posix-timers: lock_timer: kill the bogus ->it_id check

[safe/jmp/linux-2.6] / kernel / posix-timers.c

/*
 * linux/kernel/posix-timers.c
 *
 *
 * 2002-10-15  Posix Clocks & timers
 *                           by George Anzinger george@mvista.com
 *
 *                           Copyright (C) 2002 2003 by MontaVista Software.
 *
 * 2004-06-01  Fix CLOCK_REALTIME clock/timer TIMER_ABSTIME bug.
 *                           Copyright (C) 2004 Boris Hu
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or (at
 * your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.

 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * MontaVista Software | 1237 East Arques Avenue | Sunnyvale | CA 94085 | USA
 */

/* These are all the functions necessary to implement
 * POSIX clocks & timers
 */
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/mutex.h>

#include <asm/uaccess.h>
#include <linux/list.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/idr.h>
#include <linux/posix-timers.h>
#include <linux/syscalls.h>
#include <linux/wait.h>
#include <linux/workqueue.h>
#include <linux/module.h>

/*
 * Management arrays for POSIX timers.   Timers are kept in slab memory
 * Timer ids are allocated by an external routine that keeps track of the
 * id and the timer.  The external interface is:
 *
 * void *idr_find(struct idr *idp, int id);           to find timer_id <id>
 * int idr_get_new(struct idr *idp, void *ptr);       to get a new id and
 *                                                    related it to <ptr>
 * void idr_remove(struct idr *idp, int id);          to release <id>
 * void idr_init(struct idr *idp);                    to initialize <idp>
 *                                                    which we supply.
 * The idr_get_new *may* call slab for more memory so it must not be
 * called under a spin lock.  Likewise idr_remore may release memory
 * (but it may be ok to do this under a lock...).
 * idr_find is just a memory look up and is quite fast.  A -1 return
 * indicates that the requested id does not exist.
 */

/*
 * Lets keep our timers in a slab cache :-)
 */
static struct kmem_cache *posix_timers_cache;
static struct idr posix_timers_id;
static DEFINE_SPINLOCK(idr_lock);

/*
 * we assume that the new SIGEV_THREAD_ID shares no bits with the other
 * SIGEV values.  Here we put out an error if this assumption fails.
 */
#if SIGEV_THREAD_ID != (SIGEV_THREAD_ID & \
                       ~(SIGEV_SIGNAL | SIGEV_NONE | SIGEV_THREAD))
#error "SIGEV_THREAD_ID must not share bit with other SIGEV values!"
#endif


/*
 * The timer ID is turned into a timer address by idr_find().
 * Verifying a valid ID consists of:
 *
 * a) checking that idr_find() returns other than -1.
 * b) checking that the timer id matches the one in the timer itself.
 * c) that the timer owner is in the callers thread group.
 */

/*
 * CLOCKs: The POSIX standard calls for a couple of clocks and allows us
 *          to implement others.  This structure defines the various
 *          clocks and allows the possibility of adding others.  We
 *          provide an interface to add clocks to the table and expect
 *          the "arch" code to add at least one clock that is high
 *          resolution.  Here we define the standard CLOCK_REALTIME as a
 *          1/HZ resolution clock.
 *
 * RESOLUTION: Clock resolution is used to round up timer and interval
 *          times, NOT to report clock times, which are reported with as
 *          much resolution as the system can muster.  In some cases this
 *          resolution may depend on the underlying clock hardware and
 *          may not be quantifiable until run time, and only then is the
 *          necessary code is written.  The standard says we should say
 *          something about this issue in the documentation...
 *
 * FUNCTIONS: The CLOCKs structure defines possible functions to handle
 *          various clock functions.  For clocks that use the standard
 *          system timer code these entries should be NULL.  This will
 *          allow dispatch without the overhead of indirect function
 *          calls.  CLOCKS that depend on other sources (e.g. WWV or GPS)
 *          must supply functions here, even if the function just returns
 *          ENOSYS.  The standard POSIX timer management code assumes the
 *          following: 1.) The k_itimer struct (sched.h) is used for the
 *          timer.  2.) The list, it_lock, it_clock, it_id and it_process
 *          fields are not modified by timer code.
 *
 *          At this time all functions EXCEPT clock_nanosleep can be
 *          redirected by the CLOCKS structure.  Clock_nanosleep is in
 *          there, but the code ignores it.
 *
 * Permissions: It is assumed that the clock_settime() function defined
 *          for each clock will take care of permission checks.  Some
 *          clocks may be set able by any user (i.e. local process
 *          clocks) others not.  Currently the only set able clock we
 *          have is CLOCK_REALTIME and its high res counter part, both of
 *          which we beg off on and pass to do_sys_settimeofday().
 */

static struct k_clock posix_clocks[MAX_CLOCKS];

/*
 * These ones are defined below.
 */
static int common_nsleep(const clockid_t, int flags, struct timespec *t,
                         struct timespec __user *rmtp);
static void common_timer_get(struct k_itimer *, struct itimerspec *);
static int common_timer_set(struct k_itimer *, int,
                            struct itimerspec *, struct itimerspec *);
static int common_timer_del(struct k_itimer *timer);

static enum hrtimer_restart posix_timer_fn(struct hrtimer *data);

static struct k_itimer *lock_timer(timer_t timer_id, unsigned long *flags);

static inline void unlock_timer(struct k_itimer *timr, unsigned long flags)
{
        spin_unlock_irqrestore(&timr->it_lock, flags);
}

/*
 * Call the k_clock hook function if non-null, or the default function.
 */
#define CLOCK_DISPATCH(clock, call, arglist) \
        ((clock) < 0 ? posix_cpu_##call arglist : \
         (posix_clocks[clock].call != NULL \
          ? (*posix_clocks[clock].call) arglist : common_##call arglist))

/*
 * Default clock hook functions when the struct k_clock passed
 * to register_posix_clock leaves a function pointer null.
 *
 * The function common_CALL is the default implementation for
 * the function pointer CALL in struct k_clock.
 */

static inline int common_clock_getres(const clockid_t which_clock,
                                      struct timespec *tp)
{
        tp->tv_sec = 0;
        tp->tv_nsec = posix_clocks[which_clock].res;
        return 0;
}

/*
 * Get real time for posix timers
 */
static int common_clock_get(clockid_t which_clock, struct timespec *tp)
{
        ktime_get_real_ts(tp);
        return 0;
}

static inline int common_clock_set(const clockid_t which_clock,
                                   struct timespec *tp)
{
        return do_sys_settimeofday(tp, NULL);
}

static int common_timer_create(struct k_itimer *new_timer)
{
        hrtimer_init(&new_timer->it.real.timer, new_timer->it_clock, 0);
        return 0;
}

/*
 * Return nonzero if we know a priori this clockid_t value is bogus.
 */
static inline int invalid_clockid(const clockid_t which_clock)
{
        if (which_clock < 0)    /* CPU clock, posix_cpu_* will check it */
                return 0;
        if ((unsigned) which_clock >= MAX_CLOCKS)
                return 1;
        if (posix_clocks[which_clock].clock_getres != NULL)
                return 0;
        if (posix_clocks[which_clock].res != 0)
                return 0;
        return 1;
}

/*
 * Get monotonic time for posix timers
 */
static int posix_ktime_get_ts(clockid_t which_clock, struct timespec *tp)
{
        ktime_get_ts(tp);
        return 0;
}

/*
 * Initialize everything, well, just everything in Posix clocks/timers ;)
 */
static __init int init_posix_timers(void)
{
        struct k_clock clock_realtime = {
                .clock_getres = hrtimer_get_res,
        };
        struct k_clock clock_monotonic = {
                .clock_getres = hrtimer_get_res,
                .clock_get = posix_ktime_get_ts,
                .clock_set = do_posix_clock_nosettime,
        };

        register_posix_clock(CLOCK_REALTIME, &clock_realtime);
        register_posix_clock(CLOCK_MONOTONIC, &clock_monotonic);

        posix_timers_cache = kmem_cache_create("posix_timers_cache",
                                        sizeof (struct k_itimer), 0, SLAB_PANIC,
                                        NULL);
        idr_init(&posix_timers_id);
        return 0;
}

__initcall(init_posix_timers);

static void schedule_next_timer(struct k_itimer *timr)
{
        struct hrtimer *timer = &timr->it.real.timer;

        if (timr->it.real.interval.tv64 == 0)
                return;

        timr->it_overrun += (unsigned int) hrtimer_forward(timer,
                                                timer->base->get_time(),
                                                timr->it.real.interval);

        timr->it_overrun_last = timr->it_overrun;
        timr->it_overrun = -1;
        ++timr->it_requeue_pending;
        hrtimer_restart(timer);
}

/*
 * This function is exported for use by the signal deliver code.  It is
 * called just prior to the info block being released and passes that
 * block to us.  It's function is to update the overrun entry AND to
 * restart the timer.  It should only be called if the timer is to be
 * restarted (i.e. we have flagged this in the sys_private entry of the
 * info block).
 *
 * To protect aginst the timer going away while the interrupt is queued,
 * we require that the it_requeue_pending flag be set.
 */
void do_schedule_next_timer(struct siginfo *info)
{
        struct k_itimer *timr;
        unsigned long flags;

        timr = lock_timer(info->si_tid, &flags);

        if (timr && timr->it_requeue_pending == info->si_sys_private) {
                if (timr->it_clock < 0)
                        posix_cpu_timer_schedule(timr);
                else
                        schedule_next_timer(timr);

                info->si_overrun += timr->it_overrun_last;
        }

        if (timr)
                unlock_timer(timr, flags);
}

int posix_timer_event(struct k_itimer *timr, int si_private)
{
        int shared, ret;
        /*
         * FIXME: if ->sigq is queued we can race with
         * dequeue_signal()->do_schedule_next_timer().
         *
         * If dequeue_signal() sees the "right" value of
         * si_sys_private it calls do_schedule_next_timer().
         * We re-queue ->sigq and drop ->it_lock().
         * do_schedule_next_timer() locks the timer
         * and re-schedules it while ->sigq is pending.
         * Not really bad, but not that we want.
         */
        timr->sigq->info.si_sys_private = si_private;

        shared = !(timr->it_sigev_notify & SIGEV_THREAD_ID);
        ret = send_sigqueue(timr->sigq, timr->it_process, shared);
        /* If we failed to send the signal the timer stops. */
        return ret > 0;
}
EXPORT_SYMBOL_GPL(posix_timer_event);

/*
 * This function gets called when a POSIX.1b interval timer expires.  It
 * is used as a callback from the kernel internal timer.  The
 * run_timer_list code ALWAYS calls with interrupts on.

 * This code is for CLOCK_REALTIME* and CLOCK_MONOTONIC* timers.
 */
static enum hrtimer_restart posix_timer_fn(struct hrtimer *timer)
{
        struct k_itimer *timr;
        unsigned long flags;
        int si_private = 0;
        enum hrtimer_restart ret = HRTIMER_NORESTART;

        timr = container_of(timer, struct k_itimer, it.real.timer);
        spin_lock_irqsave(&timr->it_lock, flags);

        if (timr->it.real.interval.tv64 != 0)
                si_private = ++timr->it_requeue_pending;

        if (posix_timer_event(timr, si_private)) {
                /*
                 * signal was not sent because of sig_ignor
                 * we will not get a call back to restart it AND
                 * it should be restarted.
                 */
                if (timr->it.real.interval.tv64 != 0) {
                        ktime_t now = hrtimer_cb_get_time(timer);

                        /*
                         * FIXME: What we really want, is to stop this
                         * timer completely and restart it in case the
                         * SIG_IGN is removed. This is a non trivial
                         * change which involves sighand locking
                         * (sigh !), which we don't want to do late in
                         * the release cycle.
                         *
                         * For now we just let timers with an interval
                         * less than a jiffie expire every jiffie to
                         * avoid softirq starvation in case of SIG_IGN
                         * and a very small interval, which would put
                         * the timer right back on the softirq pending
                         * list. By moving now ahead of time we trick
                         * hrtimer_forward() to expire the timer
                         * later, while we still maintain the overrun
                         * accuracy, but have some inconsistency in
                         * the timer_gettime() case. This is at least
                         * better than a starved softirq. A more
                         * complex fix which solves also another related
                         * inconsistency is already in the pipeline.
                         */
#ifdef CONFIG_HIGH_RES_TIMERS
                        {
                                ktime_t kj = ktime_set(0, NSEC_PER_SEC / HZ);

                                if (timr->it.real.interval.tv64 < kj.tv64)
                                        now = ktime_add(now, kj);
                        }
#endif
                        timr->it_overrun += (unsigned int)
                                hrtimer_forward(timer, now,
                                                timr->it.real.interval);
                        ret = HRTIMER_RESTART;
                        ++timr->it_requeue_pending;
                }
        }

        unlock_timer(timr, flags);
        return ret;
}

static struct task_struct * good_sigevent(sigevent_t * event)
{
        struct task_struct *rtn = current->group_leader;

        if ((event->sigev_notify & SIGEV_THREAD_ID ) &&
                (!(rtn = find_task_by_vpid(event->sigev_notify_thread_id)) ||
                 !same_thread_group(rtn, current) ||
                 (event->sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_SIGNAL))
                return NULL;

        if (((event->sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE) &&
            ((event->sigev_signo <= 0) || (event->sigev_signo > SIGRTMAX)))
                return NULL;

        return rtn;
}

void register_posix_clock(const clockid_t clock_id, struct k_clock *new_clock)
{
        if ((unsigned) clock_id >= MAX_CLOCKS) {
                printk("POSIX clock register failed for clock_id %d\n",
                       clock_id);
                return;
        }

        posix_clocks[clock_id] = *new_clock;
}
EXPORT_SYMBOL_GPL(register_posix_clock);

static struct k_itimer * alloc_posix_timer(void)
{
        struct k_itimer *tmr;
        tmr = kmem_cache_zalloc(posix_timers_cache, GFP_KERNEL);
        if (!tmr)
                return tmr;
        if (unlikely(!(tmr->sigq = sigqueue_alloc()))) {
                kmem_cache_free(posix_timers_cache, tmr);
                tmr = NULL;
        }
        memset(&tmr->sigq->info, 0, sizeof(siginfo_t));
        return tmr;
}

#define IT_ID_SET       1
#define IT_ID_NOT_SET   0
static void release_posix_timer(struct k_itimer *tmr, int it_id_set)
{
        if (it_id_set) {
                unsigned long flags;
                spin_lock_irqsave(&idr_lock, flags);
                idr_remove(&posix_timers_id, tmr->it_id);
                spin_unlock_irqrestore(&idr_lock, flags);
        }
        sigqueue_free(tmr->sigq);
        kmem_cache_free(posix_timers_cache, tmr);
}

/* Create a POSIX.1b interval timer. */

asmlinkage long
sys_timer_create(const clockid_t which_clock,
                 struct sigevent __user *timer_event_spec,
                 timer_t __user * created_timer_id)
{
        struct k_itimer *new_timer;
        int error, new_timer_id;
        struct task_struct *process;
        sigevent_t event;
        int it_id_set = IT_ID_NOT_SET;

        if (invalid_clockid(which_clock))
                return -EINVAL;

        new_timer = alloc_posix_timer();
        if (unlikely(!new_timer))
                return -EAGAIN;

        spin_lock_init(&new_timer->it_lock);
 retry:
        if (unlikely(!idr_pre_get(&posix_timers_id, GFP_KERNEL))) {
                error = -EAGAIN;
                goto out;
        }
        spin_lock_irq(&idr_lock);
        error = idr_get_new(&posix_timers_id, new_timer, &new_timer_id);
        spin_unlock_irq(&idr_lock);
        if (error) {
                if (error == -EAGAIN)
                        goto retry;
                /*
                 * Weird looking, but we return EAGAIN if the IDR is
                 * full (proper POSIX return value for this)
                 */
                error = -EAGAIN;
                goto out;
        }

        it_id_set = IT_ID_SET;
        new_timer->it_id = (timer_t) new_timer_id;
        new_timer->it_clock = which_clock;
        new_timer->it_overrun = -1;
        error = CLOCK_DISPATCH(which_clock, timer_create, (new_timer));
        if (error)
                goto out;

        /*
         * return the timer_id now.  The next step is hard to
         * back out if there is an error.
         */
        if (copy_to_user(created_timer_id,
                         &new_timer_id, sizeof (new_timer_id))) {
                error = -EFAULT;
                goto out;
        }
        if (timer_event_spec) {
                if (copy_from_user(&event, timer_event_spec, sizeof (event))) {
                        error = -EFAULT;
                        goto out;
                }
                rcu_read_lock();
                process = good_sigevent(&event);
                if (process)
                        get_task_struct(process);
                rcu_read_unlock();
                if (!process) {
                        error = -EINVAL;
                        goto out;
                }
        } else {
                event.sigev_notify = SIGEV_SIGNAL;
                event.sigev_signo = SIGALRM;
                event.sigev_value.sival_int = new_timer->it_id;
                process = current->group_leader;
                get_task_struct(process);
        }

        new_timer->it_sigev_notify     = event.sigev_notify;
        new_timer->sigq->info.si_signo = event.sigev_signo;
        new_timer->sigq->info.si_value = event.sigev_value;
        new_timer->sigq->info.si_tid   = new_timer->it_id;
        new_timer->sigq->info.si_code  = SI_TIMER;

        spin_lock_irq(&current->sighand->siglock);
        new_timer->it_process = process;
        list_add(&new_timer->list, &current->signal->posix_timers);
        spin_unlock_irq(&current->sighand->siglock);

        return 0;
        /*
         * In the case of the timer belonging to another task, after
         * the task is unlocked, the timer is owned by the other task
         * and may cease to exist at any time.  Don't use or modify
         * new_timer after the unlock call.
         */
out:
        release_posix_timer(new_timer, it_id_set);
        return error;
}

/*
 * Locking issues: We need to protect the result of the id look up until
 * we get the timer locked down so it is not deleted under us.  The
 * removal is done under the idr spinlock so we use that here to bridge
 * the find to the timer lock.  To avoid a dead lock, the timer id MUST
 * be release with out holding the timer lock.
 */
static struct k_itimer * lock_timer(timer_t timer_id, unsigned long *flags)
{
        struct k_itimer *timr;
        /*
         * Watch out here.  We do a irqsave on the idr_lock and pass the
         * flags part over to the timer lock.  Must not let interrupts in
         * while we are moving the lock.
         */

        spin_lock_irqsave(&idr_lock, *flags);
        timr = idr_find(&posix_timers_id, (int) timer_id);
        if (timr) {
                spin_lock(&timr->it_lock);

                if (!timr->it_process ||
                    !same_thread_group(timr->it_process, current)) {
                        spin_unlock(&timr->it_lock);
                        spin_unlock_irqrestore(&idr_lock, *flags);
                        timr = NULL;
                } else
                        spin_unlock(&idr_lock);
        } else
                spin_unlock_irqrestore(&idr_lock, *flags);

        return timr;
}

/*
 * Get the time remaining on a POSIX.1b interval timer.  This function
 * is ALWAYS called with spin_lock_irq on the timer, thus it must not
 * mess with irq.
 *
 * We have a couple of messes to clean up here.  First there is the case
 * of a timer that has a requeue pending.  These timers should appear to
 * be in the timer list with an expiry as if we were to requeue them
 * now.
 *
 * The second issue is the SIGEV_NONE timer which may be active but is
 * not really ever put in the timer list (to save system resources).
 * This timer may be expired, and if so, we will do it here.  Otherwise
 * it is the same as a requeue pending timer WRT to what we should
 * report.
 */
static void
common_timer_get(struct k_itimer *timr, struct itimerspec *cur_setting)
{
        ktime_t now, remaining, iv;
        struct hrtimer *timer = &timr->it.real.timer;

        memset(cur_setting, 0, sizeof(struct itimerspec));

        iv = timr->it.real.interval;

        /* interval timer ? */
        if (iv.tv64)
                cur_setting->it_interval = ktime_to_timespec(iv);
        else if (!hrtimer_active(timer) &&
                 (timr->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE)
                return;

        now = timer->base->get_time();

        /*
         * When a requeue is pending or this is a SIGEV_NONE
         * timer move the expiry time forward by intervals, so
         * expiry is > now.
         */
        if (iv.tv64 && (timr->it_requeue_pending & REQUEUE_PENDING ||
            (timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE))
                timr->it_overrun += (unsigned int) hrtimer_forward(timer, now, iv);

        remaining = ktime_sub(timer->expires, now);
        /* Return 0 only, when the timer is expired and not pending */
        if (remaining.tv64 <= 0) {
                /*
                 * A single shot SIGEV_NONE timer must return 0, when
                 * it is expired !
                 */
                if ((timr->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE)
                        cur_setting->it_value.tv_nsec = 1;
        } else
                cur_setting->it_value = ktime_to_timespec(remaining);
}

/* Get the time remaining on a POSIX.1b interval timer. */
asmlinkage long
sys_timer_gettime(timer_t timer_id, struct itimerspec __user *setting)
{
        struct k_itimer *timr;
        struct itimerspec cur_setting;
        unsigned long flags;

        timr = lock_timer(timer_id, &flags);
        if (!timr)
                return -EINVAL;

        CLOCK_DISPATCH(timr->it_clock, timer_get, (timr, &cur_setting));

        unlock_timer(timr, flags);

        if (copy_to_user(setting, &cur_setting, sizeof (cur_setting)))
                return -EFAULT;

        return 0;
}

/*
 * Get the number of overruns of a POSIX.1b interval timer.  This is to
 * be the overrun of the timer last delivered.  At the same time we are
 * accumulating overruns on the next timer.  The overrun is frozen when
 * the signal is delivered, either at the notify time (if the info block
 * is not queued) or at the actual delivery time (as we are informed by
 * the call back to do_schedule_next_timer().  So all we need to do is
 * to pick up the frozen overrun.
 */
asmlinkage long
sys_timer_getoverrun(timer_t timer_id)
{
        struct k_itimer *timr;
        int overrun;
        unsigned long flags;

        timr = lock_timer(timer_id, &flags);
        if (!timr)
                return -EINVAL;

        overrun = timr->it_overrun_last;
        unlock_timer(timr, flags);

        return overrun;
}

/* Set a POSIX.1b interval timer. */
/* timr->it_lock is taken. */
static int
common_timer_set(struct k_itimer *timr, int flags,
                 struct itimerspec *new_setting, struct itimerspec *old_setting)
{
        struct hrtimer *timer = &timr->it.real.timer;
        enum hrtimer_mode mode;

        if (old_setting)
                common_timer_get(timr, old_setting);

        /* disable the timer */
        timr->it.real.interval.tv64 = 0;
        /*
         * careful here.  If smp we could be in the "fire" routine which will
         * be spinning as we hold the lock.  But this is ONLY an SMP issue.
         */
        if (hrtimer_try_to_cancel(timer) < 0)
                return TIMER_RETRY;

        timr->it_requeue_pending = (timr->it_requeue_pending + 2) & 
                ~REQUEUE_PENDING;
        timr->it_overrun_last = 0;

        /* switch off the timer when it_value is zero */
        if (!new_setting->it_value.tv_sec && !new_setting->it_value.tv_nsec)
                return 0;

        mode = flags & TIMER_ABSTIME ? HRTIMER_MODE_ABS : HRTIMER_MODE_REL;
        hrtimer_init(&timr->it.real.timer, timr->it_clock, mode);
        timr->it.real.timer.function = posix_timer_fn;

        timer->expires = timespec_to_ktime(new_setting->it_value);

        /* Convert interval */
        timr->it.real.interval = timespec_to_ktime(new_setting->it_interval);

        /* SIGEV_NONE timers are not queued ! See common_timer_get */
        if (((timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE)) {
                /* Setup correct expiry time for relative timers */
                if (mode == HRTIMER_MODE_REL) {
                        timer->expires =
                                ktime_add_safe(timer->expires,
                                               timer->base->get_time());
                }
                return 0;
        }

        hrtimer_start(timer, timer->expires, mode);
        return 0;
}

/* Set a POSIX.1b interval timer */
asmlinkage long
sys_timer_settime(timer_t timer_id, int flags,
                  const struct itimerspec __user *new_setting,
                  struct itimerspec __user *old_setting)
{
        struct k_itimer *timr;
        struct itimerspec new_spec, old_spec;
        int error = 0;
        unsigned long flag;
        struct itimerspec *rtn = old_setting ? &old_spec : NULL;

        if (!new_setting)
                return -EINVAL;

        if (copy_from_user(&new_spec, new_setting, sizeof (new_spec)))
                return -EFAULT;

        if (!timespec_valid(&new_spec.it_interval) ||
            !timespec_valid(&new_spec.it_value))
                return -EINVAL;
retry:
        timr = lock_timer(timer_id, &flag);
        if (!timr)
                return -EINVAL;

        error = CLOCK_DISPATCH(timr->it_clock, timer_set,
                               (timr, flags, &new_spec, rtn));

        unlock_timer(timr, flag);
        if (error == TIMER_RETRY) {
                rtn = NULL;     // We already got the old time...
                goto retry;
        }

        if (old_setting && !error &&
            copy_to_user(old_setting, &old_spec, sizeof (old_spec)))
                error = -EFAULT;

        return error;
}

static inline int common_timer_del(struct k_itimer *timer)
{
        timer->it.real.interval.tv64 = 0;

        if (hrtimer_try_to_cancel(&timer->it.real.timer) < 0)
                return TIMER_RETRY;
        return 0;
}

static inline int timer_delete_hook(struct k_itimer *timer)
{
        return CLOCK_DISPATCH(timer->it_clock, timer_del, (timer));
}

/* Delete a POSIX.1b interval timer. */
asmlinkage long
sys_timer_delete(timer_t timer_id)
{
        struct k_itimer *timer;
        unsigned long flags;

retry_delete:
        timer = lock_timer(timer_id, &flags);
        if (!timer)
                return -EINVAL;

        if (timer_delete_hook(timer) == TIMER_RETRY) {
                unlock_timer(timer, flags);
                goto retry_delete;
        }

        spin_lock(&current->sighand->siglock);
        list_del(&timer->list);
        spin_unlock(&current->sighand->siglock);
        /*
         * This keeps any tasks waiting on the spin lock from thinking
         * they got something (see the lock code above).
         */
        put_task_struct(timer->it_process);
        timer->it_process = NULL;

        unlock_timer(timer, flags);
        release_posix_timer(timer, IT_ID_SET);
        return 0;
}

/*
 * return timer owned by the process, used by exit_itimers
 */
static void itimer_delete(struct k_itimer *timer)
{
        unsigned long flags;

retry_delete:
        spin_lock_irqsave(&timer->it_lock, flags);

        if (timer_delete_hook(timer) == TIMER_RETRY) {
                unlock_timer(timer, flags);
                goto retry_delete;
        }
        list_del(&timer->list);
        /*
         * This keeps any tasks waiting on the spin lock from thinking
         * they got something (see the lock code above).
         */
        put_task_struct(timer->it_process);
        timer->it_process = NULL;

        unlock_timer(timer, flags);
        release_posix_timer(timer, IT_ID_SET);
}

/*
 * This is called by do_exit or de_thread, only when there are no more
 * references to the shared signal_struct.
 */
void exit_itimers(struct signal_struct *sig)
{
        struct k_itimer *tmr;

        while (!list_empty(&sig->posix_timers)) {
                tmr = list_entry(sig->posix_timers.next, struct k_itimer, list);
                itimer_delete(tmr);
        }
}

/* Not available / possible... functions */
int do_posix_clock_nosettime(const clockid_t clockid, struct timespec *tp)
{
        return -EINVAL;
}
EXPORT_SYMBOL_GPL(do_posix_clock_nosettime);

int do_posix_clock_nonanosleep(const clockid_t clock, int flags,
                               struct timespec *t, struct timespec __user *r)
{
#ifndef ENOTSUP
        return -EOPNOTSUPP;     /* aka ENOTSUP in userland for POSIX */
#else  /*  parisc does define it separately.  */
        return -ENOTSUP;
#endif
}
EXPORT_SYMBOL_GPL(do_posix_clock_nonanosleep);

asmlinkage long sys_clock_settime(const clockid_t which_clock,
                                  const struct timespec __user *tp)
{
        struct timespec new_tp;

        if (invalid_clockid(which_clock))
                return -EINVAL;
        if (copy_from_user(&new_tp, tp, sizeof (*tp)))
                return -EFAULT;

        return CLOCK_DISPATCH(which_clock, clock_set, (which_clock, &new_tp));
}

asmlinkage long
sys_clock_gettime(const clockid_t which_clock, struct timespec __user *tp)
{
        struct timespec kernel_tp;
        int error;

        if (invalid_clockid(which_clock))
                return -EINVAL;
        error = CLOCK_DISPATCH(which_clock, clock_get,
                               (which_clock, &kernel_tp));
        if (!error && copy_to_user(tp, &kernel_tp, sizeof (kernel_tp)))
                error = -EFAULT;

        return error;

}

asmlinkage long
sys_clock_getres(const clockid_t which_clock, struct timespec __user *tp)
{
        struct timespec rtn_tp;
        int error;

        if (invalid_clockid(which_clock))
                return -EINVAL;

        error = CLOCK_DISPATCH(which_clock, clock_getres,
                               (which_clock, &rtn_tp));

        if (!error && tp && copy_to_user(tp, &rtn_tp, sizeof (rtn_tp))) {
                error = -EFAULT;
        }

        return error;
}

/*
 * nanosleep for monotonic and realtime clocks
 */
static int common_nsleep(const clockid_t which_clock, int flags,
                         struct timespec *tsave, struct timespec __user *rmtp)
{
        return hrtimer_nanosleep(tsave, rmtp, flags & TIMER_ABSTIME ?
                                 HRTIMER_MODE_ABS : HRTIMER_MODE_REL,
                                 which_clock);
}

asmlinkage long
sys_clock_nanosleep(const clockid_t which_clock, int flags,
                    const struct timespec __user *rqtp,
                    struct timespec __user *rmtp)
{
        struct timespec t;

        if (invalid_clockid(which_clock))
                return -EINVAL;

        if (copy_from_user(&t, rqtp, sizeof (struct timespec)))
                return -EFAULT;

        if (!timespec_valid(&t))
                return -EINVAL;

        return CLOCK_DISPATCH(which_clock, nsleep,
                              (which_clock, flags, &t, rmtp));
}

/*
 * nanosleep_restart for monotonic and realtime clocks
 */
static int common_nsleep_restart(struct restart_block *restart_block)
{
        return hrtimer_nanosleep_restart(restart_block);
}

/*
 * This will restart clock_nanosleep. This is required only by
 * compat_clock_nanosleep_restart for now.
 */
long
clock_nanosleep_restart(struct restart_block *restart_block)
{
        clockid_t which_clock = restart_block->arg0;

        return CLOCK_DISPATCH(which_clock, nsleep_restart,
                              (restart_block));
}