Commit 0c96c597 authored by Thomas Gleixner's avatar Thomas Gleixner

hrtimer: raise softirq unlocked to avoid circular lock dependency

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: default avatarThomas Gleixner <>
Acked-by: default avatarPeter Zijlstra <>
parent e31a94ed
......@@ -590,7 +590,6 @@ static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer,
return 1;
......@@ -633,6 +632,11 @@ static int hrtimer_switch_to_hres(void)
return 1;
static inline void hrtimer_raise_softirq(void)
static inline int hrtimer_hres_active(void) { return 0; }
......@@ -651,6 +655,7 @@ static inline int hrtimer_reprogram(struct hrtimer *timer,
return 0;
static inline void hrtimer_raise_softirq(void) { }
......@@ -850,7 +855,7 @@ hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode)
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, ktime_t tim, const enum hrtimer_mode mode)
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)
return ret;
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