There are a few sites that do: spin_lock_irq(&foo) hrtimer_start(&bar) __run_hrtimer(&bar) func() spin_lock(&foo) which obviously deadlocks. In order to avoid this, never call __run_hrtimer() from hrtimer_start*() context, but instead defer this to softirq context. Signed-off-by: Peter Zijlstra --- include/linux/interrupt.h | 3 ++ kernel/hrtimer.c | 60 ++++++++++++++++++++-------------------------- 2 files changed, 30 insertions(+), 33 deletions(-) Index: linux-2.6/include/linux/interrupt.h =================================================================== --- linux-2.6.orig/include/linux/interrupt.h +++ linux-2.6/include/linux/interrupt.h @@ -253,6 +253,9 @@ enum BLOCK_SOFTIRQ, TASKLET_SOFTIRQ, SCHED_SOFTIRQ, +#ifdef CONFIG_HIGH_RES_TIMERS + HRTIMER_SOFTIRQ, +#endif RCU_SOFTIRQ, /* Preferable RCU should always be the last softirq */ NR_SOFTIRQS Index: linux-2.6/kernel/hrtimer.c =================================================================== --- linux-2.6.orig/kernel/hrtimer.c +++ linux-2.6/kernel/hrtimer.c @@ -634,7 +634,6 @@ static inline void hrtimer_init_timer_hr { } -static void __run_hrtimer(struct hrtimer *timer); /* * When High resolution timers are active, try to reprogram. Note, that in case @@ -646,13 +645,9 @@ static inline int hrtimer_enqueue_reprog struct hrtimer_clock_base *base) { if (base->cpu_base->hres_active && hrtimer_reprogram(timer, base)) { - /* - * XXX: recursion check? - * hrtimer_forward() should round up with timer granularity - * so that we never get into inf recursion here, - * it doesn't do that though - */ - __run_hrtimer(timer); + spin_unlock(&base->cpu_base->lock); + raise_softirq_irqoff(HRTIMER_SOFTIRQ); + spin_lock(&base->cpu_base->lock); return 1; } return 0; @@ -705,11 +698,6 @@ static inline int hrtimer_enqueue_reprog } static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base) { } static inline void hrtimer_init_timer_hres(struct hrtimer *timer) { } -static inline int hrtimer_reprogram(struct hrtimer *timer, - struct hrtimer_clock_base *base) -{ - return 0; -} #endif /* CONFIG_HIGH_RES_TIMERS */ @@ -780,9 +768,11 @@ EXPORT_SYMBOL_GPL(hrtimer_forward); * * The timer is inserted in expiry order. Insertion into the * red black tree is O(log(n)). Must hold the base lock. + * + * Returns 1 when the new timer is the leftmost timer in the tree. */ -static void enqueue_hrtimer(struct hrtimer *timer, - struct hrtimer_clock_base *base, int reprogram) +static int enqueue_hrtimer(struct hrtimer *timer, + struct hrtimer_clock_base *base) { struct rb_node **link = &base->active.rb_node; struct rb_node *parent = NULL; @@ -814,20 +804,8 @@ static void enqueue_hrtimer(struct hrtim * Insert the timer to the rbtree and check whether it * replaces the first pending timer */ - if (leftmost) { - /* - * Reprogram the clock event device. When the timer is already - * expired hrtimer_enqueue_reprogram has either called the - * callback or added it to the pending list and raised the - * softirq. - * - * This is a NOP for !HIGHRES - */ - if (reprogram && hrtimer_enqueue_reprogram(timer, base)) - return; - + if (leftmost) base->first = &timer->node; - } rb_link_node(&timer->node, parent, link); rb_insert_color(&timer->node, &base->active); @@ -836,6 +814,8 @@ static void enqueue_hrtimer(struct hrtim * state of a possibly running callback. */ timer->state |= HRTIMER_STATE_ENQUEUED; + + return leftmost; } /* @@ -912,7 +892,7 @@ hrtimer_start_range_ns(struct hrtimer *t { struct hrtimer_clock_base *base, *new_base; unsigned long flags; - int ret; + int ret, leftmost; base = lock_hrtimer_base(timer, &flags); @@ -940,12 +920,16 @@ hrtimer_start_range_ns(struct hrtimer *t timer_stats_hrtimer_set_start_info(timer); + leftmost = enqueue_hrtimer(timer, new_base); + /* * Only allow reprogramming if the new base is on this CPU. * (it might still be on another CPU if the timer was pending) + * + * XXX send_remote_softirq() ? */ - enqueue_hrtimer(timer, new_base, - new_base->cpu_base == &__get_cpu_var(hrtimer_bases)); + if (leftmost && new_base->cpu_base == &__get_cpu_var(hrtimer_bases)) + hrtimer_enqueue_reprogram(timer, new_base); unlock_hrtimer_base(timer, &flags); @@ -1163,7 +1147,7 @@ static void __run_hrtimer(struct hrtimer */ if (restart != HRTIMER_NORESTART) { BUG_ON(timer->state != HRTIMER_STATE_CALLBACK); - enqueue_hrtimer(timer, base, 0); + enqueue_hrtimer(timer, base); } timer->state &= ~HRTIMER_STATE_CALLBACK; } @@ -1305,6 +1289,11 @@ void hrtimer_peek_ahead_timers(void) local_irq_restore(flags); } +static void run_hrtimer_softirq(struct softirq_action *h) +{ + hrtimer_peek_ahead_timers(); +} + #endif /* CONFIG_HIGH_RES_TIMERS */ /* @@ -1560,7 +1549,7 @@ static void migrate_hrtimer_list(struct * is done, which will run all expired timers and re-programm * the timer device. */ - enqueue_hrtimer(timer, new_base, 0); + enqueue_hrtimer(timer, new_base); /* Clear the migration state bit */ timer->state &= ~HRTIMER_STATE_MIGRATE; @@ -1642,6 +1631,9 @@ void __init hrtimers_init(void) hrtimer_cpu_notify(&hrtimers_nb, (unsigned long)CPU_UP_PREPARE, (void *)(long)smp_processor_id()); register_cpu_notifier(&hrtimers_nb); +#ifdef CONFIG_HIGH_RES_TIMERS + open_softirq(HRTIMER_SOFTIRQ, run_hrtimer_softirq); +#endif } /** -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/