/*
* 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 <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 hardware or software interrupt
* contexts such as tasklets and timers
*
* 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;
struct list_head wait_list;
};
/*
* 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;
int *task;
};
void __attribute__ ((fastcall)) __attribute__ ((dllimport))
mutex_init(struct mutex*)__asm__("MutexInit");
void __attribute__ ((fastcall)) __attribute__ ((dllimport))
mutex_lock(struct mutex*)__asm__("MutexLock");
void __attribute__ ((fastcall)) __attribute__ ((dllimport))
mutex_unlock(struct mutex*)__asm__("MutexUnlock");
/**
* 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 mutex_is_locked(struct mutex *lock)
{
return atomic_read(&lock->count) != 1;
}
#endif