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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/timer.c | 35 ++++++++++++++++++++++++++++++++---
2 files changed, 33 insertions(+), 4 deletions(-)
Index: linux-stable/include/linux/timer.h
===================================================================
--- linux-stable.orig/include/linux/timer.h
+++ linux-stable/include/linux/timer.h
@@ -276,7 +276,7 @@ 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)
Index: linux-stable/kernel/timer.c
===================================================================
--- linux-stable.orig/kernel/timer.c
+++ linux-stable/kernel/timer.c
@@ -76,6 +76,7 @@ struct tvec_root {
struct tvec_base {
spinlock_t lock;
struct timer_list *running_timer;
+ wait_queue_head_t wait_for_running_timer;
unsigned long timer_jiffies;
unsigned long next_timer;
unsigned long active_timers;
@@ -757,12 +758,15 @@ __mod_timer(struct timer_list *timer, un
debug_activate(timer, expires);
+ preempt_disable_rt();
cpu = smp_processor_id();
#if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu))
cpu = get_nohz_timer_target();
#endif
+ preempt_enable_rt();
+
new_base = per_cpu(tvec_bases, cpu);
if (base != new_base) {
@@ -963,6 +967,29 @@ 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 tvec_base *base = timer->base;
+
+ if (base->running_timer == timer)
+ wait_event(base->wait_for_running_timer,
+ base->running_timer != timer);
+}
+
+# define wakeup_timer_waiters(b) wake_up(&(b)->wait_for_tunning_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 - deactive a timer.
* @timer: the timer to be deactivated
@@ -1020,7 +1047,7 @@ 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
@@ -1080,7 +1107,7 @@ 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);
@@ -1194,10 +1221,11 @@ static inline void __run_timers(struct t
spin_unlock_irq(&base->lock);
call_timer_fn(timer, fn, data);
+ base->running_timer = NULL;
spin_lock_irq(&base->lock);
}
}
- base->running_timer = NULL;
+ wake_up(&base->wait_for_running_timer);
spin_unlock_irq(&base->lock);
}
@@ -1698,6 +1726,7 @@ static int __cpuinit init_timers_cpu(int
}
spin_lock_init(&base->lock);
+ init_waitqueue_head(&base->wait_for_running_timer);
for (j = 0; j < TVN_SIZE; j++) {
INIT_LIST_HEAD(base->tv5.vec + j);
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