180 lines
5.1 KiB
Diff
180 lines
5.1 KiB
Diff
From f5b8bffc2c6c9158ce9618fa1240c9fe03a321ab Mon Sep 17 00:00:00 2001
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Message-Id: <f5b8bffc2c6c9158ce9618fa1240c9fe03a321ab.1601675151.git.zanussi@kernel.org>
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In-Reply-To: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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References: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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From: Ingo Molnar <mingo@elte.hu>
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Date: Fri, 3 Jul 2009 08:29:34 -0500
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Subject: [PATCH 089/333] timers: Prepare for full preemption
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.148-rt64.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 | 45 +++++++++++++++++++++++++++++++++++++++----
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3 files changed, 49 insertions(+), 7 deletions(-)
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diff --git a/include/linux/timer.h b/include/linux/timer.h
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index 7b066fd38248..54627d046b3a 100644
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--- a/include/linux/timer.h
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+++ b/include/linux/timer.h
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@@ -172,7 +172,7 @@ extern void add_timer(struct timer_list *timer);
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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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diff --git a/kernel/sched/core.c b/kernel/sched/core.c
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index 541c7222ffc2..c0058e62a3fc 100644
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--- a/kernel/sched/core.c
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+++ b/kernel/sched/core.c
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@@ -498,11 +498,14 @@ 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) && housekeeping_cpu(cpu, HK_FLAG_TIMER))
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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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@@ -521,6 +524,8 @@ int get_nohz_timer_target(void)
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cpu = housekeeping_any_cpu(HK_FLAG_TIMER);
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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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diff --git a/kernel/time/timer.c b/kernel/time/timer.c
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index 61e41ea3a96e..ecc23d2c21a9 100644
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--- a/kernel/time/timer.c
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+++ b/kernel/time/timer.c
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@@ -45,6 +45,7 @@
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#include <linux/slab.h>
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#include <linux/compat.h>
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#include <linux/random.h>
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+#include <linux/swait.h>
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#include <linux/uaccess.h>
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#include <asm/unistd.h>
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@@ -198,6 +199,9 @@ EXPORT_SYMBOL(jiffies_64);
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struct timer_base {
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raw_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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+ struct swait_queue_head wait_for_running_timer;
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+#endif
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unsigned long clk;
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unsigned long next_expiry;
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unsigned int cpu;
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@@ -1190,6 +1194,33 @@ void add_timer_on(struct timer_list *timer, int cpu)
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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 timer_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 = get_timer_base(tf);
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+ swait_event_exclusive(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) swake_up_all(&(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 - deactivate a timer.
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* @timer: the timer to be deactivated
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@@ -1245,7 +1276,7 @@ int try_to_del_timer_sync(struct timer_list *timer)
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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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@@ -1305,7 +1336,7 @@ int del_timer_sync(struct timer_list *timer)
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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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@@ -1366,13 +1397,16 @@ static void expire_timers(struct timer_base *base, struct hlist_head *head)
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fn = timer->function;
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- if (timer->flags & TIMER_IRQSAFE) {
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+ if (!IS_ENABLED(CONFIG_PREEMPT_RT_FULL) &&
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+ timer->flags & TIMER_IRQSAFE) {
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raw_spin_unlock(&base->lock);
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call_timer_fn(timer, fn);
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+ base->running_timer = NULL;
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raw_spin_lock(&base->lock);
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} else {
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raw_spin_unlock_irq(&base->lock);
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call_timer_fn(timer, fn);
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+ base->running_timer = NULL;
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raw_spin_lock_irq(&base->lock);
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}
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}
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@@ -1702,8 +1736,8 @@ static inline void __run_timers(struct timer_base *base)
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while (levels--)
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expire_timers(base, heads + levels);
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}
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- base->running_timer = NULL;
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raw_spin_unlock_irq(&base->lock);
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+ wakeup_timer_waiters(base);
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}
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/*
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@@ -1948,6 +1982,9 @@ static void __init init_timer_cpu(int cpu)
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base->cpu = cpu;
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raw_spin_lock_init(&base->lock);
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base->clk = jiffies;
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+#ifdef CONFIG_PREEMPT_RT_FULL
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+ init_swait_queue_head(&base->wait_for_running_timer);
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+#endif
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}
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}
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--
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2.17.1
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