// SPDX-License-Identifier: GPL-2.0-only
/*
 *  kernel/sched/core.c
 *
 *  Core kernel scheduler code and related syscalls
 *
 *  Copyright (C) 1991-2002  Linus Torvalds
 */
#define CREATE_TRACE_POINTS
#include <trace/events/sched.h>
#undef CREATE_TRACE_POINTS

#include "sched.h"

#include <linux/nospec.h>

#include <linux/kcov.h>
#include <linux/scs.h>

#include <asm/switch_to.h>
#include <asm/tlb.h>

#include "../workqueue_internal.h"
#include "../../fs/io-wq.h"
#include "../smpboot.h"

#include "pelt.h"
#include "smp.h"

/*
 * Export tracepoints that act as a bare tracehook (ie: have no trace event
 * associated with them) to allow external modules to probe them.
 */
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_cfs_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_rt_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_dl_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_irq_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_se_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_cpu_capacity_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_overutilized_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_cfs_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_se_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp);

DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);

#ifdef CONFIG_SCHED_DEBUG
/*
 * Debugging: various feature bits
 *
 * If SCHED_DEBUG is disabled, each compilation unit has its own copy of
 * sysctl_sched_features, defined in sched.h, to allow constants propagation
 * at compile time and compiler optimization based on features default.
 */
#define SCHED_FEAT(name, enabled)       \
        (1UL << __SCHED_FEAT_##name) * enabled |
const_debug unsigned int sysctl_sched_features =
#include "features.h"
        0;
#undef SCHED_FEAT

/*
 * Print a warning if need_resched is set for the given duration (if
 * LATENCY_WARN is enabled).
 *
 * If sysctl_resched_latency_warn_once is set, only one warning will be shown
 * per boot.
 */
__read_mostly int sysctl_resched_latency_warn_ms = 100;
__read_mostly int sysctl_resched_latency_warn_once = 1;
#endif /* CONFIG_SCHED_DEBUG */

/*
 * Number of tasks to iterate in a single balance run.
 * Limited because this is done with IRQs disabled.
 */
const_debug unsigned int sysctl_sched_nr_migrate = 32;

/*
 * period over which we measure -rt task CPU usage in us.
 * default: 1s
 */
unsigned int sysctl_sched_rt_period = 1000000;

__read_mostly int scheduler_running;

#ifdef CONFIG_SCHED_CORE

DEFINE_STATIC_KEY_FALSE(__sched_core_enabled);

/* kernel prio, less is more */
static inline int __task_prio(struct task_struct *p)
{
        if (p->sched_class == &stop_sched_class) /* trumps deadline */
                return -2;

        if (rt_prio(p->prio)) /* includes deadline */
                return p->prio; /* [-1, 99] */

        if (p->sched_class == &idle_sched_class)
                return MAX_RT_PRIO + NICE_WIDTH; /* 140 */

        return MAX_RT_PRIO + MAX_NICE; /* 120, squash fair */
}

/*
 * l(a,b)
 * le(a,b) := !l(b,a)
 * g(a,b)  := l(b,a)
 * ge(a,b) := !l(a,b)
 */

/* real prio, less is less */
static inline bool prio_less(struct task_struct *a, struct task_struct *b, bool in_fi)
{

        int pa = __task_prio(a), pb = __task_prio(b);

        if (-pa < -pb)
                return true;

        if (-pb < -pa)
                return false;

        if (pa == -1) /* dl_prio() doesn't work because of stop_class above */
                return !dl_time_before(a->dl.deadline, b->dl.deadline);

        if (pa == MAX_RT_PRIO + MAX_NICE)       /* fair */
                return cfs_prio_less(a, b, in_fi);

        return false;
}

static inline bool __sched_core_less(struct task_struct *a, struct task_struct *b)
{
        if (a->core_cookie < b->core_cookie)
                return true;

        if (a->core_cookie > b->core_cookie)
                return false;

        /* flip prio, so high prio is leftmost */
        if (prio_less(b, a, task_rq(a)->core->core_forceidle))
                return true;

        return false;
}

#define __node_2_sc(node) rb_entry((node), struct task_struct, core_node)

static inline bool rb_sched_core_less(struct rb_node *a, const struct rb_node *b)
{
        return __sched_core_less(__node_2_sc(a), __node_2_sc(b));
}

static inline int rb_sched_core_cmp(const void *key, const struct rb_node *node)
{
        const struct task_struct *p = __node_2_sc(node);
        unsigned long cookie = (unsigned long)key;

        if (cookie < p->core_cookie)
                return -1;

        if (cookie > p->core_cookie)
                return 1;

        return 0;
}

void sched_core_enqueue(struct rq *rq, struct task_struct *p)
{
        rq->core->core_task_seq++;

        if (!p->core_cookie)
                return;

        rb_add(&p->core_node, &rq->core_tree, rb_sched_core_less);
}

void sched_core_dequeue(struct rq *rq, struct task_struct *p)
{
        rq->core->core_task_seq++;

        if (!sched_core_enqueued(p))
                return;

        rb_erase(&p->core_node, &rq->core_tree);
        RB_CLEAR_NODE(&p->core_node);
}

/*
 * Find left-most (aka, highest priority) task matching @cookie.
 */
static struct task_struct *sched_core_find(struct rq *rq, unsigned long cookie)
{
        struct rb_node *node;

        node = rb_find_first((void *)cookie, &rq->core_tree, rb_sched_core_cmp);
        /*
         * The idle task always matches any cookie!
         */
        if (!node)
                return idle_sched_class.pick_task(rq);

        return __node_2_sc(node);
}

static struct task_struct *sched_core_next(struct task_struct *p, unsigned long cookie)
{
        struct rb_node *node = &p->core_node;

        node = rb_next(node);
        if (!node)
                return NULL;

        p = container_of(node, struct task_struct, core_node);
        if (p->core_cookie != cookie)
                return NULL;

        return p;
}

/*
 * Magic required such that:
 *
 *      raw_spin_rq_lock(rq);
 *      ...
 *      raw_spin_rq_unlock(rq);
 *
 * ends up locking and unlocking the _same_ lock, and all CPUs
 * always agree on what rq has what lock.
 *
 * XXX entirely possible to selectively enable cores, don't bother for now.
 */

static DEFINE_MUTEX(sched_core_mutex);
static atomic_t sched_core_count;
static struct cpumask sched_core_mask;

static void sched_core_lock(int cpu, unsigned long *flags)
{
        const struct cpumask *smt_mask = cpu_smt_mask(cpu);
        int t, i = 0;

        local_irq_save(*flags);
        for_each_cpu(t, smt_mask)
                raw_spin_lock_nested(&cpu_rq(t)->__lock, i++);
}

static void sched_core_unlock(int cpu, unsigned long *flags)
{
        const struct cpumask *smt_mask = cpu_smt_mask(cpu);
        int t;

        for_each_cpu(t, smt_mask)
                raw_spin_unlock(&cpu_rq(t)->__lock);
        local_irq_restore(*flags);
}

static void __sched_core_flip(bool enabled)
{
        unsigned long flags;
        int cpu, t;

        cpus_read_lock();

        /*
         * Toggle the online cores, one by one.
         */
        cpumask_copy(&sched_core_mask, cpu_online_mask);
        for_each_cpu(cpu, &sched_core_mask) {
                const struct cpumask *smt_mask = cpu_smt_mask(cpu);

                sched_core_lock(cpu, &flags);

                for_each_cpu(t, smt_mask)
                        cpu_rq(t)->core_enabled = enabled;

                sched_core_unlock(cpu, &flags);

                cpumask_andnot(&sched_core_mask, &sched_core_mask, smt_mask);
        }

        /*
         * Toggle the offline CPUs.
         */
        cpumask_copy(&sched_core_mask, cpu_possible_mask);
        cpumask_andnot(&sched_core_mask, &sched_core_mask, cpu_online_mask);

        for_each_cpu(cpu, &sched_core_mask)
                cpu_rq(cpu)->core_enabled = enabled;

        cpus_read_unlock();
}

static void sched_core_assert_empty(void)
{
        int cpu;

        for_each_possible_cpu(cpu)
                WARN_ON_ONCE(!RB_EMPTY_ROOT(&cpu_rq(cpu)->core_tree));
}

static void __sched_core_enable(void)
{
        static_branch_enable(&__sched_core_enabled);
        /*
         * Ensure all previous instances of raw_spin_rq_*lock() have finished
         * and future ones will observe !sched_core_disabled().
         */
        synchronize_rcu();
        __sched_core_flip(true);
        sched_core_assert_empty();
}

static void __sched_core_disable(void)
{
        sched_core_assert_empty();
        __sched_core_flip(false);
        static_branch_disable(&__sched_core_enabled);
}

void sched_core_get(void)
{
        if (atomic_inc_not_zero(&sched_core_count))
                return;

        mutex_lock(&sched_core_mutex);
        if (!atomic_read(&sched_core_count))
                __sched_core_enable();

        smp_mb__before_atomic();
        atomic_inc(&sched_core_count);
        mutex_unlock(&sched_core_mutex);
}

static void __sched_core_put(struct work_struct *work)
{
        if (atomic_dec_and_mutex_lock(&sched_core_count, &sched_core_mutex)) {
                __sched_core_disable();
                mutex_unlock(&sched_core_mutex);
        }
}

void sched_core_put(void)
{
        static DECLARE_WORK(_work, __sched_core_put);

        /*
         * "There can be only one"
         *
         * Either this is the last one, or we don't actually need to do any
         * 'work'. If it is the last *again*, we rely on
         * WORK_STRUCT_PENDING_BIT.
         */
        if (!atomic_add_unless(&sched_core_count, -1, 1))
                schedule_work(&_work);
}

#else /* !CONFIG_SCHED_CORE */

static inline void sched_core_enqueue(struct rq *rq, struct task_struct *p) { }
static inline void sched_core_dequeue(struct rq *rq, struct task_struct *p) { }

#endif /* CONFIG_SCHED_CORE */

/*
 * part of the period that we allow rt tasks to run in us.
 * default: 0.95s
 */
int sysctl_sched_rt_runtime = 950000;


/*
 * Serialization rules:
 *
 * Lock order:
 *
 *   p->pi_lock
 *     rq->lock
 *       hrtimer_cpu_base->lock (hrtimer_start() for bandwidth controls)
 *
 *  rq1->lock
 *    rq2->lock  where: rq1 < rq2
 *
 * Regular state:
 *
 * Normal scheduling state is serialized by rq->lock. __schedule() takes the
 * local CPU's rq->lock, it optionally removes the task from the runqueue and
 * always looks at the local rq data structures to find the most eligible task
 * to run next.
 *
 * Task enqueue is also under rq->lock, possibly taken from another CPU.
 * Wakeups from another LLC domain might use an IPI to transfer the enqueue to
 * the local CPU to avoid bouncing the runqueue state around [ see
 * ttwu_queue_wakelist() ]
 *
 * Task wakeup, specifically wakeups that involve migration, are horribly
 * complicated to avoid having to take two rq->locks.
 *
 * Special state:
 *
 * System-calls and anything external will use task_rq_lock() which acquires
 * both p->pi_lock and rq->lock. As a consequence the state they change is
 * stable while holding either lock:
 *
 *  - sched_setaffinity()/
 *    set_cpus_allowed_ptr():   p->cpus_ptr, p->nr_cpus_allowed
 *  - set_user_nice():          p->se.load, p->*prio
 *  - __sched_setscheduler():   p->sched_class, p->policy, p->*prio,
 *                              p->se.load, p->rt_priority,
 *                              p->dl.dl_{runtime, deadline, period, flags, bw, density}
 *  - sched_setnuma():          p->numa_preferred_nid
 *  - sched_move_task()/
 *    cpu_cgroup_fork():        p->sched_task_group
 *  - uclamp_update_active()    p->uclamp*
 *
 * p->state <- TASK_*:
 *
 *   is changed locklessly using set_current_state(), __set_current_state() or
 *   set_special_state(), see their respective comments, or by
 *   try_to_wake_up(). This latter uses p->pi_lock to serialize against
 *   concurrent self.
 *
 * p->on_rq <- { 0, 1 = TASK_ON_RQ_QUEUED, 2 = TASK_ON_RQ_MIGRATING }:
 *
 *   is set by activate_task() and cleared by deactivate_task(), under
 *   rq->lock. Non-zero indicates the task is runnable, the special
 *   ON_RQ_MIGRATING state is used for migration without holding both
 *   rq->locks. It indicates task_cpu() is not stable, see task_rq_lock().
 *
 * p->on_cpu <- { 0, 1 }:
 *
 *   is set by prepare_task() and cleared by finish_task() such that it will be
 *   set before p is scheduled-in and cleared after p is scheduled-out, both
 *   under rq->lock. Non-zero indicates the task is running on its CPU.
 *
 *   [ The astute reader will observe that it is possible for two tasks on one
 *     CPU to have ->on_cpu = 1 at the same time. ]
 *
 * task_cpu(p): is changed by set_task_cpu(), the rules are:
 *
 *  - Don't call set_task_cpu() on a blocked task:
 *
 *    We don't care what CPU we're not running on, this simplifies hotplug,
 *    the CPU assignment of blocked tasks isn't required to be valid.
 *
 *  - for try_to_wake_up(), called under p->pi_lock:
 *
 *    This allows try_to_wake_up() to only take one rq->lock, see its comment.
 *
 *  - for migration called under rq->lock:
 *    [ see task_on_rq_migrating() in task_rq_lock() ]
 *
 *    o move_queued_task()
 *    o detach_task()
 *
 *  - for migration called under double_rq_lock():
 *
 *    o __migrate_swap_task()
 *    o push_rt_task() / pull_rt_task()
 *    o push_dl_task() / pull_dl_task()
 *    o dl_task_offline_migration()
 *
 */

void raw_spin_rq_lock_nested(struct rq *rq, int subclass)
{
        raw_spinlock_t *lock;

        /* Matches synchronize_rcu() in __sched_core_enable() */
        preempt_disable();
        if (sched_core_disabled()) {
                raw_spin_lock_nested(&rq->__lock, subclass);
                /* preempt_count *MUST* be > 1 */
                preempt_enable_no_resched();
                return;
        }

        for (;;) {
                lock = __rq_lockp(rq);
                raw_spin_lock_nested(lock, subclass);
                if (likely(lock == __rq_lockp(rq))) {
                        /* preempt_count *MUST* be > 1 */
                        preempt_enable_no_resched();
                        return;
                }
                raw_spin_unlock(lock);
        }
}

bool raw_spin_rq_trylock(struct rq *rq)
{
        raw_spinlock_t *lock;
        bool ret;

        /* Matches synchronize_rcu() in __sched_core_enable() */
        preempt_disable();
        if (sched_core_disabled()) {
                ret = raw_spin_trylock(&rq->__lock);
                preempt_enable();
                return ret;
        }

        for (;;) {
                lock = __rq_lockp(rq);
                ret = raw_spin_trylock(lock);
                if (!ret || (likely(lock == __rq_lockp(rq)))) {
                        preempt_enable();
                        return ret;
                }
                raw_spin_unlock(lock);
        }
}

void raw_spin_rq_unlock(struct rq *rq)
{
        raw_spin_unlock(rq_lockp(rq));
}

#ifdef CONFIG_SMP
/*
 * double_rq_lock - safely lock two runqueues
 */
void double_rq_lock(struct rq *rq1, struct rq *rq2)
{
        lockdep_assert_irqs_disabled();

        if (rq_order_less(rq2, rq1))
                swap(rq1, rq2);

        raw_spin_rq_lock(rq1);
        if (__rq_lockp(rq1) == __rq_lockp(rq2))
                return;

        raw_spin_rq_lock_nested(rq2, SINGLE_DEPTH_NESTING);
}
#endif

/*
 * __task_rq_lock - lock the rq @p resides on.
 */
struct rq *__task_rq_lock(struct task_struct *p, struct rq_flags *rf)
        __acquires(rq->lock)
{
        struct rq *rq;

        lockdep_assert_held(&p->pi_lock);

        for (;;) {
                rq = task_rq(p);
                raw_spin_rq_lock(rq);
                if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
                        rq_pin_lock(rq, rf);
                        return rq;
                }
                raw_spin_rq_unlock(rq);

                while (unlikely(task_on_rq_migrating(p)))
                        cpu_relax();
        }
}

/*
 * task_rq_lock - lock p->pi_lock and lock the rq @p resides on.
 */
struct rq *task_rq_lock(struct task_struct *p, struct rq_flags *rf)
        __acquires(p->pi_lock)
        __acquires(rq->lock)
{
        struct rq *rq;

        for (;;) {
                raw_spin_lock_irqsave(&p->pi_lock, rf->flags);
                rq = task_rq(p);
                raw_spin_rq_lock(rq);
                /*
                 *      move_queued_task()              task_rq_lock()
                 *
                 *      ACQUIRE (rq->lock)
                 *      [S] ->on_rq = MIGRATING         [L] rq = task_rq()
                 *      WMB (__set_task_cpu())          ACQUIRE (rq->lock);
                 *      [S] ->cpu = new_cpu             [L] task_rq()
                 *                                      [L] ->on_rq
                 *      RELEASE (rq->lock)
                 *
                 * If we observe the old CPU in task_rq_lock(), the acquire of
                 * the old rq->lock will fully serialize against the stores.
                 *
                 * If we observe the new CPU in task_rq_lock(), the address
                 * dependency headed by '[L] rq = task_rq()' and the acquire
                 * will pair with the WMB to ensure we then also see migrating.
                 */
                if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
                        rq_pin_lock(rq, rf);
                        return rq;
                }
                raw_spin_rq_unlock(rq);
                raw_spin_unlock_irqrestore(&p->pi_lock, rf->flags);

                while (unlikely(task_on_rq_migrating(p)))
                        cpu_relax();
        }
}

/*
 * RQ-clock updating methods:
 */

static void update_rq_clock_task(struct rq *rq, s64 delta)
{
/*
 * In theory, the compile should just see 0 here, and optimize out the call
 * to sched_rt_avg_update. But I don't trust it...
 */
        s64 __maybe_unused steal = 0, irq_delta = 0;

#ifdef CONFIG_IRQ_TIME_ACCOUNTING
        irq_delta = irq_time_read(cpu_of(rq)) - rq->prev_irq_time;

        /*
         * Since irq_time is only updated on {soft,}irq_exit, we might run into
         * this case when a previous update_rq_clock() happened inside a
         * {soft,}irq region.
         *
         * When this happens, we stop ->clock_task and only update the
         * prev_irq_time stamp to account for the part that fit, so that a next
         * update will consume the rest. This ensures ->clock_task is
         * monotonic.
         *
         * It does however cause some slight miss-attribution of {soft,}irq
         * time, a more accurate solution would be to update the irq_time using
         * the current rq->clock timestamp, except that would require using
         * atomic ops.
         */
        if (irq_delta > delta)
                irq_delta = delta;

        rq->prev_irq_time += irq_delta;
        delta -= irq_delta;
#endif
#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
        if (static_key_false((&paravirt_steal_rq_enabled))) {
                steal = paravirt_steal_clock(cpu_of(rq));
                steal -= rq->prev_steal_time_rq;

                if (unlikely(steal > delta))
                        steal = delta;

                rq->prev_steal_time_rq += steal;
                delta -= steal;
        }
#endif

        rq->clock_task += delta;

#ifdef CONFIG_HAVE_SCHED_AVG_IRQ
        if ((irq_delta + steal) && sched_feat(NONTASK_CAPACITY))
                update_irq_load_avg(rq, irq_delta + steal);
#endif
        update_rq_clock_pelt(rq, delta);
}

void update_rq_clock(struct rq *rq)
{
        s64 delta;

        lockdep_assert_rq_held(rq);

        if (rq->clock_update_flags & RQCF_ACT_SKIP)
                return;

#ifdef CONFIG_SCHED_DEBUG
        if (sched_feat(WARN_DOUBLE_CLOCK))
                SCHED_WARN_ON(rq->clock_update_flags & RQCF_UPDATED);
        rq->clock_update_flags |= RQCF_UPDATED;
#endif

        delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;
        if (delta < 0)
                return;
        rq->clock += delta;
        update_rq_clock_task(rq, delta);
}

#ifdef CONFIG_SCHED_HRTICK
/*
 * Use HR-timers to deliver accurate preemption points.
 */

static void hrtick_clear(struct rq *rq)
{
        if (hrtimer_active(&rq->hrtick_timer))
                hrtimer_cancel(&rq->hrtick_timer);
}

/*
 * High-resolution timer tick.
 * Runs from hardirq context with interrupts disabled.
 */
static enum hrtimer_restart hrtick(struct hrtimer *timer)
{
        struct rq *rq = container_of(timer, struct rq, hrtick_timer);
        struct rq_flags rf;

        WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());

        rq_lock(rq, &rf);
        update_rq_clock(rq);
        rq->curr->sched_class->task_tick(rq, rq->curr, 1);
        rq_unlock(rq, &rf);

        return HRTIMER_NORESTART;
}

#ifdef CONFIG_SMP

static void __hrtick_restart(struct rq *rq)
{
        struct hrtimer *timer = &rq->hrtick_timer;
        ktime_t time = rq->hrtick_time;

        hrtimer_start(timer, time, HRTIMER_MODE_ABS_PINNED_HARD);
}

/*
 * called from hardirq (IPI) context
 */
static void __hrtick_start(void *arg)
{
        struct rq *rq = arg;
        struct rq_flags rf;

        rq_lock(rq, &rf);
        __hrtick_restart(rq);
        rq_unlock(rq, &rf);
}

/*
 * Called to set the hrtick timer state.
 *
 * called with rq->lock held and irqs disabled
 */
void hrtick_start(struct rq *rq, u64 delay)
{
        struct hrtimer *timer = &rq->hrtick_timer;
        s64 delta;

        /*
         * Don't schedule slices shorter than 10000ns, that just
         * doesn't make sense and can cause timer DoS.
         */
        delta = max_t(s64, delay, 10000LL);
        rq->hrtick_time = ktime_add_ns(timer->base->get_time(), delta);

        if (rq == this_rq())
                __hrtick_restart(rq);
        else
                smp_call_function_single_async(cpu_of(rq), &rq->hrtick_csd);
}

#else
/*
 * Called to set the hrtick timer state.
 *
 * called with rq->lock held and irqs disabled
 */
void hrtick_start(struct rq *rq, u64 delay)
{
        /*
         * Don't schedule slices shorter than 10000ns, that just
         * doesn't make sense. Rely on vruntime for fairness.
         */
        delay = max_t(u64, delay, 10000LL);
        hrtimer_start(&rq->hrtick_timer, ns_to_ktime(delay),
                      HRTIMER_MODE_REL_PINNED_HARD);
}

#endif /* CONFIG_SMP */

static void hrtick_rq_init(struct rq *rq)
{
#ifdef CONFIG_SMP
        INIT_CSD(&rq->hrtick_csd, __hrtick_start, rq);
#endif
        hrtimer_init(&rq->hrtick_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
        rq->hrtick_timer.function = hrtick;
}
#else   /* CONFIG_SCHED_HRTICK */
static inline void hrtick_clear(struct rq *rq)
{
}

static inline void hrtick_rq_init(struct rq *rq)
{
}
#endif  /* CONFIG_SCHED_HRTICK */

/*
 * cmpxchg based fetch_or, macro so it works for different integer types
 */
#define fetch_or(ptr, mask)                                             \
        ({                                                              \
                typeof(ptr) _ptr = (ptr);                               \
                typeof(mask) _mask = (mask);                            \
                typeof(*_ptr) _old, _val = *_ptr;                       \
                                                                        \
                for (;;) {                                              \
                        _old = cmpxchg(_ptr, _val, _val | _mask);       \
                        if (_old == _val)                               \
                                break;                                  \
                        _val = _old;                                    \
                }                                                       \
        _old;                                                           \
})

#if defined(CONFIG_SMP) && defined(TIF_POLLING_NRFLAG)
/*
 * Atomically set TIF_NEED_RESCHED and test for TIF_POLLING_NRFLAG,
 * this avoids any races wrt polling state changes and thereby avoids
 * spurious IPIs.
 */
static bool set_nr_and_not_polling(struct task_struct *p)
{
        struct thread_info *ti = task_thread_info(p);
        return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLAG);
}

/*
 * Atomically set TIF_NEED_RESCHED if TIF_POLLING_NRFLAG is set.
 *
 * If this returns true, then the idle task promises to call
 * sched_ttwu_pending() and reschedule soon.
 */
static bool set_nr_if_polling(struct task_struct *p)
{
        struct thread_info *ti = task_thread_info(p);
        typeof(ti->flags) old, val = READ_ONCE(ti->flags);

        for (;;) {
                if (!(val & _TIF_POLLING_NRFLAG))
                        return false;
                if (val & _TIF_NEED_RESCHED)
                        return true;
                old = cmpxchg(&ti->flags, val, val | _TIF_NEED_RESCHED);
                if (old == val)
                        break;
                val = old;
        }
        return true;
}

#else
static bool set_nr_and_not_polling(struct task_struct *p)
{
        set_tsk_need_resched(p);
        return true;
}

#ifdef CONFIG_SMP
static bool set_nr_if_polling(struct task_struct *p)
{
        return false;
}
#endif
#endif

static bool __wake_q_add(struct wake_q_head *head, struct task_struct *task)
{
        struct wake_q_node *node = &task->wake_q;

        /*
         * Atomically grab the task, if ->wake_q is !nil already it means
         * it's already queued (either by us or someone else) and will get the
         * wakeup due to that.
         *
         * In order to ensure that a pending wakeup will observe our pending
         * state, even in the failed case, an explicit smp_mb() must be used.
         */
        smp_mb__before_atomic();
        if (unlikely(cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL)))
                return false;

        /*
         * The head is context local, there can be no concurrency.
         */
        *head->lastp = node;
        head->lastp = &node->next;
        return true;
}

/**
 * wake_q_add() - queue a wakeup for 'later' waking.
 * @head: the wake_q_head to add @task to
 * @task: the task to queue for 'later' wakeup
 *
 * Queue a task for later wakeup, most likely by the wake_up_q() call in the
 * same context, _HOWEVER_ this is not guaranteed, the wakeup can come
 * instantly.
 *
 * This function must be used as-if it were wake_up_process(); IOW the task
 * must be ready to be woken at this location.
 */
void wake_q_add(struct wake_q_head *head, struct task_struct *task)
{
        if (__wake_q_add(head, task))
                get_task_struct(task);
}

/**
 * wake_q_add_safe() - safely queue a wakeup for 'later' waking.
 * @head: the wake_q_head to add @task to
 * @task: the task to queue for 'later' wakeup
 *
 * Queue a task for later wakeup, most likely by the wake_up_q() call in the
 * same context, _HOWEVER_ this is not guaranteed, the wakeup can come
 * instantly.
 *
 * This function must be used as-if it were wake_up_process(); IOW the task
 * must be ready to be woken at this location.
 *
 * This function is essentially a task-safe equivalent to wake_q_add(). Callers
 * that already hold reference to @task can call the 'safe' version and trust
 * wake_q to do the right thing depending whether or not the @task is already
 * queued for wakeup.
 */
void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task)
{
        if (!__wake_q_add(head, task))
                put_task_struct(task);
}

void wake_up_q(struct wake_q_head *head)
{
        struct wake_q_node *node = head->first;

        while (node != WAKE_Q_TAIL) {
                struct task_struct *task;

                task = container_of(node, struct task_struct, wake_q);
                /* Task can safely be re-inserted now: */
                node = node->next;
                task->wake_q.next = NULL;

                /*
                 * wake_up_process() executes a full barrier, which pairs with
                 * the queueing in wake_q_add() so as not to miss wakeups.
                 */
                wake_up_process(task);
                put_task_struct(task);
        }
}

/*
 * resched_curr - mark rq's current task 'to be rescheduled now'.
 *
 * On UP this means the setting of the need_resched flag, on SMP it
 * might also involve a cross-CPU call to trigger the scheduler on
 * the target CPU.
 */
void resched_curr(struct rq *rq)
{
        struct task_struct *curr = rq->curr;
        int cpu;

        lockdep_assert_rq_held(rq);

        if (test_tsk_need_resched(curr))
                return;

        cpu = cpu_of(rq);

        if (cpu == smp_processor_id()) {
                set_tsk_need_resched(curr);
                set_preempt_need_resched();
                return;
        }

        if (set_nr_and_not_polling(curr))
                smp_send_reschedule(cpu);
        else
                trace_sched_wake_idle_without_ipi(cpu);
}

void resched_cpu(int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        unsigned long flags;

        raw_spin_rq_lock_irqsave(rq, flags);
        if (cpu_online(cpu) || cpu == smp_processor_id())
                resched_curr(rq);
        raw_spin_rq_unlock_irqrestore(rq, flags);
}

#ifdef CONFIG_SMP
#ifdef CONFIG_NO_HZ_COMMON
/*
 * In the semi idle case, use the nearest busy CPU for migrating timers
 * from an idle CPU.  This is good for power-savings.

 *
 * We don't do similar optimization for completely idle system, as
 * selecting an idle CPU will add more delays to the timers than intended
 * (as that CPU's timer base may not be uptodate wrt jiffies etc).
 */
int get_nohz_timer_target(void)
{
        int i, cpu = smp_processor_id(), default_cpu = -1;
        struct sched_domain *sd;
        const struct cpumask *hk_mask;

        if (housekeeping_cpu(cpu, HK_FLAG_TIMER)) {
                if (!idle_cpu(cpu))
                        return cpu;
                default_cpu = cpu;
        }

        hk_mask = housekeeping_cpumask(HK_FLAG_TIMER);

        rcu_read_lock();
        for_each_domain(cpu, sd) {
                for_each_cpu_and(i, sched_domain_span(sd), hk_mask) {
                        if (cpu == i)
                                continue;

                        if (!idle_cpu(i)) {
                                cpu = i;
                                goto unlock;
                        }
                }
        }

        if (default_cpu == -1)
                default_cpu = housekeeping_any_cpu(HK_FLAG_TIMER);
        cpu = default_cpu;
unlock:
        rcu_read_unlock();
        return cpu;
}

/*
 * When add_timer_on() enqueues a timer into the timer wheel of an
 * idle CPU then this timer might expire before the next timer event
 * which is scheduled to wake up that CPU. In case of a completely
 * idle system the next event might even be infinite time into the
 * future. wake_up_idle_cpu() ensures that the CPU is woken up and
 * leaves the inner idle loop so the newly added timer is taken into
 * account when the CPU goes back to idle and evaluates the timer
 * wheel for the next timer event.
 */
static void wake_up_idle_cpu(int cpu)
{
        struct rq *rq = cpu_rq(cpu);

        if (cpu == smp_processor_id())
                return;

        if (set_nr_and_not_polling(rq->idle))
                smp_send_reschedule(cpu);
        else
                trace_sched_wake_idle_without_ipi(cpu);
}

static bool wake_up_full_nohz_cpu(int cpu)
{
        /*
         * We just need the target to call irq_exit() and re-evaluate
         * the next tick. The nohz full kick at least implies that.
         * If needed we can still optimize that later with an
         * empty IRQ.
         */
        if (cpu_is_offline(cpu))
                return true;  /* Don't try to wake offline CPUs. */
        if (tick_nohz_full_cpu(cpu)) {
                if (cpu != smp_processor_id() ||
                    tick_nohz_tick_stopped())
                        tick_nohz_full_kick_cpu(cpu);
                return true;
        }

        return false;
}

/*
 * Wake up the specified CPU.  If the CPU is going offline, it is the
 * caller's responsibility to deal with the lost wakeup, for example,
 * by hooking into the CPU_DEAD notifier like timers and hrtimers do.
 */
void wake_up_nohz_cpu(int cpu)
{
        if (!wake_up_full_nohz_cpu(cpu))
                wake_up_idle_cpu(cpu);
}

static void nohz_csd_func(void *info)
{
        struct rq *rq = info;
        int cpu = cpu_of(rq);
        unsigned int flags;

        /*
         * Release the rq::nohz_csd.
         */
        flags = atomic_fetch_andnot(NOHZ_KICK_MASK | NOHZ_NEWILB_KICK, nohz_flags(cpu));
        WARN_ON(!(flags & NOHZ_KICK_MASK));

        rq->idle_balance = idle_cpu(cpu);
        if (rq->idle_balance && !need_resched()) {
                rq->nohz_idle_balance = flags;
                raise_softirq_irqoff(SCHED_SOFTIRQ);
        }
}

#endif /* CONFIG_NO_HZ_COMMON */

#ifdef CONFIG_NO_HZ_FULL
bool sched_can_stop_tick(struct rq *rq)
{
        int fifo_nr_running;

        /* Deadline tasks, even if single, need the tick */
        if (rq->dl.dl_nr_running)
                return false;

        /*
         * If there are more than one RR tasks, we need the tick to affect the
         * actual RR behaviour.
         */
        if (rq->rt.rr_nr_running) {
                if (rq->rt.rr_nr_running == 1)
                        return true;
                else
                        return false;
        }

        /*
         * If there's no RR tasks, but FIFO tasks, we can skip the tick, no
         * forced preemption between FIFO tasks.
         */
        fifo_nr_running = rq->rt.rt_nr_running - rq->rt.rr_nr_running;
        if (fifo_nr_running)
                return true;

        /*
         * If there are no DL,RR/FIFO tasks, there must only be CFS tasks left;
         * if there's more than one we need the tick for involuntary
         * preemption.
         */
        if (rq->nr_running > 1)
                return false;

        return true;
}
#endif /* CONFIG_NO_HZ_FULL */
#endif /* CONFIG_SMP */

#if defined(CONFIG_RT_GROUP_SCHED) || (defined(CONFIG_FAIR_GROUP_SCHED) && \
                        (defined(CONFIG_SMP) || defined(CONFIG_CFS_BANDWIDTH)))
/*
 * Iterate task_group tree rooted at *from, calling @down when first entering a
 * node and @up when leaving it for the final time.
 *
 * Caller must hold rcu_lock or sufficient equivalent.
 */
int walk_tg_tree_from(struct task_group *from,
                             tg_visitor down, tg_visitor up, void *data)
{
        struct task_group *parent, *child;
        int ret;

        parent = from;

down:
        ret = (*down)(parent, data);
        if (ret)
                goto out;
        list_for_each_entry_rcu(child, &parent->children, siblings) {
                parent = child;
                goto down;

up:
                continue;
        }
        ret = (*up)(parent, data);
        if (ret || parent == from)
                goto out;

        child = parent;
        parent = parent->parent;
        if (parent)
                goto up;
out:
        return ret;
}

int tg_nop(struct task_group *tg, void *data)
{
        return 0;
}
#endif

static void set_load_weight(struct task_struct *p, bool update_load)
{
        int prio = p->static_prio - MAX_RT_PRIO;
        struct load_weight *load = &p->se.load;

        /*
         * SCHED_IDLE tasks get minimal weight:
         */
        if (task_has_idle_policy(p)) {
                load->weight = scale_load(WEIGHT_IDLEPRIO);
                load->inv_weight = WMULT_IDLEPRIO;
                return;
        }

        /*
         * SCHED_OTHER tasks have to update their load when changing their
         * weight
         */
        if (update_load && p->sched_class == &fair_sched_class) {
                reweight_task(p, prio);
        } else {
                load->weight = scale_load(sched_prio_to_weight[prio]);
                load->inv_weight = sched_prio_to_wmult[prio];
        }
}

#ifdef CONFIG_UCLAMP_TASK
/*
 * Serializes updates of utilization clamp values
 *
 * The (slow-path) user-space triggers utilization clamp value updates which
 * can require updates on (fast-path) scheduler's data structures used to
 * support enqueue/dequeue operations.
 * While the per-CPU rq lock protects fast-path update operations, user-space
 * requests are serialized using a mutex to reduce the risk of conflicting
 * updates or API abuses.
 */
static DEFINE_MUTEX(uclamp_mutex);

/* Max allowed minimum utilization */
unsigned int sysctl_sched_uclamp_util_min = SCHED_CAPACITY_SCALE;

/* Max allowed maximum utilization */
unsigned int sysctl_sched_uclamp_util_max = SCHED_CAPACITY_SCALE;

/*
 * By default RT tasks run at the maximum performance point/capacity of the
 * system. Uclamp enforces this by always setting UCLAMP_MIN of RT tasks to
 * SCHED_CAPACITY_SCALE.
 *
 * This knob allows admins to change the default behavior when uclamp is being
 * used. In battery powered devices, particularly, running at the maximum
 * capacity and frequency will increase energy consumption and shorten the
 * battery life.
 *
 * This knob only affects RT tasks that their uclamp_se->user_defined == false.
 *
 * This knob will not override the system default sched_util_clamp_min defined
 * above.
 */
unsigned int sysctl_sched_uclamp_util_min_rt_default = SCHED_CAPACITY_SCALE;

/* All clamps are required to be less or equal than these values */
static struct uclamp_se uclamp_default[UCLAMP_CNT];

/*
 * This static key is used to reduce the uclamp overhead in the fast path. It
 * primarily disables the call to uclamp_rq_{inc, dec}() in
 * enqueue/dequeue_task().
 *
 * This allows users to continue to enable uclamp in their kernel config with
 * minimum uclamp overhead in the fast path.
 *
 * As soon as userspace modifies any of the uclamp knobs, the static key is
 * enabled, since we have an actual users that make use of uclamp
 * functionality.
 *
 * The knobs that would enable this static key are:
 *
 *   * A task modifying its uclamp value with sched_setattr().
 *   * An admin modifying the sysctl_sched_uclamp_{min, max} via procfs.
 *   * An admin modifying the cgroup cpu.uclamp.{min, max}
 */
DEFINE_STATIC_KEY_FALSE(sched_uclamp_used);

/* Integer rounded range for each bucket */
#define UCLAMP_BUCKET_DELTA DIV_ROUND_CLOSEST(SCHED_CAPACITY_SCALE, UCLAMP_BUCKETS)

#define for_each_clamp_id(clamp_id) \
        for ((clamp_id) = 0; (clamp_id) < UCLAMP_CNT; (clamp_id)++)

static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
{
        return min_t(unsigned int, clamp_value / UCLAMP_BUCKET_DELTA, UCLAMP_BUCKETS - 1);
}

static inline unsigned int uclamp_none(enum uclamp_id clamp_id)
{
        if (clamp_id == UCLAMP_MIN)
                return 0;
        return SCHED_CAPACITY_SCALE;
}

static inline void uclamp_se_set(struct uclamp_se *uc_se,
                                 unsigned int value, bool user_defined)
{
        uc_se->value = value;
        uc_se->bucket_id = uclamp_bucket_id(value);
        uc_se->user_defined = user_defined;
}

static inline unsigned int
uclamp_idle_value(struct rq *rq, enum uclamp_id clamp_id,
                  unsigned int clamp_value)
{
        /*
         * Avoid blocked utilization pushing up the frequency when we go
         * idle (which drops the max-clamp) by retaining the last known
         * max-clamp.
         */
        if (clamp_id == UCLAMP_MAX) {
                rq->uclamp_flags |= UCLAMP_FLAG_IDLE;
                return clamp_value;
        }

        return uclamp_none(UCLAMP_MIN);
}

static inline void uclamp_idle_reset(struct rq *rq, enum uclamp_id clamp_id,
                                     unsigned int clamp_value)
{
        /* Reset max-clamp retention only on idle exit */
        if (!(rq->uclamp_flags & UCLAMP_FLAG_IDLE))
                return;

        WRITE_ONCE(rq->uclamp[clamp_id].value, clamp_value);
}

static inline
unsigned int uclamp_rq_max_value(struct rq *rq, enum uclamp_id clamp_id,
                                   unsigned int clamp_value)
{
        struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
        int bucket_id = UCLAMP_BUCKETS - 1;

        /*
         * Since both min and max clamps are max aggregated, find the
         * top most bucket with tasks in.
         */
        for ( ; bucket_id >= 0; bucket_id--) {
                if (!bucket[bucket_id].tasks)
                        continue;
                return bucket[bucket_id].value;
        }

        /* No tasks -- default clamp values */
        return uclamp_idle_value(rq, clamp_id, clamp_value);
}

static void __uclamp_update_util_min_rt_default(struct task_struct *p)
{
        unsigned int default_util_min;
        struct uclamp_se *uc_se;

        lockdep_assert_held(&p->pi_lock);

        uc_se = &p->uclamp_req[UCLAMP_MIN];

        /* Only sync if user didn't override the default */
        if (uc_se->user_defined)
                return;

        default_util_min = sysctl_sched_uclamp_util_min_rt_default;
        uclamp_se_set(uc_se, default_util_min, false);
}

static void uclamp_update_util_min_rt_default(struct task_struct *p)
{
        struct rq_flags rf;
        struct rq *rq;

        if (!rt_task(p))
                return;

        /* Protect updates to p->uclamp_* */
        rq = task_rq_lock(p, &rf);
        __uclamp_update_util_min_rt_default(p);
        task_rq_unlock(rq, p, &rf);
}

static void uclamp_sync_util_min_rt_default(void)
{
        struct task_struct *g, *p;

        /*
         * copy_process()                       sysctl_uclamp
         *                                        uclamp_min_rt = X;
         *   write_lock(&tasklist_lock)           read_lock(&tasklist_lock)
         *   // link thread                       smp_mb__after_spinlock()
         *   write_unlock(&tasklist_lock)         read_unlock(&tasklist_lock);
         *   sched_post_fork()                    for_each_process_thread()
         *     __uclamp_sync_rt()                   __uclamp_sync_rt()
         *
         * Ensures that either sched_post_fork() will observe the new
         * uclamp_min_rt or for_each_process_thread() will observe the new
         * task.
         */
        read_lock(&tasklist_lock);
        smp_mb__after_spinlock();
        read_unlock(&tasklist_lock);

        rcu_read_lock();
        for_each_process_thread(g, p)
                uclamp_update_util_min_rt_default(p);
        rcu_read_unlock();
}

static inline struct uclamp_se
uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
{
        /* Copy by value as we could modify it */
        struct uclamp_se uc_req = p->uclamp_req[clamp_id];
#ifdef CONFIG_UCLAMP_TASK_GROUP
        unsigned int tg_min, tg_max, value;

        /*
         * Tasks in autogroups or root task group will be
         * restricted by system defaults.
         */
        if (task_group_is_autogroup(task_group(p)))
                return uc_req;
        if (task_group(p) == &root_task_group)
                return uc_req;

        tg_min = task_group(p)->uclamp[UCLAMP_MIN].value;
        tg_max = task_group(p)->uclamp[UCLAMP_MAX].value;
        value = uc_req.value;
        value = clamp(value, tg_min, tg_max);
        uclamp_se_set(&uc_req, value, false);
#endif

        return uc_req;
}

/*
 * The effective clamp bucket index of a task depends on, by increasing
 * priority:
 * - the task specific clamp value, when explicitly requested from userspace
 * - the task group effective clamp value, for tasks not either in the root
 *   group or in an autogroup
 * - the system default clamp value, defined by the sysadmin
 */
static inline struct uclamp_se
uclamp_eff_get(struct task_struct *p, enum uclamp_id clamp_id)
{
        struct uclamp_se uc_req = uclamp_tg_restrict(p, clamp_id);
        struct uclamp_se uc_max = uclamp_default[clamp_id];

        /* System default restrictions always apply */
        if (unlikely(uc_req.value > uc_max.value))
                return uc_max;

        return uc_req;
}

unsigned long uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id)
{
        struct uclamp_se uc_eff;

        /* Task currently refcounted: use back-annotated (effective) value */
        if (p->uclamp[clamp_id].active)
                return (unsigned long)p->uclamp[clamp_id].value;

        uc_eff = uclamp_eff_get(p, clamp_id);

        return (unsigned long)uc_eff.value;
}

/*
 * When a task is enqueued on a rq, the clamp bucket currently defined by the
 * task's uclamp::bucket_id is refcounted on that rq. This also immediately
 * updates the rq's clamp value if required.
 *
 * Tasks can have a task-specific value requested from user-space, track
 * within each bucket the maximum value for tasks refcounted in it.
 * This "local max aggregation" allows to track the exact "requested" value
 * for each bucket when all its RUNNABLE tasks require the same clamp.
 */
static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p,
                                    enum uclamp_id clamp_id)
{
        struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
        struct uclamp_se *uc_se = &p->uclamp[clamp_id];
        struct uclamp_bucket *bucket;

        lockdep_assert_rq_held(rq);

        /* Update task effective clamp */
        p->uclamp[clamp_id] = uclamp_eff_get(p, clamp_id);

        bucket = &uc_rq->bucket[uc_se->bucket_id];
        bucket->tasks++;
        uc_se->active = true;

        uclamp_idle_reset(rq, clamp_id, uc_se->value);

        /*
         * Local max aggregation: rq buckets always track the max
         * "requested" clamp value of its RUNNABLE tasks.
         */
        if (bucket->tasks == 1 || uc_se->value > bucket->value)
                bucket->value = uc_se->value;

        if (uc_se->value > READ_ONCE(uc_rq->value))
                WRITE_ONCE(uc_rq->value, uc_se->value);
}

/*
 * When a task is dequeued from a rq, the clamp bucket refcounted by the task
 * is released. If this is the last task reference counting the rq's max
 * active clamp value, then the rq's clamp value is updated.
 *
 * Both refcounted tasks and rq's cached clamp values are expected to be
 * always valid. If it's detected they are not, as defensive programming,
 * enforce the expected state and warn.
 */
static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
                                    enum uclamp_id clamp_id)
{
        struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
        struct uclamp_se *uc_se = &p->uclamp[clamp_id];
        struct uclamp_bucket *bucket;
        unsigned int bkt_clamp;
        unsigned int rq_clamp;

        lockdep_assert_rq_held(rq);

        /*
         * If sched_uclamp_used was enabled after task @p was enqueued,
         * we could end up with unbalanced call to uclamp_rq_dec_id().
         *
         * In this case the uc_se->active flag should be false since no uclamp
         * accounting was performed at enqueue time and we can just return
         * here.
         *
         * Need to be careful of the following enqueue/dequeue ordering
         * problem too
         *
         *      enqueue(taskA)
         *      // sched_uclamp_used gets enabled
         *      enqueue(taskB)
         *      dequeue(taskA)
         *      // Must not decrement bucket->tasks here
         *      dequeue(taskB)
         *
         * where we could end up with stale data in uc_se and
         * bucket[uc_se->bucket_id].
         *
         * The following check here eliminates the possibility of such race.
         */
        if (unlikely(!uc_se->active))
                return;

        bucket = &uc_rq->bucket[uc_se->bucket_id];

        SCHED_WARN_ON(!bucket->tasks);
        if (likely(bucket->tasks))
                bucket->tasks--;

        uc_se->active = false;

        /*
         * Keep "local max aggregation" simple and accept to (possibly)
         * overboost some RUNNABLE tasks in the same bucket.
         * The rq clamp bucket value is reset to its base value whenever
         * there are no more RUNNABLE tasks refcounting it.
         */
        if (likely(bucket->tasks))
                return;

        rq_clamp = READ_ONCE(uc_rq->value);
        /*
         * Defensive programming: this should never happen. If it happens,
         * e.g. due to future modification, warn and fixup the expected value.
         */
        SCHED_WARN_ON(bucket->value > rq_clamp);
        if (bucket->value >= rq_clamp) {
                bkt_clamp = uclamp_rq_max_value(rq, clamp_id, uc_se->value);
                WRITE_ONCE(uc_rq->value, bkt_clamp);
        }
}

static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
{
        enum uclamp_id clamp_id;

        /*
         * Avoid any overhead until uclamp is actually used by the userspace.
         *
         * The condition is constructed such that a NOP is generated when
         * sched_uclamp_used is disabled.
         */
        if (!static_branch_unlikely(&sched_uclamp_used))
                return;

        if (unlikely(!p->sched_class->uclamp_enabled))
                return;

        for_each_clamp_id(clamp_id)
                uclamp_rq_inc_id(rq, p, clamp_id);

        /* Reset clamp idle holding when there is one RUNNABLE task */
        if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
                rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
}

static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
{
        enum uclamp_id clamp_id;

        /*
         * Avoid any overhead until uclamp is actually used by the userspace.
         *
         * The condition is constructed such that a NOP is generated when
         * sched_uclamp_used is disabled.
         */
        if (!static_branch_unlikely(&sched_uclamp_used))
                return;

        if (unlikely(!p->sched_class->uclamp_enabled))
                return;

        for_each_clamp_id(clamp_id)
                uclamp_rq_dec_id(rq, p, clamp_id);
}

static inline void uclamp_rq_reinc_id(struct rq *rq, struct task_struct *p,
                                      enum uclamp_id clamp_id)
{
        if (!p->uclamp[clamp_id].active)
                return;

        uclamp_rq_dec_id(rq, p, clamp_id);
        uclamp_rq_inc_id(rq, p, clamp_id);

        /*
         * Make sure to clear the idle flag if we've transiently reached 0
         * active tasks on rq.
         */
        if (clamp_id == UCLAMP_MAX && (rq->uclamp_flags & UCLAMP_FLAG_IDLE))
                rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
}

static inline void
uclamp_update_active(struct task_struct *p)
{
        enum uclamp_id clamp_id;
        struct rq_flags rf;
        struct rq *rq;

        /*
         * Lock the task and the rq where the task is (or was) queued.
         *
         * We might lock the (previous) rq of a !RUNNABLE task, but that's the
         * price to pay to safely serialize util_{min,max} updates with
         * enqueues, dequeues and migration operations.
         * This is the same locking schema used by __set_cpus_allowed_ptr().
         */
        rq = task_rq_lock(p, &rf);

        /*
         * Setting the clamp bucket is serialized by task_rq_lock().
         * If the task is not yet RUNNABLE and its task_struct is not
         * affecting a valid clamp bucket, the next time it's enqueued,
         * it will already see the updated clamp bucket value.
         */
        for_each_clamp_id(clamp_id)
                uclamp_rq_reinc_id(rq, p, clamp_id);

        task_rq_unlock(rq, p, &rf);
}

#ifdef CONFIG_UCLAMP_TASK_GROUP
static inline void
uclamp_update_active_tasks(struct cgroup_subsys_state *css)
{
        struct css_task_iter it;
        struct task_struct *p;

        css_task_iter_start(css, 0, &it);
        while ((p = css_task_iter_next(&it)))
                uclamp_update_active(p);
        css_task_iter_end(&it);
}

static void cpu_util_update_eff(struct cgroup_subsys_state *css);
static void uclamp_update_root_tg(void)
{
        struct task_group *tg = &root_task_group;

        uclamp_se_set(&tg->uclamp_req[UCLAMP_MIN],
                      sysctl_sched_uclamp_util_min, false);
        uclamp_se_set(&tg->uclamp_req[UCLAMP_MAX],
                      sysctl_sched_uclamp_util_max, false);

        rcu_read_lock();
        cpu_util_update_eff(&root_task_group.css);
        rcu_read_unlock();
}
#else
static void uclamp_update_root_tg(void) { }
#endif

int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
                                void *buffer, size_t *lenp, loff_t *ppos)
{
        bool update_root_tg = false;
        int old_min, old_max, old_min_rt;
        int result;

        mutex_lock(&uclamp_mutex);
        old_min = sysctl_sched_uclamp_util_min;
        old_max = sysctl_sched_uclamp_util_max;
        old_min_rt = sysctl_sched_uclamp_util_min_rt_default;

        result = proc_dointvec(table, write, buffer, lenp, ppos);
        if (result)
                goto undo;
        if (!write)
                goto done;

        if (sysctl_sched_uclamp_util_min > sysctl_sched_uclamp_util_max ||
            sysctl_sched_uclamp_util_max > SCHED_CAPACITY_SCALE ||
            sysctl_sched_uclamp_util_min_rt_default > SCHED_CAPACITY_SCALE) {

                result = -EINVAL;
                goto undo;
        }

        if (old_min != sysctl_sched_uclamp_util_min) {
                uclamp_se_set(&uclamp_default[UCLAMP_MIN],
                              sysctl_sched_uclamp_util_min, false);
                update_root_tg = true;
        }
        if (old_max != sysctl_sched_uclamp_util_max) {
                uclamp_se_set(&uclamp_default[UCLAMP_MAX],
                              sysctl_sched_uclamp_util_max, false);
                update_root_tg = true;
        }

        if (update_root_tg) {
                static_branch_enable(&sched_uclamp_used);
                uclamp_update_root_tg();
        }

        if (old_min_rt != sysctl_sched_uclamp_util_min_rt_default) {
                static_branch_enable(&sched_uclamp_used);
                uclamp_sync_util_min_rt_default();
        }

        /*
         * We update all RUNNABLE tasks only when task groups are in use.
         * Otherwise, keep it simple and do just a lazy update at each next
         * task enqueue time.
         */

        goto done;

undo:
        sysctl_sched_uclamp_util_min = old_min;
        sysctl_sched_uclamp_util_max = old_max;
        sysctl_sched_uclamp_util_min_rt_default = old_min_rt;
done:
        mutex_unlock(&uclamp_mutex);

        return result;
}

static int uclamp_validate(struct task_struct *p,
                           const struct sched_attr *attr)
{
        int util_min = p->uclamp_req[UCLAMP_MIN].value;
        int util_max = p->uclamp_req[UCLAMP_MAX].value;

        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
                util_min = attr->sched_util_min;

                if (util_min + 1 > SCHED_CAPACITY_SCALE + 1)
                        return -EINVAL;
        }

        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) {
                util_max = attr->sched_util_max;

                if (util_max + 1 > SCHED_CAPACITY_SCALE + 1)
                        return -EINVAL;
        }

        if (util_min != -1 && util_max != -1 && util_min > util_max)
                return -EINVAL;

        /*
         * We have valid uclamp attributes; make sure uclamp is enabled.
         *
         * We need to do that here, because enabling static branches is a
         * blocking operation which obviously cannot be done while holding
         * scheduler locks.
         */
        static_branch_enable(&sched_uclamp_used);

        return 0;
}

static bool uclamp_reset(const struct sched_attr *attr,
                         enum uclamp_id clamp_id,
                         struct uclamp_se *uc_se)
{
        /* Reset on sched class change for a non user-defined clamp value. */
        if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)) &&
            !uc_se->user_defined)
                return true;

        /* Reset on sched_util_{min,max} == -1. */
        if (clamp_id == UCLAMP_MIN &&
            attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN &&
            attr->sched_util_min == -1) {
                return true;
        }

        if (clamp_id == UCLAMP_MAX &&
            attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX &&
            attr->sched_util_max == -1) {
                return true;
        }

        return false;
}

static void __setscheduler_uclamp(struct task_struct *p,
                                  const struct sched_attr *attr)
{
        enum uclamp_id clamp_id;

        for_each_clamp_id(clamp_id) {
                struct uclamp_se *uc_se = &p->uclamp_req[clamp_id];
                unsigned int value;

                if (!uclamp_reset(attr, clamp_id, uc_se))
                        continue;

                /*
                 * RT by default have a 100% boost value that could be modified
                 * at runtime.
                 */
                if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
                        value = sysctl_sched_uclamp_util_min_rt_default;
                else
                        value = uclamp_none(clamp_id);

                uclamp_se_set(uc_se, value, false);

        }

        if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
                return;

        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN &&
            attr->sched_util_min != -1) {
                uclamp_se_set(&p->uclamp_req[UCLAMP_MIN],
                              attr->sched_util_min, true);
        }

        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX &&
            attr->sched_util_max != -1) {
                uclamp_se_set(&p->uclamp_req[UCLAMP_MAX],
                              attr->sched_util_max, true);
        }
}

static void uclamp_fork(struct task_struct *p)
{
        enum uclamp_id clamp_id;

        /*
         * We don't need to hold task_rq_lock() when updating p->uclamp_* here
         * as the task is still at its early fork stages.
         */
        for_each_clamp_id(clamp_id)
                p->uclamp[clamp_id].active = false;

        if (likely(!p->sched_reset_on_fork))
                return;

        for_each_clamp_id(clamp_id) {
                uclamp_se_set(&p->uclamp_req[clamp_id],
                              uclamp_none(clamp_id), false);
        }
}

static void uclamp_post_fork(struct task_struct *p)
{
        uclamp_update_util_min_rt_default(p);
}

static void __init init_uclamp_rq(struct rq *rq)
{
        enum uclamp_id clamp_id;
        struct uclamp_rq *uc_rq = rq->uclamp;

        for_each_clamp_id(clamp_id) {
                uc_rq[clamp_id] = (struct uclamp_rq) {
                        .value = uclamp_none(clamp_id)
                };
        }

        rq->uclamp_flags = 0;
}

static void __init init_uclamp(void)
{
        struct uclamp_se uc_max = {};
        enum uclamp_id clamp_id;
        int cpu;

        for_each_possible_cpu(cpu)
                init_uclamp_rq(cpu_rq(cpu));

        for_each_clamp_id(clamp_id) {
                uclamp_se_set(&init_task.uclamp_req[clamp_id],
                              uclamp_none(clamp_id), false);
        }

        /* System defaults allow max clamp values for both indexes */
        uclamp_se_set(&uc_max, uclamp_none(UCLAMP_MAX), false);
        for_each_clamp_id(clamp_id) {
                uclamp_default[clamp_id] = uc_max;
#ifdef CONFIG_UCLAMP_TASK_GROUP
                root_task_group.uclamp_req[clamp_id] = uc_max;
                root_task_group.uclamp[clamp_id] = uc_max;
#endif
        }
}

#else /* CONFIG_UCLAMP_TASK */
static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p) { }
static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) { }
static inline int uclamp_validate(struct task_struct *p,
                                  const struct sched_attr *attr)
{
        return -EOPNOTSUPP;
}
static void __setscheduler_uclamp(struct task_struct *p,
                                  const struct sched_attr *attr) { }
static inline void uclamp_fork(struct task_struct *p) { }
static inline void uclamp_post_fork(struct task_struct *p) { }
static inline void init_uclamp(void) { }
#endif /* CONFIG_UCLAMP_TASK */

bool sched_task_on_rq(struct task_struct *p)
{
        return task_on_rq_queued(p);
}

static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
{
        if (!(flags & ENQUEUE_NOCLOCK))
                update_rq_clock(rq);

        if (!(flags & ENQUEUE_RESTORE)) {
                sched_info_enqueue(rq, p);
                psi_enqueue(p, flags & ENQUEUE_WAKEUP);
        }

        uclamp_rq_inc(rq, p);
        p->sched_class->enqueue_task(rq, p, flags);

        if (sched_core_enabled(rq))
                sched_core_enqueue(rq, p);
}

static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
{
        if (sched_core_enabled(rq))
                sched_core_dequeue(rq, p);

        if (!(flags & DEQUEUE_NOCLOCK))
                update_rq_clock(rq);

        if (!(flags & DEQUEUE_SAVE)) {
                sched_info_dequeue(rq, p);
                psi_dequeue(p, flags & DEQUEUE_SLEEP);
        }

        uclamp_rq_dec(rq, p);
        p->sched_class->dequeue_task(rq, p, flags);
}

void activate_task(struct rq *rq, struct task_struct *p, int flags)
{

        enqueue_task(rq, p, flags);

        p->on_rq = TASK_ON_RQ_QUEUED;
}

void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
{
        p->on_rq = (flags & DEQUEUE_SLEEP) ? 0 : TASK_ON_RQ_MIGRATING;

        dequeue_task(rq, p, flags);
}

static inline int __normal_prio(int policy, int rt_prio, int nice)
{
        int prio;

        if (dl_policy(policy))
                prio = MAX_DL_PRIO - 1;
        else if (rt_policy(policy))
                prio = MAX_RT_PRIO - 1 - rt_prio;
        else
                prio = NICE_TO_PRIO(nice);

        return prio;
}

/*
 * Calculate the expected normal priority: i.e. priority
 * without taking RT-inheritance into account. Might be
 * boosted by interactivity modifiers. Changes upon fork,
 * setprio syscalls, and whenever the interactivity
 * estimator recalculates.
 */
static inline int normal_prio(struct task_struct *p)
{
        return __normal_prio(p->policy, p->rt_priority, PRIO_TO_NICE(p->static_prio));
}

/*
 * Calculate the current priority, i.e. the priority
 * taken into account by the scheduler. This value might
 * be boosted by RT tasks, or might be boosted by
 * interactivity modifiers. Will be RT if the task got
 * RT-boosted. If not then it returns p->normal_prio.
 */
static int effective_prio(struct task_struct *p)
{
        p->normal_prio = normal_prio(p);
        /*
         * If we are RT tasks or we were boosted to RT priority,
         * keep the priority unchanged. Otherwise, update priority
         * to the normal priority:
         */
        if (!rt_prio(p->prio))
                return p->normal_prio;
        return p->prio;
}

/**
 * task_curr - is this task currently executing on a CPU?
 * @p: the task in question.
 *
 * Return: 1 if the task is currently executing. 0 otherwise.
 */
inline int task_curr(const struct task_struct *p)
{
        return cpu_curr(task_cpu(p)) == p;
}

/*
 * switched_from, switched_to and prio_changed must _NOT_ drop rq->lock,
 * use the balance_callback list if you want balancing.
 *
 * this means any call to check_class_changed() must be followed by a call to
 * balance_callback().
 */
static inline void check_class_changed(struct rq *rq, struct task_struct *p,
                                       const struct sched_class *prev_class,
                                       int oldprio)
{
        if (prev_class != p->sched_class) {
                if (prev_class->switched_from)
                        prev_class->switched_from(rq, p);

                p->sched_class->switched_to(rq, p);
        } else if (oldprio != p->prio || dl_task(p))
                p->sched_class->prio_changed(rq, p, oldprio);
}

void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
{
        if (p->sched_class == rq->curr->sched_class)
                rq->curr->sched_class->check_preempt_curr(rq, p, flags);
        else if (p->sched_class > rq->curr->sched_class)
                resched_curr(rq);

        /*
         * A queue event has occurred, and we're going to schedule.  In
         * this case, we can save a useless back to back clock update.
         */
        if (task_on_rq_queued(rq->curr) && test_tsk_need_resched(rq->curr))
                rq_clock_skip_update(rq);
}

#ifdef CONFIG_SMP

static void
__do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask, u32 flags);

static int __set_cpus_allowed_ptr(struct task_struct *p,
                                  const struct cpumask *new_mask,
                                  u32 flags);

static void migrate_disable_switch(struct rq *rq, struct task_struct *p)
{
        if (likely(!p->migration_disabled))
                return;

        if (p->cpus_ptr != &p->cpus_mask)
                return;

        /*
         * Violates locking rules! see comment in __do_set_cpus_allowed().
         */
        __do_set_cpus_allowed(p, cpumask_of(rq->cpu), SCA_MIGRATE_DISABLE);
}

void migrate_disable(void)
{
        struct task_struct *p = current;

        if (p->migration_disabled) {
                p->migration_disabled++;
                return;
        }

        preempt_disable();
        this_rq()->nr_pinned++;
        p->migration_disabled = 1;
        preempt_enable();
}
EXPORT_SYMBOL_GPL(migrate_disable);

void migrate_enable(void)
{
        struct task_struct *p = current;

        if (p->migration_disabled > 1) {
                p->migration_disabled--;
                return;
        }

        /*
         * Ensure stop_task runs either before or after this, and that
         * __set_cpus_allowed_ptr(SCA_MIGRATE_ENABLE) doesn't schedule().
         */
        preempt_disable();
        if (p->cpus_ptr != &p->cpus_mask)
                __set_cpus_allowed_ptr(p, &p->cpus_mask, SCA_MIGRATE_ENABLE);
        /*
         * Mustn't clear migration_disabled() until cpus_ptr points back at the
         * regular cpus_mask, otherwise things that race (eg.
         * select_fallback_rq) get confused.
         */
        barrier();
        p->migration_disabled = 0;
        this_rq()->nr_pinned--;
        preempt_enable();
}
EXPORT_SYMBOL_GPL(migrate_enable);

static inline bool rq_has_pinned_tasks(struct rq *rq)
{
        return rq->nr_pinned;
}

/*
 * Per-CPU kthreads are allowed to run on !active && online CPUs, see
 * __set_cpus_allowed_ptr() and select_fallback_rq().
 */
static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
{
        /* When not in the task's cpumask, no point in looking further. */
        if (!cpumask_test_cpu(cpu, p->cpus_ptr))
                return false;

        /* migrate_disabled() must be allowed to finish. */
        if (is_migration_disabled(p))
                return cpu_online(cpu);

        /* Non kernel threads are not allowed during either online or offline. */
        if (!(p->flags & PF_KTHREAD))
                return cpu_active(cpu) && task_cpu_possible(cpu, p);

        /* KTHREAD_IS_PER_CPU is always allowed. */
        if (kthread_is_per_cpu(p))
                return cpu_online(cpu);

        /* Regular kernel threads don't get to stay during offline. */
        if (cpu_dying(cpu))
                return false;

        /* But are allowed during online. */
        return cpu_online(cpu);
}

/*
 * This is how migration works:
 *
 * 1) we invoke migration_cpu_stop() on the target CPU using
 *    stop_one_cpu().
 * 2) stopper starts to run (implicitly forcing the migrated thread
 *    off the CPU)
 * 3) it checks whether the migrated task is still in the wrong runqueue.
 * 4) if it's in the wrong runqueue then the migration thread removes
 *    it and puts it into the right queue.
 * 5) stopper completes and stop_one_cpu() returns and the migration
 *    is done.
 */

/*
 * move_queued_task - move a queued task to new rq.
 *
 * Returns (locked) new rq. Old rq's lock is released.
 */
static struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
                                   struct task_struct *p, int new_cpu)
{
        lockdep_assert_rq_held(rq);

        deactivate_task(rq, p, DEQUEUE_NOCLOCK);
        set_task_cpu(p, new_cpu);
        rq_unlock(rq, rf);

        rq = cpu_rq(new_cpu);

        rq_lock(rq, rf);
        BUG_ON(task_cpu(p) != new_cpu);
        activate_task(rq, p, 0);
        check_preempt_curr(rq, p, 0);

        return rq;
}

struct migration_arg {
        struct task_struct              *task;
        int                             dest_cpu;
        struct set_affinity_pending     *pending;
};

/*
 * @refs: number of wait_for_completion()
 * @stop_pending: is @stop_work in use
 */
struct set_affinity_pending {
        refcount_t              refs;
        unsigned int            stop_pending;
        struct completion       done;
        struct cpu_stop_work    stop_work;
        struct migration_arg    arg;
};

/*
 * Move (not current) task off this CPU, onto the destination CPU. We're doing
 * this because either it can't run here any more (set_cpus_allowed()
 * away from this CPU, or CPU going down), or because we're
 * attempting to rebalance this task on exec (sched_exec).
 *
 * So we race with normal scheduler movements, but that's OK, as long
 * as the task is no longer on this CPU.
 */
static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
                                 struct task_struct *p, int dest_cpu)
{
        /* Affinity changed (again). */
        if (!is_cpu_allowed(p, dest_cpu))
                return rq;

        update_rq_clock(rq);
        rq = move_queued_task(rq, rf, p, dest_cpu);

        return rq;
}

/*
 * migration_cpu_stop - this will be executed by a highprio stopper thread
 * and performs thread migration by bumping thread off CPU then
 * 'pushing' onto another runqueue.
 */
static int migration_cpu_stop(void *data)
{
        struct migration_arg *arg = data;
        struct set_affinity_pending *pending = arg->pending;
        struct task_struct *p = arg->task;
        struct rq *rq = this_rq();
        bool complete = false;
        struct rq_flags rf;

        /*
         * The original target CPU might have gone down and we might
         * be on another CPU but it doesn't matter.
         */
        local_irq_save(rf.flags);
        /*
         * We need to explicitly wake pending tasks before running
         * __migrate_task() such that we will not miss enforcing cpus_ptr
         * during wakeups, see set_cpus_allowed_ptr()'s TASK_WAKING test.
         */
        flush_smp_call_function_from_idle();

        raw_spin_lock(&p->pi_lock);
        rq_lock(rq, &rf);

        /*
         * If we were passed a pending, then ->stop_pending was set, thus
         * p->migration_pending must have remained stable.
         */
        WARN_ON_ONCE(pending && pending != p->migration_pending);

        /*
         * If task_rq(p) != rq, it cannot be migrated here, because we're
         * holding rq->lock, if p->on_rq == 0 it cannot get enqueued because
         * we're holding p->pi_lock.
         */
        if (task_rq(p) == rq) {
                if (is_migration_disabled(p))
                        goto out;

                if (pending) {
                        p->migration_pending = NULL;
                        complete = true;

                        if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask))
                                goto out;
                }

                if (task_on_rq_queued(p))
                        rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
                else
                        p->wake_cpu = arg->dest_cpu;

                /*
                 * XXX __migrate_task() can fail, at which point we might end
                 * up running on a dodgy CPU, AFAICT this can only happen
                 * during CPU hotplug, at which point we'll get pushed out
                 * anyway, so it's probably not a big deal.
                 */

        } else if (pending) {
                /*
                 * This happens when we get migrated between migrate_enable()'s
                 * preempt_enable() and scheduling the stopper task. At that
                 * point we're a regular task again and not current anymore.
                 *
                 * A !PREEMPT kernel has a giant hole here, which makes it far
                 * more likely.
                 */

                /*
                 * The task moved before the stopper got to run. We're holding
                 * ->pi_lock, so the allowed mask is stable - if it got
                 * somewhere allowed, we're done.
                 */
                if (cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) {
                        p->migration_pending = NULL;
                        complete = true;
                        goto out;
                }

                /*
                 * When migrate_enable() hits a rq mis-match we can't reliably
                 * determine is_migration_disabled() and so have to chase after
                 * it.
                 */
                WARN_ON_ONCE(!pending->stop_pending);
                task_rq_unlock(rq, p, &rf);
                stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop,
                                    &pending->arg, &pending->stop_work);
                return 0;
        }
out:
        if (pending)
                pending->stop_pending = false;
        task_rq_unlock(rq, p, &rf);

        if (complete)
                complete_all(&pending->done);

        return 0;
}

int push_cpu_stop(void *arg)
{
        struct rq *lowest_rq = NULL, *rq = this_rq();
        struct task_struct *p = arg;

        raw_spin_lock_irq(&p->pi_lock);
        raw_spin_rq_lock(rq);

        if (task_rq(p) != rq)
                goto out_unlock;

        if (is_migration_disabled(p)) {
                p->migration_flags |= MDF_PUSH;
                goto out_unlock;
        }

        p->migration_flags &= ~MDF_PUSH;

        if (p->sched_class->find_lock_rq)
                lowest_rq = p->sched_class->find_lock_rq(p, rq);

        if (!lowest_rq)
                goto out_unlock;

        // XXX validate p is still the highest prio task
        if (task_rq(p) == rq) {
                deactivate_task(rq, p, 0);
                set_task_cpu(p, lowest_rq->cpu);
                activate_task(lowest_rq, p, 0);
                resched_curr(lowest_rq);
        }

        double_unlock_balance(rq, lowest_rq);

out_unlock:
        rq->push_busy = false;
        raw_spin_rq_unlock(rq);
        raw_spin_unlock_irq(&p->pi_lock);

        put_task_struct(p);
        return 0;
}

/*
 * sched_class::set_cpus_allowed must do the below, but is not required to
 * actually call this function.
 */
void set_cpus_allowed_common(struct task_struct *p, const struct cpumask *new_mask, u32 flags)
{
        if (flags & (SCA_MIGRATE_ENABLE | SCA_MIGRATE_DISABLE)) {
                p->cpus_ptr = new_mask;
                return;
        }

        cpumask_copy(&p->cpus_mask, new_mask);
        p->nr_cpus_allowed = cpumask_weight(new_mask);
}

static void
__do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask, u32 flags)
{
        struct rq *rq = task_rq(p);
        bool queued, running;

        /*
         * This here violates the locking rules for affinity, since we're only
         * supposed to change these variables while holding both rq->lock and
         * p->pi_lock.
         *
         * HOWEVER, it magically works, because ttwu() is the only code that
         * accesses these variables under p->pi_lock and only does so after
         * smp_cond_load_acquire(&p->on_cpu, !VAL), and we're in __schedule()
         * before finish_task().
         *
         * XXX do further audits, this smells like something putrid.
         */
        if (flags & SCA_MIGRATE_DISABLE)
                SCHED_WARN_ON(!p->on_cpu);
        else
                lockdep_assert_held(&p->pi_lock);

        queued = task_on_rq_queued(p);
        running = task_current(rq, p);

        if (queued) {
                /*
                 * Because __kthread_bind() calls this on blocked tasks without
                 * holding rq->lock.
                 */
                lockdep_assert_rq_held(rq);
                dequeue_task(rq, p, DEQUEUE_SAVE | DEQUEUE_NOCLOCK);
        }
        if (running)
                put_prev_task(rq, p);

        p->sched_class->set_cpus_allowed(p, new_mask, flags);

        if (queued)
                enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
        if (running)
                set_next_task(rq, p);
}

void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
{
        __do_set_cpus_allowed(p, new_mask, 0);
}

int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
                      int node)
{
        if (!src->user_cpus_ptr)
                return 0;

        dst->user_cpus_ptr = kmalloc_node(cpumask_size(), GFP_KERNEL, node);
        if (!dst->user_cpus_ptr)
                return -ENOMEM;

        cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr);
        return 0;
}

static inline struct cpumask *clear_user_cpus_ptr(struct task_struct *p)
{
        struct cpumask *user_mask = NULL;

        swap(p->user_cpus_ptr, user_mask);

        return user_mask;
}

void release_user_cpus_ptr(struct task_struct *p)
{
        kfree(clear_user_cpus_ptr(p));
}

/*
 * This function is wildly self concurrent; here be dragons.
 *
 *
 * When given a valid mask, __set_cpus_allowed_ptr() must block until the
 * designated task is enqueued on an allowed CPU. If that task is currently
 * running, we have to kick it out using the CPU stopper.
 *
 * Migrate-Disable comes along and tramples all over our nice sandcastle.
 * Consider:
 *
 *     Initial conditions: P0->cpus_mask = [0, 1]
 *
 *     P0@CPU0                  P1
 *
 *     migrate_disable();
 *     <preempted>
 *                              set_cpus_allowed_ptr(P0, [1]);
 *
 * P1 *cannot* return from this set_cpus_allowed_ptr() call until P0 executes
 * its outermost migrate_enable() (i.e. it exits its Migrate-Disable region).
 * This means we need the following scheme:
 *
 *     P0@CPU0                  P1
 *
 *     migrate_disable();
 *     <preempted>
 *                              set_cpus_allowed_ptr(P0, [1]);
 *                                <blocks>
 *     <resumes>
 *     migrate_enable();
 *       __set_cpus_allowed_ptr();
 *       <wakes local stopper>
 *                         `--> <woken on migration completion>
 *
 * Now the fun stuff: there may be several P1-like tasks, i.e. multiple
 * concurrent set_cpus_allowed_ptr(P0, [*]) calls. CPU affinity changes of any
 * task p are serialized by p->pi_lock, which we can leverage: the one that
 * should come into effect at the end of the Migrate-Disable region is the last
 * one. This means we only need to track a single cpumask (i.e. p->cpus_mask),
 * but we still need to properly signal those waiting tasks at the appropriate
 * moment.
 *
 * This is implemented using struct set_affinity_pending. The first
 * __set_cpus_allowed_ptr() caller within a given Migrate-Disable region will
 * setup an instance of that struct and install it on the targeted task_struct.
 * Any and all further callers will reuse that instance. Those then wait for
 * a completion signaled at the tail of the CPU stopper callback (1), triggered
 * on the end of the Migrate-Disable region (i.e. outermost migrate_enable()).
 *
 *
 * (1) In the cases covered above. There is one more where the completion is
 * signaled within affine_move_task() itself: when a subsequent affinity request
 * occurs after the stopper bailed out due to the targeted task still being
 * Migrate-Disable. Consider:
 *
 *     Initial conditions: P0->cpus_mask = [0, 1]
 *
 *     CPU0               P1                            P2
 *     <P0>
 *       migrate_disable();
 *       <preempted>
 *                        set_cpus_allowed_ptr(P0, [1]);
 *                          <blocks>
 *     <migration/0>
 *       migration_cpu_stop()
 *         is_migration_disabled()
 *           <bails>
 *                                                       set_cpus_allowed_ptr(P0, [0, 1]);
 *                                                         <signal completion>
 *                          <awakes>
 *
 * Note that the above is safe vs a concurrent migrate_enable(), as any
 * pending affinity completion is preceded by an uninstallation of
 * p->migration_pending done with p->pi_lock held.
 */
static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flags *rf,
                            int dest_cpu, unsigned int flags)
{
        struct set_affinity_pending my_pending = { }, *pending = NULL;
        bool stop_pending, complete = false;

        /* Can the task run on the task's current CPU? If so, we're done */
        if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) {
                struct task_struct *push_task = NULL;

                if ((flags & SCA_MIGRATE_ENABLE) &&
                    (p->migration_flags & MDF_PUSH) && !rq->push_busy) {
                        rq->push_busy = true;
                        push_task = get_task_struct(p);
                }

                /*
                 * If there are pending waiters, but no pending stop_work,
                 * then complete now.
                 */
                pending = p->migration_pending;
                if (pending && !pending->stop_pending) {
                        p->migration_pending = NULL;
                        complete = true;
                }

                task_rq_unlock(rq, p, rf);

                if (push_task) {
                        stop_one_cpu_nowait(rq->cpu, push_cpu_stop,
                                            p, &rq->push_work);
                }

                if (complete)
                        complete_all(&pending->done);

                return 0;
        }

        if (!(flags & SCA_MIGRATE_ENABLE)) {
                /* serialized by p->pi_lock */
                if (!p->migration_pending) {
                        /* Install the request */
                        refcount_set(&my_pending.refs, 1);
                        init_completion(&my_pending.done);
                        my_pending.arg = (struct migration_arg) {
                                .task = p,
                                .dest_cpu = dest_cpu,
                                .pending = &my_pending,
                        };

                        p->migration_pending = &my_pending;
                } else {
                        pending = p->migration_pending;
                        refcount_inc(&pending->refs);
                        /*
                         * Affinity has changed, but we've already installed a
                         * pending. migration_cpu_stop() *must* see this, else
                         * we risk a completion of the pending despite having a
                         * task on a disallowed CPU.
                         *
                         * Serialized by p->pi_lock, so this is safe.
                         */
                        pending->arg.dest_cpu = dest_cpu;
                }
        }
        pending = p->migration_pending;
        /*
         * - !MIGRATE_ENABLE:
         *   we'll have installed a pending if there wasn't one already.
         *
         * - MIGRATE_ENABLE:
         *   we're here because the current CPU isn't matching anymore,
         *   the only way that can happen is because of a concurrent
         *   set_cpus_allowed_ptr() call, which should then still be
         *   pending completion.
         *
         * Either way, we really should have a @pending here.
         */
        if (WARN_ON_ONCE(!pending)) {
                task_rq_unlock(rq, p, rf);
                return -EINVAL;
        }

        if (task_running(rq, p) || READ_ONCE(p->__state) == TASK_WAKING) {
                /*
                 * MIGRATE_ENABLE gets here because 'p == current', but for
                 * anything else we cannot do is_migration_disabled(), punt
                 * and have the stopper function handle it all race-free.
                 */
                stop_pending = pending->stop_pending;
                if (!stop_pending)
                        pending->stop_pending = true;

                if (flags & SCA_MIGRATE_ENABLE)
                        p->migration_flags &= ~MDF_PUSH;

                task_rq_unlock(rq, p, rf);

                if (!stop_pending) {
                        stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,
                                            &pending->arg, &pending->stop_work);
                }

                if (flags & SCA_MIGRATE_ENABLE)
                        return 0;
        } else {

                if (!is_migration_disabled(p)) {
                        if (task_on_rq_queued(p))
                                rq = move_queued_task(rq, rf, p, dest_cpu);

                        if (!pending->stop_pending) {
                                p->migration_pending = NULL;
                                complete = true;
                        }
                }
                task_rq_unlock(rq, p, rf);

                if (complete)
                        complete_all(&pending->done);
        }

        wait_for_completion(&pending->done);

        if (refcount_dec_and_test(&pending->refs))
                wake_up_var(&pending->refs); /* No UaF, just an address */

        /*
         * Block the original owner of &pending until all subsequent callers
         * have seen the completion and decremented the refcount
         */
        wait_var_event(&my_pending.refs, !refcount_read(&my_pending.refs));

        /* ARGH */
        WARN_ON_ONCE(my_pending.stop_pending);

        return 0;
}

/*
 * Called with both p->pi_lock and rq->lock held; drops both before returning.
 */
static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
                                         const struct cpumask *new_mask,
                                         u32 flags,
                                         struct rq *rq,
                                         struct rq_flags *rf)
        __releases(rq->lock)
        __releases(p->pi_lock)
{
        const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);
        const struct cpumask *cpu_valid_mask = cpu_active_mask;
        bool kthread = p->flags & PF_KTHREAD;
        struct cpumask *user_mask = NULL;
        unsigned int dest_cpu;
        int ret = 0;

        update_rq_clock(rq);

        if (kthread || is_migration_disabled(p)) {
                /*
                 * Kernel threads are allowed on online && !active CPUs,
                 * however, during cpu-hot-unplug, even these might get pushed
                 * away if not KTHREAD_IS_PER_CPU.
                 *
                 * Specifically, migration_disabled() tasks must not fail the
                 * cpumask_any_and_distribute() pick below, esp. so on
                 * SCA_MIGRATE_ENABLE, otherwise we'll not call
                 * set_cpus_allowed_common() and actually reset p->cpus_ptr.
                 */
                cpu_valid_mask = cpu_online_mask;
        }

        if (!kthread && !cpumask_subset(new_mask, cpu_allowed_mask)) {
                ret = -EINVAL;
                goto out;
        }

        /*
         * Must re-check here, to close a race against __kthread_bind(),
         * sched_setaffinity() is not guaranteed to observe the flag.
         */
        if ((flags & SCA_CHECK) && (p->flags & PF_NO_SETAFFINITY)) {
                ret = -EINVAL;
                goto out;
        }

        if (!(flags & SCA_MIGRATE_ENABLE)) {
                if (cpumask_equal(&p->cpus_mask, new_mask))
                        goto out;

                if (WARN_ON_ONCE(p == current &&
                                 is_migration_disabled(p) &&
                                 !cpumask_test_cpu(task_cpu(p), new_mask))) {
                        ret = -EBUSY;
                        goto out;
                }
        }

        /*
         * Picking a ~random cpu helps in cases where we are changing affinity
         * for groups of tasks (ie. cpuset), so that load balancing is not
         * immediately required to distribute the tasks within their new mask.
         */
        dest_cpu = cpumask_any_and_distribute(cpu_valid_mask, new_mask);
        if (dest_cpu >= nr_cpu_ids) {
                ret = -EINVAL;
                goto out;
        }

        __do_set_cpus_allowed(p, new_mask, flags);

        if (flags & SCA_USER)
                user_mask = clear_user_cpus_ptr(p);

        ret = affine_move_task(rq, p, rf, dest_cpu, flags);

        kfree(user_mask);

        return ret;

out:
        task_rq_unlock(rq, p, rf);

        return ret;
}

/*
 * Change a given task's CPU affinity. Migrate the thread to a
 * proper CPU and schedule it away if the CPU it's executing on
 * is removed from the allowed bitmask.
 *
 * NOTE: the caller must have a valid reference to the task, the
 * task must not exit() & deallocate itself prematurely. The
 * call is not atomic; no spinlocks may be held.
 */
static int __set_cpus_allowed_ptr(struct task_struct *p,
                                  const struct cpumask *new_mask, u32 flags)
{
        struct rq_flags rf;
        struct rq *rq;

        rq = task_rq_lock(p, &rf);
        return __set_cpus_allowed_ptr_locked(p, new_mask, flags, rq, &rf);
}

int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
{
        return __set_cpus_allowed_ptr(p, new_mask, 0);
}
EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);

/*
 * Change a given task's CPU affinity to the intersection of its current
 * affinity mask and @subset_mask, writing the resulting mask to @new_mask
 * and pointing @p->user_cpus_ptr to a copy of the old mask.
 * If the resulting mask is empty, leave the affinity unchanged and return
 * -EINVAL.
 */
static int restrict_cpus_allowed_ptr(struct task_struct *p,
                                     struct cpumask *new_mask,
                                     const struct cpumask *subset_mask)
{
        struct cpumask *user_mask = NULL;
        struct rq_flags rf;
        struct rq *rq;
        int err;

        if (!p->user_cpus_ptr) {
                user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
                if (!user_mask)
                        return -ENOMEM;
        }

        rq = task_rq_lock(p, &rf);

        /*
         * Forcefully restricting the affinity of a deadline task is
         * likely to cause problems, so fail and noisily override the
         * mask entirely.
         */
        if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
                err = -EPERM;
                goto err_unlock;
        }

        if (!cpumask_and(new_mask, &p->cpus_mask, subset_mask)) {
                err = -EINVAL;
                goto err_unlock;
        }

        /*
         * We're about to butcher the task affinity, so keep track of what
         * the user asked for in case we're able to restore it later on.
         */
        if (user_mask) {
                cpumask_copy(user_mask, p->cpus_ptr);
                p->user_cpus_ptr = user_mask;
        }

        return __set_cpus_allowed_ptr_locked(p, new_mask, 0, rq, &rf);

err_unlock:
        task_rq_unlock(rq, p, &rf);
        kfree(user_mask);
        return err;
}

/*
 * Restrict the CPU affinity of task @p so that it is a subset of
 * task_cpu_possible_mask() and point @p->user_cpu_ptr to a copy of the
 * old affinity mask. If the resulting mask is empty, we warn and walk
 * up the cpuset hierarchy until we find a suitable mask.
 */
void force_compatible_cpus_allowed_ptr(struct task_struct *p)
{
        cpumask_var_t new_mask;
        const struct cpumask *override_mask = task_cpu_possible_mask(p);

        alloc_cpumask_var(&new_mask, GFP_KERNEL);

        /*
         * __migrate_task() can fail silently in the face of concurrent
         * offlining of the chosen destination CPU, so take the hotplug
         * lock to ensure that the migration succeeds.
         */
        cpus_read_lock();
        if (!cpumask_available(new_mask))
                goto out_set_mask;

        if (!restrict_cpus_allowed_ptr(p, new_mask, override_mask))
                goto out_free_mask;

        /*
         * We failed to find a valid subset of the affinity mask for the
         * task, so override it based on its cpuset hierarchy.
         */
        cpuset_cpus_allowed(p, new_mask);
        override_mask = new_mask;

out_set_mask:
        if (printk_ratelimit()) {
                printk_deferred("Overriding affinity for process %d (%s) to CPUs %*pbl\n",
                                task_pid_nr(p), p->comm,
                                cpumask_pr_args(override_mask));
        }

        WARN_ON(set_cpus_allowed_ptr(p, override_mask));
out_free_mask:
        cpus_read_unlock();
        free_cpumask_var(new_mask);
}

static int
__sched_setaffinity(struct task_struct *p, const struct cpumask *mask);

/*
 * Restore the affinity of a task @p which was previously restricted by a
 * call to force_compatible_cpus_allowed_ptr(). This will clear (and free)
 * @p->user_cpus_ptr.
 *
 * It is the caller's responsibility to serialise this with any calls to
 * force_compatible_cpus_allowed_ptr(@p).
 */
void relax_compatible_cpus_allowed_ptr(struct task_struct *p)
{
        struct cpumask *user_mask = p->user_cpus_ptr;
        unsigned long flags;

        /*
         * Try to restore the old affinity mask. If this fails, then
         * we free the mask explicitly to avoid it being inherited across
         * a subsequent fork().
         */
        if (!user_mask || !__sched_setaffinity(p, user_mask))
                return;

        raw_spin_lock_irqsave(&p->pi_lock, flags);
        user_mask = clear_user_cpus_ptr(p);
        raw_spin_unlock_irqrestore(&p->pi_lock, flags);

        kfree(user_mask);
}

void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
{
#ifdef CONFIG_SCHED_DEBUG
        unsigned int state = READ_ONCE(p->__state);

        /*
         * We should never call set_task_cpu() on a blocked task,
         * ttwu() will sort out the placement.
         */
        WARN_ON_ONCE(state != TASK_RUNNING && state != TASK_WAKING && !p->on_rq);

        /*

         * Migrating fair class task must have p->on_rq = TASK_ON_RQ_MIGRATING,
         * because schedstat_wait_{start,end} rebase migrating task's wait_start
         * time relying on p->on_rq.
         */
        WARN_ON_ONCE(state == TASK_RUNNING &&
                     p->sched_class == &fair_sched_class &&
                     (p->on_rq && !task_on_rq_migrating(p)));

#ifdef CONFIG_LOCKDEP
        /*
         * The caller should hold either p->pi_lock or rq->lock, when changing
         * a task's CPU. ->pi_lock for waking tasks, rq->lock for runnable tasks.
         *
         * sched_move_task() holds both and thus holding either pins the cgroup,
         * see task_group().
         *
         * Furthermore, all task_rq users should acquire both locks, see
         * task_rq_lock().
         */
        WARN_ON_ONCE(debug_locks && !(lockdep_is_held(&p->pi_lock) ||
                                      lockdep_is_held(__rq_lockp(task_rq(p)))));
#endif
        /*
         * Clearly, migrating tasks to offline CPUs is a fairly daft thing.
         */
        WARN_ON_ONCE(!cpu_online(new_cpu));

        WARN_ON_ONCE(is_migration_disabled(p));
#endif

        trace_sched_migrate_task(p, new_cpu);

        if (task_cpu(p) != new_cpu) {
                if (p->sched_class->migrate_task_rq)
                        p->sched_class->migrate_task_rq(p, new_cpu);
                p->se.nr_migrations++;
                rseq_migrate(p);
                perf_event_task_migrate(p);
        }

        __set_task_cpu(p, new_cpu);
}

#ifdef CONFIG_NUMA_BALANCING
static void __migrate_swap_task(struct task_struct *p, int cpu)
{
        if (task_on_rq_queued(p)) {
                struct rq *src_rq, *dst_rq;
                struct rq_flags srf, drf;

                src_rq = task_rq(p);
                dst_rq = cpu_rq(cpu);

                rq_pin_lock(src_rq, &srf);
                rq_pin_lock(dst_rq, &drf);

                deactivate_task(src_rq, p, 0);
                set_task_cpu(p, cpu);
                activate_task(dst_rq, p, 0);
                check_preempt_curr(dst_rq, p, 0);

                rq_unpin_lock(dst_rq, &drf);
                rq_unpin_lock(src_rq, &srf);

        } else {
                /*
                 * Task isn't running anymore; make it appear like we migrated
                 * it before it went to sleep. This means on wakeup we make the
                 * previous CPU our target instead of where it really is.
                 */
                p->wake_cpu = cpu;
        }
}

struct migration_swap_arg {
        struct task_struct *src_task, *dst_task;
        int src_cpu, dst_cpu;
};

static int migrate_swap_stop(void *data)
{
        struct migration_swap_arg *arg = data;
        struct rq *src_rq, *dst_rq;
        int ret = -EAGAIN;

        if (!cpu_active(arg->src_cpu) || !cpu_active(arg->dst_cpu))
                return -EAGAIN;

        src_rq = cpu_rq(arg->src_cpu);
        dst_rq = cpu_rq(arg->dst_cpu);

        double_raw_lock(&arg->src_task->pi_lock,
                        &arg->dst_task->pi_lock);
        double_rq_lock(src_rq, dst_rq);

        if (task_cpu(arg->dst_task) != arg->dst_cpu)
                goto unlock;

        if (task_cpu(arg->src_task) != arg->src_cpu)
                goto unlock;

        if (!cpumask_test_cpu(arg->dst_cpu, arg->src_task->cpus_ptr))
                goto unlock;

        if (!cpumask_test_cpu(arg->src_cpu, arg->dst_task->cpus_ptr))
                goto unlock;

        __migrate_swap_task(arg->src_task, arg->dst_cpu);
        __migrate_swap_task(arg->dst_task, arg->src_cpu);

        ret = 0;

unlock:
        double_rq_unlock(src_rq, dst_rq);
        raw_spin_unlock(&arg->dst_task->pi_lock);
        raw_spin_unlock(&arg->src_task->pi_lock);

        return ret;
}

/*
 * Cross migrate two tasks
 */
int migrate_swap(struct task_struct *cur, struct task_struct *p,
                int target_cpu, int curr_cpu)
{
        struct migration_swap_arg arg;
        int ret = -EINVAL;

        arg = (struct migration_swap_arg){
                .src_task = cur,
                .src_cpu = curr_cpu,
                .dst_task = p,
                .dst_cpu = target_cpu,
        };

        if (arg.src_cpu == arg.dst_cpu)
                goto out;

        /*
         * These three tests are all lockless; this is OK since all of them
         * will be re-checked with proper locks held further down the line.
         */
        if (!cpu_active(arg.src_cpu) || !cpu_active(arg.dst_cpu))
                goto out;

        if (!cpumask_test_cpu(arg.dst_cpu, arg.src_task->cpus_ptr))
                goto out;

        if (!cpumask_test_cpu(arg.src_cpu, arg.dst_task->cpus_ptr))
                goto out;

        trace_sched_swap_numa(cur, arg.src_cpu, p, arg.dst_cpu);
        ret = stop_two_cpus(arg.dst_cpu, arg.src_cpu, migrate_swap_stop, &arg);

out:
        return ret;
}
#endif /* CONFIG_NUMA_BALANCING */

/*
 * wait_task_inactive - wait for a thread to unschedule.
 *
 * If @match_state is nonzero, it's the @p->state value just checked and
 * not expected to change.  If it changes, i.e. @p might have woken up,
 * then return zero.  When we succeed in waiting for @p to be off its CPU,
 * we return a positive number (its total switch count).  If a second call
 * a short while later returns the same number, the caller can be sure that
 * @p has remained unscheduled the whole time.
 *
 * The caller must ensure that the task *will* unschedule sometime soon,
 * else this function might spin for a *long* time. This function can't
 * be called with interrupts off, or it may introduce deadlock with
 * smp_call_function() if an IPI is sent by the same process we are
 * waiting to become inactive.
 */
unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state)
{
        int running, queued;
        struct rq_flags rf;
        unsigned long ncsw;
        struct rq *rq;

        for (;;) {
                /*
                 * We do the initial early heuristics without holding
                 * any task-queue locks at all. We'll only try to get
                 * the runqueue lock when things look like they will
                 * work out!
                 */
                rq = task_rq(p);

                /*
                 * If the task is actively running on another CPU
                 * still, just relax and busy-wait without holding
                 * any locks.
                 *
                 * NOTE! Since we don't hold any locks, it's not
                 * even sure that "rq" stays as the right runqueue!
                 * But we don't care, since "task_running()" will
                 * return false if the runqueue has changed and p
                 * is actually now running somewhere else!
                 */
                while (task_running(rq, p)) {
                        if (match_state && unlikely(READ_ONCE(p->__state) != match_state))
                                return 0;
                        cpu_relax();
                }

                /*
                 * Ok, time to look more closely! We need the rq
                 * lock now, to be *sure*. If we're wrong, we'll
                 * just go back and repeat.
                 */
                rq = task_rq_lock(p, &rf);
                trace_sched_wait_task(p);
                running = task_running(rq, p);
                queued = task_on_rq_queued(p);
                ncsw = 0;
                if (!match_state || READ_ONCE(p->__state) == match_state)
                        ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
                task_rq_unlock(rq, p, &rf);

                /*
                 * If it changed from the expected state, bail out now.
                 */
                if (unlikely(!ncsw))
                        break;

                /*
                 * Was it really running after all now that we
                 * checked with the proper locks actually held?
                 *
                 * Oops. Go back and try again..
                 */
                if (unlikely(running)) {
                        cpu_relax();
                        continue;
                }

                /*
                 * It's not enough that it's not actively running,
                 * it must be off the runqueue _entirely_, and not
                 * preempted!
                 *
                 * So if it was still runnable (but just not actively
                 * running right now), it's preempted, and we should
                 * yield - it could be a while.
                 */
                if (unlikely(queued)) {
                        ktime_t to = NSEC_PER_SEC / HZ;

                        set_current_state(TASK_UNINTERRUPTIBLE);
                        schedule_hrtimeout(&to, HRTIMER_MODE_REL);
                        continue;
                }

                /*
                 * Ahh, all good. It wasn't running, and it wasn't
                 * runnable, which means that it will never become
                 * running in the future either. We're all done!
                 */
                break;
        }

        return ncsw;
}

/***
 * kick_process - kick a running thread to enter/exit the kernel
 * @p: the to-be-kicked thread
 *
 * Cause a process which is running on another CPU to enter
 * kernel-mode, without any delay. (to get signals handled.)
 *
 * NOTE: this function doesn't have to take the runqueue lock,
 * because all it wants to ensure is that the remote task enters
 * the kernel. If the IPI races and the task has been migrated
 * to another CPU then no harm is done and the purpose has been
 * achieved as well.
 */
void kick_process(struct task_struct *p)
{
        int cpu;

        preempt_disable();
        cpu = task_cpu(p);
        if ((cpu != smp_processor_id()) && task_curr(p))
                smp_send_reschedule(cpu);
        preempt_enable();
}
EXPORT_SYMBOL_GPL(kick_process);

/*
 * ->cpus_ptr is protected by both rq->lock and p->pi_lock
 *
 * A few notes on cpu_active vs cpu_online:
 *
 *  - cpu_active must be a subset of cpu_online
 *
 *  - on CPU-up we allow per-CPU kthreads on the online && !active CPU,
 *    see __set_cpus_allowed_ptr(). At this point the newly online
 *    CPU isn't yet part of the sched domains, and balancing will not
 *    see it.
 *
 *  - on CPU-down we clear cpu_active() to mask the sched domains and
 *    avoid the load balancer to place new tasks on the to be removed
 *    CPU. Existing tasks will remain running there and will be taken
 *    off.
 *
 * This means that fallback selection must not select !active CPUs.
 * And can assume that any active CPU must be online. Conversely
 * select_task_rq() below may allow selection of !active CPUs in order
 * to satisfy the above rules.
 */
static int select_fallback_rq(int cpu, struct task_struct *p)
{
        int nid = cpu_to_node(cpu);
        const struct cpumask *nodemask = NULL;
        enum { cpuset, possible, fail } state = cpuset;
        int dest_cpu;

        /*
         * If the node that the CPU is on has been offlined, cpu_to_node()
         * will return -1. There is no CPU on the node, and we should
         * select the CPU on the other node.
         */
        if (nid != -1) {
                nodemask = cpumask_of_node(nid);

                /* Look for allowed, online CPU in same node. */
                for_each_cpu(dest_cpu, nodemask) {
                        if (is_cpu_allowed(p, dest_cpu))
                                return dest_cpu;
                }
        }

        for (;;) {
                /* Any allowed, online CPU? */
                for_each_cpu(dest_cpu, p->cpus_ptr) {
                        if (!is_cpu_allowed(p, dest_cpu))
                                continue;

                        goto out;
                }

                /* No more Mr. Nice Guy. */
                switch (state) {
                case cpuset:
                        if (cpuset_cpus_allowed_fallback(p)) {
                                state = possible;
                                break;
                        }
                        fallthrough;
                case possible:
                        /*
                         * XXX When called from select_task_rq() we only
                         * hold p->pi_lock and again violate locking order.
                         *
                         * More yuck to audit.
                         */
                        do_set_cpus_allowed(p, task_cpu_possible_mask(p));
                        state = fail;
                        break;
                case fail:
                        BUG();
                        break;
                }
        }

out:
        if (state != cpuset) {
                /*
                 * Don't tell them about moving exiting tasks or
                 * kernel threads (both mm NULL), since they never
                 * leave kernel.
                 */
                if (p->mm && printk_ratelimit()) {
                        printk_deferred("process %d (%s) no longer affine to cpu%d\n",
                                        task_pid_nr(p), p->comm, cpu);
                }
        }

        return dest_cpu;
}

/*
 * The caller (fork, wakeup) owns p->pi_lock, ->cpus_ptr is stable.
 */
static inline
int select_task_rq(struct task_struct *p, int cpu, int wake_flags)
{
        lockdep_assert_held(&p->pi_lock);

        if (p->nr_cpus_allowed > 1 && !is_migration_disabled(p))
                cpu = p->sched_class->select_task_rq(p, cpu, wake_flags);
        else
                cpu = cpumask_any(p->cpus_ptr);

        /*
         * In order not to call set_task_cpu() on a blocking task we need
         * to rely on ttwu() to place the task on a valid ->cpus_ptr
         * CPU.
         *
         * Since this is common to all placement strategies, this lives here.
         *
         * [ this allows ->select_task() to simply return task_cpu(p) and
         *   not worry about this generic constraint ]
         */
        if (unlikely(!is_cpu_allowed(p, cpu)))
                cpu = select_fallback_rq(task_cpu(p), p);

        return cpu;
}

void sched_set_stop_task(int cpu, struct task_struct *stop)
{
        static struct lock_class_key stop_pi_lock;
        struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
        struct task_struct *old_stop = cpu_rq(cpu)->stop;

        if (stop) {
                /*
                 * Make it appear like a SCHED_FIFO task, its something
                 * userspace knows about and won't get confused about.
                 *
                 * Also, it will make PI more or less work without too
                 * much confusion -- but then, stop work should not
                 * rely on PI working anyway.
                 */
                sched_setscheduler_nocheck(stop, SCHED_FIFO, &param);

                stop->sched_class = &stop_sched_class;

                /*
                 * The PI code calls rt_mutex_setprio() with ->pi_lock held to
                 * adjust the effective priority of a task. As a result,
                 * rt_mutex_setprio() can trigger (RT) balancing operations,
                 * which can then trigger wakeups of the stop thread to push
                 * around the current task.
                 *
                 * The stop task itself will never be part of the PI-chain, it
                 * never blocks, therefore that ->pi_lock recursion is safe.
                 * Tell lockdep about this by placing the stop->pi_lock in its
                 * own class.
                 */
                lockdep_set_class(&stop->pi_lock, &stop_pi_lock);
        }

        cpu_rq(cpu)->stop = stop;

        if (old_stop) {
                /*
                 * Reset it back to a normal scheduling class so that
                 * it can die in pieces.
                 */
                old_stop->sched_class = &rt_sched_class;
        }
}

#else /* CONFIG_SMP */

static inline int __set_cpus_allowed_ptr(struct task_struct *p,
                                         const struct cpumask *new_mask,
                                         u32 flags)
{
        return set_cpus_allowed_ptr(p, new_mask);
}

static inline void migrate_disable_switch(struct rq *rq, struct task_struct *p) { }

static inline bool rq_has_pinned_tasks(struct rq *rq)
{
        return false;
}

#endif /* !CONFIG_SMP */

static void
ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
{
        struct rq *rq;

        if (!schedstat_enabled())
                return;

        rq = this_rq();

#ifdef CONFIG_SMP
        if (cpu == rq->cpu) {
                __schedstat_inc(rq->ttwu_local);
                __schedstat_inc(p->se.statistics.nr_wakeups_local);
        } else {
                struct sched_domain *sd;

                __schedstat_inc(p->se.statistics.nr_wakeups_remote);
                rcu_read_lock();
                for_each_domain(rq->cpu, sd) {
                        if (cpumask_test_cpu(cpu, sched_domain_span(sd))) {
                                __schedstat_inc(sd->ttwu_wake_remote);
                                break;
                        }
                }
                rcu_read_unlock();
        }

        if (wake_flags & WF_MIGRATED)
                __schedstat_inc(p->se.statistics.nr_wakeups_migrate);
#endif /* CONFIG_SMP */

        __schedstat_inc(rq->ttwu_count);
        __schedstat_inc(p->se.statistics.nr_wakeups);

        if (wake_flags & WF_SYNC)
                __schedstat_inc(p->se.statistics.nr_wakeups_sync);
}

/*
 * Mark the task runnable and perform wakeup-preemption.
 */
static void ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags,
                           struct rq_flags *rf)
{
        check_preempt_curr(rq, p, wake_flags);
        WRITE_ONCE(p->__state, TASK_RUNNING);
        trace_sched_wakeup(p);

#ifdef CONFIG_SMP
        if (p->sched_class->task_woken) {
                /*
                 * Our task @p is fully woken up and running; so it's safe to
                 * drop the rq->lock, hereafter rq is only used for statistics.
                 */
                rq_unpin_lock(rq, rf);
                p->sched_class->task_woken(rq, p);
                rq_repin_lock(rq, rf);
        }

        if (rq->idle_stamp) {
                u64 delta = rq_clock(rq) - rq->idle_stamp;
                u64 max = 2*rq->max_idle_balance_cost;

                update_avg(&rq->avg_idle, delta);

                if (rq->avg_idle > max)
                        rq->avg_idle = max;

                rq->wake_stamp = jiffies;
                rq->wake_avg_idle = rq->avg_idle / 2;

                rq->idle_stamp = 0;
        }
#endif
}

static void
ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
                 struct rq_flags *rf)
{
        int en_flags = ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK;

        lockdep_assert_rq_held(rq);

        if (p->sched_contributes_to_load)
                rq->nr_uninterruptible--;

#ifdef CONFIG_SMP
        if (wake_flags & WF_MIGRATED)
                en_flags |= ENQUEUE_MIGRATED;
        else
#endif
        if (p->in_iowait) {
                delayacct_blkio_end(p);
                atomic_dec(&task_rq(p)->nr_iowait);
        }

        activate_task(rq, p, en_flags);
        ttwu_do_wakeup(rq, p, wake_flags, rf);
}

/*
 * Consider @p being inside a wait loop:
 *
 *   for (;;) {
 *      set_current_state(TASK_UNINTERRUPTIBLE);
 *
 *      if (CONDITION)
 *         break;
 *
 *      schedule();
 *   }
 *   __set_current_state(TASK_RUNNING);
 *
 * between set_current_state() and schedule(). In this case @p is still
 * runnable, so all that needs doing is change p->state back to TASK_RUNNING in
 * an atomic manner.
 *
 * By taking task_rq(p)->lock we serialize against schedule(), if @p->on_rq
 * then schedule() must still happen and p->state can be changed to
 * TASK_RUNNING. Otherwise we lost the race, schedule() has happened, and we
 * need to do a full wakeup with enqueue.
 *
 * Returns: %true when the wakeup is done,
 *          %false otherwise.
 */
static int ttwu_runnable(struct task_struct *p, int wake_flags)
{
        struct rq_flags rf;
        struct rq *rq;
        int ret = 0;

        rq = __task_rq_lock(p, &rf);
        if (task_on_rq_queued(p)) {
                /* check_preempt_curr() may use rq clock */
                update_rq_clock(rq);
                ttwu_do_wakeup(rq, p, wake_flags, &rf);
                ret = 1;
        }
        __task_rq_unlock(rq, &rf);

        return ret;
}

#ifdef CONFIG_SMP
void sched_ttwu_pending(void *arg)
{
        struct llist_node *llist = arg;
        struct rq *rq = this_rq();
        struct task_struct *p, *t;
        struct rq_flags rf;

        if (!llist)
                return;

        /*
         * rq::ttwu_pending racy indication of out-standing wakeups.
         * Races such that false-negatives are possible, since they
         * are shorter lived that false-positives would be.
         */
        WRITE_ONCE(rq->ttwu_pending, 0);

        rq_lock_irqsave(rq, &rf);
        update_rq_clock(rq);

        llist_for_each_entry_safe(p, t, llist, wake_entry.llist) {
                if (WARN_ON_ONCE(p->on_cpu))
                        smp_cond_load_acquire(&p->on_cpu, !VAL);

                if (WARN_ON_ONCE(task_cpu(p) != cpu_of(rq)))
                        set_task_cpu(p, cpu_of(rq));

                ttwu_do_activate(rq, p, p->sched_remote_wakeup ? WF_MIGRATED : 0, &rf);
        }

        rq_unlock_irqrestore(rq, &rf);
}

void send_call_function_single_ipi(int cpu)
{
        struct rq *rq = cpu_rq(cpu);

        if (!set_nr_if_polling(rq->idle))
                arch_send_call_function_single_ipi(cpu);
        else
                trace_sched_wake_idle_without_ipi(cpu);
}

/*
 * Queue a task on the target CPUs wake_list and wake the CPU via IPI if
 * necessary. The wakee CPU on receipt of the IPI will queue the task
 * via sched_ttwu_wakeup() for activation so the wakee incurs the cost
 * of the wakeup instead of the waker.
 */
static void __ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags)
{
        struct rq *rq = cpu_rq(cpu);

        p->sched_remote_wakeup = !!(wake_flags & WF_MIGRATED);

        WRITE_ONCE(rq->ttwu_pending, 1);
        __smp_call_single_queue(cpu, &p->wake_entry.llist);
}

void wake_up_if_idle(int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        struct rq_flags rf;

        rcu_read_lock();

        if (!is_idle_task(rcu_dereference(rq->curr)))
                goto out;

        if (set_nr_if_polling(rq->idle)) {
                trace_sched_wake_idle_without_ipi(cpu);
        } else {
                rq_lock_irqsave(rq, &rf);
                if (is_idle_task(rq->curr))
                        smp_send_reschedule(cpu);
                /* Else CPU is not idle, do nothing here: */
                rq_unlock_irqrestore(rq, &rf);
        }

out:
        rcu_read_unlock();
}

bool cpus_share_cache(int this_cpu, int that_cpu)
{
        return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
}

static inline bool ttwu_queue_cond(int cpu, int wake_flags)
{
        /*
         * Do not complicate things with the async wake_list while the CPU is
         * in hotplug state.
         */
        if (!cpu_active(cpu))
                return false;

        /*
         * If the CPU does not share cache, then queue the task on the
         * remote rqs wakelist to avoid accessing remote data.
         */
        if (!cpus_share_cache(smp_processor_id(), cpu))
                return true;

        /*
         * If the task is descheduling and the only running task on the
         * CPU then use the wakelist to offload the task activation to
         * the soon-to-be-idle CPU as the current CPU is likely busy.
         * nr_running is checked to avoid unnecessary task stacking.
         */
        if ((wake_flags & WF_ON_CPU) && cpu_rq(cpu)->nr_running <= 1)
                return true;

        return false;
}

static bool ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags)
{
        if (sched_feat(TTWU_QUEUE) && ttwu_queue_cond(cpu, wake_flags)) {
                if (WARN_ON_ONCE(cpu == smp_processor_id()))
                        return false;

                sched_clock_cpu(cpu); /* Sync clocks across CPUs */
                __ttwu_queue_wakelist(p, cpu, wake_flags);
                return true;
        }

        return false;
}

#else /* !CONFIG_SMP */

static inline bool ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags)
{
        return false;
}

#endif /* CONFIG_SMP */

static void ttwu_queue(struct task_struct *p, int cpu, int wake_flags)
{
        struct rq *rq = cpu_rq(cpu);
        struct rq_flags rf;

        if (ttwu_queue_wakelist(p, cpu, wake_flags))
                return;

        rq_lock(rq, &rf);
        update_rq_clock(rq);
        ttwu_do_activate(rq, p, wake_flags, &rf);
        rq_unlock(rq, &rf);
}

/*
 * Invoked from try_to_wake_up() to check whether the task can be woken up.
 *
 * The caller holds p::pi_lock if p != current or has preemption
 * disabled when p == current.
 *
 * The rules of PREEMPT_RT saved_state:
 *
 *   The related locking code always holds p::pi_lock when updating
 *   p::saved_state, which means the code is fully serialized in both cases.
 *
 *   The lock wait and lock wakeups happen via TASK_RTLOCK_WAIT. No other
 *   bits set. This allows to distinguish all wakeup scenarios.
 */
static __always_inline
bool ttwu_state_match(struct task_struct *p, unsigned int state, int *success)
{
        if (IS_ENABLED(CONFIG_DEBUG_PREEMPT)) {
                WARN_ON_ONCE((state & TASK_RTLOCK_WAIT) &&
                             state != TASK_RTLOCK_WAIT);
        }

        if (READ_ONCE(p->__state) & state) {
                *success = 1;
                return true;
        }

#ifdef CONFIG_PREEMPT_RT
        /*
         * Saved state preserves the task state across blocking on
         * an RT lock.  If the state matches, set p::saved_state to
         * TASK_RUNNING, but do not wake the task because it waits
         * for a lock wakeup. Also indicate success because from
         * the regular waker's point of view this has succeeded.
         *
         * After acquiring the lock the task will restore p::__state
         * from p::saved_state which ensures that the regular
         * wakeup is not lost. The restore will also set
         * p::saved_state to TASK_RUNNING so any further tests will
         * not result in false positives vs. @success
         */
        if (p->saved_state & state) {
                p->saved_state = TASK_RUNNING;
                *success = 1;
        }
#endif
        return false;
}

/*
 * Notes on Program-Order guarantees on SMP systems.
 *
 *  MIGRATION
 *
 * The basic program-order guarantee on SMP systems is that when a task [t]
 * migrates, all its activity on its old CPU [c0] happens-before any subsequent
 * execution on its new CPU [c1].
 *
 * For migration (of runnable tasks) this is provided by the following means:
 *
 *  A) UNLOCK of the rq(c0)->lock scheduling out task t
 *  B) migration for t is required to synchronize *both* rq(c0)->lock and
 *     rq(c1)->lock (if not at the same time, then in that order).
 *  C) LOCK of the rq(c1)->lock scheduling in task
 *
 * Release/acquire chaining guarantees that B happens after A and C after B.
 * Note: the CPU doing B need not be c0 or c1
 *
 * Example:
 *
 *   CPU0            CPU1            CPU2
 *
 *   LOCK rq(0)->lock
 *   sched-out X
 *   sched-in Y
 *   UNLOCK rq(0)->lock
 *
 *                                   LOCK rq(0)->lock // orders against CPU0
 *                                   dequeue X
 *                                   UNLOCK rq(0)->lock
 *
 *                                   LOCK rq(1)->lock
 *                                   enqueue X
 *                                   UNLOCK rq(1)->lock
 *
 *                   LOCK rq(1)->lock // orders against CPU2
 *                   sched-out Z
 *                   sched-in X
 *                   UNLOCK rq(1)->lock
 *
 *
 *  BLOCKING -- aka. SLEEP + WAKEUP
 *
 * For blocking we (obviously) need to provide the same guarantee as for
 * migration. However the means are completely different as there is no lock
 * chain to provide order. Instead we do:
 *
 *   1) smp_store_release(X->on_cpu, 0)   -- finish_task()
 *   2) smp_cond_load_acquire(!X->on_cpu) -- try_to_wake_up()
 *
 * Example:
 *
 *   CPU0 (schedule)  CPU1 (try_to_wake_up) CPU2 (schedule)
 *
 *   LOCK rq(0)->lock LOCK X->pi_lock
 *   dequeue X
 *   sched-out X
 *   smp_store_release(X->on_cpu, 0);
 *
 *                    smp_cond_load_acquire(&X->on_cpu, !VAL);
 *                    X->state = WAKING
 *                    set_task_cpu(X,2)
 *
 *                    LOCK rq(2)->lock
 *                    enqueue X
 *                    X->state = RUNNING
 *                    UNLOCK rq(2)->lock
 *
 *                                          LOCK rq(2)->lock // orders against CPU1
 *                                          sched-out Z
 *                                          sched-in X
 *                                          UNLOCK rq(2)->lock
 *
 *                    UNLOCK X->pi_lock
 *   UNLOCK rq(0)->lock
 *
 *
 * However, for wakeups there is a second guarantee we must provide, namely we
 * must ensure that CONDITION=1 done by the caller can not be reordered with
 * accesses to the task state; see try_to_wake_up() and set_current_state().
 */

/**
 * try_to_wake_up - wake up a thread
 * @p: the thread to be awakened
 * @state: the mask of task states that can be woken
 * @wake_flags: wake modifier flags (WF_*)
 *
 * Conceptually does:
 *
 *   If (@state & @p->state) @p->state = TASK_RUNNING.
 *
 * If the task was not queued/runnable, also place it back on a runqueue.
 *
 * This function is atomic against schedule() which would dequeue the task.
 *
 * It issues a full memory barrier before accessing @p->state, see the comment
 * with set_current_state().
 *
 * Uses p->pi_lock to serialize against concurrent wake-ups.
 *
 * Relies on p->pi_lock stabilizing:
 *  - p->sched_class
 *  - p->cpus_ptr
 *  - p->sched_task_group
 * in order to do migration, see its use of select_task_rq()/set_task_cpu().
 *
 * Tries really hard to only take one task_rq(p)->lock for performance.
 * Takes rq->lock in:
 *  - ttwu_runnable()    -- old rq, unavoidable, see comment there;
 *  - ttwu_queue()       -- new rq, for enqueue of the task;
 *  - psi_ttwu_dequeue() -- much sadness :-( accounting will kill us.
 *
 * As a consequence we race really badly with just about everything. See the
 * many memory barriers and their comments for details.
 *
 * Return: %true if @p->state changes (an actual wakeup was done),
 *         %false otherwise.
 */
static int
try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
{
        unsigned long flags;
        int cpu, success = 0;

        preempt_disable();
        if (p == current) {
                /*
                 * We're waking current, this means 'p->on_rq' and 'task_cpu(p)
                 * == smp_processor_id()'. Together this means we can special
                 * case the whole 'p->on_rq && ttwu_runnable()' case below
                 * without taking any locks.
                 *
                 * In particular:
                 *  - we rely on Program-Order guarantees for all the ordering,
                 *  - we're serialized against set_special_state() by virtue of
                 *    it disabling IRQs (this allows not taking ->pi_lock).
                 */
                if (!ttwu_state_match(p, state, &success))
                        goto out;

                trace_sched_waking(p);
                WRITE_ONCE(p->__state, TASK_RUNNING);
                trace_sched_wakeup(p);
                goto out;
        }

        /*
         * If we are going to wake up a thread waiting for CONDITION we
         * need to ensure that CONDITION=1 done by the caller can not be
         * reordered with p->state check below. This pairs with smp_store_mb()
         * in set_current_state() that the waiting thread does.
         */
        raw_spin_lock_irqsave(&p->pi_lock, flags);
        smp_mb__after_spinlock();
        if (!ttwu_state_match(p, state, &success))
                goto unlock;

        trace_sched_waking(p);

        /*
         * Ensure we load p->on_rq _after_ p->state, otherwise it would
         * be possible to, falsely, observe p->on_rq == 0 and get stuck
         * in smp_cond_load_acquire() below.
         *
         * sched_ttwu_pending()                 try_to_wake_up()
         *   STORE p->on_rq = 1                   LOAD p->state
         *   UNLOCK rq->lock
         *
         * __schedule() (switch to task 'p')
         *   LOCK rq->lock                        smp_rmb();
         *   smp_mb__after_spinlock();
         *   UNLOCK rq->lock