hrtimer: Unify hrtimer removal handling
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This timer will fire late, if it expires before the effective first hrtimer on this CPU and the comparison was with an outdated expires_next value.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 <anna-maria@linutronix.de> Cc: Christoph Hellwig <hch@lst.de> Cc: John Stultz <john.stultz@linaro.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: keescook@chromium.org Link: http://lkml.kernel.org/r/20171221104205.7269-20-anna-maria@linutronix.de Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -521,9 +521,6 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal)
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{
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ktime_t expires_next;
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if (!__hrtimer_hres_active(cpu_base))
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return;
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expires_next = __hrtimer_get_next_event(cpu_base);
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if (skip_equal && expires_next == cpu_base->expires_next)
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@ -532,6 +529,9 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal)
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cpu_base->expires_next = expires_next;
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/*
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* If hres is not active, hardware does not have to be
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* reprogrammed yet.
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*
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* If a hang was detected in the last timer interrupt then we
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* leave the hang delay active in the hardware. We want the
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* system to make progress. That also prevents the following
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@ -545,7 +545,7 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal)
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* set. So we'd effectivly block all timers until the T2 event
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* fires.
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*/
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if (cpu_base->hang_detected)
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if (!__hrtimer_hres_active(cpu_base) || cpu_base->hang_detected)
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return;
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tick_program_event(cpu_base->expires_next, 1);
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@ -844,7 +844,6 @@ static void __remove_hrtimer(struct hrtimer *timer,
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if (!timerqueue_del(&base->active, &timer->node))
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cpu_base->active_bases &= ~(1 << base->index);
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#ifdef CONFIG_HIGH_RES_TIMERS
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/*
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* Note: If reprogram is false we do not update
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* cpu_base->next_timer. This happens when we remove the first
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@ -855,7 +854,6 @@ static void __remove_hrtimer(struct hrtimer *timer,
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*/
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if (reprogram && timer == cpu_base->next_timer)
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hrtimer_force_reprogram(cpu_base, 1);
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#endif
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}
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/*
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