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From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 3 Jul 2009 08:29:34 -0500
Subject: timers: Prepare for full preemption
When softirqs can be preempted we need to make sure that cancelling
the timer from the active thread can not deadlock vs. a running timer
callback. Add a waitqueue to resolve that.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/timer.h | 2 +-
kernel/sched/core.c | 9 +++++++--
kernel/time/timer.c | 45 +++++++++++++++++++++++++++++++++++++++++----
3 files changed, 49 insertions(+), 7 deletions(-)
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -213,7 +213,7 @@ extern void add_timer(struct timer_list
extern int try_to_del_timer_sync(struct timer_list *timer);
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT_FULL)
extern int del_timer_sync(struct timer_list *timer);
#else
# define del_timer_sync(t) del_timer(t)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -522,11 +522,14 @@ void resched_cpu(int cpu)
*/
int get_nohz_timer_target(void)
{
- int i, cpu = smp_processor_id();
+ int i, cpu;
struct sched_domain *sd;
+ preempt_disable_rt();
+ cpu = smp_processor_id();
+
if (!idle_cpu(cpu) && is_housekeeping_cpu(cpu))
- return cpu;
+ goto preempt_en_rt;
rcu_read_lock();
for_each_domain(cpu, sd) {
@@ -545,6 +548,8 @@ int get_nohz_timer_target(void)
cpu = housekeeping_any_cpu();
unlock:
rcu_read_unlock();
+preempt_en_rt:
+ preempt_enable_rt();
return cpu;
}
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -44,6 +44,7 @@
#include <linux/sched/debug.h>
#include <linux/slab.h>
#include <linux/compat.h>
+#include <linux/swait.h>
#include <linux/uaccess.h>
#include <asm/unistd.h>
@@ -197,6 +198,9 @@ EXPORT_SYMBOL(jiffies_64);
struct timer_base {
raw_spinlock_t lock;
struct timer_list *running_timer;
+#ifdef CONFIG_PREEMPT_RT_FULL
+ struct swait_queue_head wait_for_running_timer;
+#endif
unsigned long clk;
unsigned long next_expiry;
unsigned int cpu;
@@ -1140,6 +1144,33 @@ void add_timer_on(struct timer_list *tim
}
EXPORT_SYMBOL_GPL(add_timer_on);
+#ifdef CONFIG_PREEMPT_RT_FULL
+/*
+ * Wait for a running timer
+ */
+static void wait_for_running_timer(struct timer_list *timer)
+{
+ struct timer_base *base;
+ u32 tf = timer->flags;
+
+ if (tf & TIMER_MIGRATING)
+ return;
+
+ base = get_timer_base(tf);
+ swait_event(base->wait_for_running_timer,
+ base->running_timer != timer);
+}
+
+# define wakeup_timer_waiters(b) swake_up_all(&(b)->wait_for_running_timer)
+#else
+static inline void wait_for_running_timer(struct timer_list *timer)
+{
+ cpu_relax();
+}
+
+# define wakeup_timer_waiters(b) do { } while (0)
+#endif
+
/**
* del_timer - deactivate a timer.
* @timer: the timer to be deactivated
@@ -1195,7 +1226,7 @@ int try_to_del_timer_sync(struct timer_l
}
EXPORT_SYMBOL(try_to_del_timer_sync);
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT_FULL)
/**
* del_timer_sync - deactivate a timer and wait for the handler to finish.
* @timer: the timer to be deactivated
@@ -1255,7 +1286,7 @@ int del_timer_sync(struct timer_list *ti
int ret = try_to_del_timer_sync(timer);
if (ret >= 0)
return ret;
- cpu_relax();
+ wait_for_running_timer(timer);
}
}
EXPORT_SYMBOL(del_timer_sync);
@@ -1319,13 +1350,16 @@ static void expire_timers(struct timer_b
fn = timer->function;
data = timer->data;
- if (timer->flags & TIMER_IRQSAFE) {
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT_FULL) &&
+ timer->flags & TIMER_IRQSAFE) {
raw_spin_unlock(&base->lock);
call_timer_fn(timer, fn, data);
+ base->running_timer = NULL;
raw_spin_lock(&base->lock);
} else {
raw_spin_unlock_irq(&base->lock);
call_timer_fn(timer, fn, data);
+ base->running_timer = NULL;
raw_spin_lock_irq(&base->lock);
}
}
@@ -1627,8 +1661,8 @@ static inline void __run_timers(struct t
while (levels--)
expire_timers(base, heads + levels);
}
- base->running_timer = NULL;
raw_spin_unlock_irq(&base->lock);
+ wakeup_timer_waiters(base);
}
/*
@@ -1874,6 +1908,9 @@ static void __init init_timer_cpu(int cp
base->cpu = cpu;
raw_spin_lock_init(&base->lock);
base->clk = jiffies;
+#ifdef CONFIG_PREEMPT_RT_FULL
+ init_swait_queue_head(&base->wait_for_running_timer);
+#endif
}
}
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