rt-patches/0218-cpu-Make-hotplug.lock-a-sleeping-spinlock-on-RT.patch

   1 From 6932ea4614fbc294cb2213492bec79f6a0cb0b74 Mon Sep 17 00:00:00 2001
   2 From: Steven Rostedt <rostedt@goodmis.org>
   3 Date: Fri, 2 Mar 2012 10:36:57 -0500
   4 Subject: [PATCH 218/366] cpu: Make hotplug.lock a "sleeping" spinlock on RT
   5
   6 Tasks can block on hotplug.lock in pin_current_cpu(), but their state
   7 might be != RUNNING. So the mutex wakeup will set the state
   8 unconditionally to RUNNING. That might cause spurious unexpected
   9 wakeups. We could provide a state preserving mutex_lock() function,
  10 but this is semantically backwards. So instead we convert the
  11 hotplug.lock() to a spinlock for RT, which has the state preserving
  12 semantics already.
  13
  14 Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
  15 Cc: Carsten Emde <C.Emde@osadl.org>
  16 Cc: John Kacur <jkacur@redhat.com>
  17 Cc: Peter Zijlstra <peterz@infradead.org>
  18 Cc: Clark Williams <clark.williams@gmail.com>
  19
  20 Link: http://lkml.kernel.org/r/1330702617.25686.265.camel@gandalf.stny.rr.com
  21 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  22 ---
  23  kernel/cpu.c | 34 +++++++++++++++++++++++++++-------
  24  1 file changed, 27 insertions(+), 7 deletions(-)
  25
  26 diff --git a/kernel/cpu.c b/kernel/cpu.c
  27 index 494b606..5d8be91 100644
  28 --- a/kernel/cpu.c
  29 +++ b/kernel/cpu.c
  30 @@ -62,10 +62,16 @@ static int cpu_hotplug_disabled;
  31
  32  static struct {
  33         struct task_struct *active_writer;
  34 +
  35         /* wait queue to wake up the active_writer */
  36         wait_queue_head_t wq;
  37 +#ifdef CONFIG_PREEMPT_RT_FULL
  38 +       /* Makes the lock keep the task's state */
  39 +       spinlock_t lock;
  40 +#else
  41         /* verifies that no writer will get active while readers are active */
  42         struct mutex lock;
  43 +#endif
  44         /*
  45          * Also blocks the new readers during
  46          * an ongoing cpu hotplug operation.
  47 @@ -78,12 +84,26 @@ static struct {
  48  } cpu_hotplug = {
  49         .active_writer = NULL,
  50         .wq = __WAIT_QUEUE_HEAD_INITIALIZER(cpu_hotplug.wq),
  51 +#ifdef CONFIG_PREEMPT_RT_FULL
  52 +       .lock = __SPIN_LOCK_UNLOCKED(cpu_hotplug.lock),
  53 +#else
  54         .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
  55 +#endif
  56  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  57         .dep_map = {.name = "cpu_hotplug.lock" },
  58  #endif
  59  };
  60
  61 +#ifdef CONFIG_PREEMPT_RT_FULL
  62 +# define hotplug_lock()                rt_spin_lock(&cpu_hotplug.lock)
  63 +# define hotplug_trylock()     rt_spin_trylock(&cpu_hotplug.lock)
  64 +# define hotplug_unlock()      rt_spin_unlock(&cpu_hotplug.lock)
  65 +#else
  66 +# define hotplug_lock()                mutex_lock(&cpu_hotplug.lock)
  67 +# define hotplug_trylock()     mutex_trylock(&cpu_hotplug.lock)
  68 +# define hotplug_unlock()      mutex_unlock(&cpu_hotplug.lock)
  69 +#endif
  70 +
  71  /* Lockdep annotations for get/put_online_cpus() and cpu_hotplug_begin/end() */
  72  #define cpuhp_lock_acquire_read() lock_map_acquire_read(&cpu_hotplug.dep_map)
  73  #define cpuhp_lock_acquire_tryread() \
  74 @@ -120,8 +140,8 @@ retry:
  75                 return;
  76         }
  77         preempt_enable();
  78 -       mutex_lock(&cpu_hotplug.lock);
  79 -       mutex_unlock(&cpu_hotplug.lock);
  80 +       hotplug_lock();
  81 +       hotplug_unlock();
  82         preempt_disable();
  83         goto retry;
  84  }
  85 @@ -194,9 +214,9 @@ void get_online_cpus(void)
  86         if (cpu_hotplug.active_writer == current)
  87                 return;
  88         cpuhp_lock_acquire_read();
  89 -       mutex_lock(&cpu_hotplug.lock);
  90 +       hotplug_lock();
  91         atomic_inc(&cpu_hotplug.refcount);
  92 -       mutex_unlock(&cpu_hotplug.lock);
  93 +       hotplug_unlock();
  94  }
  95  EXPORT_SYMBOL_GPL(get_online_cpus);
  96
  97 @@ -249,11 +269,11 @@ void cpu_hotplug_begin(void)
  98         cpuhp_lock_acquire();
  99
 100         for (;;) {
 101 -               mutex_lock(&cpu_hotplug.lock);
 102 +               hotplug_lock();
 103                 prepare_to_wait(&cpu_hotplug.wq, &wait, TASK_UNINTERRUPTIBLE);
 104                 if (likely(!atomic_read(&cpu_hotplug.refcount)))
 105                                 break;
 106 -               mutex_unlock(&cpu_hotplug.lock);
 107 +               hotplug_unlock();
 108                 schedule();
 109         }
 110         finish_wait(&cpu_hotplug.wq, &wait);
 111 @@ -262,7 +282,7 @@ void cpu_hotplug_begin(void)
 112  void cpu_hotplug_done(void)
 113  {
 114         cpu_hotplug.active_writer = NULL;
 115 -       mutex_unlock(&cpu_hotplug.lock);
 116 +       hotplug_unlock();
 117         cpuhp_lock_release();
 118  }
 119
 120 --
 121 1.9.1
 122