From a86e9284336729a8f79a65371eacd0c1c7fae142 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 25 Apr 2023 20:49:12 +0200 Subject: [PATCH] posix-timers: Document common_clock_get() correctly Replace another confusing and inaccurate set of comments. Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Link: https://lore.kernel.org/r/20230425183313.409169321@linutronix.de --- kernel/time/posix-timers.c | 50 +++++++++++++++++++++++--------------- 1 file changed, 30 insertions(+), 20 deletions(-) diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c index 1acdd04e5d26..e1af74ca80ab 100644 --- a/kernel/time/posix-timers.c +++ b/kernel/time/posix-timers.c @@ -660,20 +660,16 @@ static s64 common_hrtimer_forward(struct k_itimer *timr, ktime_t now) } /* - * 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. + * Get the time remaining on a POSIX.1b interval timer. * - * 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. + * Two issues to handle here: * - * 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. + * 1) The timer has a requeue pending. The return value must appear as + * if the timer has been requeued right now. + * + * 2) The timer is a SIGEV_NONE timer. These timers are never enqueued + * into the hrtimer queue and therefore never expired. Emulate expiry + * here taking #1 into account. */ void common_timer_get(struct k_itimer *timr, struct itimerspec64 *cur_setting) { @@ -689,8 +685,12 @@ void common_timer_get(struct k_itimer *timr, struct itimerspec64 *cur_setting) cur_setting->it_interval = ktime_to_timespec64(iv); } else if (!timr->it_active) { /* - * SIGEV_NONE oneshot timers are never queued. Check them - * below. + * SIGEV_NONE oneshot timers are never queued and therefore + * timr->it_active is always false. The check below + * vs. remaining time will handle this case. + * + * For all other timers there is nothing to update here, so + * return. */ if (!sig_none) return; @@ -699,18 +699,29 @@ void common_timer_get(struct k_itimer *timr, struct itimerspec64 *cur_setting) now = kc->clock_get_ktime(timr->it_clock); /* - * When a requeue is pending or this is a SIGEV_NONE timer move the - * expiry time forward by intervals, so expiry is > now. + * If this is an interval timer and either has requeue pending or + * is a SIGEV_NONE timer move the expiry time forward by intervals, + * so expiry is > now. */ if (iv && (timr->it_requeue_pending & REQUEUE_PENDING || sig_none)) timr->it_overrun += kc->timer_forward(timr, now); remaining = kc->timer_remaining(timr, now); - /* Return 0 only, when the timer is expired and not pending */ + /* + * As @now is retrieved before a possible timer_forward() and + * cannot be reevaluated by the compiler @remaining is based on the + * same @now value. Therefore @remaining is consistent vs. @now. + * + * Consequently all interval timers, i.e. @iv > 0, cannot have a + * remaining time <= 0 because timer_forward() guarantees to move + * them forward so that the next timer expiry is > @now. + */ if (remaining <= 0) { /* - * A single shot SIGEV_NONE timer must return 0, when - * it is expired ! + * A single shot SIGEV_NONE timer must return 0, when it is + * expired! Timers which have a real signal delivery mode + * must return a remaining time greater than 0 because the + * signal has not yet been delivered. */ if (!sig_none) cur_setting->it_value.tv_nsec = 1; @@ -719,7 +730,6 @@ void common_timer_get(struct k_itimer *timr, struct itimerspec64 *cur_setting) } } -/* Get the time remaining on a POSIX.1b interval timer. */ static int do_timer_gettime(timer_t timer_id, struct itimerspec64 *setting) { struct k_itimer *timr; -- 2.34.1