auto_group.c

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#ifdef CONFIG_SCHED_AUTOGROUP

#include "sched.h"

#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/kallsyms.h>
#include <linux/utsname.h>
#include <linux/security.h>
#include <linux/export.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_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.  Thereafter, task_group()
     * returns &root_task_group, so zero bandwidth is required.
     */
    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;

    return ag;

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

    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 (p->sched_class != &fair_sched_class)
        return false;

    /*
     * We can only assume the task group can't go away on us if
     * autogroup_move_group() can see us on ->thread_group list.
     */
    if (p->flags & PF_EXITING)
        return false;

    return true;
}

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);

    t = p;
    do {
        sched_move_task(t);
    } while_each_thread(p, 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;
    int err;

    if (nice < -20 || nice > 19)
        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);

    down_write(&ag->lock);
    err = sched_group_set_shares(ag->tg, prio_to_weight[nice + 20]);
    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 */

#ifdef CONFIG_SCHED_DEBUG
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);
}
#endif /* CONFIG_SCHED_DEBUG */

#endif /* CONFIG_SCHED_AUTOGROUP */