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#include <linux/err.h>
  18#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  19#include <linux/osq_lock.h>
  20#endif
  21
  22struct rw_semaphore;
  23
  24#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
  25#include <linux/rwsem-spinlock.h> /* use a generic implementation */
  26#define __RWSEM_INIT_COUNT(name)        .count = RWSEM_UNLOCKED_VALUE
  27#else
  28/* All arch specific implementations share the same struct */
  29struct rw_semaphore {
  30        atomic_long_t count;
  31        struct list_head wait_list;
  32        raw_spinlock_t wait_lock;
  33#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  34        struct optimistic_spin_queue osq; /* spinner MCS lock */
  35        /*
  36         * Write owner. Used as a speculative check to see
  37         * if the owner is running on the cpu.
  38         */
  39        struct task_struct *owner;
  40#endif
  41#ifdef CONFIG_DEBUG_LOCK_ALLOC
  42        struct lockdep_map      dep_map;
  43#endif
  44};
  45
  46extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  47extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  48extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);
  49extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
  50extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  51
  52/* Include the arch specific part */
  53#include <asm/rwsem.h>
  54
  55/* In all implementations count != 0 means locked */
  56static inline int rwsem_is_locked(struct rw_semaphore *sem)
  57{
  58        return atomic_long_read(&sem->count) != 0;
  59}
  60
  61#define __RWSEM_INIT_COUNT(name)        .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)
  62#endif
  63
  64/* Common initializer macros and functions */
  65
  66#ifdef CONFIG_DEBUG_LOCK_ALLOC
  67# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
  68#else
  69# define __RWSEM_DEP_MAP_INIT(lockname)
  70#endif
  71
  72#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  73#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
  74#else
  75#define __RWSEM_OPT_INIT(lockname)
  76#endif
  77
  78#define __RWSEM_INITIALIZER(name)                               \
  79        { __RWSEM_INIT_COUNT(name),                             \
  80          .wait_list = LIST_HEAD_INIT((name).wait_list),        \
  81          .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
  82          __RWSEM_OPT_INIT(name)                                \
  83          __RWSEM_DEP_MAP_INIT(name) }
  84
  85#define DECLARE_RWSEM(name) \
  86        struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  87
  88extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  89                         struct lock_class_key *key);
  90
  91#define init_rwsem(sem)                                         \
  92do {                                                            \
  93        static struct lock_class_key __key;                     \
  94                                                                \
  95        __init_rwsem((sem), #sem, &__key);                      \
  96} while (0)
  97
  98/*
  99 * This is the same regardless of which rwsem implementation that is being used.
 100 * It is just a heuristic meant to be called by somebody alreadying holding the
 101 * rwsem to see if somebody from an incompatible type is wanting access to the
 102 * lock.
 103 */
 104static inline int rwsem_is_contended(struct rw_semaphore *sem)
 105{
 106        return !list_empty(&sem->wait_list);
 107}
 108
 109/*
 110 * lock for reading
 111 */
 112extern void down_read(struct rw_semaphore *sem);
 113
 114/*
 115 * trylock for reading -- returns 1 if successful, 0 if contention
 116 */
 117extern int down_read_trylock(struct rw_semaphore *sem);
 118
 119/*
 120 * lock for writing
 121 */
 122extern void down_write(struct rw_semaphore *sem);
 123extern int __must_check down_write_killable(struct rw_semaphore *sem);
 124
 125/*
 126 * trylock for writing -- returns 1 if successful, 0 if contention
 127 */
 128extern int down_write_trylock(struct rw_semaphore *sem);
 129
 130/*
 131 * release a read lock
 132 */
 133extern void up_read(struct rw_semaphore *sem);
 134
 135/*
 136 * release a write lock
 137 */
 138extern void up_write(struct rw_semaphore *sem);
 139
 140/*
 141 * downgrade write lock to read lock
 142 */
 143extern void downgrade_write(struct rw_semaphore *sem);
 144
 145#ifdef CONFIG_DEBUG_LOCK_ALLOC
 146/*
 147 * nested locking. NOTE: rwsems are not allowed to recurse
 148 * (which occurs if the same task tries to acquire the same
 149 * lock instance multiple times), but multiple locks of the
 150 * same lock class might be taken, if the order of the locks
 151 * is always the same. This ordering rule can be expressed
 152 * to lockdep via the _nested() APIs, but enumerating the
 153 * subclasses that are used. (If the nesting relationship is
 154 * static then another method for expressing nested locking is
 155 * the explicit definition of lock class keys and the use of
 156 * lockdep_set_class() at lock initialization time.
 157 * See Documentation/locking/lockdep-design.txt for more details.)
 158 */
 159extern void down_read_nested(struct rw_semaphore *sem, int subclass);
 160extern void down_write_nested(struct rw_semaphore *sem, int subclass);
 161extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
 162extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
 163
 164# define down_write_nest_lock(sem, nest_lock)                   \
 165do {                                                            \
 166        typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
 167        _down_write_nest_lock(sem, &(nest_lock)->dep_map);      \
 168} while (0);
 169
 170/*
 171 * Take/release a lock when not the owner will release it.
 172 *
 173 * [ This API should be avoided as much as possible - the
 174 *   proper abstraction for this case is completions. ]
 175 */
 176extern void down_read_non_owner(struct rw_semaphore *sem);
 177extern void up_read_non_owner(struct rw_semaphore *sem);
 178#else
 179# define down_read_nested(sem, subclass)                down_read(sem)
 180# define down_write_nest_lock(sem, nest_lock)   down_write(sem)
 181# define down_write_nested(sem, subclass)       down_write(sem)
 182# define down_write_killable_nested(sem, subclass)      down_write_killable(sem)
 183# define down_read_non_owner(sem)               down_read(sem)
 184# define up_read_non_owner(sem)                 up_read(sem)
 185#endif
 186
 187#endif /* _LINUX_RWSEM_H */
 188