LXR linux/include/linux/rwsem.h

   1/* rwsem.h: R/W semaphores, public interface
   2 *
   3 * Written by David Howells (dhowells@redhat.com).
   4 * Derived from asm-i386/semaphore.h
   5 */
   6
   7#ifndef _LINUX_RWSEM_H
   8#define _LINUX_RWSEM_H
   9
  10#include <linux/linkage.h>
  11
  12#include <linux/types.h>
  13#include <linux/kernel.h>
  14#include <linux/list.h>
  15#include <linux/spinlock.h>
  16#include <linux/atomic.h>
  17#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  18#include <linux/osq_lock.h>
  19#endif
  20
  21struct rw_semaphore;
  22
  23#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
  24#include <linux/rwsem-spinlock.h> /* use a generic implementation */
  25#else
  26/* All arch specific implementations share the same struct */
  27struct rw_semaphore {
  28        long count;
  29        struct list_head wait_list;
  30        raw_spinlock_t wait_lock;
  31#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  32        struct optimistic_spin_queue osq; /* spinner MCS lock */
  33        /*
  34         * Write owner. Used as a speculative check to see
  35         * if the owner is running on the cpu.
  36         */
  37        struct task_struct *owner;
  38#endif
  39#ifdef CONFIG_DEBUG_LOCK_ALLOC
  40        struct lockdep_map      dep_map;
  41#endif
  42};
  43
  44extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  45extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  46extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
  47extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  48
  49/* Include the arch specific part */
  50#include <asm/rwsem.h>
  51
  52/* In all implementations count != 0 means locked */
  53static inline int rwsem_is_locked(struct rw_semaphore *sem)
  54{
  55        return sem->count != 0;
  56}
  57
  58#endif
  59
  60/* Common initializer macros and functions */
  61
  62#ifdef CONFIG_DEBUG_LOCK_ALLOC
  63# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
  64#else
  65# define __RWSEM_DEP_MAP_INIT(lockname)
  66#endif
  67
  68#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  69#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
  70#else
  71#define __RWSEM_OPT_INIT(lockname)
  72#endif
  73
  74#define __RWSEM_INITIALIZER(name)                               \
  75        { .count = RWSEM_UNLOCKED_VALUE,                        \
  76          .wait_list = LIST_HEAD_INIT((name).wait_list),        \
  77          .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
  78          __RWSEM_OPT_INIT(name)                                \
  79          __RWSEM_DEP_MAP_INIT(name) }
  80
  81#define DECLARE_RWSEM(name) \
  82        struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  83
  84extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  85                         struct lock_class_key *key);
  86
  87#define init_rwsem(sem)                                         \
  88do {                                                            \
  89        static struct lock_class_key __key;                     \
  90                                                                \
  91        __init_rwsem((sem), #sem, &__key);                      \
  92} while (0)
  93
  94/*
  95 * This is the same regardless of which rwsem implementation that is being used.
  96 * It is just a heuristic meant to be called by somebody alreadying holding the
  97 * rwsem to see if somebody from an incompatible type is wanting access to the
  98 * lock.
  99 */
 100static inline int rwsem_is_contended(struct rw_semaphore *sem)
 101{
 102        return !list_empty(&sem->wait_list);
 103}
 104
 105/*
 106 * lock for reading
 107 */
 108extern void down_read(struct rw_semaphore *sem);
 109
 110/*
 111 * trylock for reading -- returns 1 if successful, 0 if contention
 112 */
 113extern int down_read_trylock(struct rw_semaphore *sem);
 114
 115/*
 116 * lock for writing
 117 */
 118extern void down_write(struct rw_semaphore *sem);
 119
 120/*
 121 * trylock for writing -- returns 1 if successful, 0 if contention
 122 */
 123extern int down_write_trylock(struct rw_semaphore *sem);
 124
 125/*
 126 * release a read lock
 127 */
 128extern void up_read(struct rw_semaphore *sem);
 129
 130/*
 131 * release a write lock
 132 */
 133extern void up_write(struct rw_semaphore *sem);
 134
 135/*
 136 * downgrade write lock to read lock
 137 */
 138extern void downgrade_write(struct rw_semaphore *sem);
 139
 140#ifdef CONFIG_DEBUG_LOCK_ALLOC
 141/*
 142 * nested locking. NOTE: rwsems are not allowed to recurse
 143 * (which occurs if the same task tries to acquire the same
 144 * lock instance multiple times), but multiple locks of the
 145 * same lock class might be taken, if the order of the locks
 146 * is always the same. This ordering rule can be expressed
 147 * to lockdep via the _nested() APIs, but enumerating the
 148 * subclasses that are used. (If the nesting relationship is
 149 * static then another method for expressing nested locking is
 150 * the explicit definition of lock class keys and the use of
 151 * lockdep_set_class() at lock initialization time.
 152 * See Documentation/locking/lockdep-design.txt for more details.)
 153 */
 154extern void down_read_nested(struct rw_semaphore *sem, int subclass);
 155extern void down_write_nested(struct rw_semaphore *sem, int subclass);
 156extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
 157
 158# define down_write_nest_lock(sem, nest_lock)                   \
 159do {                                                            \
 160        typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
 161        _down_write_nest_lock(sem, &(nest_lock)->dep_map);      \
 162} while (0);
 163
 164/*
 165 * Take/release a lock when not the owner will release it.
 166 *
 167 * [ This API should be avoided as much as possible - the
 168 *   proper abstraction for this case is completions. ]
 169 */
 170extern void down_read_non_owner(struct rw_semaphore *sem);
 171extern void up_read_non_owner(struct rw_semaphore *sem);
 172#else
 173# define down_read_nested(sem, subclass)                down_read(sem)
 174# define down_write_nest_lock(sem, nest_lock)   down_write(sem)
 175# define down_write_nested(sem, subclass)       down_write(sem)
 176# define down_read_non_owner(sem)               down_read(sem)
 177# define up_read_non_owner(sem)                 up_read(sem)
 178#endif
 179
 180#endif /* _LINUX_RWSEM_H */
 181