posix-cpu-timers.c

Go to the documentation of this file.

/*
 * Implement CPU time clocks for the POSIX clock interface.
 */

#include <linux/sched.h>
#include <linux/posix-timers.h>
#include <linux/errno.h>
#include <linux/math64.h>
#include <asm/uaccess.h>
#include <linux/kernel_stat.h>
#include <trace/events/timer.h>

/*
 * Called after updating RLIMIT_CPU to run cpu timer and update
 * tsk->signal->cputime_expires expiration cache if necessary. Needs
 * siglock protection since other code may update expiration cache as
 * well.
 */
void update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new)
{
    cputime_t cputime = secs_to_cputime(rlim_new);

    spin_lock_irq(&task->sighand->siglock);
    set_process_cpu_timer(task, CPUCLOCK_PROF, &cputime, NULL);
    spin_unlock_irq(&task->sighand->siglock);
}

static int check_clock(const clockid_t which_clock)
{
    int error = 0;
    struct task_struct *p;
    const pid_t pid = CPUCLOCK_PID(which_clock);

    if (CPUCLOCK_WHICH(which_clock) >= CPUCLOCK_MAX)
        return -EINVAL;

    if (pid == 0)
        return 0;

    rcu_read_lock();
    p = find_task_by_vpid(pid);
    if (!p || !(CPUCLOCK_PERTHREAD(which_clock) ?
           same_thread_group(p, current) : has_group_leader_pid(p))) {
        error = -EINVAL;
    }
    rcu_read_unlock();

    return error;
}

static inline union cpu_time_count
timespec_to_sample(const clockid_t which_clock, const struct timespec *tp)
{
    union cpu_time_count ret;
    ret.sched = 0;      /* high half always zero when .cpu used */
    if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
        ret.sched = (unsigned long long)tp->tv_sec * NSEC_PER_SEC + tp->tv_nsec;
    } else {
        ret.cpu = timespec_to_cputime(tp);
    }
    return ret;
}

static void sample_to_timespec(const clockid_t which_clock,
                   union cpu_time_count cpu,
                   struct timespec *tp)
{
    if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED)
        *tp = ns_to_timespec(cpu.sched);
    else
        cputime_to_timespec(cpu.cpu, tp);
}

static inline int cpu_time_before(const clockid_t which_clock,
                  union cpu_time_count now,
                  union cpu_time_count then)
{
    if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
        return now.sched < then.sched;
    }  else {
        return now.cpu < then.cpu;
    }
}
static inline void cpu_time_add(const clockid_t which_clock,
                union cpu_time_count *acc,
                    union cpu_time_count val)
{
    if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
        acc->sched += val.sched;
    }  else {
        acc->cpu += val.cpu;
    }
}
static inline union cpu_time_count cpu_time_sub(const clockid_t which_clock,
                        union cpu_time_count a,
                        union cpu_time_count b)
{
    if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
        a.sched -= b.sched;
    }  else {
        a.cpu -= b.cpu;
    }
    return a;
}

/*
 * Update expiry time from increment, and increase overrun count,
 * given the current clock sample.
 */
static void bump_cpu_timer(struct k_itimer *timer,
                  union cpu_time_count now)
{
    int i;

    if (timer->it.cpu.incr.sched == 0)
        return;

    if (CPUCLOCK_WHICH(timer->it_clock) == CPUCLOCK_SCHED) {
        unsigned long long delta, incr;

        if (now.sched < timer->it.cpu.expires.sched)
            return;
        incr = timer->it.cpu.incr.sched;
        delta = now.sched + incr - timer->it.cpu.expires.sched;
        /* Don't use (incr*2 < delta), incr*2 might overflow. */
        for (i = 0; incr < delta - incr; i++)
            incr = incr << 1;
        for (; i >= 0; incr >>= 1, i--) {
            if (delta < incr)
                continue;
            timer->it.cpu.expires.sched += incr;
            timer->it_overrun += 1 << i;
            delta -= incr;
        }
    } else {
        cputime_t delta, incr;

        if (now.cpu < timer->it.cpu.expires.cpu)
            return;
        incr = timer->it.cpu.incr.cpu;
        delta = now.cpu + incr - timer->it.cpu.expires.cpu;
        /* Don't use (incr*2 < delta), incr*2 might overflow. */
        for (i = 0; incr < delta - incr; i++)
                 incr += incr;
        for (; i >= 0; incr = incr >> 1, i--) {
            if (delta < incr)
                continue;
            timer->it.cpu.expires.cpu += incr;
            timer->it_overrun += 1 << i;
            delta -= incr;
        }
    }
}

static inline cputime_t prof_ticks(struct task_struct *p)
{
    return p->utime + p->stime;
}
static inline cputime_t virt_ticks(struct task_struct *p)
{
    return p->utime;
}

static int
posix_cpu_clock_getres(const clockid_t which_clock, struct timespec *tp)
{
    int error = check_clock(which_clock);
    if (!error) {
        tp->tv_sec = 0;
        tp->tv_nsec = ((NSEC_PER_SEC + HZ - 1) / HZ);
        if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
            /*
             * If sched_clock is using a cycle counter, we
             * don't have any idea of its true resolution
             * exported, but it is much more than 1s/HZ.
             */
            tp->tv_nsec = 1;
        }
    }
    return error;
}

static int
posix_cpu_clock_set(const clockid_t which_clock, const struct timespec *tp)
{
    /*
     * You can never reset a CPU clock, but we check for other errors
     * in the call before failing with EPERM.
     */
    int error = check_clock(which_clock);
    if (error == 0) {
        error = -EPERM;
    }
    return error;
}


/*
 * Sample a per-thread clock for the given task.
 */
static int cpu_clock_sample(const clockid_t which_clock, struct task_struct *p,
                union cpu_time_count *cpu)
{
    switch (CPUCLOCK_WHICH(which_clock)) {
    default:
        return -EINVAL;
    case CPUCLOCK_PROF:
        cpu->cpu = prof_ticks(p);
        break;
    case CPUCLOCK_VIRT:
        cpu->cpu = virt_ticks(p);
        break;
    case CPUCLOCK_SCHED:
        cpu->sched = task_sched_runtime(p);
        break;
    }
    return 0;
}

void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
{
    struct signal_struct *sig = tsk->signal;
    struct task_struct *t;

    times->utime = sig->utime;
    times->stime = sig->stime;
    times->sum_exec_runtime = sig->sum_sched_runtime;

    rcu_read_lock();
    /* make sure we can trust tsk->thread_group list */
    if (!likely(pid_alive(tsk)))
        goto out;

    t = tsk;
    do {
        times->utime += t->utime;
        times->stime += t->stime;
        times->sum_exec_runtime += task_sched_runtime(t);
    } while_each_thread(tsk, t);
out:
    rcu_read_unlock();
}

static void update_gt_cputime(struct task_cputime *a, struct task_cputime *b)
{
    if (b->utime > a->utime)
        a->utime = b->utime;

    if (b->stime > a->stime)
        a->stime = b->stime;

    if (b->sum_exec_runtime > a->sum_exec_runtime)
        a->sum_exec_runtime = b->sum_exec_runtime;
}

void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
{
    struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
    struct task_cputime sum;
    unsigned long flags;

    if (!cputimer->running) {
        /*
         * The POSIX timer interface allows for absolute time expiry
         * values through the TIMER_ABSTIME flag, therefore we have
         * to synchronize the timer to the clock every time we start
         * it.
         */
        thread_group_cputime(tsk, &sum);
        raw_spin_lock_irqsave(&cputimer->lock, flags);
        cputimer->running = 1;
        update_gt_cputime(&cputimer->cputime, &sum);
    } else
        raw_spin_lock_irqsave(&cputimer->lock, flags);
    *times = cputimer->cputime;
    raw_spin_unlock_irqrestore(&cputimer->lock, flags);
}

/*
 * Sample a process (thread group) clock for the given group_leader task.
 * Must be called with tasklist_lock held for reading.
 */
static int cpu_clock_sample_group(const clockid_t which_clock,
                  struct task_struct *p,
                  union cpu_time_count *cpu)
{
    struct task_cputime cputime;

    switch (CPUCLOCK_WHICH(which_clock)) {
    default:
        return -EINVAL;
    case CPUCLOCK_PROF:
        thread_group_cputime(p, &cputime);
        cpu->cpu = cputime.utime + cputime.stime;
        break;
    case CPUCLOCK_VIRT:
        thread_group_cputime(p, &cputime);
        cpu->cpu = cputime.utime;
        break;
    case CPUCLOCK_SCHED:
        thread_group_cputime(p, &cputime);
        cpu->sched = cputime.sum_exec_runtime;
        break;
    }
    return 0;
}


static int posix_cpu_clock_get(const clockid_t which_clock, struct timespec *tp)
{
    const pid_t pid = CPUCLOCK_PID(which_clock);
    int error = -EINVAL;
    union cpu_time_count rtn;

    if (pid == 0) {
        /*
         * Special case constant value for our own clocks.
         * We don't have to do any lookup to find ourselves.
         */
        if (CPUCLOCK_PERTHREAD(which_clock)) {
            /*
             * Sampling just ourselves we can do with no locking.
             */
            error = cpu_clock_sample(which_clock,
                         current, &rtn);
        } else {
            read_lock(&tasklist_lock);
            error = cpu_clock_sample_group(which_clock,
                               current, &rtn);
            read_unlock(&tasklist_lock);
        }
    } else {
        /*
         * Find the given PID, and validate that the caller
         * should be able to see it.
         */
        struct task_struct *p;
        rcu_read_lock();
        p = find_task_by_vpid(pid);
        if (p) {
            if (CPUCLOCK_PERTHREAD(which_clock)) {
                if (same_thread_group(p, current)) {
                    error = cpu_clock_sample(which_clock,
                                 p, &rtn);
                }
            } else {
                read_lock(&tasklist_lock);
                if (thread_group_leader(p) && p->sighand) {
                    error =
                        cpu_clock_sample_group(which_clock,
                                       p, &rtn);
                }
                read_unlock(&tasklist_lock);
            }
        }
        rcu_read_unlock();
    }

    if (error)
        return error;
    sample_to_timespec(which_clock, rtn, tp);
    return 0;
}


/*
 * Validate the clockid_t for a new CPU-clock timer, and initialize the timer.
 * This is called from sys_timer_create() and do_cpu_nanosleep() with the
 * new timer already all-zeros initialized.
 */
static int posix_cpu_timer_create(struct k_itimer *new_timer)
{
    int ret = 0;
    const pid_t pid = CPUCLOCK_PID(new_timer->it_clock);
    struct task_struct *p;

    if (CPUCLOCK_WHICH(new_timer->it_clock) >= CPUCLOCK_MAX)
        return -EINVAL;

    INIT_LIST_HEAD(&new_timer->it.cpu.entry);

    rcu_read_lock();
    if (CPUCLOCK_PERTHREAD(new_timer->it_clock)) {
        if (pid == 0) {
            p = current;
        } else {
            p = find_task_by_vpid(pid);
            if (p && !same_thread_group(p, current))
                p = NULL;
        }
    } else {
        if (pid == 0) {
            p = current->group_leader;
        } else {
            p = find_task_by_vpid(pid);
            if (p && !has_group_leader_pid(p))
                p = NULL;
        }
    }
    new_timer->it.cpu.task = p;
    if (p) {
        get_task_struct(p);
    } else {
        ret = -EINVAL;
    }
    rcu_read_unlock();

    return ret;
}

/*
 * Clean up a CPU-clock timer that is about to be destroyed.
 * This is called from timer deletion with the timer already locked.
 * If we return TIMER_RETRY, it's necessary to release the timer's lock
 * and try again.  (This happens when the timer is in the middle of firing.)
 */
static int posix_cpu_timer_del(struct k_itimer *timer)
{
    struct task_struct *p = timer->it.cpu.task;
    int ret = 0;

    if (likely(p != NULL)) {
        read_lock(&tasklist_lock);
        if (unlikely(p->sighand == NULL)) {
            /*
             * We raced with the reaping of the task.
             * The deletion should have cleared us off the list.
             */
            BUG_ON(!list_empty(&timer->it.cpu.entry));
        } else {
            spin_lock(&p->sighand->siglock);
            if (timer->it.cpu.firing)
                ret = TIMER_RETRY;
            else
                list_del(&timer->it.cpu.entry);
            spin_unlock(&p->sighand->siglock);
        }
        read_unlock(&tasklist_lock);

        if (!ret)
            put_task_struct(p);
    }

    return ret;
}

/*
 * Clean out CPU timers still ticking when a thread exited.  The task
 * pointer is cleared, and the expiry time is replaced with the residual
 * time for later timer_gettime calls to return.
 * This must be called with the siglock held.
 */
static void cleanup_timers(struct list_head *head,
               cputime_t utime, cputime_t stime,
               unsigned long long sum_exec_runtime)
{
    struct cpu_timer_list *timer, *next;
    cputime_t ptime = utime + stime;

    list_for_each_entry_safe(timer, next, head, entry) {
        list_del_init(&timer->entry);
        if (timer->expires.cpu < ptime) {
            timer->expires.cpu = 0;
        } else {
            timer->expires.cpu -= ptime;
        }
    }

    ++head;
    list_for_each_entry_safe(timer, next, head, entry) {
        list_del_init(&timer->entry);
        if (timer->expires.cpu < utime) {
            timer->expires.cpu = 0;
        } else {
            timer->expires.cpu -= utime;
        }
    }

    ++head;
    list_for_each_entry_safe(timer, next, head, entry) {
        list_del_init(&timer->entry);
        if (timer->expires.sched < sum_exec_runtime) {
            timer->expires.sched = 0;
        } else {
            timer->expires.sched -= sum_exec_runtime;
        }
    }
}

/*
 * These are both called with the siglock held, when the current thread
 * is being reaped.  When the final (leader) thread in the group is reaped,
 * posix_cpu_timers_exit_group will be called after posix_cpu_timers_exit.
 */
void posix_cpu_timers_exit(struct task_struct *tsk)
{
    cleanup_timers(tsk->cpu_timers,
               tsk->utime, tsk->stime, tsk->se.sum_exec_runtime);

}
void posix_cpu_timers_exit_group(struct task_struct *tsk)
{
    struct signal_struct *const sig = tsk->signal;

    cleanup_timers(tsk->signal->cpu_timers,
               tsk->utime + sig->utime, tsk->stime + sig->stime,
               tsk->se.sum_exec_runtime + sig->sum_sched_runtime);
}

static void clear_dead_task(struct k_itimer *timer, union cpu_time_count now)
{
    /*
     * That's all for this thread or process.
     * We leave our residual in expires to be reported.
     */
    put_task_struct(timer->it.cpu.task);
    timer->it.cpu.task = NULL;
    timer->it.cpu.expires = cpu_time_sub(timer->it_clock,
                         timer->it.cpu.expires,
                         now);
}

static inline int expires_gt(cputime_t expires, cputime_t new_exp)
{
    return expires == 0 || expires > new_exp;
}

/*
 * Insert the timer on the appropriate list before any timers that
 * expire later.  This must be called with the tasklist_lock held
 * for reading, interrupts disabled and p->sighand->siglock taken.
 */
static void arm_timer(struct k_itimer *timer)
{
    struct task_struct *p = timer->it.cpu.task;
    struct list_head *head, *listpos;
    struct task_cputime *cputime_expires;
    struct cpu_timer_list *const nt = &timer->it.cpu;
    struct cpu_timer_list *next;

    if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
        head = p->cpu_timers;
        cputime_expires = &p->cputime_expires;
    } else {
        head = p->signal->cpu_timers;
        cputime_expires = &p->signal->cputime_expires;
    }
    head += CPUCLOCK_WHICH(timer->it_clock);

    listpos = head;
    list_for_each_entry(next, head, entry) {
        if (cpu_time_before(timer->it_clock, nt->expires, next->expires))
            break;
        listpos = &next->entry;
    }
    list_add(&nt->entry, listpos);

    if (listpos == head) {
        union cpu_time_count *exp = &nt->expires;

        /*
         * We are the new earliest-expiring POSIX 1.b timer, hence
         * need to update expiration cache. Take into account that
         * for process timers we share expiration cache with itimers
         * and RLIMIT_CPU and for thread timers with RLIMIT_RTTIME.
         */

        switch (CPUCLOCK_WHICH(timer->it_clock)) {
        case CPUCLOCK_PROF:
            if (expires_gt(cputime_expires->prof_exp, exp->cpu))
                cputime_expires->prof_exp = exp->cpu;
            break;
        case CPUCLOCK_VIRT:
            if (expires_gt(cputime_expires->virt_exp, exp->cpu))
                cputime_expires->virt_exp = exp->cpu;
            break;
        case CPUCLOCK_SCHED:
            if (cputime_expires->sched_exp == 0 ||
                cputime_expires->sched_exp > exp->sched)
                cputime_expires->sched_exp = exp->sched;
            break;
        }
    }
}

/*
 * The timer is locked, fire it and arrange for its reload.
 */
static void cpu_timer_fire(struct k_itimer *timer)
{
    if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
        /*
         * User don't want any signal.
         */
        timer->it.cpu.expires.sched = 0;
    } else if (unlikely(timer->sigq == NULL)) {
        /*
         * This a special case for clock_nanosleep,
         * not a normal timer from sys_timer_create.
         */
        wake_up_process(timer->it_process);
        timer->it.cpu.expires.sched = 0;
    } else if (timer->it.cpu.incr.sched == 0) {
        /*
         * One-shot timer.  Clear it as soon as it's fired.
         */
        posix_timer_event(timer, 0);
        timer->it.cpu.expires.sched = 0;
    } else if (posix_timer_event(timer, ++timer->it_requeue_pending)) {
        /*
         * The signal did not get queued because the signal
         * was ignored, so we won't get any callback to
         * reload the timer.  But we need to keep it
         * ticking in case the signal is deliverable next time.
         */
        posix_cpu_timer_schedule(timer);
    }
}

/*
 * Sample a process (thread group) timer for the given group_leader task.
 * Must be called with tasklist_lock held for reading.
 */
static int cpu_timer_sample_group(const clockid_t which_clock,
                  struct task_struct *p,
                  union cpu_time_count *cpu)
{
    struct task_cputime cputime;

    thread_group_cputimer(p, &cputime);
    switch (CPUCLOCK_WHICH(which_clock)) {
    default:
        return -EINVAL;
    case CPUCLOCK_PROF:
        cpu->cpu = cputime.utime + cputime.stime;
        break;
    case CPUCLOCK_VIRT:
        cpu->cpu = cputime.utime;
        break;
    case CPUCLOCK_SCHED:
        cpu->sched = cputime.sum_exec_runtime + task_delta_exec(p);
        break;
    }
    return 0;
}

/*
 * Guts of sys_timer_settime for CPU timers.
 * This is called with the timer locked and interrupts disabled.
 * If we return TIMER_RETRY, it's necessary to release the timer's lock
 * and try again.  (This happens when the timer is in the middle of firing.)
 */
static int posix_cpu_timer_set(struct k_itimer *timer, int flags,
                   struct itimerspec *new, struct itimerspec *old)
{
    struct task_struct *p = timer->it.cpu.task;
    union cpu_time_count old_expires, new_expires, old_incr, val;
    int ret;

    if (unlikely(p == NULL)) {
        /*
         * Timer refers to a dead task's clock.
         */
        return -ESRCH;
    }

    new_expires = timespec_to_sample(timer->it_clock, &new->it_value);

    read_lock(&tasklist_lock);
    /*
     * We need the tasklist_lock to protect against reaping that
     * clears p->sighand.  If p has just been reaped, we can no
     * longer get any information about it at all.
     */
    if (unlikely(p->sighand == NULL)) {
        read_unlock(&tasklist_lock);
        put_task_struct(p);
        timer->it.cpu.task = NULL;
        return -ESRCH;
    }

    /*
     * Disarm any old timer after extracting its expiry time.
     */
    BUG_ON(!irqs_disabled());

    ret = 0;
    old_incr = timer->it.cpu.incr;
    spin_lock(&p->sighand->siglock);
    old_expires = timer->it.cpu.expires;
    if (unlikely(timer->it.cpu.firing)) {
        timer->it.cpu.firing = -1;
        ret = TIMER_RETRY;
    } else
        list_del_init(&timer->it.cpu.entry);

    /*
     * We need to sample the current value to convert the new
     * value from to relative and absolute, and to convert the
     * old value from absolute to relative.  To set a process
     * timer, we need a sample to balance the thread expiry
     * times (in arm_timer).  With an absolute time, we must
     * check if it's already passed.  In short, we need a sample.
     */
    if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
        cpu_clock_sample(timer->it_clock, p, &val);
    } else {
        cpu_timer_sample_group(timer->it_clock, p, &val);
    }

    if (old) {
        if (old_expires.sched == 0) {
            old->it_value.tv_sec = 0;
            old->it_value.tv_nsec = 0;
        } else {
            /*
             * Update the timer in case it has
             * overrun already.  If it has,
             * we'll report it as having overrun
             * and with the next reloaded timer
             * already ticking, though we are
             * swallowing that pending
             * notification here to install the
             * new setting.
             */
            bump_cpu_timer(timer, val);
            if (cpu_time_before(timer->it_clock, val,
                        timer->it.cpu.expires)) {
                old_expires = cpu_time_sub(
                    timer->it_clock,
                    timer->it.cpu.expires, val);
                sample_to_timespec(timer->it_clock,
                           old_expires,
                           &old->it_value);
            } else {
                old->it_value.tv_nsec = 1;
                old->it_value.tv_sec = 0;
            }
        }
    }

    if (unlikely(ret)) {
        /*
         * We are colliding with the timer actually firing.
         * Punt after filling in the timer's old value, and
         * disable this firing since we are already reporting
         * it as an overrun (thanks to bump_cpu_timer above).
         */
        spin_unlock(&p->sighand->siglock);
        read_unlock(&tasklist_lock);
        goto out;
    }

    if (new_expires.sched != 0 && !(flags & TIMER_ABSTIME)) {
        cpu_time_add(timer->it_clock, &new_expires, val);
    }

    /*
     * Install the new expiry time (or zero).
     * For a timer with no notification action, we don't actually
     * arm the timer (we'll just fake it for timer_gettime).
     */
    timer->it.cpu.expires = new_expires;
    if (new_expires.sched != 0 &&
        cpu_time_before(timer->it_clock, val, new_expires)) {
        arm_timer(timer);
    }

    spin_unlock(&p->sighand->siglock);
    read_unlock(&tasklist_lock);

    /*
     * Install the new reload setting, and
     * set up the signal and overrun bookkeeping.
     */
    timer->it.cpu.incr = timespec_to_sample(timer->it_clock,
                        &new->it_interval);

    /*
     * This acts as a modification timestamp for the timer,
     * so any automatic reload attempt will punt on seeing
     * that we have reset the timer manually.
     */
    timer->it_requeue_pending = (timer->it_requeue_pending + 2) &
        ~REQUEUE_PENDING;
    timer->it_overrun_last = 0;
    timer->it_overrun = -1;

    if (new_expires.sched != 0 &&
        !cpu_time_before(timer->it_clock, val, new_expires)) {
        /*
         * The designated time already passed, so we notify
         * immediately, even if the thread never runs to
         * accumulate more time on this clock.
         */
        cpu_timer_fire(timer);
    }

    ret = 0;
 out:
    if (old) {
        sample_to_timespec(timer->it_clock,
                   old_incr, &old->it_interval);
    }
    return ret;
}

static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec *itp)
{
    union cpu_time_count now;
    struct task_struct *p = timer->it.cpu.task;
    int clear_dead;

    /*
     * Easy part: convert the reload time.
     */
    sample_to_timespec(timer->it_clock,
               timer->it.cpu.incr, &itp->it_interval);

    if (timer->it.cpu.expires.sched == 0) { /* Timer not armed at all.  */
        itp->it_value.tv_sec = itp->it_value.tv_nsec = 0;
        return;
    }

    if (unlikely(p == NULL)) {
        /*
         * This task already died and the timer will never fire.
         * In this case, expires is actually the dead value.
         */
    dead:
        sample_to_timespec(timer->it_clock, timer->it.cpu.expires,
                   &itp->it_value);
        return;
    }

    /*
     * Sample the clock to take the difference with the expiry time.
     */
    if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
        cpu_clock_sample(timer->it_clock, p, &now);
        clear_dead = p->exit_state;
    } else {
        read_lock(&tasklist_lock);
        if (unlikely(p->sighand == NULL)) {
            /*
             * The process has been reaped.
             * We can't even collect a sample any more.
             * Call the timer disarmed, nothing else to do.
             */
            put_task_struct(p);
            timer->it.cpu.task = NULL;
            timer->it.cpu.expires.sched = 0;
            read_unlock(&tasklist_lock);
            goto dead;
        } else {
            cpu_timer_sample_group(timer->it_clock, p, &now);
            clear_dead = (unlikely(p->exit_state) &&
                      thread_group_empty(p));
        }
        read_unlock(&tasklist_lock);
    }

    if (unlikely(clear_dead)) {
        /*
         * We've noticed that the thread is dead, but
         * not yet reaped.  Take this opportunity to
         * drop our task ref.
         */
        clear_dead_task(timer, now);
        goto dead;
    }

    if (cpu_time_before(timer->it_clock, now, timer->it.cpu.expires)) {
        sample_to_timespec(timer->it_clock,
                   cpu_time_sub(timer->it_clock,
                        timer->it.cpu.expires, now),
                   &itp->it_value);
    } else {
        /*
         * The timer should have expired already, but the firing
         * hasn't taken place yet.  Say it's just about to expire.
         */
        itp->it_value.tv_nsec = 1;
        itp->it_value.tv_sec = 0;
    }
}

/*
 * Check for any per-thread CPU timers that have fired and move them off
 * the tsk->cpu_timers[N] list onto the firing list.  Here we update the
 * tsk->it_*_expires values to reflect the remaining thread CPU timers.
 */
static void check_thread_timers(struct task_struct *tsk,
                struct list_head *firing)
{
    int maxfire;
    struct list_head *timers = tsk->cpu_timers;
    struct signal_struct *const sig = tsk->signal;
    unsigned long soft;

    maxfire = 20;
    tsk->cputime_expires.prof_exp = 0;
    while (!list_empty(timers)) {
        struct cpu_timer_list *t = list_first_entry(timers,
                              struct cpu_timer_list,
                              entry);
        if (!--maxfire || prof_ticks(tsk) < t->expires.cpu) {
            tsk->cputime_expires.prof_exp = t->expires.cpu;
            break;
        }
        t->firing = 1;
        list_move_tail(&t->entry, firing);
    }

    ++timers;
    maxfire = 20;
    tsk->cputime_expires.virt_exp = 0;
    while (!list_empty(timers)) {
        struct cpu_timer_list *t = list_first_entry(timers,
                              struct cpu_timer_list,
                              entry);
        if (!--maxfire || virt_ticks(tsk) < t->expires.cpu) {
            tsk->cputime_expires.virt_exp = t->expires.cpu;
            break;
        }
        t->firing = 1;
        list_move_tail(&t->entry, firing);
    }

    ++timers;
    maxfire = 20;
    tsk->cputime_expires.sched_exp = 0;
    while (!list_empty(timers)) {
        struct cpu_timer_list *t = list_first_entry(timers,
                              struct cpu_timer_list,
                              entry);
        if (!--maxfire || tsk->se.sum_exec_runtime < t->expires.sched) {
            tsk->cputime_expires.sched_exp = t->expires.sched;
            break;
        }
        t->firing = 1;
        list_move_tail(&t->entry, firing);
    }

    /*
     * Check for the special case thread timers.
     */
    soft = ACCESS_ONCE(sig->rlim[RLIMIT_RTTIME].rlim_cur);
    if (soft != RLIM_INFINITY) {
        unsigned long hard =
            ACCESS_ONCE(sig->rlim[RLIMIT_RTTIME].rlim_max);

        if (hard != RLIM_INFINITY &&
            tsk->rt.timeout > DIV_ROUND_UP(hard, USEC_PER_SEC/HZ)) {
            /*
             * At the hard limit, we just die.
             * No need to calculate anything else now.
             */
            __group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
            return;
        }
        if (tsk->rt.timeout > DIV_ROUND_UP(soft, USEC_PER_SEC/HZ)) {
            /*
             * At the soft limit, send a SIGXCPU every second.
             */
            if (soft < hard) {
                soft += USEC_PER_SEC;
                sig->rlim[RLIMIT_RTTIME].rlim_cur = soft;
            }
            printk(KERN_INFO
                "RT Watchdog Timeout: %s[%d]\n",
                tsk->comm, task_pid_nr(tsk));
            __group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
        }
    }
}

static void stop_process_timers(struct signal_struct *sig)
{
    struct thread_group_cputimer *cputimer = &sig->cputimer;
    unsigned long flags;

    raw_spin_lock_irqsave(&cputimer->lock, flags);
    cputimer->running = 0;
    raw_spin_unlock_irqrestore(&cputimer->lock, flags);
}

static u32 onecputick;

static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
                 cputime_t *expires, cputime_t cur_time, int signo)
{
    if (!it->expires)
        return;

    if (cur_time >= it->expires) {
        if (it->incr) {
            it->expires += it->incr;
            it->error += it->incr_error;
            if (it->error >= onecputick) {
                it->expires -= cputime_one_jiffy;
                it->error -= onecputick;
            }
        } else {
            it->expires = 0;
        }

        trace_itimer_expire(signo == SIGPROF ?
                    ITIMER_PROF : ITIMER_VIRTUAL,
                    tsk->signal->leader_pid, cur_time);
        __group_send_sig_info(signo, SEND_SIG_PRIV, tsk);
    }

    if (it->expires && (!*expires || it->expires < *expires)) {
        *expires = it->expires;
    }
}

static inline int task_cputime_zero(const struct task_cputime *cputime)
{
    if (!cputime->utime && !cputime->stime && !cputime->sum_exec_runtime)
        return 1;
    return 0;
}

/*
 * Check for any per-thread CPU timers that have fired and move them
 * off the tsk->*_timers list onto the firing list.  Per-thread timers
 * have already been taken off.
 */
static void check_process_timers(struct task_struct *tsk,
                 struct list_head *firing)
{
    int maxfire;
    struct signal_struct *const sig = tsk->signal;
    cputime_t utime, ptime, virt_expires, prof_expires;
    unsigned long long sum_sched_runtime, sched_expires;
    struct list_head *timers = sig->cpu_timers;
    struct task_cputime cputime;
    unsigned long soft;

    /*
     * Collect the current process totals.
     */
    thread_group_cputimer(tsk, &cputime);
    utime = cputime.utime;
    ptime = utime + cputime.stime;
    sum_sched_runtime = cputime.sum_exec_runtime;
    maxfire = 20;
    prof_expires = 0;
    while (!list_empty(timers)) {
        struct cpu_timer_list *tl = list_first_entry(timers,
                              struct cpu_timer_list,
                              entry);
        if (!--maxfire || ptime < tl->expires.cpu) {
            prof_expires = tl->expires.cpu;
            break;
        }
        tl->firing = 1;
        list_move_tail(&tl->entry, firing);
    }

    ++timers;
    maxfire = 20;
    virt_expires = 0;
    while (!list_empty(timers)) {
        struct cpu_timer_list *tl = list_first_entry(timers,
                              struct cpu_timer_list,
                              entry);
        if (!--maxfire || utime < tl->expires.cpu) {
            virt_expires = tl->expires.cpu;
            break;
        }
        tl->firing = 1;
        list_move_tail(&tl->entry, firing);
    }

    ++timers;
    maxfire = 20;
    sched_expires = 0;
    while (!list_empty(timers)) {
        struct cpu_timer_list *tl = list_first_entry(timers,
                              struct cpu_timer_list,
                              entry);
        if (!--maxfire || sum_sched_runtime < tl->expires.sched) {
            sched_expires = tl->expires.sched;
            break;
        }
        tl->firing = 1;
        list_move_tail(&tl->entry, firing);
    }

    /*
     * Check for the special case process timers.
     */
    check_cpu_itimer(tsk, &sig->it[CPUCLOCK_PROF], &prof_expires, ptime,
             SIGPROF);
    check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT], &virt_expires, utime,
             SIGVTALRM);
    soft = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
    if (soft != RLIM_INFINITY) {
        unsigned long psecs = cputime_to_secs(ptime);
        unsigned long hard =
            ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_max);
        cputime_t x;
        if (psecs >= hard) {
            /*
             * At the hard limit, we just die.
             * No need to calculate anything else now.
             */
            __group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
            return;
        }
        if (psecs >= soft) {
            /*
             * At the soft limit, send a SIGXCPU every second.
             */
            __group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
            if (soft < hard) {
                soft++;
                sig->rlim[RLIMIT_CPU].rlim_cur = soft;
            }
        }
        x = secs_to_cputime(soft);
        if (!prof_expires || x < prof_expires) {
            prof_expires = x;
        }
    }

    sig->cputime_expires.prof_exp = prof_expires;
    sig->cputime_expires.virt_exp = virt_expires;
    sig->cputime_expires.sched_exp = sched_expires;
    if (task_cputime_zero(&sig->cputime_expires))
        stop_process_timers(sig);
}

/*
 * This is called from the signal code (via do_schedule_next_timer)
 * when the last timer signal was delivered and we have to reload the timer.
 */
void posix_cpu_timer_schedule(struct k_itimer *timer)
{
    struct task_struct *p = timer->it.cpu.task;
    union cpu_time_count now;

    if (unlikely(p == NULL))
        /*
         * The task was cleaned up already, no future firings.
         */
        goto out;

    /*
     * Fetch the current sample and update the timer's expiry time.
     */
    if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
        cpu_clock_sample(timer->it_clock, p, &now);
        bump_cpu_timer(timer, now);
        if (unlikely(p->exit_state)) {
            clear_dead_task(timer, now);
            goto out;
        }
        read_lock(&tasklist_lock); /* arm_timer needs it.  */
        spin_lock(&p->sighand->siglock);
    } else {
        read_lock(&tasklist_lock);
        if (unlikely(p->sighand == NULL)) {
            /*
             * The process has been reaped.
             * We can't even collect a sample any more.
             */
            put_task_struct(p);
            timer->it.cpu.task = p = NULL;
            timer->it.cpu.expires.sched = 0;
            goto out_unlock;
        } else if (unlikely(p->exit_state) && thread_group_empty(p)) {
            /*
             * We've noticed that the thread is dead, but
             * not yet reaped.  Take this opportunity to
             * drop our task ref.
             */
            clear_dead_task(timer, now);
            goto out_unlock;
        }
        spin_lock(&p->sighand->siglock);
        cpu_timer_sample_group(timer->it_clock, p, &now);
        bump_cpu_timer(timer, now);
        /* Leave the tasklist_lock locked for the call below.  */
    }

    /*
     * Now re-arm for the new expiry time.
     */
    BUG_ON(!irqs_disabled());
    arm_timer(timer);
    spin_unlock(&p->sighand->siglock);

out_unlock:
    read_unlock(&tasklist_lock);

out:
    timer->it_overrun_last = timer->it_overrun;
    timer->it_overrun = -1;
    ++timer->it_requeue_pending;
}

static inline int task_cputime_expired(const struct task_cputime *sample,
                    const struct task_cputime *expires)
{
    if (expires->utime && sample->utime >= expires->utime)
        return 1;
    if (expires->stime && sample->utime + sample->stime >= expires->stime)
        return 1;
    if (expires->sum_exec_runtime != 0 &&
        sample->sum_exec_runtime >= expires->sum_exec_runtime)
        return 1;
    return 0;
}

static inline int fastpath_timer_check(struct task_struct *tsk)
{
    struct signal_struct *sig;

    if (!task_cputime_zero(&tsk->cputime_expires)) {
        struct task_cputime task_sample = {
            .utime = tsk->utime,
            .stime = tsk->stime,
            .sum_exec_runtime = tsk->se.sum_exec_runtime
        };

        if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
            return 1;
    }

    sig = tsk->signal;
    if (sig->cputimer.running) {
        struct task_cputime group_sample;

        raw_spin_lock(&sig->cputimer.lock);
        group_sample = sig->cputimer.cputime;
        raw_spin_unlock(&sig->cputimer.lock);

        if (task_cputime_expired(&group_sample, &sig->cputime_expires))
            return 1;
    }

    return 0;
}

/*
 * This is called from the timer interrupt handler.  The irq handler has
 * already updated our counts.  We need to check if any timers fire now.
 * Interrupts are disabled.
 */
void run_posix_cpu_timers(struct task_struct *tsk)
{
    LIST_HEAD(firing);
    struct k_itimer *timer, *next;
    unsigned long flags;

    BUG_ON(!irqs_disabled());

    /*
     * The fast path checks that there are no expired thread or thread
     * group timers.  If that's so, just return.
     */
    if (!fastpath_timer_check(tsk))
        return;

    if (!lock_task_sighand(tsk, &flags))
        return;
    /*
     * Here we take off tsk->signal->cpu_timers[N] and
     * tsk->cpu_timers[N] all the timers that are firing, and
     * put them on the firing list.
     */
    check_thread_timers(tsk, &firing);
    /*
     * If there are any active process wide timers (POSIX 1.b, itimers,
     * RLIMIT_CPU) cputimer must be running.
     */
    if (tsk->signal->cputimer.running)
        check_process_timers(tsk, &firing);

    /*
     * We must release these locks before taking any timer's lock.
     * There is a potential race with timer deletion here, as the
     * siglock now protects our private firing list.  We have set
     * the firing flag in each timer, so that a deletion attempt
     * that gets the timer lock before we do will give it up and
     * spin until we've taken care of that timer below.
     */
    unlock_task_sighand(tsk, &flags);

    /*
     * Now that all the timers on our list have the firing flag,
     * no one will touch their list entries but us.  We'll take
     * each timer's lock before clearing its firing flag, so no
     * timer call will interfere.
     */
    list_for_each_entry_safe(timer, next, &firing, it.cpu.entry) {
        int cpu_firing;

        spin_lock(&timer->it_lock);
        list_del_init(&timer->it.cpu.entry);
        cpu_firing = timer->it.cpu.firing;
        timer->it.cpu.firing = 0;
        /*
         * The firing flag is -1 if we collided with a reset
         * of the timer, which already reported this
         * almost-firing as an overrun.  So don't generate an event.
         */
        if (likely(cpu_firing >= 0))
            cpu_timer_fire(timer);
        spin_unlock(&timer->it_lock);
    }
}

/*
 * Set one of the process-wide special case CPU timers or RLIMIT_CPU.
 * The tsk->sighand->siglock must be held by the caller.
 */
void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
               cputime_t *newval, cputime_t *oldval)
{
    union cpu_time_count now;

    BUG_ON(clock_idx == CPUCLOCK_SCHED);
    cpu_timer_sample_group(clock_idx, tsk, &now);

    if (oldval) {
        /*
         * We are setting itimer. The *oldval is absolute and we update
         * it to be relative, *newval argument is relative and we update
         * it to be absolute.
         */
        if (*oldval) {
            if (*oldval <= now.cpu) {
                /* Just about to fire. */
                *oldval = cputime_one_jiffy;
            } else {
                *oldval -= now.cpu;
            }
        }

        if (!*newval)
            return;
        *newval += now.cpu;
    }

    /*
     * Update expiration cache if we are the earliest timer, or eventually
     * RLIMIT_CPU limit is earlier than prof_exp cpu timer expire.
     */
    switch (clock_idx) {
    case CPUCLOCK_PROF:
        if (expires_gt(tsk->signal->cputime_expires.prof_exp, *newval))
            tsk->signal->cputime_expires.prof_exp = *newval;
        break;
    case CPUCLOCK_VIRT:
        if (expires_gt(tsk->signal->cputime_expires.virt_exp, *newval))
            tsk->signal->cputime_expires.virt_exp = *newval;
        break;
    }
}

static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
                struct timespec *rqtp, struct itimerspec *it)
{
    struct k_itimer timer;
    int error;

    /*
     * Set up a temporary timer and then wait for it to go off.
     */
    memset(&timer, 0, sizeof timer);
    spin_lock_init(&timer.it_lock);
    timer.it_clock = which_clock;
    timer.it_overrun = -1;
    error = posix_cpu_timer_create(&timer);
    timer.it_process = current;
    if (!error) {
        static struct itimerspec zero_it;

        memset(it, 0, sizeof *it);
        it->it_value = *rqtp;

        spin_lock_irq(&timer.it_lock);
        error = posix_cpu_timer_set(&timer, flags, it, NULL);
        if (error) {
            spin_unlock_irq(&timer.it_lock);
            return error;
        }

        while (!signal_pending(current)) {
            if (timer.it.cpu.expires.sched == 0) {
                /*
                 * Our timer fired and was reset.
                 */
                spin_unlock_irq(&timer.it_lock);
                return 0;
            }

            /*
             * Block until cpu_timer_fire (or a signal) wakes us.
             */
            __set_current_state(TASK_INTERRUPTIBLE);
            spin_unlock_irq(&timer.it_lock);
            schedule();
            spin_lock_irq(&timer.it_lock);
        }

        /*
         * We were interrupted by a signal.
         */
        sample_to_timespec(which_clock, timer.it.cpu.expires, rqtp);
        posix_cpu_timer_set(&timer, 0, &zero_it, it);
        spin_unlock_irq(&timer.it_lock);

        if ((it->it_value.tv_sec | it->it_value.tv_nsec) == 0) {
            /*
             * It actually did fire already.
             */
            return 0;
        }

        error = -ERESTART_RESTARTBLOCK;
    }

    return error;
}

static long posix_cpu_nsleep_restart(struct restart_block *restart_block);

static int posix_cpu_nsleep(const clockid_t which_clock, int flags,
                struct timespec *rqtp, struct timespec __user *rmtp)
{
    struct restart_block *restart_block =
        &current_thread_info()->restart_block;
    struct itimerspec it;
    int error;

    /*
     * Diagnose required errors first.
     */
    if (CPUCLOCK_PERTHREAD(which_clock) &&
        (CPUCLOCK_PID(which_clock) == 0 ||
         CPUCLOCK_PID(which_clock) == current->pid))
        return -EINVAL;

    error = do_cpu_nanosleep(which_clock, flags, rqtp, &it);

    if (error == -ERESTART_RESTARTBLOCK) {

        if (flags & TIMER_ABSTIME)
            return -ERESTARTNOHAND;
        /*
         * Report back to the user the time still remaining.
         */
        if (rmtp && copy_to_user(rmtp, &it.it_value, sizeof *rmtp))
            return -EFAULT;

        restart_block->fn = posix_cpu_nsleep_restart;
        restart_block->nanosleep.clockid = which_clock;
        restart_block->nanosleep.rmtp = rmtp;
        restart_block->nanosleep.expires = timespec_to_ns(rqtp);
    }
    return error;
}

static long posix_cpu_nsleep_restart(struct restart_block *restart_block)
{
    clockid_t which_clock = restart_block->nanosleep.clockid;
    struct timespec t;
    struct itimerspec it;
    int error;

    t = ns_to_timespec(restart_block->nanosleep.expires);

    error = do_cpu_nanosleep(which_clock, TIMER_ABSTIME, &t, &it);

    if (error == -ERESTART_RESTARTBLOCK) {
        struct timespec __user *rmtp = restart_block->nanosleep.rmtp;
        /*
         * Report back to the user the time still remaining.
         */
        if (rmtp && copy_to_user(rmtp, &it.it_value, sizeof *rmtp))
            return -EFAULT;

        restart_block->nanosleep.expires = timespec_to_ns(&t);
    }
    return error;

}

#define PROCESS_CLOCK   MAKE_PROCESS_CPUCLOCK(0, CPUCLOCK_SCHED)
#define THREAD_CLOCK    MAKE_THREAD_CPUCLOCK(0, CPUCLOCK_SCHED)

static int process_cpu_clock_getres(const clockid_t which_clock,
                    struct timespec *tp)
{
    return posix_cpu_clock_getres(PROCESS_CLOCK, tp);
}
static int process_cpu_clock_get(const clockid_t which_clock,
                 struct timespec *tp)
{
    return posix_cpu_clock_get(PROCESS_CLOCK, tp);
}
static int process_cpu_timer_create(struct k_itimer *timer)
{
    timer->it_clock = PROCESS_CLOCK;
    return posix_cpu_timer_create(timer);
}
static int process_cpu_nsleep(const clockid_t which_clock, int flags,
                  struct timespec *rqtp,
                  struct timespec __user *rmtp)
{
    return posix_cpu_nsleep(PROCESS_CLOCK, flags, rqtp, rmtp);
}
static long process_cpu_nsleep_restart(struct restart_block *restart_block)
{
    return -EINVAL;
}
static int thread_cpu_clock_getres(const clockid_t which_clock,
                   struct timespec *tp)
{
    return posix_cpu_clock_getres(THREAD_CLOCK, tp);
}
static int thread_cpu_clock_get(const clockid_t which_clock,
                struct timespec *tp)
{
    return posix_cpu_clock_get(THREAD_CLOCK, tp);
}
static int thread_cpu_timer_create(struct k_itimer *timer)
{
    timer->it_clock = THREAD_CLOCK;
    return posix_cpu_timer_create(timer);
}

struct k_clock clock_posix_cpu = {
    .clock_getres   = posix_cpu_clock_getres,
    .clock_set  = posix_cpu_clock_set,
    .clock_get  = posix_cpu_clock_get,
    .timer_create   = posix_cpu_timer_create,
    .nsleep     = posix_cpu_nsleep,
    .nsleep_restart = posix_cpu_nsleep_restart,
    .timer_set  = posix_cpu_timer_set,
    .timer_del  = posix_cpu_timer_del,
    .timer_get  = posix_cpu_timer_get,
};

static __init int init_posix_cpu_timers(void)
{
    struct k_clock process = {
        .clock_getres   = process_cpu_clock_getres,
        .clock_get  = process_cpu_clock_get,
        .timer_create   = process_cpu_timer_create,
        .nsleep     = process_cpu_nsleep,
        .nsleep_restart = process_cpu_nsleep_restart,
    };
    struct k_clock thread = {
        .clock_getres   = thread_cpu_clock_getres,
        .clock_get  = thread_cpu_clock_get,
        .timer_create   = thread_cpu_timer_create,
    };
    struct timespec ts;

    posix_timers_register_clock(CLOCK_PROCESS_CPUTIME_ID, &process);
    posix_timers_register_clock(CLOCK_THREAD_CPUTIME_ID, &thread);

    cputime_to_timespec(cputime_one_jiffy, &ts);
    onecputick = ts.tv_nsec;
    WARN_ON(ts.tv_sec != 0);

    return 0;
}
__initcall(init_posix_cpu_timers);