| From: Ingo Molnar <mingo@elte.hu> |
| Date: Fri, 3 Jul 2009 08:29:34 -0500 |
| Subject: hrtimers: prepare full preemption |
| |
| Make cancellation of a running callback in softirq context safe |
| against preemption. |
| |
| Signed-off-by: Ingo Molnar <mingo@elte.hu> |
| Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
| |
| --- |
| include/linux/hrtimer.h | 10 ++++++++++ |
| kernel/hrtimer.c | 33 ++++++++++++++++++++++++++++++++- |
| kernel/itimer.c | 1 + |
| kernel/posix-timers.c | 33 +++++++++++++++++++++++++++++++++ |
| 4 files changed, 76 insertions(+), 1 deletion(-) |
| |
| Index: linux-stable/include/linux/hrtimer.h |
| =================================================================== |
| --- linux-stable.orig/include/linux/hrtimer.h |
| +++ linux-stable/include/linux/hrtimer.h |
| @@ -192,6 +192,9 @@ struct hrtimer_cpu_base { |
| unsigned long nr_hangs; |
| ktime_t max_hang_time; |
| #endif |
| +#ifdef CONFIG_PREEMPT_RT_BASE |
| + wait_queue_head_t wait; |
| +#endif |
| struct hrtimer_clock_base clock_base[HRTIMER_MAX_CLOCK_BASES]; |
| }; |
| |
| @@ -385,6 +388,13 @@ static inline int hrtimer_restart(struct |
| return hrtimer_start_expires(timer, HRTIMER_MODE_ABS); |
| } |
| |
| +/* Softirq preemption could deadlock timer removal */ |
| +#ifdef CONFIG_PREEMPT_RT_BASE |
| + extern void hrtimer_wait_for_timer(const struct hrtimer *timer); |
| +#else |
| +# define hrtimer_wait_for_timer(timer) do { cpu_relax(); } while (0) |
| +#endif |
| + |
| /* Query timers: */ |
| extern ktime_t hrtimer_get_remaining(const struct hrtimer *timer); |
| extern int hrtimer_get_res(const clockid_t which_clock, struct timespec *tp); |
| Index: linux-stable/kernel/hrtimer.c |
| =================================================================== |
| --- linux-stable.orig/kernel/hrtimer.c |
| +++ linux-stable/kernel/hrtimer.c |
| @@ -857,6 +857,32 @@ u64 hrtimer_forward(struct hrtimer *time |
| } |
| EXPORT_SYMBOL_GPL(hrtimer_forward); |
| |
| +#ifdef CONFIG_PREEMPT_RT_BASE |
| +# define wake_up_timer_waiters(b) wake_up(&(b)->wait) |
| + |
| +/** |
| + * hrtimer_wait_for_timer - Wait for a running timer |
| + * |
| + * @timer: timer to wait for |
| + * |
| + * The function waits in case the timers callback function is |
| + * currently executed on the waitqueue of the timer base. The |
| + * waitqueue is woken up after the timer callback function has |
| + * finished execution. |
| + */ |
| +void hrtimer_wait_for_timer(const struct hrtimer *timer) |
| +{ |
| + struct hrtimer_clock_base *base = timer->base; |
| + |
| + if (base && base->cpu_base && !hrtimer_hres_active(base->cpu_base)) |
| + wait_event(base->cpu_base->wait, |
| + !(timer->state & HRTIMER_STATE_CALLBACK)); |
| +} |
| + |
| +#else |
| +# define wake_up_timer_waiters(b) do { } while (0) |
| +#endif |
| + |
| /* |
| * enqueue_hrtimer - internal function to (re)start a timer |
| * |
| @@ -1094,7 +1120,7 @@ int hrtimer_cancel(struct hrtimer *timer |
| |
| if (ret >= 0) |
| return ret; |
| - cpu_relax(); |
| + hrtimer_wait_for_timer(timer); |
| } |
| } |
| EXPORT_SYMBOL_GPL(hrtimer_cancel); |
| @@ -1509,6 +1535,8 @@ void hrtimer_run_queues(void) |
| } |
| raw_spin_unlock(&cpu_base->lock); |
| } |
| + |
| + wake_up_timer_waiters(cpu_base); |
| } |
| |
| /* |
| @@ -1671,6 +1699,9 @@ static void __cpuinit init_hrtimers_cpu( |
| } |
| |
| hrtimer_init_hres(cpu_base); |
| +#ifdef CONFIG_PREEMPT_RT_BASE |
| + init_waitqueue_head(&cpu_base->wait); |
| +#endif |
| } |
| |
| #ifdef CONFIG_HOTPLUG_CPU |
| Index: linux-stable/kernel/itimer.c |
| =================================================================== |
| --- linux-stable.orig/kernel/itimer.c |
| +++ linux-stable/kernel/itimer.c |
| @@ -213,6 +213,7 @@ again: |
| /* We are sharing ->siglock with it_real_fn() */ |
| if (hrtimer_try_to_cancel(timer) < 0) { |
| spin_unlock_irq(&tsk->sighand->siglock); |
| + hrtimer_wait_for_timer(&tsk->signal->real_timer); |
| goto again; |
| } |
| expires = timeval_to_ktime(value->it_value); |
| Index: linux-stable/kernel/posix-timers.c |
| =================================================================== |
| --- linux-stable.orig/kernel/posix-timers.c |
| +++ linux-stable/kernel/posix-timers.c |
| @@ -766,6 +766,20 @@ SYSCALL_DEFINE1(timer_getoverrun, timer_ |
| return overrun; |
| } |
| |
| +/* |
| + * Protected by RCU! |
| + */ |
| +static void timer_wait_for_callback(struct k_clock *kc, struct k_itimer *timr) |
| +{ |
| +#ifdef CONFIG_PREEMPT_RT_FULL |
| + if (kc->timer_set == common_timer_set) |
| + hrtimer_wait_for_timer(&timr->it.real.timer); |
| + else |
| + /* FIXME: Whacky hack for posix-cpu-timers */ |
| + schedule_timeout(1); |
| +#endif |
| +} |
| + |
| /* Set a POSIX.1b interval timer. */ |
| /* timr->it_lock is taken. */ |
| static int |
| @@ -843,6 +857,7 @@ retry: |
| if (!timr) |
| return -EINVAL; |
| |
| + rcu_read_lock(); |
| kc = clockid_to_kclock(timr->it_clock); |
| if (WARN_ON_ONCE(!kc || !kc->timer_set)) |
| error = -EINVAL; |
| @@ -851,9 +866,12 @@ retry: |
| |
| unlock_timer(timr, flag); |
| if (error == TIMER_RETRY) { |
| + timer_wait_for_callback(kc, timr); |
| rtn = NULL; // We already got the old time... |
| + rcu_read_unlock(); |
| goto retry; |
| } |
| + rcu_read_unlock(); |
| |
| if (old_setting && !error && |
| copy_to_user(old_setting, &old_spec, sizeof (old_spec))) |
| @@ -891,10 +909,15 @@ retry_delete: |
| if (!timer) |
| return -EINVAL; |
| |
| + rcu_read_lock(); |
| if (timer_delete_hook(timer) == TIMER_RETRY) { |
| unlock_timer(timer, flags); |
| + timer_wait_for_callback(clockid_to_kclock(timer->it_clock), |
| + timer); |
| + rcu_read_unlock(); |
| goto retry_delete; |
| } |
| + rcu_read_unlock(); |
| |
| spin_lock(¤t->sighand->siglock); |
| list_del(&timer->list); |
| @@ -920,8 +943,18 @@ static void itimer_delete(struct k_itime |
| retry_delete: |
| spin_lock_irqsave(&timer->it_lock, flags); |
| |
| + /* On RT we can race with a deletion */ |
| + if (!timer->it_signal) { |
| + unlock_timer(timer, flags); |
| + return; |
| + } |
| + |
| if (timer_delete_hook(timer) == TIMER_RETRY) { |
| + rcu_read_lock(); |
| unlock_timer(timer, flags); |
| + timer_wait_for_callback(clockid_to_kclock(timer->it_clock), |
| + timer); |
| + rcu_read_unlock(); |
| goto retry_delete; |
| } |
| list_del(&timer->list); |