From 0c96c5979a522c3323c30a078a70120e29b5bdbc Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 28 Apr 2008 09:23:24 +0200 Subject: [PATCH] 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: [] task_rq_lock+0x56/0xa0 but task is already holding lock: (&cpu_base->lock){++..}, at: [] 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 Cc: stable@kernel.org Acked-by: Peter Zijlstra --- kernel/hrtimer.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index e379ef0e9c2..dea4c9124ac 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -590,7 +590,6 @@ static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer, 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(struct hrtimer *timer, { return 0; } +static inline void hrtimer_raise_softirq(void) { } #endif /* CONFIG_HIGH_RES_TIMERS */ @@ -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) + hrtimer_raise_softirq(); + return ret; } EXPORT_SYMBOL_GPL(hrtimer_start);