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/* * Mutexes: blocking mutual exclusion locks * * started by Ingo Molnar: * * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> * * This file contains the main data structure and API definitions. */ #ifndef __LINUX_MUTEX_H #define __LINUX_MUTEX_H #include <linux/list.h> #include <linux/spinlock_types.h> #include <linux/linkage.h> #include <asm/atomic.h> /* * Simple, straightforward mutexes with strict semantics: * * - only one task can hold the mutex at a time * - only the owner can unlock the mutex * - multiple unlocks are not permitted * - recursive locking is not permitted * - a mutex object must be initialized via the API * - a mutex object must not be initialized via memset or copying * - task may not exit with mutex held * - memory areas where held locks reside must not be freed * - held mutexes must not be reinitialized * - mutexes may not be used in irq contexts * * These semantics are fully enforced when DEBUG_MUTEXES is * enabled. Furthermore, besides enforcing the above rules, the mutex * debugging code also implements a number of additional features * that make lock debugging easier and faster: * * - uses symbolic names of mutexes, whenever they are printed in debug output * - point-of-acquire tracking, symbolic lookup of function names * - list of all locks held in the system, printout of them * - owner tracking * - detects self-recursing locks and prints out all relevant info * - detects multi-task circular deadlocks and prints out all affected * locks and tasks (and only those tasks) */ struct mutex { /* 1: unlocked, 0: locked, negative: locked, possible waiters */ atomic_t count; spinlock_t wait_lock; struct list_head wait_list; #ifdef CONFIG_DEBUG_MUTEXES struct thread_info *owner; struct list_head held_list; unsigned long acquire_ip; const char *name; void *magic; #endif }; /* * This is the control structure for tasks blocked on mutex, * which resides on the blocked task's kernel stack: */ struct mutex_waiter { struct list_head list; struct task_struct *task; #ifdef CONFIG_DEBUG_MUTEXES struct mutex *lock; void *magic; #endif }; #ifdef CONFIG_DEBUG_MUTEXES # include <linux/mutex-debug.h> #else # define __DEBUG_MUTEX_INITIALIZER(lockname) # define mutex_init(mutex) __mutex_init(mutex, NULL) # define mutex_destroy(mutex) do { } while (0) # define mutex_debug_show_all_locks() do { } while (0) # define mutex_debug_show_held_locks(p) do { } while (0) # define mutex_debug_check_no_locks_held(task) do { } while (0) # define mutex_debug_check_no_locks_freed(from, len) do { } while (0) #endif #define __MUTEX_INITIALIZER(lockname) \ { .count = ATOMIC_INIT(1) \ , .wait_lock = SPIN_LOCK_UNLOCKED \ , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \ __DEBUG_MUTEX_INITIALIZER(lockname) } #define DEFINE_MUTEX(mutexname) \ struct mutex mutexname = __MUTEX_INITIALIZER(mutexname) extern void fastcall __mutex_init(struct mutex *lock, const char *name); /*** * mutex_is_locked - is the mutex locked * @lock: the mutex to be queried * * Returns 1 if the mutex is locked, 0 if unlocked. */ static inline int fastcall mutex_is_locked(struct mutex *lock) { return atomic_read(&lock->count) != 1; } /* * See kernel/mutex.c for detailed documentation of these APIs. * Also see Documentation/mutex-design.txt. */ extern void fastcall mutex_lock(struct mutex *lock); extern int fastcall mutex_lock_interruptible(struct mutex *lock); /* * NOTE: mutex_trylock() follows the spin_trylock() convention, * not the down_trylock() convention! */ extern int fastcall mutex_trylock(struct mutex *lock); extern void fastcall mutex_unlock(struct mutex *lock); #endif