* 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: rtmutex: tester: Remove the remaining BKL leftovers lockdep/timers: Explain in detail the locking problems del_timer_sync() may cause rtmutex: Simplify PI algorithm and make highest prio task get lock rwsem: Remove redundant asmregparm annotation rwsem: Move duplicate function prototypes to linux/rwsem.h rwsem: Unify the duplicate rwsem_is_locked() inlines rwsem: Move duplicate init macros and functions to linux/rwsem.h rwsem: Move duplicate struct rwsem declaration to linux/rwsem.h x86: Cleanup rwsem_count_t typedef rwsem: Cleanup includes locking: Remove deprecated lock initializers cred: Replace deprecated spinlock initialization kthread: Replace deprecated spinlock initialization xtensa: Replace deprecated spinlock initialization um: Replace deprecated spinlock initialization sparc: Replace deprecated spinlock initialization mips: Replace deprecated spinlock initialization cris: Replace deprecated spinlock initialization alpha: Replace deprecated spinlock initialization rtmutex-tester: Remove BKL tests
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| @@ -970,6 +970,25 @@ EXPORT_SYMBOL(try_to_del_timer_sync); · 969 unmodified lines | ||
| 970 | 970 | * add_timer_on(). Upon exit the timer is not queued and the handler is |
| 971 | 971 | * not running on any CPU. |
| 972 | 972 | * |
| 973 | + * Note: You must not hold locks that are held in interrupt context | |
| 974 | + * while calling this function. Even if the lock has nothing to do | |
| 975 | + * with the timer in question. Here's why: | |
| 976 | + * | |
| 977 | + * CPU0 CPU1 | |
| 978 | + * ---- ---- | |
| 979 | + * <SOFTIRQ> | |
| 980 | + * call_timer_fn(); | |
| 981 | + * base->running_timer = mytimer; | |
| 982 | + * spin_lock_irq(somelock); | |
| 983 | + * <IRQ> | |
| 984 | + * spin_lock(somelock); | |
| 985 | + * del_timer_sync(mytimer); | |
| 986 | + * while (base->running_timer == mytimer); | |
| 987 | + * | |
| 988 | + * Now del_timer_sync() will never return and never release somelock. | |
| 989 | + * The interrupt on the other CPU is waiting to grab somelock but | |
| 990 | + * it has interrupted the softirq that CPU0 is waiting to finish. | |
| 991 | + * | |
| 973 | 992 | * The function returns whether it has deactivated a pending timer or not. |
| 974 | 993 | */ |
| 975 | 994 | int del_timer_sync(struct timer_list *timer) |
| @@ -977,6 +996,10 @@ int del_timer_sync(struct timer_list *timer) · 1 unmodified line | ||
| 977 | 996 | #ifdef CONFIG_LOCKDEP |
| 978 | 997 | unsigned long flags; |
| 979 | 998 | |
| 999 | + /* | |
| 1000 | + * If lockdep gives a backtrace here, please reference | |
| 1001 | + * the synchronization rules above. | |
| 1002 | + */ | |
| 980 | 1003 | local_irq_save(flags); |
| 981 | 1004 | lock_map_acquire(&timer->lockdep_map); |
| 982 | 1005 | lock_map_release(&timer->lockdep_map); |