// SPDX-License-Identifier: GPL-2.0
/*
 * Auto-group scheduling implementation:
 */
#include <linux/nospec.h>
#include "sched.h"

unsigned int __read_mostly sysctl_sched_autogroup_enabled = 1;
static struct autogroup autogroup_default;
static atomic_t autogroup_seq_nr;

void __init autogroup_init(struct task_struct *init_task)
{
        autogroup_default.tg = &root_task_group;
        kref_init(&autogroup_default.kref);
        init_rwsem(&autogroup_default.lock);
        init_task->signal->autogroup = &autogroup_default;
}

void autogroup_free(struct task_group *tg)
{
        kfree(tg->autogroup);
}

static inline void autogroup_destroy(struct kref *kref)
{
        struct autogroup *ag = container_of(kref, struct autogroup, kref);

#ifdef CONFIG_RT_GROUP_SCHED
        /* We've redirected RT tasks to the root task group... */
        ag->tg->rt_se = NULL;
        ag->tg->rt_rq = NULL;
#endif
        sched_offline_group(ag->tg);
        sched_destroy_group(ag->tg);
}

static inline void autogroup_kref_put(struct autogroup *ag)
{
        kref_put(&ag->kref, autogroup_destroy);
}

static inline struct autogroup *autogroup_kref_get(struct autogroup *ag)
{
        kref_get(&ag->kref);
        return ag;
}

static inline struct autogroup *autogroup_task_get(struct task_struct *p)
{
        struct autogroup *ag;
        unsigned long flags;

        if (!lock_task_sighand(p, &flags))
                return autogroup_kref_get(&autogroup_default);

        ag = autogroup_kref_get(p->signal->autogroup);
        unlock_task_sighand(p, &flags);

        return ag;
}

static inline struct autogroup *autogroup_create(void)
{
        struct autogroup *ag = kzalloc(sizeof(*ag), GFP_KERNEL);
        struct task_group *tg;

        if (!ag)
                goto out_fail;

        tg = sched_create_group(&root_task_group);
        if (IS_ERR(tg))
                goto out_free;

        kref_init(&ag->kref);
        init_rwsem(&ag->lock);
        ag->id = atomic_inc_return(&autogroup_seq_nr);
        ag->tg = tg;
#ifdef CONFIG_RT_GROUP_SCHED
        /*
         * Autogroup RT tasks are redirected to the root task group
         * so we don't have to move tasks around upon policy change,
         * or flail around trying to allocate bandwidth on the fly.
         * A bandwidth exception in __sched_setscheduler() allows
         * the policy change to proceed.
         */
        free_rt_sched_group(tg);
        tg->rt_se = root_task_group.rt_se;
        tg->rt_rq = root_task_group.rt_rq;
#endif
        tg->autogroup = ag;

        sched_online_group(tg, &root_task_group);
        return ag;

out_free:
        kfree(ag);
out_fail:
        if (printk_ratelimit()) {
                printk(KERN_WARNING "autogroup_create: %s failure.\n",
                        ag ? "sched_create_group()" : "kzalloc()");
        }

        return autogroup_kref_get(&autogroup_default);
}

bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
{
        if (tg != &root_task_group)
                return false;
        /*
         * If we race with autogroup_move_group() the caller can use the old
         * value of signal->autogroup but in this case sched_move_task() will
         * be called again before autogroup_kref_put().
         *
         * However, there is no way sched_autogroup_exit_task() could tell us
         * to avoid autogroup->tg, so we abuse PF_EXITING flag for this case.
         */
        if (p->flags & PF_EXITING)
                return false;

        return true;
}

void sched_autogroup_exit_task(struct task_struct *p)
{
        /*
         * We are going to call exit_notify() and autogroup_move_group() can't
         * see this thread after that: we can no longer use signal->autogroup.
         * See the PF_EXITING check in task_wants_autogroup().
         */
        sched_move_task(p);
}

static void
autogroup_move_group(struct task_struct *p, struct autogroup *ag)
{
        struct autogroup *prev;
        struct task_struct *t;
        unsigned long flags;

        BUG_ON(!lock_task_sighand(p, &flags));

        prev = p->signal->autogroup;
        if (prev == ag) {
                unlock_task_sighand(p, &flags);
                return;
        }

        p->signal->autogroup = autogroup_kref_get(ag);
        /*
         * We can't avoid sched_move_task() after we changed signal->autogroup,
         * this process can already run with task_group() == prev->tg or we can
         * race with cgroup code which can read autogroup = prev under rq->lock.
         * In the latter case for_each_thread() can not miss a migrating thread,
         * cpu_cgroup_attach() must not be possible after cgroup_exit() and it
         * can't be removed from thread list, we hold ->siglock.
         *
         * If an exiting thread was already removed from thread list we rely on
         * sched_autogroup_exit_task().
         */
        for_each_thread(p, t)
                sched_move_task(t);

        unlock_task_sighand(p, &flags);
        autogroup_kref_put(prev);
}

/* Allocates GFP_KERNEL, cannot be called under any spinlock: */
void sched_autogroup_create_attach(struct task_struct *p)
{
        struct autogroup *ag = autogroup_create();

        autogroup_move_group(p, ag);

        /* Drop extra reference added by autogroup_create(): */
        autogroup_kref_put(ag);
}
EXPORT_SYMBOL(sched_autogroup_create_attach);

/* Cannot be called under siglock. Currently has no users: */
void sched_autogroup_detach(struct task_struct *p)
{
        autogroup_move_group(p, &autogroup_default);
}
EXPORT_SYMBOL(sched_autogroup_detach);

void sched_autogroup_fork(struct signal_struct *sig)
{
        sig->autogroup = autogroup_task_get(current);
}

void sched_autogroup_exit(struct signal_struct *sig)
{
        autogroup_kref_put(sig->autogroup);
}

static int __init setup_autogroup(char *str)
{
        sysctl_sched_autogroup_enabled = 0;

        return 1;
}
__setup("noautogroup", setup_autogroup);

#ifdef CONFIG_PROC_FS

int proc_sched_autogroup_set_nice(struct task_struct *p, int nice)
{
        static unsigned long next = INITIAL_JIFFIES;
        struct autogroup *ag;
        unsigned long shares;
        int err, idx;

        if (nice < MIN_NICE || nice > MAX_NICE)
                return -EINVAL;

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

        if (nice < 0 && !can_nice(current, nice))
                return -EPERM;

        /* This is a heavy operation, taking global locks.. */
        if (!capable(CAP_SYS_ADMIN) && time_before(jiffies, next))
                return -EAGAIN;

        next = HZ / 10 + jiffies;
        ag = autogroup_task_get(p);

        idx = array_index_nospec(nice + 20, 40);
        shares = scale_load(sched_prio_to_weight[idx]);

        down_write(&ag->lock);
        err = sched_group_set_shares(ag->tg, shares);
        if (!err)
                ag->nice = nice;
        up_write(&ag->lock);

        autogroup_kref_put(ag);

        return err;
}

void proc_sched_autogroup_show_task(struct task_struct *p, struct seq_file *m)
{
        struct autogroup *ag = autogroup_task_get(p);

        if (!task_group_is_autogroup(ag->tg))
                goto out;

        down_read(&ag->lock);
        seq_printf(m, "/autogroup-%ld nice %d\n", ag->id, ag->nice);
        up_read(&ag->lock);

out:
        autogroup_kref_put(ag);
}
#endif /* CONFIG_PROC_FS */

int autogroup_path(struct task_group *tg, char *buf, int buflen)
{
        if (!task_group_is_autogroup(tg))
                return 0;

        return snprintf(buf, buflen, "%s-%ld", "/autogroup", tg->autogroup->id);
}