[37/37] hrtimer: raise softirq unlocked to avoid circular lock dependency

Greg KH
2008-04-29T17:34:55Z

[-- Attachment #1: hrtimer-raise-softirq-unlocked-to-avoid-circular-lock-dependency.patch --]
[-- Type: text/plain, Size: 2753 bytes --]

2.6.25-stable review patch. If anyone has any objections, please let us
know.

------------------
From: Thomas Gleixner <tglx@linutronix.de>

commit 0c96c5979a522c3323c30a078a70120e29b5bdbc upstream

The scheduler hrtimer bits in 2.6.25 introduced a circular lock
dependency in a rare code path:

=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.25-sched-devel.git-x86-latest.git #19
-------------------------------------------------------
X/2980 is trying to acquire lock:
(&rq->rq_lock_key#2){++..}, at: [<ffffffff80230146>] task_rq_lock+0x56/0xa0

but task is already holding lock:
(&cpu_base->lock){++..}, at: [<ffffffff80257ae1>] lock_hrtimer_base+0x31/0x60

which lock already depends on the new lock.

The scenario which leads to this is:

posix-timer signal is delivered
-> posix-timer is rearmed
timer is already expired in hrtimer_enqueue()
-> softirq is raised

To prevent this we need to move the raise of the softirq out of the
base->lock protected code path.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
kernel/hrtimer.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)

--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -590,7 +590,6 @@ static inline int hrtimer_enqueue_reprog
list_add_tail(&timer->cb_entry,
&base->cpu_base->cb_pending);
timer->state = HRTIMER_STATE_PENDING;
- raise_softirq(HRTIMER_SOFTIRQ);
return 1;
default:
BUG();
@@ -633,6 +632,11 @@ static int hrtimer_switch_to_hres(void)
return 1;
}

+static inline void hrtimer_raise_softirq(void)
+{
+ raise_softirq(HRTIMER_SOFTIRQ);
+}
+
#else

static inline int hrtimer_hres_active(void) { return 0; }
@@ -651,6 +655,7 @@ static inline int hrtimer_reprogram(stru
{
return 0;
}
+static inline void hrtimer_raise_softirq(void) { }

#endif /* CONFIG_HIGH_RES_TIMERS */

@@ -850,7 +855,7 @@ hrtimer_start(struct hrtimer *timer, kti
{
struct hrtimer_clock_base *base, *new_base;
unsigned long flags;
- int ret;
+ int ret, raise;

base = lock_hrtimer_base(timer, &flags);

@@ -884,8 +889,18 @@ hrtimer_start(struct hrtimer *timer, kti
enqueue_hrtimer(timer, new_base,
new_base->cpu_base == &__get_cpu_var(hrtimer_bases));

+ /*
+ * The timer may be expired and moved to the cb_pending
+ * list. We can not raise the softirq with base lock held due
+ * to a possible deadlock with runqueue lock.
+ */
+ raise = timer->state == HRTIMER_STATE_PENDING;
+
unlock_hrtimer_base(timer, &flags);

+ if (raise)
+ hrtimer_raise_softirq();
+
return ret;
}
EXPORT_SYMBOL_GPL(hrtimer_start);

--