferrable
1560		 * timers may still see large granularity skew (by design).
1561		 */
1562		if ((expires - basem) > TICK_NSEC) {
1563			base->must_forward_clk = true;
1564			base->is_idle = true;
1565		}
1566	}
1567	raw_spin_unlock(&base->lock);
1568
1569	return cmp_next_hrtimer_event(basem, expires);
1570}
1571
1572/**
1573 * timer_clear_idle - Clear the idle state of the timer base
1574 *
1575 * Called with interrupts disabled
1576 */
1577void timer_clear_idle(void)
1578{
1579	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
1580
1581	/*
1582	 * We do this unlocked. The worst outcome is a remote enqueue sending
1583	 * a pointless IPI, but taking the lock would just make the window for
1584	 * sending the IPI a few instructions smaller for the cost of taking
1585	 * the lock in the exit from idle path.
1586	 */
1587	base->is_idle = false;
1588}
1589
1590static int collect_expired_timers(struct timer_base *base,
1591				  struct hlist_head *heads)
1592{
1593	/*
1594	 * NOHZ optimization. After a long idle sleep we need to forward the
1595	 * base to current jiffies. Avoid a loop by searching the bitfield for
1596	 * the next expiring timer.
1597	 */
1598	if ((long)(jiffies - base->clk) > 2) {
1599		unsigned long next = __next_timer_interrupt(base);
1600
1601		/*
1602		 * If the next timer is ahead of time forward to current
1603		 * jiffies, otherwise forward to the next expiry time:
1604		 */
1605		if (time_after(next, jiffies)) {
1606			/*
1607			 * The call site will increment base->clk and then
1608			 * terminate the expiry loop immediately.
1609			 */
1610			base->clk = jiffies;
1611			return 0;
1612		}
1613		base->clk = next;
1614	}
1615	return __collect_expired_timers(base, heads);
1616}
1617#else
1618static inline int collect_expired_timers(struct timer_base *base,
1619					 struct hlist_head *heads)
1620{
1621	return __collect_expired_timers(base, heads);
1622}
1623#endif
1624
1625/*
1626 * Called from the timer interrupt handler to charge one tick to the current
1627 * process.  user_tick is 1 if the tick is user time, 0 for system.
1628 */
1629void update_process_times(int user_tick)
1630{
1631	struct task_struct *p = current;
1632
1633	/* Note: this timer irq context must be accounted for as well. */
1634	account_process_tick(p, user_tick);
1635	run_local_timers();
1636	rcu_check_callbacks(user_tick);
1637#ifdef CONFIG_IRQ_WORK
1638	if (in_irq())
1639		irq_work_tick();
1640#endif
1641	scheduler_tick();
1642	if (IS_ENABLED(CONFIG_POSIX_TIMERS))
1643		run_posix_cpu_timers(p);
 
 
 
 
 
 
 
1644}
1645
1646/**
1647 * __run_timers - run all expired timers (if any) on this CPU.
1648 * @base: the timer vector to be processed.
1649 */
1650static inline void __run_timers(struct timer_base *base)
1651{
1652	struct hlist_head heads[LVL_DEPTH];
1653	int levels;
1654
1655	if (!time_after_eq(jiffies, base->clk))
1656		return;
1657
 
1658	raw_spin_lock_irq(&base->lock);
1659
1660	while (time_after_eq(jiffies, base->clk)) {
1661
1662		levels = collect_expired_timers(base, heads);
 
 
 
 
 
 
1663		base->clk++;
 
1664
1665		while (levels--)
1666			expire_timers(base, heads + levels);
1667	}
1668	base->running_timer = NULL;
1669	raw_spin_unlock_irq(&base->lock);
 
1670}
1671
1672/*
1673 * This function runs timers and the timer-tq in bottom half context.
1674 */
1675static __latent_entropy void run_timer_softirq(struct softirq_action *h)
1676{
1677	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
1678
1679	/*
1680	 * must_forward_clk must be cleared before running timers so that any
1681	 * timer functions that call mod_timer will not try to forward the
1682	 * base. idle trcking / clock forwarding logic is only used with
1683	 * BASE_STD timers.
1684	 *
1685	 * The deferrable base does not do idle tracking at all, so we do
1686	 * not forward it. This can result in very large variations in
1687	 * granularity for deferrable timers, but they can be deferred for
1688	 * long periods due to idle.
1689	 */
1690	base->must_forward_clk = false;
1691
1692	__run_timers(base);
1693	if (IS_ENABLED(CONFIG_NO_HZ_COMMON))
1694		__run_timers(this_cpu_ptr(&timer_bases[BASE_DEF]));
1695}
1696
1697/*
1698 * Called by the local, per-CPU timer interrupt on SMP.
1699 */
1700void run_local_timers(void)
1701{
1702	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
1703
1704	hrtimer_run_queues();
1705	/* Raise the softirq only if required. */
1706	if (time_before(jiffies, base->clk)) {
1707		if (!IS_ENABLED(CONFIG_NO_HZ_COMMON))
1708			return;
1709		/* CPU is awake, so check the deferrable base. */
1710		base++;
1711		if (time_before(jiffies, base->clk))
1712			return;
1713	}
1714	raise_softirq(TIMER_SOFTIRQ);
1715}
1716
1717/*
1718 * Since schedule_timeout()'s timer is defined on the stack, it must store
1719 * the target task on the stack as well.
1720 */
1721struct process_timer {
1722	struct timer_list timer;
1723	struct task_struct *task;
1724};
1725
1726static void process_timeout(struct timer_list *t)
1727{
1728	struct process_timer *timeout = from_timer(timeout, t, timer);
1729
1730	wake_up_process(timeout->task);
1731}
1732
1733/**
1734 * schedule_timeout - sleep until timeout
1735 * @timeout: timeout value in jiffies
1736 *
1737 * Make the current task sleep until @timeout jiffies have
1738 * elapsed. The routine will return immediately unless
1739 * the current task state has been set (see set_current_state()).
1740 *
1741 * You can set the task state as follows -
 
 
1742 *
1743 * %TASK_UNINTERRUPTIBLE - at least @timeout jiffies are guaranteed to
1744 * pass before the routine returns unless the current task is explicitly
1745 * woken up, (e.g. by wake_up_process())".
1746 *
1747 * %TASK_INTERRUPTIBLE - the routine may return early if a signal is
1748 * delivered to the current task or the current task is explicitly woken
1749 * up.
1750 *
1751 * The current task state is guaranteed to be TASK_RUNNING when this
1752 * routine returns.
1753 *
1754 * Specifying a @timeout value of %MAX_SCHEDULE_TIMEOUT will schedule
1755 * the CPU away without a bound on the timeout. In this case the return
1756 * value will be %MAX_SCHEDULE_TIMEOUT.
1757 *
1758 * Returns 0 when the timer has expired otherwise the remaining time in
1759 * jiffies will be returned.  In all cases the return value is guaranteed
1760 * to be non-negative.
1761 */
1762signed long __sched schedule_timeout(signed long timeout)
1763{
1764	struct process_timer timer;
1765	unsigned long expire;
1766
1767	switch (timeout)
1768	{
1769	case MAX_SCHEDULE_TIMEOUT:
1770		/*
1771		 * These two special cases are useful to be comfortable
1772		 * in the caller. Nothing more. We could take
1773		 * MAX_SCHEDULE_TIMEOUT from one of the negative value
1774		 * but I' d like to return a valid offset (>=0) to allow
1775		 * the caller to do everything it want with the retval.
1776		 */
1777		schedule();
1778		goto out;
1779	default:
1780		/*
1781		 * Another bit of PARANOID. Note that the retval will be
1782		 * 0 since no piece of kernel is supposed to do a check
1783		 * for a negative retval of schedule_timeout() (since it
1784		 * should never happens anyway). You just have the printk()
1785		 * that will tell you if something is gone wrong and where.
1786		 */
1787		if (timeout < 0) {
1788			printk(KERN_ERR "schedule_timeout: wrong timeout "
1789				"value %lx\n", timeout);
1790			dump_stack();
1791			current->state = TASK_RUNNING;
1792			goto out;
1793		}
1794	}
1795
1796	expire = timeout + jiffies;
1797
1798	timer.task = current;
1799	timer_setup_on_stack(&timer.timer, process_timeout, 0);
1800	__mod_timer(&timer.timer, expire, 0);
1801	schedule();
1802	del_singleshot_timer_sync(&timer.timer);
1803
1804	/* Remove the timer from the object tracker */
1805	destroy_timer_on_stack(&timer.timer);
1806
1807	timeout = expire - jiffies;
1808
1809 out:
1810	return timeout < 0 ? 0 : timeout;
1811}
1812EXPORT_SYMBOL(schedule_timeout);
1813
1814/*
1815 * We can use __set_current_state() here because schedule_timeout() calls
1816 * schedule() unconditionally.
1817 */
1818signed long __sched schedule_timeout_interruptible(signed long timeout)
1819{
1820	__set_current_state(TASK_INTERRUPTIBLE);
1821	return schedule_timeout(timeout);
1822}
1823EXPORT_SYMBOL(schedule_timeout_interruptible);
1824
1825signed long __sched schedule_timeout_killable(signed long timeout)
1826{
1827	__set_current_state(TASK_KILLABLE);
1828	return schedule_timeout(timeout);
1829}
1830EXPORT_SYMBOL(schedule_timeout_killable);
1831
1832signed long __sched schedule_timeout_uninterruptible(signed long timeout)
1833{
1834	__set_current_state(TASK_UNINTERRUPTIBLE);
1835	return schedule_timeout(timeout);
1836}
1837EXPORT_SYMBOL(schedule_timeout_uninterruptible);
1838
1839/*
1840 * Like schedule_timeout_uninterruptible(), except this task will not contribute
1841 * to load average.
1842 */
1843signed long __sched schedule_timeout_idle(signed long timeout)
1844{
1845	__set_current_state(TASK_IDLE);
1846	return schedule_timeout(timeout);
1847}
1848EXPORT_SYMBOL(schedule_timeout_idle);
1849
1850#ifdef CONFIG_HOTPLUG_CPU
1851static void migrate_timer_list(struct timer_base *new_base, struct hlist_head *head)
1852{
1853	struct timer_list *timer;
1854	int cpu = new_base->cpu;
1855
1856	while (!hlist_empty(head)) {
1857		timer = hlist_entry(head->first, struct timer_list, entry);
1858		detach_timer(timer, false);
1859		timer->flags = (timer->flags & ~TIMER_BASEMASK) | cpu;
1860		internal_add_timer(new_base, timer);
1861	}
1862}
1863
1864int timers_prepare_cpu(unsigned int cpu)
1865{
1866	struct timer_base *base;
1867	int b;
1868
1869	for (b = 0; b < NR_BASES; b++) {
1870		base = per_cpu_ptr(&timer_bases[b], cpu);
1871		base->clk = jiffies;
1872		base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
1873		base->is_idle = false;
1874		base->must_forward_clk = true;
1875	}
1876	return 0;
1877}
1878
1879int timers_dead_cpu(unsigned int cpu)
1880{
1881	struct timer_base *old_base;
1882	struct timer_base *new_base;
1883	int b, i;
1884
1885	BUG_ON(cpu_online(cpu));
1886
1887	for (b = 0; b < NR_BASES; b++) {
1888		old_base = per_cpu_ptr(&timer_bases[b], cpu);
1889		new_base = get_cpu_ptr(&timer_bases[b]);
1890		/*
1891		 * The caller is globally serialized and nobody else
1892		 * takes two locks at once, deadlock is not possible.
1893		 */
1894		raw_spin_lock_irq(&new_base->lock);
1895		raw_spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);
1896
1897		/*
1898		 * The current CPUs base clock might be stale. Update it
1899		 * before moving the timers over.
1900		 */
1901		forward_timer_base(new_base);
1902
1903		BUG_ON(old_base->running_timer);
1904
1905		for (i = 0; i < WHEEL_SIZE; i++)
1906			migrate_timer_list(new_base, old_base->vectors + i);
1907
1908		raw_spin_unlock(&old_base->lock);
1909		raw_spin_unlock_irq(&new_base->lock);
1910		put_cpu_ptr(&timer_bases);
1911	}
1912	return 0;
1913}
1914
1915#endif /* CONFIG_HOTPLUG_CPU */
1916
1917static void __init init_timer_cpu(int cpu)
1918{
1919	struct timer_base *base;
1920	int i;
1921
1922	for (i = 0; i < NR_BASES; i++) {
1923		base = per_cpu_ptr(&timer_bases[i], cpu);
1924		base->cpu = cpu;
1925		raw_spin_lock_init(&base->lock);
1926		base->clk = jiffies;
 
 
1927	}
1928}
1929
1930static void __init init_timer_cpus(void)
1931{
1932	int cpu;
1933
1934	for_each_possible_cpu(cpu)
1935		init_timer_cpu(cpu);
1936}
1937
1938void __init init_timers(void)
1939{
1940	init_timer_cpus();
 
1941	open_softirq(TIMER_SOFTIRQ, run_timer_softirq);
1942}
1943
1944/**
1945 * msleep - sleep safely even with waitqueue interruptions
1946 * @msecs: Time in milliseconds to sleep for
1947 */
1948void msleep(unsigned int msecs)
1949{
1950	unsigned long timeout = msecs_to_jiffies(msecs) + 1;
1951
1952	while (timeout)
1953		timeout = schedule_timeout_uninterruptible(timeout);
1954}
1955
1956EXPORT_SYMBOL(msleep);
1957
1958/**
1959 * msleep_interruptible - sleep waiting for signals
1960 * @msecs: Time in milliseconds to sleep for
1961 */
1962unsigned long msleep_interruptible(unsigned int msecs)
1963{
1964	unsigned long timeout = msecs_to_jiffies(msecs) + 1;
1965
1966	while (timeout && !signal_pending(current))
1967		timeout = schedule_timeout_interruptible(timeout);
1968	return jiffies_to_msecs(timeout);
1969}
1970
1971EXPORT_SYMBOL(msleep_interruptible);
1972
1973/**
1974 * usleep_range - Sleep for an approximate time
1975 * @min: Minimum time in usecs to sleep
1976 * @max: Maximum time in usecs to sleep
1977 *
1978 * In non-atomic context where the exact wakeup time is flexible, use
1979 * usleep_range() instead of udelay().  The sleep improves responsiveness
1980 * by avoiding the CPU-hogging busy-wait of udelay(), and the range reduces
1981 * power usage by allowing hrtimers to take advantage of an already-
1982 * scheduled interrupt instead of scheduling a new one just for this sleep.
1983 */
1984void __sched usleep_range(unsigned long min, unsigned long max)
1985{
1986	ktime_t exp = ktime_add_us(ktime_get(), min);
1987	u64 delta = (u64)(max - min) * NSEC_PER_USEC;
1988
1989	for (;;) {
1990		__set_current_state(TASK_UNINTERRUPTIBLE);
1991		/* Do not return before the requested sleep time has elapsed */
1992		if (!schedule_hrtimeout_range(&exp, delta, HRTIMER_MODE_ABS))
1993			break;
1994	}
1995}
1996EXPORT_SYMBOL(usleep_range);