Google Git Google Git
Sign in
zircon-guest/third_party/linux/6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f/./kernel/time/timer.c
blob: 7e1e3bde6b8b72f82fdd81103822896f5124e7f1 [file]
// 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/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"
#include "timer_migration.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 therefore each
* level has a different granularity.
*
* The level granularity is: LVL_CLK_DIV ^ level
* 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
* therefore 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
/*
* If multiple bases need to be locked, use the base ordering for lock
* nesting, i.e. lowest number first.
*/
# define NR_BASES 3
# define BASE_LOCAL 0
# define BASE_GLOBAL 1
# define BASE_DEF 2
#else
# define NR_BASES 1
# define BASE_LOCAL 0
# define BASE_GLOBAL 0
# define BASE_DEF 0
#endif
/**
* struct timer_base - Per CPU timer base (number of base depends on config)
* @lock: Lock protecting the timer_base
* @running_timer: When expiring timers, the lock is dropped. To make
* sure not to race against deleting/modifying a
* currently running timer, the pointer is set to the
* timer, which expires at the moment. If no timer is
* running, the pointer is NULL.
* @expiry_lock: PREEMPT_RT only: Lock is taken in softirq around
* timer expiry callback execution and when trying to
* delete a running timer and it wasn't successful in
* the first glance. It prevents priority inversion
* when callback was preempted on a remote CPU and a
* caller tries to delete the running timer. It also
* prevents a life lock, when the task which tries to
* delete a timer preempted the softirq thread which
* is running the timer callback function.
* @timer_waiters: PREEMPT_RT only: Tells, if there is a waiter
* waiting for the end of the timer callback function
* execution.
* @clk: clock of the timer base; is updated before enqueue
* of a timer; during expiry, it is 1 offset ahead of
* jiffies to avoid endless requeuing to current
* jiffies
* @next_expiry: expiry value of the first timer; it is updated when
* finding the next timer and during enqueue; the
* value is not valid, when next_expiry_recalc is set
* @cpu: Number of CPU the timer base belongs to
* @next_expiry_recalc: States, whether a recalculation of next_expiry is
* required. Value is set true, when a timer was
* deleted.
* @is_idle: Is set, when timer_base is idle. It is triggered by NOHZ
* code. This state is only used in standard
* base. Deferrable timers, which are enqueued remotely
* never wake up an idle CPU. So no matter of supporting it
* for this base.
* @timers_pending: Is set, when a timer is pending in the base. It is only
* reliable when next_expiry_recalc is not set.
* @pending_map: bitmap of the timer wheel; each bit reflects a
* bucket of the wheel. When a bit is set, at least a
* single timer is enqueued in the related bucket.
* @vectors: Array of lists; Each array member reflects a bucket
* of the timer wheel. The list contains all timers
* which are enqueued into a specific bucket.
*/
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_is_active())
static_branch_enable(&timers_migration_enabled);
else
static_branch_disable(&timers_migration_enabled);
}
#ifdef CONFIG_SYSCTL
static int timer_migration_handler(const 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 const 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 jiffy 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_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_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)
{
/*
* Deferrable timers do not prevent the CPU from entering dynticks and
* are not taken into account on the idle/nohz_full path. An IPI when a
* new deferrable timer is enqueued will wake up the remote CPU but
* nothing will be done with the deferrable timer base. Therefore skip
* the remote IPI for deferrable timers completely.
*/
if (!is_timers_nohz_active() || timer->flags & TIMER_DEFERRABLE)
return;
/*
* We might have to IPI the remote CPU if the base is idle and the
* timer is pinned. If it is a non pinned timer, it is only queued
* on the remote CPU, when timer was running during queueing. Then
* everything is handled by remote CPU anyway. 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) {
WARN_ON_ONCE(!(timer->flags & TIMER_PINNED ||
tick_nohz_full_cpu(base->cpu)));
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, bucket_expiry);
/*
* 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:
*/
WRITE_ONCE(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);
}
/*
* timer_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:
timer_delete_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);
}
/*
* timer_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;
}
}
/*
* timer_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:
timer_delete_sync(timer);
debug_object_free(timer, &timer_debug_descr);
return true;
default:
return false;
}
}
/*
* timer_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 timer_init_key_on_stack(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(timer_init_key_on_stack);
void timer_destroy_on_stack(struct timer_list *timer)
{
debug_object_free(timer, &timer_debug_descr);
}
EXPORT_SYMBOL_GPL(timer_destroy_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);
}
/**
* timer_init_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
*
* timer_init_key() must be done to a timer prior to calling *any* of the
* other timer functions.
*/
void timer_init_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(timer_init_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)
{
int index = tflags & TIMER_PINNED ? BASE_LOCAL : BASE_GLOBAL;
/*
* 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))
index = BASE_DEF;
return per_cpu_ptr(&timer_bases[index], cpu);
}
static inline struct timer_base *get_timer_this_cpu_base(u32 tflags)
{
int index = tflags & TIMER_PINNED ? BASE_LOCAL : BASE_GLOBAL;
/*
* 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))
index = BASE_DEF;
return this_cpu_ptr(&timer_bases[index]);
}
static inline struct timer_base *get_timer_base(u32 tflags)
{
return get_timer_cpu_base(tflags, tflags & TIMER_CPUMASK);
}
static inline void __forward_timer_base(struct timer_base *base,
unsigned long basej)
{
/*
* 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_before_eq(basej, base->clk))
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, basej)) {
base->clk = basej;
} else {
if (WARN_ON_ONCE(time_before(base->next_expiry, base->clk)))
return;
base->clk = base->next_expiry;
}
}
static inline void forward_timer_base(struct timer_base *base)
{
__forward_timer_base(base, READ_ONCE(jiffies));
}
/*
* 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;
debug_assert_init(timer);
/*
* 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);
/*
* Has @timer been shutdown? This needs to be evaluated
* while holding base lock to prevent a race against the
* shutdown code.
*/
if (!timer->function)
goto out_unlock;
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);
/*
* Has @timer been shutdown? This needs to be evaluated
* while holding base lock to prevent a race against the
* shutdown code.
*/
if (!timer->function)
goto out_unlock;
forward_timer_base(base);
}
ret = detach_if_pending(timer, base, false);
if (!ret && (options & MOD_TIMER_PENDING_ONLY))
goto out_unlock;
new_base = get_timer_this_cpu_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 timer_delete_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 absolute timeout in jiffies
*
* mod_timer_pending() is the same for pending timers as mod_timer(), but
* will not activate inactive timers.
*
* If @timer->function == NULL then the start operation is silently
* discarded.
*
* Return:
* * %0 - The timer was inactive and not modified or was in
* shutdown state and the operation was discarded
* * %1 - The timer was active and requeued to expire at @expires
*/
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 absolute timeout in jiffies
*
* mod_timer(timer, expires) is equivalent to:
*
* timer_delete(timer); timer->expires = expires; add_timer(timer);
*
* mod_timer() is more efficient than the above open coded sequence. In
* case that the timer is inactive, the timer_delete() part is a NOP. The
* timer is in any case activated with the new expiry time @expires.
*
* 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.
*
* If @timer->function == NULL then the start operation is silently
* discarded. In this case the return value is 0 and meaningless.
*
* Return:
* * %0 - The timer was inactive and started or was in shutdown
* state and the operation was discarded
* * %1 - The timer was active and requeued to expire at @expires or
* the timer was active and not modified because @expires did
* not change the effective expiry time
*/
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 absolute timeout in jiffies
*
* timer_reduce() is very similar to mod_timer(), except that it will only
* modify an enqueued timer if that would reduce the expiration time. If
* @timer is not enqueued it starts the timer.
*
* If @timer->function == NULL then the start operation is silently
* discarded.
*
* Return:
* * %0 - The timer was inactive and started or was in shutdown
* state and the operation was discarded
* * %1 - The timer was active and requeued to expire at @expires or
* the timer was active and not modified because @expires
* did not change the effective expiry time such that the
* timer would expire earlier than already scheduled
*/
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 started
*
* Start @timer to expire at @timer->expires in the future. @timer->expires
* is the absolute expiry time measured in 'jiffies'. When the timer expires
* timer->function(timer) will be invoked from soft interrupt context.
*
* The @timer->expires and @timer->function fields must be set prior
* to calling this function.
*
* If @timer->function == NULL then the start operation is silently
* discarded.
*
* If @timer->expires is already in the past @timer will be queued to
* expire at the next timer tick.
*
* This can only operate on an inactive timer. Attempts to invoke this on
* an active timer are rejected with a warning.
*/
void add_timer(struct timer_list *timer)
{
if (WARN_ON_ONCE(timer_pending(timer)))
return;
__mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
}
EXPORT_SYMBOL(add_timer);
/**
* add_timer_local() - Start a timer on the local CPU
* @timer: The timer to be started
*
* Same as add_timer() except that the timer flag TIMER_PINNED is set.
*
* See add_timer() for further details.
*/
void add_timer_local(struct timer_list *timer)
{
if (WARN_ON_ONCE(timer_pending(timer)))
return;
timer->flags |= TIMER_PINNED;
__mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
}
EXPORT_SYMBOL(add_timer_local);
/**
* add_timer_global() - Start a timer without TIMER_PINNED flag set
* @timer: The timer to be started
*
* Same as add_timer() except that the timer flag TIMER_PINNED is unset.
*
* See add_timer() for further details.
*/
void add_timer_global(struct timer_list *timer)
{
if (WARN_ON_ONCE(timer_pending(timer)))
return;
timer->flags &= ~TIMER_PINNED;
__mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
}
EXPORT_SYMBOL(add_timer_global);
/**
* add_timer_on - Start a timer on a particular CPU
* @timer: The timer to be started
* @cpu: The CPU to start it on
*
* Same as add_timer() except that it starts the timer on the given CPU and
* the TIMER_PINNED flag is set. When timer shouldn't be a pinned timer in
* the next round, add_timer_global() should be used instead as it unsets
* the TIMER_PINNED flag.
*
* See add_timer() for further details.
*/
void add_timer_on(struct timer_list *timer, int cpu)
{
struct timer_base *new_base, *base;
unsigned long flags;
debug_assert_init(timer);
if (WARN_ON_ONCE(timer_pending(timer)))
return;
/* Make sure timer flags have TIMER_PINNED flag set */
timer->flags |= TIMER_PINNED;
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);
/*
* Has @timer been shutdown? This needs to be evaluated while
* holding base lock to prevent a race against the shutdown code.
*/
if (!timer->function)
goto out_unlock;
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);
out_unlock:
raw_spin_unlock_irqrestore(&base->lock, flags);
}
EXPORT_SYMBOL_GPL(add_timer_on);
/**
* __timer_delete - Internal function: Deactivate a timer
* @timer: The timer to be deactivated
* @shutdown: If true, this indicates that the timer is about to be
* shutdown permanently.
*
* If @shutdown is true then @timer->function is set to NULL under the
* timer base lock which prevents further rearming of the time. In that
* case any attempt to rearm @timer after this function returns will be
* silently ignored.
*
* Return:
* * %0 - The timer was not pending
* * %1 - The timer was pending and deactivated
*/
static int __timer_delete(struct timer_list *timer, bool shutdown)
{
struct timer_base *base;
unsigned long flags;
int ret = 0;
debug_assert_init(timer);
/*
* If @shutdown is set then the lock has to be taken whether the
* timer is pending or not to protect against a concurrent rearm
* which might hit between the lockless pending check and the lock
* acquisition. By taking the lock it is ensured that such a newly
* enqueued timer is dequeued and cannot end up with
* timer->function == NULL in the expiry code.
*
* If timer->function is currently executed, then this makes sure
* that the callback cannot requeue the timer.
*/
if (timer_pending(timer) || shutdown) {
base = lock_timer_base(timer, &flags);
ret = detach_if_pending(timer, base, true);
if (shutdown)
timer->function = NULL;
raw_spin_unlock_irqrestore(&base->lock, flags);
}
return ret;
}
/**
* timer_delete - Deactivate a timer
* @timer: The timer to be deactivated
*
* The function only deactivates a pending timer, but contrary to
* timer_delete_sync() it does not take into account whether the timer's
* callback function is concurrently executed on a different CPU or not.
* It neither prevents rearming of the timer. If @timer can be rearmed
* concurrently then the return value of this function is meaningless.
*
* Return:
* * %0 - The timer was not pending
* * %1 - The timer was pending and deactivated
*/
int timer_delete(struct timer_list *timer)
{
return __timer_delete(timer, false);
}
EXPORT_SYMBOL(timer_delete);
/**
* timer_shutdown - Deactivate a timer and prevent rearming
* @timer: The timer to be deactivated
*
* The function does not wait for an eventually running timer callback on a
* different CPU but it prevents rearming of the timer. Any attempt to arm
* @timer after this function returns will be silently ignored.
*
* This function is useful for teardown code and should only be used when
* timer_shutdown_sync() cannot be invoked due to locking or context constraints.
*
* Return:
* * %0 - The timer was not pending
* * %1 - The timer was pending
*/
int timer_shutdown(struct timer_list *timer)
{
return __timer_delete(timer, true);
}
EXPORT_SYMBOL_GPL(timer_shutdown);
/**
* __try_to_del_timer_sync - Internal function: Try to deactivate a timer
* @timer: Timer to deactivate
* @shutdown: If true, this indicates that the timer is about to be
* shutdown permanently.
*
* If @shutdown is true then @timer->function is set to NULL under the
* timer base lock which prevents further rearming of the timer. Any
* attempt to rearm @timer after this function returns will be silently
* ignored.
*
* This function cannot guarantee that the timer cannot be rearmed
* right after dropping the base lock if @shutdown is false. That
* needs to be prevented by the calling code if necessary.
*
* Return:
* * %0 - The timer was not pending
* * %1 - The timer was pending and deactivated
* * %-1 - The timer callback function is running on a different CPU
*/
static int __try_to_del_timer_sync(struct timer_list *timer, bool shutdown)
{
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);
if (shutdown)
timer->function = NULL;
}
raw_spin_unlock_irqrestore(&base->lock, flags);
return ret;
}
/**
* timer_delete_sync_try - Try to deactivate a timer
* @timer: Timer to deactivate
*
* This function tries to deactivate a timer. On success the timer is not
* queued and the timer callback function is not running on any CPU.
*
* This function does not guarantee that the timer cannot be rearmed right
* after dropping the base lock. That needs to be prevented by the calling
* code if necessary.
*
* Return:
* * %0 - The timer was not pending
* * %1 - The timer was pending and deactivated
* * %-1 - The timer callback function is running on a different CPU
*/
int timer_delete_sync_try(struct timer_list *timer)
{
return __try_to_del_timer_sync(timer, false);
}
EXPORT_SYMBOL(timer_delete_sync_try);
#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)
__releases(&base->lock) __releases(&base->expiry_lock)
__acquires(&base->expiry_lock) __acquires(&base->lock)
{
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
/**
* __timer_delete_sync - Internal function: Deactivate a timer and wait
* for the handler to finish.
* @timer: The timer to be deactivated
* @shutdown: If true, @timer->function will be set to NULL under the
* timer base lock which prevents rearming of @timer
*
* If @shutdown is not set the timer can be rearmed later. If the timer can
* be rearmed concurrently, i.e. after dropping the base lock then the
* return value is meaningless.
*
* If @shutdown is set then @timer->function is set to NULL under timer
* base lock which prevents rearming of the timer. Any attempt to rearm
* a shutdown timer is silently ignored.
*
* If the timer should be reused after shutdown it has to be initialized
* again.
*
* Return:
* * %0 - The timer was not pending
* * %1 - The timer was pending and deactivated
*/
static int __timer_delete_sync(struct timer_list *timer, bool shutdown)
{
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_hardirq() && !(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, shutdown);
if (unlikely(ret < 0)) {
del_timer_wait_running(timer);
cpu_relax();
}
} while (ret < 0);
return ret;
}
/**
* timer_delete_sync - Deactivate a timer and wait for the handler to finish.
* @timer: The timer to be deactivated
*
* 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 callback
* function. 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.
*
* For !irqsafe timers, the caller must not hold locks that are held in
* interrupt context. 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);
* timer_delete_sync(mytimer);
* while (base->running_timer == mytimer);
*
* Now timer_delete_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.
*
* This function cannot guarantee that the timer is not rearmed again by
* some concurrent or preempting code, right after it dropped the base
* lock. If there is the possibility of a concurrent rearm then the return
* value of the function is meaningless.
*
* If such a guarantee is needed, e.g. for teardown situations then use
* timer_shutdown_sync() instead.
*
* Return:
* * %0 - The timer was not pending
* * %1 - The timer was pending and deactivated
*/
int timer_delete_sync(struct timer_list *timer)
{
return __timer_delete_sync(timer, false);
}
EXPORT_SYMBOL(timer_delete_sync);
/**
* timer_shutdown_sync - Shutdown a timer and prevent rearming
* @timer: The timer to be shutdown
*
* When the function returns it is guaranteed that:
* - @timer is not queued
* - The callback function of @timer is not running
* - @timer cannot be enqueued again. Any attempt to rearm
* @timer is silently ignored.
*
* See timer_delete_sync() for synchronization rules.
*
* This function is useful for final teardown of an infrastructure where
* the timer is subject to a circular dependency problem.
*
* A common pattern for this is a timer and a workqueue where the timer can
* schedule work and work can arm the timer. On shutdown the workqueue must
* be destroyed and the timer must be prevented from rearming. Unless the
* code has conditionals like 'if (mything->in_shutdown)' to prevent that
* there is no way to get this correct with timer_delete_sync().
*
* timer_shutdown_sync() is solving the problem. The correct ordering of
* calls in this case is:
*
* timer_shutdown_sync(&mything->timer);
* workqueue_destroy(&mything->workqueue);
*
* After this 'mything' can be safely freed.
*
* This obviously implies that the timer is not required to be functional
* for the rest of the shutdown operation.
*
* Return:
* * %0 - The timer was not pending
* * %1 - The timer was pending
*/
int timer_shutdown_sync(struct timer_list *timer)
{
return __timer_delete_sync(timer, true);
}
EXPORT_SYMBOL_GPL(timer_shutdown_sync);
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
* timer_delete_sync() by acquiring the lock_map around the fn()
* call here and in timer_delete_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 (WARN_ON_ONCE(!fn)) {
/* Should never happen. Emphasis on should! */
base->running_timer = NULL;
continue;
}
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.
*
* Store next expiry time in base->next_expiry.
*/
static void timer_recalc_next_expiry(struct timer_base *base)
{
unsigned long clk, next, adj;
unsigned lvl, offset = 0;
next = base->clk + TIMER_NEXT_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 jiffy. 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;
}
WRITE_ONCE(base->next_expiry, next);
base->next_expiry_recalc = false;
base->timers_pending = !(next == base->clk + TIMER_NEXT_MAX_DELTA);
}
#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 jiffy. 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;
}
static unsigned long next_timer_interrupt(struct timer_base *base,
unsigned long basej)
{
if (base->next_expiry_recalc)
timer_recalc_next_expiry(base);
/*
* Move next_expiry for the empty base into the future to prevent an
* unnecessary raise of the timer softirq when the next_expiry value
* will be reached even if there is no timer pending.
*
* This update is also required to make timer_base::next_expiry values
* easy comparable to find out which base holds the first pending timer.
*/
if (!base->timers_pending)
WRITE_ONCE(base->next_expiry, basej + TIMER_NEXT_MAX_DELTA);
return base->next_expiry;
}
static unsigned long fetch_next_timer_interrupt(unsigned long basej, u64 basem,
struct timer_base *base_local,
struct timer_base *base_global,
struct timer_events *tevt)
{
unsigned long nextevt, nextevt_local, nextevt_global;
bool local_first;
nextevt_local = next_timer_interrupt(base_local, basej);
nextevt_global = next_timer_interrupt(base_global, basej);
local_first = time_before_eq(nextevt_local, nextevt_global);
nextevt = local_first ? nextevt_local : nextevt_global;
/*
* If the @nextevt is at max. one tick away, use @nextevt and store
* it in the local expiry value. The next global event is irrelevant in
* this case and can be left as KTIME_MAX.
*/
if (time_before_eq(nextevt, basej + 1)) {
/* If we missed a tick already, force 0 delta */
if (time_before(nextevt, basej))
nextevt = basej;
tevt->local = basem + (u64)(nextevt - basej) * TICK_NSEC;
/*
* This is required for the remote check only but it doesn't
* hurt, when it is done for both call sites:
*
* * The remote callers will only take care of the global timers
* as local timers will be handled by CPU itself. When not
* updating tevt->global with the already missed first global
* timer, it is possible that it will be missed completely.
*
* * The local callers will ignore the tevt->global anyway, when
* nextevt is max. one tick away.
*/
if (!local_first)
tevt->global = tevt->local;
return nextevt;
}
/*
* Update tevt.* values:
*
* If the local queue expires first, then the global event can be
* ignored. If the global queue is empty, nothing to do either.
*/
if (!local_first && base_global->timers_pending)
tevt->global = basem + (u64)(nextevt_global - basej) * TICK_NSEC;
if (base_local->timers_pending)
tevt->local = basem + (u64)(nextevt_local - basej) * TICK_NSEC;
return nextevt;
}
# ifdef CONFIG_SMP
/**
* fetch_next_timer_interrupt_remote() - Store next timers into @tevt
* @basej: base time jiffies
* @basem: base time clock monotonic
* @tevt: Pointer to the storage for the expiry values
* @cpu: Remote CPU
*
* Stores the next pending local and global timer expiry values in the
* struct pointed to by @tevt. If a queue is empty the corresponding
* field is set to KTIME_MAX. If local event expires before global
* event, global event is set to KTIME_MAX as well.
*
* Caller needs to make sure timer base locks are held (use
* timer_lock_remote_bases() for this purpose).
*/
void fetch_next_timer_interrupt_remote(unsigned long basej, u64 basem,
struct timer_events *tevt,
unsigned int cpu)
{
struct timer_base *base_local, *base_global;
/* Preset local / global events */
tevt->local = tevt->global = KTIME_MAX;
base_local = per_cpu_ptr(&timer_bases[BASE_LOCAL], cpu);
base_global = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
lockdep_assert_held(&base_local->lock);
lockdep_assert_held(&base_global->lock);
fetch_next_timer_interrupt(basej, basem, base_local, base_global, tevt);
}
/**
* timer_unlock_remote_bases - unlock timer bases of cpu
* @cpu: Remote CPU
*
* Unlocks the remote timer bases.
*/
void timer_unlock_remote_bases(unsigned int cpu)
__releases(timer_bases[BASE_LOCAL]->lock)
__releases(timer_bases[BASE_GLOBAL]->lock)
{
struct timer_base *base_local, *base_global;
base_local = per_cpu_ptr(&timer_bases[BASE_LOCAL], cpu);
base_global = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
raw_spin_unlock(&base_global->lock);
raw_spin_unlock(&base_local->lock);
}
/**
* timer_lock_remote_bases - lock timer bases of cpu
* @cpu: Remote CPU
*
* Locks the remote timer bases.
*/
void timer_lock_remote_bases(unsigned int cpu)
__acquires(timer_bases[BASE_LOCAL]->lock)
__acquires(timer_bases[BASE_GLOBAL]->lock)
{
struct timer_base *base_local, *base_global;
base_local = per_cpu_ptr(&timer_bases[BASE_LOCAL], cpu);
base_global = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
lockdep_assert_irqs_disabled();
raw_spin_lock(&base_local->lock);
raw_spin_lock_nested(&base_global->lock, SINGLE_DEPTH_NESTING);
}
/**
* timer_base_is_idle() - Return whether timer base is set idle
*
* Returns value of local timer base is_idle value.
*/
bool timer_base_is_idle(void)
{
return __this_cpu_read(timer_bases[BASE_LOCAL].is_idle);
}
static void __run_timer_base(struct timer_base *base);
/**
* timer_expire_remote() - expire global timers of cpu
* @cpu: Remote CPU
*
* Expire timers of global base of remote CPU.
*/
void timer_expire_remote(unsigned int cpu)
{
struct timer_base *base = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
__run_timer_base(base);
}
static void timer_use_tmigr(unsigned long basej, u64 basem,
unsigned long *nextevt, bool *tick_stop_path,
bool timer_base_idle, struct timer_events *tevt)
{
u64 next_tmigr;
if (timer_base_idle)
next_tmigr = tmigr_cpu_new_timer(tevt->global);
else if (tick_stop_path)
next_tmigr = tmigr_cpu_deactivate(tevt->global);
else
next_tmigr = tmigr_quick_check(tevt->global);
/*
* If the CPU is the last going idle in timer migration hierarchy, make
* sure the CPU will wake up in time to handle remote timers.
* next_tmigr == KTIME_MAX if other CPUs are still active.
*/
if (next_tmigr < tevt->local) {
u64 tmp;
/* If we missed a tick already, force 0 delta */
if (next_tmigr < basem)
next_tmigr = basem;
tmp = div_u64(next_tmigr - basem, TICK_NSEC);
*nextevt = basej + (unsigned long)tmp;
tevt->local = next_tmigr;
}
}
# else
static void timer_use_tmigr(unsigned long basej, u64 basem,
unsigned long *nextevt, bool *tick_stop_path,
bool timer_base_idle, struct timer_events *tevt)
{
/*
* Make sure first event is written into tevt->local to not miss a
* timer on !SMP systems.
*/
tevt->local = min_t(u64, tevt->local, tevt->global);
}
# endif /* CONFIG_SMP */
static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem,
bool *idle)
{
struct timer_events tevt = { .local = KTIME_MAX, .global = KTIME_MAX };
struct timer_base *base_local, *base_global;
unsigned long nextevt;
bool idle_is_possible;
/*
* When the CPU is offline, the tick is cancelled and nothing is supposed
* to try to stop it.
*/
if (WARN_ON_ONCE(cpu_is_offline(smp_processor_id()))) {
if (idle)
*idle = true;
return tevt.local;
}
base_local = this_cpu_ptr(&timer_bases[BASE_LOCAL]);
base_global = this_cpu_ptr(&timer_bases[BASE_GLOBAL]);
raw_spin_lock(&base_local->lock);
raw_spin_lock_nested(&base_global->lock, SINGLE_DEPTH_NESTING);
nextevt = fetch_next_timer_interrupt(basej, basem, base_local,
base_global, &tevt);
/*
* If the next event is only one jiffy ahead there is no need to call
* timer migration hierarchy related functions. The value for the next
* global timer in @tevt struct equals then KTIME_MAX. This is also
* true, when the timer base is idle.
*
* The proper timer migration hierarchy function depends on the callsite
* and whether timer base is idle or not. @nextevt will be updated when
* this CPU needs to handle the first timer migration hierarchy
* event. See timer_use_tmigr() for detailed information.
*/
idle_is_possible = time_after(nextevt, basej + 1);
if (idle_is_possible)
timer_use_tmigr(basej, basem, &nextevt, idle,
base_local->is_idle, &tevt);
/*
* We have a fresh next event. Check whether we can forward the
* base.
*/
__forward_timer_base(base_local, basej);
__forward_timer_base(base_global, basej);
/*
* Set base->is_idle only when caller is timer_base_try_to_set_idle()
*/
if (idle) {
/*
* Bases are idle if the next event is more than a tick
* away. Caution: @nextevt could have changed by enqueueing a
* global timer into timer migration hierarchy. Therefore a new
* check is required here.
*
* If the base is marked idle then any timer add operation must
* forward the base clk itself to keep granularity small. This
* idle logic is only maintained for the BASE_LOCAL and
* BASE_GLOBAL base, deferrable timers may still see large
* granularity skew (by design).
*/
if (!base_local->is_idle && time_after(nextevt, basej + 1)) {
base_local->is_idle = true;
/*
* Global timers queued locally while running in a task
* in nohz_full mode need a self-IPI to kick reprogramming
* in IRQ tail.
*/
if (tick_nohz_full_cpu(base_local->cpu))
base_global->is_idle = true;
trace_timer_base_idle(true, base_local->cpu);
}
*idle = base_local->is_idle;
/*
* When timer base is not set idle, undo the effect of
* tmigr_cpu_deactivate() to prevent inconsistent states - active
* timer base but inactive timer migration hierarchy.
*
* When timer base was already marked idle, nothing will be
* changed here.
*/
if (!base_local->is_idle && idle_is_possible)
tmigr_cpu_activate();
}
raw_spin_unlock(&base_global->lock);
raw_spin_unlock(&base_local->lock);
return cmp_next_hrtimer_event(basem, tevt.local);
}
/**
* 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. If timer of global base was queued into
* timer migration hierarchy, first global timer is not taken into account. If
* it was the last CPU of timer migration hierarchy going idle, first global
* event is taken into account.
*/
u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
{
return __get_next_timer_interrupt(basej, basem, NULL);
}
/**
* timer_base_try_to_set_idle() - Try to set the idle state of the timer bases
* @basej: base time jiffies
* @basem: base time clock monotonic
* @idle: pointer to store the value of timer_base->is_idle on return;
* *idle contains the information whether tick was already stopped
*
* Returns the tick aligned clock monotonic time of the next pending timer or
* KTIME_MAX if no timer is pending. When tick was already stopped KTIME_MAX is
* returned as well.
*/
u64 timer_base_try_to_set_idle(unsigned long basej, u64 basem, bool *idle)
{
if (*idle)
return KTIME_MAX;
return __get_next_timer_interrupt(basej, basem, idle);
}
/**
* timer_clear_idle - Clear the idle state of the timer base
*
* Called with interrupts disabled
*/
void timer_clear_idle(void)
{
/*
* We do this unlocked. The worst outcome is a remote pinned timer
* 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. Required for BASE_LOCAL only.
*/
__this_cpu_write(timer_bases[BASE_LOCAL].is_idle, false);
if (tick_nohz_full_cpu(smp_processor_id()))
__this_cpu_write(timer_bases[BASE_GLOBAL].is_idle, false);
trace_timer_base_idle(false, smp_processor_id());
/* Activate without holding the timer_base->lock */
tmigr_cpu_activate();
}
#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;
lockdep_assert_held(&base->lock);
if (base->running_timer)
return;
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 +
* TIMER_NEXT_MAX_DELTA.
*/
WARN_ON_ONCE(!levels && !base->next_expiry_recalc
&& base->timers_pending);
/*
* While executing timers, base->clk is set 1 offset ahead of
* jiffies to avoid endless requeuing to current jiffies.
*/
base->clk++;
timer_recalc_next_expiry(base);
while (levels--)
expire_timers(base, heads + levels);
}
}
static void __run_timer_base(struct timer_base *base)
{
/* Can race against a remote CPU updating next_expiry under the lock */
if (time_before(jiffies, READ_ONCE(base->next_expiry)))
return;
timer_base_lock_expiry(base);
raw_spin_lock_irq(&base->lock);
__run_timers(base);
raw_spin_unlock_irq(&base->lock);
timer_base_unlock_expiry(base);
}
static void run_timer_base(int index)
{
struct timer_base *base = this_cpu_ptr(&timer_bases[index]);
__run_timer_base(base);
}
/*
* This function runs timers and the timer-tq in bottom half context.
*/
static __latent_entropy void run_timer_softirq(void)
{
run_timer_base(BASE_LOCAL);
if (IS_ENABLED(CONFIG_NO_HZ_COMMON)) {
run_timer_base(BASE_GLOBAL);
run_timer_base(BASE_DEF);
if (is_timers_nohz_active())
tmigr_handle_remote();
}
}
/*
* 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_LOCAL]);
hrtimer_run_queues();
for (int i = 0; i < NR_BASES; i++, base++) {
/*
* Raise the softirq only if required.
*
* timer_base::next_expiry can be written by a remote CPU while
* holding the lock. If this write happens at the same time than
* the lockless local read, sanity checker could complain about
* data corruption.
*
* There are two possible situations where
* timer_base::next_expiry is written by a remote CPU:
*
* 1. Remote CPU expires global timers of this CPU and updates
* timer_base::next_expiry of BASE_GLOBAL afterwards in
* next_timer_interrupt() or timer_recalc_next_expiry(). The
* worst outcome is a superfluous raise of the timer softirq
* when the not yet updated value is read.
*
* 2. A new first pinned timer is enqueued by a remote CPU
* and therefore timer_base::next_expiry of BASE_LOCAL is
* updated. When this update is missed, this isn't a
* problem, as an IPI is executed nevertheless when the CPU
* was idle before. When the CPU wasn't idle but the update
* is missed, then the timer would expire one jiffy late -
* bad luck.
*
* Those unlikely corner cases where the worst outcome is only a
* one jiffy delay or a superfluous raise of the softirq are
* not that expensive as doing the check always while holding
* the lock.
*
* Possible remote writers are using WRITE_ONCE(). Local reader
* uses therefore READ_ONCE().
*/
if (time_after_eq(jiffies, READ_ONCE(base->next_expiry)) ||
(i == BASE_DEF && tmigr_requires_handle_remote())) {
raise_timer_softirq(TIMER_SOFTIRQ);
return;
}
}
}
/*
* 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_hardirq())
irq_work_tick();
#endif
sched_tick();
if (IS_ENABLED(CONFIG_POSIX_TIMERS))
run_posix_cpu_timers();
}
#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 + TIMER_NEXT_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;
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);
WARN_ON_ONCE(old_base->running_timer);
old_base->running_timer = NULL;
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 + TIMER_NEXT_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 timers_init(void)
{
init_timer_cpus();
posix_cputimers_init_work();
open_softirq(TIMER_SOFTIRQ, run_timer_softirq);
}