rt-patches/0077-timers-Prepare-for-full-preemption.patch

   1 From 0c96f27da32acd7651c592add3b0c52cf4217b13 Mon Sep 17 00:00:00 2001
   2 From: Ingo Molnar <mingo@elte.hu>
   3 Date: Fri, 3 Jul 2009 08:29:34 -0500
   4 Subject: [PATCH 077/366] timers: Prepare for full preemption
   5
   6 When softirqs can be preempted we need to make sure that cancelling
   7 the timer from the active thread can not deadlock vs. a running timer
   8 callback. Add a waitqueue to resolve that.
   9
  10 Signed-off-by: Ingo Molnar <mingo@elte.hu>
  11 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  12 ---
  13  include/linux/timer.h |  2 +-
  14  kernel/sched/core.c   |  9 +++++++--
  15  kernel/time/timer.c   | 39 +++++++++++++++++++++++++++++++++++++--
  16  3 files changed, 45 insertions(+), 5 deletions(-)
  17
  18 diff --git a/include/linux/timer.h b/include/linux/timer.h
  19 index 61aa61d..299d2b7 100644
  20 --- a/include/linux/timer.h
  21 +++ b/include/linux/timer.h
  22 @@ -225,7 +225,7 @@ extern void add_timer(struct timer_list *timer);
  23
  24  extern int try_to_del_timer_sync(struct timer_list *timer);
  25
  26 -#ifdef CONFIG_SMP
  27 +#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT_FULL)
  28    extern int del_timer_sync(struct timer_list *timer);
  29  #else
  30  # define del_timer_sync(t)             del_timer(t)
  31 diff --git a/kernel/sched/core.c b/kernel/sched/core.c
  32 index e7fe1ce..ddedd34 100644
  33 --- a/kernel/sched/core.c
  34 +++ b/kernel/sched/core.c
  35 @@ -619,11 +619,14 @@ void resched_cpu(int cpu)
  36   */
  37  int get_nohz_timer_target(void)
  38  {
  39 -       int i, cpu = smp_processor_id();
  40 +       int i, cpu;
  41         struct sched_domain *sd;
  42
  43 +       preempt_disable_rt();
  44 +       cpu = smp_processor_id();
  45 +
  46         if (!idle_cpu(cpu) && is_housekeeping_cpu(cpu))
  47 -               return cpu;
  48 +               goto preempt_en_rt;
  49
  50         rcu_read_lock();
  51         for_each_domain(cpu, sd) {
  52 @@ -642,6 +645,8 @@ int get_nohz_timer_target(void)
  53                 cpu = housekeeping_any_cpu();
  54  unlock:
  55         rcu_read_unlock();
  56 +preempt_en_rt:
  57 +       preempt_enable_rt();
  58         return cpu;
  59  }
  60  /*
  61 diff --git a/kernel/time/timer.c b/kernel/time/timer.c
  62 index bbc5d11..5fa215e 100644
  63 --- a/kernel/time/timer.c
  64 +++ b/kernel/time/timer.c
  65 @@ -80,6 +80,9 @@ struct tvec_root {
  66  struct tvec_base {
  67         spinlock_t lock;
  68         struct timer_list *running_timer;
  69 +#ifdef CONFIG_PREEMPT_RT_FULL
  70 +       wait_queue_head_t wait_for_running_timer;
  71 +#endif
  72         unsigned long timer_jiffies;
  73         unsigned long next_timer;
  74         unsigned long active_timers;
  75 @@ -1006,6 +1009,33 @@ void add_timer_on(struct timer_list *timer, int cpu)
  76  }
  77  EXPORT_SYMBOL_GPL(add_timer_on);
  78
  79 +#ifdef CONFIG_PREEMPT_RT_FULL
  80 +/*
  81 + * Wait for a running timer
  82 + */
  83 +static void wait_for_running_timer(struct timer_list *timer)
  84 +{
  85 +       struct tvec_base *base;
  86 +       u32 tf = timer->flags;
  87 +
  88 +       if (tf & TIMER_MIGRATING)
  89 +               return;
  90 +
  91 +       base = per_cpu_ptr(&tvec_bases, tf & TIMER_CPUMASK);
  92 +       wait_event(base->wait_for_running_timer,
  93 +                  base->running_timer != timer);
  94 +}
  95 +
  96 +# define wakeup_timer_waiters(b)       wake_up(&(b)->wait_for_running_timer)
  97 +#else
  98 +static inline void wait_for_running_timer(struct timer_list *timer)
  99 +{
 100 +       cpu_relax();
 101 +}
 102 +
 103 +# define wakeup_timer_waiters(b)       do { } while (0)
 104 +#endif
 105 +
 106  /**
 107   * del_timer - deactive a timer.
 108   * @timer: the timer to be deactivated
 109 @@ -1123,7 +1153,7 @@ int del_timer_sync(struct timer_list *timer)
 110                 int ret = try_to_del_timer_sync(timer);
 111                 if (ret >= 0)
 112                         return ret;
 113 -               cpu_relax();
 114 +               wait_for_running_timer(timer);
 115         }
 116  }
 117  EXPORT_SYMBOL(del_timer_sync);
 118 @@ -1248,15 +1278,17 @@ static inline void __run_timers(struct tvec_base *base)
 119                         if (irqsafe) {
 120                                 spin_unlock(&base->lock);
 121                                 call_timer_fn(timer, fn, data);
 122 +                               base->running_timer = NULL;
 123                                 spin_lock(&base->lock);
 124                         } else {
 125                                 spin_unlock_irq(&base->lock);
 126                                 call_timer_fn(timer, fn, data);
 127 +                               base->running_timer = NULL;
 128                                 spin_lock_irq(&base->lock);
 129                         }
 130                 }
 131         }
 132 -       base->running_timer = NULL;
 133 +       wakeup_timer_waiters(base);
 134         spin_unlock_irq(&base->lock);
 135  }
 136
 137 @@ -1645,6 +1677,9 @@ static void __init init_timer_cpu(int cpu)
 138
 139         base->cpu = cpu;
 140         spin_lock_init(&base->lock);
 141 +#ifdef CONFIG_PREEMPT_RT_FULL
 142 +       init_waitqueue_head(&base->wait_for_running_timer);
 143 +#endif
 144
 145         base->timer_jiffies = jiffies;
 146         base->next_timer = base->timer_jiffies;
 147 --
 148 1.9.1
 149