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