1 /* rwsem.h: R/W semaphores, public interface 2 * 3 * Written by David Howells ([email protected]). 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 17 #include <asm/system.h> 18 #include <asm/atomic.h> 19 20 struct rw_semaphore; 21 22 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK 23 #include <linux/rwsem-spinlock.h> /* use a generic implementation */ 24 #else 25 /* All arch specific implementations share the same struct */ 26 struct rw_semaphore { 27 long count; 28 spinlock_t wait_lock; 29 struct list_head wait_list; 30 #ifdef CONFIG_DEBUG_LOCK_ALLOC 31 struct lockdep_map dep_map; 32 #endif 33 }; 34 35 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem); 36 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem); 37 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *); 38 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem); 39 40 /* Include the arch specific part */ 41 #include <asm/rwsem.h> 42 43 /* In all implementations count != 0 means locked */ 44 static inline int rwsem_is_locked(struct rw_semaphore *sem) 45 { 46 return sem->count != 0; 47 } 48 49 #endif 50 51 /* Common initializer macros and functions */ 52 53 #ifdef CONFIG_DEBUG_LOCK_ALLOC 54 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname } 55 #else 56 # define __RWSEM_DEP_MAP_INIT(lockname) 57 #endif 58 59 #define __RWSEM_INITIALIZER(name) \ 60 { RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED(name.wait_lock), \ 61 LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) } 62 63 #define DECLARE_RWSEM(name) \ 64 struct rw_semaphore name = __RWSEM_INITIALIZER(name) 65 66 extern void __init_rwsem(struct rw_semaphore *sem, const char *name, 67 struct lock_class_key *key); 68 69 #define init_rwsem(sem) \ 70 do { \ 71 static struct lock_class_key __key; \ 72 \ 73 __init_rwsem((sem), #sem, &__key); \ 74 } while (0) 75 76 /* 77 * lock for reading 78 */ 79 extern void down_read(struct rw_semaphore *sem); 80 81 /* 82 * trylock for reading -- returns 1 if successful, 0 if contention 83 */ 84 extern int down_read_trylock(struct rw_semaphore *sem); 85 86 /* 87 * lock for writing 88 */ 89 extern void down_write(struct rw_semaphore *sem); 90 91 /* 92 * trylock for writing -- returns 1 if successful, 0 if contention 93 */ 94 extern int down_write_trylock(struct rw_semaphore *sem); 95 96 /* 97 * release a read lock 98 */ 99 extern void up_read(struct rw_semaphore *sem); 100 101 /* 102 * release a write lock 103 */ 104 extern void up_write(struct rw_semaphore *sem); 105 106 /* 107 * downgrade write lock to read lock 108 */ 109 extern void downgrade_write(struct rw_semaphore *sem); 110 111 #ifdef CONFIG_DEBUG_LOCK_ALLOC 112 /* 113 * nested locking. NOTE: rwsems are not allowed to recurse 114 * (which occurs if the same task tries to acquire the same 115 * lock instance multiple times), but multiple locks of the 116 * same lock class might be taken, if the order of the locks 117 * is always the same. This ordering rule can be expressed 118 * to lockdep via the _nested() APIs, but enumerating the 119 * subclasses that are used. (If the nesting relationship is 120 * static then another method for expressing nested locking is 121 * the explicit definition of lock class keys and the use of 122 * lockdep_set_class() at lock initialization time. 123 * See Documentation/lockdep-design.txt for more details.) 124 */ 125 extern void down_read_nested(struct rw_semaphore *sem, int subclass); 126 extern void down_write_nested(struct rw_semaphore *sem, int subclass); 127 /* 128 * Take/release a lock when not the owner will release it. 129 * 130 * [ This API should be avoided as much as possible - the 131 * proper abstraction for this case is completions. ] 132 */ 133 extern void down_read_non_owner(struct rw_semaphore *sem); 134 extern void up_read_non_owner(struct rw_semaphore *sem); 135 #else 136 # define down_read_nested(sem, subclass) down_read(sem) 137 # define down_write_nested(sem, subclass) down_write(sem) 138 # define down_read_non_owner(sem) down_read(sem) 139 # define up_read_non_owner(sem) up_read(sem) 140 #endif 141 142 #endif /* _LINUX_RWSEM_H */ 143