// SPDX-License-Identifier: GPL-2.0-or-later
/* delayacct.c - per-task delay accounting
 *
 * Copyright (C) Shailabh Nagar, IBM Corp. 2006
 */

#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/sched/cputime.h>
#include <linux/sched/clock.h>
#include <linux/slab.h>
#include <linux/taskstats.h>
#include <linux/sysctl.h>
#include <linux/delayacct.h>
#include <linux/module.h>

DEFINE_STATIC_KEY_FALSE(delayacct_key);
int delayacct_on __read_mostly; /* Delay accounting turned on/off */
struct kmem_cache *delayacct_cache;

static void set_delayacct(bool enabled)
{
        if (enabled) {
                static_branch_enable(&delayacct_key);
                delayacct_on = 1;
        } else {
                delayacct_on = 0;
                static_branch_disable(&delayacct_key);
        }
}

static int __init delayacct_setup_enable(char *str)
{
        delayacct_on = 1;
        return 1;
}
__setup("delayacct", delayacct_setup_enable);

void delayacct_init(void)
{
        delayacct_cache = KMEM_CACHE(task_delay_info, SLAB_PANIC|SLAB_ACCOUNT);
        delayacct_tsk_init(&init_task);
        set_delayacct(delayacct_on);
}

#ifdef CONFIG_PROC_SYSCTL
int sysctl_delayacct(struct ctl_table *table, int write, void *buffer,
                     size_t *lenp, loff_t *ppos)
{
        int state = delayacct_on;
        struct ctl_table t;
        int err;

        if (write && !capable(CAP_SYS_ADMIN))
                return -EPERM;

        t = *table;
        t.data = &state;
        err = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
        if (err < 0)
                return err;
        if (write)
                set_delayacct(state);
        return err;
}
#endif

void __delayacct_tsk_init(struct task_struct *tsk)
{
        tsk->delays = kmem_cache_zalloc(delayacct_cache, GFP_KERNEL);
        if (tsk->delays)
                raw_spin_lock_init(&tsk->delays->lock);
}

/*
 * Finish delay accounting for a statistic using its timestamps (@start),
 * accumalator (@total) and @count
 */
static void delayacct_end(raw_spinlock_t *lock, u64 *start, u64 *total, u32 *count)
{
        s64 ns = local_clock() - *start;
        unsigned long flags;

        if (ns > 0) {
                raw_spin_lock_irqsave(lock, flags);
                *total += ns;
                (*count)++;
                raw_spin_unlock_irqrestore(lock, flags);
        }
}

void __delayacct_blkio_start(void)
{
        current->delays->blkio_start = local_clock();
}

/*
 * We cannot rely on the `current` macro, as we haven't yet switched back to
 * the process being woken.
 */
void __delayacct_blkio_end(struct task_struct *p)
{
        struct task_delay_info *delays = p->delays;
        u64 *total;
        u32 *count;

        if (p->delays->flags & DELAYACCT_PF_SWAPIN) {
                total = &delays->swapin_delay;
                count = &delays->swapin_count;
        } else {
                total = &delays->blkio_delay;
                count = &delays->blkio_count;
        }

        delayacct_end(&delays->lock, &delays->blkio_start, total, count);
}

int delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
{
        u64 utime, stime, stimescaled, utimescaled;
        unsigned long long t2, t3;
        unsigned long flags, t1;
        s64 tmp;

        task_cputime(tsk, &utime, &stime);
        tmp = (s64)d->cpu_run_real_total;
        tmp += utime + stime;
        d->cpu_run_real_total = (tmp < (s64)d->cpu_run_real_total) ? 0 : tmp;

        task_cputime_scaled(tsk, &utimescaled, &stimescaled);
        tmp = (s64)d->cpu_scaled_run_real_total;
        tmp += utimescaled + stimescaled;
        d->cpu_scaled_run_real_total =
                (tmp < (s64)d->cpu_scaled_run_real_total) ? 0 : tmp;

        /*
         * No locking available for sched_info (and too expensive to add one)
         * Mitigate by taking snapshot of values
         */
        t1 = tsk->sched_info.pcount;
        t2 = tsk->sched_info.run_delay;
        t3 = tsk->se.sum_exec_runtime;

        d->cpu_count += t1;

        tmp = (s64)d->cpu_delay_total + t2;
        d->cpu_delay_total = (tmp < (s64)d->cpu_delay_total) ? 0 : tmp;

        tmp = (s64)d->cpu_run_virtual_total + t3;
        d->cpu_run_virtual_total =
                (tmp < (s64)d->cpu_run_virtual_total) ? 0 : tmp;

        if (!tsk->delays)
                return 0;

        /* zero XXX_total, non-zero XXX_count implies XXX stat overflowed */

        raw_spin_lock_irqsave(&tsk->delays->lock, flags);
        tmp = d->blkio_delay_total + tsk->delays->blkio_delay;
        d->blkio_delay_total = (tmp < d->blkio_delay_total) ? 0 : tmp;
        tmp = d->swapin_delay_total + tsk->delays->swapin_delay;
        d->swapin_delay_total = (tmp < d->swapin_delay_total) ? 0 : tmp;
        tmp = d->freepages_delay_total + tsk->delays->freepages_delay;
        d->freepages_delay_total = (tmp < d->freepages_delay_total) ? 0 : tmp;
        tmp = d->thrashing_delay_total + tsk->delays->thrashing_delay;
        d->thrashing_delay_total = (tmp < d->thrashing_delay_total) ? 0 : tmp;
        d->blkio_count += tsk->delays->blkio_count;
        d->swapin_count += tsk->delays->swapin_count;
        d->freepages_count += tsk->delays->freepages_count;
        d->thrashing_count += tsk->delays->thrashing_count;
        raw_spin_unlock_irqrestore(&tsk->delays->lock, flags);

        return 0;
}

__u64 __delayacct_blkio_ticks(struct task_struct *tsk)
{
        __u64 ret;
        unsigned long flags;

        raw_spin_lock_irqsave(&tsk->delays->lock, flags);
        ret = nsec_to_clock_t(tsk->delays->blkio_delay +
                                tsk->delays->swapin_delay);
        raw_spin_unlock_irqrestore(&tsk->delays->lock, flags);
        return ret;
}

void __delayacct_freepages_start(void)
{
        current->delays->freepages_start = local_clock();
}

void __delayacct_freepages_end(void)
{
        delayacct_end(&current->delays->lock,
                      &current->delays->freepages_start,
                      &current->delays->freepages_delay,
                      &current->delays->freepages_count);
}

void __delayacct_thrashing_start(void)
{
        current->delays->thrashing_start = local_clock();
}

void __delayacct_thrashing_end(void)
{
        delayacct_end(&current->delays->lock,
                      &current->delays->thrashing_start,
                      &current->delays->thrashing_delay,
                      &current->delays->thrashing_count);
}