// SPDX-License-Identifier: GPL-2.0-only
/*
 *  kernel/sched/syscalls.c
 *
 *  Core kernel scheduler syscalls related code
 *
 *  Copyright (C) 1991-2002  Linus Torvalds
 *  Copyright (C) 1998-2024  Ingo Molnar, Red Hat
 */
#include <linux/sched.h>
#include <linux/cpuset.h>
#include <linux/sched/debug.h>

#include <uapi/linux/sched/types.h>

#include "sched.h"
#include "autogroup.h"

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_or_dl_prio(p->prio))
                return p->normal_prio;
        return p->prio;
}

void set_user_nice(struct task_struct *p, long nice)
{
        int old_prio;

        if (task_nice(p) == nice || nice < MIN_NICE || nice > MAX_NICE)
                return;
        /*
         * We have to be careful, if called from sys_setpriority(),
         * the task might be in the middle of scheduling on another CPU.
         */
        guard(task_rq_lock)(p);

        /*
         * The RT priorities are set via sched_setscheduler(), but we still
         * allow the 'normal' nice value to be set - but as expected
         * it won't have any effect on scheduling until the task is
         * SCHED_DEADLINE, SCHED_FIFO or SCHED_RR:
         */
        if (task_has_dl_policy(p) || task_has_rt_policy(p)) {
                p->static_prio = NICE_TO_PRIO(nice);
                return;
        }

        scoped_guard (sched_change, p, DEQUEUE_SAVE) {
                p->static_prio = NICE_TO_PRIO(nice);
                set_load_weight(p, true);
                old_prio = p->prio;
                p->prio = effective_prio(p);
        }
}
EXPORT_SYMBOL(set_user_nice);

/*
 * is_nice_reduction - check if nice value is an actual reduction
 *
 * Similar to can_nice() but does not perform a capability check.
 *
 * @p: task
 * @nice: nice value
 */
static bool is_nice_reduction(const struct task_struct *p, const int nice)
{
        /* Convert nice value [19,-20] to rlimit style value [1,40]: */
        int nice_rlim = nice_to_rlimit(nice);

        return (nice_rlim <= task_rlimit(p, RLIMIT_NICE));
}

/*
 * can_nice - check if a task can reduce its nice value
 * @p: task
 * @nice: nice value
 */
int can_nice(const struct task_struct *p, const int nice)
{
        return is_nice_reduction(p, nice) || capable(CAP_SYS_NICE);
}

#ifdef __ARCH_WANT_SYS_NICE

/*
 * sys_nice - change the priority of the current process.
 * @increment: priority increment
 *
 * sys_setpriority is a more generic, but much slower function that
 * does similar things.
 */
SYSCALL_DEFINE1(nice, int, increment)
{
        long nice, retval;

        /*
         * Setpriority might change our priority at the same moment.
         * We don't have to worry. Conceptually one call occurs first
         * and we have a single winner.
         */
        increment = clamp(increment, -NICE_WIDTH, NICE_WIDTH);
        nice = task_nice(current) + increment;

        nice = clamp_val(nice, MIN_NICE, MAX_NICE);
        if (increment < 0 && !can_nice(current, nice))
                return -EPERM;

        retval = security_task_setnice(current, nice);
        if (retval)
                return retval;

        set_user_nice(current, nice);
        return 0;
}

#endif /* __ARCH_WANT_SYS_NICE */

/**
 * task_prio - return the priority value of a given task.
 * @p: the task in question.
 *
 * Return: The priority value as seen by users in /proc.
 *
 * sched policy         return value   kernel prio    user prio/nice
 *
 * normal, batch, idle     [0 ... 39]  [100 ... 139]          0/[-20 ... 19]
 * fifo, rr             [-2 ... -100]     [98 ... 0]  [1 ... 99]
 * deadline                     -101             -1           0
 */
int task_prio(const struct task_struct *p)
{
        return p->prio - MAX_RT_PRIO;
}

/**
 * idle_cpu - is a given CPU idle currently?
 * @cpu: the processor in question.
 *
 * Return: 1 if the CPU is currently idle. 0 otherwise.
 */
int idle_cpu(int cpu)
{
        return idle_rq(cpu_rq(cpu));
}

/**
 * idle_task - return the idle task for a given CPU.
 * @cpu: the processor in question.
 *
 * Return: The idle task for the CPU @cpu.
 */
struct task_struct *idle_task(int cpu)
{
        return cpu_rq(cpu)->idle;
}

#ifdef CONFIG_SCHED_CORE
int sched_core_idle_cpu(int cpu)
{
        struct rq *rq = cpu_rq(cpu);

        if (sched_core_enabled(rq) && rq->curr == rq->idle)
                return 1;

        return idle_cpu(cpu);
}
#endif /* CONFIG_SCHED_CORE */

/**
 * find_process_by_pid - find a process with a matching PID value.
 * @pid: the pid in question.
 *
 * The task of @pid, if found. %NULL otherwise.
 */
static struct task_struct *find_process_by_pid(pid_t pid)
{
        return pid ? find_task_by_vpid(pid) : current;
}

static struct task_struct *find_get_task(pid_t pid)
{
        struct task_struct *p;
        guard(rcu)();

        p = find_process_by_pid(pid);
        if (likely(p))
                get_task_struct(p);

        return p;
}

DEFINE_CLASS(find_get_task, struct task_struct *, if (_T) put_task_struct(_T),
             find_get_task(pid), pid_t pid)

/*
 * sched_setparam() passes in -1 for its policy, to let the functions
 * it calls know not to change it.
 */
#define SETPARAM_POLICY -1

static void __setscheduler_params(struct task_struct *p,
                const struct sched_attr *attr)
{
        int policy = attr->sched_policy;

        if (policy == SETPARAM_POLICY)
                policy = p->policy;

        p->policy = policy;

        if (dl_policy(policy))
                __setparam_dl(p, attr);
        else if (fair_policy(policy))
                __setparam_fair(p, attr);

        /* rt-policy tasks do not have a timerslack */
        if (rt_or_dl_task_policy(p)) {
                p->timer_slack_ns = 0;
        } else if (p->timer_slack_ns == 0) {
                /* when switching back to non-rt policy, restore timerslack */
                p->timer_slack_ns = p->default_timer_slack_ns;
        }

        /*
         * __sched_setscheduler() ensures attr->sched_priority == 0 when
         * !rt_policy. Always setting this ensures that things like
         * getparam()/getattr() don't report silly values for !rt tasks.
         */
        p->rt_priority = attr->sched_priority;
        p->normal_prio = normal_prio(p);
        set_load_weight(p, true);
}

/*
 * Check the target process has a UID that matches the current process's:
 */
static bool check_same_owner(struct task_struct *p)
{
        const struct cred *cred = current_cred(), *pcred;
        guard(rcu)();

        pcred = __task_cred(p);
        return (uid_eq(cred->euid, pcred->euid) ||
                uid_eq(cred->euid, pcred->uid));
}

#ifdef CONFIG_RT_MUTEXES
static inline void __setscheduler_dl_pi(int newprio, int policy,
                              struct task_struct *p,
                              struct sched_change_ctx *scope)
{
        /*
         * In case a DEADLINE task (either proper or boosted) gets
         * setscheduled to a lower priority class, check if it neeeds to
         * inherit parameters from a potential pi_task. In that case make
         * sure replenishment happens with the next enqueue.
         */

        if (dl_prio(newprio) && !dl_policy(policy)) {
                struct task_struct *pi_task = rt_mutex_get_top_task(p);

                if (pi_task) {
                        p->dl.pi_se = pi_task->dl.pi_se;
                        scope->flags |= ENQUEUE_REPLENISH;
                }
        }
}
#else /* !CONFIG_RT_MUTEXES */
static inline void __setscheduler_dl_pi(int newprio, int policy,
                              struct task_struct *p,
                              struct sched_change_ctx *scope)
{
}
#endif /* !CONFIG_RT_MUTEXES */

#ifdef CONFIG_UCLAMP_TASK

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.
         */
        sched_uclamp_enable();

        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);
        }
}

#else /* !CONFIG_UCLAMP_TASK: */

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) { }
#endif /* !CONFIG_UCLAMP_TASK */

/*
 * Allow unprivileged RT tasks to decrease priority.
 * Only issue a capable test if needed and only once to avoid an audit
 * event on permitted non-privileged operations:
 */
static int user_check_sched_setscheduler(struct task_struct *p,
                                         const struct sched_attr *attr,
                                         int policy, int reset_on_fork)
{
        if (fair_policy(policy)) {
                if (attr->sched_nice < task_nice(p) &&
                    !is_nice_reduction(p, attr->sched_nice))
                        goto req_priv;
        }

        if (rt_policy(policy)) {
                unsigned long rlim_rtprio = task_rlimit(p, RLIMIT_RTPRIO);

                /* Can't set/change the rt policy: */
                if (policy != p->policy && !rlim_rtprio)
                        goto req_priv;

                /* Can't increase priority: */
                if (attr->sched_priority > p->rt_priority &&
                    attr->sched_priority > rlim_rtprio)
                        goto req_priv;
        }

        /*
         * Can't set/change SCHED_DEADLINE policy at all for now
         * (safest behavior); in the future we would like to allow
         * unprivileged DL tasks to increase their relative deadline
         * or reduce their runtime (both ways reducing utilization)
         */
        if (dl_policy(policy))
                goto req_priv;

        /*
         * Treat SCHED_IDLE as nice 20. Only allow a switch to
         * SCHED_NORMAL if the RLIMIT_NICE would normally permit it.
         */
        if (task_has_idle_policy(p) && !idle_policy(policy)) {
                if (!is_nice_reduction(p, task_nice(p)))
                        goto req_priv;
        }

        /* Can't change other user's priorities: */
        if (!check_same_owner(p))
                goto req_priv;

        /* Normal users shall not reset the sched_reset_on_fork flag: */
        if (p->sched_reset_on_fork && !reset_on_fork)
                goto req_priv;

        return 0;

req_priv:
        if (!capable(CAP_SYS_NICE))
                return -EPERM;

        return 0;
}

int __sched_setscheduler(struct task_struct *p,
                         const struct sched_attr *attr,
                         bool user, bool pi)
{
        int oldpolicy = -1, policy = attr->sched_policy;
        int retval, oldprio, newprio;
        const struct sched_class *prev_class, *next_class;
        struct balance_callback *head;
        struct rq_flags rf;
        int reset_on_fork;
        int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
        struct rq *rq;
        bool cpuset_locked = false;

        /* The pi code expects interrupts enabled */
        BUG_ON(pi && in_interrupt());
recheck:
        /* Double check policy once rq lock held: */
        if (policy < 0) {
                reset_on_fork = p->sched_reset_on_fork;
                policy = oldpolicy = p->policy;
        } else {
                reset_on_fork = !!(attr->sched_flags & SCHED_FLAG_RESET_ON_FORK);

                if (!valid_policy(policy))
                        return -EINVAL;
        }

        if (attr->sched_flags & ~(SCHED_FLAG_ALL | SCHED_FLAG_SUGOV))
                return -EINVAL;

        /*
         * Valid priorities for SCHED_FIFO and SCHED_RR are
         * 1..MAX_RT_PRIO-1, valid priority for SCHED_NORMAL,
         * SCHED_BATCH and SCHED_IDLE is 0.
         */
        if (attr->sched_priority > MAX_RT_PRIO-1)
                return -EINVAL;
        if ((dl_policy(policy) && !__checkparam_dl(attr)) ||
            (rt_policy(policy) != (attr->sched_priority != 0)))
                return -EINVAL;

        if (user) {
                retval = user_check_sched_setscheduler(p, attr, policy, reset_on_fork);
                if (retval)
                        return retval;

                if (attr->sched_flags & SCHED_FLAG_SUGOV)
                        return -EINVAL;

                retval = security_task_setscheduler(p);
                if (retval)
                        return retval;
        }

        /* Update task specific "requested" clamps */
        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) {
                retval = uclamp_validate(p, attr);
                if (retval)
                        return retval;
        }

        /*
         * SCHED_DEADLINE bandwidth accounting relies on stable cpusets
         * information.
         */
        if (dl_policy(policy) || dl_policy(p->policy)) {
                cpuset_locked = true;
                cpuset_lock();
        }

        /*
         * Make sure no PI-waiters arrive (or leave) while we are
         * changing the priority of the task:
         *
         * To be able to change p->policy safely, the appropriate
         * runqueue lock must be held.
         */
        rq = task_rq_lock(p, &rf);
        update_rq_clock(rq);

        /*
         * Changing the policy of the stop threads its a very bad idea:
         */
        if (p == rq->stop) {
                retval = -EINVAL;
                goto unlock;
        }

        retval = scx_check_setscheduler(p, policy);
        if (retval)
                goto unlock;

        /*
         * If not changing anything there's no need to proceed further,
         * but store a possible modification of reset_on_fork.
         */
        if (unlikely(policy == p->policy)) {
                if (fair_policy(policy) &&
                    (attr->sched_nice != task_nice(p) ||
                     (attr->sched_runtime != p->se.slice)))
                        goto change;
                if (rt_policy(policy) && attr->sched_priority != p->rt_priority)
                        goto change;
                if (dl_policy(policy) && dl_param_changed(p, attr))
                        goto change;
                if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)
                        goto change;

                p->sched_reset_on_fork = reset_on_fork;
                retval = 0;
                goto unlock;
        }
change:

        if (user) {
#ifdef CONFIG_RT_GROUP_SCHED
                /*
                 * Do not allow real-time tasks into groups that have no runtime
                 * assigned.
                 */
                if (rt_group_sched_enabled() &&
                                rt_bandwidth_enabled() && rt_policy(policy) &&
                                task_group(p)->rt_bandwidth.rt_runtime == 0 &&
                                !task_group_is_autogroup(task_group(p))) {
                        retval = -EPERM;
                        goto unlock;
                }
#endif /* CONFIG_RT_GROUP_SCHED */
                if (dl_bandwidth_enabled() && dl_policy(policy) &&
                                !(attr->sched_flags & SCHED_FLAG_SUGOV)) {
                        cpumask_t *span = rq->rd->span;

                        /*
                         * Don't allow tasks with an affinity mask smaller than
                         * the entire root_domain to become SCHED_DEADLINE. We
                         * will also fail if there's no bandwidth available.
                         */
                        if (!cpumask_subset(span, p->cpus_ptr) ||
                            rq->rd->dl_bw.bw == 0) {
                                retval = -EPERM;
                                goto unlock;
                        }
                }
        }

        /* Re-check policy now with rq lock held: */
        if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {
                policy = oldpolicy = -1;
                task_rq_unlock(rq, p, &rf);
                if (cpuset_locked)
                        cpuset_unlock();
                goto recheck;
        }

        /*
         * If setscheduling to SCHED_DEADLINE (or changing the parameters
         * of a SCHED_DEADLINE task) we need to check if enough bandwidth
         * is available.
         */
        if ((dl_policy(policy) || dl_task(p)) && sched_dl_overflow(p, policy, attr)) {
                retval = -EBUSY;
                goto unlock;
        }

        p->sched_reset_on_fork = reset_on_fork;
        oldprio = p->prio;

        newprio = __normal_prio(policy, attr->sched_priority, attr->sched_nice);
        if (pi) {
                /*
                 * Take priority boosted tasks into account. If the new
                 * effective priority is unchanged, we just store the new
                 * normal parameters and do not touch the scheduler class and
                 * the runqueue. This will be done when the task deboost
                 * itself.
                 */
                newprio = rt_effective_prio(p, newprio);
                if (newprio == oldprio && !dl_prio(newprio))
                        queue_flags &= ~DEQUEUE_MOVE;
        }

        prev_class = p->sched_class;
        next_class = __setscheduler_class(policy, newprio);

        if (prev_class != next_class)
                queue_flags |= DEQUEUE_CLASS;

        scoped_guard (sched_change, p, queue_flags) {

                if (!(attr->sched_flags & SCHED_FLAG_KEEP_PARAMS)) {
                        __setscheduler_params(p, attr);
                        p->sched_class = next_class;
                        p->prio = newprio;
                        __setscheduler_dl_pi(newprio, policy, p, scope);
                }
                __setscheduler_uclamp(p, attr);

                if (scope->queued) {
                        /*
                         * We enqueue to tail when the priority of a task is
                         * increased (user space view).
                         */
                        if (oldprio < p->prio)
                                scope->flags |= ENQUEUE_HEAD;
                }
        }

        /* Avoid rq from going away on us: */
        preempt_disable();
        head = splice_balance_callbacks(rq);
        task_rq_unlock(rq, p, &rf);

        if (pi) {
                if (cpuset_locked)
                        cpuset_unlock();
                rt_mutex_adjust_pi(p);
        }

        /* Run balance callbacks after we've adjusted the PI chain: */
        balance_callbacks(rq, head);
        preempt_enable();

        return 0;

unlock:
        task_rq_unlock(rq, p, &rf);
        if (cpuset_locked)
                cpuset_unlock();
        return retval;
}

static int _sched_setscheduler(struct task_struct *p, int policy,
                               const struct sched_param *param, bool check)
{
        struct sched_attr attr = {
                .sched_policy   = policy,
                .sched_priority = param->sched_priority,
                .sched_nice     = PRIO_TO_NICE(p->static_prio),
        };

        if (p->se.custom_slice)
                attr.sched_runtime = p->se.slice;

        /* Fixup the legacy SCHED_RESET_ON_FORK hack. */
        if ((policy != SETPARAM_POLICY) && (policy & SCHED_RESET_ON_FORK)) {
                attr.sched_flags |= SCHED_FLAG_RESET_ON_FORK;
                policy &= ~SCHED_RESET_ON_FORK;
                attr.sched_policy = policy;
        }

        return __sched_setscheduler(p, &attr, check, true);
}
/**
 * sched_setscheduler - change the scheduling policy and/or RT priority of a thread.
 * @p: the task in question.
 * @policy: new policy.
 * @param: structure containing the new RT priority.
 *
 * Use sched_set_fifo(), read its comment.
 *
 * Return: 0 on success. An error code otherwise.
 *
 * NOTE that the task may be already dead.
 */
int sched_setscheduler(struct task_struct *p, int policy,
                       const struct sched_param *param)
{
        return _sched_setscheduler(p, policy, param, true);
}

int sched_setattr(struct task_struct *p, const struct sched_attr *attr)
{
        return __sched_setscheduler(p, attr, true, true);
}

int sched_setattr_nocheck(struct task_struct *p, const struct sched_attr *attr)
{
        return __sched_setscheduler(p, attr, false, true);
}
EXPORT_SYMBOL_GPL(sched_setattr_nocheck);

/**
 * sched_setscheduler_nocheck - change the scheduling policy and/or RT priority of a thread from kernel-space.
 * @p: the task in question.
 * @policy: new policy.
 * @param: structure containing the new RT priority.
 *
 * Just like sched_setscheduler, only don't bother checking if the
 * current context has permission.  For example, this is needed in
 * stop_machine(): we create temporary high priority worker threads,
 * but our caller might not have that capability.
 *
 * Return: 0 on success. An error code otherwise.
 */
int sched_setscheduler_nocheck(struct task_struct *p, int policy,
                               const struct sched_param *param)
{
        return _sched_setscheduler(p, policy, param, false);
}

/*
 * SCHED_FIFO is a broken scheduler model; that is, it is fundamentally
 * incapable of resource management, which is the one thing an OS really should
 * be doing.
 *
 * This is of course the reason it is limited to privileged users only.
 *
 * Worse still; it is fundamentally impossible to compose static priority
 * workloads. You cannot take two correctly working static prio workloads
 * and smash them together and still expect them to work.
 *
 * For this reason 'all' FIFO tasks the kernel creates are basically at:
 *
 *   MAX_RT_PRIO / 2
 *
 * The administrator _MUST_ configure the system, the kernel simply doesn't
 * know enough information to make a sensible choice.
 */
void sched_set_fifo(struct task_struct *p)
{
        struct sched_param sp = { .sched_priority = MAX_RT_PRIO / 2 };
        WARN_ON_ONCE(sched_setscheduler_nocheck(p, SCHED_FIFO, &sp) != 0);
}
EXPORT_SYMBOL_GPL(sched_set_fifo);

/*
 * For when you don't much care about FIFO, but want to be above SCHED_NORMAL.
 */
void sched_set_fifo_low(struct task_struct *p)
{
        struct sched_param sp = { .sched_priority = 1 };
        WARN_ON_ONCE(sched_setscheduler_nocheck(p, SCHED_FIFO, &sp) != 0);
}
EXPORT_SYMBOL_GPL(sched_set_fifo_low);

/*
 * Used when the primary interrupt handler is forced into a thread, in addition
 * to the (always threaded) secondary handler.  The secondary handler gets a
 * slightly lower priority so that the primary handler can preempt it, thereby
 * emulating the behavior of a non-PREEMPT_RT system where the primary handler
 * runs in hard interrupt context.
 */
void sched_set_fifo_secondary(struct task_struct *p)
{
        struct sched_param sp = { .sched_priority = MAX_RT_PRIO / 2 - 1 };
        WARN_ON_ONCE(sched_setscheduler_nocheck(p, SCHED_FIFO, &sp) != 0);
}

void sched_set_normal(struct task_struct *p, int nice)
{
        struct sched_attr attr = {
                .sched_policy = SCHED_NORMAL,
                .sched_nice = nice,
        };
        WARN_ON_ONCE(sched_setattr_nocheck(p, &attr) != 0);
}
EXPORT_SYMBOL_GPL(sched_set_normal);

static int
do_sched_setscheduler(pid_t pid, int policy, struct sched_param __user *param)
{
        struct sched_param lparam;

        if (unlikely(!param || pid < 0))
                return -EINVAL;
        if (copy_from_user(&lparam, param, sizeof(struct sched_param)))
                return -EFAULT;

        CLASS(find_get_task, p)(pid);
        if (!p)
                return -ESRCH;

        return sched_setscheduler(p, policy, &lparam);
}

/*
 * Mimics kernel/events/core.c perf_copy_attr().
 */
static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *attr)
{
        u32 size;
        int ret;

        /* Zero the full structure, so that a short copy will be nice: */
        memset(attr, 0, sizeof(*attr));

        ret = get_user(size, &uattr->size);
        if (ret)
                return ret;

        /* ABI compatibility quirk: */
        if (!size)
                size = SCHED_ATTR_SIZE_VER0;
        if (size < SCHED_ATTR_SIZE_VER0 || size > PAGE_SIZE)
                goto err_size;

        ret = copy_struct_from_user(attr, sizeof(*attr), uattr, size);
        if (ret) {
                if (ret == -E2BIG)
                        goto err_size;
                return ret;
        }

        if ((attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) &&
            size < SCHED_ATTR_SIZE_VER1)
                return -EINVAL;

        /*
         * XXX: Do we want to be lenient like existing syscalls; or do we want
         * to be strict and return an error on out-of-bounds values?
         */
        attr->sched_nice = clamp(attr->sched_nice, MIN_NICE, MAX_NICE);

        return 0;

err_size:
        put_user(sizeof(*attr), &uattr->size);
        return -E2BIG;
}

static void get_params(struct task_struct *p, struct sched_attr *attr)
{
        if (task_has_dl_policy(p)) {
                __getparam_dl(p, attr);
        } else if (task_has_rt_policy(p)) {
                attr->sched_priority = p->rt_priority;
        } else {
                attr->sched_nice = task_nice(p);
                attr->sched_runtime = p->se.slice;
        }
}

/**
 * sys_sched_setscheduler - set/change the scheduler policy and RT priority
 * @pid: the pid in question.
 * @policy: new policy.
 * @param: structure containing the new RT priority.
 *
 * Return: 0 on success. An error code otherwise.
 */
SYSCALL_DEFINE3(sched_setscheduler, pid_t, pid, int, policy, struct sched_param __user *, param)
{
        if (policy < 0)
                return -EINVAL;

        return do_sched_setscheduler(pid, policy, param);
}

/**
 * sys_sched_setparam - set/change the RT priority of a thread
 * @pid: the pid in question.
 * @param: structure containing the new RT priority.
 *
 * Return: 0 on success. An error code otherwise.
 */
SYSCALL_DEFINE2(sched_setparam, pid_t, pid, struct sched_param __user *, param)
{
        return do_sched_setscheduler(pid, SETPARAM_POLICY, param);
}

/**
 * sys_sched_setattr - same as above, but with extended sched_attr
 * @pid: the pid in question.
 * @uattr: structure containing the extended parameters.
 * @flags: for future extension.
 */
SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
                               unsigned int, flags)
{
        struct sched_attr attr;
        int retval;

        if (unlikely(!uattr || pid < 0 || flags))
                return -EINVAL;

        retval = sched_copy_attr(uattr, &attr);
        if (retval)
                return retval;

        if ((int)attr.sched_policy < 0)
                return -EINVAL;
        if (attr.sched_flags & SCHED_FLAG_KEEP_POLICY)
                attr.sched_policy = SETPARAM_POLICY;

        CLASS(find_get_task, p)(pid);
        if (!p)
                return -ESRCH;

        if (attr.sched_flags & SCHED_FLAG_KEEP_PARAMS)
                get_params(p, &attr);

        return sched_setattr(p, &attr);
}

/**
 * sys_sched_getscheduler - get the policy (scheduling class) of a thread
 * @pid: the pid in question.
 *
 * Return: On success, the policy of the thread. Otherwise, a negative error
 * code.
 */
SYSCALL_DEFINE1(sched_getscheduler, pid_t, pid)
{
        struct task_struct *p;
        int retval;

        if (pid < 0)
                return -EINVAL;

        guard(rcu)();
        p = find_process_by_pid(pid);
        if (!p)
                return -ESRCH;

        retval = security_task_getscheduler(p);
        if (!retval) {
                retval = p->policy;
                if (p->sched_reset_on_fork)
                        retval |= SCHED_RESET_ON_FORK;
        }
        return retval;
}

/**
 * sys_sched_getparam - get the RT priority of a thread
 * @pid: the pid in question.
 * @param: structure containing the RT priority.
 *
 * Return: On success, 0 and the RT priority is in @param. Otherwise, an error
 * code.
 */
SYSCALL_DEFINE2(sched_getparam, pid_t, pid, struct sched_param __user *, param)
{
        struct sched_param lp = { .sched_priority = 0 };
        struct task_struct *p;
        int retval;

        if (unlikely(!param || pid < 0))
                return -EINVAL;

        scoped_guard (rcu) {
                p = find_process_by_pid(pid);
                if (!p)
                        return -ESRCH;

                retval = security_task_getscheduler(p);
                if (retval)
                        return retval;

                if (task_has_rt_policy(p))
                        lp.sched_priority = p->rt_priority;
        }

        /*
         * This one might sleep, we cannot do it with a spinlock held ...
         */
        return copy_to_user(param, &lp, sizeof(*param)) ? -EFAULT : 0;
}

/**
 * sys_sched_getattr - similar to sched_getparam, but with sched_attr
 * @pid: the pid in question.
 * @uattr: structure containing the extended parameters.
 * @usize: sizeof(attr) for fwd/bwd comp.
 * @flags: for future extension.
 */
SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
                unsigned int, usize, unsigned int, flags)
{
        struct sched_attr kattr = { };
        struct task_struct *p;
        int retval;

        if (unlikely(!uattr || pid < 0 || usize > PAGE_SIZE ||
                      usize < SCHED_ATTR_SIZE_VER0 || flags))
                return -EINVAL;

        scoped_guard (rcu) {
                p = find_process_by_pid(pid);
                if (!p)
                        return -ESRCH;

                retval = security_task_getscheduler(p);
                if (retval)
                        return retval;

                kattr.sched_policy = p->policy;
                if (p->sched_reset_on_fork)
                        kattr.sched_flags |= SCHED_FLAG_RESET_ON_FORK;
                get_params(p, &kattr);
                kattr.sched_flags &= SCHED_FLAG_ALL;

#ifdef CONFIG_UCLAMP_TASK
                /*
                 * This could race with another potential updater, but this is fine
                 * because it'll correctly read the old or the new value. We don't need
                 * to guarantee who wins the race as long as it doesn't return garbage.
                 */
                kattr.sched_util_min = p->uclamp_req[UCLAMP_MIN].value;
                kattr.sched_util_max = p->uclamp_req[UCLAMP_MAX].value;
#endif
        }

        kattr.size = min(usize, sizeof(kattr));
        return copy_struct_to_user(uattr, usize, &kattr, sizeof(kattr), NULL);
}

int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask)
{
        /*
         * If the task isn't a deadline task or admission control is
         * disabled then we don't care about affinity changes.
         */
        if (!task_has_dl_policy(p) || !dl_bandwidth_enabled())
                return 0;

        /*
         * The special/sugov task isn't part of regular bandwidth/admission
         * control so let userspace change affinities.
         */
        if (dl_entity_is_special(&p->dl))
                return 0;

        /*
         * Since bandwidth control happens on root_domain basis,
         * if admission test is enabled, we only admit -deadline
         * tasks allowed to run on all the CPUs in the task's
         * root_domain.
         */
        guard(rcu)();
        if (!cpumask_subset(task_rq(p)->rd->span, mask))
                return -EBUSY;

        return 0;
}

int __sched_setaffinity(struct task_struct *p, struct affinity_context *ctx)
{
        int retval;
        cpumask_var_t cpus_allowed, new_mask;

        if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL))
                return -ENOMEM;

        if (!alloc_cpumask_var(&new_mask, GFP_KERNEL)) {
                retval = -ENOMEM;
                goto out_free_cpus_allowed;
        }

        cpuset_cpus_allowed(p, cpus_allowed);
        cpumask_and(new_mask, ctx->new_mask, cpus_allowed);

        ctx->new_mask = new_mask;
        ctx->flags |= SCA_CHECK;

        retval = dl_task_check_affinity(p, new_mask);
        if (retval)
                goto out_free_new_mask;

        retval = __set_cpus_allowed_ptr(p, ctx);
        if (retval)
                goto out_free_new_mask;

        cpuset_cpus_allowed(p, cpus_allowed);
        if (!cpumask_subset(new_mask, cpus_allowed)) {
                /*
                 * We must have raced with a concurrent cpuset update.
                 * Just reset the cpumask to the cpuset's cpus_allowed.
                 */
                cpumask_copy(new_mask, cpus_allowed);

                /*
                 * If SCA_USER is set, a 2nd call to __set_cpus_allowed_ptr()
                 * will restore the previous user_cpus_ptr value.
                 *
                 * In the unlikely event a previous user_cpus_ptr exists,
                 * we need to further restrict the mask to what is allowed
                 * by that old user_cpus_ptr.
                 */
                if (unlikely((ctx->flags & SCA_USER) && ctx->user_mask)) {
                        bool empty = !cpumask_and(new_mask, new_mask,
                                                  ctx->user_mask);

                        if (empty)
                                cpumask_copy(new_mask, cpus_allowed);
                }
                __set_cpus_allowed_ptr(p, ctx);
                retval = -EINVAL;
        }

out_free_new_mask:
        free_cpumask_var(new_mask);
out_free_cpus_allowed:
        free_cpumask_var(cpus_allowed);
        return retval;
}

long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
{
        struct affinity_context ac;
        struct cpumask *user_mask;
        int retval;

        CLASS(find_get_task, p)(pid);
        if (!p)
                return -ESRCH;

        if (p->flags & PF_NO_SETAFFINITY)
                return -EINVAL;

        if (!check_same_owner(p)) {
                guard(rcu)();
                if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE))
                        return -EPERM;
        }

        retval = security_task_setscheduler(p);
        if (retval)
                return retval;

        /*
         * With non-SMP configs, user_cpus_ptr/user_mask isn't used and
         * alloc_user_cpus_ptr() returns NULL.
         */
        user_mask = alloc_user_cpus_ptr(NUMA_NO_NODE);
        if (user_mask) {
                cpumask_copy(user_mask, in_mask);
        } else {
                return -ENOMEM;
        }

        ac = (struct affinity_context){
                .new_mask  = in_mask,
                .user_mask = user_mask,
                .flags     = SCA_USER,
        };

        retval = __sched_setaffinity(p, &ac);
        kfree(ac.user_mask);

        return retval;
}

static int get_user_cpu_mask(unsigned long __user *user_mask_ptr, unsigned len,
                             struct cpumask *new_mask)
{
        if (len < cpumask_size())
                cpumask_clear(new_mask);
        else if (len > cpumask_size())
                len = cpumask_size();

        return copy_from_user(new_mask, user_mask_ptr, len) ? -EFAULT : 0;
}

/**
 * sys_sched_setaffinity - set the CPU affinity of a process
 * @pid: pid of the process
 * @len: length in bytes of the bitmask pointed to by user_mask_ptr
 * @user_mask_ptr: user-space pointer to the new CPU mask
 *
 * Return: 0 on success. An error code otherwise.
 */
SYSCALL_DEFINE3(sched_setaffinity, pid_t, pid, unsigned int, len,
                unsigned long __user *, user_mask_ptr)
{
        cpumask_var_t new_mask;
        int retval;

        if (!alloc_cpumask_var(&new_mask, GFP_KERNEL))
                return -ENOMEM;

        retval = get_user_cpu_mask(user_mask_ptr, len, new_mask);
        if (retval == 0)
                retval = sched_setaffinity(pid, new_mask);
        free_cpumask_var(new_mask);
        return retval;
}

long sched_getaffinity(pid_t pid, struct cpumask *mask)
{
        struct task_struct *p;
        int retval;

        guard(rcu)();
        p = find_process_by_pid(pid);
        if (!p)
                return -ESRCH;

        retval = security_task_getscheduler(p);
        if (retval)
                return retval;

        guard(raw_spinlock_irqsave)(&p->pi_lock);
        cpumask_and(mask, &p->cpus_mask, cpu_active_mask);

        return 0;
}

/**
 * sys_sched_getaffinity - get the CPU affinity of a process
 * @pid: pid of the process
 * @len: length in bytes of the bitmask pointed to by user_mask_ptr
 * @user_mask_ptr: user-space pointer to hold the current CPU mask
 *
 * Return: size of CPU mask copied to user_mask_ptr on success. An
 * error code otherwise.
 */
SYSCALL_DEFINE3(sched_getaffinity, pid_t, pid, unsigned int, len,
                unsigned long __user *, user_mask_ptr)
{
        int ret;
        cpumask_var_t mask;

        if ((len * BITS_PER_BYTE) < nr_cpu_ids)
                return -EINVAL;
        if (len & (sizeof(unsigned long)-1))
                return -EINVAL;

        if (!zalloc_cpumask_var(&mask, GFP_KERNEL))
                return -ENOMEM;

        ret = sched_getaffinity(pid, mask);
        if (ret == 0) {
                unsigned int retlen = min(len, cpumask_size());

                if (copy_to_user(user_mask_ptr, cpumask_bits(mask), retlen))
                        ret = -EFAULT;
                else
                        ret = retlen;
        }
        free_cpumask_var(mask);

        return ret;
}

static void do_sched_yield(void)
{
        struct rq_flags rf;
        struct rq *rq;

        rq = this_rq_lock_irq(&rf);

        schedstat_inc(rq->yld_count);
        rq->donor->sched_class->yield_task(rq);

        preempt_disable();
        rq_unlock_irq(rq, &rf);
        sched_preempt_enable_no_resched();

        schedule();
}

/**
 * sys_sched_yield - yield the current processor to other threads.
 *
 * This function yields the current CPU to other tasks. If there are no
 * other threads running on this CPU then this function will return.
 *
 * Return: 0.
 */
SYSCALL_DEFINE0(sched_yield)
{
        do_sched_yield();
        return 0;
}

/**
 * yield - yield the current processor to other threads.
 *
 * Do not ever use this function, there's a 99% chance you're doing it wrong.
 *
 * The scheduler is at all times free to pick the calling task as the most
 * eligible task to run, if removing the yield() call from your code breaks
 * it, it's already broken.
 *
 * Typical broken usage is:
 *
 * while (!event)
 *      yield();
 *
 * where one assumes that yield() will let 'the other' process run that will
 * make event true. If the current task is a SCHED_FIFO task that will never
 * happen. Never use yield() as a progress guarantee!!
 *
 * If you want to use yield() to wait for something, use wait_event().
 * If you want to use yield() to be 'nice' for others, use cond_resched().
 * If you still want to use yield(), do not!
 */
void __sched yield(void)
{
        set_current_state(TASK_RUNNING);
        do_sched_yield();
}
EXPORT_SYMBOL(yield);

/**
 * yield_to - yield the current processor to another thread in
 * your thread group, or accelerate that thread toward the
 * processor it's on.
 * @p: target task
 * @preempt: whether task preemption is allowed or not
 *
 * It's the caller's job to ensure that the target task struct
 * can't go away on us before we can do any checks.
 *
 * Return:
 *      true (>0) if we indeed boosted the target task.
 *      false (0) if we failed to boost the target.
 *      -ESRCH if there's no task to yield to.
 */
int __sched yield_to(struct task_struct *p, bool preempt)
{
        struct task_struct *curr;
        struct rq *rq, *p_rq;
        int yielded = 0;

        scoped_guard (raw_spinlock_irqsave, &p->pi_lock) {
                rq = this_rq();
                curr = rq->donor;

again:
                p_rq = task_rq(p);
                /*
                 * If we're the only runnable task on the rq and target rq also
                 * has only one task, there's absolutely no point in yielding.
                 */
                if (rq->nr_running == 1 && p_rq->nr_running == 1)
                        return -ESRCH;

                guard(double_rq_lock)(rq, p_rq);
                if (task_rq(p) != p_rq)
                        goto again;

                if (!curr->sched_class->yield_to_task)
                        return 0;

                if (curr->sched_class != p->sched_class)
                        return 0;

                if (task_on_cpu(p_rq, p) || !task_is_running(p))
                        return 0;

                yielded = curr->sched_class->yield_to_task(rq, p);
                if (yielded) {
                        schedstat_inc(rq->yld_count);
                        /*
                         * Make p's CPU reschedule; pick_next_entity
                         * takes care of fairness.
                         */
                        if (preempt && rq != p_rq)
                                resched_curr(p_rq);
                }
        }

        if (yielded)
                schedule();

        return yielded;
}
EXPORT_SYMBOL_GPL(yield_to);

/**
 * sys_sched_get_priority_max - return maximum RT priority.
 * @policy: scheduling class.
 *
 * Return: On success, this syscall returns the maximum
 * rt_priority that can be used by a given scheduling class.
 * On failure, a negative error code is returned.
 */
SYSCALL_DEFINE1(sched_get_priority_max, int, policy)
{
        int ret = -EINVAL;

        switch (policy) {
        case SCHED_FIFO:
        case SCHED_RR:
                ret = MAX_RT_PRIO-1;
                break;
        case SCHED_DEADLINE:
        case SCHED_NORMAL:
        case SCHED_BATCH:
        case SCHED_IDLE:
        case SCHED_EXT:
                ret = 0;
                break;
        }
        return ret;
}

/**
 * sys_sched_get_priority_min - return minimum RT priority.
 * @policy: scheduling class.
 *
 * Return: On success, this syscall returns the minimum
 * rt_priority that can be used by a given scheduling class.
 * On failure, a negative error code is returned.
 */
SYSCALL_DEFINE1(sched_get_priority_min, int, policy)
{
        int ret = -EINVAL;

        switch (policy) {
        case SCHED_FIFO:
        case SCHED_RR:
                ret = 1;
                break;
        case SCHED_DEADLINE:
        case SCHED_NORMAL:
        case SCHED_BATCH:
        case SCHED_IDLE:
        case SCHED_EXT:
                ret = 0;
        }
        return ret;
}

static int sched_rr_get_interval(pid_t pid, struct timespec64 *t)
{
        unsigned int time_slice = 0;
        int retval;

        if (pid < 0)
                return -EINVAL;

        scoped_guard (rcu) {
                struct task_struct *p = find_process_by_pid(pid);
                if (!p)
                        return -ESRCH;

                retval = security_task_getscheduler(p);
                if (retval)
                        return retval;

                scoped_guard (task_rq_lock, p) {
                        struct rq *rq = scope.rq;
                        if (p->sched_class->get_rr_interval)
                                time_slice = p->sched_class->get_rr_interval(rq, p);
                }
        }

        jiffies_to_timespec64(time_slice, t);
        return 0;
}

/**
 * sys_sched_rr_get_interval - return the default time-slice of a process.
 * @pid: pid of the process.
 * @interval: userspace pointer to the time-slice value.
 *
 * this syscall writes the default time-slice value of a given process
 * into the user-space timespec buffer. A value of '0' means infinity.
 *
 * Return: On success, 0 and the time-slice is in @interval. Otherwise,
 * an error code.
 */
SYSCALL_DEFINE2(sched_rr_get_interval, pid_t, pid,
                struct __kernel_timespec __user *, interval)
{
        struct timespec64 t;
        int retval = sched_rr_get_interval(pid, &t);

        if (retval == 0)
                retval = put_timespec64(&t, interval);

        return retval;
}

#ifdef CONFIG_COMPAT_32BIT_TIME
SYSCALL_DEFINE2(sched_rr_get_interval_time32, pid_t, pid,
                struct old_timespec32 __user *, interval)
{
        struct timespec64 t;
        int retval = sched_rr_get_interval(pid, &t);

        if (retval == 0)
                retval = put_old_timespec32(&t, interval);
        return retval;
}
#endif