diff options
Diffstat (limited to 'kernel/timer.c')
| -rw-r--r-- | kernel/timer.c | 37 |
1 files changed, 34 insertions, 3 deletions
diff --git a/kernel/timer.c b/kernel/timer.c index 87f656cc2a5..fd6198692b5 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -404,6 +404,11 @@ static void timer_stats_account_timer(struct timer_list *timer) {} static struct debug_obj_descr timer_debug_descr; +static void *timer_debug_hint(void *addr) +{ + return ((struct timer_list *) addr)->function; +} + /* * fixup_init is called when: * - an active object is initialized @@ -477,6 +482,7 @@ static int timer_fixup_free(void *addr, enum debug_obj_state state) static struct debug_obj_descr timer_debug_descr = { .name = "timer_list", + .debug_hint = timer_debug_hint, .fixup_init = timer_fixup_init, .fixup_activate = timer_fixup_activate, .fixup_free = timer_fixup_free, @@ -959,20 +965,45 @@ EXPORT_SYMBOL(try_to_del_timer_sync); * * Synchronization rules: Callers must prevent restarting of the timer, * otherwise this function is meaningless. It must not be called from - * hardirq contexts. The caller must not hold locks which would prevent + * interrupt contexts. The caller must not hold locks which would prevent * completion of the timer's handler. The timer's handler must not call * add_timer_on(). Upon exit the timer is not queued and the handler is * not running on any CPU. * + * Note: You must not hold locks that are held in interrupt context + * while calling this function. Even if the lock has nothing to do + * with the timer in question. Here's why: + * + * CPU0 CPU1 + * ---- ---- + * <SOFTIRQ> + * call_timer_fn(); + * base->running_timer = mytimer; + * spin_lock_irq(somelock); + * <IRQ> + * spin_lock(somelock); + * del_timer_sync(mytimer); + * while (base->running_timer == mytimer); + * + * Now del_timer_sync() will never return and never release somelock. + * The interrupt on the other CPU is waiting to grab somelock but + * it has interrupted the softirq that CPU0 is waiting to finish. + * * The function returns whether it has deactivated a pending timer or not. */ int del_timer_sync(struct timer_list *timer) { #ifdef CONFIG_LOCKDEP - local_bh_disable(); + unsigned long flags; + + /* + * If lockdep gives a backtrace here, please reference + * the synchronization rules above. + */ + local_irq_save(flags); lock_map_acquire(&timer->lockdep_map); lock_map_release(&timer->lockdep_map); - local_bh_enable(); + local_irq_restore(flags); #endif /* * don't use it in hardirq context, because it |