#include "cgroup-internal.h"

#include <linux/sched/cputime.h>

static DEFINE_MUTEX(cgroup_stat_mutex);
static DEFINE_PER_CPU(raw_spinlock_t, cgroup_cpu_stat_lock);

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

/**
 * cgroup_cpu_stat_updated - keep track of updated cpu_stat
 * @cgrp: target cgroup
 * @cpu: cpu on which cpu_stat was updated
 *
 * @cgrp's cpu_stat on @cpu was updated.  Put it on the parent's matching
 * cpu_stat->updated_children list.  See the comment on top of
 * cgroup_cpu_stat definition for details.
 */
static void cgroup_cpu_stat_updated(struct cgroup *cgrp, int cpu)
{
        raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_cpu_stat_lock, cpu);
        struct cgroup *parent;
        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_cpu_stat(cgrp, cpu)->updated_next)
                return;

        raw_spin_lock_irqsave(cpu_lock, flags);

        /* put @cgrp and all ancestors on the corresponding updated lists */
        for (parent = cgroup_parent(cgrp); parent;
             cgrp = parent, parent = cgroup_parent(cgrp)) {
                struct cgroup_cpu_stat *cstat = cgroup_cpu_stat(cgrp, cpu);
                struct cgroup_cpu_stat *pcstat = cgroup_cpu_stat(parent, cpu);

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

                cstat->updated_next = pcstat->updated_children;
                pcstat->updated_children = cgrp;
        }

        raw_spin_unlock_irqrestore(cpu_lock, flags);
}

/**
 * cgroup_cpu_stat_pop_updated - iterate and dismantle cpu_stat updated tree
 * @pos: current position
 * @root: root of the tree to traversal
 * @cpu: target cpu
 *
 * Walks the udpated cpu_stat 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_cpu_stat_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_cpu_stat_pop_updated(struct cgroup *pos,
                                                  struct cgroup *root, int cpu)
{
        struct cgroup_cpu_stat *cstat;
        struct cgroup *parent;

        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) {
                cstat = cgroup_cpu_stat(pos, cpu);
                if (cstat->updated_children == pos)
                        break;
                pos = cstat->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.
         */
        parent = cgroup_parent(pos);
        if (parent && cstat->updated_next) {
                struct cgroup_cpu_stat *pcstat = cgroup_cpu_stat(parent, cpu);
                struct cgroup_cpu_stat *ncstat;
                struct cgroup **nextp;

                nextp = &pcstat->updated_children;
                while (true) {
                        ncstat = cgroup_cpu_stat(*nextp, cpu);
                        if (*nextp == pos)
                                break;

                        WARN_ON_ONCE(*nextp == parent);
                        nextp = &ncstat->updated_next;
                }

                *nextp = cstat->updated_next;
                cstat->updated_next = NULL;
        }

        return pos;
}

static void cgroup_stat_accumulate(struct cgroup_stat *dst_stat,
                                   struct cgroup_stat *src_stat)
{
        dst_stat->cputime.utime += src_stat->cputime.utime;
        dst_stat->cputime.stime += src_stat->cputime.stime;
        dst_stat->cputime.sum_exec_runtime += src_stat->cputime.sum_exec_runtime;
}

static void cgroup_cpu_stat_flush_one(struct cgroup *cgrp, int cpu)
{
        struct cgroup *parent = cgroup_parent(cgrp);
        struct cgroup_cpu_stat *cstat = cgroup_cpu_stat(cgrp, cpu);
        struct task_cputime *last_cputime = &cstat->last_cputime;
        struct task_cputime cputime;
        struct cgroup_stat delta;
        unsigned seq;

        lockdep_assert_held(&cgroup_stat_mutex);

        /* fetch the current per-cpu values */
        do {
                seq = __u64_stats_fetch_begin(&cstat->sync);
                cputime = cstat->cputime;
        } while (__u64_stats_fetch_retry(&cstat->sync, seq));

        /* accumulate the deltas to propgate */
        delta.cputime.utime = cputime.utime - last_cputime->utime;
        delta.cputime.stime = cputime.stime - last_cputime->stime;
        delta.cputime.sum_exec_runtime = cputime.sum_exec_runtime -
                                         last_cputime->sum_exec_runtime;
        *last_cputime = cputime;

        /* transfer the pending stat into delta */
        cgroup_stat_accumulate(&delta, &cgrp->pending_stat);
        memset(&cgrp->pending_stat, 0, sizeof(cgrp->pending_stat));

        /* propagate delta into the global stat and the parent's pending */
        cgroup_stat_accumulate(&cgrp->stat, &delta);
        if (parent)
                cgroup_stat_accumulate(&parent->pending_stat, &delta);
}

/* see cgroup_stat_flush() */
static void cgroup_stat_flush_locked(struct cgroup *cgrp)
{
        int cpu;

        lockdep_assert_held(&cgroup_stat_mutex);

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

                raw_spin_lock_irq(cpu_lock);
                while ((pos = cgroup_cpu_stat_pop_updated(pos, cgrp, cpu)))
                        cgroup_cpu_stat_flush_one(pos, cpu);
                raw_spin_unlock_irq(cpu_lock);
        }
}

/**
 * cgroup_stat_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.
 */
void cgroup_stat_flush(struct cgroup *cgrp)
{
        mutex_lock(&cgroup_stat_mutex);
        cgroup_stat_flush_locked(cgrp);
        mutex_unlock(&cgroup_stat_mutex);
}

static struct cgroup_cpu_stat *cgroup_cpu_stat_account_begin(struct cgroup *cgrp)
{
        struct cgroup_cpu_stat *cstat;

        cstat = get_cpu_ptr(cgrp->cpu_stat);
        u64_stats_update_begin(&cstat->sync);
        return cstat;
}

static void cgroup_cpu_stat_account_end(struct cgroup *cgrp,
                                        struct cgroup_cpu_stat *cstat)
{
        u64_stats_update_end(&cstat->sync);
        cgroup_cpu_stat_updated(cgrp, smp_processor_id());
        put_cpu_ptr(cstat);
}

void __cgroup_account_cputime(struct cgroup *cgrp, u64 delta_exec)
{
        struct cgroup_cpu_stat *cstat;

        cstat = cgroup_cpu_stat_account_begin(cgrp);
        cstat->cputime.sum_exec_runtime += delta_exec;
        cgroup_cpu_stat_account_end(cgrp, cstat);
}

void __cgroup_account_cputime_field(struct cgroup *cgrp,
                                    enum cpu_usage_stat index, u64 delta_exec)
{
        struct cgroup_cpu_stat *cstat;

        cstat = cgroup_cpu_stat_account_begin(cgrp);

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

        cgroup_cpu_stat_account_end(cgrp, cstat);
}

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

        if (!cgroup_parent(cgrp))
                return;

        mutex_lock(&cgroup_stat_mutex);

        cgroup_stat_flush_locked(cgrp);

        usage = cgrp->stat.cputime.sum_exec_runtime;
        cputime_adjust(&cgrp->stat.cputime, &cgrp->stat.prev_cputime,
                       &utime, &stime);

        mutex_unlock(&cgroup_stat_mutex);

        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);
}

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

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

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

                cstat->updated_children = cgrp;
                u64_stats_init(&cstat->sync);
        }

        prev_cputime_init(&cgrp->stat.prev_cputime);

        return 0;
}

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

        cgroup_stat_flush(cgrp);

        /* sanity check */
        for_each_possible_cpu(cpu) {
                struct cgroup_cpu_stat *cstat = cgroup_cpu_stat(cgrp, cpu);

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

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

void __init cgroup_stat_boot(void)
{
        int cpu;

        for_each_possible_cpu(cpu)
                raw_spin_lock_init(per_cpu_ptr(&cgroup_cpu_stat_lock, cpu));

        BUG_ON(cgroup_stat_init(&cgrp_dfl_root.cgrp));
}