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posix-timers: Document common_clock_get() correctly
Replace another confusing and inaccurate set of comments. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Link: https://lore.kernel.org/r/20230425183313.409169321@linutronix.de
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1 changed files with 30 additions and 20 deletions
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@ -660,20 +660,16 @@ static s64 common_hrtimer_forward(struct k_itimer *timr, ktime_t now)
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}
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/*
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* Get the time remaining on a POSIX.1b interval timer. This function
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* is ALWAYS called with spin_lock_irq on the timer, thus it must not
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* mess with irq.
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* Get the time remaining on a POSIX.1b interval timer.
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*
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* We have a couple of messes to clean up here. First there is the case
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* of a timer that has a requeue pending. These timers should appear to
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* be in the timer list with an expiry as if we were to requeue them
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* now.
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* Two issues to handle here:
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*
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* The second issue is the SIGEV_NONE timer which may be active but is
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* not really ever put in the timer list (to save system resources).
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* This timer may be expired, and if so, we will do it here. Otherwise
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* it is the same as a requeue pending timer WRT to what we should
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* report.
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* 1) The timer has a requeue pending. The return value must appear as
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* if the timer has been requeued right now.
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*
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* 2) The timer is a SIGEV_NONE timer. These timers are never enqueued
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* into the hrtimer queue and therefore never expired. Emulate expiry
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* here taking #1 into account.
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*/
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void common_timer_get(struct k_itimer *timr, struct itimerspec64 *cur_setting)
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{
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@ -689,8 +685,12 @@ void common_timer_get(struct k_itimer *timr, struct itimerspec64 *cur_setting)
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cur_setting->it_interval = ktime_to_timespec64(iv);
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} else if (!timr->it_active) {
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/*
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* SIGEV_NONE oneshot timers are never queued. Check them
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* below.
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* SIGEV_NONE oneshot timers are never queued and therefore
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* timr->it_active is always false. The check below
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* vs. remaining time will handle this case.
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*
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* For all other timers there is nothing to update here, so
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* return.
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*/
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if (!sig_none)
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return;
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@ -699,18 +699,29 @@ void common_timer_get(struct k_itimer *timr, struct itimerspec64 *cur_setting)
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now = kc->clock_get_ktime(timr->it_clock);
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/*
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* When a requeue is pending or this is a SIGEV_NONE timer move the
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* expiry time forward by intervals, so expiry is > now.
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* If this is an interval timer and either has requeue pending or
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* is a SIGEV_NONE timer move the expiry time forward by intervals,
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* so expiry is > now.
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*/
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if (iv && (timr->it_requeue_pending & REQUEUE_PENDING || sig_none))
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timr->it_overrun += kc->timer_forward(timr, now);
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remaining = kc->timer_remaining(timr, now);
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/* Return 0 only, when the timer is expired and not pending */
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/*
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* As @now is retrieved before a possible timer_forward() and
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* cannot be reevaluated by the compiler @remaining is based on the
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* same @now value. Therefore @remaining is consistent vs. @now.
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*
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* Consequently all interval timers, i.e. @iv > 0, cannot have a
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* remaining time <= 0 because timer_forward() guarantees to move
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* them forward so that the next timer expiry is > @now.
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*/
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if (remaining <= 0) {
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/*
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* A single shot SIGEV_NONE timer must return 0, when
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* it is expired !
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* A single shot SIGEV_NONE timer must return 0, when it is
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* expired! Timers which have a real signal delivery mode
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* must return a remaining time greater than 0 because the
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* signal has not yet been delivered.
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*/
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if (!sig_none)
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cur_setting->it_value.tv_nsec = 1;
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@ -719,7 +730,6 @@ void common_timer_get(struct k_itimer *timr, struct itimerspec64 *cur_setting)
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}
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}
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/* Get the time remaining on a POSIX.1b interval timer. */
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static int do_timer_gettime(timer_t timer_id, struct itimerspec64 *setting)
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{
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struct k_itimer *timr;
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