151 lines
4.0 KiB
Diff
151 lines
4.0 KiB
Diff
From: Ingo Molnar <mingo@elte.hu>
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Date: Fri, 3 Jul 2009 08:29:34 -0500
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Subject: timers: Prepare for full preemption
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.4/patches-4.4-rt3.tar.xz
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When softirqs can be preempted we need to make sure that cancelling
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the timer from the active thread can not deadlock vs. a running timer
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callback. Add a waitqueue to resolve that.
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Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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include/linux/timer.h | 2 +-
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kernel/sched/core.c | 9 +++++++--
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kernel/time/timer.c | 41 ++++++++++++++++++++++++++++++++++++++---
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3 files changed, 46 insertions(+), 6 deletions(-)
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--- a/include/linux/timer.h
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+++ b/include/linux/timer.h
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@@ -225,7 +225,7 @@ extern void add_timer(struct timer_list
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extern int try_to_del_timer_sync(struct timer_list *timer);
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-#ifdef CONFIG_SMP
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+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT_FULL)
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extern int del_timer_sync(struct timer_list *timer);
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#else
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# define del_timer_sync(t) del_timer(t)
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--- a/kernel/sched/core.c
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+++ b/kernel/sched/core.c
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@@ -618,11 +618,14 @@ void resched_cpu(int cpu)
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*/
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int get_nohz_timer_target(void)
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{
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- int i, cpu = smp_processor_id();
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+ int i, cpu;
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struct sched_domain *sd;
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+ preempt_disable_rt();
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+ cpu = smp_processor_id();
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+
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if (!idle_cpu(cpu) && is_housekeeping_cpu(cpu))
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- return cpu;
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+ goto preempt_en_rt;
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rcu_read_lock();
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for_each_domain(cpu, sd) {
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@@ -638,6 +641,8 @@ int get_nohz_timer_target(void)
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cpu = housekeeping_any_cpu();
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unlock:
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rcu_read_unlock();
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+preempt_en_rt:
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+ preempt_enable_rt();
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return cpu;
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}
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/*
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--- a/kernel/time/timer.c
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+++ b/kernel/time/timer.c
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@@ -80,6 +80,9 @@ struct tvec_root {
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struct tvec_base {
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spinlock_t lock;
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struct timer_list *running_timer;
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+#ifdef CONFIG_PREEMPT_RT_FULL
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+ wait_queue_head_t wait_for_running_timer;
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+#endif
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unsigned long timer_jiffies;
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unsigned long next_timer;
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unsigned long active_timers;
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@@ -1006,6 +1009,33 @@ void add_timer_on(struct timer_list *tim
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}
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EXPORT_SYMBOL_GPL(add_timer_on);
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+#ifdef CONFIG_PREEMPT_RT_FULL
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+/*
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+ * Wait for a running timer
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+ */
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+static void wait_for_running_timer(struct timer_list *timer)
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+{
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+ struct tvec_base *base;
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+ u32 tf = timer->flags;
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+
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+ if (tf & TIMER_MIGRATING)
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+ return;
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+
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+ base = per_cpu_ptr(&tvec_bases, tf & TIMER_CPUMASK);
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+ wait_event(base->wait_for_running_timer,
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+ base->running_timer != timer);
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+}
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+
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+# define wakeup_timer_waiters(b) wake_up(&(b)->wait_for_running_timer)
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+#else
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+static inline void wait_for_running_timer(struct timer_list *timer)
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+{
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+ cpu_relax();
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+}
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+
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+# define wakeup_timer_waiters(b) do { } while (0)
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+#endif
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+
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/**
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* del_timer - deactive a timer.
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* @timer: the timer to be deactivated
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@@ -1063,7 +1093,7 @@ int try_to_del_timer_sync(struct timer_l
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}
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EXPORT_SYMBOL(try_to_del_timer_sync);
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-#ifdef CONFIG_SMP
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+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT_FULL)
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/**
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* del_timer_sync - deactivate a timer and wait for the handler to finish.
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* @timer: the timer to be deactivated
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@@ -1123,7 +1153,7 @@ int del_timer_sync(struct timer_list *ti
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int ret = try_to_del_timer_sync(timer);
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if (ret >= 0)
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return ret;
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- cpu_relax();
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+ wait_for_running_timer(timer);
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}
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}
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EXPORT_SYMBOL(del_timer_sync);
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@@ -1248,15 +1278,17 @@ static inline void __run_timers(struct t
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if (irqsafe) {
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spin_unlock(&base->lock);
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call_timer_fn(timer, fn, data);
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+ base->running_timer = NULL;
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spin_lock(&base->lock);
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} else {
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spin_unlock_irq(&base->lock);
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call_timer_fn(timer, fn, data);
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+ base->running_timer = NULL;
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spin_lock_irq(&base->lock);
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}
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}
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}
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- base->running_timer = NULL;
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+ wakeup_timer_waiters(base);
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spin_unlock_irq(&base->lock);
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}
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@@ -1645,6 +1677,9 @@ static void __init init_timer_cpu(int cp
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base->cpu = cpu;
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spin_lock_init(&base->lock);
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+#ifdef CONFIG_PREEMPT_RT_FULL
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+ init_waitqueue_head(&base->wait_for_running_timer);
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+#endif
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base->timer_jiffies = jiffies;
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base->next_timer = base->timer_jiffies;
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