releases/2.6.25.1/hrtimer-raise-softirq-unlocked-to-avoid-circular-lock-dependency.patch

   1 From jejb@kernel.org  Tue Apr 29 09:51:24 2008
   2 From: Thomas Gleixner <tglx@linutronix.de>
   3 Date: Tue, 29 Apr 2008 01:15:10 GMT
   4 Subject: hrtimer: raise softirq unlocked to avoid circular lock dependency
   5 To: jejb@kernel.org, stable@kernel.org
   6 Message-ID: <200804290115.m3T1FAaX028758@hera.kernel.org>
   7
   8 From: Thomas Gleixner <tglx@linutronix.de>
   9
  10 commit 0c96c5979a522c3323c30a078a70120e29b5bdbc upstream
  11
  12 The scheduler hrtimer bits in 2.6.25 introduced a circular lock
  13 dependency in a rare code path:
  14
  15 =======================================================
  16 [ INFO: possible circular locking dependency detected ]
  17 2.6.25-sched-devel.git-x86-latest.git #19
  18 -------------------------------------------------------
  19 X/2980 is trying to acquire lock:
  20  (&rq->rq_lock_key#2){++..}, at: [<ffffffff80230146>] task_rq_lock+0x56/0xa0
  21
  22 but task is already holding lock:
  23  (&cpu_base->lock){++..}, at: [<ffffffff80257ae1>] lock_hrtimer_base+0x31/0x60
  24
  25 which lock already depends on the new lock.
  26
  27 The scenario which leads to this is:
  28
  29 posix-timer signal is delivered
  30  -> posix-timer is rearmed
  31     timer is already expired in hrtimer_enqueue()
  32      -> softirq is raised
  33
  34 To prevent this we need to move the raise of the softirq out of the
  35 base->lock protected code path.
  36
  37 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  38 Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
  39 Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
  40
  41 ---
  42  kernel/hrtimer.c |   19 +++++++++++++++++--
  43  1 file changed, 17 insertions(+), 2 deletions(-)
  44
  45 --- a/kernel/hrtimer.c
  46 +++ b/kernel/hrtimer.c
  47 @@ -590,7 +590,6 @@ static inline int hrtimer_enqueue_reprog
  48                         list_add_tail(&timer->cb_entry,
  49                                       &base->cpu_base->cb_pending);
  50                         timer->state = HRTIMER_STATE_PENDING;
  51 -                       raise_softirq(HRTIMER_SOFTIRQ);
  52                         return 1;
  53                 default:
  54                         BUG();
  55 @@ -633,6 +632,11 @@ static int hrtimer_switch_to_hres(void)
  56         return 1;
  57  }
  58
  59 +static inline void hrtimer_raise_softirq(void)
  60 +{
  61 +       raise_softirq(HRTIMER_SOFTIRQ);
  62 +}
  63 +
  64  #else
  65
  66  static inline int hrtimer_hres_active(void) { return 0; }
  67 @@ -651,6 +655,7 @@ static inline int hrtimer_reprogram(stru
  68  {
  69         return 0;
  70  }
  71 +static inline void hrtimer_raise_softirq(void) { }
  72
  73  #endif /* CONFIG_HIGH_RES_TIMERS */
  74
  75 @@ -850,7 +855,7 @@ hrtimer_start(struct hrtimer *timer, kti
  76  {
  77         struct hrtimer_clock_base *base, *new_base;
  78         unsigned long flags;
  79 -       int ret;
  80 +       int ret, raise;
  81
  82         base = lock_hrtimer_base(timer, &flags);
  83
  84 @@ -884,8 +889,18 @@ hrtimer_start(struct hrtimer *timer, kti
  85         enqueue_hrtimer(timer, new_base,
  86                         new_base->cpu_base == &__get_cpu_var(hrtimer_bases));
  87
  88 +       /*
  89 +        * The timer may be expired and moved to the cb_pending
  90 +        * list. We can not raise the softirq with base lock held due
  91 +        * to a possible deadlock with runqueue lock.
  92 +        */
  93 +       raise = timer->state == HRTIMER_STATE_PENDING;
  94 +
  95         unlock_hrtimer_base(timer, &flags);
  96
  97 +       if (raise)
  98 +               hrtimer_raise_softirq();
  99 +
 100         return ret;
 101  }
 102  EXPORT_SYMBOL_GPL(hrtimer_start);