// SPDX-License-Identifier: GPL-2.0-only
#include "cgroup-internal.h"

#include <linux/sched/cputime.h>

static DEFINE_SPINLOCK(cgroup_rstat_lock);
static DEFINE_PER_CPU(raw_spinlock_t, cgroup_rstat_cpu_lock);

static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu);

static struct cgroup_rstat_cpu *cgroup_rstat_cpu(struct cgroup *cgrp, int cpu)
{
        return per_cpu_ptr(cgrp->rstat_cpu, cpu);
}

/**
 * cgroup_rstat_updated - keep track of updated rstat_cpu
 * @cgrp: target cgroup
 * @cpu: cpu on which rstat_cpu was updated
 *
 * @cgrp's rstat_cpu on @cpu was updated.  Put it on the parent's matching
 * rstat_cpu->updated_children list.  See the comment on top of
 * cgroup_rstat_cpu definition for details.
 */
void cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
{
        raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu);
        unsigned long flags;

        /*
         * Speculative already-on-list test. This may race leading to
         * temporary inaccuracies, which is fine.
         *
         * Because @parent's updated_children is terminated with @parent
         * instead of NULL, we can tell whether @cgrp is on the list by
         * testing the next pointer for NULL.
         */
        if (cgroup_rstat_cpu(cgrp, cpu)->updated_next)
                return;

        raw_spin_lock_irqsave(cpu_lock, flags);

        /* put @cgrp and all ancestors on the corresponding updated lists */
        while (true) {
                struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
                struct cgroup *parent = cgroup_parent(cgrp);
                struct cgroup_rstat_cpu *prstatc;

                /*
                 * Both additions and removals are bottom-up.  If a cgroup
                 * is already in the tree, all ancestors are.
                 */
                if (rstatc->updated_next)
                        break;

                /* Root has no parent to link it to, but mark it busy */
                if (!parent) {
                        rstatc->updated_next = cgrp;
                        break;
                }

                prstatc = cgroup_rstat_cpu(parent, cpu);
                rstatc->updated_next = prstatc->updated_children;
                prstatc->updated_children = cgrp;

                cgrp = parent;
        }

        raw_spin_unlock_irqrestore(cpu_lock, flags);
}

/**
 * cgroup_rstat_cpu_pop_updated - iterate and dismantle rstat_cpu updated tree
 * @pos: current position
 * @root: root of the tree to traversal
 * @cpu: target cpu
 *
 * Walks the updated rstat_cpu tree on @cpu from @root.  %NULL @pos starts
 * the traversal and %NULL return indicates the end.  During traversal,
 * each returned cgroup is unlinked from the tree.  Must be called with the
 * matching cgroup_rstat_cpu_lock held.
 *
 * The only ordering guarantee is that, for a parent and a child pair
 * covered by a given traversal, if a child is visited, its parent is
 * guaranteed to be visited afterwards.
 */
static struct cgroup *cgroup_rstat_cpu_pop_updated(struct cgroup *pos,
                                                   struct cgroup *root, int cpu)
{
        struct cgroup_rstat_cpu *rstatc;

        if (pos == root)
                return NULL;

        /*
         * We're gonna walk down to the first leaf and visit/remove it.  We
         * can pick whatever unvisited node as the starting point.
         */
        if (!pos)
                pos = root;
        else
                pos = cgroup_parent(pos);

        /* walk down to the first leaf */
        while (true) {
                rstatc = cgroup_rstat_cpu(pos, cpu);
                if (rstatc->updated_children == pos)
                        break;
                pos = rstatc->updated_children;
        }

        /*
         * Unlink @pos from the tree.  As the updated_children list is
         * singly linked, we have to walk it to find the removal point.
         * However, due to the way we traverse, @pos will be the first
         * child in most cases. The only exception is @root.
         */
        if (rstatc->updated_next) {
                struct cgroup *parent = cgroup_parent(pos);

                if (parent) {
                        struct cgroup_rstat_cpu *prstatc;
                        struct cgroup **nextp;

                        prstatc = cgroup_rstat_cpu(parent, cpu);
                        nextp = &prstatc->updated_children;
                        while (true) {
                                struct cgroup_rstat_cpu *nrstatc;

                                nrstatc = cgroup_rstat_cpu(*nextp, cpu);
                                if (*nextp == pos)
                                        break;
                                WARN_ON_ONCE(*nextp == parent);
                                nextp = &nrstatc->updated_next;
                        }
                        *nextp = rstatc->updated_next;
                }

                rstatc->updated_next = NULL;
                return pos;
        }

        /* only happens for @root */
        return NULL;
}

/* see cgroup_rstat_flush() */
static void cgroup_rstat_flush_locked(struct cgroup *cgrp, bool may_sleep)
        __releases(&cgroup_rstat_lock) __acquires(&cgroup_rstat_lock)
{
        int cpu;

        lockdep_assert_held(&cgroup_rstat_lock);

        for_each_possible_cpu(cpu) {
                raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock,
                                                       cpu);
                struct cgroup *pos = NULL;

                raw_spin_lock(cpu_lock);
                while ((pos = cgroup_rstat_cpu_pop_updated(pos, cgrp, cpu))) {
                        struct cgroup_subsys_state *css;

                        cgroup_base_stat_flush(pos, cpu);

                        rcu_read_lock();
                        list_for_each_entry_rcu(css, &pos->rstat_css_list,
                                                rstat_css_node)
                                css->ss->css_rstat_flush(css, cpu);
                        rcu_read_unlock();
                }
                raw_spin_unlock(cpu_lock);

                /* if @may_sleep, play nice and yield if necessary */
                if (may_sleep && (need_resched() ||
                                  spin_needbreak(&cgroup_rstat_lock))) {
                        spin_unlock_irq(&cgroup_rstat_lock);
                        if (!cond_resched())
                                cpu_relax();
                        spin_lock_irq(&cgroup_rstat_lock);
                }
        }
}

/**
 * cgroup_rstat_flush - flush stats in @cgrp's subtree
 * @cgrp: target cgroup
 *
 * Collect all per-cpu stats in @cgrp's subtree into the global counters
 * and propagate them upwards.  After this function returns, all cgroups in
 * the subtree have up-to-date ->stat.
 *
 * This also gets all cgroups in the subtree including @cgrp off the
 * ->updated_children lists.
 *
 * This function may block.
 */
void cgroup_rstat_flush(struct cgroup *cgrp)
{
        might_sleep();

        spin_lock_irq(&cgroup_rstat_lock);
        cgroup_rstat_flush_locked(cgrp, true);
        spin_unlock_irq(&cgroup_rstat_lock);
}

/**
 * cgroup_rstat_flush_irqsafe - irqsafe version of cgroup_rstat_flush()
 * @cgrp: target cgroup
 *
 * This function can be called from any context.
 */
void cgroup_rstat_flush_irqsafe(struct cgroup *cgrp)
{
        unsigned long flags;

        spin_lock_irqsave(&cgroup_rstat_lock, flags);
        cgroup_rstat_flush_locked(cgrp, false);
        spin_unlock_irqrestore(&cgroup_rstat_lock, flags);
}

/**
 * cgroup_rstat_flush_hold - flush stats in @cgrp's subtree and hold
 * @cgrp: target cgroup
 *
 * Flush stats in @cgrp's subtree and prevent further flushes.  Must be
 * paired with cgroup_rstat_flush_release().
 *
 * This function may block.
 */
void cgroup_rstat_flush_hold(struct cgroup *cgrp)
        __acquires(&cgroup_rstat_lock)
{
        might_sleep();
        spin_lock_irq(&cgroup_rstat_lock);
        cgroup_rstat_flush_locked(cgrp, true);
}

/**
 * cgroup_rstat_flush_release - release cgroup_rstat_flush_hold()
 */
void cgroup_rstat_flush_release(void)
        __releases(&cgroup_rstat_lock)
{
        spin_unlock_irq(&cgroup_rstat_lock);
}

int cgroup_rstat_init(struct cgroup *cgrp)
{
        int cpu;

        /* the root cgrp has rstat_cpu preallocated */
        if (!cgrp->rstat_cpu) {
                cgrp->rstat_cpu = alloc_percpu(struct cgroup_rstat_cpu);
                if (!cgrp->rstat_cpu)
                        return -ENOMEM;
        }

        /* ->updated_children list is self terminated */
        for_each_possible_cpu(cpu) {
                struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);

                rstatc->updated_children = cgrp;
                u64_stats_init(&rstatc->bsync);
        }

        return 0;
}

void cgroup_rstat_exit(struct cgroup *cgrp)
{
        int cpu;

        cgroup_rstat_flush(cgrp);

        /* sanity check */
        for_each_possible_cpu(cpu) {
                struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);

                if (WARN_ON_ONCE(rstatc->updated_children != cgrp) ||
                    WARN_ON_ONCE(rstatc->updated_next))
                        return;
        }

        free_percpu(cgrp->rstat_cpu);
        cgrp->rstat_cpu = NULL;
}

void __init cgroup_rstat_boot(void)
{
        int cpu;

        for_each_possible_cpu(cpu)
                raw_spin_lock_init(per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu));
}

/*
 * Functions for cgroup basic resource statistics implemented on top of
 * rstat.
 */
static void cgroup_base_stat_add(struct cgroup_base_stat *dst_bstat,
                                 struct cgroup_base_stat *src_bstat)
{
        dst_bstat->cputime.utime += src_bstat->cputime.utime;
        dst_bstat->cputime.stime += src_bstat->cputime.stime;
        dst_bstat->cputime.sum_exec_runtime += src_bstat->cputime.sum_exec_runtime;
}

static void cgroup_base_stat_sub(struct cgroup_base_stat *dst_bstat,
                                 struct cgroup_base_stat *src_bstat)
{
        dst_bstat->cputime.utime -= src_bstat->cputime.utime;
        dst_bstat->cputime.stime -= src_bstat->cputime.stime;
        dst_bstat->cputime.sum_exec_runtime -= src_bstat->cputime.sum_exec_runtime;
}

static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
{
        struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
        struct cgroup *parent = cgroup_parent(cgrp);
        struct cgroup_base_stat cur, delta;
        unsigned seq;

        /* Root-level stats are sourced from system-wide CPU stats */
        if (!parent)
                return;

        /* fetch the current per-cpu values */
        do {
                seq = __u64_stats_fetch_begin(&rstatc->bsync);
                cur.cputime = rstatc->bstat.cputime;
        } while (__u64_stats_fetch_retry(&rstatc->bsync, seq));

        /* propagate percpu delta to global */
        delta = cur;
        cgroup_base_stat_sub(&delta, &rstatc->last_bstat);
        cgroup_base_stat_add(&cgrp->bstat, &delta);
        cgroup_base_stat_add(&rstatc->last_bstat, &delta);

        /* propagate global delta to parent (unless that's root) */
        if (cgroup_parent(parent)) {
                delta = cgrp->bstat;
                cgroup_base_stat_sub(&delta, &cgrp->last_bstat);
                cgroup_base_stat_add(&parent->bstat, &delta);
                cgroup_base_stat_add(&cgrp->last_bstat, &delta);
        }
}

static struct cgroup_rstat_cpu *
cgroup_base_stat_cputime_account_begin(struct cgroup *cgrp, unsigned long *flags)
{
        struct cgroup_rstat_cpu *rstatc;

        rstatc = get_cpu_ptr(cgrp->rstat_cpu);
        *flags = u64_stats_update_begin_irqsave(&rstatc->bsync);
        return rstatc;
}

static void cgroup_base_stat_cputime_account_end(struct cgroup *cgrp,
                                                 struct cgroup_rstat_cpu *rstatc,
                                                 unsigned long flags)
{
        u64_stats_update_end_irqrestore(&rstatc->bsync, flags);
        cgroup_rstat_updated(cgrp, smp_processor_id());
        put_cpu_ptr(rstatc);
}

void __cgroup_account_cputime(struct cgroup *cgrp, u64 delta_exec)
{
        struct cgroup_rstat_cpu *rstatc;
        unsigned long flags;

        rstatc = cgroup_base_stat_cputime_account_begin(cgrp, &flags);
        rstatc->bstat.cputime.sum_exec_runtime += delta_exec;
        cgroup_base_stat_cputime_account_end(cgrp, rstatc, flags);
}

void __cgroup_account_cputime_field(struct cgroup *cgrp,
                                    enum cpu_usage_stat index, u64 delta_exec)
{
        struct cgroup_rstat_cpu *rstatc;
        unsigned long flags;

        rstatc = cgroup_base_stat_cputime_account_begin(cgrp, &flags);

        switch (index) {
        case CPUTIME_USER:
        case CPUTIME_NICE:
                rstatc->bstat.cputime.utime += delta_exec;
                break;
        case CPUTIME_SYSTEM:
        case CPUTIME_IRQ:
        case CPUTIME_SOFTIRQ:
                rstatc->bstat.cputime.stime += delta_exec;
                break;
        default:
                break;
        }

        cgroup_base_stat_cputime_account_end(cgrp, rstatc, flags);
}

/*
 * compute the cputime for the root cgroup by getting the per cpu data
 * at a global level, then categorizing the fields in a manner consistent
 * with how it is done by __cgroup_account_cputime_field for each bit of
 * cpu time attributed to a cgroup.
 */
static void root_cgroup_cputime(struct task_cputime *cputime)
{
        int i;

        cputime->stime = 0;
        cputime->utime = 0;
        cputime->sum_exec_runtime = 0;
        for_each_possible_cpu(i) {
                struct kernel_cpustat kcpustat;
                u64 *cpustat = kcpustat.cpustat;
                u64 user = 0;
                u64 sys = 0;

                kcpustat_cpu_fetch(&kcpustat, i);

                user += cpustat[CPUTIME_USER];
                user += cpustat[CPUTIME_NICE];
                cputime->utime += user;

                sys += cpustat[CPUTIME_SYSTEM];
                sys += cpustat[CPUTIME_IRQ];
                sys += cpustat[CPUTIME_SOFTIRQ];
                cputime->stime += sys;

                cputime->sum_exec_runtime += user;
                cputime->sum_exec_runtime += sys;
                cputime->sum_exec_runtime += cpustat[CPUTIME_STEAL];
                cputime->sum_exec_runtime += cpustat[CPUTIME_GUEST];
                cputime->sum_exec_runtime += cpustat[CPUTIME_GUEST_NICE];
        }
}

void cgroup_base_stat_cputime_show(struct seq_file *seq)
{
        struct cgroup *cgrp = seq_css(seq)->cgroup;
        u64 usage, utime, stime;
        struct task_cputime cputime;

        if (cgroup_parent(cgrp)) {
                cgroup_rstat_flush_hold(cgrp);
                usage = cgrp->bstat.cputime.sum_exec_runtime;
                cputime_adjust(&cgrp->bstat.cputime, &cgrp->prev_cputime,
                               &utime, &stime);
                cgroup_rstat_flush_release();
        } else {
                root_cgroup_cputime(&cputime);
                usage = cputime.sum_exec_runtime;
                utime = cputime.utime;
                stime = cputime.stime;
        }

        do_div(usage, NSEC_PER_USEC);
        do_div(utime, NSEC_PER_USEC);
        do_div(stime, NSEC_PER_USEC);

        seq_printf(seq, "usage_usec %llu\n"
                   "user_usec %llu\n"
                   "system_usec %llu\n",
                   usage, utime, stime);
}