From: Anna-Maria Gleixner Date: Sun, 22 Oct 2017 23:39:57 +0200 Subject: [PATCH 19/36] hrtimer: Unify handling of hrtimer remove Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.14/older/patches-4.14.6-rt7.tar.xz When the first hrtimer on the current CPU is removed, hrtimer_force_reprogram() is invoked but only when CONFIG_HIGH_RES_TIMERS=y and hrtimer_cpu_base.hres_active is set. hrtimer_force_reprogram() updates hrtimer_cpu_base.expires_next and reprograms the clock event device. When CONFIG_HIGH_RES_TIMERS=y and hrtimer_cpu_base.hres_active is set, a pointless hrtimer interrupt can be prevented. hrtimer_check_target() makes the 'can remote enqueue' decision. As soon as hrtimer_check_target() is unconditionally available and hrtimer_cpu_base.expires_next is updated by hrtimer_reprogram(), hrtimer_force_reprogram() needs to be available unconditionally as well to prevent the following scenario with CONFIG_HIGH_RES_TIMERS=n: - the first hrtimer on this CPU is removed and hrtimer_force_reprogram() is not executed - CPU goes idle (next timer is calculated and hrtimers are taken into account) - a hrtimer is enqueued remote on the idle CPU: hrtimer_check_target() compares expiry value and hrtimer_cpu_base.expires_next. The expiry value is after expires_next, so the hrtimer is enqueued. This timer will fire late, if it expires before the effective first hrtimer on this CPU and the comparison was with an outdated expires_next value. To prevent this scenario, make hrtimer_force_reprogram() unconditional except the effective reprogramming part, which gets eliminated by the compiler in the CONFIG_HIGH_RES_TIMERS=n case. Signed-off-by: Anna-Maria Gleixner Signed-off-by: Thomas Gleixner Signed-off-by: Sebastian Andrzej Siewior --- kernel/time/hrtimer.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -523,9 +523,6 @@ hrtimer_force_reprogram(struct hrtimer_c { ktime_t expires_next; - if (!__hrtimer_hres_active(cpu_base)) - return; - expires_next = __hrtimer_get_next_event(cpu_base); if (skip_equal && expires_next == cpu_base->expires_next) @@ -534,6 +531,9 @@ hrtimer_force_reprogram(struct hrtimer_c cpu_base->expires_next = expires_next; /* + * If hres is not active, hardware does not have to be + * reprogrammed yet. + * * If a hang was detected in the last timer interrupt then we * leave the hang delay active in the hardware. We want the * system to make progress. That also prevents the following @@ -547,7 +547,7 @@ hrtimer_force_reprogram(struct hrtimer_c * set. So we'd effectivly block all timers until the T2 event * fires. */ - if (cpu_base->hang_detected) + if (!__hrtimer_hres_active(cpu_base) || cpu_base->hang_detected) return; tick_program_event(cpu_base->expires_next, 1); @@ -848,7 +848,6 @@ static void __remove_hrtimer(struct hrti if (!timerqueue_del(&base->active, &timer->node)) cpu_base->active_bases &= ~(1 << base->index); -#ifdef CONFIG_HIGH_RES_TIMERS /* * Note: If reprogram is false we do not update * cpu_base->next_timer. This happens when we remove the first @@ -859,7 +858,6 @@ static void __remove_hrtimer(struct hrti */ if (reprogram && timer == cpu_base->next_timer) hrtimer_force_reprogram(cpu_base, 1); -#endif } /*